Lattice Mode Study of La₂CuO_4-y Implanted with Sr

Abstract

Dramatic implantation-induced changes in the Raman and infrared spectra of polycrystalline samples of La₂CuO_4-y are reported for implantation of Sr in the fluence range 0.5 to 1.5 × 10¹⁶/cm². The Raman and ir-reflectance spectra of the Sr implanted material reveal disorder-induced lines corresponding to breakdown of selection rules and to non-zone-center phonon modes. Whereas the main features in the Raman spectra of the implanted sample are broad disorder-induced lines centered at ∼ 560 ± 5 cm⁻¹, reststrahlen lineshapes are observed above ∼ 800 cm⁻¹ in the ir-reflectance spectra. After thermal annealing (550°C), the multiphonon lines in the ir spectra diminish, and the disorder-induced lines in the Raman spectra split to form well-resolved, sharper lines at 530 and 580 cm⁻¹, identified with maxima in the phonon density of states. The sensitivity and complementarity of Raman and infrared spectroscopy to implantation-induced disorder and subsequent partial recovery by thermal annealing suggest that these techniques can be used to characterize sensitively disorder in ion implanted La₂CuO_4-y high T_c, materials.