Phase Equilibria in the System BaO–TiO 2

The system BaO‐TiO 2 was investigated using quenching, strip‐furnace, and thermal techniques. Five compounds were found to exist in the system: Ba 2 TiO 4 , BaTiO 3 , BaTi 2 O 5 , BaTi 3 O 7 , and BaTi 4 O 9 . Of these, only barium metatitanate (BaTiO 3 ) melts congruently (at 1618°C.). The dititanate melts incongruently at 1322° C. to yield BaTiO 3 and liquid; the trititanate melts at 1357°C. to yield BaTi 4 O 9 and liquid; the tetra‐titanate melts to TiO 2 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 Ba 2 TiO 4 and BaTiO 3 at 1563°C. and between BaTi 2 O 5 and BaTi 3 O 7 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 TiO 2 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.