Oxygen-vacancy-ordering-induced metal-insulator transition in MgO single crystals

Abstract

Dielectric properties of MgO single crystal were investigated in the temperature range of 300–1100 K and frequency range of 4x101-106 Hz. The sample exhibits intrinsic dielectric response below 400 K, two oxygen-vacancy-related phase transitions around 800 K, and thermally activated relaxation above 815 K. Impedance analysis revealed that the first phase transition is accompanied by an electronic phase transition of metal–insulator transition (MIT) and abnormal dielectric relaxation. These results can be well understood based on the scenario of oxygen-vacancy-ordering process. The first and second phase transitions are related to oxygen vacancies changing from disordered state to ordered state and then returning back to disordered state, respectively. The appearance of oxygen-vacancy-ordered phase leads to grain-boundary-like interfaces between the ordered phase and the surrounding medium, which in turn yields positive temperature coefficient of resistance giving rise to the MIT effect and the abnormal dielectric relaxation.

Keywords

• MgO single crystal
• MIT effect
• Dielectric relaxation
• Oxygen vacancy