Thermal evolution of the metamict fergusonite-(Y)

The metamict fergusonite-(Y) with the formula (Y 0.70 Ln 0.20 Ca 0.13 U 0.02 Th 0.02 ) ∑1.07 (Nb 0.72 Ta 0.17 W 0.06 Ti 0.04 ) ∑1 (O 3.97 (OH) 0.11 F 0.08 Cl 0.03 ) · 2.12H 2 O from the Blyumovskaya Pit, Ilmeny Mountains (Russia) was studied by the means of high-temperature X-ray diffraction, thermal analysis, Raman spectroscopy and microprobe analysis. Thermal expansion was studied for both tetragonal ( α -fergusonite) and monoclinic ( β -fergusonite) polymorphs. The expansion of β -fergusonite is anisotropic and strongly negative along the α 33 . In contrast, α -fergusonite exhibits a relatively isotropic thermal expansion upon heating. The volume CTE ( α V ) for β -fergusonite varies in the range 22.87(94)–75.4(2.5) × 10 –6 ºC −1 , whereas α -fergusonite has α V = 32.33(57)–31.66(49) × 10 - 6 ºC −1 in the temperature range 850–1200 °C. After heating to 1100 °C, the mineral develops a porous texture, and the radioactivity is reduced by 37%, which can be attributed to the partial volatilization of some radionuclides. In situ experiments revealed the complete sequence of the thermal evolution of the metamict fergusonite-(Y) for the first time.