Fabrication and properties of nonreducible lead-free piezoelectric Mn-doped (Ba,Ca)TiO3 ceramics

Nonreducible lead-free (Ba,Ca)TiO3 piezoceramics were fabricated by controlling the level of Mn doping. Similar to Mn-doped (Ba0.85Ca0.15)TiO3 ceramics sintered in air, stable dielectric properties with temperature change were achieved for the nonreducible sample by stabilizing the tetragonal phase of BaTiO3 over a wide temperature range. In addition, optimization of the level of Mn doping was very effective in improving the sintered density and electrical resistivity for (Ba0.85Ca0.15)TiO3 ceramics sintered under a low oxygen partial pressure. The valence state of doped Mn in nonreducible (Ba,Ca)TiO3 after sintering was confirmed to be Mn2+ or Mn3+ by electron spin resonance analysis. Sintered bodies of 1 mol% Ba excess and 1 mol% Mn-doped (Ba0.85Ca0.15)TiO3, which were sintered at 1350 °C in a H2(0.3%)/Ar atmosphere, exhibited sufficient sintered density and resistivity to allow the characterization of several electrical properties. The ferroelectric, field-induced strain, and piezoelectric properties of the nonreducible (Ba0.85Ca0.15)TiO3 ceramics sintered in the reducing atmosphere were comparable with those of (Ba0.85Ca0.15)TiO3 samples sintered in air.