Proton incorporations and superconductivity in a cobalt oxyhydrate

Abstract

We report the evidence of proton incorporations in a newly-discovered cobalt oxyhydrate superconductor. During the hydration process for Na$_{0.32}$CoO$_{2}$ by the direct reaction with water liquid, it was shown that substantial NaOH was gradually liberated, indicating that H$^{+}$ is incorporated into the hydrated compound. Combined with the thermogravimetric analysis, the chemical composition of the typical sample is Na$_{0.22}$H$_{0.1}$CoO$_{2}\cdot 0.85$H$_{2}$O, which shows bulk superconductivity at 4.4 K.Comment: 9 pages, 4 figure

Upper critical field of an alignedNax(H3O)zCoO2Ren1, Feng2, Xu3 et al. 2007Phys. Rev. BSelf Cite3110View full textAdd to dashboardCite

“…5,20 First, parent compound Na 0.7 CoO 2 was prepared by a solid-state reaction from high purity Na 2 CO 3 and Co 3 O 4 powders. Second, the sodium was adequately deintercalated by employing Br 2 /CH 3 CN as an oxidizing agent.…”

“…The chemical composition of the sample was determined by the techniques described previously. 20 The sample used in present study has the chemical composition of Na 0.33…”

“…In our experiment we chose the saturated NaCl solution as the medium in order to suppress the ion exchange between hydroniums and Na + ions. 20,22,23 Mixture of the powdered superconductor and saturated NaCl solution in a teflon container was frozen below 250 K under an 8 T field. Magnetization measurement, performed on a Quantum Design PPMS facility, showed that the aligned sample had relatively large magnetization compared with the non-aligned sample.…”

Superconductivity in three-layer Na0.3CoO2·1.3H2O

“…Therefore the chemical changes that are taking place to yield the observations in figure 4 do not involve decomposition of the superconducting phase but rather subtle structural or chemical changes. One possibility is that some Na may be leached out of the superconductor into the surrounding intergrain water over a period of several days 6 , 7 an effect that is accelerated for hydration by immersion in large volumes of liquid water. The observed change in Tc may therefore represent the leaching of a slightly Na rich composition through the optimal composition to a Na poor composition over a period of a week, tracing out the narrow peak in Tc vs. Na content 8 .…”

Tuning Co Valence State in Cobalt Oxyhydrate Superconductor by Postreduction

“…Based upon previous experimental results, 7,8 the post reduction in aqueous NaOH solution at room temperature can be expressed as follows,…”