Phase separation and interface effect in pseudo-quaternary composites of AgxBi0.5Sb1.5−xTe3−x

Abstract We investigated anisotropic thermoelectric properties of p -type Ag x Bi 0.5 Sb 1.5− x Te 3− x ( x = 0.0, 0.1, 0.2 and 0.3) compounds, prepared by melting and hot press sintering. During hot press sintering and annealing process, the eutectoid decomposition of Ag 2 Te from (Bi,Sb) 2 Te 3 matrix induces intrinsic thermoelectric composites Ag 2+ δ Te/(Bi,Sb) 2 Te 3 . The phase separation increases the phonon scattering which lowered the lattice thermal conductivity. We also found the metallic interfacial layer in a grain boundary from the measurements of conducting atomic force microscopy (AFM) and scanning Seebeck- and scanning thermal-microscopy (SThM). Here we argue that the interfacial conductivity attributes to the increase of power factor due to increase of mobility. Thereby, the phase separation of Ag 2 Te from the (Bi,Sb) 2 Te 3 matrix gives rise to the enhanced thermoelectric properties at mild-temperature range, resulting in the enhancement of dimensionless thermoelectric figure-of-merit Z T value of 1.02 at 567 K for x = 0.1 along the vertical direction.