Development of high-performance solid-state thermal diodes using unusual behavior of thermal conductivity observed for Ag₂Ch (Ch = S, Se, Te)

Abstract

Thermal diodes are a kind of new device which controls the direction and magnitude of heat flow. The performance of thermal diode is evaluated by thermal rectification ratio (TRR) defined as | J_large | / | J_small |. Solid-state thermal diodes are made with two materials possessing different temperature dependence of thermal conductivity. Their performance is improved by the significant variation of thermal conductivity with temperature. In this study, therefore, we employed Ag₂Ch (Ch = S, Se, Te) because these materials are characterized by a drastic change in thermal conductivity due to a structural phase transition in the temperature range of 100 < T < 200℃. We prepared Ag₂Ch samples by means of self-propagating high-temperature synthesis method. The phases involved in the samples were identified using powder X-ray diffraction. We measured temperature dependence of thermal conductivity for prepared samples by means of laser flash method, and consequently observed 200 – 300% change in their thermal conductivity. The thermal diode consisting of Ag₂S and Ag₂Te was designed using the measured thermal conductivity. We experimentally confirmed that the developed thermal diode showed TRR = 2.1 ± 0.1 when it was placed between two heat reservoirs kept at T_H = 200℃ and T_L = 132℃.