Barium titanate hexagonal

FIG. 13.1. The crystal structures of barium titanate, BaTiOa (a) hexagonal, (b) cubic. 

The complex oxide BaTiOs ( barium titanate ) is remarkable in having five crystalline forms, of which three are ferroelectric. The structure of the high-temperature hexagonal form, stable from 1460°C to the melting point (1612°C), has already been described. The other forms are ... 

Low-temperature syntheses can sometimes allow unique surface phases to be stable. Tetragonal barium ti-tanate, prepared at 700°C, has hexagonal barium titanate on the surface, which is stabilized by a higher surface free energy. Normally this hexagonal phase is not formed below 1460°C. This hexagonal surface was also found to reversibly adsorb CO2 as a surface carbonate. 

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