Compositely modulated structures of phosphor materials Sr x Li2+x Al2–x O4:Eu2+

2020 ◽  
Vol 76 (1) ◽  
pp. 76-84
Author(s):  
Atsushi Ooishi ◽  
Yuichi Michiue ◽  
Shiro Funahashi ◽  
Takashi Takeda ◽  
Naoto Hirosaki
Keyword(s):  
Linear Connection ◽  
X Ray Diffraction ◽  
Interatomic Distances ◽  
3D Space ◽  
Modulated Structures ◽  
Commensurate Phase ◽  
Conventional Manner ◽  
Composite Crystals ◽  
D Model ◽  
Incommensurate Phases

Composite crystals Sr x Li2+ x Al2−x O4:Eu2+ were synthesized and their structures were determined using single-crystal X-ray diffraction. The commensurate structure with a modulation wavevector q = 5c*/6 was analyzed in a conventional manner in 3D space, while a structure model in (3+1)-dimensional superspace was used for the other two crystals with modulation wavevectors slightly differing from 5c*/6. The superstructure of the commensurate phase was described using the space group P4/n and a common superspace group I4/m(00γ)00 was used for the (3+1)D structures of all three crystals. The whole structure of each crystal consists of two substructures. Basis vectors a and b are common, but c is different for the two substructures. The first substructure is a host framework constructed by (Li/Al)O4 tetrahedra sharing edges. A linear connection of cavities is seen to be channel-like, in which Sr ions locate as guest cations forming the second substructure. The crystal of q = 5c*/6 contains five Sr ions per six cavities in a channel. Sr ions are distributed at seven sites, some of which are partially occupied. Statistical disorder of local structure models for the location of Sr ions in the channel was assumed to explain the results. Such a partially disordered character was also seen in the incommensurate phases and properly embodied by a (3+1)D model containing an atomic domain of the Sr ion with occupational modulation. Plots of the occupation factor, interatomic distances and the bond valence sum at each metal site as functions of t (= x 4 − q·r) are roughly identical in the three crystals, which are considered as members of the same series of composite crystals.

Structural Analysis of Cs2HgBr4 in Normal, Incommensurate and Twinned Phases

1998 ◽  
Vol 54 (3) ◽  
pp. 197-203 ◽  
Author(s):  
C. B. Pinheiro ◽  
A. Jório ◽  
M. A. Pimenta ◽  
N. L. Speziali
Keyword(s):  
Room Temperature ◽  
Local Symmetry ◽  
Ordered Structure ◽  
X Ray Diffraction ◽  
Orientational Disorder ◽  
X Ray ◽  
Disordered Models ◽  
Commensurate Phase ◽  
Extra Peak ◽  
Incommensurate Phases

X-ray diffraction and Raman spectroscopy experiments have been used to investigate different phases of Cs2HgBr4, dicesium mercury tetrabromide, from room temperature to 213 K. Structural analyses have shown that the crystal could be described, in the normal and in the incommensurate phases, both by ordered and disordered models, but the latter gave more consistent results. Raman results corroborate the descriptions based on X-ray analysis; the presence of an extra peak, which according to group theory should be forbidden in an ordered structure, indicates the lack of local symmetry and was associated with an orientational disorder of [HgBr4]2− tetrahedra. In the transition from the incommensurate to the commensurate phase a multi-soliton behavior was observed. The Cs2HgBr4 crystal in the low-temperature commensurate phase is composed of two types of ordered pseudomerohedral twinned domains.

Investigations of Actinide Metals and Compounds under Pressure Provide Important Insights into Bonding and Chemistry

2003 ◽  
Vol 802 ◽  
Author(s):  
R. G. Haire ◽  
S. Heathman ◽  
T. Le Bihan ◽  
A. Lindbaum ◽  
M. Iridi
Keyword(s):  
Structural Changes ◽  
Chemical Properties ◽  
X Ray Diffraction ◽  
Interatomic Distances ◽  
X Ray ◽  
Effect Of Pressure ◽  
Electronic Configurations ◽  
5F Electrons ◽  
Actinide Series ◽  
Alloys And Compounds

ABSTRACTOne effect of pressure on elements and compounds is to decease their interatomic distances, which can bring about dramatic perturbations in their electronic nature and bonding, which can be reflected in changes in physical and/or chemical properties. One important issue in the actinide series of elements is the effect of pressure on the 5f-electrons. We have probed changes in electronic behavior with pressure by monitoring structure by X-ray diffraction, and have studied several actinide metals and compounds from thorium through einsteinium. These studies have employed angle dispersive diffraction using synchrotron radiation, and energy dispersive techniques via conventional X-ray sources. The 5f-electrons of actinide metals and their alloys are often affected significantly by pressure, while with compounds, the structural changes are often not linked to the involvement of 5 f-electron. We shall present some of our more recent findings from studies of selected actinide metals, alloys and compounds under pressure. A discussion of the results in terms of the changes in electronic configurations and bonding with regard to the element's position in the series is also addressed.

Commensurate and Incommensurate Phases at Reconstructed (In,Ga)As(001) Surfaces: X-Ray Diffraction Evidence for a Composition Lock-in

1995 ◽  
Vol 75 (19) ◽  
pp. 3485-3488 ◽  
Author(s):  
M. Sauvage-Simkin ◽  
Y. Garreau ◽  
R. Pinchaux ◽  
M. B. Véron ◽  
J. P. Landesman ◽  
...  
Keyword(s):  
X Ray Diffraction ◽  
X Ray ◽  
Lock In ◽  
Incommensurate Phases

Structure determination of modulated structures by powder X-ray diffraction and electron diffraction

2016 ◽  
Vol 3 (11) ◽  
pp. 1351-1362 ◽  
Author(s):  
Zhengyang Zhou ◽  
Lukáš Palatinus ◽  
Junliang Sun
Keyword(s):  
Electron Diffraction ◽  
Structure Determination ◽  
X Ray Diffraction ◽  
X Ray ◽  
Modulated Structures ◽  
Conventional Methods

The combination of PXRD and ED is applied to determine modulated structures which resist solution by more conventional methods.

On the effect of Ga and In substitutions in the Ca11Bi10and Yb11Bi10bismuthides crystallizing in the tetragonal Ho11Ge10structure type

2018 ◽  
Vol 74 (3) ◽  
pp. 269-273 ◽  
Author(s):  
Alexander Ovchinnikov ◽  
Svilen Bobev
Keyword(s):  
Bond Length ◽  
Length Distribution ◽  
Structural Response ◽  
Structure Type ◽  
First Principle ◽  
X Ray Diffraction ◽  
Interatomic Distances ◽  
X Ray ◽  
Type Bond ◽  
Bond Length Distribution

The Ga- and In-substituted bismuthides Ca11GaxBi10–x, Ca11InxBi10–x, Yb11GaxBi10–x, and Yb11InxBi10–x(x< 2) can be readily synthesized employing molten Ga or In metals as fluxes. They crystallize in the tetragonal space groupI4/mmmand adopt the Ho11Ge10structure type (Pearson codetI84; Wyckoff sequencen2m j h2e2d). The structural response to the substitution of Bi with smaller and electron-poorer In or Ga has been studied by single-crystal X-ray diffraction methods for the case of Ca11InxBi10–x[x= 1.73 (2); octabismuth undecacalcium diindium]. The refinements show that the In atoms substitute Bi only at the 8hsite. The refined interatomic distances show an unconventional – for this structure type – bond-length distribution within the anionic sublattice. The latter can be viewed as consisting of isolated Bi3−anions and [In4Bi820−] clusters for the idealized Ca11In2Bi8model. Formal electron counting and first-principle calculations show that the peculiar bonding in this compound drives the system toward an electron-precise state, thereby stabilizing the observed bond-length pattern.

scholarly journals Ba5(IO6)2: crystal structure evolution from room temperature to 80 K

2021 ◽  
Vol 77 (6) ◽  
pp. 634-637
Author(s):  
David Wenhua Bi ◽  
Priya Ranjan Baral ◽  
Arnaud Magrez
Keyword(s):  
Crystal Structure ◽  
Room Temperature ◽  
Structural Transition ◽  
Rietveld Method ◽  
Structural Parameters ◽  
Structure Evolution ◽  
X Ray Diffraction ◽  
Lattice Contraction ◽  
Interatomic Distances ◽  
Crystallographic Axes

The crystal structure of Ba5(IO6)2, pentabarium bis(orthoperiodate), has been re-investigated at room temperature based on single-crystal X-ray diffraction data. In comparison with a previous crystal structure determination by the Rietveld method, an improved precision of the structural parameters was achieved. Additionally, low-temperature measurements allowed the crystal structure evolution to be studied down to 80 K. No evidence of structural transition was found even at the lowest temperature. Upon cooling, the lattice contraction is more pronounced along the b axis. This contraction is found to be inhomogeneous along different crystallographic axes. The interatomic distances between different Ba atoms reduce drastically with lowering temperature, resulting in a closer packing around the IO6 octahedra, which remain largely unaffected.

The Structure of Polyisoprenes. II. The Structure of β-Gutta-Percha

1945 ◽  
Vol 18 (2) ◽  
pp. 280-283
Author(s):  
G. A. Jeffrey
Keyword(s):  
Molecular Structure ◽  
Double Bond ◽  
Diffraction Data ◽  
X Ray Diffraction ◽  
Interatomic Distances ◽  
Methyl Group ◽  
X Ray ◽  
Gutta Percha ◽  
Qualitative Estimate

Abstract The x-ray diffraction data at present available from β-gutta-percha are shown to be insufficient to distinguish fine details of molecular structure. Since a qualitative estimate of the intensities on the fibre diagram can be adequately satisfied by a model having normal interatomic distances and valency angles, no evidence exists for the improbable distortion of the methyl group out of the plane of the double bond previously ascribed to the molecule.

scholarly journals Sodium carbonate revisited

2003 ◽  
Vol 59 (3) ◽  
pp. 337-352 ◽  
Author(s):  
Michal Dusek ◽  
Gervais Chapuis ◽  
Mathias Meyer ◽  
Vaclav Petricek
Keyword(s):  
Sodium Carbonate ◽  
Harmonic Approximation ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Anhydrous Sodium Carbonate ◽  
First Order ◽  
Commensurate Phase ◽  
Na Ions ◽  
Fifth Order ◽  
First Time

We present the structure of anhydrous sodium carbonate at room temperature (phase γ) and 110 K (phase δ) based on single-crystal X-ray diffraction data. The incommensurate phase γ was determined almost 30 years ago in the harmonic approximation using one modulation wave and first-order satellites. In our work we use satellites up to fifth order and additional harmonic waves to model the anharmonic features of the structure. The commensurate phase δ is presented for the first time. Using the superspace approach, both phases are compared in order to find common trends in the whole range of the sodium carbonate phases. We present arguments supporting the hypothesis that the driving force of the phase transitions may originate in the unsaturated bonding potential of one of the Na ions.

Full-Profile Approximation of the X-Ray Diffractogram for Nanographite Powder Including γ-Band by Taking into Account Radial Dependence of Interatomic Distances

2018 ◽  
Vol 386 ◽  
pp. 394-399
Author(s):  
Nikita S. Saenko ◽  
Albert M. Ziatdinov
Keyword(s):  
Structural Parameters ◽  
Radial Dependence ◽  
Angular Range ◽  
X Ray Diffraction ◽  
Interatomic Distances ◽  
Diffraction Profile ◽  
Percentage Content ◽  
X Ray ◽  
Full Profile

This paper outlines the procedure for determining the sizes, structural parameters and percentage content of various particle types in nanographite powders by full-profile approximation of the X-ray diffractogram of sample with using a set of X-ray diffraction profiles for powders of model nanographites. It was shown that taking into account the model nanographites with the radial dependence of interatomic distances within the layer and the dependence of interlayer distances on average number of atoms in the layer allows to describe the X-ray diffraction profile of nanographite powder in the wide angular range including so-called γ-band in small angles without assumptions on presence of other structures in it.

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