Structural and thermodynamic properties of anionically substituted solid solution ceramics Y(VO4)1-x(PO4)x with zircon structure

Solid solution samples of yttrium orthophosphate-yttrium orthovanadate of general formula Y(VO4)(1-x)(PO4)(x) (x = 0.25; 0.50; 0.75) were obtained using solid state synthesis. The samples crystallize in zircon structure (I4(1)/amd sp. gr.) as the pure end-members of the system do. Unit cell parameters calculated using XRD data were found to be in good agreement with those calculated from the Vegard law. SEM-EDS spectra of samples are given. Heat capacities of the samples (x = 0.50; 0.75) were measured by means of adiabatic calorimetry at low temperatures (6-344 K). Thermodynamic functions in the studied temperature range were calculated and compared to those of pure yttrium orthophosphate and orthovanadate. According to the data obtained solid solution Y(VO4)(1-x)(PO4)(x) can be considered as ideal, thus making it possible to calculate thermodynamic functions for any other substitution x by summation of obtained values for closest compounds with corresponding coefficients or pure substances.