7 research outputs found
Intergranular flux pinning in underdoped and overdoped R(1-x)CaxBa2Cu3Oz (R=Y,Gd; x=0,0.2) samples
The temperature dependences of AC magnetic susceptibility at different
magnetic field amplitudes and frequencies are investigated for underdoped and
overdoped R(1-x)Ca(x)Ba(2)Cu(3)O(7-delta)(R=Y; Gd and x=0; 0.2) polycrystalline
samples. The activation energy, Ea, for thermally assisted flux flow (TAFF) in
intergranular region is determined. It was established that a correlation
exists between the intergranular critical current and flux pinning activation
energy. In underdoped samples the intergranular current shows S-I-S behaviour
and the activation energy is small, while in overdoped samples the
intergranular current is changed to S-N-S type and the activation energy
increases. 2D pancake vortices are characteristic of underdoped samples, while
3D vortex system exists in overdoped samples. In fact we demonstrate that Ca
substitution not only increases carrier concentration, but improves
intergranular activation energy for TAFF.Comment: 20 pages including 7 figures and one Table. accepted in Physica
Effects of Substituting Calcium for Yttrium on the Superconducting Properties of YBa2Cu3Oz Bulk Samples
We report systematic studies of AC magnetic susceptibility and transport
properties of Y(1-x)Ca(x)Ba2Cu3Oz bulk samples with 0\leq x\leq 0.4. Single
phase materials, reduction of carrier concentration and decrease of Tc to 85 K
were obtained at doping levels up to 20%. For Y0.7Ca0.3Ba2Cu3Oz sample the
improvement of grains boundary transport and screening capabilities has been
observed as a result of the optimal ratio between carrier concentration and
impurity phase BaCuO2 presence. The appearence of bulk pinning and nonlinear
effects starting at the highest temperature were detected also.Comment: 12 pages, 8 figures, accepted in Physica