Thermoelectric properties of (Ba,K)Cd2As2 crystallized in the CaAl2Si2-type structure
Thermoelectric properties of (Ba,K)Cd2As2 crystallized in the CaAl2Si2-type structure
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DOI：
10.1039/c8dt02955e
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发表时间：
2018-12-07
影响因子：
4
通讯作者：
Lee, C. H.
中科院分区：
文献类型：
--
作者：
Kunioka, H.;Kihou, K.;Lee, C. H.
采用固相反应-热压法制备了具有CaAl2Si2型结构(空间群P3m1)的As基化合物Ba1-xKxCd2As2。我们成功地用K取代了高达x=0.08的Ba，产生了浓度高达1.60×10(20)cm(-3)的空穴载流子掺杂。根据电阻率随温度的变化关系，确定了未掺杂的BaCd2As2的带隙为0.40 eV。样品的电阻率和塞贝克系数都随着空穴掺杂的增加而减小，当x=0.04时，在762K时的功率因子值为1.28 mW m(-1)K-2。第一性原理能带计算表明，较大的功率因子主要来源于p(x，y)轨道组成的能带的双重简并和价带极大处的各向异性能带结构。当x=0.08时，在773K，K掺杂到0.46Wm(-1)K-1时，晶格的热导率被抑制，这可能是由于随机性的原因。随机性的影响通过电子导热系数的增加来补偿，电子导热系数保持总导热系数近似恒定。因此，当x=0.04时，无量纲品质因数ZT在762K时达到最大值0.81。
As-Based Zintl compounds Ba1-xKxCd2As2 crystallized in the CaAl2Si2-type structure (space group P3m1) were prepared using solid-state reactions followed by hot-pressing. We have successfully substituted K for Ba up to x = 0.08, producing hole-carrier doping with concentrations up to 1.60 x 10(20) cm(-3). We have determined the band-gap value of non-doped BaCd2As2 to be 0.40 eV from the temperature dependence of the electrical resistivity. Both the electrical resistivity and the Seebeck coefficient decrease with hole doping, leading to a power factor value of 1.28 mW m(-1) K-2 at 762 K for x = 0.04. A first-principles band calculation shows that the relatively large power factor mainly originates from the two-fold degeneracy of the bands comprising As p(x,y) orbitals and from the anisotropic band structure at the valence-band maximum. The lattice thermal conductivity is suppressed by the K doping to 0.46 W m(-1) K-1 at 773 K for x = 0.08, presumably due to randomness. The effect of randomness is compensated by an increase in the electronic thermal conductivity, which keeps the total thermal conductivity approximately constant. In consequence, the dimensionless figure-of-merit ZT reaches a maximum value of 0.81 at 762 K for x = 0.04.