Abstract:

We studied by Mossbauer spectroscopy the Na0.82CoO2 compound using 1% 57 Fe as a local probe which substitutes for the Co ions. Mossbauer spectra at T = 300 K revealed two sites which correspond to Fe3+ and Fe4+. 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 Fe4+ and all of Fe3+, displays broad magnetically split spectra arising either from short-range magnetic correlations or from slow electronic spin relaxation. (c) 2006 Elsevier Ltd. All rights reserved.