| Research Abstract |
β-Rhombohedral boron(β-boron) is one of polymorphs of pure boron which consists mainly of B_<12> icosahedral clusters. To search the condition in β-boron to enhance ZT, which is represented by ZT=σS^2T/κ, we investigated the change of the thermoelectric parameters, σ, S and κ, from 20K to 1073K when various metal atom(V, Co, Ni, Cu, Fe, Sr, Zr or W) was doped. The data for arc-melted and hot-pressed samples were used to see the effect of micro-structure. V, Co, Ni, Cu, Fe and Zr are successfully doped and the amount of second phases are very small. While there is only little difference on σ and S between hot-pressed and arc-melted samples, κ for hot-pressed sample is smaller than that for arc-melted one because of its porous structure or small grain size. Especially, for the V doped hot-pressed sample, in which V atoms mainly occupy A_1 site of β-boron, σ is increased very much, S is decreased even to negative value and κ is decreased. The maximum and n-type ZT value in this study is o
… More
btained for the V doped hot-pressed sample and is approaching to that of B_4C which is considered to have the largest and p-type ZT value in boron-rich icosahedral cluster solids.
We investigated the composition dependence of the Seebeck coefficient and the electrical conductivity of AlPdRe icosahedral alloys. As the concentration of transition metal (either Pd or Re) increases, the Seebeck coefficient rapidly increases. The strong composition dependence is related to the pseudogap structure in the electron density of states at the Fermi energy, and to the variation in bonding nature between Al and transition metal. Glass-like transport behavior in thermal conduction is also observed. The dimensionless thermoelectric figure of merit has a maximum value of approximately 0.1 in the temperature range from 600 to 700 K and reveals strong composition dependence. Thermoelectric properties of the quaternary AlPdReRu quasicrystal that replaced Re by Ru in AlPdRe icosahedral quasicrystals have been studied. In the middle of substitution Ru for Re, the electrical conductivity increases with increasing temperature and the peak of Seebeck coefficient shifts to a higher temperature side. By Ru addition to the AlPdRe quasicrystal, value of dimensionless figure of merit, ZT, goes up 1.5 times. Less
|
