Phase transition and physical characteristics of nanograined BaTiO3 ceramics synthesized from surface-coated nanopowders

Nanograined BaTiO3 ceramics prepared from 40-nm-size BaTiO3 nanopowders exhibited the cubic as well as the tetragonal phase, while nanograined BaTiO3 ceramics prepared from BaTiO3 nanopowders coated with Mn had only the tetragonal phase. The dielectric constant of the latter was 10 times larger than that of the former; the latter exhibited PTCR behavior with a resistivity jump ratio of about 5.0 X 10(4). These physical properties of the BaTiO3 ceramics appeared to be significantly affected by the strain near grain boundaries; such strain resulted in a phase transition from the cubic to the tetragonal phase in the nanograined BaTiO3 ceramics, even though the grain size was about 40 nm.