Investigation of dielectric response, conductivity, and thermostimulated depolarization current in PbNi$_{1/3}$Nb$_{2/3}$O$_{3}$ relaxor ferroelectric

This paper presents results of a study of temperature dependences of dielectric response and DC and AC - conductivity in single crystals of the relaxor ferroelectric PbNi$_{1/3}$Nb$_{2/3}$O$_{3}$ (PNN) in a wide range of frequencies (10 Hz – 100 kHz) and temperatures (80 – 750 K). Anomalies in the dielectric response in the form of broad frequency-dependent maxima in the vicinity of 153 and 730 K are observed. The thermal activation character of DC conductivity has been obtained, and activation energies determined as $E_a$ = 770 meV ($T$ > 310 K) and $E_a$ = 23 meV ($T$ < 310 K). The analysis of conductivity gives reason to assume the existence of local conductivity in the low-temperature region. It is shown that the conductivity character changes above 350 K from the local to the bulk one. Measurement by thermally stimulated depolarization has shown the presence of a residual polarization below 130 K.