The isothermal shrinkage of the compacts of stannic oxide powders containing 0, 1, 3 and 5 mol % of bismuth was measured by means of a shrinkage meter between 1150° and 1250 °C in air.
The shrinkage rate of stannic oxide powder was very small and its activation energy was calculated as 38 Kcal/mol.
By the addition of bismuth, the shrinkage was found to be increased. By the addition of 1-3 mol % of bismuth, no change in the lattice constant was observed from the X-ray analysis. Therefore it may be considered that bismuth ion is soluble in SnO₂ up to 3 mol % and is substituted for Sn ⁺in SnO₂. Assuming that bismuth in SnO₂ is trivalent state this substitution will increase the concentration of oxygen vacancy. Hence the diffusion of ions is promoted, as a result, the shrinkage rate of compact is accelerated.
The compound Bi₂(SnO₃) ₃ was detected in the compact containing 5 mol % of bismuth by X-ray analysis. The presence of Bi₂(SnO₃) ₃ decreases the shrinkage rate during sintering.