Influence of Sr substitution on the structure, charge distribution, and critical temperature ofY(Ba1−xSrx

Abstract

We have investigated the influence of substitution of Sr for Ba on the structure, charge distribution, and T c in the YBa 2 Cu 4 O 8 ͑Y124͒ compound. Bond valence sum and nuclear quadrupole resonance investigations show that the substitution of Sr causes a redistribution of charge in the structure. The number of holes located in plane copper ͑Cu2͒ and apical oxygen ͑O1͒ increases, hence the number of holes in chain copper ͑Cu1͒ and plane oxygen ͑O2 and O3͒ decreases. A redistribution of holes from Cu1 to O1 and from O2 and O3 to Cu2 takes place. The literature data for Y123 and the hydrostatic pressure effect on both Y124 and Y123 compounds show that oxygen doping in Y123 and the pressure effect in Y124 increase the hole number equally on copper and oxygen. Therefore, although the number of holes on copper Cu2 in the CuO 2 planes increases with Sr doping in both Y124 and Y123, T c does not rise as much as expected from the amount of charge transferred to Cu2, because of their distribution in the CuO 2 planes.

Enhancement of Tc by Sr substitution for Ba in Hg-2212 superconductor

“…The difference is larger than experimental errors. In Y-123 and Y-124 systems, the complete substitution of Ba with Sr would induce a variation of the lattice parameters equivalent to the application of an external pressure of about 26). This extrapolated value is consistent with what is observed here for the Hg-2212 system.…”

Pressure-induced lattice instabilities and superconductivity inYBa2Cu4O8and optimally dopedCalamiotou1, Gantis2, Siranidi3 et al. 2009Phys. Rev. BSelf Cite217190View full textAdd to dashboardCite

“…The correlation of the structural characteristics with the Raman frequency modifications [6] and corresponding changes of T c [7] imply that the trigger of the lattice instabilities lies among the CuO 2 and BaO planes. Charge redistribution among the planes, that has been found to occur in the case of chemical pressure [11], also affects the T c , and must certainly play a role in the observed effects.The main questions that arise is whether similar effects are present in other cuprates and how they relate to the amount of charge carriers and superconductivity. The isostructural to Y123 compound PrBa 2 Cu 3 O 7 (Pr123) is a good example to study, having apparently no free carriers [5].…”

Direct Observation of the Oxygen Isotope Effect on the In-Plane Magnetic Field Penetration Depth in Optimally DopedYBa2Cu3Khasanov1, Eshchenko2, Luetkens3 et al. 2004Phys. Rev. Lett.Self Cite143231530View full textAdd to dashboardCite

“…In the present work we provide further evidence of this scenario from measurements of the nuclear quadrupole resonance (NQR) frequency (ν Q ) of the plane (ν pl Q ) and the chain (ν ch Q ) 63 Cu in 16 O and 18 O substituted YBa 2 Cu 3 O 7−δ powder samples. It is known [18,19] that in HTSC ν pl Q and ν ch Q are very sensitive to changes in the density of mobile carriers n in the superconducting CuO 2 planes (n pl ) and CuO chains (n ch ). Both ν pl Q and ν ch Q increase with doped hole concentration roughly 20 MHz per one doped hole per Cu atom [20].…”