PROBING THE ORDERING TRANSFORMATION IN THE ALLOY CU69ZN14AL17 WITH POSITRONS

The ordering transformation in the Cu69Zn14Al17 shape-memory alloy has been studied with Doppler-broadened annihilation-radiation line-shape -parameter (S) and lifetime measurements. The S-parameter profile as a function of temperature, S(T), from room temperature to 825 K shows b eta --> B2 and B2-->DO3 transitions in conformity with resistivity mea surements. The constancy of the S(T) profile in the heating and coolin g cycles is indicative of positrons sampling the equilibrium vacancies . Results obtained from both measurement techniques are not indicative of the presence of divacancies in the disordered (beta) state. Analys is of the S(T) profile in terms of a trapping model over the entire te mperature range shows a temperature dependence for the vacancy-formati on energy, probably due to the ordering process. The results are discu ssed.