Effect of Rare-Earth Ions on Electrical Conductivity of BaTiO3 Ceramics

Lattice constants, grain size, electrical conductivity, and luminescence were measured for sintered BaTiO₃ ceramics doped with 0 to 1.2 at.% rare-earth ions. BaTiO₃ doped with low levels of rare-earth ions contains grains 10 μm in size and has lattice constants nearly equal to those of undoped ceramics. In this case, rare-earth ions occupy Ba²⁺ sites and yield donors. When grain growth is inhibited by high doping levels or by insufficient sintering, the lattice constants change, the rare-earth ions occupy both Ba²⁺ and Ti⁴⁺ sites, and, consequently, BaTiO₃ becomes insulative because of charge compensation.