STRUCTURE, SUPERCONDUCTIVITY AND MAGNETISM OF YBA2(CU(1-X)M(X))(4)O-8 (M=FE, CO, NI, ZN AND GA)

YBa2(Cu(1-x)M(x))(4)O-8 (M=Fe, Co, Ni, Zn and Ga; 0 less than or equal to x less than or equal to 0.05) have been investigated by means of X-ray diffraction, electrical-resistivity and magnetic-susceptibility measurements. X-ray-diffraction patterns show that all samples studied contain the nearly single 124 phase. They exhibit an orthorhombio-to-tetragonal structural transition at about x=0.03 for M=Fe and Co; and at x=0.04 for M=Ga; while the structure remains orthorhombic at x=0.05 for M=Ni and Zn. These results suggest that Fe, Co and Ga substitute preferentially for [Cu(1)] sites, and the Ni and Zn prefer to occupy the [Cu(2)] sites. The initial depression rates of T-c0 (temperature of zero resistance) with increasing doping concentration for various dopants are 16.85, 8.4, 23.75, 12 and 3.9 K/at.% for M=Fe, Co, Ni, Zn and Ga, respectively. Effective magnetic moments of YBa2(Cu(0.97)M(0.03))(4)O-8 are 5.63, 3.91 and 3.37 mu(B) for M=Fe, Co and Ni, respectively. In addition, the similarities and differences between YBa2(Cu(1-x)M(x))(4)O-8 and YBa2(Cu(1-x)M(x))(3)O-7-y are discussed.