Studies of alloy phase stability in relation to the Hume-Rothery rule and development of new Al-based thermoelectric materials

本工作旨在通过第一性原理能带计算和热电性质的研究来探索Hume-Rothery规则背后的物理机制，这些准晶体及其近似物和Fe_2VAl化合物都具有费米能级的赝能隙。该项目取得的主要成果如下。（1）采用LMTO-ASA方法结合NFE模型计算了Al-Li-Cu 1/1立方近似体的电子结构。证明了赝能隙是费米能级上的电子与（631），（543），（710），（550）带面相互作用的结果。(2)We测量了Al-Re-Si、Al-Mn-Si、Al-Pd-Mn-Re-Si和Al-Mn-Re-Si近似物的电子比热系数、塞贝克系数、电阻率和热导率，揭示了费米能级上的赝能隙结构如何决定这些赝能隙的热电特性 关于我们 含磷系统(3)We在Fe_2VAl系中，用Si代替Al，用Ti和Mo代替V，成功地使Seebeck系数的符号从正值变为负值（-140UNFV/K）。在Fe_2VAl中，引入V位的Fe原子引起的自旋涨落导致电阻率的增加，从而导致热电性能的降低。为了克服这一困难，我们合成了（Fe-Ru）_2VAl合金，发现磁化强度的急剧下降导致电阻率和磁电阻的显著下降。这被认为是作为一个证据，在V位上的Fe原子有助于降低该系统的热电特性。（4）对Cu_5Zn_8，Cu_9Al_4，TM_2Zn_<11>（TM=Ni，Pd，Co，Fe）γ黄铜进行了FLAPW能带计算。通过对费米能级赝能隙波函数的傅立叶谱分析，证明了（411）、（330）区确实是赝能隙形成的主要原因，从而在特定的电子浓度下稳定了复合体的独特结构。少

The present work aimed at exploring physics behind the Hume-Rothery rule by performing the first-principles band calculations and evaluating thermoelectric properties of quasicrystals and their approximants and Fe_2VAl compounds, all being characterized by the possession of the pseudogap at the Fermi level. The main results obtained in this project are listed below.(1)The electronic structure of the Al-Li-Cu 1/1-cubic approximant has been calculated in the context of the LMTO-ASA method in combination with the NFE model. We proved that the pseudogap is formed as a result of the interaction of electrons at the Fermi level with (631), (543), (710), (550) zone planes.(2)We have measured the electronic specific heat coefficient, Seebeck coefficient, electrical resistivity and thermal conductivity of the Al-Re-Si,Al-Mn-Si,Al-Pd-Mn-Re-Si and Al-Mn-Re-Si approximants and revealed how the pseudogap structure across the Fermi level determines the thermoelectric characteristics of these pseudoga … More p-bearing systems.(3)We succeeded in swinging a sign of the Seebeck coefficient from a positive to negative value (-140μV/K) by substituting Si for Al and Ti and Mo for V in the Fe_2VAl system, respectively. In the Fe_2VAl, spin fluctuations caused by Fe atoms introduced into the V site are believed to give rise to an enhancement in resistivity, thereby leading to a poor performance of thermoelectric characteristics. To get rid of this difficulty, we synthesized the (Fe-Ru)_2VAl alloys and revealed that a dramatic decrease in magnetization results in a substantial decrease in resistivity and magnetoresistance. This was taken as a proof that the Fe atoms on the V-site contribute to degrade the thermoelectric characteristics of this system.(4)The FLAPW band calculations have been performed for Cu_5Zn_8,Cu_9Al_4,TM_2Zn_<11>(TM=Ni,Pd,Co,Fe) gamma-brasses. The Fourier spectrum analysis for wave function sustaining the pseudogap at the Fermi level clearly demonstrated that (411), (330) zone are indeed responsible for the formation of the pseudogap to stabilize the unique complex structure at specific electron concentration. Less