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

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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