Daniel Schildhammer

Structural Redetermination and Photoluminescence Properties of the Niobium Oxyphosphate (NbO)2P4O13

The structure of (NbO)2P4O13 was solved and refined based on new single-crystal diffraction data revealing considerably more complexity than previously described. (NbO)2P4O13 crystallizes in the triclinic space group P1̅ with Z = 6. The lattice parameters determined at room temperature are a = 1066.42(4) pm, b = 1083.09(4) pm, c = 1560.46(5) pm, α = 98.55(1)°, β = 95.57(1)°, γ = 102.92(1)°, and V = 1.7213(2) nm3. The superstructure contains 64 unique atoms including two disordered semioccupied oxygen positions. An unusual 180° bond angle between two [P4O13]6- groups was refined to form half-occupied, split positions in agreement with previous reports. The IR and Raman spectra reflect the appearance of overlapping bands assignable to specific group vibrations as well as P-O-P linkages present in the [P4O13]6- entities. Investigation of the powdered product concerning its photoluminescence properties revealed an excitability in the UV at 270 nm assigned to O2p-Nb4d charge transfer transitions. A resulting broad-band emission with the maximum in the visible region at 455 nm was determined.

Synthesis and characterization of the alkali borate-nitrates Na3–x Kx[B6O10]NO3 (x=0.5, 0.6, 0.7)

Abstract Three novel mixed alkali borate-nitrates Na3−x Kx[B6O10]NO3 (x=0.5, 0.6, 0.7) were synthesized hydrothermally; their crystal structures were determined through Rietveld analyses, and supported through EDX as well as vibrational spectroscopy. The phases represent solid solutions of the alkali borate-nitrate Na3(NO3)[B6O10], which was reported in 2002 as a “New type of boron-oxygen framework in the Na3(NO3)[B6O10] crystal structure” (O. V. Yakubovich, I. V. Perevoznikova, O. V. Dimitrova, V. S. Urusov, Dokl. Phys. 2002, 47, 791). Only two of the three crystallographically independent Na+ positions in the new structures are partially substituted by K+; a pure potassium borate-nitrate was not formed until now. The cell parameters of the novel phases vary from a=1261.72(5)–1267.12(5), b=1004.19(5)–1007.96(4), c=770.55(3)–774.38(3) pm, and V=0.97630(6)–0.98905(6) nm3 in the orthorhombic space group Pnma (no. 62), in alignment with increasing K+ content.

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

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, Rp= 0.0143, and Rwp = 0.0186 (all data) for Y0.5Er0.5PO4 and a = 684.61(2), c = 599.31(2) pm, V = 0.28089(2) nm3, Rp = 0.0242, and Rwp = 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, R1= 0.0165, and wR2 = 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.