Estructura, propiedades electrónicas y espectroscopía del HfSe₂ en condiciones extremas

Aunque tradicionalmente se ha explorado con mayor detalle el efecto de la temperatura, el uso de la alta presión se ha consolidado como una herramienta con un elevado potencial, que permite acceder a un régimen termodinámico donde las propiedades de los sistemas experimentan en muchas ocasiones cambios sorprendentes. A lo largo de esta Tesis Doctoral, prestaremos especial atención al uso de esta magnitud para analizar desde diferentes puntos de vista el comportamiento del HfSe2. Los principales aspectos que abordaremos sobre este material serán su estructura cristalográfica, estructura electrónica, y, por último, las vibraciones y dinámica de la red cristalina. De este modo, la memoria de esta Tesis está organizada de la siguiente forma: comienza con un capítulo donde se introduce la descriptiva general de los TMDs, y se contextualiza el uso de la alta presión como herramienta de interés para acceder al estudio de estos sólidos. Seguidamente, un capítulo dedicado a las técnicas y metodología empleadas durante el transcurso de esta Tesis. El siguiente capítulo constituirá un primer bloque de resultados donde se recoge la caracterización del HfSe2 a presión ambiente. A lo largo de este primer capítulo de resultados se discutirán con detalle las cuestiones relacionadas con la estructura cristalográfica, estructura electrónica y vibraciones del sólido que servirán de referencia y sentarán la base adecuada para el posterior estudio en condiciones extremas de presión. Asimismo, estos aspectos se abordan sistemáticamente en profundidad en los siguientes capítulos, enteramente dedicados a los resultados obtenidos del HfSe2 bajo presión. Por último, se resumirán las conclusiones más destacadas de este trabajo..

Characterization and Decomposition of the Natural van der Waals SnSb2Te4 under Compression

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.inorgchem.0c01086.[EN] High pressure X-ray diffraction, Raman scattering, and electrical measurements, together with theoretical calculations, which include the analysis of the topological electron density and electronic localization function, evidence the presence of an isostructural phase transition around 2 GPa, a Fermi resonance around 3.5 GPa, and a pressure-induced decomposition of SnSb2Te4 into the high-pressure phases of its parent binary compounds (alpha-Sb2Te3 and SnTe) above 7 GPa. The internal polyhedral compressibility, the behavior of the Raman-active modes, the electrical behavior, and the nature of its different bonds under compression have been discussed and compared with their parent binary compounds and with related ternary materials. In this context, the Raman spectrum of SnSb2Te4 exhibits vibrational modes that are associated but forbidden in rocksalt-type SnTe; thus showing a novel way to experimentally observe the forbidden vibrational modes of some compounds. Here, some of the bonds are identified with metavalent bonding, which were already observed in their parent binary compounds. The behavior of SnSb2Te4 is framed within the extended orbital radii map of BA(2)Te(4) compounds, so our results pave the way to understand the pressure behavior and stability ranges of other "natural van der Waals" compounds with similar stoichiometry.This work has been performed under financial support from the Spanish MINECO under Project MALTA-CONSOLIDER TEAM network (RED2018-102612-T) and Project FIS2017-83295-P, from Generalitat Valenciana under Project PROMETEO/2018/123. This publication is a product of the "Programa de Valoracion y Recursos Conjuntos de I+D+i VLC/CAMPUS and has been financed by the Spanish Ministerio de Educacion, Cultura y Deporte, as part of "Programa Campus de Excelencia Internacional". Supercomputer time has been provided by the Red Espanola de Supercomputacion (RES) and the MALTA cluster. J.A.S. acknowledges a "Ramon y Cajal" fellowship (RYC-2015-17482) for financial support, and E.L.D.S. acknowledges Marie Sklodowska-Curie Grant No. 785789-COMEX from the European Union's Horizon 2020 research and innovation program. We also thank ALBA synchrotron and DIAMOND light source for funded experiments.Sans-Tresserras, JÁ.; Vilaplana Cerda, RI.; Da Silva, EL.; Popescu, C.; Cuenca-Gotor, VP.; Andrada-Chacón, A.; Sánchez-Benitez, J.... (2020). Characterization and Decomposition of the Natural van der Waals SnSb2Te4 under Compression. Inorganic Chemistry. 59(14):9900-9918. https://doi.org/10.1021/acs.inorgchem.0c01086S990099185914Mellnik, A. R., Lee, J. S., Richardella, A., Grab, J. L., Mintun, P. J., Fischer, M. H., … Ralph, D. C. (2014). Spin-transfer torque generated by a topological insulator. Nature, 511(7510), 449-451. doi:10.1038/nature13534Chen, Y. L., Analytis, J. G., Chu, J.-H., Liu, Z. K., Mo, S.-K., Qi, X. L., … Shen, Z.-X. (2009). 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Pressure-Induced Chemical Decomposition and Structural Changes of Boric Acid. The Journal of Physical Chemistry B, 110(28), 13858-13865. doi:10.1021/jp061650dCatafesta, J., Rovani, P. R., Perottoni, C. A., & Pereira, A. S. (2015). Pressure-enhanced decomposition of Ag3[Co(CN)6]. Journal of Physics and

Estructura, propiedades electrónicas y espectroscopía del HfSe₂ en condiciones extremas

Tesis llevada a cabo para conseguir el grado de Doctor por la Universidad Complutense de Madrid.--2018-06-29.--Sobresaliente cum laude[ES] Aunque tradicionalmente se ha explorado con mayor detalle el efecto de la temperatura, el uso de la alta presión se ha consolidado como una herramienta con un elevado potencial, que permite acceder a un régimen termodinámico donde las propiedades de los sistemas experimentan en muchas ocasiones cambios sorprendentes. A lo largo de esta Tesis Doctoral, prestaremos especial atención al uso de esta magnitud para analizar desde diferentes puntos de vista el comportamiento del HfSe2. Los principales aspectos que abordaremos sobre este material serán su estructura cristalográfica, estructura electrónica, y, por último, las vibraciones y dinámica de la red cristalina. De este modo, la memoria de esta Tesis está organizada de la siguiente forma: comienza con un capítulo donde se introduce la descriptiva general de los TMDs, y se contextualiza el uso de la alta presión como herramienta de interés para acceder al estudio de estos sólidos. Seguidamente, un capítulo dedicado a las técnicas y metodología empleadas durante el transcurso de esta Tesis. El siguiente capítulo constituirá un primer bloque de resultados donde se recoge la caracterización del HfSe2 a presión ambiente. A lo largo de este primer capítulo de resultados se discutirán con detalle las cuestiones relacionadas con la estructura cristalográfica, estructura electrónica y vibraciones del sólido que servirán de referencia y sentarán la base adecuada para el posterior estudio en condiciones extremas de presión. Asimismo, estos aspectos se abordan sistemáticamente en profundidad en los siguientes capítulos, enteramente dedicados a los resultados obtenidos del HfSe2 bajo presión. Por último, se resumirán las conclusiones más destacadas de este trabajo...[EN] Although the effect of temperature has traditionally been explored in greater detail, the use of high pressure has established itself as a tool with a high potential, which allows access to a thermodynamic regime where the properties of systems often experience surprising changes . Throughout this Doctoral Thesis, we will pay special attention to the use of this magnitude to analyze the behavior of HfSe2 from different points of view. The main aspects that we will approach about this material will be its crystallographic structure, electronic structure, and, finally, the vibrations and dynamics of the network crystalline In this way, the memory of this Thesis is organized in the following way: begins with a chapter where the general description of the TMDs is introduced, and the use of high pressure as a tool of interest to access the study of these solids is contextualized. Next, a chapter dedicated to techniques and methodology used during the course of this Thesis. The next chapter will constitute a first block of results which includes the characterization of HfSe2 at ambient pressure. Throughout this first chapter of results the issues will be discussed in detail related to the crystallographic structure, electronic structure and vibrations of the solid that will serve as a reference and will provide the appropriate basis for further study under extreme pressure conditions. In addition, these aspects are systematically addressed in depth in the following chapters, entirely dedicated to the results obtained from HfSe2 under pressure. Finally, the conclusions will be summarized outstanding of this work ...Peer reviewe

Large magnetoelectric coupling near room temperature in synthetic melanostibite Mn2FeSbO6

Multiferroic materials exhibit two or more ferroic orders and have potential applications as multifunctional materials in the electronics industry. A coupling of ferroelectricity and ferromagnetism is hereby particularly promising. We show that the synthetic melanostibite mineral MnFeSbO (R (Formula presented.) space group) with ilmenite-type structure exhibits cation off-centering that results in alternating modulated displacements, thus allowing antiferroelectricity to occur. Massive magnetoelectric coupling (MEC) and magnetocapacitance effect of up to 4000 % was detected at a record high temperature of 260 K. The multiferroic behavior is based on the imbalance of cationic displacements caused by a magnetostrictive mechanism, which sets up an unprecedented example to pave the way for the development of highly effective MEC devices operational at or near room temperature.The authors thank MINECO for funding through projects MAT2013‐44964‐R, MAT2013‐41099‐R, MAT2015‐71070‐REDC, MAT2014‐52405‐C02‐02, CTQ2015‐67755‐C2‐1‐R (MINECO/FEDER) and FPI (BES‐2013‐066112) and Ramon y Cajal (RyC‐2010–06276) fellowships, and Comunidad de Madrid through S‐2013/MIT‐2753 grant

Large magnetoelectric coupling near room temperature in synthetic Melanostibite Mn2FeSbO6

Multiferroic materials exhibit two or more ferroic orders and have potential applications as multifunctional materials in the electronics industry. A coupling of ferroelectricity and ferromagnetism is hereby particularly promising. We show that the synthetic melanostibite mineral Mn2FeSbO6 (R-3 space group) with ilmenite-type structure exhibits cation off-centering that results in alternating modulated displacements, thus allowing antiferroelectricity to occur. Massive magnetoelectric coupling (MEC) and magnetocapacitance effect of up to 4000% was detected at a record high temperature of 260 K. The multiferroic behavior is based on the imbalance of cationic displacements caused by a magnetostrictive mechanism, which sets up an unprecedented example to pave the way for the development of highly effective MEC devices operational at or near room temperature.Comunidad de MadridMINECODepto. de Química InorgánicaFac. de Ciencias QuímicasTRUEpu

Anti-site disorder and physical properties in microwave synthesized RE2Ti2O7 (RE = Gd, Ho) pyrochlores

In this work we report on the microwave assisted synthesis of nano-sized Gd2Ti2O7 (GTO) and Ho2Ti2O7 (HTO) powders from the RE2Ti2O7 pyrochlore family (RE ¼ rare earth). Synchrotron X-ray powder diffraction was used to study RE–Ti cationic anti-site defects with concentrations that decrease in both samples with increasing temperature starting from 1100 C, and the defects disappear at 1400 ºC. SQUID magnetometry measurements revealed that GTO shows a predominantly anti-ferromagnetic structure, whereas HTO exhibits magnetic saturation and a ferromagnetic component at low temperature. Impedance spectroscopy data revealed strongly increased ionic oxygen vacancy conduction in HTO ceramic pellets as compared to GTO, which may be associated with a higher degree of oxygen vacancy disorder. This argument was supported by Raman spectroscopy data.Ministerio de Ciencia e InnovaciónComunidad de MadridDepto. de Química InorgánicaFac. de Ciencias QuímicasTRUEpu