INVESTIGATIONS ON THE MIXED CONDUCTIVITY OF COPPER TANTALATE

Polycrystals of CuTa2O6 were prepared by solid-state reaction in air a t 1200 degrees C with variations of stoichiometry (x) in the copper ox ide ratio. They were examined by X-ray diffraction. A defect of copper oxide during the synthesis leads to an excess of Ta2O5 phase in the s ample and an excess of copper oxide gives a single phase compound. The total conductivity was determined by impedance measurements and the e lectronic conductivity was estimated by the Hebb-Wagner method, At roo m temperature, the total conductivity of samples in equilibrium with c opper is about 10(-7)-10(-6) S cm(-1). No significant changes were obs erved for x = 0.8 and 1.0, but the total and the partial conductivitie s are higher for x = 1.2. In all cases, the measured electronic conduc tivity seems to be mainly of n-type and the electronic transport numbe r is close to 0.5-0.6, independent of the temperature and stoichiometr y. The nature of the mixed conduction is discussed in relation to Cuions in the structure.