The structure of intercalated water in superconducting Na$_{0.35}$CoO$_{2}\cdot$1.37D$_{2}$O: Implications for the superconducting phase diagram

TL;DR

This study uses electron and neutron diffraction to analyze the structure of superconducting Na$_{0.35}$CoO$_{2}ullet$1.37D$_{2}$O, revealing supercell formations and the placement of deuterated water between CoO$_{2}$ layers, impacting the understanding of its superconducting phase diagram.

Contribution

It provides a detailed structural model of the intercalated water and sodium in the superconductor, clarifying the arrangement without requiring a separate 5K superconducting phase.

Findings

Supercells ranging from 1/3a* to 1/15a* observed.

Most common structure is a double hexagonal cell with specific dimensions.

Deuterated water forms a layered network between CoO$_{2}$ sheets.

Abstract

We have used electron and neutron powder diffraction to elucidate the structural properties of superconducting \NaD. Our measurements show that our superconducting sample exhbits a number of supercells ranging from ${1/3}a^{*}$ to ${1/15}a^{*}$, but the most predominant one, observed also in the neutron data, is a double hexagonal cell with dimensions \dhx. Rietveld analysis reveals that \deut\space is inserted between CoO$_{2}$ sheets as to form a layered network of NaO$_{6}$ triangular prisms. Our model removes the need to invoke a 5K superconducting point compound and suggests that a solid solution of Na is possible within a constant amount of water $y$.