Sammendrag
Convergent beam electron diffraction experiments on thermoelectric skutterudites R Sæterli1, Ø Prytz2, PE Vullum1, J Friis3, K Marthinsen4, R Holmestad1 and J Taftø2Department of Physics, NTNU, N-7491 Trondheim, NorwayDepartment of Physics, University of Oslo, P.O. Box 1048 Blindern, N-0316 Oslo, NorwaySINTEF Materials and Chemistry, N-7465 Trondheim, NorwayDepartment of Materials Science and Technology, NTNU, N-7491 Trondheim, NorwaySkutterudites are a class of materials recognized by their chemical formula MX3, where M is a column 9 transition metal atom and X is one of the pnictogen atom P, As or Sb. They have received attention due to their thermoelectric properties, making them interesting both for power generation and refrigeration purposes [1]. The skutterudites are cubic and belong to space group Im-3. Each unit cell consists of eight smaller cubices of which six are filled by pnictogen rectangles, and two are left open, creating large voids in the structure. The thermoelectric properties of a material are found to depend on a high electronic conductivity while keeping the thermal conductivity low. The voids in the structure can be filled by atoms, often referred to as rattlers, that decrease the phonon contribution to the thermal conductivity as compared to the unfilled structures [2]. Hence, by varying the composition of the skutterudites and the degree of filling, a large range of materials with various thermoelectric properties can be achieved. We here report on preliminary studies of the electronic structure and bonding in filled and unfilled skutterudites. Convergent beam electron diffraction (CBED) is a powerful tool in this respect, being sensitive to low-order structure factors that give information about bonding. Quantitative CBED measurements are, however, demanding. A careful microscope alignment and energy filtering of the images are required, as well as time consuming computational refinements to compare the experiments to theory [3]. Here, a d