alpha-NaFeO2: ionic conductivity and sodium extraction

Complex admittance measurements have been performed on alpha-NaFeO2 and on the product Na0.9FeO2 obtained by sodium extraction, both being polycrystal line powders. The electrical conductivity in both samples is proposed to be due to sodium ions hopping between octahedral positions through the adjace nt, empty, tetrahedral ones characteristic of a rock-salt structural framew ork. The parent material shows an activation energy in the dc conductivity of 0.31 eV between 306 and 498 K. Removal of sodium, in spite of creating o ctahedral vacancies, results in lower conductivity values, and a higher act ivation energy of 0.58 eV in a similar temperature range. (C) 1999 Publishe d by Elsevier Science B.V. All rights reserved.