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

• Main Authors: Charlotte A. L. Dixon, Jason A. McNulty, Steven Huband, Pamela A. Thomas, Philip Lightfoot
• Format: Article
• Language: English
• Published: International Union of Crystallography 2017-05-01
• Series: IUCrJ
• Subjects: perovskite; ferroelectric; powder neutron diffraction
• Online Access: http://scripts.iucr.org/cgi-bin/paper?S2052252517002226

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 and twice each, respectively, in perovskite crystallography, in each case in compositions prepared at high pressure.