Enhancement of the superconducting critical temperature ofSr2CuO3+δup to95K

Abstract

We address the question of whether the superconducting transition temperature (T c ) of high-Tc cuprates is enhanced when randomly distributed dopant atoms form an ordered array in the charge reservoir layers. This study is possible for the Sr 2 CuO 3+δ superconductor with K 2 NiF 4 -type structure in which oxygen atoms only partially occupy the apical sites next to the CuO 2 planes and act as hole-dopants. We show that remarkable T c enhancement up to 95K in this mono CuO2 layered HTS is associated with the apical oxygen ordering, not to the hole concentration change. The result points a route toward further enhancement of T c in cuprate superconductors.

Comment on “Out-of-plane effect on the superconductivity ofSr2−xBaxCuO3+δGeballe1, Marezio2 2010Phys. Rev. B7140View full textAdd to dashboardCite

“…We think that such an assumption is not likely to be valid and offer a simple explanation of the data as follows. When the Sr 2 CuO 4-v was annealed above 300K the superconductivity vanished along with a loss of weight indicating a decrease in the oxygen content [8]. We note therefore that 300C must be close to T ms where T ms is defined as the highest temperature for which the metastable superconducting phase can be retained.…”

“…They synthesized a series of Ba doped compounds up to Sr 1.4 Ba 0.6 CuO 4-v using Ba to increase the size of the unit cell while holding the doping concentration constant. The onset T c is 98K for the un-annealed Sr 1.4 Ba 0.6 CuO 4-v sample and they attribute the increase over the 75K found for similarly un-annealed Sr 2 CuO 4-v [8] to the larger size of the Ba ion. They apparently assume that since the T c of the quenched metastable of Sr 2 CuO 4-v was increased to 95K by annealing for 12 hours at 300C a similar increase would occur if the Ba-doped sample could be annealed.…”

“…A re-examination of the procedures and analysis employed on [6] shows the suggestion is without merit [7, to be published]. Nevertheless, a cessation of further research ensued until C. Q. Jin and co-workers [8] introduced an elegant synthesis that avoided the possibility of the chloride contamination and furthermore provided a method for determining the oxygen stoichiometry simply from the starting materials.…”

“…This fraction is not insignificant for multiphase samples where considerable pinning is likely. There is obviously a need for a better sample but in our opinion the superconductivity is sufficiently robust to justify inclusion in the replot of Fig 5. Gao et al [9] use the Cu-O distance given by x-ray diffraction of the Ba-doped Sr 2 CuO 4-v despite the earlier TEM work with Sr 2 CuO 4-v that led to the conclusion that the superconducting phase was not the majority phase [8]. Unfortunately, they were unable to conduct electron imaging and diffraction experiments because the electron beam decomposed the metastable sample, probably because T ms is so near to room temperature.…”

“…In [8] and [9] the assumption is made that the CuO 2 layers cannot contain oxygen vacancies based upon the overwhelming evidence that stoichiometric CuO 2 layers are a basic requirement for superconductivity. The authors, therefore, are forced to assume that the vacancies are on the apical oxygen sites in the SrO layers.…”