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

点击翻译按钮获取中文摘要

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.