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Abstract:
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.
