scholarly journals Структура и динамика решетки редкоземельных станнатов R-=SUB=-2-=/SUB=-Sn-=SUB=-2-=/SUB=-O-=SUB=-7-=/SUB=- (R=La-Lu): ab initio расчет

2021 ◽  
Vol 63 (7) ◽  
pp. 952
Author(s):  
В.А. Чернышев
Keyword(s):  
Rare Earth ◽  
Ab Initio ◽  
Phonon Modes ◽  
Rare Earth Ion ◽  
Third Order ◽  
Displacement Vectors ◽  
Degree Of Participation ◽  
Murnaghan Equation ◽  
First Time ◽  
Ir And Raman

The ab initio study of the structure and dynamics of the lattice, as well as the elastic properties of a row of rare-earth stannates R2Sn2O7 (R = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) has been carried out for first time. The IR and Raman spectra were calculated, the types of phonon modes were determined. The degree of participation of ions in phonon modes is determined. Modes with the absolute or predominant participation of oxygen in the 48f position, characterized by a shift x, were determined from an analysis of the displacement vectors obtained from the ab initio calculations. The elastic constants and the hardness HV have been calculated. The effect of hydrostatic compression on the crystal structure is investigated. It is shown that the degree of distortion of the octahedron containing the rare-earth ion changes little with pressure (up to 12 GPa). It is shown that the dependence of the unit cell volume on pressure is described by the Birch-Murnaghan equation of state of the third order.

scholarly journals Фононный спектр и упругие свойства Y-=SUB=-2-=/SUB=-Sn-=SUB=-2-=/SUB=-O-=SUB=-7-=/SUB=-

2021 ◽  
Vol 129 (8) ◽  
pp. 1027
Author(s):  
В.А. Чернышев ◽  
К.И. Глухов ◽  
П.А. Агзамова
Keyword(s):  
Ab Initio ◽  
Elastic Constants ◽  
Phonon Modes ◽  
Displacement Vectors ◽  
Raman Modes ◽  
Impurity Centers ◽  
Ab Initio Approach ◽  
Degree Of Participation ◽  
Impurity Ion ◽  
Ir And Raman

In the framework of a unified ab initio approach, the phonon spectrum of yttrium stannate Y2Sn2O7 was calculated, the frequencies and types of IR and Raman modes were determined. From an analysis of the displacement vectors obtained in ab initio calculations, the degree of participation of ions in phonon modes is determined. The elastic constants and hardness of Y2Sn2O7 are calculated. The distance "impurity ion-ligand" in impurity centers Y2Sn2O7: Yb3 +, Y2Sn2O7: Eu3 +, Lu2Sn2O7: Yb3 +, Nd2Sn2O7: Gd3 +, Nd2Sn2O7: Tb3 + is calculated.

scholarly journals Структура и динамика решетки тетрагональных германатов R-=SUB=-2-=/SUB=-Ge-=SUB=-2-=/SUB=-O-=SUB=-7-=/SUB=- (R=Tb-Lu, Y): ab initio расчет

2021 ◽  
Vol 63 (6) ◽  
pp. 797
Author(s):  
В.С. Рюмшин ◽  
В.А. Чернышев
Keyword(s):  
Ab Initio ◽  
Raman Spectra ◽  
Ab Initio Calculation ◽  
Density Functional ◽  
Ir And Raman Spectra ◽  
Displacement Vectors ◽  
Raman Modes ◽  
Degree Of Participation ◽  
First Time ◽  
Ir And Raman

Within the framework of density functional theory, an ab initio calculation was carried out to study the crystal structure, phonon spectrum and elastic constants of a series of rare-earth germanates, including yttrium germanate R2Ge2O7 (R = Tb-Lu, Y) with tetragonal structure. The frequencies and types of fundamental vibrations as well as the intensities of the IR and Raman modes were determined. The degree of participation of ions in each mode was determined from the analysis of the displacement vectors obtained from the ab initio calculation. The calculations were performed for the first time. The corresponding experimental data for the entire series, with the exception of the IR and Raman spectra of yttrium germanate, are absent. The calculations made it possible to interpret and supplement available in the scientific articles results of measurements of the IR and Raman spectra of yttrium germanate Y2Ge2O7.

Elasticity and high-pressure structure of arsenoflorencite-(La): insights into the high-pressure behaviour of the alunite supergroup

2012 ◽  
Vol 76 (4) ◽  
pp. 975-985 ◽  
Author(s):  
S. J. Mills ◽  
F. Nestola
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Phase Transformation ◽  
Volume Data ◽  
Third Order ◽  
X Ray ◽  
Compression Mechanism ◽  
Internal Angle ◽  
Murnaghan Equation ◽  
First Time

AbstractArsenoflorencite-(La), ideally LaAl3(AsO4)2(OH)6, was studied at high pressure by single-crystal X-ray diffractometry. The unit cell was determined at nine pressures up to 7.471(8) GPa; no evidence of a phase transformation was found in this range. The pressure volume data (refined simultaneously) were fitted to a third-order Birch Murnaghan equation of state which gave V0 = 710.71(8) Å3, KT0 = 106(2) GPa and K' = 9.2(9). These values were confirmed independently from an FE–fE plot. The crystal structure was refined at 1.596, 3.622, 5.749 and 7.471 GPa, the first time this has been done for a member the alunite supergroup. The compressibility of arsenoflorencite-(La) is strongly anisotropic, with βc > βa. The main compression mechanism was found to be governed by the internal angle O3 La O2 of the La polyhedron, where the O2 and O3 atoms move toward the c axis during compression.

Structural and Vibrational Properties of Crystals with a Rare-Earth Sublattice: Ab Initio Calculations

2018 ◽  
Vol 271 ◽  
pp. 85-91
Author(s):  
Vladislav P. Petrov ◽  
Vladimir A. Chernyshev ◽  
Anatoly E. Nikiforov
Keyword(s):  
Rare Earth ◽  
Ab Initio ◽  
Density Functional ◽  
Periodic Structures ◽  
X Ray Diffraction ◽  
Rare Earth Ion ◽  
Hartree Fock ◽  
Lcao Approximation ◽  
Local Contribution ◽  
Non Local

We investigated the crystal structure, vibrational and elastic properties of crystals with a rare-earth sublattice related to different structural types at ab initio level of modeling: elpasolite Cs2NaRF6 −> pyrochlore R2Ti2O7 −> ferroborate RFe3(BO3)4, where R is a rare-earth ion or yttrium. The calculations were performed in the framework of a density functional theory using the hybrid functionals containing local and non-local contribution (i.e. Hartree-Fock exchange term) to the exchange energy. We used CRYSTAL program for simulating periodic structures in the MO LCAO approximation. To describe the internal shell of a rare-earth ion up to 4f, we used the nonrelativistic pseudopotential («4f-in-core») that describes the effect of internal electrons on the outer valence shells. The results of the calculations are in good agreement with the available experimental data of IR and Raman experiments, X-ray diffraction analysis for the rows of elpasolites, pyrochlores and ferroborates.

scholarly journals The Crystal Structure of Rare-Earth Impurity Centers R3+ in MeF2: ab initio Calculation

2019 ◽  
Vol 14 (4) ◽  
pp. 91-102
Author(s):  
V. A. Chernyshev ◽  
A. V. Arkhipov
Keyword(s):  
Crystal Structure ◽  
Rare Earth ◽  
Ab Initio ◽  
Periodic Structures ◽  
Hybrid Functional ◽  
Rare Earth Ion ◽  
Hartree Fock ◽  
Impurity Centers ◽  
Angular Coordinates ◽  
Impurity Ion

Ab initio calculations of the impurity centers R3+ (R = La – Lu) in CaF2 were carried out. The calculations were performed by using hybrid functional which takes into account both local and nonlocal (at the Hartree – Fock formalism) exchange. The crystal structure of impurity centers was investigated. The distance “rare-earth ion – ligand”, the radial and angular coordinates of the ions at several coordination spheres near to the impurity ion are determined. Calculations were carried out in the program CRYSTAL17, designed to simulate periodic structures within the MO LCAO approach.

scholarly journals Phonons in Short-Period GaN/AlN Superlattices: Group-Theoretical Analysis, Ab initio Calculations, and Raman Spectra

Nanomaterials ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 286
Author(s):  
Valery Davydov ◽  
Evgenii Roginskii ◽  
Yuri Kitaev ◽  
Alexander Smirnov ◽  
Ilya Eliseyev ◽  
...  
Keyword(s):  
Theoretical Analysis ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Raman Spectra ◽  
Density Functional ◽  
Structural Characteristics ◽  
Vibrational Modes ◽  
Phonon Modes ◽  
Short Period ◽  
Group Theoretical Analysis

We report the results of experimental and theoretical studies of phonon modes in GaN/AlN superlattices (SLs) with a period of several atomic layers, grown by submonolayer digital plasma-assisted molecular-beam epitaxy, which have a great potential for use in quantum and stress engineering. Using detailed group-theoretical analysis, the genesis of the SL vibrational modes from the modes of bulk AlN and GaN crystals is established. Ab initio calculations in the framework of the density functional theory, aimed at studying the phonon states, are performed for SLs with both equal and unequal layer thicknesses. The frequencies of the vibrational modes are calculated, and atomic displacement patterns are obtained. Raman spectra are calculated and compared with the experimental ones. The results of the ab initio calculations are in good agreement with the experimental Raman spectra and the results of the group-theoretical analysis. As a result of comprehensive studies, the correlations between the parameters of acoustic and optical phonons and the structure of SLs are obtained. This opens up new possibilities for the analysis of the structural characteristics of short-period GaN/AlN SLs using Raman spectroscopy. The results obtained can be used to optimize the growth technologies aimed to form structurally perfect short-period GaN/AlN SLs.

scholarly journals Structure, Luminescence, and Magnetic Properties of Crystalline Manganese Tungstate Doped with Rare Earth Ion

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3717
Author(s):  
Jae-Young Jung ◽  
Soung-Soo Yi ◽  
Dong-Hyun Hwang ◽  
Chang-Sik Son
Keyword(s):  
Magnetic Field ◽  
Rare Earth ◽  
Sintering Temperature ◽  
Luminescent Properties ◽  
Concentration Quenching ◽  
Rare Earth Ions ◽  
Precipitation Method ◽  
Rare Earth Ion ◽  
Co Precipitation ◽  
Quenching Phenomenon

The precursor prepared by co-precipitation method was sintered at various temperatures to synthesize crystalline manganese tungstate (MnWO4). Sintered MnWO4 showed the best crystallinity at a sintering temperature of 800 °C. Rare earth ion (Dysprosium; Dy3+) was added when preparing the precursor to enhance the magnetic and luminescent properties of crystalline MnWO4 based on these sintering temperature conditions. As the amount of rare earth ions was changed, the magnetic and luminescent characteristics were enhanced; however, after 0.1 mol.%, the luminescent characteristics decreased due to the concentration quenching phenomenon. In addition, a composite was prepared by mixing MnWO4 powder, with enhanced magnetism and luminescence properties due to the addition of dysprosium, with epoxy. To one of the two prepared composites a magnetic field was applied to induce alignment of the MnWO4 particles. Aligned particles showed stronger luminescence than the composite sample prepared with unsorted particles. As a result of this, it was suggested that it can be used as phosphor and a photosensitizer by utilizing the magnetic and luminescent properties of the synthesized MnWO4 powder with the addition of rare earth ions.

Darstellung, Schwingungsspektren und Normalkoordinatenanalyse von Chloro-Bromo-Rhodaten(III) / Preparation, Vibration Spectra and Normal Coordinate Analysis of Chloro-Bromo-Rhodates(III)

1989 ◽  
Vol 44 (10) ◽  
pp. 1221-1227 ◽  
Author(s):  
W. Preetz ◽  
W. Kuhr
Keyword(s):  
Exchange Chromatography ◽  
Trans Isomers ◽  
Normal Coordinate ◽  
Valence Force ◽  
Trans Influence ◽  
Diethylaminoethyl Cellulose ◽  
Point Groups ◽  
First Time ◽  
Ir And Raman ◽  
Good Agreement

The mixed chloro-bromo-rhodates(III) [RhClnBr6-n]3-, n = 1-5, have been separated for the first time by ion exchange chromatography on diethylaminoethyl-cellulose. Due to the stronger trans-effect of Br, as compared with Cl, on treatment of [RhBr6]3- with conc. HCl nearly pure cis/fac-isomers for n = 2, 3, 4 are formed. The reaction of [RhCl6]3- with conc. HBr yields mixtures of the cis/trans-isomers for n = 2, 4, which cannot be separated, but mer-[RhCl3Br3]3 is formed stereospecifically. The IR and Raman spectra of all isolated mixed ligand complexes are completely assigned according to point groups Oh, D3d, C4v, C3v and C2v, supported by normal coordinate analyses based on a general valence force field. The good agreement of calculated and observed frequencies confirms the assignments. Due to the stronger trans-influence of Br as compared to Cl, in all asymmetric Cl—Rh—Br axes the Rh—Br bonds are strengthened and the Rh—Cl bonds are weakened, indicated by valence force constants for Rh—Br approximately 14% higher, for Rh—Cl 10% lower, as compared with the values calculated for symmetric Br—Rh—Br and Cl—Rh—Cl axes, respectively.

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