Effect of a barium deficiency on the structural and magnetic properties of RE Ba_2-xCu₃O_z(RE=Y, Nd, Eu, Er, Yb)

Abstract

A barium deficiency in the"initia1 composition for the synthesis of high-temperature supercondutors (HTSC), i.e. a nominal (RE Ba,-xCu,O,) composition with 0 $ x $ 1 leads to different materials depending on the nature of the rare earth. If the rare earth is 'yltric' (Y, Er, Yb), the resulting compound is a composite YBa,Cu,O, + Y,BaCuO,, 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 21 1-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 t h e Nd-case, the critical current density decreases strongly with increasingx. At highx (0.5 < x < 1) and low temperature, t h e magnetization-against-fieid data show paramagnetic behaviour due to the neodymium ions, with an effective momentp.,,,= 1.80 p a . The domain of the reversible behaviour in the (H, r) plane is more extended forNbBaCu0 and EuBaCuO than for YBaCuO.

Characterization of high-temperature superconductors by AC susceptibility measurements

“…By enhancing the quality of the intergrain contacts, the difference between inter-and intragrain currents vanishes, and the two steps (and peaks) merge (Sauv et al 1993, Planinić et al 1994, Vo et al 1996. However, very small fractions (∼1%) of a poorer quality superconductor or the weak links in single crystals could be detected (Moreira et al 1994, Ren et al 1994 by AC susceptibility.…”

The effect of the substitution of Sm for Ba on the superconductor

“…LnBa 2 Cu 3 O y (here Ln = La, Nd, Sm, Eu) has the same structure as YBa 2 Cu 3 O y and also has a high critical temperature that is over 90 K. It is known that Ln ions can easily be substituted for some of the Ba ions. This substitution has been found to bring about characteristic changes, such as a decrease of critical temperature [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Akinaga et al have reported changes of the hole concentration, oxygen content, crystal structure and critical temperature of Sm 1+x Ba 2−x Cu 3 O y (0 ≤ x ≤ 0.4) [14,15].…”

Detection of the flux dynamical regimes in Bi 4 O 4 S 3 by multiharmonic AC susceptibility

“…By enhancing the quality of the grain boundaries the two peaks (steps) merge [36], and the magnetic response is ascribed to the sample as a whole.…”