Pressure-Induced Structural Phase Transitions in Ln_2-xNd_xCuO₄ for Ln=La (0.6≤x≤2) and Ln=Pr (x=0)

Author： Wilhelm H. Cros C. Reny E. demazeau G. Hanfland M.

ISSN： 0022-4596

Source： Journal of Solid State Chemistry, Vol.151, Iss.2, 2000-05, pp. : 231-240

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Abstract

We have investigated the structural properties of LaNdCuO₄ and Pr₂CuO₄ under hydrostatic pressure up to 37 GPa at ambient temperature by high-resolution angle-dispersive X-ray powder diffraction. Upon increasing pressure a structural transformation into the T-structure (I4/mmm, K₂NiF₄-type) was observed at P_T=11.4 GPa and P_T=15.1 GPa, respectively. Full-profile refinements of the diffraction data give evidence for a gradual distortion of the T-structure into the orthorhombic O-phase (Cmca, distorted K₂NiF₄-type) during pressure release in a certain pressure interval. At low pressures the initial T′-structure (I4/mmm, Nd₂CuO₄-type) is eventually recovered again. The axis and volume compressibilities are well described by a simple model that considers the linear compressibilities of different polyhedra building the unit-cell. The occurrence of the O-phase can be understood within the tolerance factor t versus P_T phase diagram.