SYNTHESIS AND PROPERTIES OF NBM(2)RCU(2)O(8) AND TAM(2)RCU(2)O(8) PHASES (M=BA, SR R=PR, ND, SM, EU AND GD)

NbM(2)RCu(2)O(8) and TaM(2)RCu(2)O(8) (M = Ba, Sr; R = Pr, Nd, Sm, Eu and Gd) phases were synthesized. Electron diffraction study of TaSr2Eu Cu2O8 showed the presence of a weak superstructure (a approximate to r oot 2a(per)), like that found for a number of similar phases. Rietveld refinement of this structure based on X-ray powder diffraction data w as carried out in the space group P4/mmm (R(I) = 0.038, R(P) = 0.037) since no superstructure reflections were observed. Various types of ca tion replacement were performed in order to increase the copper valenc e. Monophasic Nb(Ta)(1-x)TixSr2EuCu2O8 samples were synthesized at P(O -2) = 1 bar and T = 1050 degrees C up to x = 0.1 (Nb) and 0.3 (Ta), bu t no superconductivity was detected down to 12 K. High pressure synthe ses were carried out to obtain Nb(Ta)Sr2Eu1-xCaxCu2O8 phases, but they were found to have a narrow homogeneity range that provides no opport unity of inducing superconductivity in such a way.