The energetics of the TiO2 polymorphs (rutile, anatase, and brookite) were studied by high temperature oxide melt drop solution calorimetry. Relative to bulk rutile, bulk brookite is 0.71 ؎ 0.38 kJ͞mol (6) and bulk anatase is 2.61 ؎ 0.41 kJ͞mol higher in enthalpy. The surface enthalpies of rutile, brookite, and anatase are 2.2 ؎ 0.2 J͞m 2 , 1.0 ؎ 0.2 J͞m 2 , and 0.4 ؎ 0.1 J͞m 2 , respectively. The closely balanced energetics directly confirm the crossover in stability of nanophase polymorphs inferred by Zhang and Banfield (7). An amorphous sample with surface area of 34,600 m 2 ͞mol is 24.25 ؎ 0.88 kJ͞mol higher in enthalpy than bulk rutile.

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