ENGINE ERING- RESEARCH INSTITUTE UIIVERSITY OF MICHIGAN ANN ARBOR QUARTERLY REPORT NO. 1 ON INFRARED STUDIES OF CRYSTALS II (Period.15 May to 15 August 1954) BY G, B. B. M, SUTHERLAND Principal Investigator C. Y. PAN LIANG M. HAAS Project 2235 SIGNAL CORPS, DEPARTMENT OF THE ARMY CONTRACT DA 36-039 sc-56736 SC PROJECT 152B, DA PROJECT 3-99-15-022 SQUIER SIGNAL LABORATORY, FORT MONMOUTH, N. J. SEPTEMBER, 1954

TABLE OF CONTENTS Page I. PURPOSE OF THE RESEARCH 1 II. ABSTRACT 1 III. PUBLICATIONS LECTURES etc. 2 IV. FACTUAL DATA A. Brucite Problem 2 B. Mica Problem 2 C. Gypsum Problem 4 D. Barium Titanate Problem 4 V. CONCLUSIONS 4 VI. FUTURE PROGRAM 5 VII. PERSONNEL 5 ii

r -- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN I QUARTERLY REPORT NO. 1 ON INFRARED STU-DIES OF CRYSTALS II I. PURPOSE OF THE RESEARCH The general purpose of this research is to complete the investigations started in May 1951 under Contract DA 36039 sc-56736 on the infrared spectra and structure of barium titanate, brucite, mica and gypsum. II. ABSTRACT In connection with the interpretation of the spectrum of brucite, the spectrum has been recorded of a single crystal of portlandite (Ca(OH)2). In connection with the mica problem, the spectrum has been recorded of synthetic phlogopite from 300 cm-1 to 100 cm1. Also the effect of temperature on the spectrum of biotite was investigated. The theoretical treatment of the 3~ absorption bands of muscovite and biotite has been completed. Models of these crystals have been constructed in an attempt to see reasons for the differences in the OH group orientations in these two micas. The reflection spectrum of gypsum has been completed in the range 500 to 4000 cm-1 for three different orientations of a single crystal. The spectrum of a single crystal of barium titanate has been obtained between 1,i and 15.uL

- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN - III. PUBLICATIONS LECTURES etc. None of the work done during the period covered by this report has yet been published. At the Ohio State Symposium on Spectroscopy and Molecular Structure held at Columbus, Ohio, a joint paper was given on June 17, 1954 by Dr. Liang and Professor Sutherland entitled "The Location of the Hydrogen Atoms in Muscovite and Biotite" t This paper contained some of the latest work on the theory of the spectra of muscovite and biotite At the Gordon Conference on Infrared Spectra of Large Molecules held at Meriden, N H., a paper was given on August 5, 1954 by Professor Sutherland entitled "Relation Between X-ray Results and Infrared Spectra of Large Molecules." This paper dealt (among other things) with the latest work on mica and on brucite and portlandite. IV. FACTUAL DATA Ao Brucite Problem The spectrum of portlandite (Ca(OH)f)in the form of a single crystal was recorded between 4500cml' and 650cm (Fig. 1). The spectrum is identical with that of brucite (Mg(OH)2) in every detail (cf. Technical Report No. 2, Sept. 1954). This is a very important result, It proves that the fine structure in the 3p region cannot be due to combinations of a single OH frequency with lattice frequencies of the heavier atoms since these would alter very significantly in going from an Mg,O lattice to a Ca,O lattice. B. Mica Problem The spectrum of synthetic phlogopite in the range 300 cm'1 to 100 cm-1 shows bands at 155, 162, 213 and 240 cm~1 It is interesting to note that the bands at 213, 240 and 162 em-1 were not observed in natural phlogopite but the band at 155 cm-1 is present in natural phlogopite and probably also in biotite where its maximum is at 148 cm-1. This proves that the band near 150 cm-1 common to biotite and natural phlogopite is not due to an OH vibration since it is still present in synthetic phlogopite which contains no OH groups.. The spectrum of biotite has been investigated in the region between 2500 and 4500 cm-1 at liquid nitrogen temperatures. The reason for this experiment was to see what light it would throw on the anomaly of the 2.72i band mentioned in our last report (Quarterly Report No. 11, p. 2, March 1954). If our original picture is correct, the 2.72i band ought to be absent unless the biotite 2

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN is tilted to make the cleavage plane oblique to the incident radiation. It was found that at low temperatures the 2.72, band increased markedly in intensity for normal incidence. However, the 2.835 band only increased very slightly at liquid nitrogen temperatures for normal or oblique incidence. On examining the 2.72p2 band with the incident ray oblique to the cleavage plane, it was clear that there was little or no temperature effect on that component of the absorption which becomes active for oblique incidence. This indicates that the small absorption observed at 2.72k for normal incidence is probably unconnected with the absorption which appears here on tilting. The exact origin of this extra absorption at 2.72p, which is very sensitive to temperature, is still unknown. It is most probably due to a combination frequency. It is interesting to note that two weak bands at 3.15[ (3174 cm-1) and 3.27k (3058 cm-1) which are present as weak absorptions at room temperature become quite marked at high temperature (450~C) and are completely missing at low temperature (90~K) (Fig. 2). Two other bands at 2.335 and 2.384 (4290 cm-1 and 4200 cm-1) show the reverse behavior in that their intensity is increased at low temperatures and slightly diminished at higher temperatures. These four bands are presumably combination frequencies as shown in the table below: cm-1 Differences cm 1 Differences in cm-1 in cmn1 2.33 4290 2.38 4200 > 614 > 524 2.72 3676 2.72 3676 > 618 > 502 3.27 3058 3.15 3174 It should be remarked that no absorption has been found in biotite either near 615 cm-l or 515 cm-1 but these frequencies may, of course, be forbidden as fundamentals and yet active in combinations with the 3676 cm-1 fundamental frequency. The theoretical work on muscovite and biotite consisted largely of studying the selection rules for the space groups C4h and C6h which are applicable to these crystals. Various possible positions of the OH groups were tried but only one reasonable arrangement was found to give predicted results consistent with our experimental data (apart from the anomaly discussed above). A full account of this work is being given in the Final Report on Contract DA 36-039 sc-5581, since it is inappropriate to divide the theoretical treatment of the spectra of muscovite and biotite into two parts. 3

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN Accurate scale models have been constructed of the unit cells of muscovite and biotite in order to study more clearly the environment of the OH groups in the two cases. This work is continuing in an attempt to see why the OH configurations are so different in these two micas. C. Gypsum Problem The infrared spectrum of a single crystal of gypsum (CaS04 2H20) has now been investigated very fully on the experimental side. The absorption spectrum has been obtained with the incident radiation normal to the best cleavage direction (i.e. normal to the (010) plane). The reflection spectrum has been obtained normal to the (010) plane, normal to the (-101) plane and normal to the (100) plane. The absorption spectra are now being derived from the reflection spectra following the method of Robinson and Price (Proc. Phys. Soc. 66, 969 (1953)). This is a very tedious process and so arrangements have been made with the Willow Run Research Center to have the computations done on their computing machine MIDAC. The programming has been completed during the past few weeks and it should now be a relatively e asy matter to obtain the absorption spectra. D. Barium Titanate Problem The spectrum of a single crystal of BaTiO3 (from the Bell Telephone Laboratories) has been obtained between 1 and 15p (Fig. 3) There is only one weak band observed at 8, followed by a steep rise in absorption at 9.5j to a "cut off" which extends beyond 15, The thickness of the crystal was approximately 0.15 mm. It is interesting to note the resemblance between this spectrtun and that recently reported by Noland (Phys. Rev. 94, 724 (1954)) for a single crystal of SrTiO3. The latter showed a steep cut off at 10t and weak bands near 5.5k and 7.5k. V. CONCLUSIONS Brucite The work on portlandite has confirmed our earlier conclusions on brucite that the hydrogen atoms do not appear to be in the positions deduced from X-ray measurements. The only alternative is that some new phenomenon has been uncovered in the infrared spectra of crystals which cannot be accounted for on present theories. 4

- ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN Muscovite and Biotite The work on the effect of temperature on the bands near 3i, together with the theoretical work, confirms our earlier conclusion that the OH groups have very different orientations in muscovite and biotite. A band near 150 cm~1 common to biotite and natural phlogopite cannot be due to OH groups. Gyp sum No conclusions can be drawn from this work until the observed data on the reflection spectra have been converted into absorption spectra Barium Titanate The difference in the new band found at 8p from that in SrTiO3 at 7.5p. may be significant. VI. FUTURE PROGRAM The work on the micas will be prepared for publication in a scientific journal. A full account of the work on brucite and portlandite will be prepared for publication. The work on gypsum will be continued. After reduction of the data to absorption spectra, the interpretation of these spectra will be sought in terms of the presently accepted structure based on X-ray data. Particular attention will be paid to the determination of the orientation of the water molecules. The differences between the spectra of BaTiO3 and SrTiO3 will be further investigated, especially at longer wavelengths. VII, PERSONNEL The following have been engaged on the work reported here: Professor G.B.B.M. Sutherland, Director (part time) Mrs. C. Y. Pan Liang (half time) Mr. Mo Haas (part time) Mr. A. Dockrill (part time) 5

100 o80 (0 (/( +" 40 t.)., Q.20 2O X2 4 6 8 10 12 14 Fig. 1. Spectra of single crystal of Portlandite Ca(OH)2 with incident beam parallel to the C-axis, (a) 100 microns thick, (b) same sample which has been exposed to source radiation and atmosphere for a long period (NaC1 prism dispersion). A -6

0 I 60-,! I L) Q1 40 20 I 2# 3# Fig. 2. Spectra of Biotite crystal with incident beam perpendicular to cleavage at (a) room temperature (b) liquid nitrogen temperature (c) 450~ C. (NaC1 prism dispersion). -7

*-OUR 0 e N n Fig. 3. Spectrum of single crystal of Barium Titanate (NaC1 prism dispersion). -8