CHEMICAL PRESSURE ANALYSIS (CPA) - YTTRIUM, BISMUTH, THALLIUM, AND MERCURY BASED HIGH-TEMPERATURE SUPERCONDUCTORS

Chemical pressure analysis (CPA) is used to determine the anisotropic dependence of the critical temperature on the lattice parameters of Bi 2Sr2CaCu2O8+x. CPA yields a quantitative expression relating T-c and l attice parameter values and offers a phenomenological approach to stud ying the effect of structure on superconductivity. Similar to previous ly reported results for YBa2Cu3O7-x and YBa2(Cu1-xFex)(3)O-7-y, CPA fo r Bi2Sr2CaCu2O8+x reveals that the dependence of the critical temperat ure is strongly anisotropic and is influenced much more by chemical pr essure than by physical (mechanical) pressure, per unit change in latt ice parameter. A positive correlation is found between unit cell volum e and T-c for Bi2Sr2CaCu2O8+x, but these parameters are negatively cor related for YBa2Cu3O7-x and YBa2(Cu1-xFex)(3)O-7-y. Physical pressure results for both Tl-2,Ba2CaCu2Ox and HgBa2Cam-1CumO2m+2+delta indicate that increases of up to 28 K (10 GPa) and 30 K (45 GPa), respectively , can be obtained from these compounds, but sufficient lattice constan t and elastic constant data for CPA are not yet available.