Phase Transition and Polymerization of Acetonitrile under High Pressure

Successful application of high pressure on synthesis of organic polymer, including the conducting polymer and super hard materials depends on the knowledge of reaction mechanism. The evolution of crystal structure under high pressure especially the structure close to transition pressure is crucial to conclude the reaction mechanism. Nitriles represent a large class of interstellar molecules and are the potential source of amino acids. Understanding its behavior at extreme conditions has gained increasing attention recently. Acetonitrile (CH3CN), the simplest organic compound with C≡N triple bond, can act as a model system for studying the pressure induced polymerization. The phase transition of acetonitrile under high pressure has been studied extensively.[1-3] However, it is still controversial and there is no any detailed discussion about its polymerization mechanism under high pressure. Here, we report the in-situ high pressure Raman spectra and powder neutron diffraction results on CD3CN, which indicates a minor phase transition at 5 GPa. The neutron diffraction shows that CD3CN keeps the orthorhombic phase from 1.66 GPa to 20.58 GPa which is very close to the reaction pressure. The week hydrogen bonding CD...N arranges the molecule into 3-dimensional framework which can be treated as two sets of diamond like structures interpenetrating with each other. Interestingly, the observed N...D distance is 1.984 Å at 20.58 GPa, shorter than the van der Waals distance of N...H (2.75 Å) by 28%. The van der Waals separation is often taken as a reference distance for the molecular instability. Thus, a hydrogen transfer process during the polymerization can be concluded. This deduction is also supported by the solid state NMR and FTIR results of the recovered polymerized CH3CN (p-CH3CN) from high pressure. In addition, the atomic pair distribution function and Raman spectra indicate the p-CD3CN or p-CH3CN has a random packed layer structure with nano-graphene lattice.

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A high-pressure neutron diffraction study of the ferroelastic phase transition in RbCaF3

Physics and Chemistry of Minerals ◽

10.1007/s00269-014-0663-3 ◽

2014 ◽

Vol 41 (6) ◽

pp. 461-472 ◽

Cited By ~ 8

Author(s):

Kevin S. Knight ◽

William G. Marshall ◽

Philip M. Hawkins

Keyword(s):

Phase Transition ◽

High Pressure ◽

Neutron Diffraction ◽

Diffraction Study ◽

Neutron Diffraction Study ◽

Ferroelastic Phase Transition

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High-Pressure X-Ray Diffraction Studies of Elastic Anomalies in Superlattice

MRS Proceedings ◽

10.1557/proc-231-355 ◽

1991 ◽

Vol 231 ◽

Cited By ~ 1

Author(s):

Y. Fujii ◽

Y. Ohishi ◽

H. Konishi ◽

N. Nakayama ◽

T. Shinjo

Keyword(s):

Phase Transition ◽

High Pressure ◽

Diamond Anvil Cell ◽

Orthorhombic Phase ◽

X Ray Diffraction ◽

X Ray ◽

Layer Stacking ◽

Diamond Anvil ◽

Elastic Anomalies ◽

Structural Aspects

AbstractThis paper has made an overview on elastic and structural aspects of three distinct superlattices under hydrostatic pressure up to about 8GPa, which were studied by our unique x-ray diffraction technique incorporated with a diamond-anvil cell. They are metallic fcc/fcc Au/Ni, bcc/fcc Mo/Ni, and semiconductive epitaxially-grown PbSe/SnSe superlattices. In their layer-stacking direction, both metallic superlattices show the supermodulus behavior while the semiconductive one doesn't. However, its pressure-driven cubic-to-orthorhombic phase transition, successively taking place in the SnSe and PbSe layers, has been found to significantly shift by stress due to its epitaxial growth.

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Raman spectra of high pressure phase and phase transition of polytetrafluoroethylene (teflon)

Chemical Physics Letters ◽

10.1016/0009-2614(73)80036-3 ◽

1973 ◽

Vol 21 (1) ◽

pp. 153-157 ◽

Cited By ~ 44

Author(s):

Chen-Kuang Wu ◽

Malcolm Nicol

Keyword(s):

Phase Transition ◽

High Pressure ◽

Raman Spectra ◽

High Pressure Phase ◽

Pressure Phase

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High Pressure Synchrotron Diffraction of KCa2Nb3O10, a Layered Perovskite Compound

MRS Proceedings ◽

10.1557/proc-524-133 ◽

1998 ◽

Vol 524 ◽

Cited By ~ 2

Author(s):

K. A. Steiner ◽

W. T. Petuskey

Keyword(s):

Phase Transition ◽

High Pressure ◽

Diamond Anvil Cell ◽

Orthorhombic Phase ◽

Layered Perovskite ◽

X Ray Diffraction ◽

Synchrotron Diffraction ◽

X Ray ◽

Lattice Constants ◽

Diamond Anvil

ABSTRACTHigh pressure synchrotron x-ray diffraction experiments were conducted on KCa2Nb3O10, to determine lattice constants as a function of pressure. A diamond anvil cell was used to produce pressures up to 66 GPa. A phase transition occurred at 13.5 GPa. From the lattice constants, linear compressibilities of 8.55 × 10-4 GPa-1 in the a direction, -9.40 × 10-4 GPa-1 in the b direction, and 142 × 10-4 GPa-1 in the c direction, and a bulk modulus of 68.5 GPa were found for the lower pressure orthorhombic phase.

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A first principles lattice dynamics and Raman spectra of the ferroelastic rutile to CaCl2 phase transition in SnO2 at high pressure

Journal of Raman Spectroscopy ◽

10.1002/jrs.4277 ◽

2013 ◽

Vol 44 (6) ◽

pp. 926-933 ◽

Cited By ~ 23

Author(s):

Sanjay D. Gupta ◽

Sanjeev K. Gupta ◽

Prafulla K. Jha ◽

N. N. Ovsyuk

Keyword(s):

Phase Transition ◽

High Pressure ◽

Raman Spectra ◽

First Principles ◽

Lattice Dynamics

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The polymorphism of alkali metal formates. Part 4. A Raman study of the phase transition in KHCOO

Canadian Journal of Chemistry ◽

10.1139/v91-260 ◽

1991 ◽

Vol 69 (11) ◽

pp. 1774-1780 ◽

Cited By ~ 6

Author(s):

A. M. Heyns ◽

K.-J. Range ◽

K. Müller

Keyword(s):

Phase Transition ◽

Phase I ◽

Raman Spectra ◽

Orthorhombic Phase ◽

Fermi Resonance ◽

Theoretical Treatment ◽

Ambient Conditions ◽

Definite Structure ◽

Raman Study ◽

Intramolecular Motions

KHCOO II is orthorhombic at ambient conditions and it is shown that traces of moisture affect the polymorphism of these very hygroscopic crystals. Dry KHCOO II transforms into phase I at 417 K (144 °C), and this phase can be supercooled to room temperature, remaining metastable for several days before transforming back to the orthorhombic phase II. The Raman spectra of phases I and II, as well as of supercooled phase I, are reported in the present study. The absence of some prominent translational modes in the Raman spectra of KHCOO II, compared to NaHCOO II, can be explained on the basis of a group-theoretical treatment. From the temperature dependence of the linewidths of various Raman-active librational and internal modes, activation energies are obtained for intramolecular motions of the formate ions. Fermi resonance occurs between the overtone of the bending mode 2ν5 and the C—H stretching mode ν1 in KHCOO II and the coupling constant W increases with temperature. The Raman and X-ray data show that KHCOO I is structurally different from NaCHOO I, but it is not possible to assign a definite structure to this phase on the basis of a Raman spectrum alone. Key words: Potassium formate, phase transition, Raman spectra.

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Pressure-Induced Phase Transformations in Li-based Complex Hydrides

MRS Proceedings ◽

10.1557/proc-987-0987-pp04-10 ◽

2006 ◽

Vol 987 ◽

Cited By ~ 1

Author(s):

Raja Chellappa ◽

Dhanesh Chandra ◽

Stephen Gramsch ◽

Maddury Somayazulu ◽

Russell Hemley

Keyword(s):

Phase Transition ◽

High Pressure ◽

Phase Transformations ◽

Raman Spectra ◽

Complex Hydrides ◽

Orientational Ordering ◽

Induced Changes

AbstractAn overview of the pressure-induced transformations and order-disorder phenomena in LiAlH4 (up to 7 GPa) and LiNH2 (up to 25 GPa) are presented. The analysis of pressure-induced changes in Raman spectra suggest a phase transition at ∼3 GPa for LiAlH4 and ∼14 GPa for LiNH2. New results on the metastable recovery of the high pressure β-LiAlH4 phase are also presented. An examination of the lattice translational and librational modes reveals that the high pressure β-LiAlH4 phase is disordered while there is evidence of orientational ordering in the high pressure beta-LiNH2 phase.

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