Grain‐Boundary and Surface Segregation of Ba‐Ti‐O Phases in Rutile

Abstract
The solubility of barium in rutile and the formation and morphology of second phase at external and internal surfaces of single‐crystal and polycrystalline rutile (TiO,2) have been studied for various heat treatments up to 1450°C and in several configurations of the barium source. It has been found that barium is not incorporated into the rutile lattice but instead forms an amorphous, quasi‐liquid film of Ba‐Ti‐O at high temperature (=1400°C) which covers the grain boundaries and the external surfaces. On cooling or annealing at lower temperature (=1100°C) the continuous film breaks up to form isolated segregation patterns. Transport of the second phase by surface and grain‐boundary diffusion is rapid and reversible by heat treatment.

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