Incorporation of Ni ions into two different sites of the Na and Co sites of NaCo_2O_4 was carried out by the processes of conventional elemental substitution for Co ion and solid state ion exchange of mobile Na^+ ion. The changes of the lattice parameters of "substituted" and "exchanged" samples were different, suggesting that the Ni ions occupy different sites. The Ni-substituted sample for Co showed a significant decrease of Seebeck coefficient keeping the electrical conductivity almost intact, while Ni-exchanged samples for Na showed a lower electrical conductivity than that of the non-substituted sample with keeping the Seebeck coefficient unchanged. These results suggest that Ni cations introduced to the Co site decouples the Co-Co spin exchange, whereas those at the Na site compensates positive holes by providing conduction electrons.
|Translated title of the contribution||Site-Selective Substitution by Transition Metal Cations for NaCo_2O_4 via Ion-Exchange|
|Number of pages||5|
|Journal||Journal of the Ceramic Society of Japan|
|Publication status||Published - Jun 1 2005|