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.

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.

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 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.

High-temperature X-ray powder diffraction study of the tetragonal-cubic phase transition in nanocrystalline, compositionally homogeneous ZrO2–CeO2 solid solutions

2008 ◽  
Vol 23 (S1) ◽  
pp. S70-S74 ◽  
Author(s):  
L. M. Acuña ◽  
R. O. Fuentes ◽  
D. G. Lamas ◽  
I. O. Fábregas ◽  
N. E. Walsöe de Reca ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
High Temperature ◽  
Powder Diffraction ◽  
Solid Solutions ◽  
Tetragonal Phase ◽  
Room Temperature ◽  
Cubic Phase ◽  
X Ray ◽  
First Order

Crystal structure of compositionally homogeneous, nanocrystalline ZrO2–CeO2 solutions was investigated by X-ray powder diffraction as a function of temperature for compositions between 50 and 65 mol % CeO2. ZrO2-50 and 60 mol % CeO2 solid solutions, which exhibit the t′-form of the tetragonal phase at room temperature, transform into the cubic phase in two steps: t′-to-t″ followed by t″-to-cubic. But the ZrO2-65 mol % CeO2, which exhibits the t″-form, transforms directly to the cubic phase. The results suggest that t′-to-t″ transition is of first order, but t″-to-cubic seems to be of second order.

scholarly journals Ba2ZnGe2S6O: Ein neues Oxidsulfid mit Tetraedergerüststruktur/On Ba2ZnGe2S6O. A New Oxide Sulfide with Tetrahedral Framework Structure

1980 ◽  
Vol 35 (6) ◽  
pp. 672-675 ◽  
Author(s):  
Chr. L. Teske
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Coordination Sphere ◽  
Framework Structure ◽  
Tetrahedral Framework ◽  
Space Group ◽  
X Ray ◽  
Lattice Constants ◽  
First Time ◽  
Ray Methods

Abstract Ba2ZnGe2S6O was prepared for the first time and the crystal structure determined by using single crystal X-ray methods. The space group is D32d-P4̄21m, tetragonal (No. 113). Lattice constants: a = 963.59 ± 0.22; c = 645.06 ± 0.25 pm. The tetrahedral framework structure is described and discussed. Zn is linked only to sulfur. The oxygen belongs to the coordination sphere of Ge and Ba.

Ammoniovoltaite, (NH4)2Fe2+5Fe3+3Al(SO4)12(H2O)18, a new mineral from the Severo-Kambalny geothermal field, Kamchatka, Russia

2018 ◽  
Vol 82 (5) ◽  
pp. 1057-1077 ◽  
Author(s):  
Elena S. Zhitova ◽  
Oleg I. Siidra ◽  
Dmitry I. Belakovsky ◽  
Vladimir V. Shilovskikh ◽  
Anton A. Nuzhdaev ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Room Temperature ◽  
Structure Refinement ◽  
Geothermal Field ◽  
Water Soluble ◽  
Ammonium Ion ◽  
New Mineral ◽  
X Ray Diffraction ◽  
X Ray ◽  
Mössbauer Data

AbstractAmmoniovoltaite, (NH4)2Fe2+5Fe3+3Al(SO4)12(H2O)18, is a new voltaite-group mineral. The mineral was discovered at the Severo-Kambalny (North-Kambalny) geothermal field, Kambalny volcanic ridge, Southern Kamchatka, Russia. Ammoniovoltaite forms at ~100°C around geothermal gas/steam vents in association with alunogen, tschermigite and pyrite. Crystals of ammoniovoltaite have euhedral habit, are up to 50 µm in size and grow on alunogen plates. Ammoniovoltaite is black with vitreous lustre, opaque, brittle and water-soluble. Neither cleavage nor parting is found, the fracture is conchoidal. The mineral is isotropic, with the refractive index n = 1.602(2) (589 nm). Infrared spectra contain an absorption band at 1433 cm–1 distinctive for the ammonium ion. The chemical composition is (iron content is given in accordance with Mössbauer data, H2O calculated from a crystal-structure refinement, wt.%): FeO 13.26, Fe2O3 11.58, MgO 2.33, ZnO 0.04, Al2O3 2.74, SO3 47.46, K2O 0.19, CaO 0.11, (NH4)2O 2.96, H2O 16.03, total 96.70. The empirical formula based on S = 12 atoms per formula unit is [(NH4)1.88K0.08Ca0.04]Σ2.00(Fe2+3.74Mg1.17Fe3+0.05Zn0.01)Σ4.97(Fe3+2.89Al0.09)Σ2.98Al1.00(SO4)12.00(H2O)18.00. The crystal structure has been refined to R1 = 0.031 and 0.030 on the basis of 1217 and 1462 unique reflections with I >2σ(I) collected at 100 K and room temperature, respectively. Ammoniovoltaite is the ammonium analogue of voltaite. The mineral is cubic, Fd$\bar{3}$c, a = 27.250(1) Å and V = 20234(3) Å3 (at 100 K); and a = 27.322(1) Å and V = 20396(3) Å3 (at RT), with Z = 16. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 9.67 (74) (022), 7.90 (56) (222), 5.58 (84) (422), 3.560 (100) (731), 3.418 (100) (008) and 2.8660 (37) (931). A brief review of ammonium minerals from various volcanically active geological environments is given.

Structure Refinement of Monoclinic Astrophyllite

1998 ◽  
Vol 54 (2) ◽  
pp. 109-114 ◽  
Author(s):  
N. Shi ◽  
Z. Ma ◽  
G. Li ◽  
N. A. Yamnova ◽  
D. Yu. Pushcharovsky
Keyword(s):  
Crystal Structure ◽  
Coordination Number ◽  
Room Temperature ◽  
Structure Refinement ◽  
Coordination Numbers ◽  
Continuous Sheet

The crystal structure of monoclinic magnesium astrophyllite has been redetermined. The samples were from Khibina alkaline massifs, Russia. K2NaNa(Fe,Mn)4Mg2Ti2[Si4O12]2(OH)4(OH,F)2, Mr = 1202.31, monoclinic, A2, a = 10.370 (3), b = 23.129 (5), c = 5.322 (1) Å, β = 99.55 (2)°, V = 1258.8 (5) Å3, Z = 2, Dx = 3.173 Mg m−3, Mo Kα, λ = 0.71069 Å, μ = 3.74 mm−1, F(000) = 1179, T = room temperature, R = 0.057 for 1720 reflections. The determination indicated that the coordination number of Ti is five. In tetrahedra of astrophyllite the open-branched Si—O chain connected with Ti—O semi-octahedra by corner-sharing formed a continuous sheet. Na atoms have two types of coordination. Their coordination numbers are eight and six. The Na atoms with coordination number eight are situated between layers. Other types of Na atoms are situated within the layers and form Na—O octahedra with partial occupancies.

scholarly journals Crystal structure of 2-bromobenzoic acid at 120 K: a redetermination

2014 ◽  
Vol 70 (10) ◽  
pp. o1139-o1140 ◽  
Author(s):  
Kornelia Kowalska ◽  
Damian Trzybiński ◽  
Artur Sikorski
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Room Temperature ◽  
Three Dimensional ◽  
Interplanar Distance ◽  
Geometrical Parameters ◽  
Framework Structure ◽  
Acta Cryst ◽  
Compound C ◽  
Centroid Distance

The crystal structure of the title compound, C7H5BrO2, was originally studied using photographic data at room temperature with Cu Kα radiation [Ferguson & Sim (1962).Acta Cryst.15, 346–350]. The present study was undertaken at 120 K with a CCD diffractometer using Cu Kα radiation, and resulted in improved geometrical parameters. In the molecule, the carboxy group is inclined to the benzene ring by 18.7 (2)° and there is a close intramolecular Br...O contact of 3.009 (3) Å. In the crystal, molecules are linked by pairs of O—H...O hydrogen bonds, forming inversion dimers with the classicalR22(8) ring motif for carboxylic acids. Neighbouring dimers are linked by weak C—H...O hydrogen bonds, forming tapes propagating in [1-10]. Adjacent tapes interact by slipped parallel π–π interactions [inter-centroid distance = 3.991 (2), interplanar distance = 3.509 (2) Å, slippage = 1.900 Å] to form columns approximately along theb-axis direction. Neighbouring columns interact dispersively, forming a three-dimensional framework structure.

scholarly journals The modulated low-temperature structure of malayaite, CaSnOSiO4

2020 ◽  
Vol 76 (3) ◽  
pp. 316-321
Author(s):  
Thomas Malcherek ◽  
Bianca Paulenz ◽  
Michael Fischer ◽  
Carsten Paulmann
Keyword(s):  
Crystal Structure ◽  
Density Functional ◽  
Room Temperature ◽  
Phonon Dispersion ◽  
Temperature Structure ◽  
X Ray Diffraction ◽  
Static Displacement ◽  
X Ray ◽  
First Order ◽  
Density Functional Perturbation Theory

The crystal structure of the mineral malayaite has been studied by single-crystal X-ray diffraction at a temperature of 20 K and by calculation of its phonon dispersion using density functional perturbation theory. The X-ray diffraction data show first-order satellite diffraction maxima at positions q = 0.2606 (8)b*, that are absent at room temperature. The computed phonon dispersion indicates unstable modes associated with dynamic displacements of the Ca atoms. The largest-frequency modulus of these phonon instabilities is located close to a wavevector of q = 0.3b*. These results indicate that the malayaite crystal structure is incommensurately modulated by static displacement of the Ca atoms at low temperatures, caused by the softening of an optic phonon with Bg symmetry.

scholarly journals Modulated structure of nepheline

2011 ◽  
Vol 67 (1) ◽  
pp. 18-29 ◽  
Author(s):  
Karen Friese ◽  
Andrzej Grzechnik ◽  
Vaclav Petříček ◽  
Andreas Schönleber ◽  
Sander van Smaalen ◽  
...  
Keyword(s):  
Electron Density ◽  
Tetrahedral Framework ◽  
Modulated Structure ◽  
First Order ◽  
Different Types ◽  
High Degree

The incommensurately modulated structure of a natural nepheline of composition K0.54Na3.24Ca0.03Al3.84Si4.16O16 has been determined in superspace. The compound crystallizes in the trigonal centered superspace group X3(00γ)0 with γ = 0.2048 (10), X = (0, 0, 0, 0), (1/3, 2/3, 0, 2/3), (2/3, 1/3, 0, 1/3), a = 17.2889 (8) and c = 8.3622 (10) Å. The structure is characterized by a framework of corner-connected (Al,Si)O4 tetrahedra. The additional cations are incorporated in two different types of channels of the framework. All atoms in the structure are displacively modulated with amplitudes below 0.1 Å. The modulation can be well described taking into account harmonics of first order only. Atomic positions in the smaller channels of the framework are fully occupied by Na+. Cationic positions in the larger channel are occupationally modulated, yet the variation of electron density as a function of the internal coordinate t is very small and indicates that the incorporation of different types of cations (K+, Na+, Ca2+) and vacancies is realised in a highly disordered way. Average T—O distances indicate a nearly complete Al/Si ordering in the tetrahedral framework. A large part of the O atoms are approximated by split-atom positions, which are additionally affected by occupational modulation resulting in a high degree of disorder in the modulated structure. Occupational probabilities for the split-atom positions are complementary. Occupational modulations of the cations in the larger channels and the O atoms of the tetrahedral framework are coupled and correlations between occupational and displacive modulations exist.

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