Unusual Thermoelectric Anisotropy in Rhombohedral Germanium Telluride
Bibliographic record
Abstract
Developing high performance thermoelectrics to convert waste heat into useful electrical power is an important challenge that has the potential to impact our energy future. This requires exploring and discovering new materials with enhanced electronic and thermal (phonon) transport properties. Advances in computational modeling now allow the thermoelectric characteristics of materials to be calculated fully predictively, and thus represents a powerful tool to be partnered with experimental efforts. In this talk, I will present our recent findings on rhombohedral GeTe, a layered quasi-2D material predicted to have unusual anisotropic transport properties [1]. Our approach combines density functional theory with the Boltzmann transport equation, to extract the detailed electron and phonon dispersions along with the electron-phonon scattering rates, in order to predict the thermoelectric transport coefficients. Our results show that the electrons preferentially conduct along the cross-plane direction, while the holes favor the in-plane direction. Interestingly, this feature enhances the thermoelectric figure-of-merit ZT for n-type GeTe, since the conductivity (and power factor) is maximized perpendicular to the atomic layers while the lattice (phonon) thermal conductivity is minimized - leading to a three-fold increase in ZT . The cross-plane power factor and mobility in n-GeTe reach roughly 32 μW/cm-K 2 and 500 cm 2 /V-s, respectively. An analysis of the band structure reveals that the large cross-plane transport originates from high-velocity conduction states, formed by the Ge p-orbitals that span across the interstitial region. These findings illustrate how the dominant electron and phonon transport directions are effectively decoupled in n-GeTe; a feature that can potentially be found in other materials to achieve enhancements in thermoelectric performance. [1] V. Askarpour and J. Maassen, “ Unusual thermoelectric transport anisotropy in quasi-two-dimensional rhombohedral GeTe ”, Phys. Rev. B 100 , 075201 (2019). Figure 1
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".