Effects of Ca and Zr additions and stoichiometry on the electrical properties of barium titanate-based ceramics

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(Ba1−xCax)m(Ti1−yZry)O3 (BCTZ-x-y-m) ceramics were studied to clarify the effects of Ca and/or Zr addition and the non-stoichiometry of BCTZ ceramics. The range of each element was 0.00 ≦ x, y ≦ 0.25 and 0.995 ≦ m ≦ 1.02. All powders were prepared by a solid state reaction method. Green bodies with disc shapes were sintered at 1500°C for 2 h in air and then reheated at 950°C for 5 h in various reducing conditions. The dielectrics with the substitution of Ca ion in BCTZ-x-0.0-1.01 (x ≦ 0.10) showed an increase in Tc and the insulation resistivity improved with increasing x. The increase of Zr content (y) in BCTZ-0.1-y-1.01 and m in BCTZ-0.1-0.1-m led to the phase transition of dielectrics to relaxors, accompanying the decrease of Tc. In BCTZ-0.1-0.1-m, Ca and Zr co-doped dielectrics showed a high insulation resistivity (IR), even though m = 1.00. There are two possible origins of the higher resistivity observed in BCTZ with m = 1.0. The first is the acceptor action of Ca ions that moved from Ba sites to Ti sites in BaTiO3; the second is the higher charge stability of the Zr ion than that of the Ti ion in a reducing atmosphere.