Structural basis for the phase transitions of Cs2HgCl4

2001 ◽  
Vol 57 (3) ◽  
pp. 231-236 ◽  
Author(s):  
Bagautdin Bagautdinov ◽  
Andreas Jobst ◽  
Jens Ludecke ◽  
Sander van Smaalen
Keyword(s):  
Phase Transitions ◽  
Room Temperature ◽  
Quantitative Comparison ◽  
Structural Basis ◽  
Stable Phase ◽  
X Ray Diffraction ◽  
Coordination Polyhedra ◽  
X Ray ◽  
Anisotropic Temperature ◽  
Temperature Factors

The a 0 × b 0 × 2c 0 twofold superstructure of dicaesium mercury tetrachloride, Cs2HgCl4, at T = 120 K has been determined by single-crystal X-ray diffraction using synchrotron radiation. Lattice parameters were found as a = 9.7105 (2), b = 7.4691 (1), c = 26.8992 (4) Å, and β = 90.368 (1)° with the supercell space group P21/c. Refinements on 1828 observed unique reflections converged to R = 0.053 (wR = 0.057) using anisotropic temperature factors for all atoms. This phase is the stable phase of Cs2HgCl4 below 163 K. A quantitative comparison is made of the distortions of the 2c 0 superstructure with the undistorted phase that is stable at room temperature, and with the 3c 0 and 5a 0 superstructures that are stable at temperatures between 163 K and room temperature. The principal difference between the 2c 0 superstructure and all other phases of Cs2HgCl4 is that the Cs cations are displaced away from the centers of their coordination polyhedra in the 2c 0 superstructure. The structural basis for the driving force of the series of phase transitions in this compound is found in the variations of the environments of Cs atoms and in the variations of the distortions of the HgCl4 tetrahedra.

Temperature-induced structural phase transitions in RERhSn (RE = Y, Gd-Tm, Lu)

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Simon Engelbert ◽  
Rolf-Dieter Hoffmann ◽  
Jutta Kösters ◽  
Steffen Klenner ◽  
Rainer Pöttgen
Keyword(s):  
Rare Earth ◽  
Phase Transitions ◽  
Driving Force ◽  
Room Temperature ◽  
Structural Phase ◽  
Structural Phase Transitions ◽  
Line Broadening ◽  
X Ray Diffraction ◽  
Temperature Dependent ◽  
X Ray

Abstract The structures of the equiatomic stannides RERhSn with the smaller rare earth elements Y, Gd-Tm and Lu were reinvestigated on the basis of temperature-dependent single crystal X-ray diffraction data. GdRhSn crystallizes with the aristotype ZrNiAl at 293 and 90 K. For RE = Y, Tb, Ho and Er the HP-CeRuSn type (approximant with space group R3m) is already formed at room temperature, while DyRhSn adopts the HP-CeRuSn type below 280 K. TmRhSn and LuRhSn show incommensurate modulated variants with superspace groups P31m(1/3; 1/3; γ) 000 (No. 157.1.23.1) (γ = 3/8 for TmRhSn and γ = 2/5 for LuRhSn). The driving force for superstructure formation (modulation) is a strengthening of Rh–Sn bonding. The modulation is expressed in a 119Sn Mössbauer spectrum of DyRhSn at 78 K through line broadening.

The structures and phase transitions in 4-aminopyridinium tetraaquabis(sulfato)iron(III), (C5H7N2)[FeIII(H2O)4(SO4)2]

2019 ◽  
Vol 75 (6) ◽  
pp. 1144-1151
Author(s):  
Tamara J. Bednarchuk ◽  
Wolfgang Hornfeck ◽  
Vasyl Kinzhybalo ◽  
Zhengyang Zhou ◽  
Michal Dušek ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Single Crystal ◽  
Room Temperature ◽  
Variable Temperature ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Hybrid Compound ◽  
Space Group ◽  
X Ray

The organic–inorganic hybrid compound 4-aminopyridinium tetraaquabis(sulfato)iron(III), (C5H7N2)[FeIII(H2O)4(SO4)2] (4apFeS), was obtained by slow evaporation of the solvent at room temperature and characterized by single-crystal X-ray diffraction in the temperature range from 290 to 80 K. Differential scanning calorimetry revealed that the title compound undergoes a sequence of three reversible phase transitions, which has been verified by variable-temperature X-ray diffraction analysis during cooling–heating cycles over the temperature ranges 290–100–290 K. In the room-temperature phase (I), space group C2/c, oxygen atoms from the closest Fe-atom environment (octahedral) were disordered over two equivalent positions around a twofold axis. Two intermediate phases (II), (III) were solved and refined as incommensurately modulated structures, employing the superspace formalism applied to single-crystal X-ray diffraction data. Both structures can be described in the (3+1)-dimensional monoclinic X2/c(α,0,γ)0s superspace group (where X is ½, ½, 0, ½) with modulation wavevectors q = (0.2943, 0, 0.5640) and q = (0.3366, 0, 0.5544) for phases (II) and (III), respectively. The completely ordered low-temperature phase (IV) was refined with the twinning model in the triclinic P{\overline 1} space group, revealing the existence of two domains. The dynamics of the disordered anionic substructure in the 4apFeS crystal seems to play an essential role in the phase transition mechanisms. The discrete organic moieties were found to be fully ordered even at room temperature.

A REFINEMENT OF THE CRYSTAL STRUCTURES OF (NH4)2TeBr6 AND Cs2TeBr6

1966 ◽  
Vol 44 (8) ◽  
pp. 939-943 ◽  
Author(s):  
A. K. Das ◽  
I. D. Brown
Keyword(s):  
Least Squares ◽  
Crystal Structures ◽  
Diffraction Data ◽  
Bromine Atom ◽  
Three Dimensional ◽  
X Ray Diffraction ◽  
Full Matrix ◽  
X Ray ◽  
Anisotropic Temperature ◽  
Temperature Factors

(NH4)2TeBr6 and Cs2TeBr6 crystals have the cubic K2PtCl6 structure with space group: [Formula: see text] with a0 = 10.728 ± 0.003 Å and 10.918 ± 0.002 Å respectively. The positional coordinate of the bromine atom, and the anisotropic temperature factors of all atoms in the unit cell, have been refined for both crystals by a full matrix least-squares analysis of the three dimensional X-ray diffraction data (R = 0.08). The Te—Br distance, corrected for probable thermal motions of atoms forming the bond, is 2.70 ± 0.01 Å in both crystals.

Low-temperature crystal structure of RS-thiocamphor

2004 ◽  
Vol 219 (9) ◽  
Author(s):  
E. Louise R. Robins ◽  
Michela Brunelli ◽  
Asiloé J. Mora ◽  
Andrew N. Fitch
Keyword(s):  
Crystal Structure ◽  
Phase Transitions ◽  
Low Temperature ◽  
Room Temperature ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
Two Phase ◽  
X Ray ◽  
Low Temperature Crystal Structure

AbstractDSC and high-resolution powder X-ray diffraction measurements in the range 295 K–100 K show that RS-thiocamphor undergoes two phase transitions. The first, at around 260 K on cooling, is from the room-temperature body-centred-cubic phase to a short-lived intermediate. At 258 K the low-temperature form starts to appear. The crystal structure of the latter is orthorhombic, space group

Phase Transitions and Recrystallization in a Ti-46at%Al-9at%Nb Alloy as Observed by In-Situ High-Energy X-ray Diffraction

2006 ◽  
Vol 980 ◽  
Author(s):  
Klaus-Dieter Liss ◽  
Helmut Clemens ◽  
Arno Bartels ◽  
Andreas Stark ◽  
Thomas Buslaps
Keyword(s):  
Phase Transitions ◽  
Room Temperature ◽  
Strain Relaxation ◽  
Reciprocal Lattice ◽  
Lamellar Microstructure ◽  
High Energy ◽  
X Ray Diffraction ◽  
Orientation Relationships ◽  
X Ray

AbstractHigh-energy synchrotron X-ray diffraction is a powerful tool for bulk studies of materials. In this investigation, it is applied to the investigation of an intermetallic γ-TiAl based alloy with a composition of Ti-46Al-9Nb. The morphology of the reflections on the Debye-Scherrer rings is evaluated in order to approach grain sizes as well as crystallographic correlations. An in-situ heating cycle from room temperature to a temperature above the α-transus temperature has been conducted starting from a massively transformed sample. With increasing temperature the occurrence of strain relaxation, chemical and phase separation, domain orientations, phase transitions, recrystallization processes, and subsequent grain growth can be observed. During cooling to room temperature, crystallographic correlations between the re-appearing γ-phase and the host α-phase, known as the Blackburn correlation, are observed in the reciprocal lattice, which splits into different twinning and domain orientation relationships present in the fully lamellar microstructure.

Untersuchungen zur Polymorphie der Cäsium-Dodekahalogeno-closo-Dodekaborate Cs2[B12X12] (X = Cl–I)

2020 ◽  
Vol 75 (8) ◽  
pp. 777-790
Author(s):  
Ioannis Tiritiris ◽  
Kevin U. Bareiß ◽  
Thomas Schleid
Keyword(s):  
Phase Transitions ◽  
Defect Structure ◽  
Room Temperature ◽  
Solid Phase ◽  
X Ray Diffraction ◽  
Temperature Dependent ◽  
Space Group ◽  
X Ray ◽  
Cubic System ◽  
Cesium Salts

AbstractThermoanalytic DSC and temperature-dependent X-ray diffraction investigations on the cesium dodecahalogeno-closo-dodecaborates Cs2[B12X12] (X = Cl–I) have revealed solid-solid phase transitions from their trigonal room-temperature α-forms (e.g. α-Cs2[B12Cl12]: a = 959.67(3) pm, c = 4564.2(2) pm, Z = 6, space group R$\overline{3}$) into cubic high-temperature modifications. The isotypic title compounds crystallize in the space group Pm$\overline{3}$n (e.g. β-Cs2[B12Cl12]: a = 1051.98(6) pm, Z = 2) with a W3O-type defect structure. The statistic occupation of six possible positions with only four Cs+ cations results in a cation-deficient A2B arrangement for Cs2[B12X12]. Upon cooling the β-phase, a third polymorph was observed, which also crystallizes in the cubic system, but now in the space group Ia$\overline{3}$d (e.g. γ-Cs2[B12Cl12]: a = 2102.2(3) pm, Z = 16), and has to be regarded as a phase with only a partially disordered cation substructure. In this crystal structure the [B12X12]2− anions exhibit a NaTl-type arrangement, in which the Cs+ cations occupy suitable interstices. The phase transitions of the differently halogenated cesium salts follow no specific trend as the transition from the trigonal α- to the cubic β-form occurs at 178 °C for the chlorinated, at 270 °C for the iodinated and at 325 °C for the brominated examples. On further heating however, β-Cs2[B12I12] starts to decompose at 945 °C first, followed by β-Cs2[B12Br12] and β-Cs2[B12Cl12] at 959 °C and 983 °C, respectively.

Room-temperature ferroelasticity and unusual sequence of phase transitions in the crystal of (N2H5)3[CdCl5]

2021 ◽  
Vol 77 (4) ◽  
Author(s):  
Monika K. Krawczyk ◽  
Zbigniew Czapla ◽  
Adam Ingram ◽  
Andrzej Kozdraś ◽  
Tadeusz Lis ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Room Temperature ◽  
Structural Changes ◽  
Structural Phase ◽  
Orthorhombic Phase ◽  
Orthorhombic Symmetry ◽  
Structural Phase Transitions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cl Atoms

On the basis of thermal analysis (DSC, DTA, DTG), single crystal X-ray diffraction experiments, dielectric studies and optical observation, it is found that the (N2H5)3[CdCl5] crystal exhibits several structural phase transitions. At room temperature, the studied crystal exhibits ferroelastic properties and undergoes phase transition from the monoclinic to the orthorhombic phase on heating above 327 K. Upon subsequent cooling, two structural phase transitions at about 323 and 319 K are observed, where the crystal adopts orthorhombic symmetry. The presented phase transitions are unique due to the fact the first heating run results in different structural changes compared to those observed during cooling and subsequent heating/cooling runs. In the studied crystal, N2H5 + ions and 1D chains built up from {CdCl5}3− units bridged by Cl atoms occur. The phase transitions observed can be associated with reorientation of cations and partial disorder of cations as well as Cl atoms.

Structure refinements of seven natural olivine crystals and the influence of the oxygen partial pressure on the cation distribution

1981 ◽  
Vol 155 (1-2) ◽  
Author(s):  
G. Nover ◽  
G. Will
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Extinction Coefficient ◽  
Diffraction Data ◽  
X Ray Diffraction ◽  
Volcanic Origin ◽  
X Ray ◽  
Anisotropic Temperature ◽  
Natural Olivine ◽  
Temperature Factors

AbstractMg/Fe order in olivine has been determined by X-ray diffraction data, for example by Wenk and Raymond (1973). We have now studied the dependence of the Mg/Fe order vs. oxygen partial pressure. Two natural olivine samples of volcanic origin containing respectively 10 and 12 % fayalite were selected. The atomic positions, anisotropic temperature factors, extinction coefficient and site occupancies have been refined toThese experiments seem to indicate that the prevailing oxygen partial pressure determines the different Mg/Fe order found in natural olivine crystals.

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