Effects of substitution of Fe and Co for Cu in Bi2Sr1.8Ca1.2Cu2O on electronic states studied by photoemission

The effects of the substitution of Fe and Co for Cu sites in Bi-2212 samples on T c , lattice parameters, and the electronic structures are studied. The T c and the length of c -axis are monotonously decreased as a function of the amount of Fe and Co. It is found that the Co in Bi 2 Sr 1.8 Ca 1.2 (Cu 1− x Co x ) 2 O y is trivalent and the density of states at the Fermi level is decreased by the substitution. These results are briefly discussed in terms of the disorder effect.