Effect of crystallite size on the ferroelectric domain growth of ultrafine BaTiO3 powders

The relationship between ferroelectric domain growth and the size of crystallites in ultrafine BaTiO3 powders has been investigated. It was observed that the critical size for the c --> t-BaTiO3 phase transformation was about 30 nm and that BaTiO3 crystallites probably transformed from single-domain to multidomain when the particle size was larger than 100 nm, X-ray diffraction patterns of BaTiO3/PVDF composites before and after poling indicated that the degree of poling efficiency for composites with fine BaTiO3 powders is much smaller than for coarser powders larger than 100 nm. The present work indicates that the presence of ferroelectric domains in BaTiO3 powder depends on the constraining force introduced by hard agglomeration of the crystallites. The particles obtained by calcining at a higher temperature (larger than 100 nm and partially sintered), composed of several crystallites, may behave similar to grains in fine-grained BaTiO3 ceramics where ferroelectric domains are generated due to mechanical clamping, On the other hand, particles of small size composed of single crystallite and without clamping force, may deform similar to a lattice cell and avoid formation of twins.