Effects of multi-doping of rare-earth oxides on the microstructure and dielectric properties of BaTiO3

Effects of multi-doping of rare-earth oxides (R = Yb, Sm, Ho, La and Nd) on the microstructure development and electric properties of BaTiO3 ceramics were studied. The addition of samarium oxide leads to poor densification and small grains, whereas ytterbium oxide develops large grains and secondary phases along the grain boundary, and Ho ion with an intermediate ionic radius gives rise to higher densities with fine grains. The grain size of Yb-doped BaTiO3 decreased with increasing Sm contents. The system coated with 2.0 at.% Sm and 2.0 at.% Yb exhibited dense microstructures with uniform small grains, and Yb-rich second phases were not observed. It was confirmed that an appropriate ratio of donor to acceptor is necessary to the optimum microstructure. Curie temperature of rare-earth doped BaTiO3 was strongly dependent on the unit-cell volume associated with the ionic sizes of rare-earth ions.