Phase relations and chemical vapor transport of hexagonal indium tungsten bronze InxWO3

• Phase relations of hexagonal bronze InxWO3 with neighboring phases.
• Chemical vapor transport experiments using NH4Cl as transport agent.
• Single crystals of InxWO3 up to a few mm in size were prepared.
• Selective synthesis of crystals of the indium poor and indium rich phase boundary.

Phase pure powder samples of hexagonal indium tungsten bronze InxWO3 (x = 0.25–0.35) were synthesized by solid state reaction at 1173 K. The phase relations of InxWO3 with neighboring binary and ternary phases were determined in the phase diagram In–W–O. Systematic chemical vapor transport experiments were carried out on source materials with compositions corresponding to miscellaneous two-phase and three-phase regions using NH4X (X = Cl, Br, I) as transport agent. Crystals of hexagonal indium tungsten bronze were deposited beside In2W3O12 with composition corresponding to the indium poor phase boundary and dimensions up to a few mm in a temperature gradient 1173 K → 1073 K starting from ternary mixtures InxWO3/In2W3O12/In0.02WO3. Sole deposition of InxWO3 single crystals with composition x ≈ 0.33 was observed from ternary mixtures InxWO3/W18O49/WO2 with a migration rate of about 0.5 mg/h (transport agent NH4Cl).