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Raman scattering measurements of phonon anharmonicity in the delafossite CuGa 1‐ x Cr x O 2 (0 ≤ x ≤ 1) films
Author(s) -
Han Meijie,
Lu Yonggeng,
Liu Yonghui,
Hu Zhigao,
Chen Guochu,
Jiang Kai,
Zhang Jinzhong,
Li Wenwu
Publication year - 2020
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.5842
Subject(s) - phonon , anharmonicity , raman spectroscopy , delafossite , condensed matter physics , raman scattering , atmospheric temperature range , brillouin zone , laser linewidth , chemistry , materials science , optics , physics , oxide , laser , meteorology , organic chemistry
Raman spectra of the delafossite CuGa 1‐ x Cr x O 2 (0 ≤ x ≤ 1) solid solution films have been measured in the temperature range from 80 to 823 K. Raman phonon modes are observed at 224 ( A g ), 328 ( A 2u ), 396 ( E g ), and 757 ( A 1 g ) cm −1 for the CuGaO 2 film, and phonon modes of the CuCrO 2 film are around 211 ( A g ), 324 ( A 2u ), 458 ( E g ), and 712 ( A 1g ) cm −1 , respectively. The A 1g phonon mode has a distinct redshift with increasing Cr composition, which indicates that the interatomic potential becomes weaker between Cu and O atoms. Except Raman modes at the Brillouin zone center, the additional phonon modes in the spectral range of 500−670 cm −1 were observed due to Raman selection rules being relaxed by the crystal defects. With increasing temperature, the A 1g phonon mode undergoes a larger phonon softening but a smaller line broadening relative to that of the E g phonon mode, which indicated the anisotropic behavior for the delafossite CuGa 1‐ x Cr x O 2 films. The nonlinear temperature dependence of the phonon frequency and linewidth is an indication of nonharmonic lattice dynamics. The Raman shift and the linewidth of the E g and A 1g optical modes as a function of temperature were studied as an experimental evidence of the combined effect of lattice expansion and anharmonic phonon–phonon interaction. And the three‐phonon anharmonic coupling plays the dominant role in the anharmonicity behavior. The phonon anharmonicity behavior of the CuGaO 2 and CuCrO 2 films is slightly different. The larger Γ 0 is intrinsic for the A 1g mode of the CuGa 0.8 Cr 0.2 O 2 film due to the broadening by the crystalline defects, which perturb the translation symmetry of the harmonic crystal, making the momentum conservation rule for phonon scattering partially relaxed.