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1.
Inorg Chem ; 2020 Jul 08.
Artigo em Inglês | MEDLINE | ID: mdl-32640163

RESUMO

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 (α-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 BA2Te4 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.

2.
Dalton Trans ; 47(31): 10654-10659, 2018 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-29850707

RESUMO

We investigate the structural response of a dense peptide metal-organic framework using in situ powder and single-crystal X-ray diffraction under high-pressures. Crystals of Zn(GlyTyr)2 show a reversible compression by 13% in volume at 4 GPa that is facilitated by the ability of the peptidic linker to act as a flexible string for a cooperative response of the structure to strain. This structural transformation is controlled by changes to the conformation of the peptide, which enables a bond rearrangement in the coordination sphere of the metal and changes to the strength and directionality of the supramolecular interactions specific to the side chain groups in the dipeptide sequence. Compared to other structural transformations in Zn(ii) peptide MOFs, this behaviour is not affected by host/guest interactions and relies exclusively on the conformational flexibility of the peptide and its side chain chemistry.

3.
Inorg Chem ; 57(14): 8241-8252, 2018 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-29944355

RESUMO

α(R)-In2Se3 has been experimentally and theoretically studied under compression at room temperature by means of X-ray diffraction and Raman scattering measurements as well as by ab initio total-energy and lattice-dynamics calculations. Our study has confirmed the α ( R3 m) → ß' ( C2/ m) → ß ( R3̅ m) sequence of pressure-induced phase transitions and has allowed us to understand the mechanism of the monoclinic C2/ m to rhombohedral R3̅ m phase transition. The monoclinic C2/ m phase enhances its symmetry gradually until a complete transformation to the rhombohedral R3̅ m structure is attained above 10-12 GPa. The second-order character of this transition is the reason for the discordance in previous measurements. The comparison of Raman measurements and lattice-dynamics calculations has allowed us to tentatively assign most of the Raman-active modes of the three phases. The comparison of experimental results and simulations has helped to distinguish between the different phases of In2Se3 and resolve current controversies.

4.
Nano Lett ; 16(5): 3221-9, 2016 05 11.
Artigo em Inglês | MEDLINE | ID: mdl-27080194

RESUMO

Manipulating properties of matter at the nanoscale is the essence of nanotechnology, which has enabled the realization of quantum dots, nanotubes, metamaterials, and two-dimensional materials with tailored electronic and optical properties. Two-dimensional semiconductors have revealed promising perspectives in nanotechnology. However, the tunability of their physical properties is challenging for semiconductors studied until now. Here we show the ability of morphological manipulation strategies, such as nanotexturing or, at the limit, important surface roughness, to enhance light absorption and the luminescent response of atomically thin indium selenide nanosheets. Besides, quantum-size confinement effects make this two-dimensional semiconductor to exhibit one of the largest band gap tunability ranges observed in a two-dimensional semiconductor: from infrared, in bulk material, to visible wavelengths, at the single layer. These results are relevant for the design of new optoelectronic devices, including heterostructures of two-dimensional materials with optimized band gap functionalities and in-plane heterojunctions with minimal junction defect density.

5.
J Phys Condens Matter ; 27(38): 385401, 2015 Sep 30.
Artigo em Inglês | MEDLINE | ID: mdl-26351272

RESUMO

This paper reports the pressure-dependent photoluminescence and Raman spectral investigation of hydrothermally synthesized ZnO nanoflowers at room temperature. Intrinsic near-band-edge UV emission from ZnO nanoflowers is monotonously blue-shifted under pressures up to 13.8 GPa with a pressure coefficient of 26 meV GPa(-1), and this pressure value is nearly 5 GPa above the transition pressure from the wurtzite to the rock salt phase for bulk ZnO. The Raman band corresponds to the wurtzite phase, the [Formula: see text] and [Formula: see text] modes were observed up to about 11 GPa from the spectra. The apparent discrepancy in the transition pressures as determined from photoluminescence and Raman studies suggests that it is a consequence of the gradual phase transition, in which the smallest nanoparticles are expected to remain in the wurtzite phase up to 13-15 GPa.

6.
Inorg Chem ; 53(21): 11598-603, 2014 Nov 03.
Artigo em Inglês | MEDLINE | ID: mdl-25338307

RESUMO

The high-pressure structural behavior of 30 nm nanoparticles of anatase TiO2 was studied under hydrostatic and quasi-hydrostatic conditions up to 25 GPa. We found that the structural sequence is not sensitive to the use of different pressure transmitting media. Anatase-type nanoparticles exhibit a phase transition beyond 12 GPa toward a baddeleyite-type structure. Under decompression this phase transition is irreversible, and a metastable columbite-type structure is recovered at ambient conditions. The bulk modulus of anatase-type nanoparticles was determined confirming that nanoparticles of TiO2 are more compressible than bulk TiO2. Similar conclusions were obtained after the determination of the bulk modulus of baddeleyite-type nanoparticles. Furthermore, axial compressibilities and the effect of pressure in atomic positions, bond distances, and bond angles are determined. Finally, a possible physical explanation for the destabilization of anatase under pressure is proposed based upon this information.

7.
Angew Chem Int Ed Engl ; 52(40): 10458-62, 2013 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-23913399

RESUMO

The first pressure-induced solid-phase synthesis of a zeolite has been found through compression of a common zeolite, ITQ-29 (see scheme, Si yellow, O red). The new microporous structure, ITQ-50, has a unique structure and improved performance for propene/propane separation with respect the parent material ITQ-29.

8.
Nanotechnology ; 24(20): 205701, 2013 May 24.
Artigo em Inglês | MEDLINE | ID: mdl-23598706

RESUMO

A study based on photoluminescence and absorption measurements as a function of temperature and pressure for PbSe nanocrystals with sizes in the range 3-13 nm reveals the influence of size quantum confinement on the observed variation. In the case of the temperature variation, the effective bandgap changes from showing a positive rate of change to showing a negative one (for a quantum dot 3 nm in diameter), which can be accounted for by incorporating a linear variation of the carrier effective masses into a simple calculation of the exciton ground state in the quantum dot. In the case of the pressure variation, we observe a clear inverse correlation between the absolute value of the pressure coefficient and the nanocrystal size, a signature of quantum size confinement, with values changing from -76 to -41 meV GPa⁻¹ for quantum dots ranging from 13 to 3 nm in diameter, respectively, clearly smaller in absolute value than the rate for bulk PbSe (-84 meV GPa⁻¹). We used again the hypothesis of a linear variation of the carrier effective masses with pressure in order to fit this experimental variation quantitatively.

9.
J Am Chem Soc ; 130(46): 15519-32, 2008 Nov 19.
Artigo em Inglês | MEDLINE | ID: mdl-18937456

RESUMO

The effect of applied pressure on the magnetic properties of the Prussian blue analogue K0.4Fe4[Cr(CN)6]2.8 x 16 H2O (1) has been analyzed by dc and ac magnetic susceptibility measurements. Under ambient conditions, 1 orders ferromagnetically at a critical temperature (T(C)) of 18.5 K. Under application of pressure in the 0-1200 MPa range, the magnetization of the material decreases and its critical temperature shifts to lower temperatures, reaching T(C) = 7.5 K at 1200 MPa. Pressure-dependent Raman and Mossbauer spectroscopy measurements show that this striking behavior is due to the isomerization of some Cr(III)-C[triple bond]N-Fe(II) linkages to the Cr(III)-N[triple bond]C-Fe(II) form. As a result, the ligand field around the iron(II) centers increases, and the diamagnetic low-spin state is populated. As the number of diamagnetic centers in the cubic lattice increases, the net magnetization and critical temperature of the material decrease considerably. The phenomenon is reversible: releasing the pressure restores the magnetic properties of the original material. However, we have found that under more severe pressure conditions, a metastable sample containing 22% Cr(III)-N[triple bond]C-Fe(II) linkages can be obtained. X-ray absorption spectroscopy and magnetic circular dichroism of this metastable sample confirm the linkage isomerization process.


Assuntos
Compostos de Cromo/química , Cianetos/química , Compostos de Ferro/química , Magnetismo , Pressão , Água/química , Raios X , Cristalização , Isomerismo , Análise Espectral , Temperatura , Difração de Raios X
10.
Rev. calid. asist ; 18(7): 570-574, nov. 2003. tab
Artigo em Espanhol | IBECS | ID: ibc-26701

RESUMO

Objetivo: Evaluar, desde el punto de vista clínico y económico, el uso de la anestesia local en la cirugía descompresiva del síndrome del túnel carpiano. Material y métodos: Se evaluaron 229 cirugías descompresivas, realizadas mediante la técnica quirúrgica clásica a cielo abierto. En 138 casos se empleó anestesia local pura en el lugar de la incisión, en 71 la técnica empleada fue la anestesia locorregional intravenosa, y 20 pacientes fueron intervenidos mediante anestesia del plexo braquial. Se evaluó la tolerancia del paciente a la técnica anestésica, mediante la escala analógica visual, referida al dolor durante la aplicación de la anestesia, al dolor del manguito de isquemia y al dolor del paciente durante la intervención. Se evaluaron los resultados finales de la intervención y los costes aproximados de la misma según la anestesia empleada. Resultados: Los resultados finales de la descompresión, así como la frecuencia de complicaciones posquirúrgicas, no estuvieron influidas por el tipo de técnica anestésica empleada. En ninguno de los pacientes en los que se planteó la intervención con anestesia local fue necesario cambiar de técnica. El bloqueo del plexo braquial se acompañó de una mayor duración de la intervención. En los pacientes intervenidos con anestesia local, la tolerancia del manguito de isquemia fue excelente, al igual que la percepción de dolor durante la intervención. Conclusiones: El uso de anestesia local en la cirugía del síndrome del túnel carpiano se tolera bien por parte del paciente y disminuye el coste de dicha intervención (AU)


Assuntos
Adolescente , Adulto , Idoso , Feminino , Masculino , Pessoa de Meia-Idade , Idoso de 80 Anos ou mais , Humanos , Síndrome do Túnel Carpal/cirurgia , Anestesia/métodos , Anestesia/economia , Síndrome do Túnel Carpal/diagnóstico , Análise de Variância , Anestesia por Condução/economia , Anestesia Local/economia , Medição da Dor
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