EFFECT OF A BARIUM DEFICIENCY ON THE STRUCTURAL AND MAGNETIC-PROPERTIES OF RE BA2-XCU3OZ (RE = Y, ND, EU, ER, YB)

A barium deficiency in the initial composition for the synthesis of high-temperature supercondutors (HTSC), i.e. a nominal (RE Ba2-xCu3xOz) composition with 0 less-than-or-equal-to x less-than-or-equal-to 1 leads to different materials depending on the nature of the rare earth. If the rare earth is 'yttric' (Y, Er, Yb), the resulting compound is a composite YBa2Cu3O7 + Y2BaCuO5, whose critical current density depends on the x-value. The determination of the irreversible behaviour by means of AC susceptibility or magnetization measurements shows that in the presence of the 211-phase, the intergranular current-density decreases whereas the intragranular current density varies very little. If the rare earth is 'ceric' (Nd, Eu), the lack of barium leads to a quasi single-phased compound. In the Nd-case, the critical current density decreases strongly with increasing x. At high x (0.5 less-than-or-equal-to x less-than-or-equal-to 1) and low temperature, the magnetization-against-field data show paramagnetic behaviour due to the neodymium ions, with an effective momentum mu(eff) = 1.80 mu(B). The domain of the reversible behaviour in the (H, T) plane is more extended for NbBaCuO and EuBaCuO than for YBaCuO.