Fault Structures in Ti₂O

Abstract

Abstract The structure of Ti 2 O can be described in terms of a hexagonal close packed arrangement of titanium atoms ( c / a = 1.637) in which oxygen atoms are ordered so that they occupy every second layer of octahedral interstices normal to the c ‐axis. The nature of possible antiphase domain boundaries and stacking faults in this ordered structure is discussed and compared with transmission electron microscope observations of fault boundaries. – Direct evidence is presented showing that cast specimens, which are ordered at room temperature, contain a high density of growth faults (1 (Δ) faults) at which neighbouring (0001) planes of octahedral interstices are either both occupied by oxygen atoms or both vacant. The (0001) faults are eliminated by high temperature annealing which gives rise to an antiphase domain structure with a morphology of the „Swiss‐cheese”︁ type. The antiphase vector is ( c /2 + Δ c ) [0001] where Δ c is a term indicating the presence of lattice strains parallel to [0001] direction at the antiphase boundary. – From the microstructural changes it is concluded that Ti 2 O solidifies as a disordered c.p.h. structure containing a high density of low energy growth faults which are modified by oxygen ordering during cooling to room temperature.