scholarly journals Exceptional phonon point versus free phonon coupling in Zn1−xBexTe under pressure: an experimental and ab initio Raman study

2022 ◽  
Vol 12 (1) ◽  
Author(s):  
M. B. Shoker ◽  
T. Alhaddad ◽  
O. Pagès ◽  
V. J. B. Torres ◽  
A. V. Postnikov ◽  
...  
Keyword(s):  
Ab Initio ◽  
Mixed Crystals ◽  
Exceptional Point ◽  
Phonon Coupling ◽  
X Ray Diffraction ◽  
X Ray ◽  
Point Versus ◽  
Raman Study ◽  
Effective Transfer

AbstractRaman scattering and ab initio Raman/phonon calculations, supported by X-ray diffraction, are combined to study the vibrational properties of Zn1−xBexTe under pressure. The dependence of the Be–Te (distinct) and Zn–Te (compact) Raman doublets that distinguish between Be- and Zn-like environments is examined within the percolation model with special attention to x ~ (0,1). The Be-like environment hardens faster than the Zn-like one under pressure, resulting in the two sub-modes per doublet getting closer and mechanically coupled. When a bond is so dominant that it forms a matrix-like continuum, its two submodes freely couple on crossing at the resonance, with an effective transfer of oscillator strength. Post resonance the two submodes stabilize into an inverted doublet shifted in block under pressure. When a bond achieves lower content and merely self-connects via (finite/infinite) treelike chains, the coupling is undermined by overdamping of the in-chain stretching until a «phonon exceptional point» is reached at the resonance. Only the out-of-chain vibrations «survive» the resonance, the in-chain ones are «killed». This picture is not bond-related, and hence presumably generic to mixed crystals of the closing-type under pressure (dominant over the opening-type), indicating a key role of the mesostructure in the pressure dependence of phonons in mixed crystals.

scholarly journals Exceptional Phonon Point Versus Free Phonon Coupling in Zn1-xBexTe Under Pressure: An Experimental and ab Initio Raman Study

2021 ◽  
Author(s):  
M. B. Shoker ◽  
T. Alhaddad ◽  
O. Pagès ◽  
V. J. B. Torres ◽  
A. V. Postnikov ◽  
...  
Keyword(s):  
Ab Initio ◽  
Mixed Crystals ◽  
Exceptional Point ◽  
Phonon Coupling ◽  
X Ray Diffraction ◽  
X Ray ◽  
Point Versus ◽  
Raman Study ◽  
Effective Transfer

Abstract Raman scattering and ab initio Raman/phonon calculations, supported by X-ray diffraction, are combined to study the vibrational properties of Zn1-xBexTe under pressure. The dependence of the Be-Te (distinct) and Zn-Te (compact) Raman doublets that distinguish between Be- and Zn-like environments is examined within the percolation model with special attention to x~(0,1). The Be-like environment hardens faster than the Zn-like one under pressure, resulting in the two sub-modes per doublet getting closer and mechanically coupled. When a bond is so dominant that it forms a matrix-like continuum, its two submodes freely couple on crossing at the resonance, with an effective transfer of oscillator strength. Post resonance the two submodes stabilize into an inverted doublet shifted in block under pressure. When a bond achieves lower content and merely self-connects via (finite/infinite) treelike chains, the coupling is undermined by overdamping of the in-chain stretching until a phonon exceptional point is reached at the resonance. Only the out-of-chain vibrations "survive" the resonance, the in-chain ones are "killed". This picture is not bond-related, and hence presumably generic to mixed crystals of the closing-type under pressure (dominant over the opening-type), indicating a key role of the mesostructure in the pressure dependence of phonons in mixed crystals.

Estimation of The Critical Radius for The Nucleation of the C54 Phase in C49 TiSi2: Role of The Difference in Density

1999 ◽  
Vol 580 ◽  
Author(s):  
D.B. Migas ◽  
M. Iannuzzi ◽  
Leo Miglio ◽  
F. La Via ◽  
M.G. Grimaldi
Keyword(s):  
Ab Initio ◽  
Elastic Strain ◽  
Critical Radius ◽  
Lattice Parameters ◽  
X Ray Diffraction ◽  
X Ray ◽  
The Difference ◽  
Two Phases ◽  
The One

AbstractWe discuss the rather scattered measurements of the lattice parameters for C49 TiSi2, which are reported in literature, along with new and accurate X-ray diffraction measurements and ab-initio calculations. Both agree in indicating that the density of the metastable C49 structure cannot be much smaller than the one for the polymorphic C54 phase, as it is commonly reported. We conclude by demonstrating that only in the case of such a smaller difference in density between the two phases, the elastic strain contribution to the nucleation energy of the C54 structure in the C49 matrix can be neglected. The estimation of the critical radius strongly depends on this issue.

scholarly journals Synthesis, Vibrational Spectroscopy and Optical Study of Bi-Tetrabutylphosphonium Hexachlorostannate

2021 ◽  
Author(s):  
I. Mbarek ◽  
M. Ben Gzaiel ◽  
A. Oueslati ◽  
M Gargouri
Keyword(s):  
Powder Diffraction ◽  
Absorption Measurement ◽  
Optical Study ◽  
X Ray Diffraction ◽  
Two Phase ◽  
Monoclinic System ◽  
X Ray ◽  
Optical Absorption Measurement ◽  
Raman Study

Abstract The single crystals of bi-tetrabutylphosphonium hexachlorostannate were grown by solvent evaporated method and characterized by X-ray powder diffraction, Raman spectroscopy and optical study. The X-ray powder diffraction indicates that it was crystallized in the monoclinic system, with C2/c space group. Besides, temperature-controlled X-ray diffraction show that the [P(C4H9)4]2SnCl6 compound indicate the presence of two phase transitions detected at 388 and 403 K. The evolution of Raman line shifts, “ν”, and the half-width, “Δν”, versus temperature show some singularities associated with the transitions, suggesting the important role of the anionic parts ((SnCl6)2-). Besides, the results of the Raman study confirms the conclusion drawn from the X-ray powder diffraction measurements that the phase transition are located near 388K and 403K.Furthermore, an optical absorption measurement confirms the semiconductor nature with a band gap equal to 3.46eV.

Infrared spectroscopic study of the YPO4-YCrO4 system

1985 ◽  
Vol 50 (10) ◽  
pp. 2139-2145
Author(s):  
Alexander Muck ◽  
Eva Šantavá ◽  
Bohumil Hájek
Keyword(s):  
Spectroscopic Study ◽  
Infrared Spectra ◽  
Point Of View ◽  
Mixed Crystals ◽  
Crystal Symmetry ◽  
Infrared Spectroscopic Study ◽  
X Ray Diffraction ◽  
X Ray ◽  
Infrared Spectroscopic ◽  
Diffraction Patterns

The infrared spectra and powder X-ray diffraction patterns of polycrystalline YPO4-YCrO4 samples are studied from the point of view of their crystal symmetry. Mixed crystals of the D4h19 symmetry are formed over the region of 0-30 mol.% YPO4 in YCrO4. The Td → D2d → D2 or C2v(GS eff) correlation is appropriate for both PO43- and CrO43- anions.

Role of the Structure and Electronic Properties of Fe2O3-MoO3 Catalyst on the Dehydration of Isopropyl Alcohol

1993 ◽  
Vol 58 (7) ◽  
pp. 1591-1599 ◽  
Author(s):  
Abd El-Aziz A. Said
Keyword(s):  
Active Sites ◽  
Isopropyl Alcohol ◽  
Oxide Catalyst ◽  
Flow System ◽  
Charge Carriers ◽  
X Ray Diffraction ◽  
X Ray ◽  
Catalyst Composition ◽  
Surface Active

Molybdenum oxide catalyst doped or mixed with (1 - 50) mole % Fe3+ ions were prepared. The structure of the original samples and the samples calcined at 400 °C were characterized using DTA, X-ray diffraction and IR spectra. Measurements of the electrical conductivity of calcined samples with and without isopropyl alcohol revealed that the conductance increases on increasing the content of Fe3+ ions up to 50 mole %. The activation energies of charge carriers were determined in presence and absence of the alcohol. The catalytic dehydration of isopropyl alcohol was carried out at 250 °C using a flow system. The results obtained showed that the doped or mixed catalysts are active and selective towards propene formation. However, the catalyst containing 40 mole % Fe3+ ions exhibited the highest activity and selectivity. Correlations were attempted to the catalyst composition with their electronic and catalytic properties. Probable mechanism for the dehydration process is proposed in terms of surface active sites.

scholarly journals Modeling of magneto-conductivity of bismuth selenide: a topological insulator

2021 ◽  
Vol 3 (4) ◽  
Author(s):  
Yogesh Kumar ◽  
Rabia Sultana ◽  
Prince Sharma ◽  
V. P. S. Awana
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Single Crystal ◽  
Single Crystals ◽  
X Ray Diffraction ◽  
Field Range ◽  
X Ray ◽  
Bulk Carriers ◽  
Different Temperatures

AbstractWe report the magneto-conductivity analysis of Bi2Se3 single crystal at different temperatures in a magnetic field range of ± 14 T. The single crystals are grown by the self-flux method and characterized through X-ray diffraction, Scanning Electron Microscopy, and Raman Spectroscopy. The single crystals show magnetoresistance (MR%) of around 380% at a magnetic field of 14 T and a temperature of 5 K. The Hikami–Larkin–Nagaoka (HLN) equation has been used to fit the magneto-conductivity (MC) data. However, the HLN fitted curve deviates at higher magnetic fields above 1 T, suggesting that the role of surface-driven conductivity suppresses with an increasing magnetic field. This article proposes a speculative model comprising of surface-driven HLN and added quantum diffusive and bulk carriers-driven classical terms. The model successfully explains the MC of the Bi2Se3 single crystal at various temperatures (5–200 K) and applied magnetic fields (up to 14 T).

scholarly journals Crystallization and X-ray diffraction data analysis of human deoxyhaemoglobin A0 fully stripped of any anions

1999 ◽  
Vol 55 (11) ◽  
pp. 1914-1916 ◽  
Author(s):  
F. A. V. Seixas ◽  
W. F. de Azevedo ◽  
M. F. Colombo
Keyword(s):  
Diffraction Data ◽  
Oxygen Affinity ◽  
X Ray Diffraction ◽  
Structural Explanation ◽  
Human Haemoglobin ◽  
X Ray ◽  
High Resolution Structure ◽  
Allosteric Properties

In this work, initial crystallographic studies of human haemoglobin (Hb) crystallized in isoionic and oxygen-free PEG solution are presented. Under these conditions, functional measurements of the O2-linked binding of water molecules and release of protons have evidenced that Hb assumes an unforeseen new allosteric conformation. The determination of the high-resolution structure of the crystal of human deoxy-Hb fully stripped of anions may provide a structural explanation for the role of anions in the allosteric properties of Hb and, particularly, for the influence of chloride on the Bohr effect, the mechanism by which Hb oxygen affinity is regulated by pH. X-ray diffraction data were collected to 1.87 Å resolution using a synchrotron-radiation source. Crystals belong to the space group P21212 and preliminary analysis revealed the presence of one tetramer in the asymmetric unit. The structure is currently being refined using maximum-likelihood protocols.

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