Investigation of interface states in (Sr,Ca)TiO3−x-based ceramics

Interface states in (Sr,Ca)TiO3−x based ceramics have been investigated in view of the oxygen chemisorption and the oxidation. By means of deep level transient spectroscopy and isothermal capacitance transient spectroscopy techniques, a discrete acceptor type trap level was detected with reoxidation below the oxidation temperature of grain surfaces, whereas two deep levels were detected with reoxidation above this temperature. Electron spin resonance spectra indicate that the chemisorbed oxygen O− and O2− are stable with reoxidizing anneals below and above the oxidation temperature, respectively. The reoxidation induced change in the interface states can be well explained by the degradation of the chemisorbed oxygen using the O-center model. These interface states are considered to originate from the chemisorbed oxygen O− and O2− on grain surfaces. It is concluded that the oxidation of the grain surfaces has a significant role in stabilizing the O2− chemisorption level.