This study prepares a group of single crystalline β-Zn_4Sb_3 with Ge and Sn codoped by the Sn-flux method according to the nominal stoichiometric ratios of Zn_（4.4）Sb_3 Ge_xSn_3（x = 0–0.15）. The prepared samples possess a metallic luster surface with perfect appearance and large crystal sizes. The microscopic cracks or defects are invisible in the samples from the back-scattered electron image. Except for the heavily Ge-doped sample of x = 0.15, all the samples are single phase with space group R3c. The thermal analysis results show that the samples doped with Ge exhibit an excellent thermal stability.Compared with the polycrystalline Ge-substituted β-Zn_4Sb_3, the present single crystals have higher carrier mobility, and hence the electrical conductivity is improved, which reaches 7.48×10~4S·m^（-1） at room temperature for the x = 0.1 sample.The change of Ge and Sn contents does not improve the Seebeck coefficient significantly. Benefiting from the increased electrical conductivity, the sample with x = 0.075 gets the highest power factor of 1.45×10^（-3）W·m^（-1）·K^（-2） at 543 K.
Single crystalline samples of type-I and type-VIII Ba8Ga16-xCuxSn30（x = 0,1） clathrates are prepared by the Snflux method.Effects of Cu-doping on stability and electrical properties of Ba8Ga16Sn30 single crystal are explored by first-principle and experiment.All samples are heated to different high temperatures and maintained at these temperatures for 120 min and then cooled to room temperature to explore their structural stabilities.Results from DTA and powder xray diffraction analysis indicate that type-I Ba8Ga16Sn30 structure is transformed into type-VIII phase after the sample has been heated to 185℃.Type-VIII BGS is stable during heating and cooling,but type-VIII Ba8Ga15CuSn30 decomposes into Sn and Ba（Ga/Sn）4 during cooling.Meanwhile,the electrical properties of type-I samples are measured,their electrical conductivities are enhanced,and the Seebeck efficient is reduced with Cu substitution.The type-I samples after phase transformations show the electrical characteristics of type-VIII samples.
采用Sn自熔剂法制备了具有n型传导的VIII型Ba8Ga16 xGexSn30(0 x 1.0)单晶笼合物,并对其结构和热电特性进行研究.研究结果表明:Ge在单晶中的实际含量较少,随着掺杂量的增加样品的晶格常数略有减小,Ge掺杂后样品的载流子浓度较掺杂前低,迁移率增加;所有样品的Seebeck系数均为负值,且绝对值较未掺杂样品低,但Ge掺杂后样品的电导率提高了62%;x=0.5的样品在500 K附近取得最大ZT值1.25.
本文采用Sn自熔剂法,制备Mg掺杂Sn基单晶笼合物Ba8Ga16-XMgXSn30(0 X 1.5),并对其结构及电传输性能进行研究.结果表明所制备化合物为具有空间群Iˉ43m的VIII型单晶笼合物,随Mg掺杂量的增加,对应化合物的熔点略有升高,晶格常数减小,掺杂样品中填充原子Ba的实际含量低于理想值8.0,其在十二面体空洞中的占有率约为0.93(Mg的名义含量X=1.5时).所有样品均表现为n型传导,Mg的掺入对材料的能带结构有一定影响,Mg掺杂后,样品的载流子浓度降低,Seebeck系数的绝对值、电阻率增加,Mg的名义含量X=1.5时,样品的功率因子在430 K附近取得最大值1.26×10-3W·m-1·K-2.
