层状热电材料SrAl_2Ge_2的制备与性质研究
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摘要
以Ⅱ、Ⅲ和Ⅳ族元素为主的笼状物热电材料研究近年来发展迅速,尤其是在优值系数ZT值上取得了重大突破,而从Sr-Al-Ge笼状物体系中获得的层状结构热电材料却鲜有人关注.本研究利用铝元素作为助溶剂,在1150℃下成功合成了层状SrAl_2Ge_2单晶.采用X射线衍射仪对样品粉末进行表征,通过Rietveld精修证明该晶体具有CaAl_2Si_2结构(空间群为P3-m1,晶胞参数a=b=4.2339(1)?,c=7.4809(0)?).变温电阻率测试发现单晶样品沿c轴方向具有p型半导体行为,此外其在2～300 K低温下的比热(C_p)数据符合德拜模型.本研究结果对于开发新型无毒、高性能热电材料具有一定参考价值.
Ⅱ,Ⅲ and Ⅳ groups were widely investigated to synthesize guest-host thermoelectric compounds in order to obtain high optimal ZT value materials. While a novel layered structure was less reported for Sr-Al-Ge system. In this study, SrAl_2Ge_2 single crystal was grown by aluminum flux at 1150 ℃ and characterized by powder X-ray methods. It is isotropic and crystallize in the CaAl_2Si_2-type structure through the Rietveld refinement method(space group P3-m1) with the lattice constants a=b=4.2339(1)?, c=7.4809(0) ?. Temperature-depended resistivity on single crystals along the c-axis shows p-type semiconducting behavior. Heat capacity(C_p) was measured in 2～300 K and low temperature C_p was consistent with data calculated by using Debye model. This work opens up a novel avenue for seeking and designing environment-friendly and high-performance thermoelectric materials.
Ⅱ,Ⅲ and Ⅳ groups were widely investigated to synthesize guest-host thermoelectric compounds in order to obtain high optimal ZT value materials. While a novel layered structure was less reported for Sr-Al-Ge system. In this study, SrAl_2Ge_2 single crystal was grown by aluminum flux at 1150 ℃ and characterized by powder X-ray methods. It is isotropic and crystallize in the CaAl_2Si_2-type structure through the Rietveld refinement method(space group P3-m1) with the lattice constants a=b=4.2339(1)?, c=7.4809(0) ?. Temperature-depended resistivity on single crystals along the c-axis shows p-type semiconducting behavior. Heat capacity(C_p) was measured in 2～300 K and low temperature C_p was consistent with data calculated by using Debye model. This work opens up a novel avenue for seeking and designing environment-friendly and high-performance thermoelectric materials.
引文
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[4] Christensen M,Johnsen S,Iversen B B.Thermoelectric clathrates of type I [J].Dalton Trans,2010,39:978.
[5] 王冰,陈顺礼,杨吉军,等.笼状热电材料p型和n型Ba8Ga16Ge30单晶之间载流子的协调研究 [J].四川大学学报:自然科学版,2016,53:361.
[6] Slack G A.New materials and performance limits for thermoelectric cooling [M].Boca Raton:CRC Press,FL,1995.
[7] Qiu L Y,Swainson I P,Nolas G S,et al.Structure,thermal,and transport properties of the clathrates Sr8Zn8Ge38,Sr8Ga16Ge30,and Ba8Ga16Si30 [J].Phys Rev B,2004,70:035208.
[8] Christensen M,Iversen B B.Host structure engineering in thermoelectric clathrates [J].Chem Mater,2007,19:4896.
[9] Christensen M,Johnsen S,S?ndergaard M,et al.Fast preparation and characterization of quarternary thermoelectric clathrates [J].Chem Mater,2009,21:122.
[10] Sales B C,Chakoumakos B C,Jin R,et al.Structural,magnetic,thermal,and transport properties of X8Ga16Ge30 (X = Eu,Sr,Ba) single crystals [J].Phys Rev B,2001,63:245113.
[11] Gou W P,Li Y,Chi J,et al.NMR study of slow atomic motion in Sr8Ga16Ge30 clathrate [J].Phys Rev B,2005,71:174307.
[12] Chakoumakos B C,Sales B C,Mandrus D G,et al.Structural disorder and thermal conductivity of the semiconducting clathrate Sr8Ga16Ge30 [J].J Alloy Comp,2000,296:80.
[13] Imai M,Abe H,Yamada K.Electrical properties of single-crystalline CaAl2Si2 [J].Inorg Chem,2004,43:5186.
[14] Khatun M,Stoyko S S,Mar A.Quaternary arsenides AM1.5Tt0.5As2 (A=Na,K,Rb;M=Zn,Cd;Tt=Si,Ge,Sn):size effects in CaAl2Si2- and ThCr2Si2-type structures [J].Inorg Chem,2013,52:3148.
[15] Canfield P C,Fisk Z.Growth of single crystals from metallic fluxes [J].Philos Mag B,1992,65:1117.
[16] Zheng C,Hoffmann R,Nesper R.Site preferences and bond length differences in CaA12Si2-type Zintl compounds [J].J Am Chem Soc,1986,108:1876.
[17] Burdett J K,Miller G J.Fragment formalism in main-group solids:applications to aluminum boride (AlB2),calcium aluminum silicide (CaAl2Si2),barium-aluminum (BaAl4),and related materials [J].Chem Mater,1990,2:12.
[18] Kauzlarich S M,Condron C L,Wassei J K,et al.Structure and high-temperature thermoelectric properties of SrAl2Si2 [J].J Solid State Chem,2009,182:240.
[19] Wu J Z,Akagi K,Xu J T,et al.Unification of the low-energy excitation peaks in the heat capacity that appears in clathrates [J].Phys Rev B,2016,93:094303.
[20] Xu J T,Heguri S,Tanabe Y,et al.Heat capacity studies on rattling vibrations in Ba-TM-Ge type I clathrates [J].J Phys Chem Solids,2012,73:1521.
[21] Xu J T,Tang J,Rachi T,et al.Low-temperature heat capacity of Sr8Ga16Ge30 and Ba8Ga16Ge30:tunneling states and electron-phonon interaction in clathrates [J].Phys Rev B,2010,82:085206.
[22] Tang J,Rachi T,Kumashiro R,et al.Energetics of endohedral atoms in type-I clathrates observed by soft X-ray spectroscopy [J].Phys Rev B,2008,78:085203.
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