Investigation of Softer Lattice Dynamics in Defect Engineered GeTe Crystals
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| Main Authors: | , , , , , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866909811401031680 |
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| author | Majumder, Saptak Singha, Pintu C., Sharath Kumar Gupta, Mayanak K. Kumar, Dharmendra Mittal, R. Shukla, D. K. Saravanan, M. P Jaiswal-Nagar, Deepshikha Kamble, Vinayak B. |
| author_facet | Majumder, Saptak Singha, Pintu C., Sharath Kumar Gupta, Mayanak K. Kumar, Dharmendra Mittal, R. Shukla, D. K. Saravanan, M. P Jaiswal-Nagar, Deepshikha Kamble, Vinayak B. |
| contents | The impact of Ge vacancies on the low-temperature lattice dynamics of single-crystalline GeTe was investigated through a comparative study of two off-stoichiometric samples: Ge$_{0.8}$Te (S$_1$) and Ge$_{0.88}$Te (S$_2$). X-ray diffraction confirms their highly oriented crystalline nature mainly along the $h0l$ plane, while temperature-dependent Raman spectroscopy reveals pronounced anharmonicity in S$_1$, indicated by stronger three-phonon scattering in the in-plane E-mode. A suppressed Raman feature at $~$ 239 $cm^{-1}$ in S$_2$ suggests fewer disordered GeTe$_{4-n}$Ge$_n$ tetrahedra, correlating with reduced Ge-Ge bonding signatures. Machine-Learned Molecular Dynamics (MLMD) simulations show dominant Te contributions below 100 $cm^{-1}$, while Ge dominates above, particularly influencing the 120 $cm^{-1}$ mode affected by defects at the Ge-site. Complementary calculation of phonon linewidth via MLMD and Temperature-Dependent Effective Potential (TDEP) methods affirm the predominance of three-phonon scattering below 300 K. Specific heat measurements, modeled using Debye-Einstein formalism, show lower Debye temperatures ($θ_D$) of 172.3 $\pm$ 1.5 K in Ge$_{0.8}$Te and 176.6 $\pm$ 1.7 K for Ge$_{0.88}$Te respectively, confirming defect-induced lattice softening. Electrical resistivity analysis further corroborates this, indicating reduced effective phonon frequencies in $S_1$. Thus, our results establish that higher Ge vacancies lead to softer, and hence more anharmonic lattice dynamics in GeTe, with its relevance in designing superior thermoelectric and phase-change memory applications. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2502_10745 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Investigation of Softer Lattice Dynamics in Defect Engineered GeTe Crystals Majumder, Saptak Singha, Pintu C., Sharath Kumar Gupta, Mayanak K. Kumar, Dharmendra Mittal, R. Shukla, D. K. Saravanan, M. P Jaiswal-Nagar, Deepshikha Kamble, Vinayak B. Materials Science The impact of Ge vacancies on the low-temperature lattice dynamics of single-crystalline GeTe was investigated through a comparative study of two off-stoichiometric samples: Ge$_{0.8}$Te (S$_1$) and Ge$_{0.88}$Te (S$_2$). X-ray diffraction confirms their highly oriented crystalline nature mainly along the $h0l$ plane, while temperature-dependent Raman spectroscopy reveals pronounced anharmonicity in S$_1$, indicated by stronger three-phonon scattering in the in-plane E-mode. A suppressed Raman feature at $~$ 239 $cm^{-1}$ in S$_2$ suggests fewer disordered GeTe$_{4-n}$Ge$_n$ tetrahedra, correlating with reduced Ge-Ge bonding signatures. Machine-Learned Molecular Dynamics (MLMD) simulations show dominant Te contributions below 100 $cm^{-1}$, while Ge dominates above, particularly influencing the 120 $cm^{-1}$ mode affected by defects at the Ge-site. Complementary calculation of phonon linewidth via MLMD and Temperature-Dependent Effective Potential (TDEP) methods affirm the predominance of three-phonon scattering below 300 K. Specific heat measurements, modeled using Debye-Einstein formalism, show lower Debye temperatures ($θ_D$) of 172.3 $\pm$ 1.5 K in Ge$_{0.8}$Te and 176.6 $\pm$ 1.7 K for Ge$_{0.88}$Te respectively, confirming defect-induced lattice softening. Electrical resistivity analysis further corroborates this, indicating reduced effective phonon frequencies in $S_1$. Thus, our results establish that higher Ge vacancies lead to softer, and hence more anharmonic lattice dynamics in GeTe, with its relevance in designing superior thermoelectric and phase-change memory applications. |
| title | Investigation of Softer Lattice Dynamics in Defect Engineered GeTe Crystals |
| topic | Materials Science |
| url | https://arxiv.org/abs/2502.10745 |