CORRELATION BETWEEN MICROSTRUCTURE AND ELECTRICAL-CONDUCTIVITY IN PB(FE1 2NB1/2)O-3-PB(FE2/3W1/3)O-3-PB(ZN-1/3 NB-2/3)O-3 RELAXOR FERROELECTRICS/

The contribution of various phases to the electrical conductivity of d ielectric materials, prepared at different firing conditions from a so lid solution of -3-Pb(Fe2/3W1/3)O-3-Pb(Zn1/3Nb2/3)O-3(PFN-PFW-PZN) per ovskites, was determined by the analysis of microstructure, d.c. condu ctivity and impedance spectroscopy. In monophase samples composed of p erovskite grains, a single slope in the Arrhenius plot (d.c. measureme nts) which corresponds to an activation energy of around 1 eV (dependi ng on the chemical composition) and a single semicircle in the impedan ce spectrum were found. In polyphase samples two slopes in the Arrheni us plot were observed, indicating two conduction mechanisms with appro ximate activation energies of 0.6 and 1 eV. In the impedance plane two thermally active semicircles were noticed with activation energies of 0.7 and 1 eV. It was shown that in the samples with lead-tungstenate liquid phase present, this phase was the main contribution to the cond uctivity at temperatures up to 300 degrees C, while the perovskite gra in contribution dominates the conductivity above this temperature. The electron-hopping conduction mechanism between Fe2+ and Fe3+ ions at t he B sites of the perovskite structure was assumed to be the principal mechanism of perovskite grain conductivity. Based on the results from impedance measurements, it was concluded that the lead-tungstenate ph ase, which was distributed between the perovskite grains, was not cont inuous.