Optical Phonon Decay and Improved Thermoelectric Efficiency in p-Type MgSb.

The MgSb-based layered compounds exhibit exceptional thermoelectric properties over a wide temperature range and possess the potential to supplant traditional BiTe modules with reliable and economical MgSb-based thermoelectric devices, contingent upon the availability of a complementary p-type MgSb material with high thermoelectric efficiency comparable to that of n-type MgSb. We provide a simpler method involving the codoping of monovalent atoms (K and Na) at the Mg site of the MgSb lattice to improve the thermoelectric performance of p-type MgSb. K-Na codoping results in a peak power factor of around 0.85 mW/mK at 675 K in MgKNaSb by enhancing the carrier concentration at the Fermi level. Furthermore, the temperature-dependent development of the Raman modes substantiates the existence of significant lattice anharmonicity in MgKNaSb, ascribed to volumetric quasi-anharmonicity and three- and four-phonon interactions. As a result, decay of optical phonon happens at higher temperatures, yielding an exceptionally low lattice thermal conductivity of 0.38 W/mK at 675 K in MgKNaSb, the lowest recorded in p-type MgSb materials. The thermoelectric figure of merit for MgKNaSb attains 0.9 at 675 K, representing the highest documented value for double-doped p-type MgSb materials thus far. Our extensive findings validate the optical phonon decay and improvement in thermoelectric efficiency of p-type MgSb via codoping with monovalent atoms for midtemperature thermoelectric applications.