Abstract
We have studied the nucleation and growth processes that occur during the irreversible structural transformation of metastable oxide phases to their thermodynamically stable polymorphs. The transformations examined were: (i) cubic pyrochlore Pb2Ti2O6 (metastable) to tetragonal perovskite PbTiO3; (ii) hexagonal BaFe2O4 (metastable) to orthorhombic BaFe2O4; and (iii) orthorhombic stibiotantalite BiNbO4 (metastable) to triclinic BiNbO4. In each case the irreversible transformation was accompanied by a marked reduction in the particle size, which can be correlated to the change in the specific volume at the transition. Solids which undergo a relatively large change in specific volume during structural transformation can therefore be obtained in fine-particle form by controlled heating of their metastable polymorphs just above the transformation temperature.
Published Version
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