Pressure-induced phonon freezing in the ZnSeS II-VI mixed crystal: phonon-polaritons and ab initio calculations
| Autor: | Hussein, R. Hajj, Pages, O., Polian, A., Postnikov, A. V., Dicko, H., Firszt, F., Strzalkowski, K., Paszkowicz, W., Broch, L., Ravy, S., Fertey, P. |
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| Rok vydání: | 2016 |
| Předmět: | |
| Zdroj: | 2016 J. Phys.: Condens. Matter 28 205401 |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1088/0953-8984/28/20/205401 |
| Popis: | Near-forward Raman scattering combined with ab initio phonon and bond length calculations is used to study the phonon-polariton transverse optical modes (with mixed electrical and mechanical character) of the II-VI ZnSeS mixed crystal under pressure. The goal of the study is to determine the pressure dependence of the poorly resolved percolation-type Zn-S Raman doublet of the three oscillator [1(Zn-Se),2(Zn-S)] ZnSe68S32 mixed crystal, which exhibits a phase transition at approximately the same pressure as its two end compounds (~14 GPa, zincblende-to-rocksalt), as determined by high-pressure x-ray diffraction. We find that the intensity of the lower Zn-S sub-mode of ZnSe68S32, due to Zn-S bonds vibrating in their own (S-like) environment, decreases under pressure (Raman scattering), whereas its frequency progressively converges onto that of the upper Zn- S sub-mode, due to Zn-S vibrations in the foreign (Se-like) environment (ab initio calculations). Ultimately, only the latter sub-mode survives. A similar phonon freezing was earlier evidenced with the well-resolved percolation-type Be-Se doublet of ZnBeSe [Pradhan et al. Phys. Rev. B 81, 115207 (2010)], that exhibits a large contrast in the pressure-induced structural transitions of its end compounds. We deduce that the above collapse and convergence process is intrinsic to the percolation doublet of a short bond under pressure, at least in a ZnSe-based mixed crystal, and not due to any pressure-induced structural transition. Comment: 20 pages, 7 figures |
| Databáze: | arXiv |
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