The effect of electronically-induced lattice distortions on the structural distortions in layered lanthanum cuprates.

The Jahn-Teller active La(2-x)Ba(x)CuO4 system undergoes a phase transition from a low-temperature orthorhombic (LTO) to a low-temperature tetragonal (LTT) phase at doping values centred around x = 0.125. The LTT phase correlates with a dramatic suppression of superconductivity, neither of which are observed in the Sr-doped lanthanum cuprate. In this work we use density-functional theory calculations to understand the extent to which structural distortions arising from the Jahn-Teller effect induce a symmetry-breaking distortion in the Ba-doped system but not in the Sr-doped system. We find that the relative stability of the LTT and LTO phases is sensitive to the magnitude of the Jahn-Teller distortion and the average A-site ionic radius, which helps explain the differences between the phase diagrams of the Ba- and Sr-doped systems.