Phase Equilibria in the System BaO–TiO2

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Abstract
The system BaO‐TiO2 was investigated using quenching, strip‐furnace, and thermal techniques. Five compounds were found to exist in the system: Ba2TiO4, BaTiO3, BaTi2O5, BaTi3O7, and BaTi4O9. Of these, only barium metatitanate (BaTiO3) melts congruently (at 1618°C.). The dititanate melts incongruently at 1322° C. to yield BaTiO3 and liquid; the trititanate melts at 1357°C. to yield BaTi4O9 and liquid; the tetra‐titanate melts to TiO2 and liquid at 1428° C. The nature of melting of the orthotitanate could not be determined accurately because of the high temperature involved and the rapid reaction with platinum. The two eutectics in the system occur between Ba2TiO4 and BaTiO3 at 1563°C. and between BaTi2O5 and BaTi3O7 at 1317°C. The temperature of the cubic‐hexagonal transition in barium metatitanate was determined as 1460°C. and the transition has been shown to be reversible. The transition temperature is raised sharply by the addition of a small percentage of TiO2 although the extent of solid solution is quite limited. Some applications to the manufacture of titanate bodies and to the growth of single crystals of barium metatitanate are discussed.