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.

Modulated structures of Cs2HgCl4: the 5a superstructure at 185 K and the 3c superstructure at 176 K

1999 ◽  
Vol 55 (6) ◽  
pp. 886-895 ◽  
Author(s):  
Bagautdin Bagautdinov ◽  
Katrin Pilz ◽  
Jens Ludecke ◽  
Sander van Smaalen
Keyword(s):  
Synchrotron Radiation ◽  
Room Temperature ◽  
Normal Phase ◽  
Lattice Parameters ◽  
Temperature Structure ◽  
Space Group ◽  
X Ray ◽  
X Ray Scattering ◽  
Modulated Structures ◽  
Modulated Phase

Crystalline dicaesium mercury tetrachloride (Cs2HgCl4) is isomorphous with \beta-K_2SO_4 (space group Pnma, Z = 4) in its normal phase at room temperature. On cooling a sequence of incommensurate and commensurate superstructures occurs, below T = 221 K with modulations parallel to a*, and below 184  K with modulations along c*. The commensurately modulated structures at T = 185 K with {\bf q}= {{1}\over{5}}\bf{a}^* and at T = 176 K with {\bf q} = {{1}\over{3}}\bf{c}^* were determined using X-ray scattering with synchrotron radiation. The structure at T = 185 K has superspace group Pnma(\alpha,0,0)0ss with \alpha = 0.2. Lattice parameters were determined as a = 5\times9.7729\kern2pt(1), b = 7.5276\kern2pt(4) and c = 13.3727\kern2pt(7) Å. Structure refinements converged to R = 0.050 (R = 0.042 for 939 main reflections and R = 0.220 for 307 satellites) for the section t = 0.05 of superspace. The fivefold supercell has space group Pn2_1a. The structure at T = 176 K has superspace group Pnma(0,0,\gamma)0s0 with \gamma = {{1}\over{3}}. Lattice parameters were determined as a = 9.789\kern2pt(3), b = 7.541 \kern2pt(3) and c = 3 \times 13.418\kern2pt(4) Å. Structure refinements converged to R = 0.067 (R = 0.048 for 2130 main reflections, and R = 0.135 for 2382 satellite reflections) for the section t = 0. The threefold supercell has space group P112_1/a. It is shown that the structures of both low-temperature phases can be characterized as different superstructures of the periodic room-temperature structure. The superstructure of the 5a-modulated phase is analysed in terms of displacements of the Cs atoms, and rotations and distortions of HgCl4 tetrahedral groups. In the 3c-modulated phase the distortions of the tetrahedra are relaxed, but they are replaced by translations of the tetrahedral groups in addition to rotations.

Melilite-like modulation and temperature-dependent evolution in the framework structure of K2Sc[Si2O6]F

2016 ◽  
Vol 72 (2) ◽  
pp. 209-222 ◽  
Author(s):  
Clivia Hejny ◽  
Volker Kahlenberg ◽  
Tim Eberhard ◽  
Hannes Krüger
Keyword(s):  
Crystal Structure ◽  
Room Temperature ◽  
Structure Refinement ◽  
Normal Structure ◽  
Framework Structure ◽  
Temperature Dependent ◽  
Tetrahedral Framework ◽  
Modulated Structure ◽  
First Order ◽  
Variable Coordination

The crystal structure of synthetic K2Sc[Si2O6]F has been solved and refined as an incommensurately modulated structure in (3 + 2)-dimensional superspace. This paper describes the tetragonal structure in the superspace groupP42/mnm(α,α,0)000s(−α,α,0)0000 [a= 8.9878 (1),c= 8.2694 (2) Å,V= 668.01 (2) Å3] with modulation wavevectorsq1= 0.2982 (4)(a* + b*) andq2= 0.2982 (4)(−a* + b*). Structure refinement taking into account the modulation of positional and ADP parameters for all atoms from 3074 observed mainhkl00 and satellite reflectionshklmnof first order with single,m·n= 0, and mixed,m·n= ±1, indices converged to a finalRvalue of 0.0514. The structure is a mixed octahedral–tetrahedral framework composed of [ScO4F2] octahedra, [Si4O12] rings and K in variable coordination. Due to the modulation the O atoms move into and out of the first coordination sphere of K leading to a minimum of five and a maximum of 10 interatomic K—O distances up to 3.1 Å. Although this feature is comparable to observations in modulated fresnoite and melilite group compounds, these structures differ from K2Sc[Si2O6]F with respect to their topology. On temperature increase the intensity of the satellite reflections decreases until they disappear just above 443 K. The high-temperature normal structure, in space groupP42/mnm, is identical to the room-temperature average structure of K2Sc[Si2O6]F.

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.

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.

Single-crystal investigation of Ce5AgxGe4−x (x = 0.1−1.08) with Sm5Ge4 type

2020 ◽  
Vol 75 (8) ◽  
pp. 765-768
Author(s):  
Bohdana Belan ◽  
Dorota Kowalska ◽  
Mariya Dzevenko ◽  
Mykola Manyako ◽  
Roman Gladyshevskii
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Diffraction Data ◽  
Binary Compound ◽  
Lattice Parameters ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray

AbstractThe crystal structure of the phase Ce5AgxGe4−x (x = 0.1−1.08) has been determined using single-crystal X-ray diffraction data for Ce5Ag0.1Ge3.9. This phase is isotypic with Sm5Ge4: space group Pnma (No. 62), Pearson code oP36, Z = 4, a = 7.9632(2), b = 15.2693(5), c = 8.0803(2) Å; R1 = 0.0261, wR2 = 0.0460, 1428 F2 values and 48 variables. The two crystallographic positions 8d and 4c show Ge/Ag mixing, leading to a slight increase in the lattice parameters as compared to those of the pure binary compound Ce5Ge4.

Crystal structure of KCaF3 determined by the Rietveld profile method

1997 ◽  
Vol 12 (2) ◽  
pp. 70-75 ◽  
Author(s):  
Alicja Ratuszna ◽  
Michel Rousseau ◽  
Philippe Daniel
Keyword(s):  
Crystal Structure ◽  
Room Temperature ◽  
Lattice Parameters ◽  
Profile Method ◽  
Anisotropic Temperature ◽  
Monoclinic Distortion ◽  
Refinement Procedure ◽  
Watson Statistic ◽  
Temperature Factors ◽  
Atomic Coordinates

Using the Rietveld profile method, the atomic coordinates and anisotropic temperature factors of KCaF3 were refined. At room temperature, KCaF3 crystallizes in monoclinic B21/m symmetry, with the lattice parameters: a=8.754(2) Å, b=8.765(4) Å, c=8.760(5) Å, β=90.48(3)°, V=672.1(3) Å3, Z=8. The refinement procedure was stopped when RB=0.05 and the Durbin–Watson statistic factor=0.85 had been reached. The structure determined is related to the tilting of CaF6 octahedra of the a−b+c− type, which are responsible for the monoclinic distortion in perovskite crystals.

Betaine arsenate, (CH3)3NCH2COO · D3AsO4: structure refinement using multiple-wavelength synchrotron radiation data

1997 ◽  
Vol 212 (9) ◽  
Author(s):  
S. Kek ◽  
M. Grotepaß-Deuter ◽  
K. Fischer ◽  
K. Eichhorn
Keyword(s):  
Crystal Structure ◽  
Synchrotron Radiation ◽  
Room Temperature ◽  
Structure Refinement ◽  
Temperature Phase ◽  
Space Group ◽  
Radiation Data ◽  
Multiple Wavelength

AbstractThe crystal structure of deuterated betaine arsenate, (CHThe both paraelectric and ferroelastic room-temperature phase of betaine arsenate crystallizes in space group

scholarly journals β-Y(BO2)3 – a new member of the β-Ln(BO2)3 (Ln=Nd, Sm, Gd–Lu) structure family

2017 ◽  
Vol 72 (12) ◽  
pp. 983-988 ◽  
Author(s):  
Martin K. Schmitt ◽  
Hubert Huppertz
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Lattice Parameters ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
X Ray

Abstractβ-Y(BO2)3 was synthesized in a Walker-type multianvil module at 5.9 GPa/1000°C. The crystal structure has been elucidated through single-crystal X-ray diffraction. β-Y(BO2)3 crystallizes in the orthorhombic space group Pnma (no. 62) with the lattice parameters a=15.886(2), b=7.3860(6), and c=12.2119(9) Å. Its crystal structure will be discussed in the context of the isotypic lanthanide borates β-Ln(BO2)3 (Ln=Nd, Sm, Gd–Lu).

NQR and Crystal Structure of 4,5-Dichloroimidazole, C3H2N2Cl2

1992 ◽  
Vol 47 (1-2) ◽  
pp. 177-181 ◽  
Author(s):  
Shi-Qi Dou ◽  
Alarich Weiss
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Temperature Dependence ◽  
Room Temperature ◽  
Unit Cell ◽  
Space Group ◽  
Temperature Range ◽  
Temperature Coefficients ◽  
Group D

AbstractThe two line 35Cl NQR spectrum of 4,5-dichloroimidazole was measured in the temperature range 77≦ T/K ≦ 389. The temperature dependence of the NQR frequencies conforms with the Bayer model and no phase transition is indicated in the curves v ( 35Cl)= f(T). Also the temperature coefficients of the 35Cl NQR frequencies are "normal". At 77 K the 35Cl NQR frequencies are 37.409 MHz and 36.172 MHz and at 389 K 35.758 MHz and 34.565 MHz. The compound crystallizes at room temperature with the tetragonal space group D44-P41212, Z = 8 molecules per unit cell; at 295 K : a = 684.2(5) pm, c = 2414.0(20) pm. The relations between the crystal structure and the NQR spectrum are discussed.

CRYSTAL STRUCTURE OF ZIRCONIUM TRICHLORIDE

1964 ◽  
Vol 42 (10) ◽  
pp. 1886-1889 ◽  
Author(s):  
B. Swaroop ◽  
S. N. Flengas
Keyword(s):  
Crystal Structure ◽  
Room Temperature ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Main Cell ◽  
Diffraction Patterns

The crystal structure of zirconium trichloride was determined from X-ray diffraction patterns. Zirconium trichloride belongs to the [Formula: see text]space group. The dimensions of the main cell at room temperature are: a = 5.961 ± 0.005 Å and c = 9.669 ± 0.005 Å.The density of zirconium trichloride was measured and gave the value of 2.281 ± 0.075 g/cm3 while, from the X-ray calculations, the value was found to be 2.205 g/cm3.

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