References of "Guennou, Mael 50034741"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailRules and mechanisms governing octahedral tilts in perovskites under pressure
Xiang, H. J.; Guennou, Mael UL; Iniguez, Jorge et al

in Physical Review. B (2017), 96(5),

The rotation of octahedra (octahedral tilting) is common in ABO(3) perovskites and relevant to many physical phenomena, ranging from electronic and magnetic properties, metal-insulator transitions to ... [more ▼]

The rotation of octahedra (octahedral tilting) is common in ABO(3) perovskites and relevant to many physical phenomena, ranging from electronic and magnetic properties, metal-insulator transitions to improper ferroelectricity. Hydrostatic pressure is an efficient way to tune and control octahedral tiltings. However, the pressure behavior of such tiltings can dramatically differ from one material to another, with the origins of such differences remaining controversial. In this paper we discover several new mechanisms and formulate a set of simple rules that allow us to understand how pressure affects oxygen octahedral tiltings via the use and analysis of first-principles results for a variety of compounds. Besides the known A-O interactions, we reveal that the interactions between specific B ions and oxygen ions contribute to the tilting instability. We explain the previously reported trend that the derivative of the oxygen octahedral tilting with respect to pressure (dR/dP) usually decreases with both the tolerance factor and the ionization state of the A ion by illustrating the key role of A-O interactions and their change under pressure. Furthermore, three new mechanisms/rules are discovered, namely that (i) the octahedral rotations in ABO(3) perovskites with empty low-lying d states on the B site are greatly enhanced by pressure, in order to lower the electronic kinetic energy; (ii) dR/dP is enhanced when the system possesses weak tilt instabilities, and (iii) for the most common phase exhibited by perovskites-the orthorhombic Pbnm state-the in-phase and antiphase octahedral rotations are not automatically both suppressed or both enhanced by the application of pressure because of a trilinear coupling between these two rotation types and an antipolar mode involving the A ions. We further predict that the polarization associated with the so-called hybrid improper ferroelectricity could be manipulated by hydrostatic pressure by indirectly controlling the amplitude of octahedral rotations. [less ▲]

Detailed reference viewed: 99 (3 UL)
Full Text
Peer Reviewed
See detailConductivity and Local Structure of LaNiO3 Thin Films
Fowlie, Jennifer; Gibert, Marta; Tieri, Giulio et al

in ADVANCED MATERIALS (2017), 29(18),

A marked conductivity enhancement is reported in 6-11 unit cell LaNiO3 thin films. A maximal conductivity is also observed in ab initio calculations for films of the same thickness. In agreement with ... [more ▼]

A marked conductivity enhancement is reported in 6-11 unit cell LaNiO3 thin films. A maximal conductivity is also observed in ab initio calculations for films of the same thickness. In agreement with results from state of the art scanning transmission electron microscopy, the calculations also reveal a differentiated film structure comprising characteristic surface, interior, and heterointerface structures. Based on this observation, a three-element parallel conductor model is considered and leads to the conclusion that the conductivity enhancement for films of 6-11 unit cells, stems from the onset of intercompetition between the three local structures in the film depth. [less ▲]

Detailed reference viewed: 87 (0 UL)
Full Text
Peer Reviewed
See detailControl of surface potential at polar domain walls in a nonpolar oxide
Nataf, G. F.; Guennou, Mael UL; Kreisel, Jens UL et al

in PHYSICAL REVIEW MATERIALS (2017), 1(7),

Ferroic domain walls could play an important role in microelectronics given their nanometric size and often distinct functional properties. Until now, devices and device concepts were mostly based on ... [more ▼]

Ferroic domain walls could play an important role in microelectronics given their nanometric size and often distinct functional properties. Until now, devices and device concepts were mostly based on mobile domain walls in ferromagnetic and ferroelectric materials. A less explored path is to make use of polar domain walls in nonpolar ferroelastic materials. Indeed, while the polar character of ferroelastic domain walls has been demonstrated, polarization control has been elusive. Here, we report evidence for the electrostatic signature of the domain-wall polarization in nonpolar calcium titanate (CaTiO3). Macroscopic mechanical resonances excited by an ac electric field are observed as a signature of a piezoelectric response caused by polar walls. On the microscopic scale, the polarization in domain walls modifies the local surface potential of the sample. Through imaging of surface potential variations, we show that the potential at the domain wall can be controlled by electron injection. This could enable devices based on nondestructive information readout of surface potential. [less ▲]

Detailed reference viewed: 93 (0 UL)
Full Text
Peer Reviewed
See detailMultiple strain-induced phase transitions in LaNiO3 thin films
Weber, M. C.; Guennou, Mael UL; Dix, N. et al

in Physical Review. B (2016), 94(1),

Strain effects on epitaxial thin films of LaNiO3 grown on different single crystalline substrates are studied by Raman scattering and first-principles simulation. New Raman modes, not present in bulk or ... [more ▼]

Strain effects on epitaxial thin films of LaNiO3 grown on different single crystalline substrates are studied by Raman scattering and first-principles simulation. New Raman modes, not present in bulk or fully relaxed films, appear under both compressive and tensile strains indicating symmetry reductions. Interestingly, the Raman spectra and the underlying crystal symmetry for tensile and compressively strained films are different. Extensive mapping of LaNiO3 phase stability is addressed by simulations, showing that a variety of crystalline phases are indeed stabilized under strain. The calculated Raman frequencies reproduce the principal features of the experimental spectra, supporting the validity of the multiple strain-driven structural transitions predicted by the simulations. [less ▲]

Detailed reference viewed: 54 (1 UL)
Full Text
Peer Reviewed
See detailEvolution of defect signatures at ferroelectric domain walls in Mg-doped LiNbO3
Nataf, Guillaume F.; Guennou, Mael UL; Haussmann, Alexander et al

in Physica Status Solidi. Rapid Research Letters (2016), 10(3), 222-226

The domain structure of uniaxial ferroelectric lithium niobate single crystals is investigated using Raman spectroscopy mapping. The influence of doping with magnesium and poling at room temperature is ... [more ▼]

The domain structure of uniaxial ferroelectric lithium niobate single crystals is investigated using Raman spectroscopy mapping. The influence of doping with magnesium and poling at room temperature is studied by analysing frequency shifts at domain walls and their variations with dopant concentration and annealing conditions. It is shown that defects are stabilized at domain walls and that changes in the defect structures with Mg concentration can be probed by the shift of Raman modes. We show that the signatures of polar defects in the bulk and at the domain walls differ. (C) 2016 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim [less ▲]

Detailed reference viewed: 95 (1 UL)
Full Text
Peer Reviewed
See detailLow energy electron imaging of domains and domain walls in magnesium-doped lithium niobate
Nataf, G. F.; Grysan, P.; Guennou, Mael UL et al

in SCIENTIFIC REPORTS (2016), 6

The understanding of domain structures, specifically domain walls currently attracts a significant attention in the field of (multi)-ferroic materials. In this article, we analyze contrast formation in ... [more ▼]

The understanding of domain structures, specifically domain walls currently attracts a significant attention in the field of (multi)-ferroic materials. In this article, we analyze contrast formation in full field electron microscopy applied to domains and domain walls in the uniaxial ferroelectric lithium niobate, which presents a large 3.8 eV band gap and for which conductive domain walls have been reported. We show that the transition from Mirror Electron Microscopy (MEM - electrons reflected) to Low Energy Electron Microscopy (LEEM - electrons backscattered) gives rise to a robust contrast between domains with upwards (P-up) and downwards (P-down) polarization, and provides a measure of the difference in surface potential between the domains. We demonstrate that out-of-focus conditions of imaging produce contrast inversion, due to image distortion induced by charged surfaces and also carry information on the polarization direction in the domains. Finally, we show that the intensity profile at domain walls provides experimental evidence for a local stray, lateral electric field. [less ▲]

Detailed reference viewed: 62 (0 UL)
Full Text
Peer Reviewed
See detailUltrafast acousto-optic mode conversion in optically birefringent ferroelectrics
Lejman, Mariusz; Vaudel, Gwenaelle; Infante, Ingrid C. et al

in NATURE COMMUNICATIONS (2016), 7

The ability to generate efficient giga-terahertz coherent acoustic phonons with femtosecond laser makes acousto-optics a promising candidate for ultrafast light processing, which faces electronic device ... [more ▼]

The ability to generate efficient giga-terahertz coherent acoustic phonons with femtosecond laser makes acousto-optics a promising candidate for ultrafast light processing, which faces electronic device limits intrinsic to complementary metal oxide semiconductor technology. Modern acousto-optic devices, including optical mode conversion process between ordinary and extraordinary light waves (and vice versa), remain limited to the megahertz range. Here, using coherent acoustic waves generated at tens of gigahertz frequency by a femtosecond laser pulse we reveal the mode conversion process and show its efficiency in ferroelectric materials such as BiFeO3 and LiNbO3. Further to the experimental evidence, we provide a complete theoretical support to this all-optical ultrafast mechanism mediated by acousto-optic interaction. By allowing the manipulation of light polarization with gigahertz coherent acoustic phonons, our results provide a novel route for the development of next-generation photonic-based devices and highlight new capabilities in using ferroelectrics in modern photonics. [less ▲]

Detailed reference viewed: 88 (0 UL)
Full Text
Peer Reviewed
See detailRaman spectroscopy of rare-earth orthoferrites RFeO3 (R=La, Sm, Eu, Gd Tb, Dy)
Weber, Mads Christof; Guennou, Mael UL; Zhao, Hong Jian et al

in Physical Review. B (2016), 94(21),

We report a Raman scattering study of six rare-earth orthoferrites La, Sm, Eu, Gd, Tb, Dy. The use of extensive polarized Raman scattering of SmFeO3 and first-principles calculations enable the assignment ... [more ▼]

We report a Raman scattering study of six rare-earth orthoferrites La, Sm, Eu, Gd, Tb, Dy. The use of extensive polarized Raman scattering of SmFeO3 and first-principles calculations enable the assignment of the observed phonon modes to vibrational symmetries and atomic displacements. The assignment of the spectra and their comparison throughout the whole series allow correlating the phonon modes with the orthorhombic structural distortions of RFeO3 perovskites. In particular the positions of two specific A(g) modes scale linearly with the two FeO6 octahedra tilt angles, allowing the distortion to be tracked throughout the series. At variance with literature, we find that the two octahedra tilt angles scale differently with the vibration frequencies of their respective A(g) modes. This behavior, as well as the general relations between the tilt angles, the frequencies of the associated modes, and the ionic radii are rationalized in a simple Landau model. The reported Raman spectra and associated phonon-mode assignment provide reference data for structural investigations of the whole series of orthoferrites. [less ▲]

Detailed reference viewed: 115 (3 UL)