Large Thermal Rectification in a Solid-State Thermal Diode Constructed of Iron-Doped Nickel Sulfide and Alumina

Thermal diodes, which allow heat flow in one direction but prohibit it in the reverse direction, are fundamental for thermal manipulation. Here, we report the construction of a thermal diode consisting of ${\mathrm{Ni}}_{0.85}{\mathrm{Fe}}_{0.15}\mathrm{S}$ (bonded with 10 wt % silver) and alumina. A high rectification factor \ensuremath{\gamma} of 1.51 is achieved with a relatively small temperature bias of 97 K near room temperature, indicating great potential applications in the field of nonlinear thermal control. The excellent rectification effect is attributed to the high contrast change in thermal conductivity of ${\mathrm{Ni}}_{0.85}{\mathrm{Fe}}_{0.15}\mathrm{S}$. In addition, we demonstrate that the maximum thermal rectification ratio is strongly dependent on the cold-terminal temperature of the thermal diode, the length ratio between the two segments, and the steepness of the first-order phase transition of ${\mathrm{Ni}}_{0.85}{\mathrm{Fe}}_{0.15}\mathrm{S}$.