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

赝隙在费米能级上的存在被认为是准晶体及其近似中最具特征的特征之一，并被认为对电子输运性质有重要影响。伪间隙的概念是1968年莫特在讨论高温高压下液态汞的金属-绝缘体转变时提出的。通过证明电导率与赝隙深度的平方成正比，证明了Mott理论在准晶体及其近似物中的有效性，为准晶体及其近似物独特输运性质的应用研究提供了坚实的基础。在本项目中，我们主要研究热电效应。热电装置是能够将热能转化为电能或电能转化为热能的装置。后者预计将适用于电子冰箱。我们测量了80 ~ 400k温度范围内的热电功率，旨在为开发准晶体和助剂类热电器件材料建立指导原则。在平成10年，我们利用这笔资金购买了热电采集系统，并通过测量Al-Mg-Pd和Al-Mg-Zn准晶的塞贝克系数对机器进行了成功的测试。在平成11年，我们将测量扩展到Al-Cu-Fe， Al-Cu-Fe- si和Al-Pd-Mn体系。我们发现，在Al-Cu-Fe体系中，随着Fe浓度的变化，Seebeck系数和Hall系数的符号同时由正变为负。我们由此得出系统由电子态转变为空穴态的结论。Al-Mn-Pd单晶准晶的Seebeck系数为80 μV/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.