Mechanical and thermal processing effects on crystal defects and thermoelectric transport properties of Bi2(Se,Te)3 compounds

• Mechanically and thermally induced crystal defects in Bi2(Se,Te)3 are studied.
• Donor-type Te vacancy is the major crystal defect caused by mechanical milling.
• A two-step thermal annealing improves thermoelectric power factor of Bi2(Se,Te)3.

Charged crystal defects generally play the roles of electron donor or acceptor and affect thermoelectric properties of bismuth telluride compounds profoundly. In this study the effects of ball milling, pressing and thermal annealing on populations of various crystal defects and electrical/thermal transport properties of Bi2(Se,Te)3 compounds are investigated. It has been found that abundant donor-type Te vacancies are introduced during mechanical milling process, leading to high electron concentration and reduced carrier mobility for cold-pressed Bi2(Se,Te)3. A two-step annealing method consisting of pre-press and post-press annealing is presented for improving thermoelectric power factor while retaining low thermal conductivity of Bi2(Se,Te)3 compounds by tweaking crystal defect population and carrier scattering mechanism.