Dielectric and impedance characteristics of KTaO₃ modified BiFeO₃ multiferroics

Polycrystalline (Bi_1−x, K_x) (Fe_1−x, Ta_x) O₃ (x = 0.0, 0.1, 0.2, 0.3) materials were synthesized by a mixed-oxide method. The formation of single-phase compound in hexagonal crystal system was confirmed by X-ray diffraction analysis. Through scanning electron microscope the surface texture of the prepared material was recorded. It exhibits a uniform grain distribution with few small voids suggesting the formation of high-density (except BiFeO₃) pellet samples. For different concentration (x) of KTaO₃ the impedance and dielectric properties of the materials were investigated as a function of temperature and frequency. The grain and grain boundary contributions in the resistive and capacitive components of the samples were estimated using complex impedance spectroscopy technique. A strong correlation between these electrical parameters and microstructures (bulk, grain boundary, nature of charge carriers, etc.) of the material was established. The value of activation energy due to both grain and grain boundary is nearly same, but increases with an increase in composition (x). The nature of variation of direct-current conductivity confirms the Arrhenius-behavior of the materials. Study of frequency dependence of alternating-current conductivity suggests that the material obeys Jonscher’s universal power law, and the presence of ionic conductivity is observed. I–V characteristics curve confirms the NTCR-type behavior.