Compositions and thermoelectric properties of XNiSn (X = Ti, Zr, Hf) half-Heusler alloys
Compositions and thermoelectric properties of XNiSn (X = Ti, Zr, Hf) half-Heusler alloys
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DOI：
10.1039/c5tc02025e
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发表时间：
2015-01-01
影响因子：
6.4
通讯作者：
Bos, J. W. G.
中科院分区：
文献类型：
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作者：
Downie, R. A.;Barczak, S. A.;Bos, J. W. G.
用Rietveld中子粉末衍射数据分析了固相反应制备的XNiSn（X = Ti，Zr，Hf）半Heusler合金的成分。所有含Ti的样品都有2-3%的过量Ni，而X = Zr，Hf的样品几乎是化学计量的。具有混合X-金属的样品的特征在于存在3-4个不同的X1-xX'xNi 1 +ySn半Heusler相。X = Ti和X = Ti0.5Hf0.5的可变温度和时间相关的中子粉末衍射表明，过量Ni的量和相分布在高达至少600 ℃时是稳定的。由热位移参数得到德拜温度分别为367（2）K和317（2）K。含有Ti的样品的特征在于由一个类似于0.15 eV的带隙和单调递减的塞贝克系数。具有Zr和Hf的组合物具有类似的带隙值，但显示双极转变。利用单抛物带模型对简并掺杂的Ti0.5Zr0.5NiSn1-zSbz样品的热电输运数据进行了分析，结果表明，输运受到合金散射的限制，并产生了2.5（1）m（e）的有效载流子质量。
Rietveld analysis of neutron powder diffraction data has been used to investigate the compositions of XNiSn (X = Ti, Zr, Hf) half-Heusler alloys prepared by solid state reactions. All samples containing Ti have 2-3% excess Ni, whereas the samples with X = Zr, Hf are almost stoichiometric. Samples with mixed X-metals are characterised by the presence of 3-4 distinct X1-xX'xNi1+ySn half-Heusler phases. Variable temperature and time dependent neutron powder diffraction for X = Ti and X = Ti0.5Hf0.5 demonstrates that both the amount of excess Ni and the phase distribution are stable up to at least 600 degrees C. Debye temperatures of 367(2) K and 317(2) K were obtained from the thermal displacement parameters. The samples containing Ti are characterised by a similar to 0.15 eV bandgap and a monotonously decreasing Seebeck coefficient. The compositions with Zr and Hf have similar bandgap values but show ambipolar transitions. Analysis of the thermoelectric transport data of degenerately doped Ti0.5Zr0.5NiSn1-zSbz samples using a single parabolic band model demonstrates that the transport is limited by alloy scattering and yielded an effective carrier mass of 2.5(1) m(e).