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.

Neutron Diffraction Study of the Ambient-Pressure, Rutile-Type and the High-Pressure, CaCl2-Type Phases of Ruthenium Dioxide

1997 ◽  
Vol 53 (6) ◽  
pp. 880-884 ◽  
Author(s):  
J. Haines ◽  
J. M. Léger ◽  
O. Schulte ◽  
S. Hull
Keyword(s):  
High Pressure ◽  
Soft Mode ◽  
Ambient Pressure ◽  
Neutron Diffraction Study ◽  
Normal Coordinate ◽  
Oxygen Ions ◽  
Type Phase ◽  
Principal Axes ◽  
Pressure Phase

The structures of the ambient-pressure, rutile-type and the high-pressure, CaCl2-type phases of RuO2 were refined by time-of-flight neutron powder diffraction. Refinement of the data obtained from the ambient-pressure phase (P42/mnm, Z = 2) yielded cell constants a = 4.49307 (7) and c = 3.10639 (7) Å and an oxygen positional parameter x = 0.3056 (1). The principal axes of the displacement ellipsoids of the oxygen ions lie along the directions which correspond to the normal coordinate of the B 1g soft mode that drives the transition to the CaCl2-type structure. The CaCl2-type phase (Pnnm, Z = 2) was refined in situ at 5.3 (3) GPa and the following cell constants and oxygen positional parameters were obtained: a = 4.4865 (5), b = 4.4347 (5), c = 3.0934 (3) Å, x = 0.3101 (5) and y = 0.3005 (5). In the CaCl2-type phase at 5.3 (3) GPa the RuO6 octahedra are rotated by 1.1 (2)° with respect to their orientation in the ruffle-type phase. There is little change in the internal angles of the octahedron between 0.1 MPa and 5.3 GPa. Compression of the octahedron is anisotropic with a much greater reduction of the Ru—O contacts in the ab plane.

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.

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.

High-Pressure Synthesis and Crystal Structure of the New Orthorhombic Polymorph β-HgB4O7

2005 ◽  
Vol 60 (8) ◽  
pp. 815-820 ◽  
Author(s):  
Holger Emme ◽  
Matthias Weil ◽  
Hubert Huppertz
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Ambient Pressure ◽  
Normal Pressure ◽  
High Pressure Phase ◽  
Synthesis And Crystal Structure ◽  
Space Group ◽  
High Pressure Synthesis ◽  
Pressure Synthesis ◽  
Pressure Phase

The new orthorhombic polymorph β-HgB4O7 has been synthesized under high-pressure and hightemperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 600 °C. β-HgB4O7 is isotypic to the known ambient pressure phases MB4O7 (M = Sr, Pb, Eu) and the high-pressure phase β-CaB4O7 crystallizing with two formula units in the space group Pmn21 with lattice parameters a = 1065.6(2), b = 438.10(9), and c = 418.72(8) pm. The relation of the crystal structure of the high-pressure phase β-HgB4O7 to the normal pressure phase α-HgB4O7 as well as the relation to the isotypic phases MB4O7 (M = Sr, Pb, Eu) and β-CaB4O7 are discussed.

High pressure phase behavior for the supercritical ethylene+cyclohexane+hexane+polyethylene systems

2009 ◽  
Vol 49 (2) ◽  
pp. 125-134 ◽  
Author(s):  
Masashi Haruki ◽  
Kiyoshi Sato ◽  
Shin-ichi Kihara ◽  
Shigeki Takishima
Keyword(s):  
High Pressure ◽  
Phase Behavior ◽  
High Pressure Phase ◽  
High Pressure Phase Behavior ◽  
Pressure Phase
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