Structure and thermoelectric performance of AgyIn3.33-y/3Se5 compounds

Abstract

In this study, we find new AgyIn3.33-y/3Se5 compounds in Ag-In-Se system by static diffusion method combined with common X-ray diffraction and backscattering electron analysis. The crystal structure belongs to the trilateral system with theP3m1 space group, which features a two-dimensional layered structure. The unit cell is composed of 9-atom quantum layers arranged in the sequence of Se1-In1-Se2-In2-Se3-Ag/In3-Se4-In4-Se5, and in-between these layers are bonded by the weak van der Waals force. The sintered bulk samples show highly anisotropic transport properties and have an ultra-low lattice thermal conductivity along the direction parallel to sintering pressure about 0.15 W·m-1·K-1 at 873 K. The intrinsically ultra-low lattice thermal conductivity mainly comes from low phonon velocity and the strong coupling between low frequency optical phonon and acoustic phonons. The AgyIn3.33-y/3Se5 compounds behave as an n-type conduction. The electrical conductivity is 4×104 S·m-1 and the Seebeck coefficient is -80 μV·K -1 at room temperature. Therefore, AgyIn3.33-y/3Se5 compounds show high electrical transport properties in a wide temperature range, and the power factor is around 5 μW·cm-1·K-2 in a range of 450-800 K. Owing to the ultra-low lattice thermal conductivity along the direction parallel to sintering pressure, Ag0.407In3.198Se5 reaches a maximum ZT of 1.01 at 873 K and an average ZT of 0.45 at 300-850 K. The discovery of AgyIn3.33-y/3Se5 expands the n-type copper based chalcogenide and lays an important foundation for the application of copper based chalcogenide.