Stacking faults and dislocations in titanium dioxide, with special reference to non-stoichiometry

Abstract A detailed electron microscopical investigation has been made of the stacking faults and dislocations observed in thin films of titanium dioxide grown on the (100) faces of titanium carbide crystals. The large stacking faults formed during the growth process lie on a {101} plane, but they often change from one plane to another of the same family, sometimes on too fine a scale to be clearly resolved. The fault is terminated by a partial dislocation having a vector of the 1/2<101>-type; if the specimen is heated in the microscope, when it becomes non-stoichiometric, the fault anneals out by one of two mechanisms. The first mechanism involves the glide of the partial dislocation terminating the fault, and the second the growth of small dislocation loops formed by the condensation of vacancies introduced as a result of deviations from the stoichiometric composition. Contrast experiments show that the observed dislocations are of two types. The first are dissociated dislocations having a partial 1/2<101> vector, glissile on {101} planes and associated with a stacking fault. The second type of dislocation are undissociated and have a <001> Burgers vector. A sessile configuration is also formed by an interaction between dislocations with 1/2<101> and <001> and Burgers vector. An interaction between glissile partial dislocations and vacancy clusters also occurs, and it is suggested that this is a possible mechanism for the increased yield stress produced when TiO2 becomes substoichiometric.