PHASE-STABILITY AND IONIC-CONDUCTIVITY IN BISMUTH LEAD (ANTIMONY) OXIDE

Ionic conductivity was measured on (Bi1-xSbx)5Pb8O17 for x=0 to 0.2, from room temperature to 600-degrees-C, in air. At x=0, X-ray analysis and differential thermal analysis (DTA) showed that 3 distinct phase-regions were present in the material. At room temperature, a tetragonal beta2-phase which decomposed to a mixed state (including the stoichiometric Bi8Pb5O17) at approximately 500-degrees-C, which further decomposed, at 590-degrees-C into the high ionic conducting cubic beta-phase. Increasing x caused a lowering of the temperature that the beta2-phase decomposed into the mixed state (with a drop in the conductivity of the mixed state) but, in general, caused an increase in the temperature of the beta-phase formation. This paper describes the effect on the phase and ionic conductivity of substituting zero to 20% Sb for Bi and 10% substitutions of Dy, Gd and Tm for Bi. Ionic conductivity was high for all these materials, but was reduced below that of the undoped material in the order Sb < Tm < Gd < Dy < undoped. However, Sb substitutions at concentrations as low as 2.5 mol% improved the mechanical integrity of the material over that of the undoped alloy.