Preparation, Characterization and Crystal Structure of the Room Temperature Phase of [(CH3)(C6H5)3P]2[ZnBr4]: A Member of the A2BX4 Family

2007 ◽  
Vol 62 (9) ◽  
pp. 549-554 ◽  
Author(s):  
Mohga F. Mostafa ◽  
Ahmed A. Youssef ◽  
Thanaa S. El-Dean ◽  
Aisha M. Mostafa ◽  
Ibrahim S Farag
Keyword(s):  
Crystal Structure ◽  
Room Temperature ◽  
Lattice Parameters ◽  
Order Transition ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
Higher Symmetry ◽  
First Order ◽  
Second Order Transition ◽  
First Order Transition

The compound bis(methyltriphenylphosphonium) tetrabromozincate(II), [C19H18P]2[ZnBr4], Mr = 939.640, has a monoclinic unit cell, space group P21. The lattice parameters are a = 9.7693(4) Å , b = 12.5508(4) Å , c = 16.5372(6) Å , α = 90.00°, β = 105.2670(11)°, γ = 90.00°, V = 1956.11(11) Å3, Z = 2, Dx = 1.595 mgm−3 at T = 298 K. The structure consists of one distorted [ZnBr4]2− tetrahedron and two [(CH3)(C6H5)3P]+ cations. Differential scanning calorimetry indicates a continuous second-order transition at (276±2) K that may be classified as a commensurate to incommensurate transformation. A first-order transition to a higher symmetry is associated with a four-fold rotation of the [ZnBr4]2− ion and a change of entropy ΔS = 22.92 J/(K· mol) at T = (362±3) K.Dilatometric measurements showed a decrease of the lattice parameters in the temperature range 230 - 260 K, confirmed the transition at (276±2) K, and indicated the presence of a third transition at 282 K.

Structural analysis of lanthanum gallate

1991 ◽  
Vol 6 (1) ◽  
pp. 97-100 ◽  
Author(s):  
J. Kobayashi ◽  
Y. Tazoh ◽  
M. Sasaura ◽  
S. Miyazawa
Keyword(s):  
Structural Phase ◽  
Order Transition ◽  
Lanthanum Gallate ◽  
Rhombohedral Structure ◽  
Structural Phase Transitions ◽  
Scanning Calorimetry ◽  
First Order ◽  
Dsc Measurements ◽  
Second Order Transition ◽  
First Order Transition

High temperature x-ray diffractometry (HT-XRD) and differential scanning calorimetry (DSC) measurements confirm that two kinds of structural phase transitions exist in LaGaO3. One is the first order transition from the orthorhombic to the rhombohedral structure at ∼150 °C. The other is the second order transition from the rhombohedral to the monoclinic structure from ∼750 °C to ∼1000 °C.

scholarly journals 127I NQR and Crystal Structure Studies of [N(CH3)4]2 CdI4

2000 ◽  
Vol 55 (1-2) ◽  
pp. 225-229 ◽  
Author(s):  
Hideta Ishihara ◽  
Keizo Horiuchi ◽  
Thorsten M. Gesing ◽  
Shi-qi Dou ◽  
J.-Christian Buhl ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Order Phase Transition ◽  
Intensity Ratio ◽  
Room Temperature ◽  
Liquid Nitrogen Temperature ◽  
Temperature Phase ◽  
First Order ◽  
First Order Phase Transition ◽  
First Order Phase

The temperature dependence of 127I NQR and DSC as well as the crystal structure at room temperature of the title compound were determined. This compound shows a first-order phase transition of an order-disorder type at 245 K. Eight 127I(v1:m = ±1/2 ↔ ±3/2) NQR lines of 79.57, 81.86, 82.56, 83.36, 84.68, 87.72, 88.34, and 88.86 MHz, and corresponding eight 127I(v2: m = ±3/2 ↔±5/2) NQR lines were observed at liquid nitrogen temperature. Three 127I(υi) NQR lines wfth an intensity ratio of 1:1:2 in the order of decreasing frequency were observed just above the transition point and two NQR lines except for the middle-frequency line disappeared around room temperature. This temperature behavior of NQR lines is very similar to that observed in [N(CH3)4]2Hgl4. Another first-order phase transition takes place at 527 K. The structure of the room-temperature phase was redetermined: orthorhombic, Pnma, Z = 4, a = 1342.8(3), b = 975.7(2), c = 1696.5(3) pm. The NQR result of three lines with an intensity ratio of 1:1:2 is in agreement with this structure. The thermal displacement parameters of atoms in both cations and anions are large.

Incommensurately modulated phase of Rb2CoBr4 at 295 and 200 K

2000 ◽  
Vol 56 (1) ◽  
pp. 17-21 ◽  
Author(s):  
K. Friese ◽  
G. Madariaga ◽  
T. Breczewski
Keyword(s):  
Crystal Structure ◽  
Close Relationships ◽  
Room Temperature ◽  
Lattice Parameters ◽  
Modulated Structure ◽  
Space Group ◽  
Average Structure ◽  
First Order ◽  
Modulation Function ◽  
Modulated Phase

The crystal structure of Rb_2CoBr_4 at 295 and 200 K has been determined. At these temperatures Rb_2CoBr_4 exhibits an incommensurately modulated structure with wavevector {\bf q} = (1/3+\delta){\bf a}^*. At room temperature only the average structure was refined. Lattice parameters are a = 9.732 (3), b = 13.328 (4), c = 7.654 (3) Å, space group Pnam. The R(F) value was 0.0414 for 286 observed reflections (0.0778 for all 477 reflections). At 200 K the lattice parameters are a = 9.691 (4), b = 13.278 (5), c = 7.630 (6) Å, superspace group P:Pnam:\overline{1}ss. Main reflections and satellite reflections of first order were measured. The refinement converged at R(F) = 0.052 for 309 observed reflections (255 main reflections and 54 satellites) and 0.2971 for all reflections (1849; 695 main reflections and 1154 satellites). Amplitudes and phases of the modulation function as well as bond distances show close relationships to those observed in the incommensurately modulated phase of Rb_2ZnBr_4.

Structural and thermal properties of Cu1.75−xMxTe crystals

2020 ◽  
Vol 34 (19) ◽  
pp. 2050180
Author(s):  
Y. I. Aliyev ◽  
Y. G. Asadov ◽  
L. B. Rustamova ◽  
A. O. Dashdemirov ◽  
N. A. Ismayilova ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Thermal Expansion ◽  
Room Temperature ◽  
Lattice Parameters ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cubic Phases ◽  
Temperature Dependences ◽  
Cubic Structure

Single crystals of Cu[Formula: see text]Te, Cu[Formula: see text]Zn[Formula: see text]Te and Cu[Formula: see text]Cd[Formula: see text]Te compounds were synthesized by Brijmen method and their crystal structure was studied by X-ray diffraction. The hexagonal, orthorhombic aand cubic structure phases of these compounds have been determined at room-temperature. Phase transitions at high-temperatures were observed. Lattice parameters for hexagonal, orthorhombic and cubic phases have been determined in the temperature range of [Formula: see text]–1073 K. From the temperature dependences of the lattice parameters, the coefficients of thermal expansion of the existing modifications in the main crystallographic directions were calculated.

scholarly journals The Haus-Tanaka Model for the Ice VII-Ice VIII Phase Transition

1980 ◽  
Vol 33 (1) ◽  
pp. 107 ◽  
Author(s):  
J Ho-Ting-Hun ◽  
J Oitmaa
Keyword(s):  
Phase Transition ◽  
Mean Field ◽  
Field Approximation ◽  
Order Transition ◽  
Mean Field Approximation ◽  
First Order ◽  
Second Order Transition ◽  
The Mean ◽  
First Order Transition ◽  
Temperature Susceptibility

The high temperature susceptibility series of the model proposed by Haus and Tanaka (1977) to account for the transition of the orientationally disordered ice VII phase to the orientationally ordered ice VIII phase does not provide evidence for the possible occurrence of a first-order transition, as predicted by the mean field approximation, but gives a second-order transition instead.

scholarly journals Crystal structure of K[Hg(SCN)3] – a redetermination

2014 ◽  
Vol 70 (9) ◽  
pp. i46-i46 ◽  
Author(s):  
Matthias Weil ◽  
Thomas Häusler
Keyword(s):  
Crystal Structure ◽  
Room Temperature ◽  
Three Dimensional ◽  
Lattice Parameters ◽  
Bond Lengths ◽  
Dimensional Network ◽  
Anisotropic Displacement Parameters ◽  
Precision And Accuracy ◽  
Standard Deviations ◽  
Atomic Coordinates

The crystal structure of the room-temperature modification of K[Hg(SCN)3], potassium trithiocyanatomercurate(II), was redetermined based on modern CCD data. In comparison with the previous report [Zhdanov & Sanadze (1952).Zh. Fiz. Khim.26, 469–478], reliability factors, standard deviations of lattice parameters and atomic coordinates, as well as anisotropic displacement parameters, were revealed for all atoms. The higher precision and accuracy of the model is, for example, reflected by the Hg—S bond lengths of 2.3954 (11), 2.4481 (8) and 2.7653 (6) Å in comparison with values of 2.24, 2.43 and 2.77 Å. All atoms in the crystal structure are located on mirror planes. The Hg2+cation is surrounded by four S atoms in a seesaw shape [S—Hg—S angles range from 94.65 (2) to 154.06 (3)°]. The HgS4polyhedra share a common S atom, building up chains extending parallel to [010]. All S atoms of the resulting1∞[HgS2/1S2/2] chains are also part of SCN−anions that link these chains with the K+cations into a three-dimensional network. The K—N bond lengths of the distorted KN7polyhedra lie between 2.926 (2) and 3.051 (3) Å.

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