Preparation and thermal expansion of (M0.5IIIM′0.5V)P2O7 with the cubic ZrP2O7 structure

A series of compounds (M0.5IIIM′0.5V)P2O7, MIIIM′VMIIIM′V=AlTa, FeTa, GaTa, InNb, YNb, NdTa, and BiTa that are close structural relatives of cubic ZrP2O7 were prepared. Annealing samples with MIIIM′VMIIIM′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 MIIIM′VMIIIM′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 ZrP2O7. (Al0.5Ta0.5)P2O7 and (In0.5Nb0.5)P2O7 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 ZrP2O7 structure. However, the linear CTE for (Y0.5Nb0.5)P2O7 (4.8(2)×10−6 K−1) is similar to that of the high-temperature form of ZrP2O7.

The average linear coefficient of thermal expansion (∼25–600 °C) for M0.5III(Nb/Ta)0.5P2O7 decreases dramatically on going from In to Y. The behavior of the Y compound is similar to that of ZrP2O7 at high temperatures (>290 °C), whereas the In compound is similar to ZrP2O7 at low temperature.Figure optionsDownload as PowerPoint slide