M. Lepple, S.V. Ushakov, K. Lilova, C.A. Macauley, A.N. Fernandez, C.G. Levi, A. Navrotsky
Journal of the European Ceramic Society In Press, Corrected Proof, DOI: 10.1016/j.jeurceramsoc.2020.10.039
Reprinted from Journal of the European Ceramic Society, M. Lepple, S.V. Ushakov, K. Lilova, C.A. Macauley, A.N. Fernandez, C.G. Levi, A. Navrotsky, Thermochemistry and phase stability of the polymorphs of yttrium tantalate, YTaO4, Copyright (2020), with permission from Elsevier
Thermodynamic parameters of the three fergusonite-related polymorphs M’, M and T of YTaO4 and their phase stabilities were investigated experimentally. The debate on the relative stability of the M and M’ phases was resolved, and it was shown that the compound does not transform to a cubic polymorph prior to melting. The enthalpies of formation of M and M’ were determined using high temperature oxide melt solution calorimetry, and the heat capacities and heat contents were measured. The enthalpy of the M’ to T phase transition was measured by differential thermal analysis. The stability of the T phase up to its melting at 2090 °C was demonstrated using high temperature X-ray diffraction and thermal analysis. Its enthalpy of fusion was determined using drop-and-catch calorimetry. The thermodynamic properties of YTaO4 assessed in this study enable the thermodynamic modeling of its polymorphs and related materials systems of technological importance.