Pressure-Induced Order–Disorder Phase Transition of Spinel Single Crystals

1998 ◽  
Vol 54 (6) ◽  
pp. 714-721 ◽  
Author(s):  
J. Wittlinger ◽  
S. Werner ◽  
H. Schulz
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Single Crystal ◽  
Structural Changes ◽  
X Ray ◽  
Disorder Phase Transition ◽  
X Ray Scattering ◽  
Structure Investigations ◽  
Pressure Phase ◽  
Oxygen Framework

The present study deals with single-crystal structure investigations by means of X-ray scattering of a pressure-induced phase transition of Mg0.4Al2.4O4. The compressibility of the substance is very small, whereas the structural changes are surprisingly high. A non-identified high-pressure phase turns out to be reversible considering the existence of a spinel single crystal, but not reversible with regard to the ordering of the cations in the oxygen framework. The pressure-induced disordering of the cations is preserved on abrupt pressure decrease and can be detected in a recovered specimen.

A new high-pressure phase transition in clinoferrosilite: In situ single-crystal X-ray diffraction study

2017 ◽  
Vol 102 (3) ◽  
pp. 666-673 ◽  
Author(s):  
Anna Pakhomova ◽  
Leyla Ismailova ◽  
Elena Bykova ◽  
Maxim Bykov ◽  
Tiziana Boffa Ballaran ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Single Crystal ◽  
Diffraction Study ◽  
High Pressure Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
High Pressure Phase Transition ◽  
Pressure Phase

scholarly journals Crystal Structure and Dielectric Property of Endohedral Lithium Fullerene

2014 ◽  
Vol 70 (a1) ◽  
pp. C195-C195
Author(s):  
Shinobu Aoyagi ◽  
Kunihisa Sugimoto ◽  
Hiroshi Okada ◽  
Norihisa Hoshino ◽  
Tomoyuki Akutagawa
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Dielectric Property ◽  
Low Temperature ◽  
Dielectric Permittivity ◽  
Single Crystal ◽  
Temperature Dependence ◽  
Structure Analysis ◽  
X Ray ◽  
Dielectric Phase

Endohedral lithium fullerene Li+@C60 can have a dielectric polarization by the off-centered location of the Li+ cation inside the C60 cage. The x-ray structure analysis of the PF6– salt [Li@C60](PF6) revealed that the Li+ cation occupies two off-centered equivalent positions at 20 K and hence the crystal is non-polar [1]. The disordered structure at low temperature is explained by a static orientation disorder of polar Li+@C60 cations and/or a dynamic tunneling of the Li+ cation inside the C60 cage. The Li+ tunneling would be suppressed by an intermolecular interaction at lower temperature and a dielectric phase transition might be induced. We reveal the dielectric property and crystal structure of [Li@C60](PF6) below 20 K in this study. The temperature dependence of the dielectric permittivity was measured for the single crystal down to 9 K. The dielectric permittivity increases with decreasing temperature according to the Curie-Weiss law. Such a behavior was also observed in H2O@C60 crystal but not in empty C60 crystal [2]. No dielectric phase transition was observed in H2O@C60 down to 8 K. In contrast, a dielectric anomaly suggesting a phase transition was observed in [Li@C60](PF6) around 18 K. The single-crystal x-ray diffraction experiment below 20 K was also performed at SPring-8 BL02B1. The crystal has a cubic structure at 20 K [1]. The temperature dependence of the cubic lattice constant shows no anomaly around 18 K. However, diffraction peaks that are forbidden for the given structure appear below 18 K. Thus the crystal symmetry is lowered by the dielectric phase transition. We present the result of the crystal structure analysis of the newly discovered low-temperature phase.

A Re-investigation of the Crystal Structure of the Perovskite PbZrO3 by X-ray and Neutron Diffraction

1997 ◽  
Vol 53 (1) ◽  
pp. 135-142 ◽  
Author(s):  
D. L. Corker ◽  
A. M. Glazer ◽  
J. Dec ◽  
K. Roleder ◽  
R. W. Whatmore
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Neutron Diffraction ◽  
Single Crystal ◽  
Lead Zirconate ◽  
Conclusive Evidence ◽  
X Rays ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structure Investigations

The crystal structure of the perovskite lead zirconate PbZrO3 has been redetermined using single-crystal X-ray diffraction (Mo Kα radiation, λ = 0.71069 Å). Single-crystal data at 100 K: space group. Pbam, a = 5.884 (1), b = 11.787 (3), c = 8.231 (2) Å, V = 570.85 Å3 with Z = 8, μ = 612.6 cm−1, D x = 8.06 Mg m−3, F(000) = 1168, final R = 0.033, wR = 0.061 over 555 reflections with I > 2σ(I). An investigation is made into previous contradicting reports of a possible disorder in the O atoms and their origin by examining the crystal pseudo-symmetry. Information distinguishing an ordered and disordered oxygen substructure is shown to reside in weak l odd reflections. Because of their extremely low intensities these reflections have not contributed sufficiently in previous X-ray structure investigations and hence, to date, conclusive evidence differentiating between ordered and disordered models has not been possible. By collecting single-crystal X-ray data at low temperature and by using exceptionally long scans on selected hkl, l odd, reflections, a new accurate structure determination is presented and discussed, showing the true ordered oxygen positions. Because of the large difference in scattering factors between lead and oxygen when using X-rays, a neutron diffraction Rietveld refinement using polycrystalline samples (D1A instrument, ILL, λ = 1.90788 Å) is also reported as further evidence to support the true ordered oxygen structure revealed by the low-temperature X-ray analysis.

Crystal structure of a high-pressure phase of magnesium chloride hexahydrate determined by in-situ X-ray and neutron diffraction methods

2019 ◽  
Vol 75 (12) ◽  
pp. 1605-1612 ◽  
Author(s):  
Keishiro Yamashita ◽  
Kazuki Komatsu ◽  
Takanori Hattori ◽  
Shinichi Machida ◽  
Hiroyuki Kagi
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Neutron Diffraction ◽  
Single Crystal ◽  
Magnesium Chloride ◽  
High Pressure Phase ◽  
X Ray ◽  
Magnesium Chloride Hexahydrate ◽  
Chloride Hexahydrate ◽  
Pressure Phase

A high-pressure phase of magnesium chloride hexahydrate (MgCl2·6H2O-II) and its deuterated counterpart (MgCl2·6D2O-II) have been identified for the first time by in-situ single-crystal X-ray and powder neutron diffraction. The crystal structure was analyzed by the Rietveld method for the neutron diffraction pattern based on the initial structure determined by single-crystal X-ray diffraction. This high-pressure phase has a similar framework to that in the known ambient-pressure phase, but exhibits some structural changes with symmetry reduction caused by a subtle modification in the hydrogen-bond network around the Mg(H2O)6 octahedra. These structural features reflect the strain in the high-pressure phases of MgCl2 hydrates.

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