Raman response of quantum critical ferroelectric pb-doped srtio3

A quantum paraelectric SrTiO3 is a material situated in close proximity to a quantum critical point (QCP) of ferroelectric transition in which the critical temperature to the ferroelectric state is suppressed down to 0 K. However, the understanding of the behavior of the phase transition in the vicinity of this point remains challenging. Using the concentration x of Pb in solid solution Sr1−x Pbx TiO3 (PSTx) as a tuning parameter and applying the combination of Raman and dielectric spectroscopy methods, we approach the QCP in PSTx and study the interplay of classical and quantum phenomena in the region of criticality. We obtain the critical temperature of PSTx and the evolution of the temperature-dependent dynamical properties of the system as a function of x to reveal the mechanism of the transition. We show that the ferroelectric transition occurs gradually through the emergence of the polar nanoregions inside the non-polar tetragonal phase with their further expansion on cooling. We also study the ferroelastic cubic-to-tetragonal structural transition, occurring at higher temperatures, and show that its properties are almost concentration-independent and not affected by the quantum criticality.Fil: Linnik, Ekaterina D.. Southern Federal University; RusiaFil: Mikheykin, Alexey S.. Southern Federal University; RusiaFil: Rubi, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Constituyentes | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Constituyentes; ArgentinaFil: Shirokov, Vladimir B.. No especifíca;Fil: Mezzane, Daoud. No especifíca;Fil: Kondovych, Svitlana V.. No especifíca;Fil: Lukyanchuk, Igor A.. No especifíca;Fil: Razumnaya, Anna G.. Southern Federal University; Rusi

Electrochemical Methods for Reprocessing Defective Fuel Elements and for Decontaminating Equipment

Reprocessing of fuel elements receives much consideration in nuclear engineering. Chemical and electrochemical methods are used for the purpose. For difficultly soluble materials based on zirconium alloys chemical methods are not suitable. Chemical reprocessing of defective or irradiated fuel elements requires special methods for their decladding because the dissolution of the clad material in nitric acid is either impossible (stainless steel, Zr alloys) or quite slow (aluminium). Fuel elements are cut in air-tight glove-boxes equipped with a dust collector and a feeder for crushed material. Chemical treatment is not free from limitations. For this reason we started a study of the feasibility of electrochemical methods for reprocessing defective and irradiated fuel elements. A simplified electrochemical technology developed makes it possible to recover expensive materials which were earlier wasted or required multi-step treatment. The method and an electrochemical cell are suitable for essentially complete dissolution of any fuel elements, specifically those made of materials which are difficultly soluble by chemical methods

Twin-boundary engineering and thickness effect on strontium-barium niobate thin films on MgO substrate

International audienceThe Sr0.5Ba0.5Nb2O6 (SBN50) films with different thicknesses synthesized by a high-current discharge rfsputtering in an oxygen atmosphere. All synthesized films have the structure of tetragonal tungsten bronze. The dependence of the unit cell parameters of the film material demonstrates a size effect, the magnitude of which is comparable to the distortions resulting from the ferroelectric relaxor phase transformation of SBN crystals of the same composition. The twinning of the same type is observed in all films when the twinned film components are rotated relative to each other by 36.8 degrees around the fourth-order rotational axis. The orientation of the films relative to the substrate can be written as [001]SBN parallel to[001]MgO; [100] SBN+parallel to[310]MgO and [100]SBN-parallel to[3 (1) over bar0]MgO, where the sign ``+'' and ``-'' marks the twin components. It is noteworthy that such an orientation of the film relative to the substrate corresponds to the maximum possible tensile stress of heteroepitaxial films acting from the MgO single crystal substrate. This type of twinning is not typical for SBN50 films on MgO grown by other synthesis methods. The appearance of this unusual type of twinning is associated with the peculiarities of synthesis. At the initial moment of sputtering, the substrate is additionally heated by the sputtered substance's plasma. The substrate temperature can also be used in other synthesis methods to control twinning and strain in barium strontium niobate thin films. (C) 2021 Elsevier B.V. All rights reserved

Lattice anharmonicity and polar soft mode in ferrimagnetic M-type hexaferrite BaFe

The polar phonon modes in BaFe12O19 single crystal are studied in the temperature range from 6 to 300 K by polarized infrared spectroscopy. The phonon spectrum of the crystal is strongly anharmonic and unstable with respect to long-wavelength fluctuations of the dielectric permittivity along the hexagonal axis. Our results suggests that in BaFe12O19 hexaferrite symmetry lowering to the polar phase with the space group P63mc can be expected