crystallography-2018-posters-accepted-abstracts

21 / 22

Crystallography 2018 Structural Chemistry & Crystallography Communication
ISSN: 2470-9905 Page 73
June 04-05, 2018
London, UK
3rd Edition of International Conference on
Advanced Spectroscopy,
Crystallography and Applications
in Modern Chemistry
Since their first discovery in 1965 [1] the intermetallic clathrates
attracted attention of materials scientists, chemists and
physicists in particular due to their fascinating crystal structures,
especially the formation of large cavities within the three-
dimensional framework which are usually occupied by filler
species [2]. These cavities may be also un-occupied (empty
clathrates [3]). From the point of view of chemical bonding,
three types of atomic interactions are present in this family of
inorganic materials: polar and non-polar covalent interactions in
the framework, ionic forces and strongly polar covalent dative
bonds between the filler atoms in the cavities and the framework
[4]. The coexistence of the different bond kinds (inhomogeneity
of the bonding) causes the reduced thermal conductivity and
opens the possibility to tune the charge carrier concentration,
which makes these materials interesting for thermoelectric
applications. The combination of the electronic and phononic
transport in clathrates suitable for thermoelectric application was
recognized and proven quite early [5,6]. One of the challenges on
the way to an application is the preparation of large amounts of
the material with reproducible properties, and its control by the
up-scaling of the manufacture processes, due to the complexity
of the phase diagrams [7]. Another challenge is the understanding
of the low thermal conductivity of this family of materials One
possible mechanism is associated with the presence of low-
energy non-dispersive optical phonons caused by vibrations
(‘rattling’) of the filler atoms within the cage-like crystal structure
[8,9]. Recently was shown, that these optic modes of the fillers
hybridize with that of the framework, and there are no indications
for the formation of isolated oscillators in the system. Moreover,
the low thermal conductivity is characteristic also for the empty
clathrates. A new phonon-filter mechanism was proven by the
inelastic neutron scattering experiments [10,11].
CRYSTALLOGRAPHY AND THERMAL CONDUCTIVITY OF THERMOELECTRIC
CLATHRATES
Yuri Grin
Max-Planck-Institut fur Chemische Physik fester Stoffe, Germany
Struct Chem Crystallogr Commun 2018, Volume 4
DOI: 10.21767/2470-9905-C1-006