Synthesis and characterization of the novel rare earth orthophosphates Y0.5Er0.5PO4 and Y0.5Yb0.5PO4

Abstract

Abstract The new mixed rare earth (RE) orthophosphates Y0.5Er0.5PO4 and Y0.5Yb0.5PO4 were synthesized by a classical solid state reaction in an electrical furnace at 1200 °C. As starting materials, the corresponding rare earth oxides and diammonium hydrogen phosphate were used. The powder diffraction analyses revealed that the new compounds Y0.5Er0.5PO4 and Y0.5Yb0.5PO4 crystallize in a zircon-type structure being isostructural with the rare earth orthophosphate YPO4. Y0.5Er0.5PO4 and Y0.5Yb0.5PO4 crystallize in the tetragonal space group I41/amd (no. 141) with four formula units in the unit cell. The structural parameters based on Rietveld refinements are a = 687.27(2), c = 601.50(2) pm, V = 0.28412(1) nm3, R p= 0.0143, and R wp = 0.0186 (all data) for Y0.5Er0.5PO4 and a = 684.61(2), c = 599.31(2) pm, V = 0.28089(2) nm3, R p = 0.0242, and R wp = 0.0313 (all data) for Y0.5Yb0.5PO4. Furthermore, the structure of Y0.5Er0.5PO4 was refined from single-crystal X-ray diffraction data: a = 687.78(5), c = 601.85(4) pm, V = 0.28470(5) nm3, R 1= 0.0165, and wR 2 = 0.0385 (all data). In both compounds, the rare earth metal ions are eightfold coordinated by oxygen atoms, forming two unique interlocking tetrahedra with two individual RE–O distances. The tetrahedral phosphate groups [PO4]3– are slightly distorted in both compounds. The individual rare earth ions share a common position (Wyckoff site 4a). The presence of two rare earth ions in the structures of the new orthophosphates Y0.5Er0.5PO4 and Y0.5Yb0.5PO4 was additionally confirmed by single-crystal EDX spectroscopy revealing a ratio of 1:1.