scholarly journals ζ-Glycine: insight into the mechanism of a polymorphic phase transition

IUCrJ ◽  
2017 ◽  
Vol 4 (5) ◽  
pp. 569-574 ◽  
Author(s):  
Craig L. Bull ◽  
Giles Flowitt-Hill ◽  
Stefano de Gironcoli ◽  
Emine Küçükbenli ◽  
Simon Parsons ◽  
...  
Keyword(s):  
High Pressure ◽  
Structure Prediction ◽  
Room Temperature ◽  
Ambient Pressure ◽  
Crystal Structure Prediction ◽  
Polymorphic Phase Transition ◽  
Neutron Powder Diffraction Data ◽  
Five Phases ◽  
Pressure Phase ◽  
Insight Into

Glycine is the simplest and most polymorphic amino acid, with five phases having been structurally characterized at atmospheric or high pressure. A sixth form, the elusive ζ phase, was discovered over a decade ago as a short-lived intermediate which formed as the high-pressure ∊ phase transformed to the γ form on decompression. However, its structure has remained unsolved. We now report the structure of the ζ phase, which was trapped at 100 K enabling neutron powder diffraction data to be obtained. The structure was solved using the results of a crystal structure prediction procedure based on fullyab initioenergy calculations combined with a genetic algorithm for searching phase space. We show that the fate of ζ-glycine depends on its thermal history: although at room temperature it transforms back to the γ phase, warming the sample from 100 K to room temperature yielded β-glycine, the least stable of the known ambient-pressure polymorphs.

scholarly journals Unbiased crystal structure prediction of NiSi under high pressure

2015 ◽  
Vol 48 (3) ◽  
pp. 906-908 ◽  
Author(s):  
Pavel N. Gavryushkin ◽  
Zakhar I. Popov ◽  
Konstantin D. Litasov ◽  
Alex Gavryushkin
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Structure Prediction ◽  
Type Structure ◽  
Stable Phase ◽  
Stable Form ◽  
Model Structure ◽  
Crystal Structure Prediction ◽  
Cscl Type ◽  
Pressure Phase

On the basis of an unbiased structure prediction, it is shown that the stable form of NiSi under pressures of 100 and 200 GPa is thePmmnstructure. Furthermore, a new stable phase has been discovered: the deformed tetragonal CsCl-type structure witha= 2.174 Å andc= 2.69 Å at 400 GPa. Specifically, the sequence of high-pressure phase transitions is the following: thePmmnstructure below 213 GPa, the tetragonal CsCl type in the range 213–522 GPa, and cubic CsCl higher than 522 GPa. As the CsCl-type structure is considered as the model structure of the FeSi compound at the conditions of the Earth's core, this result implies restrictions on the Fe–Ni isomorphic miscibility in FeSi.

High-pressure phase transition of cesium chloride and cesium bromide

2014 ◽  
Vol 16 (33) ◽  
pp. 17924-17929 ◽  
Author(s):  
Shubo Wei ◽  
Chunye Zhu ◽  
Qian Li ◽  
Yuanyuan Zhou ◽  
Quan Li ◽  
...  
Keyword(s):  
High Pressure ◽  
First Principles ◽  
Structure Prediction ◽  
Cesium Chloride ◽  
Crystal Structure Prediction ◽  
First Principles Calculations ◽  
Phase Boundaries ◽  
Cesium Bromide ◽  
High Pressure Phase Transition ◽  
Pressure Phase

Using the CALYPSO method for crystal structure prediction combined with first-principles calculations, we have investigated the high-pressure crystal structures and established the corresponding phase boundaries for the prototypical AB-type compounds of CsCl and CsBr.

scholarly journals Pressure-Induced Polymorphism of Caprolactam: A Neutron Diffraction Study

Molecules ◽  
2019 ◽  
Vol 24 (11) ◽  
pp. 2174 ◽  
Author(s):  
Ian B. Hutchison ◽  
Craig L. Bull ◽  
William G. Marshall ◽  
Andrew J. Urquhart ◽  
Iain D.H. Oswald
Keyword(s):  
High Pressure ◽  
Ambient Pressure ◽  
Neutron Diffraction Study ◽  
High Pressure Phase Behavior ◽  
Hydrogen Bonding Pattern ◽  
Neutron Powder Diffraction Data ◽  
Region Of Stability ◽  
Pressure Region ◽  
Pressure Form ◽  
Pressure Phase

Caprolactam, a precursor to nylon-6 has been investigated as part of our studies into the polymerization of materials at high pressure. Single-crystal X-ray and neutron powder diffraction data have been used to explore the high-pressure phase behavior of caprolactam; two new high pressure solid forms were observed. The transition between each of the forms requires a substantial rearrangement of the molecules and we observe that the kinetic barrier to the conversion can aid retention of phases beyond their region of stability. Form II of caprolactam shows a small pressure region of stability between 0.5 GPa and 0.9 GPa with Form III being stable from 0.9 GPa to 5.4 GPa. The two high-pressure forms have a catemeric hydrogen-bonding pattern compared with the dimer interaction observed in ambient pressure Form I. The interaction between the chains has a marked effect on the directions of maximal compressibility in the structure. Neither of the high-pressure forms can be recovered to ambient pressure and there is no evidence of any polymerization occurring.

scholarly journals New high-pressure phases of Fe7N3 and Fe7C3 stable at Earth's core conditions: evidences for carbon–nitrogen isomorphism in Fe-compounds

RSC Advances ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 3577-3581 ◽  
Author(s):  
Nursultan Sagatov ◽  
Pavel N. Gavryushkin ◽  
Talgat M. Inerbaev ◽  
Konstantin D. Litasov
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Ab Initio ◽  
Structure Prediction ◽  
Harmonic Approximation ◽  
Crystal Structure Prediction ◽  
Earth’S Core ◽  
Earth's Core ◽  
Core Conditions

We carried out ab initio calculations on the crystal structure prediction and determination of P–T diagrams within the quasi-harmonic approximation for Fe7N3 and Fe7C3.

scholarly journals Minimizing Polymorphic Risk Through Cooperative Computational and Experimental Exploration

2020 ◽  
Author(s):  
Christopher R. Taylor ◽  
Matthew T. Mulvee ◽  
Domonkos S. Perenyi ◽  
Michael R. Probert ◽  
Graeme Day ◽  
...  
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Structure Prediction ◽  
Experimental Approach ◽  
Significant Risk ◽  
Free Energy Calculations ◽  
Crystal Structure Prediction ◽  
Crystal Forms ◽  
Wide Range ◽  
Solid Form

<div> <p>We combine state-of-the-art computational crystal structure prediction (CSP) techniques with a wide range of experimental crystallization methods to understand and explore crystal structure in pharmaceuticals and minimize the risk of unanticipated late-appearing polymorphs. Initially, we demonstrate the power of CSP to rationalize the difficulty in obtaining polymorphs of the well-known pharmaceutical isoniazid and show that CSP provides the structure of the recently discovered, but unsolved, Form III of this drug despite there being only a single known form for almost 70 years. More dramatically, our blind CSP study predicts a significant risk of polymorphism for the related iproniazid. Employing a wide variety of experimental techniques, including high-pressure experiments, we experimentally obtained the first three known non-solvated crystal forms of iproniazid, all of which were successfully predicted in the CSP procedure. We demonstrate the power of CSP methods and free energy calculations to rationalize the observed elusiveness of the third form of iproniazid, the success of high-pressure experiments in obtaining it, and the ability of our synergistic computational-experimental approach to “de-risk” solid form landscapes.</p> </div>

Phase transitions in ReO3studied by high-pressure X-ray diffraction

2000 ◽  
Vol 33 (2) ◽  
pp. 279-284 ◽  
Author(s):  
J.-E. Jørgensen ◽  
J. Staun Olsen ◽  
L. Gerward
Keyword(s):  
High Pressure ◽  
Phase Transitions ◽  
Powder Diffraction ◽  
Ambient Pressure ◽  
Rhombohedral Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Oxygen Ions ◽  
Pressure Phase ◽  
Related Phase

ReO3has been studied at pressures up to 52 GPa by X-ray powder diffraction. The previously observed cubicIm3¯ high-pressure phase was shown to transform to a monoclinic MnF3-related phase at about 3 GPa. All patterns recorded above 12 GPa could be indexed on rhombohedral cells. The compressibility was observed to decrease abruptly at 38 GPa. It is therefore proposed that the oxygen ions are hexagonally close packed above this pressure, giving rise to two rhombohedral phases labelled I and II. The zero-pressure bulk moduliBoof the observed phases were determined and the rhombohedral phase II was found to have an extremely large value of 617 (10) GPa. It was found that ReO3transforms back to thePm3¯mphase found at ambient pressure.

High-Pressure Synthesis, Crystal Structure, and Properties of the New Orthorhombic Rare-Earth meta-Oxoborates RE(BO2)3 (RE = Dy – Lu)

2004 ◽  
Vol 59 (2) ◽  
pp. 202-215 ◽  
Author(s):  
Holger Emme ◽  
Tanja Nikelski ◽  
Thomas Schleid ◽  
Rainer Pöttgen ◽  
Manfred Heinrich Möller ◽  
...  
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Ambient Pressure ◽  
Structure And Properties ◽  
Crystal Data ◽  
Temperature Conditions ◽  
Pressure Synthesis ◽  
Ir Spectroscopic ◽  
Pressure Phase

The new orthorhombic meta-oxoborates RE(BO2)3 (≡REB3O6) (RE = Dy-Lu) have been synthesized under high-pressure and high-temperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 1100 °C. They are isotypic to the known ambient pressure phase Tb(BO2)3, space group Pnma. In contrast to Dy(BO2)3, which was also obtained in small amounts under high-temperature conditions, the preparation of the higher orthorhombic homologues RE(BO2)3 (RE = Ho-Lu) was only possible using high-pressure. The meta-oxoborates RE(BO2)3 (RE = Dy-Er) were synthesized as pure products, whereas the orthorhombic phases with RE = Tm-Lu were only obtained as byproducts. With the exception of Yb(BO2)3 it was possible to establish single crystal data for all compounds. The results of temperature-resolved in-situ powder-diffraction measurements, DTA, IR-spectroscopic investigations, and magnetic properties are also presented.

Crystal structure prediction of ReN2 under high pressure

2019 ◽  
Vol 94 (11) ◽  
pp. 1711-1716
Author(s):  
H. Y. Wang ◽  
P. Yan ◽  
L. Xu ◽  
D. W. Zhou ◽  
D. Li
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Structure Prediction ◽  
Crystal Structure Prediction
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