Spontaneous emergence of free carrier at phase transitions of insulating BaTiO₃ single crystals: Experimental analyses

The conductance of BaTiO 3 and the relaxor single crystals is measured. Unlike conventional insulators, the stoichiometric crystals in which the conductance due to the impurities are rendered negligible exhibit an intrinsic conductance that is manifested as the sharp peaks at the phase transitions, and the peaks become evident with purity, and its values are nearly independent of the samples that are grown by the different methods and the conditions, whereas the conductance above T C depends critically on the samples. Especially, these findings are verified by the measurements of the current at constant voltages. These observations elucidate that the ferroelectrics posses a carrier generation mechanism, which has been invisible in semiconducting samples.