Kinetics of Spinodal Decomposition in the TiO ₂ ‐SnO ₂ System: The Effect of Aliovalent Dopants

Abstract

Dense samples in the TiO 2 ‐SnO 2 system were fabricated by pressureless sintering in air using commercial powders as well as powders obtained by coprecipitation. Phase equilibria in the system were examined using X‐ray diffraction on samples that were annealed for long periods of time. Samples of near equi‐molar composition made with controlled amounts of Al and Ta (separately) as dopants were annealed inside the coherent spinodal. X‐ray diffraction and electron microscopy were the principal characterization tools used to follow the kinetics of phase transformation. The composition modulations occurred along the [001] direction consistent with prior work. During the early stages of the decomposition process, interlamellar surfaces were coherent. At later stages, strain mismatch was accommodated by interface dislocations. The kinetics of decomposition were strongly influenced by the type and the amount of dopant. Specifically, trivalent aluminum enhanced the decomposition while pentavalent tantalum suppressed it. The kinetics in a sample doped with 0.5 mol% Al 2 O 3 were more than 3 orders of magnitude more rapid than a sample doped with 1.0 mol% Ta 2 O 5 . These observations are rationalized on the premise that cation interstitial mobility is greater than cation vacancy mobility.