A New Thermoelectric Material: CsBi4Te6

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Abstract
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) Å3, 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 [Bi4Te6] 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 CsBi4Te6 can be tuned to yield an optimized thermoelectric material which is promising for low-temperature applications. SbI3 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 CsBi4Te6 and comparisons to those of p-type.