Necessary conditions for the formation of {111} twins in barium titanate

The experimental conditions for {111} twin formation in BaTiO3 mere investi gated, When BaTiO3 compacts without excess TiO2 were sintered either in an oxidizing atmosphere lair) or in a reducing atmosphere (95N(2)-5H(2) no {11 1} twins formed within the BaTiO3 grains and no abnormal grain growth occur red. In contrast, many {111} twins were present within the abnormally grown grains in the eseess-TiO2-containing BaTiO3 samples sintered in air, while no twins were observed in the excess-TiO2-containing samples sintered in 9 5N(2)-5H(2). X-ray diffraction analysis showed that excess TiO2 forms a Ba6 Ti17O40 phase during sintering with the space group A2/a in air and a Ba6Ti 17O40-x phase with the space group C in 95N(2)-5H(2). It appears therefore that excess TiO2 and an oxidizing atmosphere are necessary for (111) twin f ormation in BaTiO3. These results may also indicate that the interface stru cture between BaTiO3 and Ba6Ti17O40 influences the twin formation.