Wednesday, June 26, 2013

1306.5916 (Mael Guennou et al.)

Jahn-Teller, giant strain and insulator-to-metal transition in BiMnO3 at
high pressure

Mael Guennou, Pierre Bouvier, Pierre Toulemonde, Céline Darie, Céline Goujon, Pierre Bordet, Michael Hanfland, Jens Kreisel
The interaction of coexisting structural instabilities in multiferroic materials gives rise to intriguing coupling phenomena and extraordinarily rich phase diagrams, both in bulk materials and strained thin films. Here we investigate the multiferroic BiMnO3 with its peculiar 6s2 electrons and four interacting mechanisms: electric polarity, octahedra tilts, magnetism and cooperative Jahn-Teller distortion. We have probed structural transitions under high pressure by synchrotron X-ray diffraction and Raman spectroscopy up to 60 GPa. We show that BiMnO3 displays under pressure a rich sequence of five phases with a great variety of structures and properties, including between 37 and 53 GPa a polar phase with an unexpectedly strong distortion and a metallic phase above 53 GPa. Between 7 and 37 GPa, the Pnma structure remains remarkably stable but shows a reduction of the Jahn-Teller distortion in a way that differs from the behaviour observed in the archetypal orthorhombic Jahn-Teller distorted perovskite LaMnO3.
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