The effects of Co substitutions for Cu in YBa 2Cu 3O 6+x on the phonon Raman spectrum

Abstract

We have investigated the phonon Raman spectra of YBa 2Cu 3−xCo xO 7−δ ceramic samples prepared by both solid state reaction and a polymerized complex method using Raman microprobe collection optics. With increasing Co content the frequencies of the Ba, Cu(2), O(2)-O(3) and the apical oxygen O(4) c-axis vibrational modes change considerably. The changes are compared with changes of interatomic bond distances as obtained by neutron diffraction and indicate charge transfer effects between the CuO 2 planes and the CuO chains with increasing Co substitution. The CuO 2 plane oxygen mode at 336 cm −1 exhibits slightly decreased coupling to the electronic states with increasing Co content.