The effect of Sr substitution on superconductivity in Hg₂(Ba_1 ySr_y)₂Y Cu₂O₈  : II. A bond valence sum approach to the hole distribution

Abstract

The effects of Sr substitution on superconductivity, and more particularly the changes induced in the hole doping mechanism, were investigated in Hg 2 (Ba 1−y Sr y ) 2 YCu 2 O 8−δ by a 'bond valence sum' analysis, with Sr content going from y = 0.0 to 1.0. A comparison with CuBa 2 YCu 2 O 7−δ and Cu 2 Ba 2 YCu 2 O 8 systems suggests a possible explanation of the T c enhancement from 0 K for y = 0.0 to 42 K for y = 1.0. The charge distribution among atoms of the unit cell was determined from the refined structure, for y = 0.0-1.0. It shows a charge transfer to the superconducting CuO 2 plane via two doping channels π(1) and π(2), i.e. through O2 apical -Cu and Ba/Sr-O1 bonds respectively.

Effect of Substitution Sr Cations on the Structure in the Gd<sub>1</sub>(Ba<sub>2</sub><sub>−<i>x</i></sub>Sr<sub><i>x</i></sub>)Cu<sub>3</sub>O<sub>7−<i>δ</i></sub> Phases

“…The effect of Sr substitution on superconductivity, especially the hole doping mechanism in the Hg 2 (Ba 1−y Sr y ) 2 YCu 2 O 8−δ system has been investigated by Toulemonde et al [4]. It was explained that it was possible to increase Tc from 0 K for y = 0 to 42 K for y = 1.0.…”

Chemical Control of Hole Distribution and Superconductivity in (Cu,Mo)Sr2(Ce,R)sCu2O5+2s+δ (s = 2, 3; R = Y, La−Yb)

“…“Chemical pressure” is a widely appreciated tool for fine-tuning the functional properties of multilayered oxides. A variety of examples of such chemical-pressure utility are found among, e.g., high- T c superconductive (HTS) copper oxides and colossal magnetoresistance (CMR) manganese oxides. − Chemical pressure is generated through “isovalent smaller-for-larger” cation substitution, typically involving either divalent alkaline earth or trivalent rare earth elements. To detect pure pressure effects, the substitution should proceed such that the overall cation charge is kept constant.…”

“…Chemical pressure is often taken as an analogue to “physical pressure” . However, the two pressures often act to opposite directions in complex multilayered systems. − , Despite the widespread utilization of the pressure effects, real understanding behind the apparent outcomes of them is lacking yet.…”

The effect of Sr substitution on superconductivity in Hg2(Ba1 ySry)2YCu2O8 : I. A neutron powder diffraction study

“…In a second paper [26], we have investigated the charge repartition into the cell by 'bond valence sum' analysis, starting from the structure (determined by NPD analysis). Different origins of a charge transfer to the superconducting CuO 2 plane are identified, which could explain the T c enhancement with Sr.…”