Thermoelectric Properties of Mixed Rhenium Chalcogenides Re6Te15-x Sex (0 ≤ × ≤ 8)

Abstract

AbstractReported are the temperature dependencies of the thermoelectric power and electrical resistivity of mixed rhenium chalcogenides Re6Te15-x,Sex (0 ≤ x ≤ 8) in the range 90–420 K. Influence of the partial chalcogen exchange on thermoelectric properties of these compounds is discussed. The samples are prepared by sintering elemental powders inside evacuated and sealed quartz ampoules at 1150 K for 170 hours. X-ray analysis reveals an orthorhombic lattice for samples with x < 8 and a tetragonal lattice for the Re6Te7Se8. sample. The lattice parameters and the unit cell volume decrease with increasing selenium concentration.The measurements indicate p-type semiconducting behavior for all samples. The presence of the energy gap is observed at higher temperatures (T ≥ 180–220 K) for all x. Data suggest hopping conduction at lower temperatures. Room temperature resistivities increase non-linearly from 6.9 to 20.4 Ω m with the increasing selenium content. Initially, the thermoelectric power a increases with temperature for all samples, with the fastest increase in Re6Se8 Te7 and the slowest in Re6Te15. The temperature at which a reaches maximum decreases with the increasing Se content. Above this temperature, a decreases uniformly as the temperature increases, the slowest increase being for Re6Se8Te7 and the fastest for Re6Te15. Such α(T) dependence is also discussed. The temperature dependence of the power factor, α2/ρ, is presented. Comparison of ρ, α, and the power factor in Re6SexTe15-x with currently used state-of-the-art materials is given.