Facile Ni-induced in situ formation of multi-dimensional defects in Bi2Se3: A synergistic approach to thermoelectric efficiency enhancement

Improving thermoelectric performance typically relies on either enhancing the power factor or suppressing lattice thermal conductivity, yet achieving both concurrently remains challenging. Here, we demonstrate a precipitation-triggered defect architecture in Bi 2 Se 3 via nominal Ni alloying (Bi 2- x Ni x Se 3 ) synthesized by a conventional solid-state route. During synthesis, Ni preferentially reacts with Se to form highly conductive NiSe 2 inclusions, leaving a Se-deficient Bi 2 Se 3 matrix. Microstructural analysis confirms embedded NiSe 2 precipitates and a Ni-free, Se-deficient matrix, indicating that the dominant role of Ni is not the conventional substitutional doping but in situ phase separation. The resulting dual-defect system, that is 3-dimensional (3D) NiSe 2 inclusions and 0-dimensional (0D) Se vacancies, increases electron carrier concentration and electrical conductivity, improving the power factor, while simultaneously reducing lattice thermal conductivity through enhanced phonon scattering at point defects and interfaces. Consequently, the thermoelectric figure of merit is improved across the measured temperature range, reaching a maximum zT of ∼0.30 at 520 K ( x = 0.20). These results establish precipitation-enabled multi-dimensional defect engineering as an effective pathway to optimize coupled carrier and phonon transport in Bi 2 Se 3 -based thermoelectric materials.