Nucleation of twins by grain coalescence during the sintering of BaTiO3ceramics

Abstract

Abstract As shown by means of sintering procedures and electron microscopy studies, the grains of BaTiO3 ceramics develop crystallographic facets, preferentially of {111} octahedron and {100} cube types, below and above the eutectic temperature respectively of liquid-phase sintering. This faceting, in conjunction with a high mobility or the grains and suitable driving forces, yields a certain probability of forming twins and even double twins by the coalescence of suitably oriented grains during shrinkage. Such a double twin represents a grain which has a size and growth advantage during subsequent sintering. It can therefore be considered to represent the nucleus of the known doubly twinned ‘anomalous’ grains characterized by a central twin lamella. During its preferential growth, one anomalous grain consumes some 104−106 normal grains. Owing to this large number, the probability that grain coalescence events form a twin is quite a reasonable value as theoretically estimated. With some generalization, th...