Lattice thermal expansion of zircon-type LuPO4 and LuVO4: A comparative study

We report the lattice thermal expansion of zircon-(xenotime-)type LuPO 4 and LuVO 4 in the temperature range of 25-1000 °C from high-temperature powder XRD studies. The details of the high-temperature crystal chemistry of both phases have been determined from Rietveld analysis of the powder XRD data. Both the compounds show appreciably higher thermal expansion than analogous zircon-type silicates. Despite isomorphism, the axial thermal expansion of LuVO 4 shows significant anisotropy compared to LuPO 4 . In the studied temperature range, the average axial thermal expansion coefficients of LuPO 4 are α a = 6.0 × 10 -6 and α c = 7.2 × 10 -6 (°C -1 ) and those of LuVO 4 are α a = 3.6 × 10 -6 and α c = 11.8 × 10 -6 (°C -1 ). However, the average volume thermal expansion coefficients are almost identical. The differences in the thermal expansion behavior of the two structures originate from differences in the expansion and distortion of the LuO 8 polyhedra. The LuO 8 polyhedron in LuVO 4 shows about 30% higher thermal expansion than that in LuPO 4 . The overall thermal expansion behaviors of these two structures are predominantly related to the distortion in the LuO 8 unit, inter-cation distances and spatial arrangement of the Lu-O bonds in the structure.