Subsolidus phase relations and crystal structures of the mixed-oxide phases in the In2O3-WO3 system

Subsolidus phase relationships in the In2O3-WO3 system at 800-1400degreesC were investigated using X-ray diffraction. Two binary-oxide phases-In6WO12 and In-2(WO4)(3)-were found to be stable over the range 800-1200degreesC. Heating the binary-oxide phases above 1200degreesC resulted in the preferential volatilization of WO3. Rietveld refinement was performed on three structures using X-ray diffraction data from nominally phase-pure In6WO12 at room temperature and from nominally phase-pure In-2(WO4)(3) at 225degreesC and 310degreesC. The indium-rich phase, In6WO12, is rhombohedral, space group R (3) over bar (rhombohedral), with Z = 1, a = 6.22390(4) Angstrom, alpha = 99.0338(2)degrees [hexagonal axes: a(H) = 9.48298(6) Angstrom, c = 8.94276(6) Angstrom, a(H)/c = 0.9430(9)]. In6WO12 can be viewed as an anion-deficient fluorite structure in which 1/7 of the fluorite anion sites are vacant. Indium tungstate, In-2(WO4)(3), undergoes a monoclinic-orthorhombic transition around 250degreesC. The high-temperature polymorph is orthorhombic, space group Pnca, with a = 9.7126(5) Angstrom, b = 13.3824(7) Angstrom, c 9.6141(5) Angstrom, and Z = 4. The low-temperature polymorph is monoclinic, space group P2(1)/a, with a = 16.406(2) Angstrom, b = 9.9663(1) Angstrom, c = 19.099(2) Angstrom, beta = 125.411(2)degrees, and Z = 8. The structures of the two In-2(WO4)(3) polymorphs are similar, consisting of a network of corner sharing InO6 octahedra and WO4 tetrahedra. (C) 2004 Elsevier Inc. All rights reserved.