Defect Structure and Electrical Properties of KTaO3

The electrical conductivity and thermoelectric power of KTaO₃ were measured from 900° to 1300°C over a range of oxygen partial pressures. The isothermal electrical conductivity showed a minimum at an oxygen partial pressure corresponding to the transition between p-type and n-type behavior. A point defect model was developed which involved fully ionized potassium and tantalum vacancies, singly and doubly ionized oxygen vacancies, holes, and electrons. The values of all pertinent equilibrium constants were calculated from the experimental data and the nonsimplified neutrality condition was solved to give each of the defect concentrations as a function of temperature and oxygen partial pressure. The calculated conductivity agreed extremely well with the experimental data over the full temperature and oxygen partial pressure range, and the band gap derived from these calculations (3.43 eV) was in excellent agreement with the reported value (3.5 eV).