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.

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.

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.

Effect of high hydrostatic pressure on the enzymic hydrolysis of β-lactoglobulin B by trypsin, thermolysin and pepsin

1996 ◽  
Vol 63 (1) ◽  
pp. 111-118 ◽  
Author(s):  
Henrik Stapelfeldt ◽  
Per Hjort Petersen ◽  
Kristian Rotvig Kristiansen ◽  
Karsten Bruun Qvist ◽  
Leif H. Skibsted
Keyword(s):  
High Pressure ◽  
Hydrostatic Pressure ◽  
High Hydrostatic Pressure ◽  
Pressure Effect ◽  
Ambient Pressure ◽  
Apparent Volume ◽  
Enzymic Hydrolysis ◽  
Ambient Conditions ◽  
Β Lactoglobulin ◽  
Hydrolysis Of

SummaryHydrolysis of β-lactoglobulin B (β-lg B) by pepsin, a process slow at ambient conditions, is facilitated at a moderately high hydrostatic pressure such as 300 MPa, corresponding to an apparent volume of activation ΔV# = −63 ml mol−1 at pH 2·5, 30 °C and Γ/2=0·16. Digestion of β-lg by trypsin and thermolysin is likewise enhanced by pressure, and the pressure effect has been traced to pressure denaturation of β-lg B, which by high-pressure fluorescence spectroscopy has been shown to have a large negative volume of reaction, ΔV° = −98 ml mol−1, at pH 6·7, 30 °C and Γ/2 = 0·16. Pressure denaturation is only slowly reversed following release of pressure and the enhanced digestibility is maintained at ambient pressure for several hours.

Phase transitions of BaCO3 at high pressures

2008 ◽  
Vol 72 (2) ◽  
pp. 659-665 ◽  
Author(s):  
S. Ono ◽  
J. P. Brodholt ◽  
G. D. Price
Keyword(s):  
Phase Transition ◽  
Experimental Study ◽  
High Pressure ◽  
Phase Transitions ◽  
Bulk Modulus ◽  
First Principles ◽  
High Pressures ◽  
Ambient Conditions ◽  
The Stability ◽  
Previous Experimental Study

AbstractFirst-principles simulations and high-pressure experiments were used to study the stability of BaCO3 carbonates at high pressures. Witherite, which is orthorhombic and isotypic with CaCO3 aragonite, is stable at ambient conditions. As pressure increases, BaCO3 transforms from witherite to an orthorhombic post-aragonite structure at 8 GPa. The calculated bulk modulus of the post-aragonite structure is 60.7 GPa, which is slightly less than that from experiments. This structure shows an axial anisotropicc ompressibility and the a axis intersects with the c axis at 70 GPa, which implies that the pressure-induced phase transition reported in previous experimental study is misidentified. Although a pyroxene-like structure is stable in Mg- and Ca-carbonates at pressures >100 GPa, our simulations showed that this structure does not appear in BaCO3.

scholarly journals The untypical high-pressure Zintl phase SrGe6

2020 ◽  
Vol 75 (1-2) ◽  
pp. 209-216 ◽  
Author(s):  
Ulrich Schwarz ◽  
Rodrigo Castillo ◽  
Julia M. Hübner ◽  
Aron Wosylus ◽  
Yurii Prots ◽  
...  
Keyword(s):  
High Pressure ◽  
Ambient Pressure ◽  
Three Dimensional ◽  
Structure Type ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
Quantum Chemical Analysis ◽  
Electronic Density ◽  
X Ray ◽  
High Pressure High Temperature

AbstractThe binary strontium germanide SrGe6 was synthesized at high-pressure high-temperature conditions of approximately 10 GPa and typically 1400 K before quenching to ambient conditions. At ambient pressure, SrGe6 decomposes in a monotropic fashion at T = 680(10) K into SrGe2 and Ge, indicating its metastable character. Single-crystal X-ray diffraction data indicate that the compound SrGe6 adopts a new monoclinic structure type comprising a unique three-dimensional framework of germanium atoms with unusual cages hosting the strontium cations. Quantum chemical analysis of the chemical bonding shows that the framework consists of three- and four- bonded germanium atoms yielding the precise electron count Sr[(4bGe0]4[(3b)Ge−]2 in accordance with the 8 − N rule and the Zintl concept. Conflicting with that, a pseudo-gap in the electronic density of states appears clearly below the Fermi level, and elaborate bonding analysis reveals additional Sr–Ge interactions in the concave coordination polyhedron of the strontium atoms.

Evidence for a Structural Transition to a Superprotonic CsH2PO4 Phase Under High Pressure

2006 ◽  
Vol 929 ◽  
Author(s):  
Cristian E. Botez ◽  
Russell R. Chianelli ◽  
Jianzhong Zhang ◽  
Jiang Qian ◽  
Yusheng Zhao ◽  
...  
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Structural Transition ◽  
Heating Temperature ◽  
Ambient Pressure ◽  
High Temperature Phase ◽  
Cubic Phase ◽  
Dihydrogen Phosphate ◽  
Temperature Phase ◽  
Ambient Conditions

ABSTRACTWe have used synchrotron X-ray powder diffraction (SXRPD) to investigate the structural behavior of cesium dihydrogen phosphate upon heating. Temperature-resolved data collected at ambient-pressure demonstrate that a transition from the room-temperature monoclinic phase (P21/m; a=7.90Å, b=6.39Å, c=4.87Å, and β=107.64°) to a high-temperature cubic phase (Pm3m; a=4.96Å) occurs at T=237°C. The high-temperature phase is not stable under ambient-pressure conditions, even in the absence of further heating. On the other hand, SXRPD measurements carried out under high-pressure (∼1GPa) evidence a transition from monoclinic to a stable cubic phase (Pm3m, a=4.88Å) at a temperature within the 255°C-275°C range. A 1000-fold increase in the proton conductivity (indicating the transition to the superprotonic phase) was previously observed under the same non-ambient conditions. Therefore, our results represent strong evidence that the superprotonic behavior in cesium dihydrogen phosphate is associated with a monoclinic-to-cubic polymorphic structural transition and not with chemical modifications.

Synthese und Hochdruckverhalten quaternärer Chalkogenidhalogenide M2M′X3Y (M = Zn, Cd; M′ = Al, Ga, In; X = Se, Te; Y = CI, Br, I) / Synthesis and High-Pressure Behaviour of Quaternary Chalcogenide Halides M2M′X3Y (M = Zn, Cd; M′ = Al, Ga, In; X = Se, Te; Y = Cl, Br, I)

1988 ◽  
Vol 43 (2) ◽  
pp. 153-158 ◽  
Author(s):  
Klaus-Jürgen Range ◽  
Karin Handrick
Keyword(s):  
High Pressure ◽  
Ambient Pressure ◽  
Type Structure ◽  
Zinc Blende ◽  
Binary Compounds ◽  
Gallium Compounds

Quaternary chalcogenide halides M2M′X3Y (M = Zn, Cd; M′ = Al, Ga, In; X = Se, Te; Y = Cl, Br, I) can be synthesized by heating stoichiometric amounts of the binary components MX. MY2, and M′2X3 in evacuated sealed quartz ampoules. In the case of aluminium and gallium compounds, a mixture of the M′ and X elements rather than the binary compounds has been used. The products are typical tetrahedral compounds, crystallizing with either the defect wurtzite-type or the defect zinc-blende-type structure. At 25 kbar, and 1400 °C, Cd2InSe3Cl, Cd2InSe3Br, and Cd2InSe3I transform from the defect wurtzite-type structure to quenchable high-pressure phases with defect NaCl-type structure. The retransformation to the ambient-pressure phases proceeds via intermediates having the defect zinc-blende-type structure. Some aspects of the apparent non-stoichiometry in the high-pressure phases are discussed

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.

Structure of a high-pressure phase of vanadium pentoxide, β-V2O5

2004 ◽  
Vol 60 (4) ◽  
pp. 375-381 ◽  
Author(s):  
V. P. Filonenko ◽  
M. Sundberg ◽  
P.-E. Werner ◽  
I. P. Zibrov
Keyword(s):  
High Pressure ◽  
Vanadium Pentoxide ◽  
Layer Structure ◽  
Ambient Pressure ◽  
High Pressure Phase ◽  
X Ray ◽  
Transmission Electron ◽  
Structural Relationships ◽  
Oxide Bronzes ◽  
Pressure Phase

A high-pressure phase of vanadium pentoxide, denoted β-V2O5, has been prepared at P = 6.0 GPa and T = 1073 K. The crystal structure of β-V2O5 has been studied by X-ray and neutron powder diffraction, and high-resolution transmission electron microscopy. The V atoms are six-coordinated within distorted VO6 octahedra. The structure is built up of quadruple units of edge-sharing VO6 octahedra linked by sharing edges along [010] and mutually connected by sharing corners along [001]. This arrangement forms layers of V4O10 composition in planes parallel to (100). The layers are mutually held together by weak forces. β-V2O5 is metastable and transforms to α-V2O5 at 643–653 K under ambient pressure. Structural relationships between β- and α-V2O5, and between β-V2O5 and B-Ta2O5-type structures are discussed. The high-pressure β-V2O5 layer structure can be considered as the parent of a new series of vanadium oxide bronzes with cations intercalated between the layers.

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