Electron paramagnetic centers in donor-doped CaTiO3 single crystals

Electron spin resonance signals observed in donor-doped CaTiO3 single crystals (Ca12xYxTiO3 orCaTi12xNbxO3) were analyzed and the results were discussed from a viewpoint of carrier generation. Severaltypes of signals were observed in insulating samples, and they were tentatively assigned to some acceptorssuch as Al impurity and the defects relating oxygen excess. Two types of signals with sharp and broad features,both of which are assignable to electron-trapped-type centers, were observed in conductive samples. Theorigins of the sharp and broad signals were attributed to electrons tightly trapped on Ti41 ions and electronsloosely localized around donors, respectively, from analysis of angular and temperature dependence of thesignals. The concentrations of the centers for the sharp and broad signals were estimated at ;3 K to be;331018 cm23 in the H2-reduced samples with x51024 and ;331019 cm23 in the as-prepared sampleswith x51022, respectively. Although no obvious correlation between electroconductive behavior and signalintensity was observed for the sharp signals, intensities of the broad signal increased as the electroconductivebehavior turned from metallic to semiconducting below ;25 K. Therefore, it was found that the electronsresponsible for the broad signals convert into conduction electrons when they are thermally released at hightemperatures, and their concentration is high enough to influence the electroconductive behavior