Pressure-induced structural changes and elemental dissociation of cadmium and mercury chalcogenides

RSC Advances ◽  
2015 ◽  
Vol 5 (126) ◽  
pp. 104426-104432 ◽  
Author(s):  
Yan Yan ◽  
Shoutao Zhang ◽  
Yanchao Wang ◽  
Guochun Yang ◽  
Yanming Ma
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Structural Changes ◽  
Strong Compression ◽  
Mercury Chalcogenides

The high-pressure structures and phase-transition sequences of the cadmium and mercury chalcogenides were unambiguously determined. An intriguing dissociation into Cd (or Hg) + X under strong compression was observed.

scholarly journals Crystal Structure of Urotropine Under High Pressure and Non-Hydrostatic Stress-Induced Phase Transitions in Cage Compounds

2020 ◽  
Author(s):  
Piotr A. Guńka ◽  
Anna Olejniczak ◽  
Samuele Fanetti ◽  
Roberto Bini ◽  
Ines E. Collings ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
High Pressure ◽  
Structural Changes ◽  
Hydrostatic Stress ◽  
Atomic Displacement ◽  
Deviatoric Stress ◽  
Cage Compounds ◽  
First Order Phase Transition ◽  
Atomic Displacement Parameters

High-pressure behavior of hexamthyleneteramine (urotropine) was studied <i>in situ</i> using angle-dispersive single-crystal synchrotron X-ray diffraction (XRD) and Fourier transform infrared absorption (FTIR) spectroscopy. Experiments were conducted in various pressure transmitting media (helium and neon for XRD, nitrogen and KBr for FTIR experiments) to study the effect of deviatoric stress on phase transformations. Contrary to As<sub>4</sub>O<sub>6</sub> arsenolite, a material of similar cage-like molecular structure, no pressure-induced helium penetration into the crystal structure was observed. Instead, two pressure-induced structural changes are observed. The first one is suggested by the following occurrences: (i) gradual quenching of the magnitudes of atomic displacement parameters, (ii) diminishing libration contribution to the experimental C−N bond length, (iii) discontinuity in calculated IR-active vibrational modes and (iv) asymptotically vanishing discrepancy between the experimental and DFT‑calculated unit cell volume. All these features reach a plateau at ~4 GPa and can be attributed to a damping of molecular librations and atomic thermal motion, pointing to the existence of a second-order isostructural phase transition. The second transformation, with an onset at ~12.5 GPa is a first-order phase transition to a tetragonal structure, characterized by sluggish kinetics and considerable hysteresis upon decompression. However, it occurs only in non-hydrostatic conditions, induced by a deviatoric stress in the sample. This behavior finds analogies in similar cubic crystals built of highly symmetric cage-like molecules and <a>may be considered a common feature</a> of such systems. Last but not least, it is worth noting successful Hirshfeld atom refinements, carried out for the incomplete high-pressure diffraction data up to 14 GPa, yielded more realistic C−H bond lengths than the independent atom model.

scholarly journals Crystal structure of the high-pressure phase of the oxonitridosilicate chloride Ce4[Si4O3 + x N7 − x ]Cl1 − x O x , x ≃ 0.2

2006 ◽  
Vol 62 (2) ◽  
pp. 205-211 ◽  
Author(s):  
Alexandra Friedrich ◽  
Eiken Haussühl ◽  
Wolfgang Morgenroth ◽  
Alexandra Lieb ◽  
Björn Winkler ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Single Crystal ◽  
Structural Changes ◽  
Low Pressure ◽  
First Order Phase Transition ◽  
Compression Mechanism ◽  
Diamond Anvil ◽  
Structural Mechanisms ◽  
First Order Phase

The structural compression mechanism of Ce4[Si4O3 + x N7 − x ]Cl1 − x O x , x ≃ 0.2, was investigated by in situ single-crystal synchrotron X-ray diffraction at pressures of 3.0, 8.5 and 8.6 GPa using the diamond–anvil cell technique. On increasing pressure the low-pressure cubic structure first undergoes only minor structural changes. Between 8.5 and 8.6 GPa a first-order phase transition occurs, accompanied by a change of the single-crystal colour from light orange to dark red. The main structural mechanisms, leading to a volume reduction of about 5% at the phase transition, are an increase in and a rearrangement of the Ce coordination, the loss of the Ce2, Ce3 split position, and a bending of some of the inter-polyhedral Si—N—Si angles in the arrangement of the corner-sharing Si tetrahedra. The latter is responsible for the short c axis of the orthorhombic high-pressure structure compared with the cell parameter of the cubic low-pressure structure.

Crystal Structure of Urotropine Under High Pressure and Non-Hydrostatic Stress-Induced Phase Transitions in Cage Compounds

2020 ◽  
Author(s):  
Piotr A. Guńka ◽  
Anna Olejniczak ◽  
Samuele Fanetti ◽  
Roberto Bini ◽  
Ines E. Collings ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
High Pressure ◽  
Structural Changes ◽  
Hydrostatic Stress ◽  
Atomic Displacement ◽  
Deviatoric Stress ◽  
Cage Compounds ◽  
First Order Phase Transition ◽  
Atomic Displacement Parameters

High-pressure behavior of hexamthyleneteramine (urotropine) was studied <i>in situ</i> using angle-dispersive single-crystal synchrotron X-ray diffraction (XRD) and Fourier transform infrared absorption (FTIR) spectroscopy. Experiments were conducted in various pressure transmitting media (helium and neon for XRD, nitrogen and KBr for FTIR experiments) to study the effect of deviatoric stress on phase transformations. Contrary to As<sub>4</sub>O<sub>6</sub> arsenolite, a material of similar cage-like molecular structure, no pressure-induced helium penetration into the crystal structure was observed. Instead, two pressure-induced structural changes are observed. The first one is suggested by the following occurrences: (i) gradual quenching of the magnitudes of atomic displacement parameters, (ii) diminishing libration contribution to the experimental C−N bond length, (iii) discontinuity in calculated IR-active vibrational modes and (iv) asymptotically vanishing discrepancy between the experimental and DFT‑calculated unit cell volume. All these features reach a plateau at ~4 GPa and can be attributed to a damping of molecular librations and atomic thermal motion, pointing to the existence of a second-order isostructural phase transition. The second transformation, with an onset at ~12.5 GPa is a first-order phase transition to a tetragonal structure, characterized by sluggish kinetics and considerable hysteresis upon decompression. However, it occurs only in non-hydrostatic conditions, induced by a deviatoric stress in the sample. This behavior finds analogies in similar cubic crystals built of highly symmetric cage-like molecules and <a>may be considered a common feature</a> of such systems. Last but not least, it is worth noting successful Hirshfeld atom refinements, carried out for the incomplete high-pressure diffraction data up to 14 GPa, yielded more realistic C−H bond lengths than the independent atom model.

scholarly journals Crystal structure and non-hydrostatic stress-induced phase transition of urotropine under high pressure

2020 ◽  
Author(s):  
Piotr A. Guńka ◽  
Anna Olejniczak ◽  
Samuele Fanetti ◽  
Roberto Bini ◽  
Ines E. Collings ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
High Pressure ◽  
Structural Changes ◽  
Hydrostatic Stress ◽  
Atomic Displacement ◽  
Deviatoric Stress ◽  
First Order Phase Transition ◽  
Atomic Displacement Parameters ◽  
First Order Phase

High-pressure behavior of hexamthyleneteramine (urotropine) was studied <i>in situ</i> using angle-dispersive single-crystal synchrotron X-ray diffraction (XRD) and Fourier transform infrared absorption (FTIR) spectroscopy. Experiments were conducted in various pressure transmitting media (helium and neon for XRD, nitrogen and KBr for FTIR experiments) to study the effect of deviatoric stress on phase transformations. Contrary to As<sub>4</sub>O<sub>6</sub> arsenolite, a material of similar cage-like molecular structure, no pressure-induced helium penetration into the crystal structure was observed. Instead, two pressure-induced structural changes are observed. The first one is suggested by the following occurrences: (i) gradual quenching of the magnitudes of atomic displacement parameters, (ii) diminishing libration contribution to the experimental C−N bond length, (iii) discontinuity in calculated IR-active vibrational modes and (iv) asymptotically vanishing discrepancy between the experimental and DFT‑calculated unit cell volume. All these features reach a plateau at ~4 GPa and can be attributed to a damping of molecular librations and atomic thermal motion, pointing to the existence of a second-order isostructural phase transition. The second transformation, with an onset at ~12.5 GPa is a first-order phase transition to a tetragonal structure, characterized by sluggish kinetics and considerable hysteresis upon decompression. However, it occurs only in non-hydrostatic conditions, induced by a deviatoric stress in the sample. This behavior finds analogies in similar cubic crystals built of highly symmetric cage-like molecules and <a>may be considered a common feature</a> of such systems. Last but not least, it is worth noting successful Hirshfeld atom refinements, carried out for the incomplete high-pressure diffraction data up to 14 GPa, yielded more realistic C−H bond lengths than the independent atom model.

scholarly journals The structure of P21/c (Ca0.2Co0.8)CoSi2O6 pyroxene and the C2/c–P21/c phase transition in natural and synthetic Ca–Mg–Fe2+ pyroxenes

2018 ◽  
Vol 82 (1) ◽  
pp. 211-228 ◽  
Author(s):  
Mario Tribaudino ◽  
Luciana Mantovani ◽  
Francesco Mezzadri ◽  
Gianluca Calestani ◽  
Geoffrey Bromiley
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Ionic Radius ◽  
Structural Changes ◽  
Local Level ◽  
Chemical Mechanism ◽  
Slow Cooling ◽  
Cation Radius ◽  
The Difference ◽  
Natural And Synthetic

ABSTRACTA P21/c synthetic (Ca0.2Co0.8)CoSi2O6 pyroxene was synthesized by slow cooling from melt at high pressure. Single crystals suitable for X-ray diffraction were obtained and refined. The results were compared to those of C2/c pyroxenes along the series CaCoSi2O6–Co2Si2O6. Strong similarities in the crystal chemical mechanism of the transition with the synthetic CaFeSi2O6–Fe2Si2O6 and CaMgSi2O6–Mg2Si2O6 pyroxenes, both at an average and local level are apparent.The results, examined together with two new refinements of pigeonite in the ureilites ALHA77257 and RKPA80239 and with a set of natural and synthetic C2/c and P21/c pyroxenes, show that the average cation radius in the M2 site is the driving force for the phase transition from C2/c to P21/c. The longest M2–O3 distances and the O3–O3–O3 angles follow the same trend, dictated only by the ionic radius in M2, in either synthetic or natural pyroxenes, regardless of the ionic radius of the M1 cations. The transition also affects the difference between bridging and non-bridging oxygen atoms and the extent of tetrahedral deformation, whereas the M1–O, M2–O1 and M2–O2 distances are unaffected by the transition and are determined only by the ionic radius of the bonding cation. The structural changes between the ionic radius and the high temperature C2/c and P21/c transitions are similar, and different to the high-pressure transition.Analysis of natural and synthetic pyroxenes shows that the transition with composition occurs in strain free pyroxenes for a critical radius of 0.85 Å. Increasing strain stabilizes the P21/c structure to a higher temperature and larger cation radius.Finally, our results show that the monoclinic P21/c Ca-poor clinopyroxene, i.e the mineral pigeonite, crystallizes only at conditions where the structure is HT-C2/c, and changes to the P21/c symmetry during cooling.

scholarly journals Crystal structure and non-hydrostatic stress-induced phase transition of urotropine under high pressure

2020 ◽  
Author(s):  
Piotr A. Guńka ◽  
Anna Olejniczak ◽  
Samuele Fanetti ◽  
Roberto Bini ◽  
Ines E. Collings ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
High Pressure ◽  
Structural Changes ◽  
Hydrostatic Stress ◽  
Atomic Displacement ◽  
Deviatoric Stress ◽  
First Order Phase Transition ◽  
Atomic Displacement Parameters ◽  
First Order Phase

High-pressure behavior of hexamthyleneteramine (urotropine) was studied <i>in situ</i> using angle-dispersive single-crystal synchrotron X-ray diffraction (XRD) and Fourier transform infrared absorption (FTIR) spectroscopy. Experiments were conducted in various pressure transmitting media (helium and neon for XRD, nitrogen and KBr for FTIR experiments) to study the effect of deviatoric stress on phase transformations. Contrary to As<sub>4</sub>O<sub>6</sub> arsenolite, a material of similar cage-like molecular structure, no pressure-induced helium penetration into the crystal structure was observed. Instead, two pressure-induced structural changes are observed. The first one is suggested by the following occurrences: (i) gradual quenching of the magnitudes of atomic displacement parameters, (ii) diminishing libration contribution to the experimental C−N bond length, (iii) discontinuity in calculated IR-active vibrational modes and (iv) asymptotically vanishing discrepancy between the experimental and DFT‑calculated unit cell volume. All these features reach a plateau at ~4 GPa and can be attributed to a damping of molecular librations and atomic thermal motion, pointing to the existence of a second-order isostructural phase transition. The second transformation, with an onset at ~12.5 GPa is a first-order phase transition to a tetragonal structure, characterized by sluggish kinetics and considerable hysteresis upon decompression. However, it occurs only in non-hydrostatic conditions, induced by a deviatoric stress in the sample. This behavior finds analogies in similar cubic crystals built of highly symmetric cage-like molecules and <a>may be considered a common feature</a> of such systems. Last but not least, it is worth noting successful Hirshfeld atom refinements, carried out for the incomplete high-pressure diffraction data up to 14 GPa, yielded more realistic C−H bond lengths than the independent atom model.

scholarly journals High-pressure structural study of L-α-glutamine and the use of Hirshfeld surfaces and graph-set notation to investigate the hydrogen bonding present in the structure up to 4.9 GPa

2008 ◽  
Vol 64 (4) ◽  
pp. 466-475 ◽  
Author(s):  
P. Lozano-Casal ◽  
D. R. Allan ◽  
S. Parsons
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
High Pressure ◽  
Room Temperature ◽  
Structural Changes ◽  
X Ray Diffraction ◽  
X Ray ◽  
Layer Arrangement ◽  
Hirshfeld Surfaces ◽  
Graph Set

The crystal structure of L-α-glutamine has been elucidated at room temperature at pressures between 0 and 4.9 GPa by using single-crystal high-pressure X-ray diffraction techniques. The structure is primarily stabilized by five N—H...O intermolecular interactions, which link molecules in a herringbone-like layer arrangement, giving rise to voids within the solid. The application of pressure on the structure results in a reduction in the size of the voids, as a consequence of the shortening of the N—H...O hydrogen bonds, which compress to minimum N...O distances of around 2.6 Å, without driving the crystal structure to a phase transition. The decrease in the hydrogen-bond distances is due to the necessary stabilization of the structure, which arises from molecules modifying their positions to optimize electrostatic contacts and minimize the occupied space. Hirshfeld surfaces and fingerprint plots have been used to rapidly assess the structural changes that occur on application of pressure.

scholarly journals Orpiment under compression: metavalent bonding at high pressure

2020 ◽  
Vol 22 (6) ◽  
pp. 3352-3369 ◽  
Author(s):  
Vanesa Paula Cuenca-Gotor ◽  
Juan Ángel Sans ◽  
Oscar Gomis ◽  
Andres Mujica ◽  
Silvana Radescu ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Strong Change ◽  
Isostructural Phase Transition

Orpiment (α-As2S3) under compression reports a strong change in the coordination of As atoms at 25 GPa, which can be ascribed to an isostructural phase transition. These changes are consistent with the formation of metavalent bonds in orpiment.

scholarly journals Crystal and electronic structure engineering of tin monoxide by external pressure

2021 ◽  
Author(s):  
Kun Li ◽  
Junjie Wang ◽  
Vladislav A. Blatov ◽  
Yutong Gong ◽  
Naoto Umezawa ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Band Gap ◽  
High Pressures ◽  
Low Pressure ◽  
Widespread Application ◽  
Space Group ◽  
Tin Monoxide ◽  
High Possibility ◽  
Pressure Phase

AbstractAlthough tin monoxide (SnO) is an interesting compound due to its p-type conductivity, a widespread application of SnO has been limited by its narrow band gap of 0.7 eV. In this work, we theoretically investigate the structural and electronic properties of several SnO phases under high pressures through employing van der Waals (vdW) functionals. Our calculations reveal that a metastable SnO (β-SnO), which possesses space group P21/c and a wide band gap of 1.9 eV, is more stable than α-SnO at pressures higher than 80 GPa. Moreover, a stable (space group P2/c) and a metastable (space group Pnma) phases of SnO appear at pressures higher than 120 GPa. Energy and topological analyses show that P2/c-SnO has a high possibility to directly transform to β-SnO at around 120 GPa. Our work also reveals that β-SnO is a necessary intermediate state between high-pressure phase Pnma-SnO and low-pressure phase α-SnO for the phase transition path Pnma-SnO →β-SnO → α-SnO. Two phase transition analyses indicate that there is a high possibility to synthesize β-SnO under high-pressure conditions and have it remain stable under normal pressure. Finally, our study reveals that the conductive property of β-SnO can be engineered in a low-pressure range (0–9 GPa) through a semiconductor-to-metal transition, while maintaining transparency in the visible light range.

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