Synthesis And Optimization Of Bismuth Telluride Based Thermoelectric Materials

As an important part of the energy revolution in the new century,thermoelectric devices and materials are attracting more and more attentions worldwide.Higher conversion efficiency of thermoelectric devices is demanded for potential application.An important factor affecting the conversion efficiency of thermoelectric device is the performance of thermoelectric materials used in the device,which is generally measured by the thermoelectric figure of merit(ZT).Therefore,how to improve the ZT value of materials is the most important research topic currently.Among all thermoelectric materials,bismuth telluride-based thermoelectric materials have been widely used because of their excellent properties at room temperature.In this work,the optimization of the thermoelectric performance of Bi2Te2.7Se0.3(BTS),i.e.the most commonly used n-type bismuth telluride-based thermoelectric material,was studied in details.The thermoelectric properties of BTS were optimized by liquid phase sintering doping and alkali metal ions via hydrothermal,respectively.Liquid KOH was introduced into the grain boundary of BTS by liquid sintering during the hot-pressing process.The liquid KOH flowed through the grain boundary of the sample and condensed afterwards,which played a role in modifying the grain boundary of the sample.The modified grain boundary produces energy filtering effect,improves the Seebeck coefficient and power factor of the sample,reduces the thermal conductivity,and sebsequently improves the ZT value of the sample.Moreover,it is found that the maximum ZT can be tuned gradually in the temperature range from 450 to 375 K by tuning the weight percent of KOH.Besides,another study was carried out.The nanoparticles of BTS were dispersed in ethylene glycol solution of hydroxide of alkali metal by ultrasonic wave,and then hydrothermal reaction was carried out to realize the doping of alkali metal ions.The effects of different alkali metal ions(K,Na)and hydrothermal solutions of different concentrations on the doping effect were investigated.We found that potassium ion is a better doping material than sodium ion.