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Unprecedented phase transition sequence in the perovskite Li0.2Na0.8NbO3

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Author(s)

Charlotte A. L. Dixon, Jason A. McNulty, Steven Huband, Pamela A. Thomas, Philip Lightfoot

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Abstract

We demonstrate the existence of a novel phase transition sequence in the perovskite Li0.2Na0.8NbO3 at elevated temperature. The rare Glazer tilt system, a+a+c-, is observed in both polar and centrosymmetric polymorphs.

The perovskite Li0.2Na0.8NbO3 is shown, by powder neutron diffraction, to display a unique sequence of phase transitions at elevated temperature. The ambient temperature polar phase (rhombohedral, space group R3c) transforms via a first-order transition to a polar tetragonal phase (space group P42mc) in the region 150 – 300 °C; these two phases correspond to Glazer tilt systems a-a-a- and a+a+c-, respectively. At 500 °C a ferroelectric – paraelectric transition takes place from P42mc to P42/nmc, retaining the a+a+c- tilt. Transformation to a single-tilt system, a0a0c+ (space group P4/mbm), occurs at 750 °C, with the final transition to the aristotype cubic phase at 850 °C. The P42mc and P42/nmc phases have each been seen only once previously in perovskite crystallography, in both cases in compositions prepared at high pressure.
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Details

Original languageEnglish
Pages (from-to)215-222
JournalInternational Union of Crystallography Journal (IUCrJ)
Volume4
Issue number3
Early online date8 Mar 2017
DOIs
Publication statusPublished - May 2017

    Research areas

  • Perovskite, Ferroelectric, Powder neutron diffraction

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