Correlating resistivity with the oxidation state of europium in doped barium titanate

Barium titanate is a ceramic insulator that becomes an n-type semiconductor when doped with small amounts of rare earth trivalent ions in the Ba 2+ site. N-type semiconducting BaTiO₃ exhibits a positive temperature coefficient of resistivity effect at the Curie temperature.; The theory for the PTCR effect has not been established completely. In this study, rare earth divalent ion Eu2+-doped BaTiO₃ was synthesized, characterized, oxidized, and its resistivity was measured by the two-point probe technique to correlate the resistivity behavior with the oxidation state of Eu.; The synthesis of Eu-doped BaTiO₃ was performed via a wet-chemical and two solid-state methods. The XRD patterns indicated a limit to the incorporation of EU₂O₃ and 2 TiO₂ into BaTiO₃ at a doping level between 5 and 10%.; To verify the presence of Eu, XRF spectra were obtained. To determine the oxidation state of Eu, fluorescence spectroscopy, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy were performed. It is concluded that the presence and oxidation state of Eu can best be determined using Mössbauer spectroscopy.; Resistivity results showed that semiconducting BaTiO₃, 5%, and 0.5% Eu-doped BaTiO₃ can be made in a reducing atmosphere that introduces oxygen vacancies. The resistivity curve of a sample of EU ₂O₃ and 2 TiO₂ subjected to the same heating and sintering treatment showed a slight PTCR effect. The resistances of 5% and 0.5% Eu-doped BaTiO₃ synthesized and sintered under oxidizing conditions showed insulator behavior.; The resistivity curves of Eu-doped BaTiO₃ samples that were synthesized in a reducing atmosphere and then sintered in an oxidizing atmosphere showed insulator behavior. The resistivity curve of 0.5% Eu-doped BaTiO ₃ that was synthesized and sintered under reducing conditions and then oxidized in air at 1150°C for 20 hours showed PTCR behavior.; This behavior supports the current model that asserts that conditions under which samples are processed in an oxidizing environment where donor ions are able to migrate to grain boundaries are responsible for the PTCR effect.