Long‐Wavelength Optical Phonons of AgBr_xCl_1−x Mixed Crystals

Abstract

Infrared reflectivity and second-order Raman scattering in the mixed crystal system AgBr,C11-, were studied a t 77 K. The T O ( r ) and L O ( r ) phonon frequencies obtained by means of a Kramers-Kronig analysis shift continuously between their energetic positions in the pure components indicating one-mode behaviour of the system. This result is discussed in view of a recent model that describes the optical modes of a mixed crystal.The LO(r) phonon frequencies taken from the Raman spectra are found to be slightly lower. A resonant enhancement of the 2 L 0 scattering process that occurs for z = 0.42 with shorter-wavelength excitation is used to determine the longitudinal optical phonon frequency. Infrarot-Reflexionsvermogen und Ramanstreuung zweiter Ordnung werden im

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