Browsing by Author "Cai, K"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Single crystal neutron diffraction on the clathrates of Sr8Ga16Ge30, Ba8Ga16Ge30 and Sr4Ba4Ga16Ge30
    (Australian Institute of Physics, 2006-12-05) Tayebjee, M; Piltz, RO; Yu, DH; Cai, K; Wong, L; Stampfl, APJ
    The key consideration in the development of more efficient thermoelectric materials is to design materials that conduct heat like a glass but maintain good crystal-like electrical conductivities, that is to design so called “phonon glass and electron crystals (PGEC’s), as proposed by Slack [1]. One potential PGEC are clathrates that consist of a cage framework of the group 13/14 elements and alkali, alkaline earth or rare earth atoms trapped within the cages. The properties of such clathrates strongly depend on the details of their structures, the dynamic disorder of the trapped atoms as well as the distribution of framework atoms. The structure of single crystals of Sr8Ga16Ge30, Ba8Ga16Ge30 and Sr4Ba4Ga16Ge30 are characterized by single crystal neutron diffraction. The general gallium-doped germanium cage structure with strontium or barium guest atoms inside is confirmed. The lattice constants are 10.704(1)Å, 10.759(2)Å and 10.757(2)Å for Sr8Ga16Ge30, Ba8Ga16Ge30 and Sr4Ba4Ga16Ge30 respectively. Each unit cell contains two 20-atom cages and six 24-atom cages containing strontium/barium atoms. Analysis of the Sr8Ga16Ge30 cage structure shows that gallium atoms preferentially occupied the 6c site and avoided the 16i site. At the 6d site in the 24-atom cage, large atomic displacement parameters (ADP) from guest-atoms are determined for all structures. Further experiment at low temperature is in progress. [1] G. A. Slack, in CRC Handbook of Thermoelectrics, Edited by D. M. Rowe (CRC Boca Raton, FL, 1995), pp 407-440