Electron transport behaviours in Nb-doped SrTiO3 bicrystals

In order to elucidate the relationship between electron transport behaviour and defect chemistry, grain boundary structure and current-voltage characteristics across the boundary were investigated for Nb-doped SrTiO3 bicrystals. Two kinds of boundaries, i.e. small angle and random boundaries, were prepared for 0.2at% and 1.0at% Nb-doped SrTiO3. The bicrystals were prepared by joining two single crystals at 1400degreesC for 10 h under a pressure of 0.4 MPa in air. High-resolution transmission electron microscopy (HRTEM) study revealed that all of the joined boundaries are free from any secondary phases or amorphous films. On the other hand, it was found that non-linearity in current-voltage dependence becomes remarkable by reduction of cooling rate after joining in small angle boundaries of 0.2at% Nb-doped SrTiO3 bicrystal. in addition, the random boundary of 1.0at% Nb-doped SrTiO3 bicrystal exhibits clear alpha = 2 I-V relation, which appears across a contact of semiconductor-insulator-semiconductor (n-i-n). From the results of HRTEM study and I-V behaviours, it could be concluded that the electron transport mechanism is controlled mainly by defect chemistry and not by the grain boundary structure.