INFRARED-ABSORPTION OF ND2-XCEXCUO4 AND R2CUO4 (R=PR, ND, SM, AND GD)

Infrared absorption spectra of Nd2-xCe(x)CuO4 and R2CuO4 (R = Pr, Nd, Sm, and Gd) have been measured in the energy region between 250 and 80 0 cm-1 at room temperature. For Nd2-xCe(x)CuO4, it is found that the m ode at about 350cm-1, which is the vibration of oxygen in the R-O laye rs along the a-axis, disappears both for the as-grown Nd2-xCe(x)CuO4 o f x greater-than-or-equal-to 0.08 and for the oxygen-reduced Nd2-xCe(x )CuO4 of x>0, and the disappearance is correlated to the resistivity. For R2CuO4, it is found that the energy of the A2u symmetry mode, whic h is the oxygen vibration along the c-axis, increases by about 50cm-1 between Pr to Gd, and this fact suggests that the three dimensional ch aracter increases in a sequence of Pr, Nd, Sm, and Gd.