Thermal expansion and heat capacities of holmium and erbium orthotantalates ceramics

Abstract

Monoclinic M-orthotantalates of holmium and erbium ceramics were obtained by co-precipitation and annealing at 1773 K and characterized by X-ray powder diffraction, scanning electron microscopy, and chemical analysis. Using the high-temperature X-ray diffraction method, the temperature dependence of the monoclinic lattice parameters of both ceramics were determined at range 298-1273 K. The molar heat capacity of M-HoTaO 4 and M-ErTaO 4 were measured by adiabatic (7-350 K) and differential scanning (320-1350 K) calorimetry. Standard thermodynamic function (entropy, enthalpy change, and reduced Gibbs energy) were calculated on the smoothed values of molar capacity, without taking into account contribution of low-temperature interval: 0-7 K for M-HoTaO 4 and 0-8 K for M-ErTaO 4. The general shape of the anomalous Schottky contribution to the molar heat capacity was determined.