|Reference : Lattice dynamics in thermoelectric Zintl phases|
|Dissertations and theses : Doctoral thesis|
|Physical, chemical, mathematical & earth Sciences : Physics|
|Lattice dynamics in thermoelectric Zintl phases|
|Möchel, Anne [Université de Liège - ULg > > > Doct. sc. (chimie - Bologne)]|
|Doctorat en sciences|
|[en] thermoelectricity ; Lattice dynamics ; inelastic neutron scattering ; phonon density of states ; diffraction|
|[en] A brief introduction to the thermoelectric eﬀects, the studied materials, and the experimen-
tal methods is given in the ﬁrst chapter. The introduction is not intended to be exhaustive,
but only to summarize important basic information for the reader. The introduction is
followed by four chapters dedicated to detailed experimental studies of the lattice dynamics
in selected thermoelectric Zintl phases.
First, the lattice dynamics in the unﬁlled and ﬁlled skutterudites FeSb3 , CoSb3 , and
YbFe4 Sb12 were studied by nuclear inelastic scattering, inelastic neutron scattering, and
several macroscopic methods. These studies reveal that FeSb3 exhibits softer Sb bonds than
CoSb3 , that the density of phonon states is shifted towards lower energies and the velocity
of sound is lower in FeSb3 as compared to CoSb3 . It appears thus that the soft [Fe4 Sb12 ]
framework dynamics might play an important role in the thermoelectric properties of ﬁlled
skutterudites. The observed anomalous temperature dependence of the elastic constants
and the rearrangement of the spectral weight of the Yb phonon states in YbFe4 Sb12 can be
explained by a change of the Yb valence state with the temperature.
Second, the lattice dynamics in the Sr8 Ga16 Ge30 clathrate was investigated by inelastic
neutron scattering measurements on a single crystal. We found that several mechanisms
contribute to the low thermal conductivity in this system and that the reduction of the heat
capacity contribution to the thermal conductivity plays a signiﬁcant role to the low thermal
conductivity, besides the reduction in the phonon lifetime and the phonon group velocity
that is related to the guest atom.
Third, the lattice dynamics of the Zintl phase Yb14 MnSb11 was studied by inelastic neu-
tron scattering and nuclear inelastic scattering measurements. All phonon modes of these
complex crystal systems are in a narrow energy range below ∼25 meV and the Debye tem-
perature, the velocity of sound and the mean force constants are small compared to those
of other thermoelectric materials such as Zn4 Sb3 . By comparing the lattice dynamics in
Yb14 MnSb11 and Zn4 Sb3 diﬀerent mechanisms which lead to the low thermal conductivity
in Zintl phases have been identiﬁed. Between 300 and 1200 K no softening of the velocity of
sound in Yb14 MnSb11 was observed by temperature dependent inelastic neutron scattering
measurements, which is in line with its large melting temperature.
|Researchers ; Professionals ; Students|
|Chapter 3 to 5 are not included in this version, because these chapter contain manuscripts, which are not yet submitted.|
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