Design and applications of low-temperature barium titanate-based conductive oxides

The conductivities of barium titanate (BaTiO3) systems doped with yittrium oxide (Y2O3) and Zr3Y (97mol.% ZrO2:3mol.%Y2O3)are studied in this thesis. Different amounts of Y2O3 and Zr3Y were added to study their influences on conductivity. Conventional oxide-mixing methods were adopted to produce the BaTiO3-based ceramics. The sintering temperature for the ceramics was varied in between 1340-1500℃ to study the influence of sintering temperature on conductivity.
For the Y2O3-doped BaTiO3 system, the conductivity is at the highest when the BaTiO3 is doped with 0.1wt%Y2O3. The conductivity decreases significantly when the Y2O3 content increases to 1wt%. For the Zr3Y-doped BaTiO3 system, the conductivity with 5wt%Zr3Y doping is similar to that with 0.1wt% Y2O3 doping. Furthermore, if the Zr3Y doping is less than 0.5wt%, the conductivity is low. It is therefore concluded that in both the Y2O3-and Zr3Y-doped BaTiO3 systems, the dominant factor for the conductivity is the amount of yittrium doping. The origin of conductivity for the Y2O3-and Zr3Y-doped BaTiO3 system is investigated by studying the evolution of conductivity at different temperatures and reducing atmospheres. Donor-doped and acceptor-doped BaTiO3 systems are therefore defined. It is found that the room-temperature conductivity of BaTiO3 is governed by the amounts of its chemical defects, such as free electrons, electron holes, oxygen vacancies, and cation vacancies.