PRESSURE-DEPENDENCE OF THE STRUCTURE OF LA-SR-CU-O

A high-resolution neutron powder diffraction study has been carried out to study the effect of pressure on the structure of the oxide superconductor La1.85Sr0.15CuO4 in its room-temperature tetragonal phase. The refined atomic coordinates indicate an anomalous behaviour of the bond linking the cooper atom to the apical oxygen atom (Cu-O2) of the CuO6 octahedra. The length of this bond increases significantly when the pressure is raised from its atmospheric value to 6 kbar, before decreasing again when the pressure is increased further to 10 kbar. By contrast, the superconducting transition temperature increases linearly with pressure to well above 10 kbar. This result differs from recent work on other oxide superconductors in which increases in Tc have been attributed to linearly related decreases in the corresponding apical Cu-O distance. © 1990.