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

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.

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Single-Crystal X-Ray Scattering Study of Superstructures and Phase Transitions in Graphite-Hno3 and Graphite-Br2 Intercalation Compounds

MRS Proceedings ◽

10.1557/proc-20-27 ◽

1982 ◽

Vol 20 ◽

Cited By ~ 5

Author(s):

R. Moret ◽

R. Comes ◽

G. Furdin ◽

H. Fuzellier ◽

F. Rousseaux

Keyword(s):

Phase Transitions ◽

Low Temperature ◽

Room Temperature ◽

Temperature Phase ◽

Temperature Structure ◽

X Ray ◽

X Ray Scattering ◽

Scattering Study ◽

Temperature Liquid ◽

Low Temperature Phase

ABSTRACTIn α-C5n-HNO3 the condensation of the room-temperature liquid-like diffuse ring associated with the disorder-order transition around 250 K is studied and the low-temperature. superstructure is examined.It is found that β-C8n-HNO3 exhibits an in-plane incommensurate order at room temperature.Two types of graphite-Br2 are found. Low-temperature phase transitions in C8Br are observed at T1 ≍ 277 K and T2 ≍ 297 K. The room-temperature structure of C14Br is reexamined. Special attention is given to diffuse scattering and incommensurability.

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Incommensurately modulated phase of Rb2CoBr4 at 295 and 200 K

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768199010629 ◽

2000 ◽

Vol 56 (1) ◽

pp. 17-21 ◽

Cited By ~ 4

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.

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Evidence for differentiation in the iron-helicoidal chain in GdFe3(BO3)4

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768105017362 ◽

2005 ◽

Vol 61 (5) ◽

pp. 481-485 ◽

Cited By ~ 96

Author(s):

S. A. Klimin ◽

D. Fausti ◽

A. Meetsma ◽

L. N. Bezmaternykh ◽

P. H. M. van Loosdrecht ◽

...

Keyword(s):

Low Temperature ◽

Room Temperature ◽

Structural Phase ◽

Structure Study ◽

Temperature Structure ◽

Space Group ◽

X Ray ◽

First Order ◽

New Perspective ◽

Insight Into

A single-crystal X-ray structure study of gadolinium triiron tetraborate, GdFe_3(BO_3)_4, at room temperature and at 90 K is reported. At room temperature GdFe_3(BO_3)_4 crystallizes in a trigonal space group, R32 (No. 155), the same as found for other members of the iron borate family RFe_3(BO_3)_4. At 90 K the structure of GdFe_3(BO_3)_4 transforms to the space group P3_{1}21 (No. 152). The low-temperature structure determination gives new insight into the weakly first-order structural phase transition at 156 K and into the related Raman phonon anomalies. The presence of two inequivalent iron chains in the low-temperature structure provides a new perspective on the interpretation of the low-temperature magnetic properties.

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X-ray powder diffraction study on ErNi2Ge2

Powder Diffraction ◽

10.1017/s0885715600010472 ◽

1999 ◽

Vol 14 (2) ◽

pp. 145-146

Author(s):

Liangqin Nong ◽

Lingmin Zeng

Keyword(s):

Least Squares ◽

Diffraction Study ◽

Diffraction Pattern ◽

Powder Diffraction ◽

Room Temperature ◽

Rietveld Analysis ◽

Lattice Parameters ◽

X Ray Diffraction ◽

Space Group ◽

X Ray

An X-ray diffraction pattern for ErNi2Ge2 at room temperature is reported. ErNi2Ge2 is tetragonal with lattice parameters a=4.0191(2) Å, c=9.7643(2) Å, space group I4/mmm, and Z=2. The lattice parameters derived from Rietveld analysis agree well with the results of a least-squares refinement.

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Crystal Structure and Phase Transitions of [C(NH2)3]3l3Sb2Cl9· 0.9 H2O

Zeitschrift für Naturforschung A ◽

10.1515/zna-1994-0913 ◽

1994 ◽

Vol 49 (9) ◽

pp. 895-901 ◽

Cited By ~ 6

Author(s):

Jacek Zaleski ◽

Adam Pietraszko

Keyword(s):

Crystal Structure ◽

Phase Transition ◽

Room Temperature ◽

The Other ◽

Temperature Structure ◽

X Ray ◽

Dsc Studies ◽

X Ray Scattering ◽

Mixed Order ◽

Atomic Parameters

Abstract The room temperature structure of [C(NH2)3]3Sb2Cl9 · 0.9 H2O (GNCA) was solved. It crystal lizes in the monoclinic C2/c space group with a = 15.275, b = 8.794, c = 17.904 (in Å), β = 96.40°, V = 2390 Å3, Z = 4. Refinement of the atomic parameters by a least squares methods gave R = 0.042, wR = 0.039 for 1958 reflections with F>4σ(F). The structure consists of polyanionic (Sb2Cl93-)n layers built of deformed corner connected SbX63-octahedra. Two crystallographically inequivalent guanidinium cations are present, one situated between polyanionic layers, the other one together with a disordered water molecule inside cavities formed by polyanions. Temperature X-ray scattering experiments together with DSC studies were carried out above room temperature. Temperature dependence of the lattice parameters between 300 K and 380 K was determined and a phase transition of mixed order at 364 K was revealed.

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Powder X-ray diffraction of azelastine hydrochloride, C22H25ClN3O·Cl

Powder Diffraction ◽

10.1017/s0885715620000664 ◽

2020 ◽

pp. 1-2

Author(s):

James A. Kaduk ◽

Amy M. Gindhart ◽

Thomas N. Blanton

Keyword(s):

Synchrotron Radiation ◽

Powder Diffraction ◽

Lattice Parameters ◽

Powder Pattern ◽

Monoclinic Space Group ◽

X Ray Diffraction ◽

Powder Diffraction File ◽

Space Group ◽

X Ray

Commercial azelastine hydrochloride crystallizes in the monoclinic space group P21/n (#14) with a = 13.7844(5), b = 16.39920(14), c = 9.41231(22) Å, β = 97.5340(20)°, V = 2109.32(4) Å3, and Z = 4. The lattice parameters differ by −0.02, +0.04, and +0.04% from those in the previous determination (reflecting differences in the temperature and the sample source), and are more precise, from the use of synchrotron radiation. The experimental powder pattern is included in the Powder Diffraction File™ (PDF®) as entry 00-070-1219.

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Synchrotron X-Ray Powder Diffraction Studies of Structural Phase Transitions in Perovskite Oxides

Australian Journal of Chemistry ◽

10.1071/ch11313 ◽

2012 ◽

Vol 65 (3) ◽

pp. 229 ◽

Cited By ~ 5

Author(s):

Brendan J. Kennedy ◽

Ilyas Qasim ◽

Emily Reynolds ◽

Teck-Yee Tan ◽

Qingdi Zhou

Keyword(s):

High Resolution ◽

Powder Diffraction ◽

Room Temperature ◽

Structural Parameters ◽

Structural Phase ◽

Temperature Structure ◽

Space Group ◽

X Ray ◽

Pbnm Space Group ◽

Perovskite Type

The utilization of the high resolution powder diffractometer at the Australian Synchrotron to obtain accurate and precise structures of some perovskite-type oxides is described. The structure of CdTiO3 has been studied from room temperature to 1000°C by high-resolution synchrotron X-ray powder diffraction. It was found that CdTiO3 remains orthorhombic in the Pbnm space group over the entire temperature range, with the expansion in the cell volume well fitted to the expression . The magnitudes of the TiO6 tilts are estimated from the refined structural parameters and these progressively reduce as the temperature is increased. The effect of Sr content on the room temperature structure of the double perovskites Ba2–xSrxInTaO6 is also described. At room temperature Ba2InTaO6 crystallizes in a cubic structure in space group . Doping with Sr results in tilting of the corner sharing octahedra with a concurrent lowering of symmetry with the sequence of structures being

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Crystal structures of room- and low-temperature phases in oxyfluoride (NH4)2KWO3F3

Powder Diffraction ◽

10.1154/1.2759491 ◽

2007 ◽

Vol 22 (3) ◽

pp. 227-230 ◽

Cited By ~ 8

Author(s):

M. S. Molokeev ◽

A. D. Vasiliev ◽

A. G. Kocharova

Keyword(s):

Low Temperature ◽

Crystal Structures ◽

Powder Diffraction ◽

Diffraction Data ◽

Room Temperature ◽

Monoclinic Phase ◽

Temperature Structure ◽

Powder Diffraction Data ◽

Space Group ◽

X Ray

Crystal structures of (NH4)2KWO3F3 at 298 K and 113 K were solved from X-ray powder diffraction data and refined by the Rietveld technique. The compound is isostructural with elpasolite K2NaAlF6 at room temperature with space group Fm-3m, a=8.95850(5) Å, V=718.961(7) Å3, Z=4, Dx=3.363 g/cm3, and MW=364.02. The structure was refined over 18 parameters to Rwp=12.6%, Rp=10.9%, Rexp=5.03%, and RB=3.27% from 40 independent reflections. (NH4)2KWO3F3 was transformed upon cooling to a ferroelastic monoclinic phase with space group P21/n, a′=6.3072(3) Å, b′=6.3028(3) Å, c′=8.9882(3) Å, β′=90.242(2)°, V=357.30(3) Å3, Z=2, and Dx=3.383 g/cm3. The low-temperature structure at 113 K was refined over 28 parameters to Rwp=20.9%, Rp=21.3%, Rexp=12.5%, and RB=6.93% from 453 independent reflections.

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