Remarkable effects of shear-exfoliation and restacking on microstructural texturing and thermoelectric properties of AgCrSe₂

Layer-structured AgCrSe₂ has attracted much attention for thermoelectrics for its low lattice thermal conductivity, however, the intrinsic electrical transport properties are poor. Here, remarkable effects of an exfoliation-restacking process were demonstrated for a series of Ag-deficient Ag_1-xCrSe₂ bulk ceramics by comparison. An effectively increased crystallographic orientation together with a reduction of grain size was obtained in such processed samples compared to that for the simply Ag-deficient ones. Electrical conductivity was significantly improved due to the increase in carrier mobility, while Seebeck coefficient was affected little with the unchanged carrier concentration and effective mass, leading to an optimal power factor of 7.3 μWcm⁻¹K⁻² at 773 K with x = 0.06; Meanwhile, lattice thermal conductivity was further reduced due to the enhanced phonon scattering by grain boundaries. Ultimately, a maximal ZT of ∼0.79 was achieved with x = 0.06 at 773 K, which stands among the tops so far for AgCrSe₂-based thermoelectric materials. These results demonstrated a remarkable effectiveness of shear-exfoliation and restacking on tuning the thermoelectric performance of AgCrSe₂-like layered superionic compounds.