Phase transition generates rapid changes of transport parameters and poor mechanical property, and thus restricts the application of thermoelectric materials. AgBiSe₂ exhibits cubic phase at above 580 K with high-symmetry structure and low lattice thermal conductivity, indicating the potentiality of high thermoelectric performances. In this work, the cubic structure of AgBiSe₂ was achieved at ambient conditions by alloying with PbS, enhancing the configurational entropy at both cationic and anionic sites. The cubic structure was rather stable after several measurement cycles. Nb substitution at cationic sites effectively reduced band gap, and increased both carrier concentration and effective mass. All samples exhibited relatively low lattice thermal conductivity (0.68–0.34 W/(m·K)) in the temperature range of 300–773 K, due to the nanoscale inhomogeneity and the random distribution of multiple species at some atomic sites. A maximum zT of 0.65 at 773 K was obtained for (Ag_0.99Nb_0.01BiSe₂)_0.8(PbS)_0.2 sample. The entropy-driven structural stabilization is a promising strategy to achieve stable structure for practical thermoelectric applications.

Polycrystalline Cu₂Se bulk materials were synthesized by high-pressure and high-temperature (HPHT) technique. The effects of synthetic temperature and pressure on the thermoelectric properties of Cu₂Se materials were investigated. The results indicate that both synthetic temperature and pressure determine the microstructure and thermoelectric performance of Cu₂Se compounds. The increase of synthetic temperature can effectively enhance the electrical conductivity and decrease the lattice thermal conductivity. A two-fold improvement in the power factor is obtained at synthetic temperature of 1000 ℃ compared to that obtained at room temperature. All β-Cu₂Se samples exhibit low and temperature-independent lattice thermal conductivity ranging from 0.3 to 0.5 Wm⁻¹K⁻¹ due to the intrinsic superionic feature and the abundant lattice defects produced at high pressure. A maximum zT of 1.19 at 723 K was obtained for the sample synthesized at 3 GPa and 1000 ℃. These findings indicate that HPHT technology is an efficient approach to synthesize Cu₂Se-based bulk materials.