THE HEAT-CAPACITY AND DERIVED THERMOPHYSICAL PROPERTIES OF THE HIGH-TC SUPERCONDUCTOR YBA2CU3O7-DELTA FROM 5.3 TO 350-K

The heat capacity of the perovskite high-Tc superconductor YBa2Cu3O7-δ was measured from 5.3 to 350 K in an adiabatic calorimetric cryostat. A break in the heat-capacity curve, associated with the critical temperature for superconductivity was observed between 90.09 and 92.59 K. The transition temperature was identified as 91.44 K, and ΔCp,m was calculated to be 0.559R at that temperature. The lattice heat capacity was evaluated by means of the recently developed Komada/Westrum phonon distribution model and the apparent characteristic temperature ΘKW was calculated to be 107.7 K. The excess electronic heat capacity for the superconducting phase was evaluated and the energy gap was identified as 234. R K. Excess contribution, resulting from magnetic impurities, was noted below 20 K. Thermodynamic properties at selected temperatures are presented. © 1990 American Institute of Physics.