TAXNB1-XVO5 (0 LESS-THAN X LESS-THAN 1) TERNARY OXIDES - SYNTHESIS BY SOL-GEL AND STRUCTURAL CHARACTERIZATION

Ternary oxides of general formula TaxNb1-xVO5 (0 < x < 1) have been synthesized by thermal treatment (873 K, 6 hr) of the corresponding mixed precursor xerogels obtained via sol-gel. The TaxNb1-xVO5 compounds, characterized by XRD, ED, TEM-EDAX, IR spectroscopy, and chemical and thermal analysis are isostructural with the binary MVO5 (M =Nb, Ta) oxides. They are orthorhombic, space group Pnma, Z = 4, and the cell parameters are for x = 0.79; a = 11.8899(7)Å, b = 5.5294(4)Å, c = 6.9505(5)Å; for x = 0.53: a = 11.8916(9)Å, b = 5.5309(4)Å, c = 6.9502(6)Å; and for x = 0.26: a = 11.893(1)Å, b = 5.5327(6)Å, c = 6.9468(9)Å. All these materials can be considered as members of the structural family of the so-called "monophosphate tungsten bronzes,", (MPTB), (PO2)4(WO3)2m, with a value of m = 2. The refinements of the atomic positions have been obtained by Rietveld's method. The TaxNb1-xVO5 compounds constitute a solid solution in the studied composition range. XRD and ED indicate the random distribution of Nb and Ta in these ternary mixed oxides. © 1992 Academic Press, Inc.