EFFECT OF SUBSTITUTIONAL DOPING ON PHONON-SPECTRA OF YBA2(CU1-XCOX)3O7-DELTA

The effect of substitutional doping in the superconductor YBa2(Cu1-xCox)3O7-δ on infrared absorption spectra and Raman spectra have been studied for x = 0.0% to 4.0%. Simultaneously strong changes in both Raman and IR spectra were observed in the 500-700 cm-1 frequency region. Specifically the 500 cm-1 Raman frequency broadens and continuously shifts downward and the IR absorption line at 580 cm-1 also displays a general downward shift in frequency with an increase in Co content. These modes have been assigned to the Ag and B1u oxygen vibrations about Cu(1). Therefore evidence that Co preferentially goes into Cu(1) chain sites is supported. Additionally, the IR absorption modes indicate a structural phase transformation for Co concentrations between x = 2.0-3.0%, which is confirmed by X-ray powder diffraction measurements on our samples. The observed mode softening of the axial O(4) vibrations is consistent with previous neutron diffraction work showing bond length changes with Co substitution. © 1990.