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Modelling the contribution of point defects to the Raman spectrum of crystalline materials

Abstract : Raman spectroscopy is a widely used tool for the characterization of insulating or semiconducting materials of various kinds. The Raman shift is related to vibrationals modes of the probed sample and, as such, can be related to the atomic scale structure of the materials. However, when Raman spectrometry is used to probe materials featuring disorder, radiation damage or simply a large enough concentration of point defects, the relationship between the spectrum and the atomic structure cannot be easily unraveled. In this paper we present a method to extend the scale of the ab initio calculation of first order Raman spectra, based on Density Functional Perturbation Theory (DFPT), to cope with larger systems, in order to be able to describe point defects in the limit of low concentration. The goal is to provide a quantitative basis for the interpretation of experimental Raman spectra. The procedure consists in embedding force constants matrices, Born effective charges, and Raman tensor, calculated with DFPT for a supercell with a point defect, into a corresponding perfect bulk matrix to simulate a larger system. After describing in detail the procedure, we present benchmark applications to three quite different materials, containing defects of various kinds: silicon carbide with an intrinsic defect (a carbon antisite), boron carbide with helium impurities |also in combination with vacancies|, and caesium lead iodide with two different alloying impurities. Strengths and limitations of the approach are discussed in the light of the three examples.
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Submitted on : Monday, July 11, 2022 - 3:25:36 PM
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Guido Roma. Modelling the contribution of point defects to the Raman spectrum of crystalline materials. Modelling and Simulation in Materials Science and Engineering, IOP Publishing, 2019, 27, pp.074001. ⟨10.1088/1361-651X/ab2962⟩. ⟨cea-03719926⟩

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