scholarly journals Pressure-induced coherent sliding-layer transition in the excitonic insulator Ta2NiSe5

IUCrJ ◽  
2018 ◽  
Vol 5 (2) ◽  
pp. 158-165 ◽  
Author(s):  
Akitoshi Nakano ◽  
Kento Sugawara ◽  
Shinya Tamura ◽  
Naoyuki Katayama ◽  
Kazuyuki Matsubayashi ◽  
...  
Keyword(s):  
Phase Transition ◽  
Phase I ◽  
Phase Ii ◽  
Ambient Pressure ◽  
Structural Phase ◽  
Orthorhombic Phase ◽  
Phase Iii ◽  
Layer Transition ◽  
Coulombic Interactions ◽  
Excitonic Insulator

The crystal structure of the excitonic insulator Ta2NiSe5has been investigated under a range of pressures, as determined by the complementary analysis of both single-crystal and powder synchrotron X-ray diffraction measurements. The monoclinic ambient-pressure excitonic insulator phase II transforms upon warming or under a modest pressure to give the semiconductingC-centred orthorhombic phase I. At higher pressures (i.e.>3 GPa), transformation to the primitive orthorhombic semimetal phase III occurs. This transformation from phase I to phase III is a pressure-induced first-order phase transition, which takes place through coherent sliding between weakly coupled layers. This structural phase transition is significantly influenced by Coulombic interactions in the geometric arrangement between interlayer Se ions. Furthermore, upon cooling, phase III transforms into the monoclinic phase IV, which is analogous to the excitonic insulator phase II. Finally, the excitonic interactions appear to be retained despite the observed layer sliding transition.

scholarly journals High-pressure polymorphism in L-cysteine: the crystal structures of L-cysteine-III and L-cysteine-IV

2006 ◽  
Vol 62 (2) ◽  
pp. 296-309 ◽  
Author(s):  
Stephen A. Moggach ◽  
David R. Allan ◽  
Stewart J. Clark ◽  
Matthias J. Gutmann ◽  
Simon Parsons ◽  
...  
Keyword(s):  
Phase Transition ◽  
Hydrogen Bonds ◽  
Single Crystal ◽  
Intermediate Phase ◽  
Ambient Pressure ◽  
Orthorhombic Phase ◽  
Phase Iii ◽  
Crystal Phase Transition ◽  
Main Effects ◽  
New Phase

The crystal structure of the orthorhombic phase of L-cysteine (hereafter L-cysteine-I) consists of chains of molecules linked via NH...O hydrogen bonds. The chains are linked into a layer by other NH...O hydrogen bonds, forming R_4^4(16) ring motifs. The layers are linked by further NH...O and disordered SH...S/SH...O interactions. The main effects of compression to 1.8 GPa are to contract voids in the middle of the R_4^4(16) rings and to reduce S...S distances from 3.8457 (10) to 3.450 (4) Å. The latter is at the lower limit for S...S distances and we suggest that strain about the S atom is responsible for the formation of a new phase of L-cysteine, L-cysteine-III, above 1.8 GPa. The phase transition is accompanied by a change in the NCCS torsion angle from ca 60 to ca −60° and small positional displacements, but with no major changes in the orientations of the molecules. The structure of L-cysteine-III contains similar R-type ring motifs to L-cysteine-I, but there are no S...S contacts within 3.6 Å. L-Cysteine-III was found to be stable to at least 4.2 GPa. On decompression to 1.7 GPa, another single-crystal to single-crystal phase transition formed another previously uncharacterized phase, L-cysteine-IV. This phase is not observed on increasing pressure. The structure consists of two crystallographically independent cysteine molecules in the same conformations as those found in L-cysteine-I and L-cysteine-III. The structure separates into zones with are alternately phase I-like and phase III-like. L-Cysteine-IV can therefore be thought of as an unusual example of an intermediate phase. Further decompression to ambient pressure generates L-cysteine-I.

The low-temperature phase III structure and phase transition behaviour of cyclohexanone

2006 ◽  
Vol 62 (4) ◽  
pp. 592-598 ◽  
Author(s):  
Richard M. Ibberson
Keyword(s):  
Phase Ii ◽  
Ambient Pressure ◽  
Isotope Effects ◽  
Orthorhombic Phase ◽  
Phase Behaviour ◽  
Phase Iii ◽  
Temperature Phase ◽  
Space Group ◽  
Low Temperature Phase ◽  
Transition Behaviour

The crystal structure of phase III of perdeuterocyclohexanone, C6D10O, has been determined at 5 K using high-resolution neutron powder diffraction. Below its melting point of 245 K cyclohexanone forms a plastic crystal in the space group Fm\bar 3m. On cooling below 225 K the crystal transforms to the monoclinic phase III structure in the space group P21/n. The orthorhombic phase II structure exists under high pressure, but the triple point for all three phases is close to atmospheric pressure. Details of the phase II structure are also reported at 4.8 kbar (273 K) and ambient pressure. The phase behaviour of the compound and isotope effects are discussed.

scholarly journals High-Pressure Behaviors of Ag2S Nanosheets: An in Situ High-Pressure X-Ray Diffraction Research

Nanomaterials ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1640
Author(s):  
Ran Liu ◽  
Bo Liu ◽  
Quan-Jun Li ◽  
Bing-Bing Liu
Keyword(s):  
High Pressure ◽  
Phase I ◽  
Phase Ii ◽  
Structural Phase ◽  
Phase Iii ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structure Phase ◽  
Ag2s Nanoparticles

An in situ high-pressure X-ray diffraction study was performed on Ag2S nanosheets, with an average lateral size of 29 nm and a relatively thin thickness. Based on the experimental data, we demonstrated that under high pressure, the samples experienced two different high-pressure structural phase transitions up to 29.4 GPa: from monoclinic P21/n structure (phase I, α-Ag2S) to orthorhombic P212121 structure (phase II) at 8.9 GPa and then to monoclinic P21/n structure (phase III) at 12.4 GPa. The critical phase transition pressures for phase II and phase III are approximately 2–3 GPa higher than that of 30 nm Ag2S nanoparticles and bulk materials. Additionally, phase III was stable up to the highest pressure of 29.4 GPa. Bulk moduli of Ag2S nanosheets were obtained as 73(6) GPa for phase I and 141(4) GPa for phase III, which indicate that the samples are more difficult to compress than their bulk counterparts and some other reported Ag2S nanoparticles. Further analysis suggested that the nanosize effect arising from the smaller thickness of Ag2S nanosheets restricts the relative position slip of the interlayer atoms during the compression, which leads to the enhancing of phase stabilities and the elevating of bulk moduli.

Temperature-induced reversible structural phase transition and X-ray diffuse scattering in 2-amino-3-nitropyridinium hydrogen sulfate

2017 ◽  
Vol 73 (3) ◽  
pp. 337-346 ◽  
Author(s):  
Tamara J. Bednarchuk ◽  
Dorota Kowalska ◽  
Vasyl Kinzhybalo ◽  
Marek Wołcyrz
Keyword(s):  
Phase Transition ◽  
Phase I ◽  
Phase Ii ◽  
Diffuse Scattering ◽  
Structural Phase ◽  
Type Model ◽  
Hydrogen Sulfate ◽  
Space Group ◽  
X Ray ◽  
Reversible Phase Transition

The novel polar material 2-amino-3-nitropyridinium hydrogen sulfate, C5H6N3O2(HSO4) (abbreviated as 2A3NP-HS), was obtained and structurally characterized by means of single-crystal X-ray diffraction. At room temperature, 2A3NP-HS crystallizes as a non-centrosymmetric disordered phase (I) in the orthorhombicPna21space group. On cooling below 298 K, 2A3NP-HS undergoes a reversible phase transition to phase (II) with the monoclinic non-centrosymmetricP21space group. This transition might be classified as an `order–disorder' type. The structural details in both phases are analysed. Additionally, for phase (I), in the 304–365 K temperature range, diffuse scattering was found to be present in the form of elongated streaks parallel to thea* direction. This can be unravelled when implementing a short-range order affecting anionic cationic ribbons occurring in the structure, with correlations acting both in thea-direction and in thebc-plane. The results of Monte Carlo simulations, adapting a two-dimensional Ising-type model, reveal the formation of domains, which areb-elongated and thin alonga. Locally, the stacking of the ribbons in the domains reflects the ordered arrangement observed in the low-temperature monoclinic phase (II).

scholarly journals Structural phases of hexamethylenetetramine–pimelic acid (1/1): a unified description based on a stacking model

2003 ◽  
Vol 59 (4) ◽  
pp. 527-536 ◽  
Author(s):  
Manuel Gardon ◽  
Carlos B. Pinheiro ◽  
Gervais Chapuis
Keyword(s):  
Phase Transition ◽  
Phase Ii ◽  
Ambient Pressure ◽  
Phase Iii ◽  
Pimelic Acid ◽  
Unified Framework ◽  
Ferroelastic Phase Transition ◽  
Unusual Distribution ◽  
Diffraction Patterns ◽  
Lower Temperature

The thermotropic phase diagram of 1:1 co-crystals of hexamethylenetetramine and pimelic acid (heptanedioic acid) is investigated. Three crystalline phases are identified at ambient pressure. Phase I is disordered, as revealed by diffuse rods in its diffraction pattern. When the temperature is lowered the diffuse streaks disappear in Phase II, but superstructure reflections emerge indicating an ordering process of the structure through a non-ferroic, or at least non-ferroelastic, phase transition. Phase II is mainly characterized by an unusual distribution of its reflection intensities. Phase III is reached through a ferroelastic phase transition that induces twinned domains. A model based on the stacking of an elementary layer is proposed with the aim of describing the structures in a unified framework. Depending on the value of the unique stacking parameter η, each of the different structures observed can be reproduced by this model. Its validity is then tested by a series of simulations reproducing the main features of the diffraction patterns such as the diffuse scattering streaks, the occurrence of superstructure peaks at lower temperature and twinning.

Structure–property correlation over five phases and four transitions in Pb5Al3F19

2003 ◽  
Vol 59 (5) ◽  
pp. 557-574 ◽  
Author(s):  
S. C. Abrahams ◽  
J. Ravez ◽  
H. Ritter ◽  
J. Ihringer
Keyword(s):  
Phase I ◽  
Phase Ii ◽  
Thermal Hysteresis ◽  
Ambient Pressure ◽  
Entropy Change ◽  
Phase Iii ◽  
Mode Analysis ◽  
First Order ◽  
Five Phases ◽  
Phase Iv

The calorimetric and dielectric properties of Pb5Al3F19 in the five phases stable under ambient pressure are correlated with structure for fuller characterization of each phase. The first-order transition between ferroelectric phase V and antiferroelectric phase IV at T V,IV = 260 (5) K exhibits a thermal hysteresis of 135 (5) K on heating, with a maximum atomic displacement Δ(xyz)max = 1.21 (6) Å; the transition from phase IV to ferroelastic phase III at 315 (5) K is also first order but with a thermal hysteresis of 10 (5) K and Δ(xyz)max = 0.92 (7)  Å; that from phase III to paraelastic phase II at 360 (5) K is second order without hysteresis and has Δ(xyz)max = 0.69 (4) Å; and the transition from phase II to paraelectric phase I at 670 (5) K is second or higher order, with Δ(xyz)max = 0.7 (4) Å. The measured entropy change ΔS at T V,IV agrees well with ΔS as derived from the increased configurational energy by Stirling's approximation. For all other phase transitions, 0.5 ≥ ΔS > 0 J mol−1 K−1 is consistent with an entropy change caused primarily by the changes in the vibrational energy. The structure of phase III is determined both by group theoretical/normal mode analysis and by consideration of the structures of phases II, IV and V reported previously; refinement is by simultaneous Rietveld analysis of the X-ray and neutron diffraction powder profiles. The structure of prototypic phase I is predicted on the basis of the atomic arrangement in phases II, III, IV and V. The introduction of 3d electrons into the Pb5Al3F19 lattice disturbs the structural equilibrium, the addition of 0.04% Cr3+ causing significant changes in atomic positions and increasing T IV,III by ∼15 K. Substitution of Al3+ by 20% or more Cr3+ eliminates the potential minima that otherwise stabilize phases IV, III and II.

Bewegungstherapie und körperliche Aktivität bei Patienten mit Herzinsuffizienz

Praxis ◽  
2018 ◽  
Vol 107 (17-18) ◽  
pp. 951-958 ◽  
Author(s):  
Matthias Wilhelm
Keyword(s):  
Phase I ◽  
Phase Ii ◽  
Körperliche Aktivität ◽  
Phase Iii

Zusammenfassung. Herzinsuffizienz ist ein klinisches Syndrom mit unterschiedlichen Ätiologien und Phänotypen. Die überwachte Bewegungstherapie und individuelle körperliche Aktivität ist bei allen Formen eine Klasse-IA-Empfehlung in aktuellen Leitlinien. Eine Bewegungstherapie kann unmittelbar nach Stabilisierung einer akuten Herzinsuffizienz im Spital begonnen werden (Phase I). Sie kann nach Entlassung in einem stationären oder ambulanten Präventions- und Rehabilitationsprogramm fortgesetzt werden (Phase II). Typische Elemente sind Ausdauer-, Kraft- und Atemtraining. Die Kosten werden von der Krankenversicherung für drei bis sechs Monate übernommen. In erfahrenen Zentren können auch Patienten mit implantierten Defibrillatoren oder linksventrikulären Unterstützungssystemen trainieren. Wichtiges Ziel der Phase II ist neben muskulärer Rekonditionierung auch die Steigerung der Gesundheitskompetenz, um die Langzeit-Adhärenz bezüglich körperlicher Aktivität zu verbessern. In Phase III bieten Herzgruppen Unterstützung.

scholarly journals AB0332 IMMUNOSUPPRESSIVE AND IMMONOMODULATING AGENTS IN RHEUMATOID ARTHRITIS: A SYSTEMATIC REVIEW OF CLINICAL TRIALS AND THEIR CURRENT DEVELOPMENT STAGE

2020 ◽  
Vol 79 (Suppl 1) ◽  
pp. 1464.1-1465
Author(s):  
J. Blaess ◽  
J. Walther ◽  
J. E. Gottenberg ◽  
J. Sibilia ◽  
L. Arnaud ◽  
...  
Keyword(s):  
Rheumatoid Arthritis ◽  
Systematic Review ◽  
B Cells ◽  
Phase I ◽  
Phase Ii ◽  
Clinical Development ◽  
Phase Iii ◽  
Jak Inhibitors ◽  
Exclusion Criteria ◽  
Immunomodulating Drugs

Background:Rheumatoid arthritis (RA) is the most frequent chronic inflammatory diseases with an incidence of 0.5% to 1%. Therapeutic arsenal of RA has continuously expanded in recent years with the recent therapeutic progress with the arrival of conventional synthetic disease-modifying anti-rheumatic drugs (csDMARDs), biological (bDMARDs) and targeted synthetic (tsDMARDs), JAK inhibitors. However, there are still some unmet needs for patients who do not achieve remission and who continue to worsen despite treatments. Of note, only approximately 40% of patients are ACR70 responders, in most randomized controlled trials. For these patients, finding new therapeutic avenues is challenging.Objectives:The objective of our study was to analyze the whole pipeline of immunosuppressive and immunomodulating drugs evaluated in RA and describe their mechanisms of action and stage of clinical development.Methods:We conducted a systematic review of all drug therapies in clinical development in RA in 17 databases of international clinical trials. Inclusion criterion: study from one of the databases using the keywords “Rheumatoid arthritis” (search date: June 1, 2019). Exclusion criteria: non-drug trials, trials not related to RA or duplicates. We also excluded dietary regimen or supplementations, cellular therapies, NSAIDs, glucorticoids or their derivatives and non-immunosuppressive or non-immunomodulating drugs. For each csDMARD, bDMARD and tsDMARD, we considered the study at the most advanced stage. For bDMARDs, we did not take into account biosimilars.Results:The research identified 4652 trials, of which 242 for 243 molecules met the inclusion and exclusion criteria. The developed molecules belong to csDMARDs (n=21), bDMARDs (n=117), tsDMARDs (n=105).Among the 21 csDMARDs molecules: 8 (38%) has been withdrawn, 4 (19%) are already labelled in RA (hydroxychloroquine, leflunomide, methotrexate and sulfasalazine) and 9 (43%) are in development: 1 (11%) is in phase I/II, 5 (56%) in phase II, 3 (33%) in phase IV.Among the 117 bDMARDs molecules: 69 (59%) has been withdrawn, 9 (8%) are labeled in RA (abatacept, adalimumab, anakinra, certolizumab, etanercept, golimumab, infliximab, rituximab, sarilumab, tocilizumab) and 39 (33%) are in development: 9 (23%) in phase I, 3 (8%) in phase I/II, 21 (54%) in phase II, 5 (12%) are in phase III, 1 (3%) in phase IV. bDMARDs currently under development target B cells (n=4), T cells (n=2), T/B cells costimulation (n=2),TNF alpha (n=2), Interleukine 1 or his receptor (n=3), Interleukine 6 or his receptor (n=7), Interleukine 17 (n=4), Interleukine 23 (n=1), GM-CSF (n=1), other cytokines or chemokines (n=5), integrins or adhesion proteins (n=3), interferon receptor (n=1) and various other targets (n=4).Among the 105 tsDMARDs molecules: 64 (61%) has been withdrawn, 6 (6%) JAK inhibitors, have just been or will probably soon be labelled (baricitinib, filgotinib, peficitinib, tofacitinib and upadacitinib), 35 (33%) are in development: 8 (24%) in phase I, 26 (74%) in phase II, 1 (3%) in phase III and. tsDMARDs currently under development target tyrosine kinase (n=12), janus kinase (JAK) (n=3), sphingosine phostate (n=3), PI3K pathway (n=1), phosphodiesterase-4 (n=3) B cells signaling pathways (n=3) and various other targets (n=10).Conclusion:A total of 242 therapeutic trials involving 243 molecules have been or are being evaluated in RA. This development does not always lead to new treatments since 141 (58%) have already been withdrawn. Hopefully, some of the currently evaluated drugs will contribute to improve the therapeutic management of RA patients, requiring a greater personalization of therapeutic strategies, both in the choice of molecules and their place in therapeutic sequences.Disclosure of Interests:Julien Blaess: None declared, Julia Walther: None declared, Jacques-Eric Gottenberg Grant/research support from: BMS, Pfizer, Consultant of: BMS, Sanofi-Genzyme, UCB, Speakers bureau: Abbvie, Eli Lilly and Co., Roche, Sanofi-Genzyme, UCB, Jean Sibilia: None declared, Laurent Arnaud: None declared, Renaud FELTEN: None declared

scholarly journals Direct observation of excitonic instability in Ta2NiSe5

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Kwangrae Kim ◽  
Hoon Kim ◽  
Jonghwan Kim ◽  
Changil Kwon ◽  
Jun Sung Kim ◽  
...  
Keyword(s):  
Phase Transition ◽  
Direct Observation ◽  
Structural Phase ◽  
Temperature Phase ◽  
Phonon Coupling ◽  
Strong Electron ◽  
Weiss Temperature ◽  
Excitonic Insulator ◽  
Electron Phonon Coupling ◽  
Low Temperature Phase

AbstractCoulomb attraction between electrons and holes in a narrow-gap semiconductor or a semimetal is predicted to lead to an elusive phase of matter dubbed excitonic insulator. However, direct observation of such electronic instability remains extremely rare. Here, we report the observation of incipient divergence in the static excitonic susceptibility of the candidate material Ta2NiSe5 using Raman spectroscopy. Critical fluctuations of the excitonic order parameter give rise to quasi-elastic scattering of B2g symmetry, whose intensity grows inversely with temperature toward the Weiss temperature of TW ≈ 237 K, which is arrested by a structural phase transition driven by an acoustic phonon of the same symmetry at TC = 325 K. Concurrently, a B2g optical phonon becomes heavily damped to the extent that its trace is almost invisible around TC, which manifests a strong electron-phonon coupling that has obscured the identification of the low-temperature phase as an excitonic insulator for more than a decade. Our results unambiguously reveal the electronic origin of the phase transition.

scholarly journals Unconventional Anticancer Agents: A Systematic Review of Clinical Trials

2006 ◽  
Vol 24 (1) ◽  
pp. 136-140 ◽  
Author(s):  
Andrew J. Vickers ◽  
Joyce Kuo ◽  
Barrie R. Cassileth
Keyword(s):  
Clinical Trials ◽  
Phase I ◽  
Cancer Patients ◽  
Phase Ii ◽  
Dose Finding ◽  
Phase Iii ◽  
High Dose ◽  
Free Text ◽  
Phase Ii Trials ◽  
Off Label

Purpose A substantial number of cancer patients turn to treatments other than those recommended by mainstream oncologists in an effort to sustain tumor remission or halt the spread of cancer. These unconventional approaches include botanicals, high-dose nutritional supplementation, off-label pharmaceuticals, and animal products. The objective of this study was to review systematically the methodologies applied in clinical trials of unconventional treatments specifically for cancer. Methods MEDLINE 1966 to 2005 was searched using approximately 200 different medical subject heading terms (eg, alternative medicine) and free text words (eg, laetrile). We sought prospective clinical trials of unconventional treatments in cancer patients, excluding studies with only symptom control or nonclinical (eg, immune) end points. Trial data were extracted by two reviewers using a standardized protocol. Results We identified 14,735 articles, of which 214, describing 198 different clinical trials, were included. Twenty trials were phase I, three were phase I and II, 70 were phase II, and 105 were phase III. Approximately half of the trials investigated fungal products, 20% investigated other botanicals, 10% investigated vitamins and supplements, and 10% investigated off-label pharmaceuticals. Only eight of the phase I trials were dose-finding trials, and a mere 20% of phase II trials reported a statistical design. Of the 27 different agents tested in phase III, only one agent had a prior dose-finding trial, and only for three agents was the definitive study initiated after the publication of phase II data. Conclusion Unconventional cancer treatments have not been subject to appropriate early-phase trial development. Future research on unconventional therapies should involve dose-finding and phase II studies to determine the suitability of definitive trials.

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