Raman spectroscopy study of NaxCoO2 and superconducting NaxCoO2.yH2O

TL;DR

This study uses Raman spectroscopy to analyze structural phonon changes in NaxCoO2 and its superconducting hydrate form, revealing correlations between phonon frequencies and superconducting temperatures.

Contribution

It provides new insights into how intercalation of water affects phonon modes and superconductivity in NaxCoO2-based materials.

Findings

Raman active phonons decrease in frequency with increasing Tc

Systematic spectral changes correlate with water intercalation

Oxygen-related phonons show monotonic frequency decrease

Abstract

The Raman spectra of the parent compound NaxCoO2 (x=0.75) and the superconducting oxyhydrates NaxCoO2.yH2O with different superconducting temperatures (Tc) have been measured. Five Raman active phonons around 195 cm-1 (E1g), 482 cm-1, 522 cm-1, 616 cm-1 (3E2g), 663 cm-1 (A1g) appear in all spectra. These spectra change systematically along with the intercalation of H2O and superconducting properties. In particular, the Raman active phonons (A1g and E1g) involving the oxygen motions within the Co-O layers show up monotonous decrease in frequency along with superconducting temperature Tc. The fundamental properties and alternations of other active Raman phonons in the superconducting materials have also been discussed.