Self-doped apical O- can lead to plane expansion and/or proposed 3-D superconductivity in YBa2Cu3Oy

TL;DR

This paper proposes that self-doped apical oxygen ions in YBa2Cu3Oy influence plane expansion and can induce three-dimensional superconductivity, with implications for understanding and enhancing high-temperature superconductivity.

Contribution

It introduces the role of self-doped apical O- ions in plane expansion and 3-D superconductivity, linking structural changes to superconducting properties in YBa2Cu3Oy.

Findings

Self-doped apical O- ions correlate with increased Tc and plane expansion.

Transition between cell volume states involves electronic rearrangement of oxygen.

Elevated temperature superconductivity (ETS) linked to plane expanding n-doping.

Abstract

The distance of apical O to planes, d, is introduced as serving as an arbiter in the dispute between different local O coordination (n) in determining charge equilibration in YBa2Cu3Oy. We assign reported cell volume and plane expansion (V+P+) on shot quenching (SQ) from above 600K to O- connected with (3) at a critical cluster size for increased d, maximizing at 673K and y=6.44. This and a Tc=100K level is ascribed to self-doped apical O-, acting as a plane reducer and expander (P+). By contrast, slow cooling to 260K produces conventional cell volume contracted varieties (V-P-), based on plane oxidizing (4) with its small d=2.3A at a Tc=50K level. V+P+ to V-P- transformation is slow due to electronic rearrangement involving O-, compared to the primarily structural one within V-. A SQ minority at Tc=200K* level and related effects observed on laser pulsing (for y=6.5 Tc=552K*), termed as elevated temperature superconductivity (ETS), are also explained as due to plane expanding n-doping. We assume that central (2) connect p-doped pairs in the bonds of both apical O- with plane Cu, in line with retrograde increases in Tc with increasing %(2). 3-D superconductivity is a result of d now being comparable to plane dimensions.