Infrared reflectivity spectra of a La2CuO4+x single crystal have been studied over a spectral range of 50"5500 cm-1. Anisotropy of the spectra has been observed, indicating a strong anisotropy of the high-frequency conductivity of the crystal. New lines have been found in the optical-phonon excitation spectra. A classification of lattice optical vibrations has been proposed. Spectral reconstruction has been observed in the phonon region of 370 and 445 cm-1 at T0=220±5 K, which correlates with the antiferromagnetic transition. © 1989 The American Physical Society.
