H Oesterreicher | Searcharxiv

arXiv2015

Slow electronic rearrangement kinetic involving O- after shot quenching from >600K of YBa2Cu3Oy

Analysis of kinetic literature suggests several electronic rearrangements above 600K involving O- (subperoxides) in YBa2Cu3Oy. Slow cooling to 260K produces a Tc=50K level with conventional plane and cell volume contracted varieties (P-V-), based on plane oxidizing (4) where (n) denotes local O coordination. When these materials are quenched from <600K, the subsequent changes at 298K of structural parameters or Tc have activation energies E=92kJ and A=1.0x10-12s. The changes saturate at temperatures where they are faster than the time constant t of quenching. This temperature is extended to 473K with SQ, indicating t=0.1s. SQ of y near 6.44 from >600K leads to increased axial ratios, plane and V expansion (P+V+), in a process which is complete near 670 and extending to 950K. P+V+ effects can far exceed P0V0 of the respective semiconductor. The relative stability at elevated temperatures indicates another intrinsically slower transformation mechanism of primarily electronic nature with E=280kJ, involving O-. V+ and its Tc=100K level, is ascribed to (3) with doped charge on apical O-, acting as a plane expander and n-doper. Similar slowing of kinetic through O- also hold for the more complex range of Tq>950K. It can produce a c-axis contracted non-superconductor (P+C-) and indications for elevated temperature superconductivity (ETS) with Tc>150K*. Kinetic data are embedded into general thermodynamic arguments concerning peroxide stability belts.

cond-mat.mtrl-sci↗

arXiv2015

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

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.

cond-mat.supr-con↗