Impedance spectroscopy of Bi1.6Mg0.24Cu0.56Ta1.6O7.2

Compounds with pyrochlore structure attract a persistent interest of researchers due to their wide range of practically useful characteristics such as semiconductor, photocatalytic, dielectric and piezoelectric properties. Of a particular interest are triple pyrochlores, the characteristic feature of which is the placement of metal cations M on two non-equivalent cationic positions A and B in the structure of pyrochlore A2B2O7. Such compounds include complex bismuth-containing pyrochlores, most of which exhibit excellent dielectric properties — low dielectric loss tangent and dielectric permeability. In the presented work, results of impedance-spectroscopy studies of electric properties of copper containing bismuth-magnesium tantalum Bi1.6Mg0.24Cu0.56Ta1.6O7.2 with pyrochlore structure are reported. Copper-containing solid solutions of bismuth-magnesium tantalum with pyrochlore structure were synthesized by solid phase method. The samples are characterized by a low-porous microstructure. The parameter of the unit cell was 10.5341 Å. Studies by impedance-spectroscopy in wide temperature (25 – 450°С) and frequency (10 Hz – 1 МHz) intervals have shown that the samples have wide impedance-spectra, demonstrating three relaxation processes with distinct frequencies. An equivalent scheme has been proposed and its parameters have been calculated, which satisfactorily describe the electrical characteristics of the material. As a result of the performed modeling of the electrical properties of material, it has been established that the observed processes are related to electronic and ionomigration polarization as well as electrode process. The sample Bi1.6Mg0.24Cu0.56Ta1.6O7.2 shows ionic conductivity even at room temperature. The local extremum of electrical parameters at 200°С may indicate a decrease in the homogeneity of the medium.

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