ELECTRICAL PROPERTIES OF Bi5Nb3-3xCr3xO15-δ CHARACTERIZED BY IMPEDANCE SPECTROSCOPY

N.A. Sekushin, N.A. Zhuk, E.A. Belyaeva, V.A. Belyj, V.E. Grass, M.V. Ermolina

Abstract

The electric properties of Bi5Nb3O15 bismuth niobate polycrystalline samples and chromium-containing solid solutions Bi5Nb3-3хCr3хO15-δ (х≤0.08) were studied using impedance spectroscopy.On the grounds of the performed researches the conclusion about the electron-ionic character of conductivity of solid solutions Bi5Nb3-3хCr3хO15-δ was made.The majority of bismuth-containing oxide compounds with layered perovskite-like structure are ferroelectric with high Curie temperatures. Bismuth niobate Bi5Nb3O15 belongs to the group of layered perovskite-like compounds and is characterized by relaxation-like ferroelectric behavior. Previous studies have shown that bismuth niobate forms a limited range of solid solutions containing atoms of transition elements. In this connection, we studied the influence of the heterovalent substitution of niobium by chromium atoms on the phase transition and electrophysical properties of bismuth niobate. The electrical properties of the polycrystalline samples of bismuth niobate and chromium-containing solid solutions Bi5Nb3-3хCr3хO15-δ (х≤0.08) were studied using impedance spectroscopy. Bismuth niobate is crystallized in tetragonal syngony; the solid solutions with х≥0.04 have a monoclinic distortion of the tetragonal structure. We did not find any phase transitions significantly changing electrical properties of the oxide materials Bi5Nb3O15 and Bi5Nb3-3хCr3хO15-δ in the temperature range of 350–600С; this can be caused by relaxation character of dielectric polarization and blurring of the phase transition. The equivalent circuits were developed for Bi5Nb3O15 and the solid solutions. The circuits consisted of the resistors and two elements for space-distributed polarization. The accuracy of the equivalent circuits was checked by the agreement between the experimental and calculated values. The Bi5Nb3-3хCr3хO15-δ samples exhibited dielectric properties with extremely low conductivity at temperatures under 350С. At the higher temperature, the materials demonstrated semiconducting properties with the activation energy of the conductivity of ~0.6 eV. The performed study allows us to conclude about the mixed electronic-ionic character of conductivity in the Bi5Nb3-3хCr3хO15-δ.

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