Effect of Annealing on Structural and Thermodynamic Properties of ThSiO-ErPO Xenotime Solid Solution.

The effect of annealing on structural and thermochemical properties of a thorite-xenotime solid solution ThEr(SiO)(PO) was assessed. The samples synthesized at low temperatures and stored at room temperature for 2 years retained their tetragonal structures. This structure was also maintained after heating to 1100 °C. During annealing, the structure lost water and exsolved some thorianite phases. The thermodynamic parameters did not change much after annealing, suggesting that xenotime was not a low-temperature metastable phase but rather a stable structure able to withstand elevated temperatures regardless of the thorium content. The solid solution exhibited subregular behavior with the Margules function () = (73.1 ± 20.1) - (125.7 ± 49.8)·.