Defect structure in non-stoichiometric CoTi with CsCl-type ordered structure

Positron lifetimes in CsCl-type intermetallic compounds Co100–XTiX (X ¼ 48 –50:3) water-quenched and furnace-cooled from 1323 K have been measured to study their defect structures. Positron mean lifetimes in water-quenched specimens of both Co-rich and Ti-rich compositions are much longer than the calculated positron lifetime in the perfect lattice, and no matrix component is observed. The positron mean lifetimes in the furnace-cooled specimens of Ti-rich compositions do not have large difference from those for the water-quenched specimens, whereas the furnace-cooled specimens of Co-rich compositions show short positron mean lifetimes, which are almost equal to the calculated lifetime in the perfect lattice. These results indicate that Co-antistructure atoms and Co-vacancies are formed in CoTi as constitutional defects in accord with the model proposed by Bradley and Taylor.