Two-step polarization reversal in biased ferroelectrics

Polarization reversal in polycrystalline ferroelectrics is shown to occur via two distinct and sequential domain reorientation steps. This reorientation sequence, which cannot be readily discriminated in the overall sample polarization, is made apparent using time-resolved high-energy x-ray diffraction. Upon application of electric fields opposite to the initial poling direction, two unique and significantly different time constants are observed. The first (faster time constant) is shown to be derived by the release of a residual stress due to initial electrical biasing and the second (slower time constant) due to the redevelopment of residual stress during further domain wall motion. A modified domain reorientation model is given that accurately describes the domain volume fraction evolution during the reversal process.open1

Transport Properties of the Metallic State of TMTSF-DMTCNQ

We report the transport properties (longitudinal and transverse conductivity, magnetoresistance and thermopower) of TMTSF-DMTCNQ for pressures up to 13 kbar and temperatures down to 1.2 K together with the phase diagram which results from these measurements. The most striking results are the occurrence of a first order insulator-metal low temperature transition as pressure is increased above 9.75 kbar and the properties of the metallic state. At pressures sufficiently high to quench the Peierls transition the helium temperature conductivity is greater than that found in any organic conductor at any temperature (σ∥ ≳ 105 (Ωcm)-1) and an enormous magnetoresistance (Δρ/ρ0 ~ 15) is found for a field of 75 kOe perpendicular to the conducting chains.Nous présentons des mesures des propriétés de transport (conductibilité longitudinale et transversale, magnétorésistance et pouvoir thermoélectrique) dans le composé TMTSF-DMTCNQ sous pression jusqu'à 13 kbar et à basse température jusqu'à 1,2 K. Un diagramme de phases a été obtenu à partir de ces mesures. Les résultats les plus frappants sont : l'existence d'une transition isolant-métal du premier ordre à 9,75 kbar pour une pression croissante et les propriétés de l'état métallique. A des pressions suffisamment élevées pour faire disparaitre la transition de Peierls la conductibilité atteint à la température de l'hélium liquide une valeur supérieure à ce qui a été observé jusqu'à présent dans un conducteur organique à n'importe quelle température (σ|| ≳ 105 (Ωcm) -1). De plus, une magnétorésistance très importante (Δρ/ρ 0 ~ 15) est détectée lorsqu'un champ de 75 kOe est placé perpendiculairement aux chaînes conductrices

In-situ hydrogen charging of zirconium powder to study isothermal precipitation of hydrides and determination of Zr-hydride crystal structure

Zirconium alloys are widely used in the nuclear industry because of their high strength, good corrosion resistance and low neutron absorption cross-section. However, zirconium has strong affinity for hydrogen which leads to hydrogen concentration build-up over time. It is well known that the formation of hydrides will degrade the material and leads to, for example, delayed hydride cracking during high burn up. Even though zirconium hydrides have been studied for several decades, there still remain some controversies regarding the formation mechanisms, exact crystal structure, and stability of various hydride phases. This study uses high resolution synchrotron radiation as a probing tool to observe the precipitation and dissolution of hydrides in highly pure zirconium powder during in-situ hydrogen charging. The experiment enabled the direct observation of the hydride formation and phase transformations. It, also, provided high quality data for crystal structure determination

Hydrological processes in farmed basins across scales, from plot to catchment: stakes and examples / Procesos hidrológicos en cuencas cultivadas a través de escalas, de la parcela a la cuenca: intereses y ejemplos

International audienc

Innovative insights in a plug flow microreactor for operando X-ray studies

© 2013 International Union of CrystallographyDifferent solutions have been proposed over the years to optimize control of the temperature and atmosphere over a catalyst in order to reach an ideal reactor behavior. Here, a new innovative solution which aims to minimize temperature gradients along the catalyst bed is demonstrated. This was attained by focusing the infrared radiation generated from the heating elements onto the catalyst bed with the aid of an aluminium shield. This method yields a ∼0.13Kmm-1 axial temperature gradient ranging from 960 to 1173K. With the selection of appropriate capillaries, pressures of 20bar (2MPa) can be attained.The research leading to these results has been funded by the Spanish CICYT (CTQ2010-14872/BQU) and the European Union's Seventh Framework Programme (FP7/2007–2013) under grant agreement No. 253445. KCC acknowledges Marie Curie Action – Intra-European Fellowship (FP7-PEOPLE-2009-IEF-253445) for a postdoctoral fellowship.Peer Reviewe