THERMAL-STABILITY AND IONIC-CONDUCTIVITY OF THE BIMEVOX.10 CERAMICS (ME=ZN, NI)

Ceramics of the nominal composition Bi2Zn0.1V0.9O5.35 and Bi2Ni0.1V0.9 O5.35 were obtained. The crystal structure was examined by X-ray diffr action from room temperature to 973 K. TGA and DTA were done in air, n itrogen and oxygen between 370 and 970 K. For both ceramics TGA cycles indicate no visible change in sample mass during measurements. DTA cu rves, on the other hand, exhibit peaks due to phase transitions in bot h heating and cooling runs. The thermal heat effects per mass of exami ned material are stronger for BIZNVOX.10. The impedance of the ceramic s with Pt electrodes was measured in the frequency range 5-10(7) Hz at constant temperatures between 410 and 980 K. The conductivity of the samples was determined by nonlinear least-squares analysis of the impe dance spectra. The temperature dependence of the conductivities in Arr henius type plots is presented. A change of slope of the total conduct ivity occurs for both materials. A time dependence of conductivity in a limited temperature range is observed only for BIZNVOX.10. The trans ition temperatures observed in DTA coincide with those observed in con ductivity measurements. A phase transition, involving a reordering pro cess of the oxygen ions, is considered responsible for this phenomenon .