A new thermoelectric material: CsBi₄Te₆

The highly anisotropic material CsBi₄Te₆ was prepared by the reaction of Cs/Bi₂Te₃ around 600 °C. The compound crystallizes in the monoclinic space group C2/m with a = 51.9205(8) Å, b = 4.4025(1) Å, c = 14.5118(3) Å, β = 101.480(1)°, V = 3250.75(11) ų, and Z = 8. The final R values are R₁ = 0.0585 and wR₂ = 0.1127 for all data. The compound has a 2-D structure composed of NaCl-type [Bi₄Te ₆] anionic layers and Cs⁺ ions residing between the layers. The [Bi₄Te₆] layers are interconnected by Bi-Bi bonds at a distance of 3.2383(10) Å. This material is a narrow gap semiconductor. Optimization studies on the thermoelectric properties with a variety of doping agents show that the electrical properties of CSBi ₄Te₆ can be tuned to yield an optimized thermoelectric material which is promising for low-temperature applications. Sbl₃ doping resulted in p-type behavior and a maximum power factor of 51.5 μW/cm·K² at 184 K and the corresponding ZT of 0.82 at 225 K. The highest power factor of 59.8 μW/cm·K² at 151 K was obtained from 0.06% Sb-doped material. We report here the synthesis, physicochemical properties, doping characteristics, charge-transport properties, and thermal conductivity. Also presented are studies on n-type CsBi ₄Te₆ and comparisons to those of p-type.