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Spontaneous ordering as an intrinsic effect at the mesoscopic scale: A vibrational insight in (Zn,Be)Se by Raman scattering and first-principles calculations

O. Pages·A. V. Postnikov·A. Chafi·D. Bormann·P. Simon·F. Firszt·W. Paszkowicz·E. Tournie
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Abstract

The recent finding of a 1-bond->2-phonon `percolation'-type behaviour in several random zincblende alloys, supporting an unsuspected 1-bond->2-mode behaviour in the bond length distribution, renews interest for a discussion of CuPt-type spontaneous ordering (CPSO) as a purely intrinsic effect. We investigate this key issue from both experimental (Raman scattering) and theoretical (first-principles bond length and phonon calculations) sides, focusing on Zn[1-x]Be[x]Se (0 2-phonon behaviour for the Be-Se species. Based on percolation, CPSO finds a previously missing natural explanation, at the mesosocopic scale. Also, the transfer of oscillator strength from the high- to the low-frequency Be-Se mode in the Raman spectra potentially emerges as a sensitive probe of CPSO in ZnBeSe. First-principles calculations indicate that the transfer is completed for the value of the long range order parameter of eta~0.5 in ZnBeSe2 (x~0.5), corresponding to a pure 1-bond->1-mode behaviour. With further ordering the alloy is forced to re-adopt a non-rewarding 1-bond->2-mode behaviour, due to the formation of ZnSe/BeSe micro-domains in the crystal. Therefore eta~0.5 appears as an intrinsic limit to CPSO in ZnBeSe2, and possibly in stoichiometric alloys in general.

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O. Pages, A. V. Postnikov, A. Chafi, D. Bormann, P. Simon, F. Firszt, W. Paszkowicz, E. Tournie. 2007-09-02. Spontaneous ordering as an intrinsic effect at the mesoscopic scale: A vibrational insight in (Zn,Be)Se by Raman scattering and first-principles calculations. https://arxiv.org/abs/cond-mat/0610682

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