Average Structure, Local Structure, Photoluminescence, and NLO Properties of Scheelite Type NaCe(WO4)2

AbstractThe local atomic structure of PbZrO3 (PZ) as a function of temperature has been examined using the atomic pair distribution function (PDF) analysis of the pulsed neutron powder-diffraction data. The local structure was found to be deviated significantly from the crystallographic average structure, and to vary less with the composition than the crystallographic average structure. Disordered oxygen octahedral rotations have been observed in the low-temperature antiferroelectric state. With heating the M-type rotation of octahedra becomes dominant and it persists through the intermediate phase into the high-temperature paraelectric state. The Pb displacements reflect these strong deviations, and locally have a large z-component. At room temperature, deviation of Pb displacements from the antiparallel [110] pattern was found. With increasing temperature disorder in the Pb displacement increases.

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Total neutron diffraction: a route to the correct local structure of disordered LaMo2O5 and its application to the model compound Zn2Mo3O8

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768199004103 ◽

1999 ◽

Vol 55 (5) ◽

pp. 683-697 ◽

Cited By ~ 10

Author(s):

Simon J. Hibble ◽

Steven P. Cooper ◽

Saban Patat ◽

Alex. C. Hannon

Keyword(s):

Neutron Diffraction ◽

Local Structure ◽

Model Compound ◽

Group Symmetry ◽

Total Neutron ◽

Space Group Symmetry ◽

Space Group ◽

Average Structure ◽

Local Structures ◽

Insight Into

Analysis of Bragg diffraction is the normal route to the structure of crystalline materials. Here we demonstrate the use of total neutron diffraction in determining the local structure in the disordered lanthanum molybdate LaMo2O5. An average structure with space-group symmetry P63/mmc accounts for the Bragg scattering and shows that the compound contains the rare Mo6O18 cluster and a unique type of Mo—Mo bonded sheet. However, this gives an incomplete picture of the structure, since it does not reveal how the sites with fractional occupancy are occupied at a local level. Two models describing possible local structures are constructed by removing symmetry elements present in the average structure. Total correlation functions, T(r), calculated from these structures, with space-group symmetry P63 mc and P3¯m1, are compared with the experimental T(r) to show the validity of these local structures. The close relationship between the T(r)'s of the component structures gives an insight into why disorder occurs in LaMo2O5. The calculated and experimental T(r)'s for a model compound, Zn2Mo3O8, are compared to show the agreement expected from an ordered crystalline material. Remaining discrepancies between our model and the experimental T(r) give an insight into the origin of additional disorder in LaMo2O5.

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Orientational disorder of monomethyl-quinacridone investigated by Rietveld refinement, structure refinement to the pair distribution function and lattice-energy minimizations

Acta Crystallographica Section B Structural Science Crystal Engineering and Materials ◽

10.1107/s2052520620003984 ◽

2020 ◽

Vol 76 (3) ◽

pp. 353-365

Author(s):

Carina Schlesinger ◽

Sonja M. Hammer ◽

Tatiana E. Gorelik ◽

Martin U. Schmidt

Keyword(s):

Distribution Function ◽

Rietveld Refinement ◽

Local Structure ◽

Pair Distribution Function ◽

Structure Refinement ◽

Lattice Energy ◽

Orientational Disorder ◽

Organic Pigment ◽

Average Structure ◽

Long Range Ordering

The crystal structure of the organic pigment 2-monomethyl-quinacridone (Pigment Red 192, C21H14N2O2) was solved from X-ray powder diffraction data. The resulting average structure is described in space group P\overline 1, Z = 1 with the molecule on the inversion centre. The molecules are arranged in chains. The molecules, which have no inversion symmetry, show orientational head-to-tail disorder. In the average structure, the methyl group is disordered and found on both ends of the molecule with an occupancy of 0.5 each. The disorder and the local structure were investigated using various ordered structural models. All models were analysed by three approaches: Rietveld refinement, structure refinement to the pair distribution function (PDF) and lattice-energy minimization. All refinements converged well. The Rietveld refinement provided the average structure and gave no indication of a long-range ordering. The refinement to the PDF turned out to be very sensitive to small structural details, giving insight into the local structure. The lattice-energy minimizations revealed a significantly preferred local ordering of neighbouring molecules along the [0\bar 11] direction. In conclusion, all methods indicate a statistical orientational disorder with a preferred parallel orientation of molecules in one direction. Additionally, electron diffraction revealed twinning and faint diffuse scattering.

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Local Structure and in-Situ Average Structure Analysis of LiNi0.8Co0.2O2 Electrode during Charge-Discharge Process By Using Quantum Beam

ECS Meeting Abstracts ◽

10.1149/ma2016-02/53/3939 ◽

2016 ◽

Keyword(s):

Structure Analysis ◽

Local Structure ◽

Discharge Process ◽

Average Structure ◽

Charge Discharge

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X-ray microprobe for materials science

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100168013 ◽

1994 ◽

Vol 52 ◽

pp. 56-57

Author(s):

G.E. Ice

Keyword(s):

Crystallographic Orientation ◽

Local Structure ◽

Materials Science ◽

Chemical Information ◽

X Ray Diffraction ◽

Ray Optics ◽

X Ray ◽

Novel Materials ◽

New Information ◽

Elemental Sensitivity

The increasing availability of synchrotron x-ray sources has stimulated the development of advanced hard x-ray (E≥5 keV) microprobes. With new x-ray optics these microprobes can achieve micron and submicron spatial resolutions. The inherent elemental and crystallographic sensitivity of an x-ray microprobe and its inherently nondestructive and penetrating nature will have important applications to materials science. For example, x-ray fluorescent microanalysis of materials can reveal elemental distributions with greater sensitivity than alternative nondestructive probes. In materials, segregation and nonuniform distributions are the rule rather than the exception. Common interfaces to whichsegregation occurs are surfaces, grain and precipitate boundaries, dislocations, and surfaces formed by defects such as vacancy and interstitial configurations. In addition to chemical information, an x-ray diffraction microprobe can reveal the local structure of a material by detecting its phase, crystallographic orientation and strain.Demonstration experiments have already exploited the penetrating nature of an x-ray microprobe and its inherent elemental sensitivity to provide new information about elemental distributions in novel materials.

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