PRESSURE EFFECTS ON THE STRUCTURAL PHASE-TRANSITIONS AND SUPERCONDUCTIVITY OF LA2-XBAXCUO4 (X = 0.125)

Neutron-diffraction experiments have been performed to study the effec ts of hydrostatic pressure on the structural phase transitions of La2- xBaxCuO4 with x = 0.125. The phase transition to the low-temperature t etragonal (LTT) structure is greatly suppressed by the application of pressure. The LTT transition temperature, observed at around 80 K at a mbient pressure, decreases at the rate of about -135 K/GPa, and this L TT phase disappears under a pressure of around 0.6 GPa. The supercondu cting properties of this compound under high pressure have also been i nvestigated in detail by measurements of the ac magnetic susceptibilit y. The bulk superconducting transition temperature T(c) remains consta nt at pressures of up to 0.5 GPa, and then increases with pressure at the rate of 10 K/GPa up to about 15 K at 1.5 GPa, From these results i t is concluded that there is a clear correlation between the disappear ance of the LTT phase and the enhancement of superconductivity. This c onclusion supports earlier suggestions that there is a strong relation ship between the crystal structure and superconductivity and that, in particular, the LTT phase is detrimental to the superconductivity in t he La2-xBaxCuO4 system.