AM{sub 1-x}Al{sub x}O{sub 3}{sub -x} (A = Na or K; M = Nb or Ta): New anion-deficient perovskite oxides exhibiting oxide ion conduction
- Indian Institute of Science, Bangalore (India)
Anion-deficient perovskite oxides of the formula AM{sub 1}{sub -x}Al{sub X}O{sub 3}{sub -x} (A = Na or K; M = Nb or Ta) have been prepared for 0 < x {le} 0.5. Diffraction experiments reveal that while the potassium compounds adopt orthorhombic/cubic provskite structures similar to the parent KNbO{sub 3}/KTaO{sub 3}, the sodium compound, NaNb{sub 0.5}O{sub 2.5}, possesses a brownmillerite/LaSr-CuAlO{sub 5}-like superstructure. {sub 27} Al NMR spectra show an exclusive tetrahedral oxygen coordination for Al(III) in NaNb{sub 0.5}O{sub 2.5} (I) and both tetrahedral and octahedral coordination for Al(III) in KNb{sub 0.5}Al{sub 0.5}O{sub 2.5} (II). The results suggest a long-range and short -range ordering of oxide ion vacancies in I and II respectively. Electrical conductivity measurements show a significant oxide ion conduction for KNb{sub 1-x}Al{sub x}O{sub 3}{sub -x}, with the conductivity increasing with x up to x = 0.5. The differences in the Arrhenius plots of the ionic conductivity of I and II have been rationalized in terms of the long-range and short-range ordering of oxide ion vacancies in the anion-deficient perovskite oxides. 12 refs., 8 figs., 4 tabs.
- OSTI ID:
- 391030
- Journal Information:
- Chemistry of Materials, Journal Name: Chemistry of Materials Journal Issue: 6 Vol. 8; ISSN CMATEX; ISSN 0897-4756
- Country of Publication:
- United States
- Language:
- English
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