Microstructural study for a homologous series of Cr₂Ti_n−2O_2n−1 with (12̄1)_r crystallographic shear structure

Electron microscopy and X-ray diffraction studies revealed that the homologous series of Cr₂Ti_n−2O_2n−1 with n = 6, 7, and 8 were the members of (12̄1)r crystallographic shear (CS) family derived from rutile-type structure. The highest end member of (12̄1)r CS family below 1420°C appeared to be n = 8 instead of n = 9 which was previously regarded as a discrete phase by X-ray diffraction technique. All the members belonged to the triclinic system with almost constant cell parameters except for the c-axis which increased according to the increasing values of n. Their microstructures showed well ordered features with equally spaced shear planes parallel to (12̄1)r. The adjacent members could be detected in different crystal fragments and sometimes observed to be coherently intergrown within one fragment with compositions of intermediate values of n.