Microstructure, magnetization and dc transport properties of MTG-YBa_1.8Na_0.2Cu₃O_ycrystal

Abstract

The Na-doping MTG-YBCO crystal with the nominal composition YBa1.8Na0.2Cu3Oy + 40 mol% Y211 has been successfully synthesized by the melted-textured-growth (MTG) method with top seed. The microstructure photographs show that the crystal has a good layered structure with a number of twins. There is a second peak in the magnetization curve for the magnetic field parallel to the c-axis and at 77 K. The field of zero resistance temperature Tc0 shows a power law, H = H0 (Tc0(0)-Tc0(H))n with n = 1.52 for H∥ab and n = 1.41 for H∥c, respectively. The thermally activated flux creep model can scale the dissipative resistivity below the peak temperature Tp. The temperature and field dependences of the effective activation energy can be described by the formula U = U0(1-T/Tp)mH-α, where m = 1.75, α = 0.75 for H∥ab and m = 2.5, α = 1.52 for H∥c, respectively. The effect of Na-doping induced disorder on flux pinning has been discussed.

Gadolinium diffusion-doping for enhancing activation energy in superconducting YBa2Cu3O7−x

“…5). A universal viewpoint is that the intrinsic planar defects are responsible for U ≈ H −0.5 , while the extrinsic point defects are responsible for U ≈ H −1[14,25]. For our samples the changing of α values from 0.42 to 0.61 imply that the thermally activated dissipative resisThe magnetic field dependence of activation energy for samples with different Gd-diffusion-doping annealing temperatures.…”

“…Various studies along these lines have been carried out on the different basic forms of high-T c oxide superconductors such as YBa 2 Cu 3 O 7−δ , RBa 2 Cu 3 O 7−δ (R = Nd, Eu, Gd, Dy, Ho and Er), Bi 2 Sr 2 Ca 0.8 Cu 2 O 8+δ , etc. [13][14][15][16].…”

Effect of Na doping on flux pinning of YBa1.9Na0.1Cu3O7−δ

“…The details of the method were reported elsewhere [7]. The crystal samples with platelet splitted up from the cleaved plane of the bulk with a single domain.…”

“…These studies have shown that Na + favors both theY 3+ as well as the Ba 2+ sites [1][2][3] since the ionic radius of Na + (0.095nm) is comparable to that of Y 3+ (0.093nm) and Ba 2+ (0.135nm). No change in T c has been observed when the doped concentration x < 0.2 in the YBa 2-x Na x Cu 3 O y (YBNCO) [4][5][6][7][8].…”

“…Recent measurements, such as resistance and magnetization curves, have found that with certain Na doping, J c of YBCO was changed and the magnetization curves showed a second peak [6][7][8]. It was expected that flux pinning in YBCO might be improved by Na doping.…”