Occupational sites and dielectric properties of rare-earth and Mn substituted BaTiO3

The effect of re-oxidation treatment on the solubility in dopants and the dielectric properties of La–Mn- and Ho–Mn-substituted BaTiO3 (ABO3) was investigated. The lattice parameter and electrical resistivity results indicated that La ions occupied A-sites and Ho ions occupied both A- and B-sites. In the case of Ho–Mn-substituted samples, the decrease in lattice parameter and a shift of the Curie point (Tc) to higher temperatures by re-oxidation treatment were observed in the range in which Ho ions predominantly occupy B-sites (act as acceptors). On the other hand, La–Mn-substituted samples showed little change. Electron spin resonance measurements revealed that these changes due to re-oxidation were based on the decrease of the ionic size of Mn due to the oxidation of Mn2+ to Mn3+ or Mn4+. The occupational sites of Ho ions strongly affected the valence state of Mn and the dielectric properties of BaTiO3.