On a minimum grain size for domain formation in lanthanum-modified lead titanate ferroelectric ceramics

When cubic lead titanate, point group m3m, is cooled below its Curie point, it transforms into 100>, becoming tetragonal, point group 4mm. This is the ferroelectric state. In order to relieve the transformation strain, twins (ferroelectric domains) form, with {101} habit. A critical grain size for twinning has also been found using transmission electron microscopy. The experimentally observed minimum grain size (<0.3 μm) is consistent with values derived from a balance of the cubic to tetragonal elastic strain and twin surface energies. The samples under consideration were lanthanum-modified lead titanate, Pb/sub 0.7/La/sub 0.2/O/sub 3/ + 0.1 PbO, prepared by sintering