Analysis of defect formation in Nb-doped SrTiO₃ by impedance spectroscopy

The thermal activation energies for conduction of Nb-doped SrTiO₃ grains and grain boundaries have been investigated by impedance spectroscopy. First, to observe the effect of electrode/SrTiO₃ bulk interface, the varied impedances of SrTiO₃ single crystal were measured with temperatures. The activation energy of an electrode/bulk interface was determined to be 1.3 eV, whereas that of bulk was 0.8 eV. When the impedances of Nb-doped SrTiO₃ ceramics were measured, it was suggested that the more precise impedance values of a single grain and a single grain to grain junction be obtained using a microelectrode method. The activation energies for a grain, a grain boundary, and an electrode/bulk interface were determined to be about 0.8, 1.3, and 1.5 eV, respectively. From these measured results, it was suggested that the activation energy, 0.8 eV, measured in grain was originated from oxygen vacancies and the activation energy, 1.3 eV, in grain boundary was from strontium vacancies.