Abstract
The Na+ in NaBiO3·nH2O was partially ion-exchanged with Sr2+ and Ba2+ to yield AxNa1−2xBiO3·nH2O (A=Sr,Ba) phases. The only value of x obtained 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 is unchanged during the ion-exchange reaction. The X-ray powder patterns for the ion-exchanged compounds were indexed in the hexagonal system as for the starting compound, NaBiO3·nH2O. The Sr derivative releases water molecules up to 300°C and changes to a cubic perovskite phase after evolution of O2 and reduction of bismuth at about 400°C. The Ba derivatives with x≤0.29 release water molecules up to 300°C to yield ilmenite-type phases and decompose on reduction of bismuth at about 400°C. The maximally Ba2+ ion-exchanged derivative (x=0.36) releases water molecules up to 300°C and changed to a cubic perovskite phase on reduction of bismuth at about 400°C. This black cubic perovskite phase has a mean bismuth valence of 3.57 and shows no evidence of superconductivity down to 4 K.
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