Electron paramagnetic resonance investigations of lanthanide-doped barium titanate: Dopant site occupancy

Air-fired barium titanate samples doped with cerium, neodymium, samarium, gadolinium, dysprosium, erbium, or ytterbium were examined by electron paramagnetic resonance (EPR). Reducing atmosphere-fired europium-doped barium titanate was also investigated with EPR. Each dopant was studied in both Ba- and Ti-rich (Ba/Ti = 1.01, 0.99) samples. Point charge calculations were used to predict the EPR spectrum of each lanthanide in A- and B-sites. Different EPR spectra are expected for A- versus B-site substitution when Ce³⁺, Sm³⁺, Dy³⁺, and Yb³⁺ are the dopants. The experimentally observed Ba/Ti doping behavior of Ce³⁺ in BaTiO₃ suggests that as a 3+ cation it is on the A-site. No EPR active signal was observed for Sm³⁺ in BaTiO₃. Eu²⁺ and Gd³⁺, as previously discussed in the literature, were found to be an A-site dopant and amphoteric, respectively. Dy³⁺ was found to be a B-site dopant with an EPR signal intensity suggesting amphoteric behavior, whereas Yb³⁺ showed only B-site occupancy. Nd³⁺ and Er³⁺ could not easily be assigned to a particular site by EPR methods alone. We also discuss the lanthanide dopant's effect on the observed levels of titanium vacancies, barium vacancies, and Mn²⁺ impurities.