Effects of alloying elements on thermoelectric properties of ReSi 1.75
- PDF / 499,857 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 25 Downloads / 248 Views
S9.5.1
Effects of alloying elements on thermoelectric properties of ReSi1.75 Min Wook Oh, Jia-Jun Gu, Kosuke Kuwabara and Haruyuki Inui Department of Materials Science and Engineering, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan ABSTRACTS The thermoelectric properties as well as microstructure of binary and some ternary ReSi1.75 have been investigated. Binary ReSi1.75 exhibits a nice thermoelectric property as exemplified by the high value of dimensionless figure of merit (ZT) of 0.70 at 800 °C when measured along [001], although the ZT value along [100] is just moderately high. Mo substitution for Re in ReSi1.75 considerably increases the ZT value along [001] because of the decreased electrical resistivity, while the property improvement is not significant along [100]. On the other hand, Al and Ge substitutions for Si in ReSi1.75 considerably increase the ZT value along [100]. This is also because of the decreased electrical resistivity. When Al is added to ReSi1.75, the value of electrical resistivity is significantly reduced when compared to the binary counterpart and the temperature dependence of electrical resistivity changes from of semiconductor for the binary alloy to of metal for the Al-added alloys. INTRODUCTION Binary rhenium disilicide is of interest owing to its potentials as a promising candidate material for thermoelectric applications [1]. The stoichiometry of the silicide is determined to be ReSi1.75 instead of ReSi2 and the crystal structure belongs to the monoclinic system with an ordered arrangement of Si vacancies in the parent tetragonal C11b lattice [2, 3]. Although the electrical transport properties of the disilicide have been reported by several researchers, they are controversial. Siegrist et al. [4] reported the value of Seebeck coefficients ranging from -90 to 130 µV at 310 K. On the other hand, Neshpor et al. [5, 6] reported the value, which is in fair agreement with that reported by Siegrist et al. [4] but the sign is reversed. The Hall mobility in single crystals measured by Gottlieb et al. [7] at room temperature was 370 cm2/Vs, whereas it is 30 cm2/Vs in single crystals measured by Ivanenko et al. [8]. Our recent measurements on the electrical transport properties as well as thermal transport properties for single crystals of ReSi1.75 indicated that the value of electrical resistivity along [001] shows a higher value than that along [100] and that the temperature dependence of electrical resistivity for both orientations shows a semiconducting behavior. The Seebeck coefficients showed highly anisotropic behaviors. The value of Seebeck coefficients along [100] is positive (+230 µV/K at 330 K) while it is negative along [001] (-300 µV/K at 600 K). The values of thermal conductivity at room temperature are 5.72 W/mK and 5.65 W/mK along [100] and [001], respectively and increase gradually as the temperature is increased. The value of dimensionless figure of merit (ZT) along [001] at 1073 K is 0.7 (n-type), which is comparable with the value of Si-Ge alloys currently used as a the
Data Loading...
