The thermoresponsive behaviour of selected rare-earth hafnate, zirconate, and titanate compounds

Abstract

The lattice parameters and thermal expansion coefficients for La2Hf2O7, Eu2Hf2O7, Gd2Hf2O7, Y2Hf2O7, Gd2Zr2O7, Y2Zr2O7, Eu2Ti2O7, Gd2Ti2O7, and Y2Ti2O7 were determined relative to temperature over the range of 30°C to 850°C. All materials were determined to be of the pyrochlore phase expect for Y2Hf2O7, which crystallised in the defect fluorite phase. All materials were shown to have positive thermal expansion, which was not consistent over the experimental temperature range. The change in the thermal expansion coefficient was positive for La2Hf2O7, Y2Zr2O7, Eu2Ti2O7 and Y2Ti2O7, of which the largest change was experienced by Y2Zr2O7. The remaining materials experienced a negative change in their thermal expansion coefficients. The largest negative change was experienced by Gd2Ti2O7. It was shown that the x parameter of the 48f oxygen atom increased with increasing temperature. This had the effect of distorting the transition metal octahedral, and creating a more perfect rare-earth cube as the parameter increased.