Thermal equation of state study of polymorphic phases of Y2O3

Abstract

Pressure and temperature dependences of the unit cell volumes of Y2O3’s three polymorphs (cubic, monoclinic, and hexagonal) have been measured by synchrotron energy dispersive x-ray diffraction in conjunction with a cubic anvil technique to pressures and temperatures up to 7.5 GPa and 1073 K, respectively. The measured pressure–volume–temperature (P–V–T) data were used to obtain thermoelastic parameters of the polymorphs by fitting the modified high temperature third-order Birch–Murnaghan equation of state and a thermal pressure approach. The thermoelastic properties that were determined in this study are the ambient bulk modulus with fixed pressure derivative of the bulk modulus (K0′=4.0), the isobaric temperature derivative of the bulk modulus (∂K/∂T)P, the volumetric thermal expansion coefficient along with the isothermal pressure derivative of thermal expansion (∂α/∂P)T, and the isometric temperature derivative of the bulk modulus (∂K/∂T)V. The ambient bulk modulus for cubic [152(7) GPa] and monoclinic [197(9) GPa] polymorphs agrees well with previous reports. There is no precedence for all other thermophysical properties of all three polymorphs of Y2O3 reported in this study. For instance, (∂K/∂T)P is the highest for the monoclinic polymorph, while (∂α/∂P)T and (∂K/∂T)V are the highest for the cubic polymorph. The results of this study add to the stock of knowledge on the thermophysical properties of Y2O3, which is a technologically relevant solid state material.