Abstract
Far-infrared reflectivity spectra R( v) in polarization E ⊥ C and DC-conductivity σ DC have been studied in a semiconducting phase of La 2CuO 4+ x single crystals with various oxygen contents. The spectrum of infrared-active optical phonons has been obtained for stoichiometric La 2CuO 4. It has been shown that the phonon spectrum should be analyzed in a framework of the orthorhombic crystal structure at T≤300 K. Extra lines have been found in the phonon spectrum upon doping the crystals with oxygen. The results of studying the temperature dependence of R( v) and σ DC allow one to interpret these features as vibrational modes, which are active in the Raman scattering spectrum and displayed in the IR spectrum due to their interaction with self-localized holes.
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