CoGe 1.5 Se 1.5 : Synthesis and characterization
- PDF / 52,568 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 61 Downloads / 152 Views
S8.15.1
CoGe 1.5Se 1.5: Synthesis and characterization R. Ertenberg1, M. Beekman1, J. Martin1, G. Fowler1, G.S. Nolas1 Department of Physics, University of South Florida, Tampa, FL 33620
1
ABSTRACT Polycrystalline CoGe1.5Se1.5 was synthesized and characterized. The compound is a member of the class of compounds with the skutterudite crystal structure. Synthesis assuming the above stoichiometry resulted in a n-type semiconductor with composition CoGe 1.452Se 1.379. The specimen exhibits a large room temperature Seebeck coefficient and resistivity. The electron mobility is very low and the thermal conductivity is lower than that of the binary skutterudite CoSb3. These properties can be attributed to the vacancies in the crystal lattice due to the non-stoichiometric nature of the specimen. The potential for thermoelectric applications of ternary skutterudites is also discussed. INTRODUCTION Over the past thirty years, alloys based on the Bi2Te3 and Si-Ge systems have been extensively studied and optimized for their use as thermoelectric materials to perform a variety of solid-state thermoelectric refrigeration and power generation applications. Recently there has been a resurgence of research efforts related to the investigation of new and novel materials with improved thermoelectric properties [1, 2]. These materials require optimization of a variety of properties in order to exhibit the necessary thermoelectric figure of merit, the numerical expression used to compare one potential thermoelectric material to another. The figure of merit relates the materials properties directly to the coefficient of performance of a particular device. The best thermoelectric material would possess a low thermal conductivity and good electrical properties. Skutterudites are materials that fulfill these basic criteria. They are also of scientific interest as they exhibit many different types of interesting properties, for example, electrical properties ranging from that of low temperature superconductors to narrow gap semiconductors. EXPERIMENTAL TECHNIQUES The CoGe1.5Se1.5 specimen prepared for this report was synthesized by mixing and reacting high purity constituent elements inside a boron nitride crucible that was itself sealed inside a fused quartz ampoule under a nitrogen atmosphere at 700 °C for several days. The product was then ground to fine powder inside a glove box, cold pressed into a pellet and sintered at 700 °C for several more days. X-ray diffraction analysis of the powdered specimen revealed only the diffraction lines associated with the skutterudite structure (space group Im3) with a lattice parameter of 8.306±0.008 Å. For transport measurements and electron beam microanalysis (EPMA), the powdered specimen was hot pressed in a nitrogen atmosphere at 600 °C and 25×10-3 psi for two hours, yielding a pellet that is 90 % of the theoretical (x-ray)
S8.15.2
density. EPMA indicated that the specimen was single phase with composition CoGe1.452Se1.379. It is apparent that the relatively high Se vapor pressure resulted i
Data Loading...
