1:2:3 superconductors (M_xLa_1 x)(La_uBa_1 u)₂Cu₃O_ywith M = Ca or Y: lattice constants andT_c

Abstract

The effect of a substitute ion on the lattice constants and Tc of the optimal oxygen doped (MxLa1−x)(LauBa1−u)2Cu3Oy has been studied. This series is variously called CLBLCO, CLBCO or CaLaBaCuO when M = Ca2+, or YLBLCO when M = Y3+. We found that the lattice constants depend linearly on x and u. The size of M is the main contributor that affects the lattice constant a, while its valence mainly influences the lattice constant c. The size and valence of the ions located on the Ba-site have no significant effect on the lattice constant a, in contrast to the lattice constant c, for which the effect of the substitute on the Ba-site is significant. The Cu–O bond covalence increases, which is probably the reason for the increase of Tc,max with the content of M. However, the decrease of the valence of M affects the increase of Tc,max to a greater extent than the character of the Cu–O bond.

Epitaxial growth of differently doped (CaxLa1−x)(Ba1.75−xLa0.25+x)Cu3Oythin films byin situdc magnetron sputtering

“…In this case, a long annealing time is not necessary and in fact we found that a long time is no help in improving the superconducting transition temperature. To obtain relatively high transition temperatures in thin films, we believe that a suitable quenching method is a good choice with reference to our studies and a series of previous studies [1][2][3][4][5][6][7][8][9][10][11]. The importance is that previous studies suggested a quenching method that led to maintaining the equilibrium oxygen content and the homogeneity of its distribution.…”

“…The relatively large rms roughness in figure 2(b) is due to the distribution of several large precipitation particles (for which the peak heights are in the range 20-100 nm) in the surface that is studied. One of the origins of the particles is probably due to off-stoichiometry in the local regions, since foreign phases can be with x = 0.5 samples, as mentioned in the literature [1][2][3][4][5][6][7][8][9][10][11].…”

“…To obtain a relatively high transition temperature, a bulk sample ought to be cooled very slowly or very quickly after a long annealing time [1][2][3][4][5][6][7][8][9][10][11]. In preparing thin films, the situation is not exactly the same, as the thickness of a thin film is much thinner than that of the bulk.…”

“…In particular, they do not have an ordered chain structure in the layers which correspond to the chain layers of 1:2:3 superconductors. A highest superconducting transition temperature of about 80 K was reported for bulk samples with 0.4 x 0.5 [1][2][3][4][5][6][7][8][9][10][11]. Two different cooling processes were reported for reaching the highest transition temperature.…”

The influence of La substitution and oxygen reduction in ambipolar La-doped YBa2Cu3Oythin films

“…The substitution of various rare earths for Y leaves the compound isostructural and isoelectronic, with general superconductivity with T c ∼ 90 K [1][2][3]. However, the substitution of trivalent elements such as La at a Ba-site results in an orthorhombic-to-tetragonal phase transition and destruction of T c [4][5][6][7]. The destruction of T c is attributed to the decrease in hole concentration caused by the introduction of donor electrons when La 3+ is substituted for Ba 2+ .…”