In situ Raman spectroscopy of pressure-induced phase transformations in DyPO₄ and GdxDy(1-x)PO₄
Xenotime DyPO4 and GdxDy(1-x)PO4 (x = 0.4, 0.5, 0.6) (tetragonal I41/amd zircon structure) have been studied at ambient temperature under high pressures inside a diamond anvil cell with in situ Raman spectroscopy. The Raman active modes of the xenotime structure were observed at low pressures and the appearance of new Raman peaks at higher pressures indicate a phase transformation to a lower symmetry structure, likely monoclinic. The onset phase transformation pressure of DyPO4 was 15.3 GPa. The transformation pressures of the solid solutions (GdxDy(1-x)PO4) were 12.2 GPa (40/60, x=0.4), 10.1 GPa (50/50, x=0.5), and 11.9 GPa (60/40, x=0.6). The addition of Gd resulted in a decrease in transformation pressure from pure DyPO4. A line crossing as a result of Raman mode softening is observed at approximately 7-8 GPa for each material, preceding the phase transformation. DyPO4 underwent a reversible phase transformation and returned to the xenotime phase after decompression. The solid solutions yielded partially reversible phase transformations and retained peaks from the high-pressure phase while reforming xenotime peaks upon decompression.
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