Anomalies of heat capacity and spontaneous polarization of nonstoichiometric KTiOPO4 crystals in the low-temperature region

The data of experiments that characterize the dependences of the unit cell volume, heat capacity, and spontaneous polarization of a nonstoichiometric KTiOPO4 sample are presented for the low-temperature region. It is shown that the influence of the electric field leads to variation in the sample nonstoichiometry, which is characterized by the appearance of anomalous behavior of spontaneous polarization in the region below 30 K. This experimental fact is associated with the appearance of the donor-acceptor pairs possessing the dipole moment. As the temperature increases, they gradually dissociate with the subsequent appearance of the cationic component of conduction.