Use of resonance Raman spectroscopy to study the phase diagram of PbZr0.52Ti0.48O3

Evidence is presented for the first time that the sharp and continuous spectral changes observed in PbZr0.52Ti0.48O3 (PZT) between 350 and 10 K with the 647.1 nm wavelength are due to a resonance Raman effect. Such a phenomenon can be explained by means of a self-trapped exciton emission oxygen deficient complex (TiTi' - VO-) of PZT powder whose energy is close to the radiation line of the laser. This kind of approach should also be very useful to distinguish the phase transition sequence for other related ferro/ piezoelectric systems

Role of Zinc and Niobium in the Giant Piezoelectric Response of PbZn1/3Nb2/3O3

International audienceRelaxor ferroelectric perovskites are highly polarizable and can exhibit giant coupling between elastic strain and an applied electric field. Here, we report an in situ extended X-ray absorption fine structure (EXAFS) study of a PbZn1/3Nb2/3O3 (PZN) single crystal as a function of the electric field. We show that the strong dipoles in the NbO6 octahedra bonds are aligned along the four directions close to the orientation of the electric field, while a small reversible polar shift occurs for Zn in the direction of the electric field, i.e., positive or negative. This reversible Zn-O polar shift is proposed to play an important role in both the "easy" switching of the ferroelectric polarization and the giant piezoelectric effect in PZN

Polar space group and complex magnetism in Ni-11 square(HPO3)(8)(OH)(6): towards a new multiferroic material?

International audienceThe Ni-11 square(HPO3)(8)(OH)(6) phosphite was prepared using a hydrothermal method. Depending on the pressure used during the synthesis, different hierarchical superstructures were encountered, including a new original cross-shaped star. The as-obtained products were characterized by X-ray diffraction, scanning and transmission electron microscopy and magnetization. In agreement with the presence of transition metal dimers in the structure, a complex magnetic behavior is observed at low temperature. This magnetic ground-state, combined with the non-centrosymmetry of the space group, creates new opportunities for applications in this class of open framework inorganic materials. (C) 2014 Elsevier Masson SAS. All rights reserved

Polar space group and complex magnetism in Ni-11 square(HPO3)(8)(OH)(6): towards a new multiferroic material?

International audienceThe Ni-11 square(HPO3)(8)(OH)(6) phosphite was prepared using a hydrothermal method. Depending on the pressure used during the synthesis, different hierarchical superstructures were encountered, including a new original cross-shaped star. The as-obtained products were characterized by X-ray diffraction, scanning and transmission electron microscopy and magnetization. In agreement with the presence of transition metal dimers in the structure, a complex magnetic behavior is observed at low temperature. This magnetic ground-state, combined with the non-centrosymmetry of the space group, creates new opportunities for applications in this class of open framework inorganic materials. (C) 2014 Elsevier Masson SAS. All rights reserved

High pressure single crystal x-ray and neutron powder diffraction study of the ferroelectric-paraelectric phase transition in PbTiO3

International audienceThe results obtained by high pressure neutron powder diffraction and single-crystal x-ray diffraction for the P4mm–Pm $\bar{3}$ m phase transition in the prototype ferroelectric perovskite lead titanate are shown. Neutron diffraction is found to be strongly sensitive to the dipolar moment in the PbTiO3 unit cell due to the gradual reduction of the displacement of the Ti and O atoms from centrosymmetric positions in the cubic perovskite structure which exhibits anti-phase scattering of Pb, Ti and O atoms. From applying both techniques, the anomalously high Debye–Waller factor for the lead atoms confirms the disordered character of the cubic phase. High pressure single crystal x-ray diffraction also perfectly describes the ferroelectric–paraelectric transition and will be the technique of choice to solve higher pressure structures for PbTiO3

A High-Temperature Molecular Ferroelectric Zn/Dy Complex Exhibiting Single-Ion-Magnet Behavior and Lanthanide Luminescence

Multifunctional molecular ferroelectrics are exciting materials synthesized using molecular chemistry concepts, which may combine a spontaneous electrical polarization, switched upon applying an electric..

Dimerization of Uracil in a simulated Mars-like UV radiation environment

International audienceThe search for organic molecules at the surface of Mars is a key objective in astrobiology, given that many organic compounds are possible biosignatures and their presence is of interest with regard to the habitability of Mars. Current environmental conditions at the martian surface are harsh and affect the stability of organic molecules. For this reason, and because current and future Mars rovers collect samples from the upper surface layer, it is important to assess the fate of organic molecules under the conditions at the martian surface. Here, we present an experimental study of the evolution of uracil when exposed to UV radiation, pressure, and temperature conditions representative of the surface of Mars. Uracil was selected because it is a nucleobase that composes RNA, and it has been detected in interplanetary bodies that could be the exogenous source of this molecule by meteoritic delivery to the surface of Mars. Our results show that the experimental quantum efficiency of photodecomposition of uracil is 0.16 ± 0.14 molecule/photon. Although these results suggest that uracil is quickly photodegraded when directly exposed to UV light on Mars, such exposure produces dimers that are more stable over time than the monomer. The identified dimers could be targets of interest for current and future Mars space missions

High-pressure polymorph of LuFe2O4 with room-temperature antiferromagnetic order

International audienceBranded for its potential electronic ferroelectricity, charge-ordered LuFe2O4 has a layered Fe triangular framework, whose topology is a source of degeneracy, both at the charge and spin levels. Here we present an in-depth characterization of LuFe2O4-hp, the high-pressure (hp) polymorph of LuFe2O4, using electron, x-ray, and neutron diffraction, combined with transport and magnetization measurements. We show that LuFe2O4-hp is characterized by a misfit-related monoclinic structure, accommodating a buckled triangular [Lu](infinity) layer and two shifted adjacent rectangular [Fe](infinity) planes belonging to a distorted rock salt-type layer. The release of the geometric frustration of the Fe magnetic lattice in the hp form leads to collinear antiferromagnetic ordering at T-N = 380 K. Possible coexistence of charge and magnetic orders in this material opens research pathways for the design of tunable multifunctional devices using high-pressure techniques