Tailoring the photovoltaic effect in (111) oriented BiFeO3_3/LaFeO3_3 superlattices

Ferroelectric and photovoltaic properties of (BiFeO$_3$)$_{(1-x)Λ}$/(LaFeO$_3$)$_{xΛ}$ superlattices grown by pulsed laser deposition have been investigated (Λ being the bilayer thickness). For a high concentration of BiFeO$_3$ a ferroelectric state is observed simultaneously with a switchable photovoltaic response. In contrast for certain concentration of LaFeO$_3$ a non-switchable photovoltaic effect is evidenced. Such modulation of the PV response in the superlattices is attributed to the ferroelectric to paraelectric phase transition which is controlled with the increase of x. Remarkably, concomitant to this change of PV mechanism, a change of the conduction mechanism also seems to take place from a bulk-limited to an interface-limited transport as x increases

X-ray study of structural domains in the near-surface region of SrTiO₃ substrates with Y_0.6Pr_0.4Ba₂Cu₃O₇/La_2/3Ca_1/3MnO₃ superlattices grown on top

We investigated with synchrotron x-ray diffraction and reflectometry the formation of structural domains in the near-surface region of single crystalline SrTiO₃ (001) substrates with Y0.6Pr0.4Ba₂Cu₃O₇/La2/3Ca1/3MnO₃ superlattices grown on top. We find that the antiferrodistortive cubic to tetragonal transition, which occurs at TSTO=104  K in the bulk and at a considerably higher temperature of at least 120 K in the surface region of SrTiO₃, has only a weak influence on the domain formation. The strongest changes occur instead in the vicinity of the tetragonal to orthorhombic transition in SrTiO₃ around 65 K where pronounced surface facets develop that reach deep (at least several micrometers) into the SrTiO₃ substrate. These micrometer-sized facets are anisotropic and tilted with respect to one another by up to 0.5° along the shorter direction. Finally, we find that a third structural transition below 30 K gives rise to significant changes in the spread of the c-axis parameters. Overall, our data provide evidence for a strong mutual interaction between the structural properties of the SrTiO₃ surface and the multilayer grown on top

Under pressure:Mechanochemical effects on structure and ion conduction in the sodium-ion solid electrolyte Na₃PS₄

10.1021/jacs.0c06668Journal of the American Chemical Society1424318422-1843

Hétérostructures et super-réseaux à base du relaxeur PbMg1/3Nb2/3O3 et du ferroélectrique PbTiO3@ (croissance et étude des effets de contraintes par diffraction de rayons X et spectroscopie Raman)

AMIENS-BU Sciences (800212103) / SudocSudocFranceF

Tunable Redox Potential, Optical Properties, and Enhanced Stability of Modified Ferrocene-Based Complexes

International audienc

High-Temperature Lattice-Dynamics Evolution of YMnO3 and YbMnO3

International audienceThe exact mechanism responsible for the ferroelectricity in hexagonal manganite has been the subject of intense debate. Whether ferroelectricity and ferroelastic order appear at the same temperature and the role of covalency in the ferroelectric order are still discussed. High-temperature phase transitions are here investigated through the prism of lattice-dynamics evolution with temperature. Comparison is made between the YMnO3 and YbMnO3 behavior using polarized Raman spectroscopy. While YMnO3 shows two phase transitions (isosymetric at about 900 K and ferroelastic at 1200 K) YbMnO3 presents no lattice instability up to 1350 K. Phonons involved in the lattice instability and the zone tripling transition are identified. Moreover, peculiar hardening on heating of some YbMnO3 phonons is revealed and discussed, which further highlights the dynamical difference between these two hexagonal manganites

Phase stability frustration on ultra-nanosized anatase TiO 2

cited By 8International audienceThis work sheds light on the exceptional robustness of anatase TiO 2 when it is downsized to an extreme value of 4â €‰nm. Since at this size the surface contribution to the volume becomes predominant, it turns out that the material becomes significantly resistant against particles coarsening with temperature, entailing a significant delay in the anatase to rutile phase transition, prolonging up to 1000â €‰°C in air. A noticeable alteration of the phase stability diagram with lithium insertion is also experienced. Lithium insertion in such nanocrystalline anatase TiO 2 converts into a complete solid solution until almost Li 1 TiO 2, a composition at which the tetragonal to orthorhombic transition takes place without the formation of the emblematic and unwished rock salt Li 1 TiO 2 phase. Consequently, excellent reversibility in the electrochemical process is experienced in the whole portion of lithium content

Influence of the stoichiometry, microstructure, and metallization method on the dielectric properties of 0.94 Na 0.5 Bi 0.5 TiO 3 ‐0.06 BaTiO 3

International audienc

Stress and orientation in the relaxor/ferroelectric superlattices (PbMg1/3Nb2/3O3)((1-x)Lambda)/(PbTiO3)(x Lambda)

International audienceWe have grown a series of [PbMg1/3Nb2/3O3]((1-x)Lambda)/[PbTiO3](xLambda)(PMN1-x/PTx) superlattices for which the composition varies, 0.1less than or equal toxless than or equal to0.8, but the modulation period Lambda is kept constant at about 130 A. X-ray diffraction indicates that the polar c axis of the PT layers lies in the plane of the films. The Raman spectra, which reflect the sum of the spectra of PMN and the PT layers, confirm the a-domain orientation of the PT layers. A downshift of the E(1TO) soft mode of the PT layers was attributed to tensile stress, estimated to be in the range of 2.5-3.6 GPa, induced by the lattice mismatch of PMN/PT layers. We observe the splitting of the "silent" mode in PT into distinct modes B-1 and E and attribute this to the strains present in the layers

Structural studies of relaxor/ferroelectric Pb(Mg1/3Nb2/3)O-3/PbTiO3 superlattices

We have synthesized [Pb(Mg1/3Nb2/3)O-3]((1-x)Lambda)/[PbTiO3](x Lambda) (PMN(1-x)LambdaPT(x)Lambda) super-lattices by pulsed laser ablation onto MgO substrates buffered with La1/2Sr1/2CoO3 (LSCO). We varied the composition (0.1 <= x <= 0.8), and kept the modulation period A constant at about 140 angstrom. X-ray diffraction indicates that the polar c-axis of the PT layers lies in the plane of the films. This is confirmed by the Raman spectra. There is a shift to lower frequencies of the PT soft mode due to stress but we observe no indications of stress dependence in the Raman spectra of the PMN layers