YBa2(Cu1-xMx)4O8 (M=Fe, Zn; x=0 to 0.05) has been investigated by means of X-ray diffraction, thermogravimetric analysis, electrical resistivity and magnetic susceptibility measurements. X-ray diffraction patterns show that all samples contain the nearly single YBa2Cu4O8 phase. The results of structural analysis indicate that the orthorhombic-to-tetragonal transition occurs at about x=0.03 for M=Fe, whereas the structure remains orthorhombic until x=0.05 for M=Zn. Thermal stability is reduced with increasing Fe concentration, but is nearly unchanged in the case of Zn substitution. The suppressed rates of Tco with increasing dopant content are 17.81 K/at.% and 15.69 K/at.% for Fe and Zn. Effective magnetic moments of YBa2(Cu1-xFex)4O8 are 5.99, 5.63 and 5.37 µB for x=0.01, 0.03 and 0.05, respectively. In addition, the similarities and differences between YBa2(Cu1-xMx)4O8 and YBa2(Cu1-xMx)3O7-y are discussed.
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