scholarly journals CoSO4·H2O and its continuous transition compared to the compression properties of isostructural kieserite-type polymorphs

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Manfred Wildner ◽  
Martin Ende ◽  
Johannes M. Meusburger ◽  
Roland Kunit ◽  
Philipp Matzinger ◽  
...  
Keyword(s):  
Phase Transition ◽  
Phase Space ◽  
Equations Of State ◽  
Driving Mechanism ◽  
Volume Data ◽  
Continuous Transition ◽  
Space Group ◽  
Β Phase ◽  
Bonding System ◽  
Α Phase

Abstract The kieserite-type compound cobalt(II) sulfate monohydrate, CoSO4·H2O, has been investigated under isothermal (T = 295 K) hydrostatic compression up to 10.1 GPa in a diamond anvil cell by means of single-crystal X-ray diffraction and Raman spectroscopy. The monoclinic α-phase (space group C2/c) undergoes a second-order ferroelastic phase transition at P c  = 2.40(3) GPa to a triclinic β-phase (space group P 1 ‾ $‾{1}$ ). Lattice elasticities derived from fitting third-order Birch-Murnaghan equations of state to the pressure dependent unit-cell volume data yield V 0 = 354.20(6) Å3, K 0 = 53.0(1.7) GPa, K′ = 5.7(1.8) for the α-phase and V 0 = 355.9(8) Å3, K 0 = 45.2(2.6) GPa, K′ = 6.6(6) for the β-phase. Crystal structure data of the high-pressure polymorph were determined at 2.98(6) and 4.88(6) GPa. The most obvious structural feature and thus a possible driving mechanism of the phase transition, is a partial rearrangement in the hydrogen bonding system. However, a comparative analysis of pressure-induced changes in the four kieserite-type compounds investigated to date suggests that the loss of the point symmetry 2 at the otherwise rather rigid SO4 tetrahedron, allowing symmetrically unrestricted tetrahedral rotations and edge tiltings in the β-phase, could be the actual driving mechanism of the phase transition.

scholarly journals Phase transition and structures of the twinned low-temperature phases of (Et4N)[ReS4]

2020 ◽  
Vol 76 (3) ◽  
pp. 231-235
Author(s):  
Eduard Bernhardt ◽  
Regine Herbst-Irmer
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Title Compound ◽  
Room Temperature ◽  
Monoclinic Space Group ◽  
Rapid Cooling ◽  
Space Group ◽  
Disordered Structure ◽  
Β Phase ◽  
Α Phase

The title compound, tetraethylammonium tetrathiorhenate, [(C2H5)4N][ReS4], has, at room temperature, a disordered structure in the space group P63 mc (Z = 2, α-phase). A phase transition to the monoclinic space group P21 (Z = 2, γ-phase) at 285 K leads to a pseudo-merohedral twin. The high deviation from the hexagonal metric causes split reflections. However, the different orientations could not be separated, but were integrated using a large integration box. Rapid cooling to 110–170 K produces a metastable β-phase (P63, Z = 18) in addition to the γ-phase. All crystals of the β-phase are contaminated with the γ-phase. Additionally, the crystals of the β-phase are merohedrally twinned. In contrast to the α-phase, the β- and γ-phases do not show disorder.

scholarly journals Prediction of 10-fold coordinated TiO2 and SiO2 structures at multimegabar pressures

2015 ◽  
Vol 112 (22) ◽  
pp. 6898-6901 ◽  
Author(s):  
Matthew J. Lyle ◽  
Chris J. Pickard ◽  
Richard J. Needs
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Electronic Properties ◽  
First Principles ◽  
Pressure Range ◽  
Extrasolar Planets ◽  
Equations Of State ◽  
Space Group ◽  
P Type ◽  
Pressure Phase

We predict by first-principles methods a phase transition in TiO2 at 6.5 Mbar from the Fe2P-type polymorph to a ten-coordinated structure with space group I4/mmm. This is the first report, to our knowledge, of the pressure-induced phase transition to the I4/mmm structure among all dioxide compounds. The I4/mmm structure was found to be up to 3.3% denser across all pressures investigated. Significant differences were found in the electronic properties of the two structures, and the metallization of TiO2 was calculated to occur concomitantly with the phase transition to I4/mmm. The implications of our findings were extended to SiO2, and an analogous Fe2P-type to I4/mmm transition was found to occur at 10 TPa. This is consistent with the lower-pressure phase transitions of TiO2, which are well-established models for the phase transitions in other AX2 compounds, including SiO2. As in TiO2, the transition to I4/mmm corresponds to the metallization of SiO2. This transformation is in the pressure range reached in the interiors of recently discovered extrasolar planets and calls for a reformulation of the equations of state used to model them.

Topotactic, pressure-driven, diffusion-less phase transition of layered CsCoO2 to a stuffed cristobalite-type configuration

2019 ◽  
Vol 75 (4) ◽  
pp. 704-710
Author(s):  
Naveed Zafar Ali ◽  
Branton J. Campbell ◽  
Martin Jansen
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Three Dimensional ◽  
Phase Cell ◽  
Ambient Conditions ◽  
Space Group ◽  
Layered Architecture ◽  
Β Phase ◽  
Vertex Sharing ◽  
Two Phases

CsCoO2, featuring a two-dimensional layered architecture of edge- and vertex-linked CoO4 tetrahedra, is subjected to a temperature-driven reversible second-order phase transformation (α → β) at 100 K, which corresponds to a structural relaxation with concurrent tilting and breathing modes of edge-sharing CoO4 tetrahedra. In the present investigation, it was found that pressure induces a phase transition, which encompasses a dramatic change in the connectivity of the tetrahedra. At 923 K and 2 GPa, β-CsCoO2 undergoes a first-order phase transition to a new quenchable high-pressure polymorph, γ-CsCoO2. It is built up of a three-dimensional cristobalite-type network of vertex-sharing CoO4 tetrahedra. According to a Rietveld refinement of high-resolution powder diffraction data, the new high-pressure polymorph γ-CsCoO2 crystallizes in the tetragonal space group I41/amd:2 (Z = 4) with the lattice constants a = 5.8711 (1) and c = 8.3214 (2) Å, corresponding to a shrinkage in volume by 5.7% compared with the ambient-temperature and atmospheric pressure β-CsCoO2 polymorph. The pressure-induced transition (β → γ) is reversible; γ-CsCoO2 stays metastable under ambient conditions, but transforms back to the β-CsCoO2 structure upon heating to 573 K. The transformation pathway revealed is remarkable in that it is topotactic, as is demonstrated through a clean displacive transformation track between the two phases that employs the symmetry of their common subgroup Pb21 a (alternative setting of space group No. 29 that matches the conventional β-phase cell).

Structural phase transitions, and Br...N and Br...Br interactions in 1-phenyl-2-methyl-4-nitro-5-bromoimidazole

2004 ◽  
Vol 60 (3) ◽  
pp. 333-342 ◽  
Author(s):  
Maciej Kubicki
Keyword(s):  
Phase Transitions ◽  
Crystal Packing ◽  
Structural Phase ◽  
Molecular Geometry ◽  
Second Phase ◽  
Triclinic Space Group ◽  
Space Group ◽  
Β Phase ◽  
Α Phase ◽  
Second Order Transition

Crystals of C10H8N3O2Br undergo two reversible phase transitions between 295 and 100 K. The first, of an order–disorder nature, is a second-order transition and takes place continuously over a wide temperature range. This transition is connected with the doubling of the length of the c axis of the unit cell and with the change of the space group from P21/m with Z′ = 1/2 (room-temperature α-phase) to P21/c, Z′ = 1 (β-phase, 200–120 K). During this transition the molecule loses the C s symmetry of the α-phase. The second transition takes place between 118 and 115 K, and is accompanied by a change of the crystal symmetry to the triclinic space group P\bar 1 (low-temperature γ-phase). This second phase transition is accompanied by the twinning of the crystal. Neither the molecular geometry nor the crystal packing shows any dramatic changes during these phase transitions. Halogen bonds C—Br...N and dihalogen interactions Br...Br play a crucial role in determining the crystal packing and compete successfully with other kinds of weak intermolecular interactions.

Brillouin scattering near the α–β phase transitions of N2 and CO

1988 ◽  
Vol 66 (4) ◽  
pp. 541-548 ◽  
Author(s):  
V. Askarpour ◽  
H. Klefte ◽  
M. J. Clouter
Keyword(s):  
Phase Transition ◽  
Single Crystals ◽  
Elastic Constants ◽  
Brillouin Scattering ◽  
X Ray Diffraction ◽  
X Ray ◽  
Β Phase ◽  
Α Phase ◽  
Mode Softening ◽  
Cubic Structure

The technique of high resolution Brillouin spectroscopy has been used to determine the adiabatic elastic constants of single crystals of β-N2 and β-CO as a function of temperature, in an effort to study the α–β phase transition. For all elastic constants, there is an increase of approximately 1%/K on cooling and there is no evidence of further mode softening, even within 0.5 K of the phase transition. Three large single crystals of α-CO were grown. The orientations were determined, by Laue X-ray diffraction, and correlated to the orientations of the parent β-crystals. The β-phase hexagonal basal planes appear to transform to planes of the form {110} in the α-phase cubic structure.

scholarly journals Investigation of phase transformation in Fe microalloyed Ti6Al4V alloy during continuous heating process

2020 ◽  
Vol 321 ◽  
pp. 12010
Author(s):  
Changliang Wang ◽  
Feng Li ◽  
Can Ding ◽  
Hui Chang ◽  
Lian Zhou
Keyword(s):  
Phase Transition ◽  
Phase Transformation ◽  
Expansion Method ◽  
Ti6al4v Alloy ◽  
Continuous Heating ◽  
Heating Process ◽  
Β Phase ◽  
Α Phase ◽  
Phase Transition Temperatures ◽  
Evolution Of Microstructure

The phase transformation and dilatometric curves in Fe microalloyed Ti6Al4V alloy (Ti6Al4V-Fe) during continuous heating at 1 ℃ /min heating rate had been studied by dilatometer and metallographic methods, and β phase transition temperatures of alloy were obtained. In order to validate the accuracy of these β phase transition temperature and microstructure evolution, the relative phase concentration and the evolution of microstructure which were acquired by cooling after tempering were analyzed by metallographic microscope. The results illuminated that the expansion method was able to accurately measure the β transformation temperature of Ti6Al4V-Fe alloy. The lathy-shaped α phase decreased significantly disappeared in the range of 838℃ to 988℃, and the α→β phase transformation occurred.

TEM characterization of the α' and β phases in polycrystalline distrontium silicate (Sr2SiO4)

1992 ◽  
Vol 50 (1) ◽  
pp. 354-355
Author(s):  
Y. J. Kim ◽  
J. L. Shull ◽  
W. M. Kriven
Keyword(s):  
Electron Beam ◽  
Phase Space ◽  
Atmospheric Pressure ◽  
Sintering Temperature ◽  
Major Phase ◽  
Space Group ◽  
Temperature Range ◽  
Β Phase ◽  
Tem Characterization

Two polymorphs, α' and β, are known to be major phases in pure distrontium silicate (Sr2SiO4) at atmospheric pressure. Fully dense pellets were fabricated by sintering chemically prepared powders in the temperature range of 900° to 1400°C for 1 to 5 hours. Their phases and microstructures were studied by TEM. At lower sintering temperatures such as 900°C, the major phase was orthorhombic α' (space group, Pmnb). The euhedral α' grains had a size of about 1 μm diameter (Fig. la). As the sintering temperature increased, the amount of monoclinic β phase (space group, P21/n) tended to increase. These β grains were usually irregular and twinned on {100}β or {001}β planes. Concentration of the electron beam on the grains gave rise to a disappearance of twins (Fig. lb).

scholarly journals Über Verbindungen subvalenter Hauptgruppenmetallkationen mit Dithiolaten, 1. Mitteilung. Das dimorphe Blei(II)-l,l-dicyanoethylen-2,2-dithiolat: Darstellung und Kristallstrukturen / Compounds of Subvalent Main Group Metal Cations with Dithiolates, 1. Contribution. Dimorphie Lead(II) l,l-Dicyanoethylene-2,2-dithiolate: Preparation and Crystal Structures

1988 ◽  
Vol 43 (4) ◽  
pp. 389-398 ◽  
Author(s):  
Hans-U. Hummel ◽  
Hermann Meske
Keyword(s):  
Crystal Structures ◽  
Lone Pair ◽  
Metal Cations ◽  
Hydrothermal Conditions ◽  
Space Group ◽  
Β Phase ◽  
Α Phase ◽  
Small Crystals ◽  
Main Group Metal ◽  
Two Phases

Abstract By reaction of Pb(CH3COO)2 · 3H2O with Na2S2C=C(CN)2 · 3H2O in water, α-PbS2C=C(CN)2 is obtained. Hydrothermal conditions give small crystals of the α-and β-phase. The crystal structures of the two phases have been determined. The α-phase is monoclinic with space group P21/n and a = 11.879(5), b = 12.027(5), c = 4.655(1) Å, β = 96.94(3)°, Z = 4. The compound contains PbS2C4N2 molecules with Pb-S = 2.66 and 2.90 Å. Two molecules are connected to dimers with Pb···Pb = 4.44 Å. The β-phase also crystallizes monoclinically, space group C2/c, a = 9.613(1), b = 13.579(1), c -16.052(2) Å, β = 98.36°, and Z = 12. There are two independent lead positions, with the metals integrated in PbS2C = C(CN)2 groups with a stereochemically active lone-pair, and dimers Pb2(S2C4N2)2 with Pb···Pb distance = 3.80 Å.

TWO EQUATIONS OF STATE CONSIDERING THE THERMAL EFFECT FOR α, β AND ω PHASES OF ZIRCONIUM

2008 ◽  
Vol 22 (03) ◽  
pp. 167-180
Author(s):  
RONGGANG TIAN ◽  
JIUXUN SUN ◽  
CHAO ZHANG ◽  
FULONG WANG
Keyword(s):  
Experimental Data ◽  
Thermal Effect ◽  
Equations Of State ◽  
Zero Point ◽  
Hexagonal Structure ◽  
Zero Temperature ◽  
Β Phase ◽  
Ω Phase ◽  
Α Phase ◽  
Einstein Model

The Baonza and mGLJ equations of state (EOS) modified previously to consider the thermal effect are applied to study the thermodynamic properties of Zirconium (Zr) . It is proposed that the zero-point vibration term should be deleted in a thermal EOS, and the parameters cannot be directly taken as experimental data at a reference temperature, [Formula: see text] and [Formula: see text], but their values at absolute zero temperature, [Formula: see text] and [Formula: see text]. Based on the Einstein model, an approach is proposed to solve [Formula: see text] and [Formula: see text] from [Formula: see text] and [Formula: see text]. For the hcp (α phase), bcc (β phase) and hexagonal structure (ω phase) of Zr , the molar volume (V), isothermal bulk modulus (B) and thermal expansion coefficient (α) was calculated as a function of pressure and temperature. The predictive capabilities of the complete EOS are discussed and compared with experimental data.

Stretching Induced Crystalline-Phase Transition in Energy-Conversion Poly(Vinylidene Fluoride) (PVDF) Films

2014 ◽  
Vol 1070-1072 ◽  
pp. 589-593
Author(s):  
Fei Peng Wang ◽  
Zheng Yong Huang ◽  
Jian Li
Keyword(s):  
Phase Transition ◽  
Crystalline Phase ◽  
High Speed ◽  
Vinylidene Fluoride ◽  
X Ray Diffraction ◽  
X Ray ◽  
Β Phase ◽  
Α Phase ◽  
Poly Vinylidene Fluoride ◽  
Crystalline Phase Transition

Commercial poly (vinylidene fluoride) (PVDF) films are uniaxially stretched with varying rates at 110 °C in order to endow PVDF piezo-and pyroelectric by crystalline-phase transition from α to β during the stretching. The crystalline phases are determined by infrared spectroscopy. The β-phase content and its fraction in films increase as a result of stretching with high rates. In addition, higher stretching rates yield a slight increase of γ phase. The crystallite size is evaluated by means of X-ray diffraction. It is found that the β-phase crystallites become smaller with fast stretching, whereas the α-phase crystallites are cracked and disappear at high-speed stretching of 2.5 /min.

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