Control of the charge inhomogeneity and high-Tc superconducting properties in homologous series of multi-layered copper oxides

OK-edge and CuL23-edge XANES study on the concentration and distribution of holes in the(Pb2/Karppinen1, Kotiranta2, Yamauchi3 et al. 2001Phys. Rev. B214170View full textAdd to dashboardCite

“…1 Even though the CuO 2 -plane hole concentration is known to crucially control the superconductivity characteristics, determination of the local hole concentration of individual CuO 2 planes and M O 1Ϯ␦ Ј layers, i.e., the distribution of holes among the different layers over the unit cell, has remained an unsolved problem for most of the known M -m2(nϪ1)n phases. In the case of, e.g., Bi-, Pb-, Tl-, Hg-and Cu-m2(nϪ1)n superconductors, one of the uncertainties arises from the fact that, besides the CuO 2 -plane Cu, also the charge-reservoir constituent M is likely to possess a mixed-valence value.…”

Effect of Sr-for-Ba isovalent substitution on the local structure, hole distribution and magnetic irreversibility of Cu(Ba,Sr)2YbCu2O6.95(2)

“…In fact, the first observation of the decrease in the critical current (J c ) characteristics in Cu-1212 with Sr substitution is from 1991 by Parent and Moreau [21]. Here we report the results of our systematic study on the Cu(Ba 1-y Sr y ) 2 YbCu 2 O 6.95 (2) (Cu-1212) system, to reveal that the depression in the H irr characteristics due to the Sr substitution most likely originates from the decrease in the concentration of mobile holes within the BB. (Note that the R = Yb system was selected rather than the prototype R = Y one, as it possesses higher intrinsic H irr (T) values [16].)…”

“…Previously we have shown that the H irr characteristics depend not only on the total amount of doped holes but also on their distribution over the unit cell [2,13]. The latter may be altered when changing the former but also through "isovalent" cation substitution.…”

“…It is thus essential for obtaining a high-H irr -characteristics material that the intrinsic H irr property is improved. Considering the crystal structure of HTSCs [2], i.e. piling up of a superconductive block (SB) and a nonsuperconductive blocking block (BB ) along the c-axis direction, the ways so-far suggested for enhancing the H irr characteristics are roughly classified into two categories: ( i) increasing the overall hole -doping level [3][4][5] to enhance the thermodynamical stability of magnetic fluxons in SB, and (ii) enhancing the conductivity of BB [6][7][8] and/or decreasing the thickness of BB [8][9][10][11] to improve the correlation of fluxons (through BB) between two adjacent SBs.…”

“…The pellets of the Cu-1212 phase were then crushed and fully oxygenated by annealing in flowing O 2 gas at 350 o C for 48 h ours. The oxygenated samples were characterized for the phase purity and the lattice parameters by x-ray diffraction (XRD; MAC Science: MXP18VAHF 22 ; CuK α radiation), and for the precise oxygen content by a Cu + /Cu 2+ coulometric titrat ion technique [2]. The precision of the coulometric titration method applied was better than ±0.01 with respect to the amount of excess oxygen, z [13,16,19].…”