Abstract: Superconductors of type YBa₂Cu_3-xM_xO_7-y(M_y=V,Nb,Ta;x=0.0～0.7) have been prepared. No phase-transition from orthorhombie to tetragonal for x≤0.6 were found by X-ray diffractometry. The lattice parameters of the system vary with the number of x. The D.C. resistivities and the values of Hall effect measured at room temperature showed a progressive increase, but the concentration and the mobility of the carrier decreased gradually with the increase of x. This reveals that the partial substitution by the element of the V B group affects the electronic structure of the superconductor. The change of the electronic structure has been discussed in terms of the crystal field theory.

Key words: yttrium, vanadium, niobium, tantalum, superconductor, electronic structure