Solvothermal synthesis of micro-pillar shaped Ag2Se and its thermoelectric potential

Solvothermal method can synthesize ultralarge and high-performance thermoelectric powders with controllable structure, morphology, composition, and grain size. Here, we have developed a facile and surfactant-free solvothermal method for the synthesis of ultralarge Ag2Se powders. The as-synthesized Ag2Se powders exhibit the morphology of micro-pillar with the length ranging from several to hundreds of microns, and the average length-diameter ratio of ∼4.9. In as-synthesized Ag2Se micro-pillars, regardless of the high crystallinity and closely perfect Ag/Se ratio of ∼2, the highly localized lattice distortions and strain fields might indicate partial superionicity of room-temperature orthorhombic Ag2Se. Compositional and structural analysis after spark plasma sintering indicates the formation of additional Se vacancies due to Se sublimation during the sintering process, which leads to high carrier concentration of ∼1.3 × 1019 cm−3 and limits the room-temperature dimensionless figure of merit to ∼0.46. Further optimizing the carrier concentration to ∼1 × 1018 cm−3 can theoretically lead to high room-temperature dimensionless figure of merit of ∼1.4. Our study not only renders a facile solvothermal method for the synthesis of Ag2Se micro-pillars with extensive thermoelectric application potentials.