Preparation and thermal expansion of [formula omitted] with the cubic ZrP 2O 7 structure

Abstract

A series of compounds ( M 0 . 5 III M ′ 0 . 5 V ) P 2 O 7 , M III M ′ V =AlTa, FeTa, GaTa, InNb, YNb, NdTa, and BiTa that are close structural relatives of cubic ZrP 2O 7 were prepared. Annealing samples with M III M ′ V =InNb or YNb at temperatures above 600 °C did not lead to any long-range cation ordering. The thermal expansion characteristics of samples quenched from 1000 °C with M III M ′ V =AlTa, InNb and YNb were investigated by high-temperature powder diffraction over the temperature range 25–600 °C. There are no lattice constant discontinuities in this range, unlike ZrP 2O 7. (Al 0.5Ta 0.5)P 2O 7 and (In 0.5Nb 0.5)P 2O 7 show linear coefficients of thermal expansion (CTEs) of 11.5(2)×10 −6 and 11.8(2)×10 −6 K −1, respectively. These values are similar to that for the low-temperature ZrP 2O 7 structure. However, the linear CTE for (Y 0.5Nb 0.5)P 2O 7 (4.8(2)×10 −6 K −1) is similar to that of the high-temperature form of ZrP 2O 7.