Unusual thermoelectric transport anisotropy in quasi-two-dimensional rhombohedral GeTe
Bibliographic record
Abstract
In this study, we calculate the $T=300\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ scattering and thermoelectric transport properties of rhombohedral GeTe using first-principles modeling. The room-temperature phase of GeTe has a layered structure, with cross-plane and in-plane directions oriented parallel and perpendicular to [111], respectively. Based on rigorous electron-phonon scattering, our transport calculations reveal unusual anisotropic properties; $n$-type GeTe has a cross-plane electrical conductivity that is roughly $3\ifmmode\times\else\texttimes\fi{}$ larger than in plane. $p$-type GeTe, however, displays opposite anisotropy with in-plane conducting roughly $2\ifmmode\times\else\texttimes\fi{}$ more than cross plane, as is expected in quasi-two-dimensional materials. The power factor shows the same anisotropy as the electrical conductivity, since the Seebeck coefficient is relatively isotropic. Interestingly, cross-plane $n$-GeTe shows the largest mobility and power factor approaching $500\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{2}/\mathrm{V}$-s and $32\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{W}/\mathrm{cm}\text{\ensuremath{-}}{\mathrm{K}}^{2}$, respectively. The thermoelectric figure of merit, $zT$, is enhanced as a result of this unusual anisotropy in $n$-GeTe since the lattice thermal conductivity is minimized along cross plane. This decouples the preferred transport directions of electrons and phonons, leading to a threefold increase in $zT$ along cross plane compared to in plane. The $n$-type anisotropy results from high-velocity electron states formed by Ge $p$ orbitals that span across the interstitial region. This surprising behavior, that would allow the preferential conduction direction to be controlled by doping, could be observed in other quasi-two-dimensional materials and exploited to achieve higher-performance thermoelectrics.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| 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 | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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 source (direct Gemma or distilled Codex), 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".