Pressure-induced structural phase transitions in Ln(2-x)Nd(x)CuO(4) for Ln= La (0.6 <= x <= 2) and Ln = Pr (x=0)

We have investigated the structural properties of LaNdCuO4 and Pr2CuO4 unde r hydrostatic pressure up to 37 GPa at ambient temperature by high-resoluti on angle-dispersive X-ray powder diffraction, Upon increasing pressure a st ructural transformation into the T-structure (I4/mmm, K2NiF4-type) was obse rved at P-T = 11.4 GPa and P-T = 15.1 GPa, respectively. Full-profile refin ements of the diffraction data give evidence for a gradual distortion of th e T-structure into the orthorhombic O-phase (Cmca, distorted K2NiF4-type) d uring pressure release in a certain pressure interval. At low pressures the initial T'-structure (I/4mmm, Nd2CuO4-type) is eventually recovered again. The asis and volume compressibilities are well described by a simple model that considers the linear compressibilities of different polyhedra buildin g the unit-cell. The occurrence of the O-phase can be understood within the tolerance factor t versus P-T phase diagram. (C) 2000 Academic Press.