Browsing by Subject "Anharmonicity"
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Item Open Access Anharmonic line shift and linewidth of the Raman modes in TlInS2 layered crystals(John Wiley & Sons Ltd., 2004) Yuksek, N. S.; Gasanly, N. M.; Aydınlı, AtillaThe temperature dependence of the unpolarized Raman spectra from TlInS 2 layered crystal was measured between 10 and 300 K. The analysis of the experimental data showed that the temperature dependences of wavenumbers and linewidths are well described by considering the contributions from thermal expansion and lattice anharmonicity. The purely anharmonic contribution (phonon-phonon coupling) was found to be due to three-phonon processes. This work demonstrates that the two Raman modes at 280.9 and 292.3 cm-1 exhibit changes toward high wavenumbers as the temperature is raised from 10 to 300 K.Item Open Access Low-temperature thermodynamics of finite and discrete quartic quantum oscillator in one dimension(Bilkent University, 1999) Sıddıki, AfifI.' this work we examined a quartic Hamiltonian using two different approaches. We first introduced a mean-field Gaussian approximation in order to handle this Hamiltonian analytically and observed that this approximation is insufficient for all coupling strengths. Hence we applied second and third order non-degenerate time-independent perturbation and obtained third or- ■ ler correcHoItem Open Access Temperature dependence of Raman-active modes of TIGaS2 layered crystals: An anharmonicity study(Korean Physical Society, 2004) Yuksek, N. S.; Gasanly, N. M.; Ozkan, H.; Aydınlı, AtillaThe temperature dependence (16 - 300 K) of unpolarized Raman spectra from TIGaS2 layered crystals was measured in the frequency range of 10 - 400 cm-1. The analysis of the experimental data showed that the temperature dependencies of the phonon frequencies and linewidths were well described by considering the contributions from thermal expansion and lattice anharmonicity. The anharmonic contribution (phonon-phonon coupling) was found to be due to three-phonon processes. The present work demonstrates that the interlayer Raman mode at 42.6 cm-1 shifts toward high frequency as the temperature is raised from 16 to 300 K.