Thermochemistry and Chemical Vapor Transport of In₂M₃O₁₂ (M = Mo, W)

Abstract

The standard entropy of compounds In2M3O12 (M = Mo, W) were determined to be S°298 = 390 ± 6 (M = Mo] and S°298 = 404 ± 6 J·mol–1·K–1 (M = W). The entropies of formation from the binary oxides are ΔS°R, 298 = 52 J·mol–1·K–1 (M = Mo] and ΔS°R, 298 = 72 J·mol–1·K–1 (M = W). Both compounds possess positive enthalpies of formation from the oxides at 298 K and are entropically stabilized. Transition enthalpies of the monoclinic to orthorhombic phase transition were measured for In2M3O12 by differential scanning calorimetry. Crystals of In2M3O12 (size up to a few mm) were deposited by means of chemical vapor transport along a temperature gradient ΔT = 100 K using transport agent chlorine. Deposition rates are between 0.2 and about 15 mg·h–1, depending on mean transport temperature and amount of chlorine. Experimental results were compared to predictions by means of thermodynamic modelling. A detailed analysis of the chemical vapor transport behavior was carried out regarding gaseous compounds involved in the transport process, dominant transport reactions and influence of moisture content.