PRECIPITATION AND DISSOLUTION OF EXTENDED DEFECTS IN CHROMIA-DOPED RUTILE.

Electron microscopy of chromia-doped rutile with in situ high-temperature observations complemented by ex situ furnace-heating experiments has established the following: (i) that (Ti, Cr)O//2// minus //x is a true non-stoichiometric phase containing small defects which are coherent with and highly mobile within the rutile lattice, such small defects being effectively randomized homogeneously throughout the lattice; (ii) the precipitation and dissolution temperatures for small/extended defect equilibria in (Tr, Cr)O//1//. //9//7//5, thus establishing a novel technique for determination of the stoichiometry dependence of the phase limits; (iii) the evolution of a characteristic sequence of microstructural textures prior to the formation of ordered crystallographic shear structures outside the phase limits; and (iv) the existence of hysteresis phenomena for the precipitation and dissolution temperatures. Refs.