Low-temperature behaviour of K2Sc[Si2O6]F: determination of the lock-in phase and its relationships with fresnoite- and melilite-type compounds

2017 ◽  
Vol 73 (5) ◽  
pp. 923-930
Author(s):  
C. Hejny ◽  
L. Bindi
Keyword(s):  
Low Temperature ◽  
Room Temperature ◽  
Temperature Structure ◽  
X Ray Diffraction ◽  
Temperature Behaviour ◽  
Modulated Structure ◽  
Incommensurate Structure ◽  
Commensurate Phase ◽  
Lock In

K2Sc[Si2O6]F exhibits, at room temperature, a (3 + 2)-dimensional incommensurately modulated structure [a= 8.9878 (1),c= 8.2694 (2) Å,V= 668.01 (2) Å3; superspace groupP42/mnm(α,α,0)000s(−α,α,0)0000] with modulation wavevectorsq1= 0.2982 (4)(a* +b*) andq2= 0.2982 (4)(−a* +b*). Its low-temperature behaviour has been studied by single-crystal X-ray diffraction. Down to 45 K, the irrational component α of the modulation wavevectors is quite constant varying from 0.2982 (4) (RT), through 0.2955 (8) (120 K), 0.297 (1) (90 K), 0.298 (1) (75 K), to 0.299 (1) (45 K). At 25 K it approaches the commensurate value of one-third [i.e.0.332 (3)]: thus indicating that the incommensurate–commensurate phase transition takes place between 45 K and 25 K. The commensurate lock-in phase of K2Sc[Si2O6]F has been solved and refined with a 3 × 3 × 1 supercell compared with the tetragonal incommensurately modulated structure stable at room temperature. This corresponds to a 3 × 1 × 3 supercell in the pseudo-orthorhombic monoclinic setting of the low-temperature structure, space groupP2/m, with lattice parametersa= 26.786 (3),b= 8.245 (2)c= 26.824 (3) Å, β = 90.00 (1)°. The structure is a mixed tetrahedral–octahedral framework composed of chains of [ScO4F2] octahedra that are interconnected by [Si4O12] rings with K atoms in fourfold to ninefold coordination. Distorted [ScO4F2] octahedra are connected to distorted Si tetrahedra to form octagonal arrangements closely resembling those observed in the incommensurate structure of fresnoite- and melilite-type compounds.

Order and disorder in acenaphthylene

1973 ◽  
Vol 334 (1596) ◽  
pp. 19-48 ◽  
Keyword(s):  
Low Temperature ◽  
Room Temperature ◽  
Temperature Structure ◽  
Intermediate Form ◽  
X Ray Diffraction ◽  
Space Group ◽  
Order And Disorder ◽  
Temperature Form ◽  
Diffraction Effects

Acenaphthylene, C 12 H 8 , occurs in space group Pbam (or Pba2) at room temperatures (23 °C) with a = 7.705 (5), b = 7.865 (5), c = 14.071 (5) Å and Z = 4, and is disordered. At about 130 K it undergoes a reversible transition to space group P2 1 nm with a = 7.588 (13), b = 7.549 (10), c = 27.822 (2) Å and Z = 8 (85 K) with an ordered structure. A general study of the system has revealed that the structure of both forms consists of layers of closely packed molecules stacked in the c direction. The room temperature structure has a two-layer repeat and the low temperature form a four-layer repeat. Observation of diffuse X-ray diffraction effects at temperatures close to the transition indicates that an intermediate form having a six-layer repeat is formed. A preliminary structure determination of the low-temperature form reveals that the four layers though having a similar packing scheme differ in the orientation of the constituent molecules relative to c . It is proposed that the almost circular shape of the molecules allows each layer to change its identity under thermal agitation by a rotation of its constituent molecules in their own planes. The transition can be explained in terms of changes of the correlations between neighbouring layers. A simple model based on short-range order parameters is described, which explains the occurrence of the six-layer intermediate and the observed sequence of diffuse diffraction phenomena. The nature of the structure of the disordered room temperature form, which is predicted by this model, is confirmed as far as possible with the data available which are limited because of the dearth of high-angle diffraction maxima.

The role of hydrogen bonds in order-disorder transition of a new incommensurate low temperature phase β-[Zn-(C7H4NO4)2]·3H2O

2018 ◽  
Vol 233 (1) ◽  
pp. 17-25 ◽  
Author(s):  
Masoumeh Tabatabaee ◽  
Morgane Poupon ◽  
Václav Eigner ◽  
Přemysl Vaněk ◽  
Michal Dušek
Keyword(s):  
Low Temperature ◽  
Hydrogen Bonds ◽  
Dicarboxylic Acid ◽  
Room Temperature ◽  
Temperature Phase ◽  
Temperature Structure ◽  
Modulated Structure ◽  
Q Vector ◽  
Low Temperature Phase

AbstractThe room temperature structure withP21/csymmetry of the zinc(II) complex of pyridine-2,6-dicarboxylic acid was published by Okabe and Oya (N. Okabe, N. Oya, Copper(II) and zinc(II) complexes of pyridine-2,6-dicarboxylic acid.Acta Crystallogr. C.2000,56, 305). Here we report crystal structure of the low temperature phaseβ-[Zn(pydcH)2]·3H2O, pydc=C7H3NO4, resulting from the phase transition around 200K. The diffraction pattern of the low temperature phase revealed satellite reflections, which could be indexed with q-vector 0.4051(10)b* corresponding to (3+1)Dincommensurately modulated structure. The modulated structure was solved in the superspace groupX21/c(0b0)s0, whereXstands for a non-standard centring vector (½, 0, 0, ½), and compared with the room temperature phase. It is shown that hydrogen bonds are the main driving force of modulation.

Investigation into the Crystal Structure of the Perovskite Lead Hafnate, PbHfO3

1998 ◽  
Vol 54 (1) ◽  
pp. 18-28 ◽  
Author(s):  
D. L. Corker ◽  
A. M. Glazer ◽  
W. Kaminsky ◽  
R. W. Whatmore ◽  
J. Dec ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Room Temperature ◽  
Lead Zirconate ◽  
Crystal Structure Analysis ◽  
Temperature Structure ◽  
X Ray Diffraction ◽  
Neutron Data ◽  
X Ray

The room-temperature crystal structure of the perovskite lead hafnate PbHfO3 is investigated using both low-temperature single crystal X-ray diffraction (Mo Kα radiation, λ = 0.71069 Å) and polycrystalline neutron diffraction (D1A instrument, ILL, λ = 1.90788 Å). Single crystal X-ray data at 100 K: space group Pbam, a = 5.856 (1), b = 11.729 (3), c = 8.212 (2) Å, V = 564.04 Å3 with Z = 8, μ = 97.2 mm−1, F(000) = 1424, final R = 0.038, wR = 0.045 over 439 reflections with F >1.4σ(F). Polycrystalline neutron data at 383 K: a = 5.8582 (3), b = 11.7224 (5), c = 8.2246 (3) Å, V = 564.80 Å3 with χ2 = 1.62. Although lead hafnate has been thought to be isostructural with lead zirconate, no complete structure determination has been reported, as crystal structure analysis in both these materials is not straightforward. One of the main difficulties encountered is the determination of the oxygen positions, as necessary information lies in extremely weak l = 2n + 1 X-ray reflections. To maximize the intensity of these reflections the X-ray data are collected at 100 K with unusually long scans, a procedure which had previously been found successful with lead zirconate. In order to establish that no phase transitions exist between room temperature and 100 K, and hence that the collected X-ray data are relevant to the room-temperature structure, birefringence measurements for both PbZrO3 and PbHfO3 are also reported.

Transition from the incommensurately modulated structure to the lock-in phase in Co-åkermanite

2001 ◽  
Vol 57 (4) ◽  
pp. 443-448 ◽  
Author(s):  
Andreas K. Schaper ◽  
Michael Schosnig ◽  
Ali Kutoglu ◽  
Werner Treutmann ◽  
Helmut Rager
Keyword(s):  
Room Temperature ◽  
Domain Walls ◽  
Modulated Structure ◽  
Incommensurate Structure ◽  
Transmission Electron ◽  
Structure Modulation ◽  
Lock In ◽  
Highly Strained ◽  
Single Orientation

The adaptation of the incommensurate structure modulation in Ca2CoSi2O7 (dicalcium cobalt disilicate) single crystals to decreasing temperature has been examined using in situ high-resolution transmission electron microscopy and electron diffraction. The transition from the incommensurate to the commensurate lock-in phase of Co-åkermanite exhibits a pronounced hysteresis of a highly strained metastable state with a characteristic microdomain morphology. A network of domain walls surrounding single orientation domains develops out of the room-temperature tartan pattern, the domains increase in size and their alignment changes from crystallographic to random. At 100 K the phase transition becomes almost complete. In parallel, the evolution of the modulation structure can be described by a change from a loose arrangement of octagonal tilings into a close-packed configuration of overlapping octagons in the commensurate low-temperature lock-in phase. Thereby, the octagon represents the ordered distribution of low-coordinated Ca clusters within a nanodomain extending over 4 × 4 subunits, on average [Riester et al. (2000). Z. Kristallogr. 215, 102–109]. The modulation wavevector was found to change from q 1,2 = 0.295 (a* ± b*) at 300 K to q 1,2 = 0.320 (a* ± b*) at 100 K.

scholarly journals (E)-4-Bromo-2-[(phenylimino)methyl]phenol: a new polymorph and thermochromism

2020 ◽  
Vol 76 (11) ◽  
pp. 1001-1004
Author(s):  
Helen E. Mason ◽  
Judith A. K. Howard ◽  
Hazel A. Sparkes
Keyword(s):  
Hydrogen Bond ◽  
Low Temperature ◽  
Structure Determination ◽  
Room Temperature ◽  
Dihedral Angles ◽  
Temperature Structure ◽  
Aromatic Rings

A new polymorph of (E)-4-bromo-2-[(phenylimino)methyl]phenol, C13H10BrNO, is reported, together with a low-temperature structure determination of the previously published polymorph. Both polymorphs were found to have an intramolecular O—H...N hydrogen bond between the phenol OH group and the imine N atom, forming an S(6) ring. The crystals were observed to have different colours at room temperature, with the previously published polymorph being more orange and the new polymorph more yellow. The planarity of the molecule in the two polymorphs was found to be significantly different, with dihedral angles (Φ) between the two aromatic rings for the previously published `orange' polymorph of Φ = 1.8 (2)° at 120 K, while the new `yellow' polymorph had Φ = 45.6 (1)° at 150 K. It was also observed that both polymorphs displayed some degree of thermochromism and upon cooling the `orange' polymorph became more yellow, while the `yellow' polymorph became paler upon cooling.

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

1982 ◽  
Vol 20 ◽  
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.

Polymorphs of Neutral Red, a Redox-Mediating Phenazine in Biological Systems

2017 ◽  
Vol 70 (9) ◽  
pp. 1032 ◽  
Author(s):  
Mackenzie Labine-Romain ◽  
Sabrina Beckmann ◽  
Mohan Bhadbhade ◽  
Saroj Bhattacharyya ◽  
Michael Manefield ◽  
...  
Keyword(s):  
Room Temperature ◽  
Control Method ◽  
Scale Up ◽  
Industrial Process ◽  
Neutral Red ◽  
Crystalline Solid ◽  
Temperature Structure ◽  
X Ray Diffraction ◽  
Methane Generation ◽  
Raman And Infrared Spectroscopy

Neutral red 1 is a heterocyclic phenazine that, as a crystalline solid, has been observed to accelerate microbial methane generation from coal. Scale-up to an industrial process will require large quantities of neutral red crystals, hence an understanding of any polymorphic behaviour is essential for careful control of this process. A room-temperature structure of 1 (Form I) has been reported previously, and this study describes a new polymorph (Form II) crystallising from aqueous solution at 50°C, or transforming from Form I over an incubation time of one week at 70°C. Single-crystal X-ray diffraction has been used to study the molecular arrangements and intermolecular interactions in the new polymorph, and compared with those found in the room temperature form. Both polymorphs have been characterised using Raman and infrared spectroscopy, and a synthetic mixture of polymorphs successfully imaged using Raman spectroscopy. Raman imaging is proposed as a quality control method for small quantities of sample to ensure the correct polymorph is produced as a feedstock for this new methanogenesis process.

Interface and Volume Anisotropy of MBE-Grown Co/Pt (111), (110) and (001) and Sputtered CO/Pt Multilayers

1993 ◽  
Vol 313 ◽  
Author(s):  
D. Weiler ◽  
R.F.C. Farrow ◽  
R.F. Marks ◽  
G.R. Harp ◽  
H. Notarys ◽  
...  
Keyword(s):  
Room Temperature ◽  
Good Accuracy ◽  
Anisotropy Constant ◽  
X Ray Diffraction ◽  
X Ray ◽  
Gaas Substrates ◽  
Plane Anisotropy ◽  
Plane Direction ◽  
Total Average

ABSTRACTA quantitative determination of interface (Ks) and volume anisotropy {?ψ) constants of MBE and sputtered CO/Pt Multilayers is reported. Torque and VSM Magnetometry were used to determine the total average anisotropy and the room temperature magnetization of four different series of films with varying Co thickness and nearly constant Pt thickness. All films were characterized with X-ray diffraction and X-ray fluorescence, allowing the determination of the “Magnetic” volume with good accuracy. Both Ks and Jeff are found to be orientation dependent. We find the following results for MBE films grown on Ag buffered GaAs substrates and highly < 111 > textured films, grown on etched SiNx buffers:(111) Ks = 0.97mJ/m2, Kveff =-0.74MJ/m3 MBE(111) Ks = 0.92mJ/m2, Kveff =-l.lIMJ/m3 sputtered(110) Ks = 0.42mJ/m2, Kveff =-l.95MJ/m3 MBE(001) Ks = 0.59mJ/m2, Kveff =-5.98MJ/m3 MBEThe [110]-oriented MBE films show in addition a large (intrinsic) in-plane anisotropy constant K‖0≃-3MJ/m3 which is found to be independent of the Co thickness. [100] is the easy and [110] the hard in-plane direction.

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