No abstract

Si-based thermoelectric materials have attracted attention in recent decades with their advantages of low toxicity, low production costs, and high stability. Here, we report recent achievements on the synthesis and characterization of Si-based thermoelectric materials. In the first part, we show that bulk Si synthesized through a natural nanostructuring method exhibits an exceptionally high thermoelectric figure of merit zT value of 0.6 at 1050 K. In the second part, we show the synthesis and characterization of nanocomposites of Si and metal silicides including CrSi2, CoSi2, TiSi2, and VSi2. These are synthesized by the rapid-solidification melt-spinning (MS) technique. Through MS, we confirm that silicide precipitates are dispersed homogenously in the Si matrix with desired nanoscale sizes. In the final part, we show a promising new metal silicide of YbSi2 for thermoelectrics, which exhibits an exceptionally high power factor at room temperature.

No abstract

A pair of n-type Bi2Te3–x Se x and p-type (Bi,Sb)2Te3 is known as a promising candidate for assembling a high thermoelectric efficiency module operating at near room temperature. While the dimensionless figure of merit (zT) of p-type (Bi,Sb)2Te3 is commonly larger than 1.0, n-type Bi2Te3–x Se x has a lower zT value of ∼0.8 at room temperature. Here, we aim to enhance the zT of n-type Bi2Te3–x Se x through the energy filtering effect that can improve the Seebeck coefficient by adding Au. In the Bi2Te2.8Se0.2 + 5 at % Au composite, the Seebeck coefficient is significantly improved, and the electrical resistivity does not change significantly, leading to an approximately twice as high power factor as that of the non-Au-added one at near room temperature. Also, the addition of Au suppresses the thermal conductivity. These advantages result in a maximum zT of over 1.0 at room temperature and average zT value of 1.05 at T = 300–400 K, an ∼75% improvement, which is comparable to those of the reported n-type Bi2Te3-based materials. Also, Au addition shows no negative effect on the mechanical properties as well as high-temperature stability of Bi2Te3–x Se x . These results indicate that Au addition is a promising method to improve the thermoelectric properties of n-type Bi2Te3–x Se x used for assembling a practical thermoelectric module operating at near room temperature.

ZrW2O8 is known as a negative coefficient of thermal expansion (CTE) material. In contrast, the studies of other properties than the CTE of ZrW2O8, such as thermal conductivity and mechanical properties, are limited. Herein, a highly dense bulk sample (%T.D. > 95%) of ZrW2O8 from very fine powder (D50 0.3 μm) with a crystalline size of 31 nm using a spark plasma sintering (SPS) technique is synthesized. It is revealed that ZrW2O8 exhibits the lowest level of thermal conductivity among various oxides in a wide temperature range from 300 to 823 K. Furthermore, various physical properties such as a peculiar CTE, elastic constant, and Grüneisen parameter are reported. Owing to its exceptional thermal properties, ZrW2O8 is expected to be used in various thermal management areas.