Phonon Bridge Effect in Superlattices of Thermoelectric TiNiSn/HfNiSn With Controlled Interface Intermixing

The implementation of thermal barriers in thermoelectric materials improves their power conversion rates effectively. For this purpose, material boundaries are utilized and manipulated to affect phonon transmissivity. Specifically, interface intermixing and topography represents a useful but complex...

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Published inNanomaterials (Basel, Switzerland) Vol. 10; no. 6; p. 1239
Main Authors Heinz, Sven, Angel, Emigdio Chavez, Trapp, Maximilian, Kleebe, Hans-Joachim, Jakob, Gerhard
Format Journal Article
LanguageEnglish
Published Basel MDPI AG 25.06.2020
MDPI
Subjects
Boundaries
Boundary layer transition
Boundary layers
coherent phonon
Crystal structure
Electrical resistivity
Energy conversion
Heat
interface
Interfaces
intermixing
Multilayers
Parameter modification
Phonons
Plasma sintering
Quality
roughness
Satellites
superlattice
Superlattices
Thermal conductivity
Thermal resistance
Thermoelectric materials
Thin films
Transmission electron microscopy
Transmissivity
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Summary:The implementation of thermal barriers in thermoelectric materials improves their power conversion rates effectively. For this purpose, material boundaries are utilized and manipulated to affect phonon transmissivity. Specifically, interface intermixing and topography represents a useful but complex parameter for thermal transport modification. This study investigates epitaxial thin film multilayers, so called superlattices (SL), of TiNiSn/HfNiSn, both with pristine and purposefully deteriorated interfaces. High-resolution transmission electron microscopy and X-ray diffractometry are used to characterize their structural properties in detail. A differential 3 ω -method probes their thermal resistivity. The thermal resistivity reaches a maximum for an intermediate interface quality and decreases again for higher boundary layer intermixing. For boundaries with the lowest interface quality, the interface thermal resistance is reduced by 23% compared to a pristine SL. While an uptake of diffuse scattering likely explains the initial deterioration of thermal transport, we propose a phonon bridge interpretation for the lowered thermal resistivity of the interfaces beyond a critical intermixing. In this picture, the locally reduced acoustic contrast of the less defined boundary acts as a mediator that promotes phonon transition.
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ISSN:2079-4991
2079-4991
DOI:10.3390/nano10061239