scholarly journals High-pressure polymorphism in l-threonine between ambient pressure and 22 GPa

CrystEngComm ◽  
2019 ◽  
Vol 21 (30) ◽  
pp. 4444-4456 ◽  
Author(s):  
Nico Giordano ◽  
Christine M. Beavers ◽  
Konstantin V. Kamenev ◽  
William G. Marshall ◽  
Stephen A. Moggach ◽  
...  
Keyword(s):  
High Pressure ◽  
Hydrogen Bonding ◽  
Phase Transitions ◽  
Amino Acid ◽  
Molecular Conformation ◽  
Ambient Pressure ◽  
Three Phase

The amino acid l-threonine undergoes three phase transitions between ambient pressure and 22.3 GPa which modify both hydrogen bonding and the molecular conformation.

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.

A new high-pressure benzocaine polymorph — towards understanding the molecular aggregation in crystals of an important active pharmaceutical ingredient (API)

2020 ◽  
Vol 76 (1) ◽  
pp. 56-64 ◽  
Author(s):  
Ewa Patyk-Kaźmierczak ◽  
Michał Kaźmierczak
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Hydrogen Bonding ◽  
Hydrogen Bonds ◽  
Ambient Pressure ◽  
Active Pharmaceutical Ingredient ◽  
Molecular Packing ◽  
Molecular Aggregation ◽  
Pressure Release ◽  
Hydrogen Bonding Pattern

Benzocaine (BZC), an efficient and highly permeable anaesthetic and an active pharmaceutical ingredient of many commercially available drugs, was studied under high pressure up to 0.78 GPa. As a result, new BZC polymorph (IV) was discovered. The crystallization of polymorph (IV) can be initiated by heating crystals of polymorph (I) at a pressure of at least 0.45 GPa or by their compression to 0.60 GPa. However, no phase transition from polymorph (I) to (IV) was observed. Although polymorph (IV) exhibits the same main aggregation motif as in previously reported BZC polymorphs (I)–(III), i.e. a hydrogen-bonded ribbon, its molecular packing and hydrogen-bonding pattern differ considerably. The N—H...N hydrogen bonds joining parallel BZC ribbons in crystals at ambient pressure are eliminated in polymorph (IV), and BZC ribbons become positioned at an angle of about 80°. Unfortunately, crystals of polymorph (IV) were not preserved on pressure release, and depending on the decompression protocol they transformed into polymorph (II) or (I).

Phase transitions and hydrogen bonding in deuterated calcium hydroxide: High-pressure and high-temperature neutron diffraction measurements

2014 ◽  
Vol 218 ◽  
pp. 95-102 ◽  
Author(s):  
Riko Iizuka ◽  
Kazuki Komatsu ◽  
Hiroyuki Kagi ◽  
Takaya Nagai ◽  
Asami Sano-Furukawa ◽  
...  
Keyword(s):  
High Pressure ◽  
Hydrogen Bonding ◽  
Phase Transitions ◽  
High Temperature ◽  
Neutron Diffraction ◽  
Calcium Hydroxide

scholarly journals Brief Review of the Effects of Pressure on Wolframite-Type Oxides

2018 ◽  
Author(s):  
Daniel Errandonea ◽  
Javier Ruiz-Fuertes
Keyword(s):  
High Pressure ◽  
Phase Transitions ◽  
Band Gap ◽  
Ambient Pressure ◽  
Structural Phase ◽  
Band Gap Energy ◽  
Structural Phase Transitions ◽  
Gap Energy ◽  
Raman Modes ◽  
Oxygen Bond

In this article we review the advances that have been made on the understanding of the high-pressure structural, vibrational, and electronic properties of wolframite-type oxides since the first works in the early 1990s. Mainly tungstates, which are the best known wolframites, but also tantalates and niobates, with an isomorphic ambient-pressure wolframite structure, have been included in this review. Apart from estimating the bulk moduli of all known wolframites; the cation-oxygen bond distances and their change with pressure have been correlated with their compressibility. The composition variations of all wolframites have been employed to understand their different structural phase transitions to post-wolframite structures as a response to high pressure. The number of Raman modes and band gap energy changes have been also analyzed in the basis of these compositional differences. The reviewed results are relevant for both fundamental science and for the development of wolframites as scintillating detectors. The possible next research venues of wolframites have also been evaluated.

Structural relationships between cations and alloys; an equivalence between oxidation and pressure

2001 ◽  
Vol 58 (1) ◽  
pp. 38-51 ◽  
Author(s):  
Angel Vegas ◽  
Martin Jansen
Keyword(s):  
High Pressure ◽  
Phase Transitions ◽  
General Principle ◽  
Physical Meaning ◽  
Ambient Pressure ◽  
Ambient Conditions ◽  
Ionic Model ◽  
Structural Relationships ◽  
Structural Identity ◽  
Binary Compounds

More than 100 examples are provided of the structural identity between the cation arrays in oxides and their corresponding alloys (binary compounds). Halides and halogenates, sulfides and sulfites and/or sulfates, selenides and selenates, phosphides and phosphates show this behaviour. In some cases, the structure of the cation subarray corresponds to the structure of the alloy at ambient conditions, but in other cases, cations stabilize structures which correspond to those of the high-pressure phases of the alloy, from which an analogy between the insertion of oxygen and the application of pressure can be established. In this last case, the oxides show polymorphism with temperature and when heated, the structure of the ambient pressure of the alloy is recovered as if heating would compensate the effect of pressure. From the results reported here, it is concluded that cations do not seem to be either the isolated entities, predicted by the ionic model, which occupy interstices of an oxygen matrix, or they arrange in a more or less arbitrary way, but they try to reproduce the structure of their corresponding alloy. Many of the phase transitions and the polymorphism exhibited by the oxides described here are better explained when they are considered as formed by previous entities which are the alloys. Oxides should be considered as `real stuffed alloys'. These features do not seem to be casual, but they obey a general principle: Cations recognize themselves in spite of being embedded in an oxygen bulk. The nature and the physical meaning of this recognition are problems which remain unsolved.

scholarly journals Comparison of the effects of pressure on three layered hydrates: a partially successful attempt to predict a high-pressure phase transition

2009 ◽  
Vol 65 (6) ◽  
pp. 731-748 ◽  
Author(s):  
Russell D. L. Johnstone ◽  
Alistair R. Lennie ◽  
Simon Parsons ◽  
Elna Pidcock ◽  
John E. Warren
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Single Crystal ◽  
Molecular Conformation ◽  
Ambient Pressure ◽  
High Pressure Phase ◽  
Cysteic Acid ◽  
Water Molecules ◽  
High Pressure Phase Transition ◽  
Pressure Phase

We report the effect of pressure on the crystal structures of betaine monohydrate (BTM), L-cysteic acid monohydrate (CAM) and S-4-sulfo-L-phenylalanine monohydrate (SPM). All three structures are composed of layers of zwitterionic molecules separated by layers of water molecules. In BTM the water molecules make donor interactions with the same layer of betaine molecules, and the structure remains in a compressed form of its ambient-pressure phase up to 7.8 GPa. CAM contains bi-layers of L-cysteic acid molecules separated by water molecules which form donor interactions to the bi-layers above and below. This phase is stable up to 6.8 GPa. SPM also contains layers of zwitterionic molecules with the waters acting as hydrogen-bond donors to the layers above and below. SPM undergoes a single-crystal to single-crystal phase transition above 1 GPa in which half the water molecules reorient so as to form one donor interaction with another water molecule within the same layer. In addition, half of the S-4-sulfo-L-phenylalanine molecules change their conformation. The high-pressure phase is stable up to 6.9 GPa, although modest rearrangements in hydrogen bonding and molecular conformation occur at 6.4 GPa. The three hydrates had been selected on the basis of their topological similarity (CAM and SPM) or dissimilarity (BTM) with serine hydrate, which undergoes a phase transition at 5 GPa in which the water molecules change orientation. The phase transition in SPM shows some common features with that in serine hydrate. The principal directions of compression in all three structures were found to correlate with directions of hydrogen bonds and distributions of interstitial voids.

scholarly journals Packing Rearrangements in 4-Hydroxycyanobenzene Under Pressure

Molecules ◽  
2019 ◽  
Vol 24 (9) ◽  
pp. 1759 ◽  
Author(s):  
Ines E. Collings ◽  
Michael Hanfland
Keyword(s):  
High Pressure ◽  
Hydrogen Bonding ◽  
Phase Transitions ◽  
X Ray Diffraction ◽  
Two Phase ◽  
Face To Face ◽  
Π Interactions ◽  
High Pressure Studies ◽  
Benzene Rings ◽  
Semiconductor Properties

4-hydroxycyanobenzene (4HCB) is a dipolar molecule formed of an aromatic substituted benzene ring with the CN and OH functional groups at the 1 and 4 positions. In the crystalline state, it forms spiral chains via hydrogen bonding, which pack together through π − π interactions. The direct stacking of benzene rings down the a- and b-axes and its π − π interactions throughout the structure gives rise to its semiconductor properties. Here, high-pressure studies are conducted on 4HCB in order to investigate how the packing and intermolecular interactions, related to its semiconductor properties, are affected. High-pressure single-crystal X-ray diffraction was performed with helium and neon as the pressure-transmitting mediums up to 26 and 15 GPa, respectively. The pressure-dependent behaviour of 4HCB in He was dominated by the insertion of He into the structure after 2.4 GPa, giving rise to two phase transitions, and alterations in the π − π interactions above 4 GPa. 4HCB compressed in Ne displayed two phase transitions associated with changes in the orientation of the 4HCB molecules, giving rise to twice as many face-to-face packing of the benzene rings down the b-axis, which could allow for greater charge mobility. In the He loading, the hydrogen bonding interactions steadily decrease without any large deviations, while in the Ne loading, the change in 4HCB orientation causes an increase in the hydrogen bonding interaction distance. Our study highlights how the molecular packing and π − π interactions evolve with pressure as well as with He insertion.

scholarly journals Phase transitions and enhanced conductivity of CaC2under high pressure

2014 ◽  
Vol 70 (a1) ◽  
pp. C159-C159
Author(s):  
Kuo Li ◽  
Haiyan Zheng ◽  
Chris. Tulk ◽  
Ilia Ivanov ◽  
Wenge Yang ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Phase Transitions ◽  
Neutron Diffraction ◽  
Phase I ◽  
Turning Point ◽  
Ambient Pressure ◽  
Experimental Investigations ◽  
Pressure Curve ◽  
Structural Transitions

Calcium carbide is widely used in the industry for the production of acetylene and other purposes. Its phase transitions under ambient pressure have been studied since 1930s [1]. In recent years, with the development of high pressure science, its phase transitions under high pressure attracted more attentions [2], and its physical properties such as conductivity and superconductivity were focused [3]. Up to now, most of the researches on CaC2 under high pressure are theoretical, and experimental investigations are expected to figure out the structural transitions. In this work, we investigated the structural transitions of CaC2 (phase I, tetragonal, I4/mmm) up to ~30 GPa by powder XRD, neutron diffraction, and neutron PDF analysis on the recovered samples, and measured the conductivity of CaC2 up to ~20 GPa. XRD data are employed to refine the unit cell parameters, based on which the equation of state is fitted. As identified by series of fittings, the tetragonal phase stabilizes up to 10 GPa, above which it has a minor phase transition. The crystal structures were refined by the structural model of phase I with in-situ neutron diffraction data. Both of the bond length of C-C triple bond and the nearest intergroup C...C distance show a turning point at around 10-12 GPa. The critical pressure is in consistent with the predicted phase transition from phase I to phase VI (monoclinic, I2/m), though the phase VI can't be identified and refined with the data under the current resolution. The resistivity of CaC2 decreases from 1000 Ω·m at 2 GPa to 0.0001 Ω·m at 22 GPa, which can be attributed to the compression of intergroup C...C distance from 0.335nm to 0.315nm. The resistivity-pressure curve also shows a turning point at ~10GPa, corresponding to the phase transition. Above 18 GPa, CaC2 starts to amorphize, which is reversible but sluggish. The C22- may get connected to each other, as observed in the neutron PDF data of the recovered sample.

Hydrogen bonding in liquid methanol at ambient conditions and at high pressure

2000 ◽  
Vol 98 (3) ◽  
pp. 125-134 ◽  
Author(s):  
T. Weitkamp, J. Neuefeind, H. E. Fisch
Keyword(s):  
High Pressure ◽  
Hydrogen Bonding ◽  
Ambient Conditions
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