scholarly journals Local and average structures of BaTiO3-Bi(Zn1/2Ti1/2)O3

2016 ◽  
Vol 120 (18) ◽  
pp. 184102 ◽  
Author(s):  
Tedi-Marie Usher ◽  
Thanakorn Iamsasri ◽  
Jennifer S. Forrester ◽  
Natthaphon Raengthon ◽  
Narit Triamnak ◽  
...  
Keyword(s):  
Average Structures

High Resolution Infrared Spectra of the ν2 and 2ν1 Bands of 14N16O2

1975 ◽  
Vol 53 (19) ◽  
pp. 1902-1926 ◽  
Author(s):  
Aldée Cabana ◽  
Michel Laurin ◽  
Walter J. Lafferty ◽  
Robert L. Sams
Keyword(s):  
High Resolution ◽  
Infrared Spectra ◽  
Ground State ◽  
Equilibrium Structure ◽  
Coriolis Interaction ◽  
Rotational Constants ◽  
Average Structures

The infrared spectra of two B type bands, ν2 and 2ν1, of 14N16O2 have been recorded under high resolution. Ground state combination differences from these bands have been combined with combination differences obtained in previous studies and eight pure rotational microwave transitions to yield improved ground state rotational constants. Upper state constants and band centers for the ν2 and 2ν1 bands are also reported. The 2ν1 band contains internal intensity anomalies believed to arise from a weak Coriolis interaction with the much stronger ν1 + ν3 band. Equilibrium rotational constants have been calculated. The equilibrium structure of the molecule is: rc = 1.1945 ± 0.0005 Å and Θc = 133.85 ± 0.10°. For the sake of comparison, effective, substitution, and average structures are also reported.

The chemical nature of supercritical gas extracts from low-rank U. K. coals

1981 ◽  
Vol 300 (1453) ◽  
pp. 183-192 ◽  
Keyword(s):  
Spectroscopic Analysis ◽  
Chemical Nature ◽  
Development Programme ◽  
Low Rank ◽  
Mineral Matter ◽  
Gas Extraction ◽  
Chemical Structures ◽  
Aromatic Clusters ◽  
Methylene Ether ◽  
Average Structures

Two processes are being developed by the National Coal Board for producing liquids from coal. Both involve extraction of the coal to produce an extract, freed from mineral matter, which is then catalytically hydrocracked. This approach is particularly suitable for producing transport fuels and chemical feedstocks. One process uses as solvent a process-derived liquid. The other uses a compressed supercritical gas to extract the more hydrogen-rich parts of the coal, leaving a reactive char which can provide the necessary hydrogen, heat and power for the process. As part of the development programme, extracts have been prepared by gas extraction over a range of conditions, and their chemical structures investigated by elemental and spectroscopic analysis. The average structures so derived consist of small aromatic clusters joined by methylene, ether and diphenyl linkages. Extracts produced by the liquid solvent route contain larger aromatic clusters.

Seismic ground-motion computations at low probabilities

1986 ◽  
Vol 13 (6) ◽  
pp. 595-599
Author(s):  
W. G. Milne ◽  
D. H. Weichert
Keyword(s):  
Ground Motion ◽  
Basic Assumption ◽  
Seismic Source ◽  
Risk Level ◽  
Frequency Of Occurrence ◽  
Probability Level ◽  
Dominant Contribution ◽  
Attenuation Relationships ◽  
Source Zones ◽  
Average Structures

The seismic provisions for the National Building Code of Canada are based on assumptions that seismic source zones can be defined within which earthquakes are distributed uniformly according to a magnitude/frequency-of-occurrence relation, and that a set of attenuation relationships hold for the earthquake magnitudes and distances that dominate the selected risk level of 10% probability of exceedence in 50 years. These assumptions appear to be reasonable at the probability level used for the average structures included in the code. However, attempts of extending the calculations to significantly lower levels of probability for special structures may invalidate the original assumptions, because the dominant contribution ranges of magnitudes and distances are outside of the intended scope of the ground-motion relations. Moreover, the basic assumption that earthquakes are uniformly distributed over large source zones is seriously compromised.

A Vacancy-Disordered, Oxygen-Deficient Perovskite with Long-Range Magnetic Ordering: Local and Average Structures and Magnetic Properties of Sr2Fe1.5Cr0.5O5

2012 ◽  
Vol 51 (4) ◽  
pp. 2638-2644 ◽  
Author(s):  
Farshid Ramezanipour ◽  
John E. Greedan ◽  
Joan Siewenie ◽  
Ronald L. Donaberger ◽  
Stuart Turner ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Long Range ◽  
Magnetic Ordering ◽  
Average Structures

The periodic average structure of particular quasicrystals

1999 ◽  
Vol 55 (1) ◽  
pp. 48-57 ◽  
Author(s):  
Walter Steurer ◽  
Torsten Haibach
Keyword(s):  
Physical Space ◽  
Maximum Distance ◽  
Oblique Projection ◽  
Bond Lengths ◽  
Average Structure ◽  
Lattice Periodicity ◽  
Crystallographic Symmetry ◽  
Quasiperiodic Structures ◽  
Quasiperiodic Structure ◽  
Average Structures

The non-crystallographic symmetry of d-dimensional (dD) quasiperiodic structures is incompatible with lattice periodicity in dD physical space. However, dD quasiperiodic structures can be described as irrational sections of nD (n > d) periodic hypercrystal structures. By appropriate oblique projection of particular hypercrystal structures onto physical space, discrete periodic average structures can be obtained. The boundaries of the projected atomic surfaces give the maximum distance of each atom in a quasiperiodic structure from the vertices of the reference lattice of its average structure. These maximum distances turn out to be smaller than even the shortest atomic bond lengths. The metrics of the average structure of a 3D Ammann tiling, for instance, with edge lengths of the unit tiles equal to the bond lengths in elemental aluminium, correspond almost exactly to the metrics of face-centred-cubic aluminium. This is remarkable since most stable quasicrystals contain aluminium as the main constitutent. The study of the average structure of quasicrystals can be a valuable aid to the elucidation of the geometry of quasicrystal-to-crystal transformations. It can also contribute to the derivation of the physically most relevant Brillouin (Jones) zone.

Structure of Two Disordered Molybdates, Li2MoIVO3 and Li4Mo3 IVO8, from Total Neutron Scattering

1997 ◽  
Vol 53 (4) ◽  
pp. 604-612 ◽  
Author(s):  
S. J. Hibble ◽  
I. D. Fawcett ◽  
A. C. Hannon
Keyword(s):  
Neutron Scattering ◽  
Rietveld Analysis ◽  
Total Neutron ◽  
Bragg Scattering ◽  
Pair Correlations ◽  
X Ray ◽  
Metal Metal ◽  
X Ray Absorption ◽  
Average Structures ◽  
Insight Into

The structures of the disordered lithium molybdates Li2MoO3 and Li4Mo3O8 have been investigated using total neutron scattering from polycrystalline powders. Rietveld analysis of the Bragg scattering is used to determine the average structures. Shortcomings in this method of analysis are demonstrated by comparing the total correlation function, T(r), determined from total neutron scattering, with those calculated from the structures determined from Rietveld analysis. Much more satisfactory models for these materials are derived from the structurally related ordered material LiZn2Mo3O8, using information from Mo K-edge extended X-ray absorption fine-structure spectroscopy (EXAFS). These models include metal–metal-bonded Mo3O13 clusters [d(Mo—Mo) = 2.58 Å in Li2MoO3 and 2.56 Å in Li4Mo3O8] not present in the average structure determined from Rietveld analysis [d(Mo—Mo) = 2.88 Å in Li2MoO3]. In contrast to EXAFS studies neutron diffraction yields information on all the pair correlations in the material, not merely those involving molybdenum, and allows, for example, the location of lithium. Remaining discrepancies between our models and the experimental T(r)'s give an insight into the disorder in the two materials.

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