Thermoelectric effect of quasicrystals and development of thermoelectric-device materials by controlling the psuedogap

跨费米能级的赝隙的存在一直被认为是准晶及其近似物中最具特征的特征之一，并被认为是影响电子输运性质的关键因素。赝隙的概念是由莫特在1968年讨论高温高压下液态汞的金属-绝缘体转变时提出的。主要的研究人员证明了Mott理论对于准晶及其近似物的有效性，证明了电导率与伪隙深度的平方成正比，为研究准晶及其近似物独特的输运性质的应用提供了坚实的基础。在本课题中，我们主要关注热电效应。热电装置是一种能够将热量转化为电能或电能转化为热量的装置。后者有望应用于电子冰箱。我们在80-400K的温度范围内进行了温差电势的测量，旨在建立准晶和准晶系热电器件材料开发的指导原则。平成十年，我们用这笔资金购买了温差电功率采集系统，并成功地测试了Al-Mg-Pd和Al-Mg-Zn准晶的Seebeck系数。平成11年，我们将测量扩展到Al-Cu-Fe，Al-Cu-Fe-Si和Al-Pd-Mn系统。我们发现，随着Al-Cu-Fe系中Fe含量的变化，Seebeck系数和霍尔系数都同时由正向负号变化。由此我们得出结论，系统从电子态转变为空穴态。我们还发现Al-Mn-Pd单晶的塞贝克系数为80μV/K，几乎与准晶的取向无关。

The presence of the pseudogap across the Fermi level has been regarded as one of the most characteristic features in quasicrystals and their approximates and is known to affect critically the electron transport properties. The concept of the pseudogap has been established by Mott in 1968 in his discussion of the metal-insulator transition of liquid mercury at high temperatures and high pressures. The principal investigator demonstrated the validity of the Mott theory for quasicrystals and their approximants by showing that the electrical conductivity is proportional to the square of the depth of the pseudogap and provided firm basis for the research aiming at the application of unique transport properties of quasicrystals and their approximants.In the present project, we focused on the thermoelectric effect. The thermoelectric device is the device, which is capable of transforming heat into electricity or electricity into heat. The latter is expected to be applicable to the electronic refrigerator. We have measured the thermoelectric power in the temperature range 80-400 K and aimed at establishing the guiding principles to develop the thermoelectric device materials in the family of quasicrystals and apploximants.In the year of Heisei 10, we purchased the thermoelectric power acquisition system by using this fund and could successfully test the machine by measuring the Seebeck coefficient of Al-Mg-Pd and Al-Mg-Zn quasicrystals.In the year of Heisei 11, we extended the measurements to Al-Cu-Fe, Al-Cu-Fe-Si and Al-Pd-Mn systems. We revealed that both Seebeck coefficient and Hall coefficient concomitantly change the sign from a positive to negative one by varying Fe concentration in the Al-Cu-Fe system. We concluded from this that the system changes from the electron to hole states. We also revealed that the single quasicrystal Al-Mn-Pd exhibits the Seebeck coefficient of 80 μV/K, which is almost independent of the orientation of the quasicrystal.