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Abstract Hafnium pentatelluride (HfTe5) has attracted extensive interest due to its exotic electronic, optical, and thermal properties. As a highly anisotropic crystal (layered structure with in‐plane chains), it has highly anisotropic electrical‐transport properties, but the anisotropy of its thermal‐transport properties has not been established. Here, accurate experimental measurements and theoretical calculations are combined to resolve this issue. Time‐domain thermoreflectance measurements find a highly anisotropic thermal conductivity, 28:1:8, with values of 11.3 ± 2.2, 0.41 ± 0.04, and 3.2 ± 2.0 W m-1K-1along the in‐planea‐axis, through‐planeb‐axis, and in‐planec‐axis, respectively. This anisotropy is even larger than what was recently established for ZrTe5(12:1:6), but the individual values are somewhat higher, even though Zr has a smaller atomic mass than Hf. Density‐functional‐theory calculations predict thermal conductivities in good agreement with the experimental data, provide comprehensive insights into the results, and reveal the origin of the apparent anomaly of the relative thermal conductivities of the two pentatellurides. These results establish that HfTe5and ZrTe5, and by implication their alloys, have highly anisotropic and ultralow through‐plane thermal conductivities, which can provide guidance for the design of materials for new directional‐heat‐management applications and potentially other thermal functionalities.
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Orientation-Controlled Anisotropy in Single Crystals of Quasi-1D BaTiS 3
Low-dimensional materials with chain-like (one-dimensional) or layered (two-dimensional) structures are of significant interest due to their anisotropic electrical, optical, and thermal properties. One material with a chain-like structure, BaTiS3 (BTS), was recently shown to possess giant in-plane optical anisotropy and glass-like thermal conductivity. To understand the origin of these effects, it is necessary to fully characterize the optical, thermal, and electronic anisotropy of BTS. To this end, BTS crystals with different orientations (a- and c-axis orientations) were grown by chemical vapor transport. X-ray absorption spectroscopy was used to characterize the local structure and electronic anisotropy of BTS. Fourier transform infrared reflection/transmission spectra show a large in-plane optical anisotropy in the a-oriented crystals, while the c-axis oriented crystals were nearly isotropic in-plane. BTS platelet crystals are promising uniaxial materials for infrared optics with their optic axis parallel to the c-axis. The thermal conductivity measurements revealed a thermal anisotropy of ∼4.5 between the c- and a-axis. Time-domain Brillouin scattering showed that the longitudinal sound speed along the two axes is nearly the same, suggesting that the thermal anisotropy is a result of different phonon scattering rates.
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- PAR ID:
- 10332595
- Date Published:
- Journal Name:
- Chemistry of Materials
- ISSN:
- 0897-4756
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.chemmater.2c01046
