Simulation study of pressure-induced structural changes in La 2CuO 4 and in La 1.83Sr 0.17CuO 4

Abstract

We have used atomistic simulation techniques to investigate the structure of La 2CuO 4 and La 1.83Sr 0.17CuO 4 as a function of pressure up to a value of 140 kbar using two sets of potentials. The pressure-induced orthorhombic-tetragonal phase transition has been simulated. The relative compressibilities of the three axes in the orthorhombic phase are found to be in the order a > b > c whereas in the tetragonal phase the compressibilities of the ‘ a’ and the ‘ c’ parameters are found to be closer. We observe no anomalous change in the Cu-O(2) (apical) bond length in the pressure range studied. However, the effect of the pressure-induced shortening of the Cu-O(2) bond is larger than the cell compression along the same direction. Moreover, the fractional atomic coordinates z(O(2)) change systematically with pressure, but z(La) remains almost constant in both phases. The detail of the change of the tilt of the CuO 6 octahedra and the deformation of CuO 6 basal plane as a function of pressure have also been investigated. In addition, we simulated the pressure-induced structural changes in La 1.83Sr 0.17CuO 4 and again observed no anomalous change of the Cu-O(2) bond length.