Charge Transfer in Polar Materials

In some non-centrosymmetric crystals and polycrystals, their internal polarity can significantly affect the transfer of electrical charge. Mixed ionic-covalent bonds inherent in polar crystals can be very finely balanced in the spatial structure of the substance, so external effects (temperature, pressure, or electric field) can lead to a large change in the electrical conductivity. The quasi-one-dimensionality of the polar structure, enhanced by an externally applied electric field, leads to a much lower resistance to the electronic transport compared to a complex multidirectional arrangement of the polar bonds, which contributes to the high electrical resistance because of polaron formation. Even a small change in the sensitively balanced polarity structure of material under the external influence can lead to a significant jump in conductivity. This explains, for example, the very sharp (almost critically) changing with temperature resistance of “critistors” and “posistors”, as well as the extremely sharp change in resistance in an electric field of “varistors” and the electrically or magnetically controlled “switches”. Investigations of the external factors impact on the electric charges transfer in some polar structures might be important for improving the parameters of the transformative materials important for electronics. For example, the high sensitivity of conductivity to various features of the environment, caused by the imbalance of internal polarity, is used in sensors.