Reducing of the thermal conductivity of f-electron Perche materials

本研究合成了YbAl_3，并测定了其热电性能。研究了Yb和Al取代对热电性能的影响。以Yb块、Al板和Tm、Lu、B、In、Cu、Ag粉末为原料。混合粉末主要在真空中熔化和退火。含Tm和Lu的试样在Ar中热处理以防止蒸发。将样品在1M NaOH溶液中进行研磨和冲洗，去除多余的Al，并在31.2 MPa和1123 K的氩气中进行热压，用x射线衍射仪检测了样品的相和晶格常数。根据热电动势与温差的线性关系，确定了塞贝克系数（α）。电阻率ρ和导热系数κ分别用直流四探针法和激光闪蒸法测定。测量在温度(T)从100到800 K进行。从α^2/ρ和α^2/ρκ方程分别计算了功率因子和无因次优度（ZT）。本研究合成的YbAl_3的ρ值与文献中固相反应和电弧熔炼所得的ρ值基本一致。虽然文献值在200 K左右达到最大值，但随着温度的降低，|α|的值逐渐升高。108 K时最大值为116 μVK^<-1>。功率因数也随着温度的降低而增加，在118 K时为797×10^<-4> Wm^<-1> K^<-2>。该值是YbAl_3的3.5倍，是Bi_2Te_3的17倍。本研究首次确定了YbAl_3中κ的温度依赖性。ZT随温度的降低而增大，在307 K时ZT为0.29。Yb位点被Tm和Lu取代，转化率达0.3 mol%。取代引起ρ和|α|的降低。这表明取代使传导电子的散射比Yb^<3+>降低了4f^<13>。YbAl_3的Al位点未被B、Cu和Ag取代。证实In取代Al位的比例高达0.05mol%。YbAl_<2.95>In_<0.05>的ρ与YbAl_3的ρ基本一致，但|α|al因取代而降低。少

In this study, YbAl_3 was synthesized and the thermoelectric properties were determined. The effect of substitution for Yb and Al sites on the thermoelectric properties was also investigated.Yb lump, Al plate, and powders of Tm, Lu, B, In, Cu and Ag were used as the starting materials. The mixed powders were melted and annealed mainly in vacuum. Tm and Lu containing specimens were heat-treated in Ar to prevent the evaporation. The specimens were grinded and rinsed in 1M NaOH solution to remove excess Al. The rinsed powders were hot-pressed at 31.2 MPa and 1123 K in Ar. The phase and lattice constant were examined by X-ray diffraction. The Seebeck coefficient (α) was determined from the linear relationship between thermoelectromotive force and temperature difference. The electrical resistivity (ρ) and the thermal conductivity (κ) were measured by a dc four-probe method and a laser flash method, respectively. The measurements were conducted at temperature (T) from 100 to 800 K. The power … More factor and dimensionless figure-of-merit (ZT) were evaluated from the equations of α^2/ρ and α^2/ρκ, respectively. The ρ of YbAl_3 synthesized in this study was almost in agreement with the literature values prepared by solid state reaction and arc melting. Although the literature values showed maximum around 200 K, present values of |α| increased with decreasing temperature. The greatest value was 116 μVK^<-1> at 108 K. The power factor also increased with decreasing temperature, being 797×10^<-4> Wm^<-1> K^<-2> at 118 K. This value was 3.5 times as large as reported values of YbAl_3, and was 17 times as large as that of Bi_2Te_3. The temperature dependence of κ for YbAl_3 was first determined in this study. The ZT increased with decreasing temperature, and was 0.29 at 307 K. The Yb sites were substituted with Tm and Lu up to 0.3 mol%. The substitution caused the decrease of ρ and |α|. This suggests that the substitution decreased the scattering of conduction electrons by 4f^<13> level of Yb^<3+>. The Al sites of YbAl_3 were not substituted by B, Cu and Ag. It is confirmed that In substitutes the Al sites up to 0.05mol%. The ρ of YbAl_<2.95>In_<0.05> was almost in agreement with that of YbAl_3, but |α|al decreased by the substitution. Less