Dissociation of GaSb in n-Type PbTe: off-Centered Gallium Atom and Weak Electron–Phonon Coupling Provide High Thermoelectric Performance

Abstract

Many strategies have been employed to maintain an "optimal carrier concentration" to achieve a high thermoelectric power factor in n-type PbTe. Here, we show that a high power factor can also be achieved over a broad temperature range without attaining the optimal carrier concentration by alloying n-type PbTe with GaSb. We find that GaSb dissociates into Ga and Sb and dissolves into the PbTe matrix. Ga atoms introduce impurity levels above the valence band of PbTe giving rise to diminished electron–phonon coupling and an increased carrier effective mass leading to a high Seebeck coefficient of −87 μV K–1 and a high carrier mobility of 810 cm2 V–1s–1 at 300 K. As a result, a high power factor of 29 μW cm–1 K–2 at 323 K is achieved. Phonon band-structure calculations show that Ga is off-centered (0.05 Å) from Pb site along the ⟨111⟩ direction leading to a reduced lattice thermal conductivity of 0.7 W m–1 K–1 and a maximum thermoelectric figure of merit of 1.35 at 773 K in PbTe0.997I0.003–2 mol % GaSb. The dissolution of III–V semiconductors in lead telluride is a new finding with broader implications and opens new avenues in controlling thermal and charge transport in advanced thermoelectric materials.