Dynamical variation of carrier concentration and colossal Seebeck effect in Cu2S low-temperature phase

Abstract To understand the colossal Seebeck effect recently found in metallic Cu2Se at the phase transition from low-to high-temperature phase, we investigated the behaviors of thermoelectric properties during the phase transition of Cu2S and Ag2Se, both of which possess a phase transition in the same manner as Cu2Se. It has clearly revealed that the colossal Seebeck effect reported for metallic Cu2Se was not observable in Ag2Se but in Cu2S. The main reason for this difference between Cu2S and Ag2Se dwells in the difference of the phase diagrams: presence and absence of two-phase region where the low- and high-temperature phases coexist together in a stable condition. Unique temperature gradient, that allows us to spatially separate the two phases, produced a dynamical variation of carrier concentration in the low-temperature phase and, hence, the colossal Seebeck effect during the phase transition.