Change from Metastable Cubic to Stable Tetragonal Form of Submicron Barium Titanate

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Abstract
The change from metastable cubic to stable tetragonal form was investigated on the submicron BaTiO3 which was prepared by the hydrolysis of titanium tetraisopropoxide in barium hydroxide solution and by crystallization in the glass of BaO–TiO2–SiO2–Al2O3 system. The precipitated BaTiO3 was found to be the aggregates of minute grains of about 100 Å, to have large amount of strain and to absorb about 6% of OH and alcoholic radicals, some of them absorbed chemically. It is in a metastable cubic form. After the heating above 800 °C, it changed to stable tetragonal form in association with weight loss and decrease in lattice strain. The samples heated at 800–900 °C did not show the Curie point on the DTA curve although they were tetragonal. The samples heated at 1300 °C had the Curie point about 122 °C. The glass-devitrified BaTiO3 was also cubic and had large lattice strain. In order to change to tetragonal form, the heating above 1000 °C was needed. The metastable cubic form of submicron BaTiO3 seemed to be stabilized by the absorbants on the surface which balanced with large amount of strain in the lattice.