Control of (111) twin formation and abnormal grain growth in BaTiO3

Abstract

To investigate the experimental conditions for {111} twin formation and abnormal grain growth in BaTiO3, various powder compacts with and without excess TiO2 were sintered either in an oxidizing atmosphere (air) or in a reducing atmosphere (95N(2)-5H(2)). In all the samples sintered in 95N(2)-5H(2), no twins formed and no abnormal grain growth occurred. On the other hand, when the samples with excess TiO2 were sintered in air, abnormal grain growth occurred and all the abnormal grains contained {111} twins. X-ray diffraction analysis showed that, during sintering, the excess TiO2 formed a Ba6Ti17O40 phase with the space group A2/a in air and a Ba6Ti17O40-x phase with the space group C in 95N(2)-5H(2). These results show that the {111} twins form and the abnormal grain growth occurs only when the powder compact contains excess TiO2 to form a Ba6Ti17O40 phase and is sintered in an oxidizing atmosphere. The results may also suggest that the Ba6Ti17O40 phase acts as the nucleation site of {111} twins. The suggestion has been further confirmed via a TEM observation.