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

The standard entropy of compounds In2M3O12 (M = Mo, W) were determined to be S-298 degrees = 390 +/- 6 (M = Mo] and S-298 degrees = 404 +/- 6 J.mol(-1).K-1 (M = W). The entropies of formation from the binary oxides are Delta S-R,S-298 degrees = 52 J.mol(-1).K-1 (M = Mo] and Delta S-R,S-298 degrees = 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 Delta T = 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.

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