Compositional Modulation of Agsbte2 Materials by Csi Doping and Optimisation of Electro-Phonon Transport Properties

Abstract

A series of CsI-doped AgSbTe2 thermoelectric materials, Ag1-xSbTe2(CsI)x (x = 0, 0.05, 0.07, 0.10), were synthesized using a vacuum melting–spark plasma sintering (VM-SPS) method. CsI doping effectively suppressed the formation of Ag2Te impurity phase, enhancing the phase purity of AgSbTe2 and improving both its electrical and thermal transport properties. Cs doping introduced impurity energy levels near the valence band edge, reduced the bandgap, and increased carrier concentration. Consequently, the electrical conductivity of Ag0.9SbTe2(CsI)0.1 reached 408 S/cm at room temperature, representing a significant increase of 237% compared to the undoped sample. Additionally, CsI doping increased the density of states near the Fermi level, maintaining the Seebeck coefficient and significantly enhancing the power factor. Specifically, the sample Ag0.93SbTe2(CsI)0.07 achieved a power factor of 14.42 μW·cm-1·K-2 at 450 K. The introduction of CsI heavy-ion doping generated numerous point defects, intensifying phonon scattering and thus reducing thermal conductivity. At 535 K, the Ag0.9SbTe2(CsI)0.1 sample exhibited the lowest lattice thermal conductivity of 0.32 W·m−1·K−1, approaching the theoretical minimum (κlat,min = 0.30 W·m−1·K−1) of AgSbTe2. At 586 K, the Ag0.95SbTe2(CsI)0.05 composition achieved a power factor of 12.6 μW·cm−1·K−2 and a reduced thermal conductivity of 0.56 W·m−1·K−1. Its maximum ZT reached 1.32, approximately 52% higher than that of undoped AgSbTe2.

Keywords: AgSbTe2, CsI, Second phase deposition, ZT