Study of occupational sites and dielectric properties of Ho-Mg and Ho-Mn substituted BaTiO3

The effect of re-oxidation treatment on the solubility in dopants and the dielectric properties of Ho-Mg- and Ho-Mn-substituted BaTiO3 was investigated. The lattice parameter and electrical resistivity results indicated that the pre dominant occupational sites of Ho ions changed from A-sites to B-sites by increasing the doped content in both systems. In the case of Ho-Mn-substituted samples, the decrease in lattice parameter and a shift of the Curie point (T-c) to higher temperatures by re-oxidation treatment were observed in the range in which Ho ions predominantly occupy B-sites (act as accepters). On the other hand, Ho-Mg-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.