Effect of ball milling and post treatment on crystal defects and transport properties of Bi2(Se,Te)3 compounds

Ionized point defects that act as electron donors or acceptors can strongly affect thermoelectric transport properties of bismuth telluride compounds. These crystal imperfections including antisite defects and vacancies can be generated or annihilated during material processing. Here, we reported the effect of ball milling, thermal annealing, and electrical stressing on defect population in the Bi2(Se,Te)3 prepared by powder metallurgy. The milling process can modulate the relative portion of antisite defects and vacancies in crystal, and the Bi2(Se,Te)3 made of the powders with extended milling time showed high electron concentration and poor carrier mobility. The crystal defects, Te vacancies in particular, were eliminated to some degree during subsequent thermal treatment. An electric-current assisted thermal treatment was found to be very efficient in eliminating crystal defects, which can improve transport properties of Bi2(Se,Te)3 without causing re-evaporation of volatile Te and Se elements during high-temperature annealing.