The Effects of Hydrogen on the Stability of the Orthorhombic Phase in Ti-24Al-11Nb

Easy crystallization distinguishes xylitol from other sugars, which usually condense into a syrup from aqueous solution. Although two polymorphs, i.e. metastable monoclinic and high-density orthorhombic, have been reported for xylitol, only the latter is in practical use. Under high pressure, the same orthorhombic phase has been obtained by both isothermal and isochoric recrystallization. The stability of the orthorhombic xylitol phase to 5.0 GPa has been correlated with a uniform compression of all hydrogen bonds and some flexibility of the molecular conformation, which cushion the pressure-induced local strains. The anisotropic compressibility of xylitol and its thermal expansion are consistent with the rule of inverse effects of pressure and temperature. This inverse strain relationship has been correlated with the dimensions and orientation of xylitol molecules in the crystal structure.

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Phase Stability of Sigma + Beta Microstructures in the Ternary Nb-Ti-Al System

MRS Proceedings ◽

10.1557/proc-194-393 ◽

1990 ◽

Vol 194 ◽

Cited By ~ 4

Author(s):

D. T. Hoelzer ◽

F. Ebrahimi

Keyword(s):

Phase Stability ◽

Orthorhombic Phase ◽

Beta Phase ◽

Phase Region ◽

Nominal Composition ◽

Two Phase ◽

Σ Phase ◽

Β Phase ◽

Heat Treated ◽

The Stability

AbstractAn alloy with the nominal composition 42Nb-28Ti-30Al (at.%) was heat treated in the sigma + beta phase region. The evolution of σ phase from the metastable β phase and the stability of the two-phase microstructure at various aging temperatures were evaluated using TEM techniques. The results indicate that the β phase in equilibrium with the σ phase at high temperatures decomposes to the orthorhombic phase at temperatures below 1200°C.

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Phase transitions in silicate perovskites from first principles

Mineralogical Magazine ◽

10.1180/002646198547981 ◽

1998 ◽

Vol 62 (5) ◽

pp. 585-598 ◽

Cited By ~ 27

Author(s):

Michele C. Warren ◽

Graeme J. Ackland ◽

Bijaya B. Karki ◽

Stewart J. Clark

Keyword(s):

Phase Transitions ◽

First Principles ◽

Orthorhombic Phase ◽

Magnesium Silicate ◽

Phonon Modes ◽

Equilibrium Structures ◽

Zone Centre ◽

The Stability ◽

Dynamics Simulations ◽

Structure Calculations

AbstractThe equilibrium structures of cubic, tetragonal and orthorhombic phases of magnesium silicate perovskite are found from first principles electronic structure calculations. Zone centre and zone boundary phonons of each phase are also calculated from ab initio forces from finite displacments, and phase transitions between the phases are analysed in terms of phonon instabilities, and coupling between modes. Both the cubic and tetragonal phases have strongly unstable modes dominated by rotation of the SiO6 octahedra, which freeze in to ultimately form the orthorhombic phase. First priniciples molecular dynamics simulations at finite temperatures are used to further investigate the stability of the intermediate tetragonal phase and the coupling between participating phonon modes. The implications for a transition temperature between orthorhombic and tetragonal phases are discussed.

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On the Twin Formation in Orthorhombic Y1Ba2Cu3O7-Y

MRS Proceedings ◽

10.1557/proc-99-233 ◽

1987 ◽

Vol 99 ◽

Cited By ~ 1

Author(s):

D. Rios-Jara ◽

C. Varea ◽

A. Robledo ◽

A. Huanosta ◽

J. M. Dominguez ◽

...

Keyword(s):

Oxygen Content ◽

Orthorhombic Phase ◽

Electron Energy Loss Spectrometry ◽

Relative Value ◽

Kinetics Of Formation ◽

Twin Formation ◽

The Stability ◽

Electron Energy Loss ◽

Kinetics Of ◽

Scanning Electron

ABSTRACTTransmission and scanning electron microscopy were used to study some features of twins in the orthorhombic phase of Y1Ba2Cu3O7-Y compounds. A model that explains the formation and proliferation of thene defectr, is proposed. Some conclusions about the kinetics of formation of these defects are stated, which agree with observed changes in twin densities produced by different cooling rates. Electron energy loss spectrometry (EELS) was ucod to measure relative changes in oxygen, which give some information about the relative value and the stability of oxygen content in twinned regions. A Braggs-Williams model of the order-disorder transition, for oxygen occupancies in the Cu-O2 planes, predicts an enrichment of vacancies at the boundaries in these oxygen deficient perovskites. This could explain the observed deficiency in oxygen content with respect to the perfect Y1Ba2Cu3O7 stoichio-metry.

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Pressure-induced transformations in deep mantle and core minerals

Mineralogical Magazine ◽

10.1180/002646100549265 ◽

2000 ◽

Vol 64 (2) ◽

pp. 157-184 ◽

Cited By ~ 15

Author(s):

R. J. Hemley ◽

H. K. Mao ◽

S. A. Gramsch

Keyword(s):

Room Temperature ◽

Orthorhombic Phase ◽

Stability Field ◽

Single Crystal Diffraction ◽

X Ray ◽

Deep Mantle ◽

Diamond Anvil ◽

The Stability ◽

Experimental And Theoretical Studies ◽

Insight Into

AbstractRecent experimental and theoretical studies provide new insight into the variety of high-pressure transformations in minerals that comprise the Earth’s deep mantle and core. Representative examples of reconstructive, displacive, electronic and magnetic transformations studied by new diamond-anvil cell techniques are examined. Despite reports for various transitions in (Mg,Fe)SiO3-perovskite, the stability field of the orthorhombic phase expands relative to magnesiowüstite + SiO2 with increasing pressure and temperature. The partitioning of Fe and Mg between Mg-rich silicate perovskite magnesiowüstite depends strongly on pressure, temperature, bulk Fe/Mg ratio, and ferric iron content. The soft-mode transition in SiO2 from the rutile- to CaCl2-type structure, originally documented by X-ray powder diffraction, Raman scattering, and first-principles theory has been explored in detail by single crystal diffraction, and transitions to higher-pressure forms have been examined. The effect of H on the transformations of various nominally anhydrous phases and transitions in dense hydrous Mg-silicates are also examined. New studies of the phase diagram of FeO include the transition to rhombohedral and higher-pressure NiAs polymorphs, and provide prototypical examples of coupled structural, electronic, and magnetic transitions. High-spin/low-spin transitions in FeO have been examined by high-resolution X-ray emission spectroscopy to 150 GPa, and the results are compared with similar studies of Fe2O3 and FeS. Finally, laser-heating studies to above 150 GPa and 2500K show that (hcp) ε-Fe has a large P-T stability field. Radial XRD measurements carried out at room temperature to 220 GPa have constrained the elasticity, rheology and sound velocities of ε-Fe at core pressures.

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Trimorphism of 2,2'-dipyridylamine: structures, phase transitions and thermodynamic stabilities

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768196004624 ◽

1996 ◽

Vol 52 (5) ◽

pp. 842-853 ◽

Cited By ~ 39

Author(s):

H. Schödel ◽

C. Näther ◽

H. Bock ◽

F. Butenschön

Keyword(s):

Single Crystals ◽

Room Temperature ◽

Orthorhombic Phase ◽

Detailed Comparison ◽

Molecular Structures ◽

Monoclinic Form ◽

Triclinic Phase ◽

Different Temperatures ◽

Stability Order ◽

The Stability

Crystals of an unknown third crystalline modification of 2,2′-dipyridylamine were obtained from acetone solution and their crystal structure was determined at both 150 K and room temperature. In contrast to the known orthorhombic and triclinic forms, which contain hydrogen-bridged dimers, the molecules of the monoclinic polymorph are arranged in tetramers. The crystallographic results for the monoclinic form are presented here, as well as a detailed comparison of crystal and molecular structures of the three polymorphs. Studies by differential thermal analysis (DTA) and optical microscopy, performed with single crystals, show a transformation of the orthorhombic phase at ~323 K and of the monoclinic form at ~368 K. According to powder diffraction studies, transformation of the low melting orthorhombic polymorph results in a mixture of monoclinic and triclinic phases, whereas the monoclinic modification transforms into the triclinic phase just below its melting point at 368 K. The single crystals of both forms are destroyed during the conversion and, therefore, in both cases a reconstructive transition via nucleation and growth should occur. The conditions for the crystallization of the distinct modifications and their relative thermodynamic stabilities are investigated in different solvents and at different temperatures. Independent of the solvent chosen, the orthorhombic form is the most stable below 263 K. In the range between 263 and 313 K the monoclinic form appears to be thermodynamically advantageous and above that temperature, the stability order is changed in favour of the triclinic polymorph. Based on the experimental results, a qualitative free energy-temperature diagram is provided.

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The Orthorhombic Phase of CaSiO3 Perovskite

MRS Proceedings ◽

10.1557/proc-718-d6.5 ◽

2002 ◽

Vol 718 ◽

Author(s):

Blanka Magyari-Köpe ◽

Levente Vitos ◽

Göran Grimvall ◽

Börje Johansson ◽

János Kollár

Keyword(s):

Crystal Structure ◽

Hydrostatic Pressure ◽

Total Energy ◽

Ab Initio ◽

Orthorhombic Phase ◽

Orthorhombic Distortion ◽

Gradual Reduction ◽

Energy Calculations ◽

Casio3 Perovskite ◽

The Stability

AbstractAb initio total energy calculations, combined with the global parametrization method of perovskite structures, are used to investigate the stability of cubic CaSiO3 against octahedral rotations. We propose an equilibrium crystal structure of orthorhombic Pbnm symmetry. The larger compressibility of the SiO6 octahedra relative to the CaO12 polyhedra is reflected in gradual reduction of the orthorhombic distortion with hydrostatic pressure.

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THEORETICAL ANALYSIS OF COEXISTING TETRAGONAL AND RHOMBOHEDRAL PHASE IN PB(ZR0.35TI0.65)O3 FILMS

International Journal of Modern Physics B ◽

10.1142/s0217979211058791 ◽

2011 ◽

Vol 25 (11) ◽

pp. 1467-1473

Author(s):

QINGDONG CHEN ◽

XINZHONG LI ◽

LIBEN LI ◽

JINGHAN YOU ◽

JINSONG ZHU

Keyword(s):

Phase Diagrams ◽

Tetragonal Phase ◽

Rhombohedral Phase ◽

Orthorhombic Phase ◽

Misfit Strain ◽

Temperature Phase ◽

Stability Range ◽

Pzt Film ◽

The Stability ◽

Stability Ranges

Within the framework of Pertsev's thermodynamic theory, the equilibrium polarization states and the physical properties of single-domain Pb ( Zr 0.35 Ti 0.65) O 3 (PZT) thin films epitaxially grown on dissimilar cubic substrates are investigated. The "misfit strain-temperature" phase diagrams are obtained for the films. The presence of stability range of the rhombohedral phase is the characteristic feature of these phase diagrams, which separates the stability ranges of the tetragonal phase and the orthorhombic phase. The coexistence of the rhombohedral phase and the tetragonal phase in PZT film can be explained by Pertsev's theory with the gradient strain case with a suitable stress form.

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Open discussion

Symposium - International Astronomical Union ◽

10.1017/s0074180900029533 ◽

1982 ◽

Vol 99 ◽

pp. 605-613

Author(s):

P. S. Conti

Keyword(s):

Buenos Aires ◽

Large Mass ◽

List Type ◽

Common Phenomenon ◽

Open Discussion ◽

The Stability ◽

Ring Nebulae

Conti: One of the main conclusions of the Wolf-Rayet symposium in Buenos Aires was that Wolf-Rayet stars are evolutionary products of massive objects. Some questions:–Do hot helium-rich stars, that are not Wolf-Rayet stars, exist?–What about the stability of helium rich stars of large mass? We know a helium rich star of ∼40 MO. Has the stability something to do with the wind?–Ring nebulae and bubbles : this seems to be a much more common phenomenon than we thought of some years age.–What is the origin of the subtypes? This is important to find a possible matching of scenarios to subtypes.

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Symmetric Multistep Methods Revisited: II. Numerical Experiments

International Astronomical Union Colloquium ◽

10.1017/s0252921100031602 ◽

1999 ◽

Vol 173 ◽

pp. 309-314 ◽

Cited By ~ 3

Author(s):

T. Fukushima

Keyword(s):

Multistep Methods ◽

Computational Time ◽

Integration Time ◽

Implicit Methods ◽

Symmetric Methods ◽

Celestial Bodies ◽

The Stability ◽

Predictor Corrector ◽

Symmetric Multistep Methods ◽

Integration Errors

AbstractBy using the stability condition and general formulas developed by Fukushima (1998 = Paper I) we discovered that, just as in the case of the explicit symmetric multistep methods (Quinlan and Tremaine, 1990), when integrating orbital motions of celestial bodies, the implicit symmetric multistep methods used in the predictor-corrector manner lead to integration errors in position which grow linearly with the integration time if the stepsizes adopted are sufficiently small and if the number of corrections is sufficiently large, say two or three. We confirmed also that the symmetric methods (explicit or implicit) would produce the stepsize-dependent instabilities/resonances, which was discovered by A. Toomre in 1991 and confirmed by G.D. Quinlan for some high order explicit methods. Although the implicit methods require twice or more computational time for the same stepsize than the explicit symmetric ones do, they seem to be preferable since they reduce these undesirable features significantly.

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