Exploiting optical properties of nanopolycrystalline diamond in high pressure experiments

We investigated the optical properties (absorption, luminescence and Raman spectra) of nanopolycrystalline diamond (NPD) aiming at exploring its capabilities as a pressure sensor and as a pressure-cell anvil for combined X-ray/neutron and optical studies. Notably, we analysed the Raman peak shift and broadening with pressure using a Moissanite Anvil Cell (MAC). The results are compared with those obtained in a DAC, where Raman signals from NPD chips and diamond anvils strongly overlap. Its pressure behaviour in the hydrostatic and non-hydrostatic regimes were investigated. We showed that the nanopolycrystalline structure induces remarkable differences in the peak shift and broadening between NPD and natural type IIa single-crystal diamond, making NPD suitable as pressure gauge for pressure determination and testing hydrostaticity of pressure transmitting medium.Financial support from Projects MAT2015-69508-P; PGC2018-101464-B-I00 and MALTA -Consolider Team RED2018-102612-T (Ministerio de Ciencia, Innovación y Universidades) is acknowledged

Origin of the piezochromism in Cs2CuCl4: Electron-phonon and crystal-structure correlations

By using optical absorption and Raman spectroscopy, we have investigated the effects of pressure in the structural, electronic, and vibrational properties of Cs2CuCl4 in the 0?20 GPa range. Our study has provided a complete characterization of the electronic and vibrational structures of Cs2CuCl4 in the low-pressure Pnma phase as a function of cell volume and the Cu-Cl bond length, RCu-Cl. We have focused on the electronic structure in the Pnma phase, which is mainly related to the tetrahedral CuCl2?4 units distorted by the Jahn-Teller effect. The strong piezochromism of Cs2CuCl4 is caused by the opposite shift of the charge-transfer band gap and the Cu2+ d-d crystal-field transitions with pressure. The high-pressure structure of Cs2CuCl4 above 4.9 GPa yields structural transformations that we ascribe to a change of coordination around Cu2+. The high-pressure phase appears largely amorphized, therefore any structural information from x-ray diffraction is ruled out. Here we use electronic and vibrational probes to get inside the structural information.Financial support from the Spanish Ministerio de Economía, Industria y Competitividad (MAT2015-69508-P) and MALTA-CONSOLIDER (MAT2015-71010REDC)

Vidrios de alta transmitancia, procedimiento de obtención y aplicaciones fotovoltaicas

La presente invención describe un vidrio que presenta la siguiente composición (porcentajes expresados en % en peso respecto al peso total de la composición): 60-80% de SiO2; 10-20% de Na2O; 5-15% de CaO; 0,01-5% de Al2O3; 0,01-1% de SO3; 0,01-5% de MgO; 0,01-5% de Bi2O3 y/o CeO2 y 0,01-6% de uno ó más aditivos seleccionados del grupo formado por Eu2O3, Pr6O11, Yb2O3, Er2O3 y Al2O3:Cr2O3. La presente invención describe asimismo un procedimiento para su obtención a partir de materia prima o vidrio reciclado y sus aplicaciones en paneles fotovoltaicos.Solicitud: 201200258 (07.03.2012)Nº Pub. de Solicitud: ES2381948A1 (04.06.2012)Nº de Patente: ES2381948B2 (18.09.2012

Comment on "mechanisms for Pressure-Induced Isostructural Phase Transitions in EuO"

Authors thank the financial support from Projects PGC2018-101464-B-I00, PGC2018-097520-A-I00, and MALTA-Consolider Team RED2018-102612-T (Ministerio de Ciencia, Innovaci´on y Universidades) is acknowledged. V. Monteseguro acknowledges the “Beatriz Galindo” fellowship (BG20/000777) and the “Juan de la Cierva” fellowship (IJC2019-041586-I)

Behavior of au nanoparticles under pressure observed by in situ small-angle X-ray scattering

The mechanical properties and stability of metal nanoparticle colloids under high-pressure conditions are investigated by means of optical extinction spectroscopy and small-angle X-ray scattering (SAXS), for colloidal dispersions of gold nanorods and gold nanospheres. SAXS allows us to follow in situ the structural evolution of the nanoparticles induced by pressure, regarding both nanoparticle size and shape (form factor) and their aggregation through the interparticle correlation function S(q) (structure factor). The observed behavior changes under hydrostatic and nonhydrostatic conditions are discussed in terms of liquid solidification processes yielding nanoparticle aggregation. We show that pressure-induced diffusion and aggregation of gold nanorods take place after solidification of the solvent. The effect of nanoparticle shape on the aggregation process is additionally discussed.We thank Professor Jan Dhont for helpful comments about nanoparticle diffusion in solid ethanol. F.R. acknowledges financial support from Projects PID2021-127656NB-I00 and MALTA-Consolider Team (RED2018-102612-T), and L.M.L.-M. from PID2020-117779RB-I00 and MDM-2017-0720, from the State Research Agency of Spain, Ministry of Science and Innovation. C.M.-S. acknowledges funding from the Spanish Ministry of Universities and the European Union-NextGeneration EU through the Margarita Salas research grant (C21.I4.P1). We acknowledge SOLEIL for the provision of synchrotron radiation facilities, and we would like to thank Dr. Javier Pérez, beamline supervisor, for assistance in using beamline SWING (proposals 20191731 and 20210678). This work benefited from the use of the SasView application, originally developed under NSF award DMR-0520547. SasView contains code developed with funding from the European Union’s Horizon 2020 research and innovation program under the SINE2020 project, grant agreement no. 654000

Crystal-field mediated electronic transitions of EuS up to 35 GPa

An advanced experimental and theoretical model to explain the correlation between the electronic and local structure of Eu2+ in two diferent environments within a same compound, EuS, is presented. EuX monochalcogenides (X: O, S, Se, Te) exhibit anomalies in all their properties around 14 GPa with a semiconductor to metal transition. Although it is known that these changes are related to the 4f 75d0 ?4f 65d1 electronic transition, no consistent model of the pressure-induced modifcations of the electronic structure currently exists. We show, by optical and x-ray absorption spectroscopy, and by ab initio calculations up to 35 GPa, that the pressure evolution of the crystal feld plays a major role in triggering the observed electronic transitions from semiconductor to the half-metal and fnally to the metallic state.Authors thank the financial support from Projects PGC2018-101464-B-I00, PGC2018-097520-A-I00 and MALTA-Consolider Team RED2018-102612-T (Ministerio de Ciencia, Innovación y Universidades) is acknowledged. V. Monteseguro acknowledges the “Beatriz Galindo” fellowship (BG20/000777) and the “Juan de la Cierva” fellowship (IJC2019-041586-I). Authors are grateful to the staff of the BM23 beamline and the high-pressure laboratory at the ESRF for their support during the experiment (proposal number HC-3913), and the SERCAMAT (SCTI) of the University of Cantabria for FTIR facilities

On the Stiffness of Gold at the Nanoscale

The density and compressibility of nanoscale gold (both nanospheres and nanorods) and microscale gold (bulk) were simultaneously studied by X-ray diffraction with synchrotron radiation up to 30 GPa. Colloidal stability (aggregation state and nanoparticle shape and size) in both hydrostatic and nonhydrostatic regions was monitored by small-angle X-ray scattering. We demonstrate that nonhydrostatic effects due to solvent solidification had a negligible influence on the stability of the nanoparticles. Conversely, nonhydrostatic effects produced axial stresses on the nanoparticle up to a factor 10× higher than those on the bulk metal. Working under hydrostatic conditions (liquid solution), we determined the equation of state of individual nanoparticles. From the values of the lattice parameter and bulk modulus, we found that gold nanoparticles are slightly denser (0.3%) and stiffer (2%) than bulk gold: V0 = 67.65(3) Å3 , K0 = 170(3)GPa, at zero pressure

Pressure-induced spin transition and site-selective metallization in CoCl2

The interplay between spin states and metallization in compressed CoCl 2 is investigated by combining diffraction, resistivity and spectroscopy techniques under high-pressure conditions and ab-initio calculations. A pressure-induced metallization along with a Co 2+ high-spin (S = 3/2) to low-spin (S = 1/2) crossover transition is observed at high pressure near 70 GPa. This metallization process, which is associated with the p-d charge-transfer band gap closure, maintains the localization of 3d electrons around Co 2+ , demonstrating that metallization and localized Co 2+ -3d low-spin magnetism can coexist prior to the full 3d-electron delocalization (Mott-Hubbard d-d breakdown) at pressures greater than 180 GPa.Financial support from the Spanish Ministerio de Economıa y Competitividad (Project No. MAT2015-69508-P, MAT2016-80438-P) and MALTA-CONSOLIDER (Ref. No. MAT2015-71070-REDC) is acknowledged

Técnicas espectroscópicas para micromuestras en condiciones extremas : fenómenos luminiscentes y transiciones de fase a altas presiones

RESUMEN: La presente memoria de Tesis recoge los resultados experimentales que se pueden resumir por un doble objetivo. En primer lugar, desarrollar una labor de carácter experimental dedicada al diseño y desarrollo de nuevos dispositivos que permitan realizar medidas espectroscópicas en condiciones extremas de presión y temperatura. De entre todos los montajes destaca el Microscopio de Caracterización Espectroscópica (patente ES2461015B2). En segundo lugar, aplicar las técnicas desarrolladas al caso científico. Cabe destacar el interés por la correlación entre la estructura cristalina y electrónica en sistemas de Co2+: CoF2, CoCl2 y KCoF3. Otro compuesto ha sido el GeCuO3, sistema que presenta transiciones tipo Spin-Peierls, un rico piezocroismo y que depende del medio hidrostático transmisor de presión. Por último, por sus aplicaciones optoelectrónicas, se ha investigado el LiNbO3:Tm3+, permitiendo de esta manera, comprobar el funcionamiento de diversas técnicas aplicadas al estudio de materiales dopados con tierras raras.ABSTRACT: This Thesis includes the experimental results can be summarized by two objectives. First, develop an experimental work dedicated to design and development of new devices that allow for spectroscopic measurements under extreme conditions of pressure and temperature. Between all the productions highlights the Spectroscopic Characterization Microscope (ES2461015B2 patent). Second, to apply the techniques developed to scientific case. Notably, the interest in the correlation between the crystalline and electronic structure systems Co2+: CoF2, CoCl2 and KCoF3. Another compound has been GeCuO3 system that presents transitions Spin-Peierls type, a rich piezocroism and depends on the average hydrostatic pressure transmitter. Finally, thus its optoelectronic applications, LiNbO3: Tm3+ have investigated allowing test the operation of various techniques applied to the study of rare earth doped materials.Este trabajo se ha podido realizar gracias a tener la suerte de estar en un grupo en el que se lucha cada proyecto, cada convocatoria. Fruto de ese esfuerzo, de Fernando Rodríguez, he sido por concurso de méritos contratado por los siguientes proyectos: IDICAN2007, INNPACTO IPT-2011-1868-920000, MAT2008-06873- C02-01/MAT, MALTA-Ingenio Consolider 2010 CDS2007-0045, UC-Sodercan “Incentivación de proyectos de I+D” 2015