Thermal expansion and high-temperature phase transformation of the yttrium silicate Y₂SiO₅

The linear thermal-expansion coefficients of yttrium silicate Y₂SiO₅, [Y₂(SiO₄)O] were measured in the temperature range from 20 to 1400 °C using x-ray diffraction. The anomalous behavior of thermal expansion was observed above T_c = 850 °C and was attributed to the displacive phase transformation. The transformation was reversible and resulted from the local order °C the compositional disorder and local fluctuation in the elastic free energy constrained a secondary transformation related to the polymorphic twin transformation. This created an additional peak in x-ray diffraction patterns at 2 's intensity. The characteristic of phase transformation both on heating and on cooling of the sample was also investigated using the differential thermal analysis method. The thermogravimetric technique did not indicate on a change of weight at T_c.