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      The ferroelectric-paraelectric phase transition in BiFeO3: crystal structure of the orthorhombic beta-phase

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          Abstract

          A detailed investigation using variable temperature powder neutron diffraction demonstrates that BiFeO3 undergoes a phase transition from the ferroelectric alpha phase (rhombohedral, R3c) to a paraelectric beta phase (orthorhombic, Pbnm) between 820 oC and 830 oC. Co-existence of both phases over a finite temperature interval, together with abrupt changes in key structural parameters, confirm that the transition is firstorder. The beta phase corresponds to the GdFeO3-type perovskite. The metastability of BiFeO3 relative to Bi2Fe4O9 above 810 oC precludes observation of a reported cubic gamma phase above 925 oC under the present experimental conditions.

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          The beta Phase of Multiferroic Bismuth Ferrite and its beta-gamma Metal-Insulator Transition

          We show that epitaxial (001) thin films of multiferroic bismuth ferrite BiFeO3 are monoclinic at room temperature instead of tetragonal or Rhombohedral as reported earlier . We report a orthorhombic order-disorder beta-phase between 820C and 950C contrary to the earlier report. The transition sequence monoclinic-orthorhombic phase in (001)BiFeO3 thin film (rhombohedral-orthorhombic transition in single crystal) resembles that of BaTiO3 or PbSc1/2Ta1/2O3. The transition to the cubic \(\gamma\)-phase causes an abrupt collapse of the bandgap toward zero (insulator-metal transition) at the orthorhombic-cubic beta-gamma transition around 950C. This transition is similar to the metal-insulator transition in Ba0.6K0.4BiO3.
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            Finite-Temperature Properties of MultiferroicBiFeO3

            An effective Hamiltonian scheme is developed to study finite-temperature properties of multiferroic BiFeO3. This approach reproduces very well (i) the symmetry of the ground state, (ii) the Néel and Curie temperatures, and (iii) the intrinsic magnetoelectric coefficients (that are very weak). This scheme also predicts (a) an overlooked phase above Tc approximately 1100 K that is associated with antiferrodistortive motions, as consistent with our additional x-ray diffractions, (b) improperlike dielectric features above Tc, and (c) that the ferroelectric transition is of first order with no group-subgroup relation between the paraelectric and polar phases.
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              Colossal Spin-Phonon Anomalies and the Ferroelectric Phase Transition in the Model Multiferroic Bifeo3

              We report a temperature-dependent Raman and neutron scattering investigation of the multiferroic material bismuth ferrite BiFeO3 (BFO).
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                Author and article information

                Journal
                10 November 2008
                Article
                10.1103/PhysRevLett.102.027602
                19257319
                0811.1501
                ba7fa543-c9e0-45ca-8bce-05d3cbf2777a

                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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                Custom metadata
                Phys. Rev. Lett., 102, 027602, 2009
                cond-mat.mtrl-sci

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