Mael Guennou

Bismuth-based perovskites under high pressure
1
M. Guennou1*, P. Bouvier2, J. Kreisel1,3
Materials Research and Technology Department, Luxembourg Institute of Science and Technology
41 rue du Brill, 4422 Belvaux, Luxembourg
2
Institut Néel, Université Grenoble-Alpes, CNRS, F-38042 Grenoble, France
3
Physics and Materials Science Research Unit, University of Luxembourg
41 rue du Brill, 4422 Belvaux Luxembourg
*e-mail: mael.guennou@list.lu
The peculiar crystal chemistry of bismuth-based perovskites has attracted a considerable attention in the
field of functional oxides, in relation to important scientific and technological issues, such as the
elimination of lead from piezoelectric devices, and the design of intrinsic multiferroic materials. The key
element is the presence of an electron “lone pair” 6s2, which imparts to the Bi3+ ion a tendency to off-center
in its coordination polyhedron, and, from a macroscopic point of view, induce ferroelectric and
piezoelectric properties. Yet, not all BiMO3 are ferroelectric [1,2]; but ferroelectricity has to compete with
other structural distortions of the perovskite structure, notably the tilts of the oxygen octahedra, and
cooperative Jahn-Teller distortion. The delicate balance between these competing – or sometimes
collaborating – instabilities can be further tuned by external parameters, such as electric field, pressure, or
epitaxial strain in thin films.
Over the past few years, we have investigated phase diagrams of Bi-based perovskites using high
hydrostatic pressure, which allows modifying the interatomic distances and, thus the interactions, to a much
larger extent than any other parameter. Our complementary use of Raman scattering and synchrotron X-ray
diffraction has revealed a variety of phase transitions and exciting phenomena in significant Bi-based
perovskites, notably: (i) a remarkable sequence of transitions in the model multiferroic BiFeO3 [3,4]
interpreted as the presence of “nano-twins”[5]; (ii) an unexpected polar phase with giant distortion in
BiMnO3 at very high pressure, associated to a reduction of the cooperative Jahn-Teller distortion [6]; (iii) a
comparatively puzzling stability of the orthorhombic phase up to unprecedented strain states in BiCrO3; and
(iv) insulator-to-metal transitions in the 50 GPa range in all cases. This talk will summarize our
investigations of high-pressure phase diagrams, with emphasis on the most recent results.
1. Polar and non-polar phases of BiMO3: A review, Belik A, J. Solid State Chem., 195, 32 (2012)
2. Bismuth-based perovskites as multiferroics, Guennou M, Viret M, Kreisel J, Compte Rendus Physique,
in print (2015);
3. Multiple high-pressure phase transitions in BiFeO3, Guennou M, Bouvier P, Chen G, Dkhil B,
Haumont R, Garbarino G, Kreisel J, Phys. Rev. B; 84, 174107 (2011)
4. High-pressure phase transitions in BiFeO3: hydrostatic versus non-hydrostatic conditions, Guennou M,
Bouvier P, Haumont R, Garbarino G, Kreisel J, Phase Transitions 84, 474 (2011)
5. Novel Nanoscale Twinned Phases in Perovskite Oxides, Prosandeev S, Wang D, Ren W, Íñiguez J,
Bellaiche L, Adv. Func. Mat. 23, 234 (2013)
6. Jahn-Teller, Polarity, and Insulator-to-Metal Transition in BiMnO3 at High Pressure, Guennou M,
Bouvier P, Toulemonde P, Darie C, Goujon C, Bordet P, Hanfland M, Kreisel J, Phys. Rev. Letters;
112, 075501 (2014)
Curriculum Vitae
Mael Guennou obtained his PhD from the Ecole Centrale Paris (France) in 2007
for his work on electromechanical properties and domain structures in relaxorbased piezoelectric single crystals. After subsequent post-docs in Grenoble
(France) and Prague (Czech Republic), he is now working as a researcher at the
Luxembourg Institute of Science and Technology. His research interests are related
to structures and properties of ferroic oxides, including notably domain walls and
phase transitions under high hydrostatic pressure, with a special emphasis on
Raman spectroscopy.