Identifying and explaining vibrational modes of sanbornite (low- BaSi2O5) and Ba5Si8O21: A joint experimental and theoretical study

We report here the analysis of vibrational properties of the sanbornite (low-BaSi2O5) and Ba5Si8O21 using theoretical and experimental approaches, as well as results of high temperature experiments up to 1100-1150 ̊C. The crystal parameters derived from Rietveld refinement and calculations show excellent agreement, within 4%, while the absolute mean difference between the theoretical and experimental results for the IR and Raman vibrational frequencies was <6 cm -1. The temperature-dependent Raman study renders that both sanbornite and Ba5Si8O21 display21 specific Ba and Si sites and their Ba-O and Si-O bonds. In the case of the stretching modes assigned to specific Si sites, the frequency dependence on the Si-O bond length exhibited very strong correlations. Both phases showed that for a change of 0.01 Å, the vibrational mode shifted 10 ± 2 cm-1. These results are promising for using Raman spectroscopy to track in situ reactions under a wide variety of conditions, especially during crystallization

Influence of synthesis conditions on carbonate entrapment in perovskite SrSnO 3

Strontium stannate (SrSnO 3 ), a perovskite material, was synthesized by the polymeric precursor method, with different routes to eliminate organic matter. The utilization of pure oxygen for the elimination of organic matter changed the Raman spectra, especially in the low frequency region. Some peaks, which were previously assigned to the perovskite phase, were not noticed when the carbonate amount was lower. On the other hand, the profile of the IR spectra and XRD patterns did not change. These results suggest that carbonate may be present inside the perovskite lattice

Efectos estructurales en el semiconductor insb, por la aplicación de diferentes métodos de presión

This paper studies the modifications suffered by the Indium Antimonnide (InSb), grown in the [100], when subjected to mechanical tests of micro-indentations, high hydrostatic pressure and pressure impact. Tomographic surveying and samples were made by micro-Raman spectroscopy with different wavelengths of excitation light. The shift of the position of the phonons and the emergence of new Raman peaks allow both chemical and structural analysis of the systemEn este trabajo se estudia las modificaciones sufridas por el Antimoneto de Indio (InSb), crecido en la dirección [100], cuando es sometido a testes de micro-indentación mecánica, altas presiones hidrostáticas y presión por impacto. Los estudios topográficos y tomográficos de las muestras fueron hechos por medio de espectroscopia micro-Raman con diferentes longitudes de onda de la luz de excitación. El corrimiento de la posición de los fonones y el surgimiento de nuevos picos Raman permite el análisis tanto químico como estructural del sistema en estudi

Efectos estructurales en el semiconductor insb, por la aplicación de diferentes métodos de presión

En este trabajo se estudia las modificaciones sufridas por el antimoneto de indio (InSb), crecido en la dirección [100], cuando es sometido a testes de micro-indentación mecánica, altas presiones hidrostáticas y presión por impacto. Los estudios topográficos y tomográficos de las muestras fueron hechos por medio de espectroscopia micro-Raman con diferentes longitudes de onda de la luz de excitación. El corrimiento de la posición de los fonones y el surgimiento de nuevos picos Raman permite el análisis tanto químico como estructural del sistema en estudio

Combining Raman spectroscopy and synchrotron X-ray diffraction to unveil the order types in A3CaNb2O9 (A = Ba, Sr) complex perovskites

[EN] The structural ordering process in complex perovskites has a pivotal role for tuning many physical properties for broad applications, ranging from microwave technology, proton-conduction, multiferroicity, and so on. Therefore, the characterization of order type in these materials is essential for designing new devices with high-performance. Here, the coexistence of B-site 1:1 and 1:2 order types in mixed ordered ACaNbO (A = Ba, Sr) perovskite was investigated by combining Raman spectroscopy and high-resolution synchrotron X-ray powder diffraction. High-wavenumber interval 700–825 cm exhibits two bands concerning the symmetric breathing modes of [NbO] octahedra in ACaNbO, which were ascribed to the 1:1 and 1:2 domain regions in coexistence. This model was fully corroborated using two phases for describing the synchrotron X-ray pattern of the BaCaNbO sample. Therefore, the Raman spectroscopy can be indeed applied as a rapid tool for probing the achievement of ordered, partially ordered, or disordered structures in complex perovskites. For the first time, BaLaCaNbO was synthesized and structural characterized, being indexed by the monoclinic unit cell belonging to the space group (Formula presented.).Ministerio de Ciencia e Innovación, Grant/Award Number: MAT2017-84496-R; Spanish Ministry of Science, Innovation, and Universities; FAPESP, Grant/Award Number: 13/07793-

Preparação de LiNbO3 e LiNbO3:Eu3+ pelo método dos precursores poliméricos

The ferroelectric compound LiNbO3 was prepared by the polymeric precursors method in the polycrystalline form containing different concentrations of Eu3+. The compounds were characterized by X-ray diffraction, vibrational and electronic spectroscopy. Electronic spectroscopy was shown to be sensitive to small concentrations of contaminating phases allowing a good control of the compound purity. The presence of Eu3+ ions leads to the formation of the LiNb3O8 phase in the range of 500 to 800 degreesC. Above this temperature range LiNbO3 and tetragonal (T') EuNbO4 were obtained

A theoretical and experimental investigation of hetero- vs. homo-connectivity in barium silicates

Barium silicates may be found in contact aureoles and are used in several important technologies (e.g., LEDs). The BaO-SiO2 system stabilizes 13 crystalline phases with different silicate tetrahedral and connectivity profiles. Aside from phases composed of a single structural unit (isolated or homo-connected tetrahedra), one encounters the relatively rare case of hetero-connected tetrahedra in which varying proportions of several Qn species are linked together. Here, we analyze the 29Si MAS NMR and Raman spectroscopic manifestations of the connectivities in seven barium silicates: Ba2SiO4, high-BaSiO3, Ba4Si6O16, Ba5Si8O21, Ba6Si10O26, high-BaSi2O5, and sanbornite (low-BaSi2O5). The structures and purity of these phases were confirmed by Rietveld refinement. From a Raman spectroscopic database of 144 predominantly homo-connected crystalline silicates, the mean Qn mode frequencies νQn (±1σ) are found at 828 (±14) cm−1 for Q0, 905 (±22) cm−1 for Q1, 994 (±26) cm−1 for Q2, and 1068 (±18) cm−1 for Q3 units. Experimentally, homo-connected barium silicates show good agreement with these values, whereas the hetero-connected phases show a wider range of νQ2 than of νQ3 frequencies. While the 29Si NMR chemical shifts of the barium silicates are in agreement with known structural trends, those measured for the Q2 resonances remain essentially constant, which may be caused by the lattice distortion around the large Ba2+ cations. To complement and rationalize experimental measurements, first-principles calculations at the density functional theory level have reproduced measured frequencies within a mean absolute deviation of <7 cm−1. Our work highlights how the results provided by 29Si NMR and Raman spectroscopies and ab initio calculations can be combined to rationalize the structure of complex systems. The present findings also shed light on the vibrational modes that may be used to track bond lengths in situ at extreme conditions and the behavior of homo- vs. hetero-connectivity, revealing clear implications for evaluating silicate glasses and melts where hetero-connectivity is the rule rather than the exception.We thank Mario Tribaudino and the referees for their critical comments, which have and will continue to improve this research. B.J.A.M., T.R.C., and C.D. are grateful to the SAo Paulo Research Foundation (FAPESP) for funding this research through post-doctoral fellowship grants: 2016/18567-5, 2019/12383-8, and 2017/06649-0. The work was further supported by FAPESP grant number 2013/07793-6. We appreciate the support of CNPq and CAPES support to PSP. B.J.A.M. thanks Harold Lozano (NMR experiments), Millena Logrado (precursor NMR data reduction), and Valmor Mastelaro for making this collaboration possible. E.O.G. acknowledges Generalitat Valenciana for the Santiago Grisolia program (2018/064). E.O.G. and J.A. acknowledge financial support from Universitat Jaume I, for project UJI-B2019-30. EY.O.G., J.A., and L.G. appreciate support from the Ministerio de Ciencia, Innovacion y Universidades (Spain) project PGC2018-094417-B-I00. We also thank the Servei d'Informatica, Universitat Jaume I, for their generous allocation of computer time

Surface amorphization in diamond turning of silicon crystal investigated by transmission electron microscopy

Silicon crystal exhibits a ductile regime during machining prior to the onset of fracture when appropriate cutting conditions are applied. The present study shows that the ductile regime is a result of a phase transformation which is indirectly evidenced by the amorphous phase detected in the machined surface. Transmission electron microscopy (TEM) planar view studies were successfully performed on monocrystalline silicon (1 0 0) single point diamond turned. TEM electron diffraction patterns show that the machined surface presents diffuse rings along with traces of crystalline material. This is attributed to crystalline silicon immersed in an amorphous matrix. Furthermore, only diffuse rings in the diffraction patterns of the ductile chip are detected, indicating that it is totally amorphous. © 2000 Elsevier Science B.V. All rights reserved