CALCULATION OF LOW-TEMPERATURE THERMAL-EXPANSION OF THE HIGH-TEMPERATURE SUPERCONDUCTOR BI2SR2CACU2O8

The anisotropy of low-temperature thermal expansion of the high-temper ature superconductor Bi2Sr2CaCu2O8 (Bi-2:2:1:2) is analyzed theoretica lly. The generalized Gruneisen parameters (GPs) of elastic waves propa gating in different directions of Bi-2:2:1:2 are calculated using the measured values of second order elastic constants and first order pres sure derivatives of second order elastic constants, For this, we have used the measured values of the second order elastic constants of G. A . Saunders et al, The 12 third order elastic constants of the Bi-2:2:1 :2 system are calculated from the expressions of effective second orde r elastic constants, All the third order elastic constants are negativ e except C-155 and C-112, Some values of generalized Gruneisen paramet ers are negative. The generalized GPs gamma(j) '' are all positive exc ept gamma(2) '' (-0.048) at theta = 85 degrees, The Brugger gammas are calculated and the low-temperature limits of the Gruneisen gamma are determined using the procedure of Menon and Ramji Rao, gamma(L)(-) has the value of 4.4 for the Bi-2:2:1:2 system, The low-temperature limit of the Gruneisen gamma is positive, Therefore, we expect volume expan sion to be positive down to absolute zero for the Bi-2:2:1:2 system, T he anisotropy of thermal expansion along the c axis of the compound is very much higher than that along other directions. (C) 1996 Academic Press, Inc.