Structure change of monoclinic ZrO2 baddeleyite involving softenings of bulk modulus and atom vibrations

2019 ◽  
Vol 75 (4) ◽  
pp. 742-749
Author(s):  
Hiroshi Fukui ◽  
Manato Fujimoto ◽  
Yuichi Akahama ◽  
Asami Sano-Furukawa ◽  
Takanori Hattori
Keyword(s):  
Bulk Modulus ◽  
Ab Initio ◽  
Powder Diffraction ◽  
Structure Change ◽  
Neutron Powder Diffraction ◽  
The Other ◽  
Vibrational Modes ◽  
Oxygen Sublattice ◽  
Monoclinic Zro2 ◽  
Pressure Evolution

Monoclinic ZrO2 baddeleyite exhibits anomalous softenings of the bulk modulus and atom vibrations with compression. The pressure evolution of the structure is investigated using neutron powder diffraction combined with ab initio calculations. The results show that the anomalous pressure response of the bulk modulus is related not to the change in the bonding characters but to the deformation of an oxygen sublattice, especially one of the layers made of oxygen atoms in the crystallographic a* plane. The layer consists of two parallelograms; one is rotated with little distortion and the other is distorted with increasing pressure. The deformation of this layer lengthens one of the Zr—O distances, resulting in the softening of some atom vibrational modes.

Structures of 6H perovskites Ba3CaSb2O9 and Ba3SrSb2O9 determined by synchrotron X-ray diffraction, neutron powder diffraction and ab initio calculations

2008 ◽  
Vol 64 (2) ◽  
pp. 154-159 ◽  
Author(s):  
Budwy Rowda ◽  
Maxim Avdeev ◽  
Peter L. Lee ◽  
Paul F. Henry ◽  
Chris D. Ling
Keyword(s):  
Ab Initio ◽  
Powder Diffraction ◽  
Ionic Radius ◽  
Geometry Optimization ◽  
Neutron Powder Diffraction ◽  
Group Symmetry ◽  
Effective Ionic Radius ◽  
Space Group ◽  
X Ray ◽  
Neutron Powder Diffraction Data

The structures of the 6H perovskites Ba3 B 2+Sb5+ 2O9, B = Ca and Sr, have been solved and refined using synchrotron X-ray and neutron powder diffraction data. Ba3CaSb2O9 and Ba3SrSb2O9 have monoclinic C2/c and triclinic P\bar 1 space-group symmetries, respectively, while Ba3MgSb2O9 has ideal hexagonal P63/mmc space-group symmetry. The symmetry-lowering distortions are a consequence of internal `chemical pressure' owing to the increasing effective ionic radius of the alkaline-earth cation in the perovskite B site from Mg2+ (0.72 Å) to Ca2+ (1.00 Å) to Sr2+ (1.18 Å). Increasing the effective ionic radius further to Ba2+ (1.35 Å) leads to decomposition at room temperature. The driving force behind the transition from P63/mmc to C2/c is the need to alleviate underbonding of Ba2+ cations in the perovskite A site via octahedral rotations, while the transition from C2/c to P\bar 1 is driven by the need to regularize the shape of the Sb2O9 face-sharing octahedral dimers. Ab initio geometry-optimization calculations were used to find a triclinic starting model for Ba3SrSb2O9.

Magnetic structure and properties of centrosymmetric twisted-melilite K2CoP2O7

2017 ◽  
Vol 46 (19) ◽  
pp. 6409-6416 ◽  
Author(s):  
Matthew Sale ◽  
Maxim Avdeev ◽  
Zakiah Mohamed ◽  
Chris D. Ling ◽  
Prabeer Barpanda
Keyword(s):  
Dft Calculations ◽  
Ab Initio ◽  
Magnetic Structure ◽  
Powder Diffraction ◽  
Neutron Powder Diffraction ◽  
Structure And Properties ◽  
Antiferromagnetic Structure

The magnetic structure and properties of K2CoP2O7 were studied by magnetometry and neutron powder diffraction. Below 11 K the material adopts a G-type antiferromagnetic structure in contrast to the melilite-type Sr2CoGe2O7 which orders in a C-type. Ab initio DFT calculations were performed to understand this difference.

scholarly journals Structural Chemistry of Some Phases in The YC-Ni-B System

1994 ◽  
Vol 376 ◽  
Author(s):  
B. C. Chakoumakos
Keyword(s):  
Powder Diffraction ◽  
Single Phase ◽  
Rietveld Analysis ◽  
Neutron Powder Diffraction ◽  
The Other ◽  
Powder Diffraction Data ◽  
X Ray ◽  
Neutron Powder Diffraction Data ◽  
Arc Melting ◽  
Phase Pure

ABSTRACTNiB, monoclinic Ni4B3, Ni2B and Ni3B were prepared by arc-melting and their roomtemperature crystal structures were refined by Rietveld analysis of neutron powder diffraction data. The NiB refinement is altogether new data. Although the B atoms in NiB form characteristic zigzag chains, the primary coordination of each atom by atoms of the other kind is similar and distinctively sevenfold, with one short (2.117 Å), two intermediate (2.152 Å), and four long (2.163 Å) bonds. Other samples with stoichiometries (YC)nNi2B2, n = 3, 4, did not yield single-phase material, but both x-ray and neutron powder diffraction suggest that the n = 4 structure is present in both of these samples. Phase-pure samples of these homologues may require non-stoichiometry and a more controlled thermal history than is attainable by arc melting.

scholarly journals Hydrogen bonds in crystalline D-alanine: diffraction and spectroscopic evidence for differences between enantiomers

IUCrJ ◽  
2018 ◽  
Vol 5 (1) ◽  
pp. 6-12 ◽  
Author(s):  
Ezequiel A. Belo ◽  
Jose E. M. Pereira ◽  
Paulo T. C. Freire ◽  
Dimitri N. Argyriou ◽  
Juergen Eckert ◽  
...  
Keyword(s):  
Amino Acids ◽  
Solid State ◽  
Hydrogen Bonds ◽  
Raman Scattering ◽  
Powder Diffraction ◽  
Spectroscopic Studies ◽  
Neutron Powder Diffraction ◽  
Vibrational Modes ◽  
Polarized Raman ◽  
Shed Light

Enantiomeric amino acids have specific physiological functions in complex biological systems. Systematic studies focusing on the solid-state properties of D-amino acids are, however, still limited. To shed light on this field, structural and spectroscopic studies of D-alanine using neutron powder diffraction, polarized Raman scattering and ab initio calculations of harmonic vibrational frequencies were carried out. Clear changes in the number of vibrational modes are observed as a function of temperature, which can be directly connected to variations of the N—D bond lengths. These results reveal dissimilarities in the structural properties of D-alanine compared with L-alanine.

The ab initio crystal structure determination of vapour-deposited methyl fluoride by high-resolution neutron powder diffraction

1996 ◽  
Vol 52 (5) ◽  
pp. 892-895 ◽  
Author(s):  
R. M. Ibberson ◽  
M. Prager
Keyword(s):  
Crystal Structure ◽  
High Resolution ◽  
Ab Initio ◽  
Bond Length ◽  
Powder Diffraction ◽  
Structure Refinement ◽  
Neutron Powder Diffraction ◽  
Methyl Halides ◽  
Methyl Fluoride ◽  
Neutron Powder Diffraction Data

The crystal structure of methyl fluoride (m.p. = 131 K, b.p. = 195 K) at 5 K has been solved ab initio from high-resolution neutron powder diffraction data. A good quality powder sample was produced using a vapour deposition technique and enabled an accurate and precise structure refinement to be carried out; the C—F bond length is 1.399 (4) Å, and the average C—D bond length is 1.070 (4) Å. The monoclinic structure may be described in terms of dipole-dipole intermolecular interactions and is distinct from the structures of the other methyl halides.

Neutron Powder Diffraction Study of the Structures of La1.9Ca1.1Cu2O6 and La1.9Sr1.1Cu2O6+δ

1989 ◽  
Vol 166 ◽  
Author(s):  
A. Santoro ◽  
F. Beech ◽  
R. J. Cava
Keyword(s):  
Diffraction Study ◽  
Powder Diffraction ◽  
Rock Salt ◽  
Neutron Powder Diffraction ◽  
The Other ◽  
Structural Configuration ◽  
Group 14 ◽  
Space Group ◽  
Metal Atoms ◽  
Perovskite Type

ABSTRACTThe title compounds are structurally isomorphous and crystallize with the symmetry of space group 14/mmm. The lattice parameters are a = 3.8248(1), c = 19.4286(5)Å for La1.9Ca1.1Cu2O6 and a = 3.8601(1), c = 19.9994(5)Å for La1.9Sr1.1Cu2O6+δ. The structure can be easily derived from that of La2CuO4 by substituting the layers of composition CuO2 present in La2CuO4 with a block of three layers having composition and sequence (CuO2) - (R) - (CuO2), where R is Ca, Sr, and/or La. Although the general structural configuration is the same for the Ca and the Sr compounds, the distribution of the metal atoms is different in the two cases. More specifically, in La1.9Ca1.1Cu2O6 the perovskite-type layers form blocks with sequence (CuO2) - (Ca) - (CuO2), and are separated by rock-salt blocks of two layers (LaO) - (LaO). In La1.9Sr1.1Cu2O6+δ, on the other hand, the perovskite-type blocks have composition and sequence (CuO2) - (R) - (CuO2) and they are separated by blocks (NO) - (NO), where both R and N are about 65%La and 35%Sr.

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