Solid Solution Formation between Vanadium(V) and Tungsten(V) Oxide Phosphate

The solid solutions (V 1– x W x )OPO 4 with β‐VOPO 4 structure type (0.0 ≤ x ≤ 0.01) and α II ‐VOPO 4 structure type (0.04 ≤ x ≤ 0.26) were obtained from mixtures of V V OPO 4 and W V OPO 4 by conventional solid state reactions and by solution combustion synthesis. Single crystals of up to 3 mm edge length were obtained by chemical vapor transport (CVT) (800 → 700 °C, Cl 2 as a transporting agent). Single crystal structure refinements of crystals at x = 0.10 [ a = 6.0503(2) Å, c = 4.3618(4) Å, R 1 = 0.021, wR 2 = 0.058, 21 parameters, 344 independent reflections] and x = 0.26 [ a = 6.0979(2) Å, c = 4.2995(1) Å, R 1 = 0.030, wR 2 = 0.081, 21 parameters, 346 independent reflections] confirm the α II ‐VOPO 4 structure type ( P 4/ n , Z = 2) with mixed occupancy V/W for the metal site. Due to the specific redox behavior of W 5+ and V 5+ , solid solutions (V 1– x W x )OPO 4 should be formulated as (V IV x V V 1–2 x W VI x )OPO 4 . The valence states of vanadium and tungsten are confirmed by XPS measurements. V 4+ with d 1 configuration was identified by EPR spectroscopy and magnetic measurements. Electronic spectra of the solid solutions show the IVCT(V 4+ → V 5+ ) and the LMCT(O 2– → V 5+ ). (V 0.74 W 0.26 )OPO 4 powders exhibit semi‐conducting behavior ( E g = 0.7 eV).