The formation of {111} twins was investigated via systematic studies of the effects of processing parameters; especially the presence of excess TiO2, the initial particle size of the raw materials, and the sintering atmosphere (oxidizing or reducing). Study of the effect of excess TiO2 revealed that second-phase Ti17Ba6O40 particles provided the nucleation sites for {111} twins. Study of the initial particle size showed that the {111} twins formed during the growth of BaTiO3 grains around Ti17Ba6O40 particles. However, twins formed only when the Ti17Ba6O40 interface and the BaTiO3 grain boundaries were faceted in an oxidizing atmosphere. In a reducing atmosphere, the Ti17Ba6O40 interface and the grain boundaries were de-faceted, and no {111} twins formed. On the basis of these experimental observations, a second-phase (Ti17Ba6O40) assisted formation mechanism was proposed for (111) twins in BaTiO3.

Second-Phase Assisted Formation of {111) Twins in Barium Titanate. B.K.Lee, S.J.L.Kang: Acta Materialia, 2001, 49[8], 1373-81