Second-phase assisted formation of {111} twins in barium titanate Original Research Article

We investigated the formation mechanism of {111} twins in BaTiO3 through systematic studies of the effects of various processing parameters on the {111} twin formation, in particular, excess TiO2, initial particle sizes of raw materials and sintering atmosphere (either oxidizing or reducing). Our study on the effect of excess TiO2 revealed that the second-phase Ba6Ti17O40 particles provided the nucleation sites of the {111} twins. The study on the initial particle size showed that the {111} twins formed during the growth of BaTiO3 grains around the Ba6Ti17O40 particles. The twins, however, formed only when the Ba6Ti17O40 interface and the BaTiO3 grain boundaries were faceted in an oxidizing atmosphere. In a reducing atmosphere, the Ba6Ti17O40 interface and the grain boundaries were defaceted (rough), and no {111} twins formed. Based on these experimental observations, we proposed a second-phase (Ba6Ti17O40) assisted formation mechanism of {111} twins in BaTiO3. The proposed mechanism explained well, all of the observed effects of the processing parameters. The mechanism may also account for the formation of annealing twins in single-phase systems with faceted grain boundaries.