Modulation structure in Bi₂Sr_1.8La_0.2Cu_1-xM _xO_y, (M=Fe, Co, Ni, and Zn)

Transition-metal-doped Bi₂Sr_1.8La_0.2Cu_1-xM _XO_y (M=Fe, Co, Ni, and Zn) samples were synthesized. X-ray diffraction analysis showed that these 3d elements had different solubility in Bi₂Sr_1.8La_0.2CuO_y. The limits of solid solution formation were at x=0.5 for the Fe system, x= 1.0 for the Co system, and x=0.1 for the Ni and Zn systems. The effect of these 3d metal substitutions for Cu on the incommensurate modulation structure in Bi₂Sr_1.8La_0.2CuO_y, was examined by means of electron diffraction. The experimental results showed that all the substitutions of Fe, Co, Ni, and Zn for Cu decreased the modulation periodicity. It decreased from 4.32b at x=0 to 3.95b at x=0.5 for the Fe system, 3.82b at x= 1.0 for the Co system, 4.24b at x=0.1 for the Ni system, and 4.18b at X=0.1 for the Zn system, respectively. In addition, the structure distortion characteristic related to the change in the incommensurate modulation was examined with Raman scattering. The experimental data showed that the vibration properties of the oxygen atoms in both Bi-O and Sr-O bondings also changed with the decrease in the modulation periodicity. This behavior can be considered a consequence of structural relaxation caused by the enhancement of the degree of crystal misfit.