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

Abstract

Subsolidus phase relationships in the In2O3–WO3 system at 800–1400°C were investigated using X-ray diffraction. Two binary-oxide phases—In6WO12 and In2(WO4)3—were found to be stable over the range 800–1200°C. Heating the binary-oxide phases above 1200°C 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 In2(WO4)3 at 225°C and 310°C. The indium-rich phase, In6WO12, is rhombohedral, space group R3̄ (rhombohedral), with Z=1, a=6.22390(4) Å, α=99.0338(2)° [hexagonal axes: aH=9.48298(6) Å, c=8.94276(6) Å, aH/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, In2(WO4)3, undergoes a monoclinic–orthorhombic transition around 250°C. The high-temperature polymorph is orthorhombic, space group Pnca, with a=9.7126(5) Å, b=13.3824(7) Å, c=9.6141(5) Å, and Z=4. The low-temperature polymorph is monoclinic, space group P21/a, with a=16.406(2) Å, b=9.9663(1) Å, c=19.099(2) Å, β=125.411(2)°, and Z=8. The structures of the two In2(WO4)3 polymorphs are similar, consisting of a network of corner sharing InO6 octahedra and WO4 tetrahedra.