Infrared and Raman Study of (La_1−xSr_x)₂NiO₄ and La₂(Ni_1−xCu_x)O₄

Abstract

Motivated by the observation of the close correlation between disappearance of the infrared absorption peak at about 680 cm⁻¹ and the appearance of high-T_c superconductivity in (La_1−xM_x)₂CuO₄ (M=Ca, Sr, and Ba), we have measured infrared absorption spectra of (La_1−xSr_x)₂NiO₄ (x=0.0, 0.01, 0.02, 0.03 0.04, 0.07, 0.10 and 0.15), La₂(Ni_1−xCu_x)O₄ (x=0.0, 0.20, 0.40 0.60, 0.70, 0.80, 0.85, 0.90, 0.95 and 1.00), and Raman spectrum of La₂NiO₄. No disappearance of the infrared absorption peak at about 680 cm⁻¹ has been observed in (La_1−xSr_x)₂NiO₄. By assigning the peaks to characteristic lattice vibrational modes, discussions have been devoted to the possible origin of the infrared anomaly.