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Durham University

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Publication details for Prof. Ivana Evans

Tate, Matthew L., Blom, Douglas A., Avdeev, Maxim, Brand, Helen E. A., McIntyre, Garry J., Vogt, Thomas & Evans, Ivana Radosavljevic (2017). New Apatite-Type Oxide Ion Conductor, Bi2La8[(GeO4)6]O3: Structure, Properties, and Direct Imaging of Low-Level Interstitial Oxygen Atoms Using Aberration-Corrected Scanning Transmission Electron Microscopy. Advanced Functional Materials 27(8): 1605625.

Author(s) from Durham


The new solid electrolyte Bi2La8[(GeO4)6]O3 is prepared and characterized by variable-temperature synchrotron X-ray and neutron diffraction, aberration-corrected scanning transmission electron microscopy, and physical property measurements (impedance spectroscopy and second harmonic generation). The material is a triclinic variant of the apatite structure type and owes its ionic conductivity to the presence of oxide ion interstitials. A combination of annular bright-field scanning transmission electron microscopy experiments and frozen-phonon multislice simulations enables direct imaging of the crucial interstitial oxygen atoms present at a level of 8 out of 1030 electrons per formula unit of the material, and crystallographically disordered, in the unit cell. Scanning transmission electron microscopy also leads to a direct observation of the local departures from the centrosymmetric average structure determined by diffraction. As no second harmonic generation signal is observed, these displacements are non-cooperative on the longer length scales probed by optical methods.