Electrical and thermoelectrical properties of Bi2−xNaxTe3 alloys

For the first time, Bi ₂Te ₃ alloys, which have long been known as promising thermoelectric materials for room temperature applications, have been doped with Na atoms to enhance their thermoelectric performance. Bi ₂Te ₃ and Bi _2−xNa _xTe ₃ alloys were prepared by mono-temperature melting synthesis. Their structural, crystallographic properties and surface morphology were investigated by XRD and SEM analyses. All the prepared alloys showed perfect crystalline structure of single Bi _2−xNa _xTe ₃ phase. The thermoelectric properties of the synthesized alloys were measured in the temperature range of 273–473 K. Electrical conductivity of the concerned alloys were measured by the standard four probe method and studied as a function of temperature, showing metal-like behavior. Na-doping enhanced the electrical conductivity significantly due to enhancing of the carrier concentration. The Seebeck coefficient of all alloys exhibited a positive sign, confirming the p-type conduction. Significantly high Seebeck coefficient values were observed at high temperatures. The maximum value was recorded at 266 μV K ^{− 1} for Bi ₂Te ₃ at 473 K. Electronic thermal conductivity of the prepared alloys was estimated from Wiedemann-Franz equation. A remarkable reduction of the electronic thermal conductivity was observed against temperature, in correspondence with the electrical conductivity. The materials thermoelectric power factor was calculated based on electrical conductivity and Seebeck coefficient measurements. Also, the power factor was investigated as a function of temperature. The largest value was found for the most Na-doped samples at 299.6 µW/mK ², observed at 413 K.