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

Abstract

We investigated the formation mechanism of {111} twins in BaTiO 3 through systematic studies of the effects of various processing parameters on the {111} twin formation, in particular, excess TiO 2, initial particle sizes of raw materials and sintering atmosphere (either oxidizing or reducing). Our study on the effect of excess TiO 2 revealed that the second-phase Ba 6Ti 17O 40 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 BaTiO 3 grains around the Ba 6Ti 17O 40 particles. The twins, however, formed only when the Ba 6Ti 17O 40 interface and the BaTiO 3 grain boundaries were faceted in an oxidizing atmosphere. In a reducing atmosphere, the Ba 6Ti 17O 40 interface and the grain boundaries were defaceted (rough), and no {111} twins formed. Based on these experimental observations, we proposed a second-phase (Ba 6Ti 17O 40) assisted formation mechanism of {111} twins in BaTiO 3. 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.