Spontaneous polarization of non-stoichiometric LiIO3 crystals in the low-temperature region

摘要

Measurements of the total charge Q(T) - S Delta P-s(T) in non-stoichiometric z-cut LiIO3 samples in the temperature range of 4.2-300K were reported. The measurements were supplemented with the data on thermally stimulated depolarization induced by an external electric field of different magnitude and polarity. For T> 130K, anomalies in the Delta P-s(T, U) dependence were observed, which are commonly caused by the deviation of the crystal composition from stoichiometry. The possible nature of the non-stoichiometry was clarified with magnetic measurements, which allowed us to detect interstitial Li below 100K, as well as two paramagnetic associates of unknown nature at 25K and 50K. Increasing temperature led to ionization of lithium with formation of Li_ ions and associates, (V(O)(+)2e)(-) and (VO++VLi)(+), responsible for ionic conductivity. It cannot be excluded that during the charge measurements at T> 140K the associates of a different type (V-Li(-), Li) are formed, which possess a dipole moment and can be oriented opposite to Delta P-s. It was shown that in a limited temperature range from 18K to 35K, the temperature dependence of Delta P-s similar to T-4 agrees with the Born theory. Considerable fluctuations of the pyroelectric coefficient were observed, which were presumably related with the disorder of the crystal structure of the non-stoichiometric sample leading to the distribution of relaxation times of the elements of the defect subsystem. Published by AIP Publishing.