Preparation, Thermal Stability And Electrical Transmission Properties Of β-Zn <4 Sb <3> Single Crystal Thermoelectric Materials

The development and utilization of new energy became the focal point all over the world in the past two decades due to the energy crisis and environment issues, and thermoelectric(TE) materials have drawn significant interest. The p-type β-Zn4Sb3 compound has attracted much attention due to its cheap elements and eco-friendly as well as high TE performance at medium temperature range(400-700K). Althoughβ-Zn4Sb3 has a high TE performance, the micro crack and evaporation of Zn at high temperature of polycrystalline β-Zn4Sb3 leading the weak mechanical property and poor thermal stability which became a bottleneck for its practical application. For the above problems, we use the Sn-flux method to prepare the β-Zn4Sb3 single crystals in this work, the high temperature thermal stability and electrical properties of the samples have been studied.Adjusting the preparation process, obtained the most suitable process to prepare the β-Zn4Sb3 single crystal: Using Sn as the flux, high-purity element Zn(grain,99.999%), Sb(grain, 99.999%) and Sn(ingot, 99.999%) were weighed according to stoichiometric ratios of Zn4+x Sb3Sn3(x= 0-0.8), the weighed elements were put into quartz tube and sealed in the vacuum. The sealed tube was placed into furnace and heated to 853 K in 2 h, incubated at this temperature for 12 h, cooled to 723 K in 15 minutes and then heated to 753 K rapidly, followed by cooling to 593 K in 40 hours,the remaining molten Sn was separated from β-Zn4Sb3 single crystals by centrifugation technique.Using Sn as the flux, according to stoichiometric ratios of Zn4+x Sb3Sn3(x= 0-0.8)to prepare the β-Zn4Sb3 single crystal, the corrsponding results indicated that all crystals are with the space group of c R3 and behave characteristic of p-type conduction; The Sn atoms are prefer to replace Zn and the normalized chemical formula of the samples can be recorded as(Zn Sn)3.877Sb3;Thermogravimetric-differential thermal analysis(TG-DTA) shows that there has no weight loss untill temperature reaches to melting point of 821 K, indicating the excellent high temperature thermal stability of the prepared samples;The sample withx=0.4 possess the higher electrical conductivity and higher Seebeck coefficient synchronously.In/Sn co-doped β-Zn4Sb3 single crystals with space group c R3 were prepared by the Sn-flux method according to the formula of Zn4.4Sb3Sn3Inx(x= 0-0.5). The prepared samples exhibite excellent high temperature thermal stability, and it is enhanced by the increasing co-doped content of In and Sn. All prepared samples behave characteristic of p-type conduction. Comparing to the β-Zn4Sb3 poly-crystal sample, the carrier mobility is increased significantly. Also the prepared single crystals possess higher electrical conductivity. The Seebeck coefficient of the crystal samples is increased by the increasing total content of In and Sn. The sample with x =0.5 behaves the excellent electrical properties, which shows maximal power factor of1.53×10-3Wm-1K-2 at 603 K.