Effect Of Annealing On Structural And Thermodynamic Properties Of Thsio4-Erpo4 Xenotime Solid Solution

The effect of annealing on structural and thermochemical properties of a thorite-xenotime solid solution Th1-xErx(SiO4)(1-x)(PO4)(x) 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 degrees 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 W(x) = (73.1 +/- 20.1) - (125.7 +/- 49.8).x.