Grain boundary and surface segregation of Ba-Ti-0-Phases in rutile.
01 January 1987
The solid solubility of barium in rutile and the formation and morphology of second phase at external and internal surfaces of single- and poly-crystalline rutile (Ti0(2)) has been studied for various heat treatments up to 1450C and in several configurations of the barium source. It has been found that barium is not incorporated in the rutile lattice but rather forms an amorphous, quasi liquid film of Ba-Ti-0 at high temperature (~~1400C) which covers the grain boundaries and the external surfaces. On cooling or annealing at lower temperature (~~1100C) the continuous film breaks up to form isolated segregation patterns due to an interfacial contact angle which becomes nonzero as the temperature is lowered. Transport of the second phase by surface and grain boundary diffusion is rapid and reversible by heat treatment. The precipitate morphologies strongly depend on the kinetics of nucleation and growth.