Abstract
The effects of Ho (holmium) doping on the electrical properties and microstructural development of (Ba1-xHox)TiO3 were investigated by means of defect chemistry on the basis of equilibrium electrical conductivity data measured at 1300°C, as a function of oxygen activity. Ho2O3 additions to BaTiO3 up to 0.3 mol% were compensated by electrons under all oxygen partial pressures and the samples exhibited a low insulating resistance at room temperature. However, at Ho>0.3 mol%, the compensation mode switched from electrons to cation vacancies in the region of high oxygen partial pressure. The solubility limit of HoBa• was confirmed to be less than 3.0 mol%. The specimens doped with Ho<0.5 mol% had a low insulating resistance and large grains, whereas high insulating resistance and fine grains were observed in the samples doped with Ho grater than 0.5 mol%.