Defect chemistry of lithium-doped magnesium oxide

Abstract

The dc conductivity of lithium-doped magnesium oxide has been measured, as a function of water vapour and oxygen partial pressure, using the four-point probe method. Proton species were found to dominate the conduction mechanism at low temperatures (673 K); increase in temperature (773–973 K) led to a mixed conduction mechanism: i.e. by protons and by holes (p-type conductivity). In the high-temperature region (1073–1173 K) 1% Li/MgO shows only p-type conduction, the proton contribution to the overall conductivity being negligible. Defect chemistry equations were used to describe the mechanism of formation of hydrogen and hole defects. The proposed mechanism assumes oxygen vacancies, created by lithium doping, play a crucial role in O ⁻ site generation. At low temperatures, the oxygen vacancies are blocked by hydrogen defects; as the temperature increases, the free oxygen vacancies created can interact with gas-phase oxygen and generate O ⁻ sites (holes).