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HL: Fachverband Halbleiterphysik

HL 10: Functional materials I - Energy storage (organized by MM)

HL 10.5: Vortrag

Montag, 31. März 2014, 11:15–11:30, IFW A

NMR Investigations of the Aluminium Substituted Barium Clathrate Ba₈Si₄₆ — •Matej Bobnar, Iryna Antonyshyn, Michael Wedel, Duong Nguyen, Ulrich Burkhardt, Yurii Prots, Bodo Böhme, Liudmila Muzica, Raul Cardoso, Walter Schnelle, Igor Veremchuk, Michael Baitinger, and Juri Grin — Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Str. 40, 01187 Dresden

Clathrates are interesting for their thermoelectric properties, due to their heigh electric and low thermal conductivity. Ba_8−xSi₄₆ is a type I clathrate obtained at 800 ^∘C and at high pressure of 2-5 GPa. The covalently bonded Si atoms form a framework of small, 20 atom, and large, 24 atom, cages that are fully or partially filled by Ba atoms. Some of the Si atoms may be substituted by a number of other atoms, including Al. Ba₈Al_xSi_46−x is reported with a homogeneity range of 8 ≤ x ≤ 15. Our investigations, however, begin with a clathrate of even lower Al content, Ba₈Al_6.8Si₃₉ and continue towards the Al-rich phases. We try to determine, which Si atoms are substituted by Al and how a disorder increases or decreases with a growing Al content. Since Al and Si stand next to each other in the periodic table of elements, they are very difficult to discern by X-ray. For this reason, the NMR was employed, which observes local environments of each nucleus separately and gives some hints about the intrinsic properties of the samples. In this work, we present a model for Al and Si distribution in the clathrate I framework based on ²⁹Si and ²⁷Al NMR results.