INFLUENCE OF RARE-EARTH IONIC RADIUS ON THE PROPERTIES OF NI-SUBSTITUTED AND FE-SUBSTITUTED RBA(2)(CU(1-X)M(X))(3)O-7-GAMMA SYSTEMS (R=Y,ND,EU,GD,HO,TM, M=NI,FE)

The crystal structure parameters, temperature dependences of resistanc e R(T), and concentration dependences of superconducting transition te mperature T-c(x) for the Ni- and Fe-substituted RBa(2)Cu(1-x)M(x))3O(7 -y) systems based on Y and several rare earths (R=Y,Nd,Eu,Gd,Ho,Tm; M= Ni,Fe) have been investigated. It was found that the \partial derivati ve T-c/partial derivative x\ parameter for both kinds of substitution depends mainly on the value of R(3+) ionic radius of the host matrix. As R changes from Tm to Nd the value of \partial derivative T-c/partia l derivative x\ increases by approximately three and four times for Ni and Fe substitutions correspondingly. No correlations of the \partial derivative T-c/partial derivative x\ value with R(3+) localized magne tic moment were observed. The prime role of R(3+) ionic radius variati on on the properties of RBa(2)(Cu(1-x)M(x))3O(7-y) systems as well as the same effect observed earlier for R(1-x)Pr(x)Ba(2)Cu(3)O(7-y) syste ms are discussed. The essentially different shapes of superconducting transitions for the Ni- and Fe-substituted systems are pointed out.