Zirconia-tungsten composites: synthesis and characterisation for different metal volume fractions

Zirconia-tungsten composites have been obtained by the densification of ceramic-metal powders. The influence of the sintering conditions and the metal volume fraction on the morphology, the porosity, the linear shrinkage, the microhardness and on the linear expansion coefficient has been evidenced. Using a general effective medium equation to fit the electrical resistivity of the composites (1400°C-3h) a percolation threshold of 0.26 has been found. The distribution functions of relaxation times obtained from impedance spectroscopy measurements show that the higher is the thermal treatment the sharper are the peaks and the lower is the relaxation time τp. The intragrain zirconia ionic conductivity is improved for high tungsten volume fractions below the percolation threshold.