| In the past century,it has been seen that the consumption of non-renewable sources of energy?oil,coal and natural gas?has caused more environmental damage than any other human activity,and then finding renewable alternative sources of energy is extremely urgent.Thermoelectric?TE?effect enables direct and reversible conversion between thermal and electric energy,and provides a viable route for power generation from waste heat.Therefore,the research of thermoelectric materials has been paid more and more attention.The new generation of thermoelectric materials,which aim at noise-free,long-life and environment-friendly,has become one of the hot spots in the research of clean energy.High cost and low thermoelectric conversion efficiency has been limiting the extensive application of thermoelectric materials for a long time in the past.?-Zn4Sb3 is an example of semiconductor that was identified as a potential candidate for TE devices in the medium temperature due to its low thermal conductivity and relatively inexpensive and non-toxic constituent elements.Unfortunately,the compounds are still in the stage of experimental exploration and need to be further studied.In the present paper,the electrical transport properties,thermal stability and oxidation resistance of the double-doped samples prepared by flux-method combing with melting and slow cooling technology will be discussed in ?-Zn4Sb3 system.And the samples will be of practical importance in the TE application at high temperature.The main conclusions are as follows:The Pb-Sn co-doping samples are prepared adjusting the Pb doping content.The thermal analysis result of the weight loss of the sample is hardly detected below 900K,and samples exhibit an excellent thermal stability.Electrical transport properties of the samples were optimized by Pb doping.With the increase of Pb initial content,Seebeck coefficient increases and electrical conductivity decreases.The sample with x=0.6 possesses higher values of power factor in the temperature range from 390 K to 550 K and obtains the minimum power factor of 1.69×10-3 W·m-1·K-2 at 390 KIn a series of samples prepared from the atomic ratios of Zn:Sb:Cd:Sn=4.4:3:x:3?x=0.2,0.4,0.6 and 0.8?are obtained using Sn-flux method.Carrier concentration of all samples varies from 4.52×1019 to 6.42×1019cm-3as carrier mobility changes from58.27 to 67.93 cm2?V-1?s-1 at room temperature.As a result,electrical transport properties of the samples were optimized by Cd-Sn co-doped.Consequently,the maximal power factor of 1.70×10-3 W·m-1·K-2 is achieved at 540 K for the sample with Cd initial content x=0.2.Several Ga/Sn codoped ?-Zn4Sb3 single crystals were prepared basing on the nominal stoichiometric ratios of Zn4-xSb3GaxSn3?x=0,0.25,0.5,0.6 and 0.75?.The electrical transport properties of the samples were optimized by Ga and Sn doping.Consequently,the sample with Ga initial content x=0.5 exhibits an excellent electrical property,and the maximum power factor of 1.56×10-3 W·m-1·K-2 is obtained at approximately 450 K.We prepared several single crystals?-Zn4Sb3 via Bi-Sn mixed-flux method to investigate the electrical transport properties,thermal stability and oxidation resistance according to the nominal stoichiometric ratios of Bi/Sn=1/10,1/6,1/4,1/3and 1/2,respectively.Electrical transport properties of ?-Zn4Sb3 are further improved via adjusting Bi and Sn flux content.The S2 sample exhibits the maximum power factor of 1.45×10-3 W·m-1·K-2 at 510 K.Compared with the?-Zn4Sb3 sample prepared using Zn-Sn mixed-flux method,the S2 sample still possesses an excellent oxidation resistance and thermal stability after the four times heat treatment process in air at 573 K for 20 h. |
PDF Full Text Request