Thermodynamics of the (lanthanum + strontium + copper + oxygen) high-Tc superconductors I. Heat capacities of SrCuO2, Sr2CuO3, and Sr14Cu24O41

Abstract

The subambient heat capacities of three (SrO)x(CuO)y inter-oxide samples with x = Y = 1; x = 2, y = 1; and x = 1, y = 2, were measured as a part of an investigation into the chemical thermodynamics of the high-Tc superconducting system (lanthanum + strontium + copper + oxygen). No anomalous contribution to the heat capacity was observed over the experimental region. The heat capacity of the Sr14Cu24O41 phase was derived from that of the mixed phase of nominal composition x = 1, y = 2. All samples exhibit a Debye-like behavior at low temperatures with finite linear electronic terms. Thermophysical properties at selected temperatures are presented and compared for the three compounds. The values of Smo at 298.15 K for the three compounds Sr1/2Cu1 2O, Sr2/3Cu1/3O, and Sr14/38Cu24 38O41/38 were: 5.828[middle dot]R, 5.953[middle dot]R, and 6.032[middle dot]R, respectively.