Surface structures and dielectric response of ultrafine BaTiO3 particles

Characteristic differences are observed for the dielectric response and microstructures of BaTiO3 nanoscale fine powders prepared using sol gel (SG) and steric acid gel (SAG) methods. The former exhibit a critical size below which there is no paraelectric/ferroelectric phase transition whereas Ba-TiO3 prepared via the SAG route remained cubic for all conditions, Atomic resolution images of both varieties showed a high density of interesting surface steps and facets. Computer simulated images of surface structure models showed that the outer (100) surface was typically a BaO layer and that at corners and ledges the steps are typically finished with Ba+2 ions; i.e., the surfaces and steps are Ba-rich. Otherwise the surfaces were typically clean and free of amorphous layers. The relationship between the observed surfaces structures and theoretical models for size effects on the dielectric properties is discussed.