Theoretical Studies on Phonon Spectra of High Temperature Tl-Ba-Ca-Cu-O Superconductors


Strong electron-phonon coupling may be one of the origins of the high Tc superconductor. Thus, knowledge and understanding concerning phonons in these materials are essential. To investigate phonon spectra, Raman and infrared spectra of these systems have been studied; however, there are a few reports available in the literature with complete Raman and infrared absorption spectra. Due to the nature of these superconductive materials, it is not possible to experimentally obtain all of the phonon frequencies through Raman and infrared spectra. Therefore, a theoretical evaluation of the phonon frequencies of high temperature superconductors becomes important. Due to strong, covalent nature of the bonding in high temperature superconductors, a normal coordinate analysis using Wilson’s FG matrix was applied herein to evaluate the phonon frequencies of Tl-Ba-Ca-Cu-O. Calculations of lattice dynamics were also performed using the modified three-body-force shell model. The various interactions between ions were treated in a general way without making them numerically equal. These calculations yielded the zone centre phonon modes and potential energy distributions that helped to identify the pure and mixed frequencies. Thus, the present approach is useful not only to obtain all of the phonon frequencies of the high temperature Tl-Ba-Ca-Cu-O superconductor but also to characterise it. The vibrational frequencies and the potential energy distribution (PED) of the optically active phonon modes are also presented.


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