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

corrigendum to ferroelectric and dielectric properties in Li-doped ZnO nanorods

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Influence de la température et de la pression hydrostatique sur l'instabilité ferroélectrique et l'instabilité rotationnelle de la structure pérovskite dans les solutions solides Pb(Zr1-xTix)O3

Nous avons étudié l'influence de la température et de la pression hydrostatique sur l'instabilité ferroélectrique et l'instabilité rotationnelle de la structure pérovskite dans les solution solides Pb(Zr1-xTix)O3 (PZT) à l'aide d'une série de techniques complémentaires sondant différentes échelles de temps et de distance. Cette étude a permis de montrer tout d'abord que les phases ferroélectriques haute température et basse température des solutions solides riches en zirconium qui étaient considérées jusqu'alors comme étant de symétrie rhomboédrique sont en fait de plus basse symétrie (monoclinique de type MB ou triclinique). En outre, les résultats obtenus par spectroscopie Raman de résonance ont permis de confirmer que cette technique est une technique particulièrement efficace pour déterminer les transitions de phase dans les matériaux à base de titanate de plomb. Par ailleurs, nous avons montré qu'à l'instar des réflexions de surstructure qui permettent de suivre l'instabilité rotationnelle de la structure pérovskite directement sur les profils de diffraction neutronique, les réflexions pseudocubiques d'indices de Miller pair pair impair sont une sonde puissante de l'instabilité ferroélectrique. Finalement, grâce à ces deux familles de réflexions, nous avons montré que la maille fortement pseudocubique observée à haute pression juste avant la transition vers la phase paraélectrique résultait de la compétition entre l'instabilité ferroélectrique et l'instabilité rotationnelle (antiferrodistorsive)MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Interest of binary PMMA/p(VDF-TrFE) blend thin films

International audienceThin films of binary amorphousPMMA–ferroelectric P(VDF–17 mol%TrFE) copolymerhave been produced by spin-coating on Ti-covered siliconwafers. Thermal, structural, dielectric, ferroelectric and pyroelectric propertieswere investigated as a function of PMMA content up to 10 wt%. If functional properties slightly decrease with increasing PMMA content, both the adhesion of such binary-copolymer thin films on metal electrodes and the reliability of as-grown devices can be dramatically improved. 1–2 wt% PMMA-based binary blends appear as very promising alternative materials for pyroelectric applications

Phase transformation in SrTi0.6Zr0.4O3 : a high-pressure Raman and X-ray diffraction study

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Phase transformation in SrTi0.6Zr0.4O3 : a high-pressure Raman and X-ray diffraction study

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Probing High-Pressure Phase Transitions in Ti-Based Perovskite-Type Ferroelectrics Using Visible Resonance Raman Spectroscopy

International audienceWe report unprecedented dramatic changes in the 647.1 nm Raman signal of PbZr0.6Ti0.4O3 occurring in the same pressure ranges as the critical pressures of the antiferrodistortive and ferroelectric-paraelectric phase transitions. This huge decrease in intensity of both the Raman modes and the background, observed for both pressure transmitting media used (glycerol or 4:1 methanol ethanol mixture), is shown to originate from the two-step loss of a resonance Raman effect and the concomitant fluorescence. Changes in the local titanium environment (first with the onset of octahedral tilting and then with the removal of polar cation displacements) alter the electronic band structure and modify the resonance conditions. Furthermore, the optimal resonance conditions are found to be particularly narrow, as shown by the fluorescence spectrum of PbZr0.6Ti0.4O3 at atmospheric pressure characterized by the presence of a very well-defined sharp peak (fwhm = 8 nm) centered around 647.1 nm. These results thus demonstrate that visible resonance Raman spectroscopy can be used as a quick and efficient technique for probing phase transitions in PbZr1-xTixO3 (PZT) and other technologically important perovskite-type materials such as PMN-xPT, PZN-xPT relaxors, lead free piezoelectrics, and ferroelectric nanopowders. This technique appears also a good alternative to UV Raman spectroscopy for probing the polar order at the nanoscale in ultrathinfilms and superlattices

Low-symmetry phases at the tilt boundary of the Pb„Zr1−xTix...O3 solid solution

International audienceThe tilt boundary that separates the well-known rhombohedral phases R3m and R3c of the Pb_Zr1−xTix_O3 solid solution was investigated by means of time-of-flight neutron powder diffraction, dielectric measurements, and resonance Raman spectroscopy. Careful Rietveld refinements yield significantly better agreement factors using monoclinic models for the long-range structure of PbZr0.6Ti0.4O3 with a Cc space group at low temperature and with a Cm space group at high temperature rather than the widely accepted rhombohedral symmetry. The spontaneous polarization was found to lie along the pseudocubic _112_ direction instead of along the _111_ direction. This polarization direction is shown to be adopted for a wide variety of compositions, temperatures, and pressures and has major implications for the domain structure of these materials. Furthermore, the transition between the untilted and the tilted structures was found to be very diffuse and strongly dependent on the thermal history of the sample

Competing order parameters in the Pb(Zr1−xTix)O3 solid solution at high pressure

International audiencePerovskite-type ferroelectric Pb(Zr1−xTix)O3 (x = 0.3; 0.4) compounds were investigated at high pressure by means of time-of-flight neutron powder and angle dispersive x-ray diffraction (NPD and XRD) with special emphasis on the interactions between the ferroelectric Γ4− and antiferrodistortive R4+ instabilities. A simple and fast way for probing at the long-range level the ferroelectric Γ4− instability in perovskite compounds is reported, which unlike Rietveld refinement neither requires numerous reflections to be collected nor a structural model to be chosen. This method, built upon the fact that the imaginary component of the structure factor Fhkl of general hkl reflections cancels itself in centrosymmetric perovskite structures, consists in the monitoring of the integrated intensities of these reflections directly on neutron powder diffraction profiles. Thanks to this powerful probe, the passage by a metrically cubic unit cell at high pressure, which appears to be a common feature of PZT ceramics, is shown unambiguously to originate from the competition between polar cation displacements and antiphase tilting of (Zr,Ti)O6 octahedra. Furthermore, based on the high-pressure behavior of the lead isotropic displacement parameter, significant static disorder is found to persist a few GPa beyond the critical pressure of the ferroelectric-paraelectric phase transition, corroborating recent findings reported for the two other cations (Zr, Ti), namely that this phase transition has an order-disorder component