Crystal structure and phase transformations of calcium yttrium orthophosphate, Ca3Y(PO4)(3)

摘要

Crystal structure and phase transformations of calcium yttrium orthophosphate Ca3Y(PO4)(3) were investigated by X-ray powder diffraction, selected-area electron diffraction, transmission electron microscopy and optical microscopy. The high-temperature phase is isostructural with eulytite, cubic (space group I (4) over bar 3d) with a = 0.983320(5) nm, V = 0.950790(8) nm(3), Z = 4 and D-x = 3.45 Mg m(-3). The crystal structure was refined with a split-atom model, in which the oxygen atoms are distributed over two partially occupied sites. Below the stable temperature range of eulytite, the crystal underwent a martensitic transformation, which is accompanied by the formation of platelike surface reliefs. The inverted crystal is triclinic (space group P1) with a = 1.5726(1) nm, b = 0.84267(9) nm, c = 0.81244(8) nm, alpha = 109.739(4)degrees, beta = 90.119(5)degrees, gamma = 89.908(7)degrees, V = 1.0134(1) nm(3), Z = 4 and D-x = 3.24 Mg m(-3). The crystal grains were composed of pseudo-merohedral twins. The adjacent twin domains were related by the pseudo-symmetry mirror planes parallel to {10 (1) over bar} with the composition surface {10 (1) over bar}. When the eulytite was cooled relatively slowly from the stable temperature range, the decomposition reaction of Ca(3)y(PO4)(3)->beta-Ca-3(PO4)(2)+YPO4 occurred. (c) 2006 Elsevier Inc. All rights reserved.