Controlling the Thermal Stability, Threshold Voltage, and Thermoelectric Properties of Cuprous Sulfide Thermoelectrics.

Cu-ion liquid-like copper sulfide materials have excellent thermoelectric properties, while their applications are limited by their high-temperature decomposition and electric field-driven Cu precipitation issues. In particular, high thermoelectric properties and electric field-driven degradation are difficult to reconcile because liquid-like Cu ions are dominant in low κ and high , while they cause electric field-driven degradation. Here, we control the sintering current and duration time to remove the CuS phase, thereby inhibiting the thermal decomposition of the copper sulfide samples, and introduce the Fe element into the sample matrix to improve its resistance to electric field-driven degradation. We reveal that the kinetic process of CuS phase decomposition can be suppressed by increasing the relative density of the sample or covering a layer of dense coating/film on the surface of the sample. However, as long as the CuS phase is present in the sample, it cannot maintain thermal stability above 450 °C. Furthermore, we find that the Fe element forms a nanogrid spinodal decomposition structure in the sample matrix, which acts as a barrier wall to prevent the long-range diffusion of liquid-like Cu ions and inhibit the electric field-driven degradation. The freely movable liquid-like Cu ions in the grid maintain a strong scattering of phonons in a short range, so the sample possesses low κ and high . Then, a strategy to unify the high thermal decomposition temperature, high threshold voltage, and high thermoelectric performance of copper sulfide thermoelectric materials is proposed: transforming the CuS phase and introducing a liquid-like Cu ion migration barrier.