Enhanced thermoelectric performance in Na-doped p-type nonstoichiometric AgSbTe2 compound

Graphical abstract: Display Omitted Research highlights: → Na doping decreases the electrical conductivity and increases the thermal conductivity. → Na doping largely increases the Seebeck coefficient. → Na doping degrades the TE performance. → Excess Te optimizes the electrical and thermal conductivity simultaneously. → Na doped nonstoichiometric AgSbTe2+y compounds show excellent TE performance. - Abstract: Polycrystalline Na-doped p-type AgSbTe2+y (y = 0, 0.02) compounds were prepared from high purity elements by a melt-quench technique followed by spark plasma sintering. The influences of Na doping and excess Te on the thermoelectric transport properties were investigated. Both Na and Te act as acceptor in AgSbTe2 compound. Substituting Ag with Na has great influence on electron band structure and can enhance the Seebeck coefficient effectively. Adding excess Te in Na-doped samples plays a great role in optimizing the electrical and thermal conductivity. Overall, the thermoelectric performance of the Na doped nonstoichiometric AgSbTe2 samples is greatly improved and a ZT of 1.50 is achieved at about 570 K for Ag0.99Na0.01SbTe2.02 sample, representing a 30% enhancement with respect to an undoped sample at the same temperature.