2900-139- R Memorandum of Project MICHIGAN THE PHASE DIAGRAM FOR THE BINARY SYSTEM CADMIUM-TELLURIUM DONALD R. MASON BERNARD M. KULWICKI Department of Chemical and Metallurgical Engineering April 1960 THE U N I V E R S I T Y OF M I C H I G A N Ann Arbor, Michigan

Distribution control of Project MICHIGAN Reports has been delegated by the U. S. Army Signal Corps to: Commanding Officer U. S. Army Liaison Group Project MICHIGAN Willow Run Laboratories Ypsilanti, Michigan It is requested that information or inquiry concerning distribution of reports be addressed accordingly. Project MICHIGAN is carried on for the U. S. Army Signal Corps under Department of the Army Prime Contract Number DA-36-039 SC-78801, University contract administration is provided to the Willow Run Laboratories through The University of Michigan Research Institute.

WI LLOW RUN LABORATORIES TECHNICAL MEMORANDUM PREFACE Documents issued in this series of Technical Memorandums are published by Willow Run Laboratories in order to disseminate scientific and engineering information as speedily and as widely as possible. The work reported may be incomplete, but it is considered to be useful, interesting, or suggestive enough to warrant this early publication. Any conclusions are tentative, of course. Also included in this series will be reports of work in progress which will later be combined with other materials to form a more comprehensive contribution in the field. A primary reason for publishing any paper in this series is to invite technical and professional comments and suggestions. All correspondence should be addressed to the Technical Director of Project MICHIGAN. Project MICHIGAN, which engages in research and development for the U. S. Army Combat Surveillance Agency of the U. S. Army Signal Corps, is carried on by the Willow Run Laboratories as part of The University of Michigan's service to various government agencies and to industrial organizations. Robert L. Hess Technical Director Project MICHIGAN 111

WI LLOW RUN LABORATORIES TECHNICAL MEMORANDUM CONTENTS Preface................................ iii Lists of Figures and Tables....................... vi Abstract............................. 1 1. Introduction.......................... 1 2. Experimental Procedures.............. 2 2. 1. Sample Preparation 2 2. 2, Equipment and Procedures 3 2. 3. Preliminary Data Interpretation 4 3. Thermodynamic Theory of Solid-Liquid Equilibrium.......... 6 3. 1. Calculation of the Latent Heat of Fusion, AHf 8 3. 2. Theoretical Forms of the Liquidus Lines 9 3. 3. Calculation of Eutectic Compositions 10 3. 4. Slope and Curvature of the Liquidus Lines 11 4. Discussion of Results.13 4. 1. Validity of the Experimental Work 13 4. 2. Accord between Theory and Experiment 14 4. 3. Theoretical Significance 14 Appendix: Derivation of Thermodynamic Equations for Liquidus Curves... 16 References.............................. 28 Distribution List............................ 29 v

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM FIGURES 1. Schematic Diagram of DTA Equipment.................. 3 2. Diagram of Differential Thermocouples and Sample Tubes........ 4 3. Plot of AH/R Vs. y, Derived from Experimental Data and Equation 1... 8 4. Plot of a Vs. T, for Evaluation of Constants a and b in Equation 2.... 9 5. Phase Diagram for the Binary System Cd-Te......... 11 TABLES I. Experimental Data for the Cd-Te Phase Diagram............ 5 II. Summary of Phase-Diagram Data Available from the Literature..... 6 vi

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM The Phase Diagram for the Binary System Cadmium-Tellurium' ABSTRACT The phase diagram for the cadmium-tellurium system has been redetermined by measuring the thermal behavior of representative compositions in the system by the method of differential thermal analysis. The experimental details and the resulting data are described and discussed. Thermodynamic analysis shows that the system CdTe-Te appears to form an ideal solution. The latent heat of fusion of CdTe is estimated to be 10, 700 cal/gm mol. The system Cd-CdTe is an elementary solution and has a relatively large excess partial molar entropy of solution and a large partial molar enthalpy of solution. These partial molar qualities are independent functions of composition, but not of temperature. The eutectic compositions have been determined as 106 atom-fraction Te and about 0. 99 atom-fraction Te. The validity of this work vis-a-vis that of other investigators is discussed. INTRODUCTION Cadmium telluride is receiving considerable scientific attention because of its interesting semiconductor properties (References 1-5). The Semiconductor Materials Research Laboratory of The University of Michigan has prepared samples of this material in conjunction with studies on ternary semiconductor compounds in the binary system CdTe-In2Te3. These materials are being measured to ascertain their utility as sensors in infrared systems for battlefield surveillance. The results obtained in this work showed a serious discrepancy in the widely published melting point of CdTe. In the original work done on this system, Kobayashi (Reference 6) found 1This research was carried on at the Semiconductor Materials Research Laboratory, College of Engineering, The University of Michigan, Ann Arbor, Michigan. It was supported in part by Project MICHIGAN, and in part by grant NSF-G4127 from the National Science F oundation. The authors are indebted to Dr. C. D. Thurmond for providing a preprint of his paper referred to in this memorandum.

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM that CdTe is the only compound formed between these elements, and reported that the two eutectics between the pure elements and CdTe occur very close to the Cd and Te ends of the diagram. The original data indicate that the melting point of CdTe would be in the range of 10410C to 10500C, the values commonly reported in the literature (References 7, 8, 9). More recently, Lawson, Nielsen, Putley, and Young (Reference 4) have reported a value of 1106~C, without describing the details of their measuring technique. DeNobel (Reference 5) has published values for several additional points on the liquidus line in the Cd-Te system, and represents the melting point of CdTe to be 10900C. Visual observations of the first-to-freeze temperatures were made at each composition reported. In working with this compound in the binary system CdTe-In2Te3, Thomassen and Mason (Reference 10) observed recently that the melting point of CdTe is 1098 ~ 30C. In view of these discrepancies, we have redetermined the phase diagram for the Cd-Te system. A series of samples was prepared in which the Cd-Te compositions were varied over the range from 1 mol % Te to 98.7 mol % Te, using the purest available elements for their preparation. The latent heat transitions in each sample were determined by using the method of differential thermal analysis. On the basis of these experiments and subsequent thermodynamic analysis, our work appears to be more precise than that of previous investigators, and has special theoretical significance. The system CdTe-Te appears to be an ideal solution. The latent heat of fusion of CdTe from these measurements is estimated as 10, 700 cal/gm mol. The system Cd-CdTe is an elementary solution, and has a relatively large excess partial molar entropy of solution and a large partial molar enthalpy of solution. These partial molar quantities are independent functions of composition, but not of temperature. The eutectic compositions have been estimated -6 as 10 atom-fraction Te and about 0. 99 atom-fraction Te. 2 EXPERIMENTAL PROCEDURES The experimental operations comprise three categories: the sample preparation, the DTA (differential thermal analysis) equipment and procedures, and the preliminary interpretation of the data. 2. 1. SAMPLE PREPARATION The samples for thermal analysis were prepared by weighing stoichiometric amounts of the pure elements (99. 99% Cd and 99. 999% Te from American Smelting and Refining Company) into

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM specially cleaned, clear, fused-silica tubes, and sealing them off under moderate (below -4 10 mm Hg) vacuum. The samples were reacted by heating to temperatures well above the liquidus in a rotating, rocking furnace, and were rapidly cooled or air-quenched to room temperature to obtain a homogeneous sample. In many instances the samples wet the fused-silica tube and induced cracks and fractures in the containers during cooling. Only those samples which remained bright, shiny, and unoxidized after fusion were processed further. Each fused sample was crushed as much as possible (which was impossible with the high-cadmium samples) and 15 gm of the material was resealed into a new, specially cleaned, clear, fused-silica tube equipped with a concentric thermocouple well in the bottom end about 1 inch deep. 2.2. EQUIPMENT AND PROCEDURES A schematic diagram of the DTA apparatus is shown in Figure 1. The power input to the DTA furnace is controlled by means of an automatically programmed motor-driven autotransformer. The system is purged with dry nitrogen in order to prevent corrosion of the nickel sample holder, which is provided with three sample wells spaced at 1200 intervals. Two specimens may be measured at one time, the third well being occupied by the reference material. The sample temperature is measured by means of a chromel-alumel thermocouple, the output of which is measured on a Leeds and Northrup precision potentiometer. The output of the differential thermocouple (Figure 2) is amplified and recorded using a Leeds and Northrup Speedomax recorder. The thermocouples were calibrated against standards of indium (156 0C), lead (3270C), and silver (9610C) and found to agree within 10C. POWER SUPPLY Cu WIRE a: + Co TURN. FLOW 22L X 1I F MET. 220v I o-220v - 0-60v a, ~I ~: 0 o X FURNACE PULSE oP CIRCUIT 0 o 0 - COQ H20 OUT N2 SAMPLE TEMP. aS DIFF. MEASUREMENT L~fN NICKEL SAMPLE SPEEDO- LBN HOLDER NITROGEN = -,MAX StN. PURGE i=TX-T,1yCERAMIC PLUG CERAMIC PLUG FIGURE 1. SCHEMATIC DIAGRAM OF DTA EQUIPMENT 3

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM FCLEAR L FUSED SILICA TUBING 1.5 gm 15 gm 10mm ID. SAMPLE REFERENCE, LIQUID INDIUM -_. M.P. 156~C C CUL IVALUMEL CHROMEL CHROMEL Tr-iTs Ts -Tr - FIGURE 2. DIAGRAM OF DIFFERENTIAL THERMOCOUPLES AND SAMPLE TUBES The samples were heated and cooled inside the nickel block using a liquid-indium standard, at a rate of about 2. 50C/min from room temperature to a maximum temperature well above that of the highest transition, and back to room temperature. Although the DTA sample tubes sometimes cracked at low temperatures as the sample contracted around the thermocouple well, they were not wet significantly by the samples, and no apparent oxidation occurred. The sample temperature and the differential emf (electromotive force) were both measured as functions of time, and the data were replotted to show the differential emf as a function of sample temperature. 2.3. PRELIMINARY DATA INTERPRETATION In interpreting the experimental differential curves, the liquidus line was chosen on the heating curves as the point where the differential completed its last deviation. The presence of chunks and large crystals in many of the samples gave rise to erratic deviations in the region of the liquidus, so that the liquidus was relatively difficult to establish. In some instances, considerable supercooling occurred on the cooling cycle, as was evidenced by a large initial differential emf which sometimes actually induced an increase in the sample temperature. In those cases where the initial cooling emf was moderate and/or the heating curves were difficult to interpret, the cooling curves were used to establish the liquidus lines. These results are indicated in Table I. The data of deNobel (Reference 5) and Kobayashi (Reference 6) are summarized in Table II. 4

TABLE I. EXPERIMENTAL DATA FOR THE Cd-Te PHASE DIAGRAM Sample Composition Maximum Liquidus Temperatures Number Atom %o Fusion Te = y Cd = 1 - y Temperature Eutectic Heat Cool "Chosen" Calc'd (OC) (OC) (OC) (OC) (0C) (OC) 0 0 100 --- --- 321 --- 376 1. 0 99. 0 980 (333) 730 730 728 380 3.0 97.0 970 (340) 845 808 808 808 -4 379 10. 0 90.0 97 5 322 940 895 895 893 0 384 25.0 75.0 1050 323 1000 963 963 963 385 40.0 60.0 1100 325 1035 1015 1035 1034 m 402 45.0 55.0 1150 325 1089 1067 1067 1066 354 50.0 50.0 1200 --- 1100 1099 1098 362 50.0 50.0 1200 1097 1096 1098 -4 389 54.0 46.0 1100 450 1075 1052* 1075 1069 rr 383 62.5 37. 5 1100 450 1000 950' 1000 1005 375 75.0 25.0 1000 450 885 860*' 885 894 382 85.0 15.0 900 449 735 755 755 777 381 95.0 5.0 750 450 640 602 602 593 388 98.2 1. 8 850 448 480 480 469 396 98.7 1. 3 800 450 480 480 006 100 0 --- --- 456 452 454 G-1 100 0 --- 454 --- 454 "n ~Considerably supercooled 0 z C

W I L L O W RUN L A B O R A T O R I E S T E C H N I C A L MEMORANDUM TABLE II. SUMMARY OF PHASE-DIAGRAM DATA AVAILABLE FROM THE LITERATURE Composition Atom % Eutectic Liquidus Reference Te = y Cd = 1 - y Temperature Temperature (~C) (~C) 0 100 322 322 6 0.88 99. 12 322 692 6 8.94 91.06 322 --- 6 8.94 91.06 --- 885 5 18.10 81.90 322 --- 6 18.10 81.90 --- 940 5 27.45 72.55 321.5 - 6 27.45 72.55 --- 974 5 37.00 63.00 321 --- 6 37.00 63.00 --- 983 5 41.92 58.08 --- 1006 5 46. 95 53.05 321 --- 6 46. 95 53.05 --- 1036 5 50.07 49.93 --- 1090 5 51.90 48.10 1068 5 52.10 47.90 366.5 1041.5 6 52.4 47.6 383.5 1032.5 6 56.97 43.03 --- 1024 5 60.5 39.5 408 1001 6 67.2 32.8 --- 926 5 69.5 30.5 422.5 893 6 77. 95 22.05 --- 840 5 79.7 20.3 437 815 6 85.8 14.2 437 741.5 6 93.7 6.3 437 604 6 97.2 2.8 437 506.5 6 100 0 437 437 6 THERMODYNAMIC THEORY OF SOLID-LIQUID EQUILIBRIUM From thermodynamic analysis of the data, it is possible to obtain an estimate of the latent heat of fusion of CdTe, to establish the form of the liquidus lines on a theoretical basis, to predict the eutectic compositions, and to gain some insight as to the nature of the liquid regions. A more detailed derivation of the thermodynamic equations is presented in the appendix. For purposes of calculation, the diagram can be considered to be comprised of two separate binaries: (I) the system Cd-CdTe, and (II) the system CdTe-Te. 6

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM The liquidus curve for a binary system which exhibits ideal solution behavior can be represented by the Schroeder-vanLaar equation (Reference 11). in x = -T) (1) where x = mol fraction of component A in solution at T~K Tf = melting point of component A (OK) R = gas constant, 1. 987 cal/gm mol OK AHf = latent heat of fusion of component A (cal/gm mol) This equation has been derived by assuming that the system is in equilibrium, that component B does not form a mixed crystal with component A, and that the change in specific heat between liquid and solid (AC ) for component A is negligible or zero. For an ideal solution the values of AHf derived from the T vs. x data should be substantially independent of composition. In nonideal solutions the departures from ideality are characterized by an activity coefficient, y. By analyzing the liquidus data for a large number of binary systems containing germanium and silicon, Thurmond and Kowalchik (Reference 12) have postulated a new class of solutions, called elementary solutions, wherein the relative partial molar excess entropy and the relative partial molar enthalpy of mixing exhibit a particular dependence on concentration, but are not direct functions of temperature. The relationship between the activity coefficients and the excess thermodynamic functions can be represented by an equation in the form RT In y AH T AS E aRn = 2 a- bT (2) (1- x)2 (1- x)2 (1- x)2 AH where a = constant 2 (1 - x) -S E b = 2 = constant (1 - x)2 2 AH = a( 1- x) = partial molar excess enthalpy of mixing of component A in elementary solutions -E 2 = b(l - x) = partial molar excess entropy of mixing of component A in elementary solutions 7 = activity coefficient at composition x

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM Since the activity coefficients in the ideal solutions are equal to unity, the partial molar excess enthalpy and entropy are zero. 3.1. CALCULATION OF THE LATENT HEAT OF FUSION, AtHf Using those liquidus data points from each DTA run which were considered to be the most reliable ("chosen" values), an estimate for the latent heat of fusion of CdTe at each data point was made, using Equation 1. The compound CdTe was chosen as component A. Cadmium was taken as component B in the system I, and tellurium was taken as component B in system II. Define the atom fraction of Te in Cd as y. Hence in system I x dTe 2y (3) and in system II XCdTe = 2(1- y) (4) Figure 3 presents the results of the calculations on the basis of atom-fraction Te, y, in Cd. Calculations made from the data of deNobel (Reference 5) and Kobayashi (Reference 6) are also presented for comparative purposes, Kobayashi's data having been calculated on the basis of his reported melting point of 10420C. On the Te-rich half of the system, the values of AHf/R appear to be substantially independent of composition, and ideal solution behavior seems to be indicated. I I I I I I I I I 20,000 18,000_ 0 - MASON, KULWICKI _ X - KOBAYASHI 16,000_ O0 - de NOBEL 14,000- CdTe 12,000 AH A 10,000 8,000- X 4,000- 0 X 0 I 0 2,000 I I() I I I I I X _ Cd y ATOM % Te Te FIGURE 3. PLOT OF LH/R VS. y, DERIVED FROM EXPERIMENTAL DATA AND EQUATION 1. O = Mason, Kulwicki; X = Kobayashi; J = deNobel.

WI LLOW RUN LABORATORIES TECHNICAL MEMORANDUM On the Cd-rich half of the diagram, the derived values of ALHf/R are not independent of composition, and the solution is nonideal. At the composition CdTe the two segments of the curve apparently intersect at approximately the point where AHf/R = 5400, or AHf == 10, 700 cal/gm mol. 3.2. THEORETICAL FORMS OF THE LIQUIDUS LINES By using the value of AHf estimated above, a quantitive measure of the nonideality of both binary systems can be obtained by calculating the activity coefficients and the a-functions defined in Equation 2. A plot of a vs. T is shown in Figure 4. Here again the data of deNobel and Kobayashi are presented for the larger values of (1- x) where they fall within the domain shown on the figure. For very small values of (1 - x) the evaluation of the liquidus temperature becomes quite critical, and small errors are magnified greatly in calculating the a-function. This is apparent from the measurement at 45 atom % Te, where a change of 20C in the experimental liquidus temperature changes a by almost 50%. 6000 C X 0 -MASON, KULWICKI X - KOBAYASHI 5000 0 - de NOBEL 4000 Cd-CdTe SYSTEM: 0 1o = 16,000 - 10.85T 3000 a _ 2000 1000 CdTe-Te SYSTEM:'=O 0 O X oX 0-1000 -1000 800 1000 1200 1400 TOK FIGURE 4. PLOT OF ca VS. T, FOR EVALUATION OF CONSTANTS a AND b IN EQUATION 2. O = Mason, Kulwicki; X = Kobayashi; 0 = deNobel. 9

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM From these calculations it again appears that the system (II) CdTe-Te is an ideal solution. As Te is dissolved in liquid CdTe there are no significant heat or excess entropy effects on mixing, and the liquidus curve can be approximated by the expression AHf 10,700 T = (5) ASf- R in x 7. 80 - 1. 987 1n x where x = 2(1 - y) = mol fraction of CdTe in Te ASf = AHf/Tf = entropy of fusion, cal/gm mol OK From the inspection of Figure 4 it is also apparent that the system I (Cd-CdTe) forms an elementary solution, with a = 16, 000 - 10. 85T; i. e., iH = 16, 000 (1 - x)2 cal/gm mol and ASE =10.85 (1 - x)2 cal/gm mol OK The liquidus curve in this region can be approximated by the expression AHf + a (1 - x) 2 TiHf 1+a (1 - x)210, 700 + 16, 000(1 - x) f T= 2 (6) ASf +b(l- x) - R lnx 7.80 + 10.85(1- x) - 1.987 lnx where x = 2y = mol fraction of CdTe in Cd. 3.3. CALCULATION OF EUTECTIC COMPOSITIONS The experimental melting point of CdTe (13710K), the experimentally measured eutectic temperature on the Te side (7230K), and the derived latent heat of fusion (10, 700 cal/mol) were used in Equation 1 to predict the eutectic composition in the system II (CdTe-Te). The predicted value of 0. 986 atom-fraction Te in Cd indicates that-the eutectic should be distinguishable from pure Te. The same relationship can also be used to calculate the eutectic composition from the properties of pure Te. From its melting point (7270K) and latent heat of fusion (3230 cal/gm mol) (Reference 13) the eutectic composition is calculated to be x = 0. 014; hence y = 0. 993. An experimental check was carried out using a sample containing 0. 987 atom-fraction Te in Cd. The check was made on the presumption that the eutectic point predicted from the CdTe was more accurate than that predicted from the Te. It was found that the measurement was almost indistinguishable from that made at 0. 982 atom-fraction Te. This discrepancy apparently arises because the liquidus curve rises so steeply on the left side of the eutectic that slight inhomogeneities in the sample tend to give erratic results. We conclude that the eutectic lies at approximately 0. 99 atom-fraction Te. 10

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM In order to calculate the eutectic composition on the Cd side from Equation 6 the mol fraction of CdTe at the eutectic can be approximated as zero in all the terms except the logarithmic factor. Since the experimental eutectic temperature is known (595~K), the eutectic composition is calculated to be 10 atom-fraction Te in Cd, which is experimentally indistinguishable from pure Cd. However, our data would seem to indicate that the solidus transition temperature (322 C) is higher than the melting point of Cd (3210C), and a peritectic pattern may be present. The liquidus curves and eutectic points derived above are plotted on Figure 5 along with all the experimental data from Table I, deNobel (Reference 5), and Kobayashi (Reference 6). The liquidus temperatures calculated from Equations 5 and 6 at the experimental compositions are also tabulated in Table I. 1100 I I I' I 1098oC I I I I I100 0 MASON, KULWICKI 10 0 0 ~ | )2 <>\ X KOBAYASHI 1000 X 900 X 800 TOC 7000 LIQUID + Cd Te CdTe + LIQUID 600) 50O 4500C X 400 X X 3220C 300 0 10 20 30 40 50 60 70 80 90 100 Cd y=ATOM % Te Te FIGURE 5. PHASE DIAGRAM FOR THE BINARY SYSTEM Cd-Te. The liquidus curves are drawn using Equations 3 and 4. 0 = Mason, Kulwicki; X = Kobayashi; 0= deNobel. 3.4. SLOPE AND CURVATURE OF THE LIQUIDUS LINES The abrupt change in slope and curvature of the liquidus lines at the melting point of CdTe is also of interest. For system II (CdTe-Te), the slope is obtained by differentiating Equation 5. _T = AHfR 10, 700R (7) x(ASf - R in x) x(7.80 - R ln x) 11

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM As x->1l, lnx —O, and 6T = 10, 700R 349 (8) 7 = 349.5 (8) x 7.80 For the system I (Cd-CdTe), the slope is obtained by differentiating Equation 6. 6T _S[~Sf +b(- x) - R In x] 2a( l- x) - AH + a(1- x)2] [b(l- x) - R/x] (9) Sf + b(1- x)2 -R inx] As x ->,( - x) -> 0 and ln x ->0, giving 6T AHfR = —-— ~~~~~~- ~~(10) 6x 2 x-> 1 x(AS )2 which is identical with Equation 8. Hence the slope of the liquidus curve is discontinuous at the composition CdTe but symmetrical on either side as x approaches unity. The curvature of the liquidus curve is given by the second derivative of the T vs. x expressions. For the system II (CdTe-Te) which approximates an ideal solution,differentiation of Equation 7 gives d2T AHR 2R1 (11) d 2 2 f 2 R In x 2 (11) dx (AS- R in x) f x which for the system under discussion as x-> 1 (pure CdTe) becomes d T = f 2R10, 700 x 1. 987 3_8_ 1 = -171 (12) 2 2 S -i) 2 7. 8 dx A / 7.8 x-> 1 The moderately large negative value of the second derivative indicates that the liquidus curve should be convex upwards as x approaches unity from the Te side as shown on the right half of the diagram; i. e., as x increases the slope is decreasing. In contrast, however, for the system I (Cd-CdTe) the expression for the second derivative of the elementary-solution curve is obtained by differentiation of Equation 9. d T 2- RT/x 2RT + 4RTb x(l- x)- 4Rax(l- x) - 8abx2(1- x) 2 D2 2(13) dx D x 12

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM where D is the denominator in Equation 6. For the special case wherein x -> 1, then D ASf = 7. 80, and T-> T = 13710K. This gives d2T 2a0 f (14) dx2,ASf ASf Sf x >1 - From Figure 4 or Equation 2 we can find a = 1110, whence d T 2220 1.987 x 1371 (3. 975 ) 2 2 ~ 7.80 7.80 7.8 = 3 dx XCdTe 1 The positive second derivative indicates that the slope is positive and increasing, thus giving the observed curvature to the liquidus curve as x approaches unity from the Cd side. In fact, in order for the second derivative of the elementary-solution liquidus curve to be negative at the melting point of component A, it is necessary that a R b R AH 2 AS + 2 — (16) f AS f f DISCUSSION OF RESULTS The verisimilitude of the results obtained from this work can be discussed from three different points of view: the validity of the experimental work, the accord between theory and experiment, and the theoretical insights which the results give toward a better comprehension of the structure of the liquid. 4. 1. VALIDITY OF THE EXPERIMENTAL WORK The large discrepancy between the melting point of CdTe reported by Kobayashi (Reference 6) and later investigators can be attributed to three factors; (a) the purity of the Te used in preparing the compounds, as indicated by the melting points (Kobayashi's 4370C vs. 4540C in this work),(b) Kobayashi's use of cooling curves only, instead of combining results from both heating and cooling curves, (c) unequal volatilization of the elemental constituents, particularly Cd, since Kobayashi's samples were open to the atmosphere instead of being sealed. A close comparison of our data with that of deNobel (Reference 5) indicates that the agreement is excellent below about 25 atom % Cd. Above this range, our liquidus temperatures are 13

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM consistently higher than those reported by deNobel. In order to explain this descrepancy, we suggest that the error lies in deNobel's method of measurement. If the thermocouple and support rod in deNobel's experimental systems extract heat from the sample holder, it is conceivable that CdTe would freeze out on the bottom of the sample holder before solidification became apparent by visual observation on the surface of the sample. The liquid remaining after partial solidification and precipitation of CdTe (component A) would be more rich in component B (either Cd or Te,depending on which element was in excess over the stoichiometry of CdTe). The remaining liquid then would freeze at a temperature lower than the true liquidus temperature defined by the sample composition in the absence of partial segregation. By using thermal means to sense the onset of solidification, we feel that the effects of temperature gradients in our equipment are thereby significantly decreased. In the absence of a detailed description of the method used by Larson, Nielsen, Putley, and Young (Reference 4), we cannot account for the discrepancy between 1098 ~ 30C and 1106 0C, which we feel is significant. 4.2. ACCORD BETWEEN THEORY AND EXPERIMENT On the Te half of the diagram the average discrepancy in our data between the observed and derived liquidus temperature is about 10 C. The solubility of excess Te in CdTe may account for this discrepancy. It is also probable that a slight excess entropy and enthalpy of mixing are associated with this system which would alter the shape of the liquidus curve slightly. However, since the plot of the data in Figure 4 fails to show any clear trend, and in the absence of information on the solubility of Te in CdTe, perfect solution behavior has been assumed in deriving the theoretical liquidus curve. On the Cd half of the diagram, the average discrepancy between the observed and derived liquidus temperatures is only about 1~C. This unusually good agreement not only substantiates the conclusion that this system is an elementary solution, but also gives an example for the existence of elementary solutions between elements and compounds. At the same time the validity of the derived value for AHf is indirectly substantiated. 4.3. THEORETICAL SIGNIFICANCE In attempting to interpret the physical significance of the relative partial molar enthalpy and the relative partial molar excess entropy, we can consider first the CdTe-Te system. The absence of substantial energy and entropy effects suggests that the environment of the Cd atoms is not changed appreciably as excess molten Te is added to molten CdTe. 14

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM However, as excess molten Cd is added to molten CdTe, the Cd atoms form additional bonds with the Te atoms. The Te atoms are subsequently surrounded by a much larger average number of Cd atoms. There is a discontinuity in the solution behavior on either side of the compound CdTe, and the slope of the liquidus curve is discontinuous at that point. A. M. G. D. 15

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM Appendix DERIVATION of THERMODYNAMIC EQUATIONS FOR LIQUIDUS CURVES 1. INTRODUCTION This appendix describes the theoretical foundations for the conclusions of this memorandum. First to be developed will be the appropriate thermodynamic equations, serving also as a means of review for those readers not immediately concerned with the formal study of thermodynamics; then the definitions will be reviewed both for ideal solutions (Reference 11) and the various other classes of nonideal solutions that have been defined (Reference 11), including elementary solutions (Reference 12). 2. DERIVATION of GIBBS-HELMHOLTZ EQUATION Since the system was maintained at constant volume and there is no pressure-volume work effect in the system, the thermodynamic quantity describing the equilbrium condition will be the thermodynamic work function, A, rather than the free energy, F. Starting from elementary thermodynamics, consider first the following definitions for a system of constant total mols, N: A = E - TS (A-l) where A = thermodynamic work function E = internal energy S = entropy T = absolute temperature Hence, dA = dE - TdS - SdT (A-2) But since, from the First Law T dS = dE + P dV (A-3) substitution of Equation A-3 into Equation A-2 gives dA = -PdV - SdT (A-4) 16

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM Defining A as a function of T and V gives dA = dV + dT (A-5) T,N V, N from which, by comparing coefficients between Equations A-4 and A-5 we find /6) -P N(A-6) T,N and =T ~ -S (A-7) V, N From Equations A-1 and A-7 we find A = E + T (A-8) V,N Division by T2 and rearrangement of Equation A-8 gives E 116A\ A 6A'9I 2 T 6) T2 )6T V, N (A-9) T V,N T V, This is the Gibbs-Helmholtz equation for a fixed —composition system at constant volume. 2. 1. CHEMICAL POTENTIAL IN MULTICOMPONENT OPEN SYSTEMS. In an open system where compositions and masses may vary, the thermodynamic work function at equilibrium may be expressed in the general form A = f(T, V, n1, n2,... ni,...) (A- 10) By using Equations A-6 and A-7 the change in work function in a differential displacement from equilibrium in an open system can be shown to be dA = -PdV- SdT + dn1 +. + dni +... (A-ll) T,V,n2... TVn,1... At constant temperature and volume the partial differentials in Equation A-ii vare expressions for the chemical potential. Hence the chemical potential can be defined in a variety of ways. 17

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM 6F\F /6E\ /6H\ Pi. = =-n T, P, n... S, V, n..., P, n = -T(A> (A-12) E,V, n T, V, n From Equation A- 12 we find pi = (A- 13) T, V, n... 2.2. CLOSED CONSTANT VOLUME SYSTEM. The Gibbs-Helmholtz equation for a closed system can be written in terms of partial molar quantities at constant temperature and volume. For a system of definite composition, Equation A- 1i1 can be integrated with the aid of Equation A- 13 to give A = nl 2 2n2 + +... +ini +. (A-14) By maintaining temperature and volume constant in the system during an equilibrium change in phase, then dA = 0, and O —dn +p dn. dn. +... (A- 15) = dn1 +22 +' +i 15) for any phase. Differentiation of Equation A-13 with respect to T at constant total mols N give6T N, V 6n T (A-16) Differentiation of Equation A-7 with respect to ni gives 16 S 2A1 A) = (6) -Si (A- 17) V, N V, N But Equations A-16 and A-17 are equal, hence -S = ) (A-18) i \ 18

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM Differentiating Equation A-1 with respect to n. gives 6A \ (6E 6S ( -i -( 1 -T (A- 19) T, V, n1... T V, n1... T V, n.... D efining ( )Tn = Ei and substituting from Equations A-13 and A-17 we find TV, n'... i E. - TS. (A-20) 1 1 1 Substitutions from Equation A-18 and rearrangement gives Mi - 6TI T=-E (A-21) V, N Dividing by T gives the desired result, [0I( 1S~l ~ "2T (A-22) 2 T \6T/v 2 6T T V,N T V,N 2. 3. FUGACITY AND ACTIVITY. The thermodynamic equations for liquid and solid systems are derived from concepts established for gaseous systems through a consideration of the behavior of the fugacity and activity in the various phases. For 1 mol of a constituent of an ideal gas mixture in a closed system with partial pressure Pi, = iMO(T) + RT In Pi: ( 1 i =- R (A-23) / i P. T, N 1 For a system containing 1 mol of an ideal gas, with mol fraction of constituent i equal to x. at constant temperature and composition at constant total pressure P, Pi = p.(T, P) + RT In x. (A-24) i 1 1 In general, to accommodate nonideal systems the partial pressure is replaced by the fugacity. Hence 6.i = RTd In f. (A-25) Integration gives p. = RT ln f. + C (A-26) 1 1 19

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM To define the constant of integration, we can define a reference state as the pure constituent in the gas phase at the same temperature under one atmosphere pressure or its own vapor pressure (if a condensable vapor, with vapor pressure below one atmosphere) such that it is substantially a perfect gas. Hence, 0 pi - i = n RTlnf./fO RTlna (A-27) where a.i = fi/fi = activity = fugacity/fugacity of standard state. Rearranging and differentiating with respect to temperature at constant volume and composition gives d Mi d _ (d in ai. dT\~T/ (X)i d } =R dt (A-28) N, N V, NN Substitution from Equation A-22 gives d In a. E~- E (k[~....dT_ =1 1 (A-29) dT / 2 V, N RT 3. CHANGE OF STATE These basic thermodynamic concepts can now be utilized to investigate the phenomena accompanying changes in state. It is necessary to apply these definitions to the particular situations of interest. If we consider a phase change of a pure constituent from solid to the reference state in the vapor, then in Equation A-29 the various terms evaluated for this special case become EO~ = E~ = internal energy of pure vapor in standard state (A-30) 1 v E. = ES = internal energy in solid state (A-31) 1 i then E~ - Es = AE = internal energy of sublimation (A-32) 1 1 sv If instead of the preceding change of state we consider a phase change from liquid to the vapor reference state, then the various terms in Equation A-29 become E~= E~ = internal energy of pure vapor in standard state (A-33) 1 v E. = EL = internal energy in liquid bath (A-34) 1 1 20

WI LLOW RUN LABORATORIES TECH NICAL MEMORANDUM hence, E~ - E. = AE internal energy of vaporization (A-35) 1 1 V 3. 1. TWO COMPONENT CONSTANT VOLUME SYSTEM. Consider now a closed system of three phases (gas, liquid, solid) and two components. At equilibrium from Equation A-15 we must have g dn ++5 LdnddnL +y Mdn+2 0 (A-36) 11n 1 1 1 22 22 2 2 Also the total mass of each component must be constant, hence dn. +dn~ L + dn = 0 (A-37) 1 1 1 dn2 + dn + dn = (A-38) 2 2 2 These relationships can be satisfied for all variations in n1, n2 only if g L s 1 1 1 (A g L s =" 2 2 = 2 (A-40) 3. 2. SOLID-LIQUID EQUILIBRIA. When the temperature of a closed solid-liquid system is changed slightly, then the activities of the constituents also change slightly. However, under equilibrium conditions the activity in the liquid remains equal to the activity in the solid, although the magnitude of the activities can change as a result of the temperature change. Applying Equations A-27 and A-39 to constituent 1 this result can be expressed as,n1 dT1 dxL = dT+ 1 ds (A-41) 6TI aL in ax (X) L L1Sdx1 -1 X VX =dT (A-42) weAf- = inter rearrangement and substitution of om Equationent A-2 = 9,Ef L 1 ___ x T Vx (RT 21

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM 3. 3. IDEAL SOLUTIONS. For an ideal solution the fugacity of the constituent is equal to the product of the mol fraction times the fugacity of the pure substance f. =x.f or ai X. 1 11 1 1 Hence by definition /ln aL l na1 1 (A-43) ax x 6 1 /1 V, T and 6 in a (A-44) k xlT 1 T 1 Substituting into Equation A-42 finally gives 6n Xl/x AE ),V RT2 (A-45) 2T 6T JT, V RT 2 If component 1 is considered as the solute, which separates as a pure constituent on freezing s from the solution (hence x1 = 1), then integration of Equation A-45 from the solute fusion L temperature, Tf, and composition xi = 1, to the equilibrium-solution temperature T and comL. 1 position x1 gives XnL AEO dT d Iln x X (A-46) 1 R T ~1 1 =RTf T AEf /1 =) ln x = = f. 1 (A-47) 1 RITf T/ assuming AEf to be independent of temperature and (L- CS) = 0. If the difference in heat f p V capacities at constant volume is not zero, then an additional integral is introduced into Equation A-46 which should produce another term in Equation A-47. In most cases of practical interest, the heat capacity difference is neglected. Not only are the calculations simplified, but also the precise data are often not available to make the corrections. In any event, the consistency of the results obtained by ignoring this factor give tacit evidence that it is negligible. 22

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM 3. 4. NONIDEAL SOLUTIONS. Most solutions are not ideal solutions. However, the deviation from ideality can be lumped into a single parameter, the activity coefficient, such that a. = iy x (A-48) 1 1 1 Under these circumstances, Equation A-47 would be rewritten as In ly1 Xi i f ( 1(1 (A-49) As the mol fraction approaches unity, then by definition the activity also approaches unity and equation A-49 can be rearranged to 0 In Y1 + In x1 (f 1 ) (A-50) In accordance with the required boundary limitations on y, it is possible to express In y as a function of mol fraction by oo in y = C(1 - x)n (A-51) n=1 which satisfies the relationship that y —>1 as x->l. For nonelectrolytic solutions, the Gibbs-Duhem equation can be used to show that C, = 0. Hence oo In y= Cn( l-x)n (A-52) n=2 The simplest concentration dependence obtainable from Equation A-52 is given by the first term, or we can let 2 In T = C2(1 - x) (A-53) By defining the partial molar free energy of the solute in solution as F - F = F = RT In yx = AH- TAS (A-54) L L 23

WILLOW RUN LABORATORIES TECH NICAL MEMORANDUM the relative partial molar entropy AS can be expressed as the sum of two terms, the ideal -~i ~~-E entropy of mixing AS and an excess entropy of mixing AS - - i Z- E =- E = AS + S = S - R. In x (A-55) Substitution of Equation A-55 into Equation A-54 gives In = RT (A-56) RT R where AH = relative partial molar enthalpy of mixing of the solute -E S E = relative partial molar excess entropy of mixing of the solute Several types of nonideal solutions have been defined according to the various dependencies of in y. 3. 4. 1. Regular Solutions. Regular solutions have been defined as those solutions wherein the partial molar excess entropy of mixing is zero, but the partial molar enthalpy of mixing is not zero. In particular, if 2 AH = a (1 - x) (A-57) r and. —, E.= SE o then a strictly regular solution has been defined. 3. 4. 2. Athermal Solutions. Athermal solutions have been defined as solutions wherein the partial molar excess entropy of mixing is finite, whereas the partial molar enthalpy of mixing is zero. A particular example of this type of behavior could be represented by the relationship SE = b (1 - x)2 (A-58) AH = 0 This definition is of value predominantly for conceptual purposes. 3. 4. 3. Elementary Solutions. In general, both the partial molar enthalpy and partial molar excess entropy need not be zero. However, the particular manner in which these properties depend on temperature and composition is of considerable importance. 24

WILLOW RUN LABORATORIES TECHNIC AL MEMORANDUM If the dependence is as defined below, the resulting solutions have been called "Elementary Solutions"(Reference 12). AH = a(l - x) (A-59) sE = b(l - x)2 (A-60) Substitution of Equations A-59 and A-60 into Equation A-56 gives in (1 - x (A-61) In y(1 - x )(A Equation A-61 can be rearranged to give a function a, which varies linearly with temperature. RT In 7= a = a - bT (A-62) (1 - x) As noted in the text of the memorandum, the function a was calculated for the system I (Cd-CdTe) and found to be a = 16, 000 - 10. 85 T. Elementary solution behavior is thus indicated for this system. 3. 5. LIQUIDUS CURVES. The dependency of T on x can be obtained from Equation A-50 to define the liquidus curves explicitly. The various dependencies of in - for ideal, regular, athermal, and elementary solutions must be substituted appropriately. For ideal solutions AHf T. Rl (A-63)! ASf - R In x For strictly regular solutions AHf +a (1- x)2 f r T = (A-64) r ASf - R In x For strictly athermal solutions AHf T = (A-65) a 2 AS+ +b (1 - x) R In x f a For elementary solutions AHf +a(l - x) T = (A-66) e 2 ASf +b(l - x) - R in x 25

WI L L O W RUN L A B O R A T O R I E S T E C H N I C-A L MEMORANDUM 3. 6. THE SLOPES OF THE LIQUIDUS CURVES. The slopes of the various types of liquidus curves can be obtained by taking the derivatives of the equations in Section 3. 5 with respect to the composition variable x. For ideal solutions dT. AHfR RT. 1 A~f 1 (A-67) x( ASf - R In x)2R n x) where T. is defined by Equation A-63. 1 For strictly regular solutions dT (RT )- 2a (1 - x)x dr r r (A-68) dx x(ASf - R In x) where T is defined by Equation A-64. r For strictly athermal solutions dT RT + 2 b (1- x)x a a a a a a 2 (A-69) dx x[ XASf + b (l1 - R In x] where T is defined by Equation A-65. For elementary solutions dT RT - 2a(1 - x)x e e -e e 2(A-70) dx x[ ASf + b(l - x)2_-R n x] where T is defined by Equation A-66 and a is defined in Equation A-62. 3.7. THE CURVATURES OF THE LIQUIDUS CURVES. The curvatures of the various types of liquidus curves can be obtained by taking the derivatives of the slopes with respect to the composition variable x. For ideal solutions 2 dTi RTi 2R1 d2 (S - R In x) (Sf R In x) ] 2 (A-71) 26

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM For strictly regular solutions 62T RT 2a r r 2R 1 2R( x) Tr2 (ASf - R In x) L(ASf -R ln x) 2 (ASf - R ln x) x(zSf -R lnx) (A- 7 2) 2 2 6 T RT + 2b(1 - x)x 1 RT + 2b( 1 - x)x L R(2 - T n ] s +b( x2 R n x x2 [AS + b( - x) - R In x] 1AS- + b(1 - x) - R ln x f (A-73) For elementary solutions 6 T 2a - RT /x 2R T - 4aR(1 - x)x - 8aRb(l - x) (A-74) 2 = 2 dx [Sf b(l -x) -Rlnx] x[Sf +b(l - x) -R lnx] f 27

WI LLOW RUN LABORATORIES TECHNICAL MEMORANDUM REFERENCES 1. F. A. Kroger, and D. deNobel, "Preparation and Electrical Properties of CdTe Single Crystals, " J. Electronics, 1955, Vol. 1, pp. 190-202. 2. G. G. Kretschmar, and L. E. Schilberg, "Preparation and Photoconductive Properties of Cadmium Telluride Films, " J. Appl. Phys., 1957, Vol. 28, pp. 865-867. 3. J. L. Stull, "Semiconductivity in Cadmium Telluride, " PhD Thesis, State University of New York, 1958, p. 29. 4. W. P. Lawson, S. Nielsen, E. H. Putley, and A. S. Young, "Preparation and Properties of HgTe and Mixed Crystals of HgTe-CdTe, " J. Phys. Chem. Solids, 1959, Vol. 9, pp. 325-329. 5. D. deNobel, "Phase Equilibria and Semiconducting Properties of Cadmium Telluride," Phillips Research Rept., 1959, Vol. 14, pp. 361-399. 6. M. Kobayashi, "Uber die Legierungendes des Tellurs mit Cadmium und Zinn," Zeits. Anorg. Chem., 1910, Vol. 69, pp. 1-9. 7. M. Hansen, Constitution of Binary Alloys, 2nd ed., McGraw-Hill, New York, N. Y., 1958, pp. 444-445. 8. International Critical Tables, McGraw-Hill, New York, N. Y., 1927, Vol. II, p. 430. 9. Handbook of Chemistry & Physics, 40th ed., Chemical Rubber Publishing Co., Cleveland, O., 1958, p. 548. 10. L. Thomassen, and D. R. Mason, "Phase Diagram for the Binary System CdTe-In2Te3, " abstract in J. Electrochem., 1959, Vol. 106, p. 206c. Paper presented at the Electrochemical Society, fall meeting, Columbus, O., 21 October 1959. 11. I. Prigogine, and R. Defay, Chemical Thermodynamics, Longmans, Green &Company, New York, N.Y. 1954, p. 358. 12. C. D. Thurmond, and M. Kowalchik, "Germanium and Silicon Liquidus Curves, " Bell System Tech. J., in press, January 1960. 13. J. H. Perry, Chemical Engineers Handbook, 3rd ed., McGraw-Hill, New York, N.Y., 1950, p. 212. 28

WI LLOW RUN LABORATORIES TECH NICAL MEMORANDUM DISTRIBUTION LIST 5, PROJECT MICHIGAN REPORTS 1 April 1960-Effective Date Copy No. Addressee Copy No. Addressee 1-2 Commanding General, U. S. Army 39-41 Director, U. S. Army Engineer Combat Surveillance Agency Research & Development Laboratories 1124 N. Highland Street Fort Belvoir, Virginia Arlington 1, Virginia ATTN: Chief, Electrical Engineering 3-28 Department 3-28 Commanding Officer, U. S. Army Signal Research & Development 42 Director, U. S. Army Engineer Laboratories Research & Development Laboratories Fort Monmouth, New Jersey Fort Belvoir, Virginia ATTN: SIGM/EL-DR ATTN: Technical Documents Center 29 Commanding General 43 Commandant, U. S. ArmyWar College U. S. Army Electronic Proving Ground Carlisle Barracks, Pennsylvania Fort Huachuca, Arizona ATTN: Library ATTN: Technical Library 44 Commandant, U. S. Army Command & General Staff College 30 Chief of Engineers Fort Leavenworth, Kansas Department of the Army Washington 25, D. C. ATTN: Archives ATTN: Research & Development Division 45-46 Assistant Commandant, U. S. Army Artillery & Missile School 31 Commanding General Fort Sill, Oklahoma Quartermaster, Research & Engineering 47 Assistant Commandant, U. S. Army Air Natick, Massachusetts Fort Belvoir, Virginia 32 Chief, Human Factors Research ATTN: CombatDevelopment Group Division, Office of the Chief of Research & Development 48 Commandant, U. S. Army Aviation School Department of the Army Fort Rucker, Alabama Washington 25, D. C. 49 Commanding Officer, U. S. Army Signal Electronic Research Unit 33-34 Commander, Army Rocket & Guided P. O. Box 205 Missile Agency Mountain View, California Redstone Arsenal, Alabama ATTN: Technical Library, ORDXR-OTL 50 Office of Naval Operations Department of the Navy, Washington 25, D. C. 35 Commanding Officer, Headquarters ATTN: OP-07T U. S. Army Transportation Research 51-53 Office of Naval Research & Engineering Command Department of the Navy Fort Eustis, Virginia 17th & Constitution Ave., N. W. ATTN: Chief, TechnicalServices Washington 25, D. C. Division ATTN: Code 463 36 Commanding General, Ordnance 54 Chief, Bureau of Ships Tank-Automotive Command Departmentof the Navy, Washington 25, D. C. Detroit Arsenal 28251 Van Dyke Avenue ATTN: Code 312 Center Line, Michigan 55-56 Director, U. S. NavalResearch Laboratory ATTN: Chief, ORDMC-RRS Washington 25, D. C. 37 Commanding General, Army Medical ATTN: Code 2027 Research & Development Command Main Navy Building, Washington 25, D. C. 57 Commanding Officer, U. S. Navy Ordnance Laboratory ATTN: Neurophychiatry & Psychophysiol- Ordnance Laboratory ogy Research Branch ATTN: Library 38 Director, U. S. Army Engineer Research & Development Laboratories 58 Commanding Officer & Director Fort Belvoir, Virginia U. S. Navy Electronics Laboratory ATTN: Chief, Topographic San Diego 52, California EChief, Topographic Engineer Department ATTN: Library 29

WI LLOW RUN LABORATORIES TECHNICAL MEMORANDUM DISTRIBUTION LIST 5 1 April 1960-Effective Date Copy No. Addressee Copy No. Addressee 59 Department of the Air Force 94 The RAND Corporation Headquarters, USAF 1700 Main Street Washington 25, D. C. Santa Monica, California ATTN: Directorate of Requirements ATTN: Library 60 Commander, Air Technical 95 Chief, U. S. Army Armor Intelligence Center Human Research Unit Wright-Patterson Air Force Base, Ohio Fort Knox, Kentucky ATTN: Administrative Assistant 61-70 ASTIA (TIPCR) Arlington Hall Station 96 Director of Research, U. S. Army Arlington 12, Virginia Infantry Human Research Unit 71-75 Commander, Wright Air Development P. O. Box 2086, FortBenning, Georgia 71-75 Commander, Wright AirDevelopment C enter 97 Chief, U. S. Army Leadership Wright-Patterson Air Force Base, Ohio Human Research Unit ATTN: WCLROR P. O. Box 787 Presidio of Monterey, California 76 Commander, Wright Air Development ATTN: Librarian Center Wright-Patterson Air Force Base, Ohio 98 Chief Scientist, Research &Development Division, Office of the Chief Signal ATTN: WCLDRFV Officer 77 Commander, Wright Air Development Department of the Army, Washington 25, D. C. 77 Commander, Wright Air Development Center 99 Stanford Research Institute Wright-Patterson Air Force Base, Ohio Document Center ATTN: WCOSI-Library Menlo Park, California ATTN: Acquisitions 78 Commander, Rome Air Development Center Griffiss Air Force Base, New York 100 Operations Research Office The Johns Hopkins University 6935 Arlington Road 79 Commander, Rome Air Development Center Bethesda, Maryland, Washington 14, D. C. 79 CCommander, Rome Air Development Center Griffiss Air Force Base, New York ATTN: Chief, Intelligence Division ATTN: RCVH 101-102 Cornell Aeronautical Laboratory, Incorporated 80-81 Commander, Air Force Incorporated Cammridge Reseairch Center 4455 Genesee Street, Buffalo 21,NewYork Cambridge Research Center Laurence G. Hanscom Field ATTN: Librarian Bedford, Massachusetts VIA: Bureau of Aeronautics ATTN: CRES, Stop 36 Representative 4455 Genesee Street 82-85 Central Intelligence Agency Buffalo 21, New York 2430 E. Street, N. W., Washington 25, D. C. 103-104 Control Systems Laboratory ATTN: OCR Mail Room University of Illinois Urbana, Illinois 86-90 National Aeronautics & Space Administration ATTN: Librarian 1520 H. Street, N. W. Washington 25, D. C. VIA: ONR Resident Representative 1209 W. Illinois Street 91 U. S. Army Air Defense Human Urbana, Illinois Research Unit 105-106 Director,Human Resources Research Office Fort Bliss, Texas The George Washington University ATTN: Library P. O. Box 3596, Washington25, D. C. ATTN: Library 92-93 Combat Surveillance Project Cornell Aeronautical Laboratory, 107 Massachusetts Institute of Technology, Incorporated Research Laboratory of Electronics Box 168, Arlington 10, Virginia Cambridge 39, Massachusetts ATTN: Technical Library ATTN: Document Room 26-327 30

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM DISTRIBUTION LIST 5 1 April 1960-Effective Date Copy No. Addressee Copy No. Addressee 108 The U. S. Army Aviation HRU 115 Director, Electronic Defense Group P. O. Box 428, Fort Rucker, Alabama U of M Research Institute The University of Michigan Ann Arbor, Michigan 109-110 Visibility Laboratory, Scripps Institution ATTN: Dr. H. W. Ferris of Oceanography University of California 116-118 Assistant Commandant San Diego 52, California U. S. Army Air Defense School Fort Bliss, Texas 111-113 Bureau of Aeronautics 119 U. S. Continental Army Command Liaison Department of the Navy, Washington 25, D. C. Officer ATTN: RAAV-43 Project MICHIGAN, Willow Run Laboratories Ypsilanti, Michigan 114 Office of Naval Research 120 Commanding Officer Department of the Navy U. S. Army Liaison Group 17th & Constitution Ave., N. W. Project MICHIGAN, Willow Run Washington 25, D. C. Laboratories ATTN: Code 461 Ypsilanti, Michigan 31

AD Div. 4/4 UNCLASSIFIED AD Div. 4/4 UNCLA Willow Run Laboratories, U. of Michigan, Ann Arbor 1. Semiconductors Willow Run Laboratories, U. of Michigan, Ann Arbor 1. SemiconRductorsTHE PHASE DIAGRAM FOR THE BINARY SYSTEM CADMIUM- Thermodynamic THE PHASE DIAGRAM FOR THE BINARY SYSTEM CADMIUM- Thermo TELLURIUM by Donald R. Mason and Bernard M. Kulwicki. properties TELLURIUM by Donald R. Mason and Bernard M. Kulwicki. proper Memo, of ProjMICHIGAII. Apr 60. 21 p. ic. illus. 2 tables, 2. Semiconductors Memo. of Proj.MICHIGAN. Apr 60. 28 p. incl. illus. 2 tables, 2. Semiconductors13 refs. Chemical properties 13 refs. Chemical properties (Memo. no. 2900-139-R) 3. Cadmium telluride- (Memo. no. 2900-139-R) 3. Cadmium (Contract DA-36-039 SC-78801) Unclassified memorandum Thermal analysis (Contract DA-36-039 SC-78801) Unclassified memorandum Therma The phase diagram for lbe cadmium'-tellurium system has been I. Title: Project MICHIGAN The phase diagram for the cadmium-tellurium system has been. Title: en Tephase diagram for te cadmium-telurium system has been I il:Ntoa cec redetermined by measuring the thermal behavior of representative F. Title. National Science redetermined by measuring the thermal behavior of representative Foundation Foundation Fud Foundation ~~~~~~~compositions in the system by the method of differential thermal compositions in the system by the method of differential thermal IHI. Mason, Donald R., analysis The expementa e adthe res ting tarar IlL Mason, D analysis ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~~I. Maren Duwioenard M., analysis. The experimental details and the resulting data are de- Kuwci enr.analysis. The experimental details and the resulting data are de- KulwickiBradM The eperienta detils nd th resltin dat de-Kulwicki, BernardM. scribed and discussed. Thermodynamic analysis shows that the scribed and discussed. Thermodynamic analysis shows that thescieandiusd.Trmyaicnlssshwtathe I.US.A scribed ddiscussed. appearst rmod c aniealysotis. shos tatenth IV. U. S. Army Signal Corps system CdTe-Te appears to form an ideal solution. The latentIV. system CdTe-Te appears to form an ideal solution. The latent V. Contract DA36035 heat of fusion of Cd~e is estimated-tohbef10,f700ecal/gm mol./ThehV. Contract DA-36-0 39 heat of fusion of CdTe is estimated to be 10, 700 cal/gm mol. The SC-788 Cd-CdTe is an elementary solution and c al/gm y5C78801 system Cd-CdTe is an elementary solution and has a relatively ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~system CCdeianlmntrsouonndhas a relatively large excess partial molar entropy of solution and a large partial Armed Services large excess partial molar entropy of solution and a large partial Armed Services molar enthalpy of solution. Technical Information Agency molar enthalpy of solution. (over) Technical Info (over) UNCLASSIFIED UNCLA AD Div. 4/4 UNCLASSIFIED AD Div. 4/4 UNCL Willow Run Laboratories, U. of Michigan, Ann Arbor 1. Semiconductors - Willow Run Laboratories, U. of Michigan, Ann Arbor 1. Semicon THE PHASE DIAGRAM FOR THE BINARY SYSTEM CADMIUM- Thermodynamic THE PHASE DIAGRAM FOR THE BINARY SYSTEM CADMIUM- Therm TELLURIUM by Donald R. Mason and Bernard M. Kulwicki. properties TELLURIUM by Donald R. Mason and Bernard M. Kulwicki. propei Memo. of Proj.MICHIGAN. Apr 60. 28 p. incl. illus. 2 tables, 2. Semiconductors- Memo. of Proj.MICHIGAN. Apr 60. 21 p. incl illus. 2 tables, 2. Semicond 13 refs. Chemical properties 13 refs. Chemic (Memo. no. 2900-139-R) 3. Cadmium telluride- (Memo, no, 2900-13-R) 3. Cadmim (Contract DA-36-039 SC-78801) Unclassified memorandum Thermal analysis (Contract DA-36-039 SC-78801) Unclassified memorandum Therm The phase*diagram for the cadmium-tellurium system has Leen I. Title: Project MICHIGAN The phase diagram for the cadmium-tellurium system has been I. Title: P The phase diagram for the cadmium-tellurium system has been IL. Title: National Science redetermined by measuring the thermal behavior of representative FTi nation redetermined by measuring the thermal behavior of representative Founda ~~~~~~~~~~~~~~~~~~Fonaincompositions in the system by the method of differential thermal compositions in the system by the method of differential thermal III. Mason, Donald R., analysitins. inthesexp erimen ytalhdets athedof differes ting data mar IL Mason, onal rma analysis. The experimental details and the resulting data are de- Kulwicki, BernardM. scribedsandhdiscussed. Thermodynaic analyis swta the Kulwici, scribed and discussed. Thermodynamic analysis shows that the IV.U. S. Arm SignalCorpssystbem Cnd e-Tcappears Tohformodynamic aniealysotio. Thes late IV.' U. S. Ar S a o systm Cde-Teappars o fom a idel soutin. Te laent IV. U. S. Army Signal Corps system CdTe-Te appears to form an ideal solution. ThIaetV.Cota system CdTe-Te appears to form an ideal solution. The latent V. Contract DA-36-039 ffso fC~ setmtdt e1,70clg o.Te ~ Cnrc A63 heat of fusion of CdTe is estimated to be 10, 700 cal/gm tol. The heat of fusion of CdTe is estimated to be 10,700 cal/gm tol. The SC-7801 systm CdCd~eis a eleentay soutio andhas rcal/gm y5C78801 system Cd-CdTe is an elementary solution and has a relatively ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~system Cd-CdTe is an elementary solution and has a relatively large excess partial molar entropy of solution and a large partial Armed Services large excess partial molar entropy of solution and a large partial Arme molar enthalpy of solution. (over) Technical Information Agency molar enthalpy of solution. (over) Technical Inf UNCLASSIFIED UNCLIF

AD UNCLASSIFIED AD UNCLASFE These partial molar qualities are independent functions of composi- UNITERMS These partial molar qualities are independent functions of compost- UNIEM tions, hut not of temperature. The eutectic compositions have been lhs iga ions, but not of temperature. The eutectic compositions have been Phase diagra determined as 10-6 atom-fraction tellurium and about 0. 99 atom- Cadmium-tellurium fetracione telrim The6 vtmfalidityof thluismwork aboutvi th99at of otherm-t fraction tellurium. The validity of this work vis-a'vsta fohr Temlbhvo rcintluim h aiiyof this work vis--Cadha fter Temium-tellru investigators is discussed. Differential thermal analysis investigators is discussed. Differential temlaayi Latent heat Latent heat Fusion Fusion Solution Solution Eutectic Eutectic UNCLASSIFIED UNCLASFE AD UNCLASSIFIED AD UNCLASFE These partial molar qualities are independent functions of composi- UNITERMS These partial molar qualities are independent functions of composi- UNIEM tions, hut not of temperature. The eutectic compositions have heen Phsdiga tions, hut not of temperature. The eutectic compositions have heen Phase diagra determined as 10l6 atom-fraction tellurium and about 0. 99 atom- Phasedmiagtelram m determined as 10t6 atom-fraction tellurium and about 0. 99 atom- Camut fraction tellurium, The validity of tis work vis-~-vis that of other hra eair fraction tellurium. The validity of this work vis-~-vis that of other Temlb investigators is discussed. Differential thermal analysis investigators is discussed. Differential'hra aayi Latent heat Latent heat Fusion Fusion Solution Solution Eutectic Eutectic UNCLASSIFIED UNCLASFE

AD Div. 4/4 UNCLASSIFIED AD Div. 4/4 UNC S Willow Run Laboratories, U. of Michigan, Ann Arbor 1. Semiconductors - Willow Run Laboratories, U. of Michigan, Ann Arbor 1. Semicon THE PHASE DIAGRAM FOR THE BINARY SYSTEM CADMIUM- Thermodynamic THE PHASE DIAGRAM FOR THE BINARY SYSTEM CADMIUM- Therm TELLURIUM by Donald R. Mason and Bernard M. Kulwicki. properties TELLURIUM by Donald R. Mason and Bernard M. Kulwicki. prope Memo. of Proj.MICHIGAN. Apr 60. 28 p. incl. illus. 2 tables, 2. Semiconductors- Memo, of Proj.MICHIGAN. Apr 60. 28 p. id. illus. 2 tables, 2. Semicon 13 refs. Chemical properties 13 refs. Chemie (Memo. no. 290t-139-R) 3. Cadmium telluride- (Memo. no. 2900-139-R) 3. Cadmium telluride(Contract DA-36-039 SC-78801) Unclassified memorandum Thermal analysis (Contract DA-36-t39 SC-788t1) Unclassified memorandum Therm The phase diagram for the cadmium-tellurium system has been L Title: Project MICHIGAN The phase diagram for the cadmium-tellurium system has been I. Title: II. Title: National Science redetermined by measuring the thermal behavior of representative IL Title: redetermined by measuring the thermal behavior of representativeFon Foundation rdtriebymauigtetemlbhvoofrpeettvFonaincompositions in the system by the method of differential thermal compositions in the system by the method of differential thermal III. Mason, Donald R., analysis.thensinthe experimentl dhets athedof riffesulting data mar Il Mason, onal r.a analysis. The experimental details and the resulting data are de- Kulwicki, BernardM. scribe and dsued.Termodeamic analysise shows ta the Kulwici scribed and discussed. Thermodynamic analysis shows that the system CdTe-Te appears to form an ideal solution. The latent. U.Strmy Sigal orp system CdTe-Te appears to form an ideal solution. The latent V. U.Strm a.CotatD 36t5V. Contract DA-36-039 heat of fusion of CdTe is estimated to be 10, 700 cal/gm mol. The SCr7880 heat of fusion of CdTe is estimated to be 11, 701 cal/gm mol. The SC-78 system Cd-CdTe is an elementary solution and has a relatively system Cd-CdTe ix an elementary solution and has a relatively large excess partial molar entropy of solution and a large partial Armed Services large excess partial molar entropy of solution and a large partial Arme molar enthalpy of solution. (over) Technical Information Agency molar enthalpy of solution. (over) Technical In UNCLASSIFIED UNCL AD Div. 4/4 UNCLASSIFIED AD Div. 4/4 UNC Willow Run Laboratories, U. of Michigan, Ann Arbor 1. Semiconductors - Willow Run Laboratories, U. of Michigan, Ann Arbor 1. Semico THE PHASE DIAGRAM FOR THE BINARY SYSTEM CADMIUM- Thermodynamic THE PHASE DIAGRAM FOR THE BINARY SYSTEM CADMIUM- Therm TELLURIUM by Donald R. Mason and Bernard M. Kulwicki. properties TELLURIUM by Donald R. Mason and Bernard M. Kulwicki. prope Memo, of Proj.MICHIGAN. Apr 60. 28 p inclM illus. 2 tables, 2. Semiconductors Memo. of Proj.MICHIGAN. Apr 60. 28 p. incl. illus. 2 tables, 2. Semiconductors13 refs. Chemical properties 13 refs. Chem (Memo. no. 2900-139-R) 3. Cadmium telluride- (Memo. no. 290-139-R) 3. Cadmit (Contract DA-36-039 SC-78801) Unclassified memorandum Thermal analysis (Contract DA-36-039 SC-76611) Unclassified memorandum Therm The phase diagram for the cadmium-tellurium system has been L Title: Project MICHIGAN The phase diagram for the cadmium-tellurium system has been L Title: IL Title: National Science redetermined by measuring the thermal behavior of representative IL. Title: National Science redetermined by measuring the thermal behavior of representative Foundation compsfitins e s b metouoreina thermal Foundation compositions in the system by the method of differential thermal cMD la sithe expermena de adthe resulting tarar III. Mason, analysis ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~~~~~I. Mare n Kuwikoenard M., a nalysis. The experimental details and the resulting data are de- KuMwicki, scribe and dsued.Termodynamic analysiseshows tat the scribed and discussed. Thermodynamic analysis shows that the TVKU. S.Army Signal CorpssystribemCd e-T a ppdiscuseas T rmodynac aniealysouio. The latent TV; U. S. Army Sgal Cop system CdTe-Te appears to form an ideal solution. The latent v V. ContractgDA-po-lil hystea offuion ofpCdpeais estiformate ideto 10,l700i mo. The lat. Contract DA36039 heat of fusion of CdTe is estimated to be 15, 711 cal/gm mol. The V C Contr heat of fusion of C is estimated to be 700 cal/gm TC78801 system Cd-CdTe is an elementary solution and has a relatively system Cd-CdTe is an elementary solution and has a relatively large excess partial molar entropy of solution and a large partial Armed Services large excess partial molar entropy of solution and a large partial Arm molar enthalpy of solution. Technical Information Agency molar enthalpy of solution. (over) Technical I UNCLASSIFIED UNC

AD UNCLASSIFIED AD UNCLASSIFIED These partial molar qualities are independent functions of composi- UNITERMS These partial molar qualities are independent functions of composi- UNITERMS tions, but not of temperature. The eutectic compositions have been tions, but not of temperature. The eutectic compositions have been determined as 10-6 atom-fraction tellurium and about 0. 99 atom- Phase diagram determined as 10-6 atom-fraction tellurium and about. 99 atom- Phase diagram Cfraction tellurium. The validity of this work vis-~-vis that of other Cadmium-tellurium fraction tellurium. The validity of this work vis-a-vis that of other Thermal ehavior fraction tellurium. The validity of this work vis-s-vis that of other Th ehi investigators is discussed. Differential thermal analysis vestigators is discussed. Differential thermal analysis I Latent heat Latent heat Fusion Fusion Solution Solution Eutectic Eutectic i ~ UNCLASSIFIED UNCLASSIFIED CO > AD UNCLASSIFIED AD UNCLASSIFIED These partial molar qualities are independent functions of composi- UNITERMS These partial molar qualities are independent functions of composi- UNITERMS tions, but not of temperature. The eutectic compositions have been tions, but not of temperature. The eutectic compositions have been determined as 10-6 atom-fraction tellurium and about 0.99 atom- Phase diagram determined as 10-6 atom-fraction tellurium and about. 99 atom- Phase diagram fraction tellurium. The validity of this work vis-a-vis that of other Cadmum-tellurum fraction tellurium. The validity of this work vis —vis that of other Th b Thermal behavior Thermal behavior investigators is discussed. Differential thermal analysis investigators is discussed. Differential Latent heat Latent heat Fusion Fusion Solution Solution Eutectic Eutectic UNCLASSIFIED UNCLASSIFIED