Nucleation of twins by grain coalescence during the sintering of BaTiO3ceramics

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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, the conditions for this kind of twin nucleation are concisely summarized.

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