The effect of Zn-substitution and carrier doping on vortex pinning in YBa2Cu3O7−δ single crystals

Evidence for enhancement of vortex matching field above 5 T and oxygen-deficient annuli around barium-niobate nanorods

“…According to the results in Er123þBNO 5,6 and Sm123þBZO, 36 nanorod densities calculated from B cr s (or K end in Ref. 33) in ILs were coincident well with the B / s estimated from microstructures of the nanorods by TEM. This means that appropriate B cr s in RE123 films with nanorods are different from those for the irradiated Y123 crystals, 25,28 in which B cr appeared at B / /3.…”

“…However, as shown in Fig. 5(b), B irr at t ¼ 0.9 increased with the increase in B cr up to B cr $ 5 T and saturated (or decreased) for B cr > 5 T. Masui et al 33 reported that B irr for B//c at t ¼ 0.9 in a Y123 single crystal monotonically decreased with the promotion of the underdoping of carriers (or with an increase in oxygen deficiency). In detail, it was reported that the B irr values were drastically changed from $5 T (y ¼ 6.96) to $1.3 T (y ¼ 6.77) despite the samples with T c > 90 K. Therefore, depletion of the carriers from the optimally carrier-doped level in Y123 seriously decreases the elemental vortex-pinning force.…”

“…Here, d, l, and D are, respectively, average diameter of the BNO nanorods, distance from the matrix/nanorod interface on a relatively lower T c region, and average inter-nanorod distance. This model suggests that relatively higher vortexpinning properties are expected for D > 2 l þ d, whereas a serious reduction of vortex pinning is apparent for D 2 l þ d. Based on the relationship between B irr and y in the Y123 single crystal, 33 the decrease in T c leads directly to the reduction of B irr . It is well recognized that the B irr value is correlated with the magnitude of vortex-pinning energy through the change in electromagnetic anisotropy 34,35 in high-T c cuprate superconductors.…”

Growth of (Y1−xCax)Ba2Cu4O8in ambient pressure and its tri-axial magnetic alignment

“…This tendency was qualitatively consistent with the result for epitaxially grown (Y 1−x Ca x )124 films, indicating that Ca-doping into Y124 is obviously effective for increasing not only the T c but also the vortex pinning potential under H//c. In the case of a Y123 superconductor with oxygen nonstoichiometry, H irr was reported to be clearly improved with the increase in the oxygen content of Y123 [36]. Furthermore, the ILs of Y123 were sensitive to slight changes in y, even at the optimal carrier-doping level, and, specifically, the μ 0 H irr values were drastically reduced from ∼8 T to 4 T with the slight decrease of Δy∼0.1 from the optimal carrier-doped condition [35].…”

Effect of the oxygen distribution and inhomogeneity on the superconducting properties of YBa2Cu3O7−δ+xmol% Y2Ba4CuMoOysuperconductors

“…YBCO is generally evaluated by its critical temperature (T c ), critical current density (J c ), and critical magnetic field (H c2 ). These properties can be modified either by the substitution of elements with changing ionic radii and bonding characteristics, by additives or by an excess of the oxygen concentration [2][3][4][5][6][7][8][9]. It has been demonstrated that the introduction of non-superconducting defects into single crystal YBCO correlates most effectively with achieving high critical current density and negligible effect on the superconducting transition temperature in these materials [10][11][12].…”