Emergence of Long-Range Order in BaTiO_{3} from Local Symmetry-Breaking Distortions.
By using a symmetry motivated basis to evaluate local distortions against pair distribution function data, we show without prior bias, that the off-center Ti displacements in the archetypal ferroelectric BaTiO_{3} are zone centered and rhombohedral-like across its known ferroelectric and paraelectric phases. We construct a simple Monte Carlo model that captures our main experimental findings and demonstrate how the rich crystallographic phase diagram of BaTiO_{3} emerges from correlations of local symmetry-breaking distortions alone. Our results strongly support the order-disorder picture for these phase transitions, but can also be reconciled with the soft-mode theory of BaTiO_{3} that is supported by some spectroscopic techniques.
Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, United Kingdom.
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Senn
ISIS, Rutherford Appleton Laboratory, Harwell Campus, Didcot OX11 0QX, United Kingdom.
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Keen
School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
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Lucas
School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
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Hriljac
Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, United Kingdom.
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Goodwin