Mössbauer study of Na${}_{0.82}$CoO${}_2$ (doped by 1% ${}^{57}$Fe)

Abstract

We studied by Mössbauer spectroscopy the Na${}_{0.82}$CoO${}_2$ compound using 1% ${}^{57}$Fe as a local probe which substitutes for the Co ions. Mössbauer spectra at T=300 K revealed two sites which correspond to Fe${}^{3+}$ and Fe${}^{4+}$. The existence of two distinct values of the quadrupole splitting instead of a continuous distribution should be related with the charge ordering of Co${}^{+3}$, Co${}^{+4}$ ions and ion ordering of Na(1) and Na(2). Below T=10 K part of the spectrum area, corresponding to Fe${}^{4+}$ and all of Fe${}^{3+}$, displays broad magnetically split spectra arising either from short-range magnetic correlations or from slow electronic spin relaxation.