Ion-exchange reaction of Na+ in NaBiO3 center dot nH(2)O with Sr2+ and Ba2+

The Na+ in NaBiO3. nH(2)O was partially ion-exchanged with Sr2+ and Ba2+ to yield A(x)Na(1-2x)BiO(3). nH(2)O (A = Sr,Ba) phases. The only value of x o btained for the Sr derivative was 0.48, but x ranged from 0.11 to 0.36 for the Ba derivative, depending on the reaction time. The valence of bismuth i s unchanged during the ion-exchange reaction. The X-ray powder patterns for the ion-exchanged compounds were indexed in the hexagonal system as for th e starting compound, NaBiO3. nH(2)O. The Sr derivative releases water molec ules up to 300 degrees C and changes to a cubic perovskite phase after evol ution of O, and reduction of bismuth at about 400 degrees C. The Ba derivat ives with x less than or equal to 0.29 release water molecules up to 300 de grees C to yield ilmenite-type phases and decompose on reduction of bismuth at about 400 degrees C. The maximally Ba2+ ion-exchanged derivative (x = 0 .36) releases water molecules up to 300 degrees C and changed to a cubic pe rovskite phase on reduction of bismuth at about 400 degrees C. This black c ubic perovskite phase has a mean bismuth valence of 3.57 and shows no evide nce of superconductivity down to 4 K. (C) 1999 Elsevier Science BN. All rig hts reserved.