scholarly journals Could incommensurability in sulfosalts be more common than thought? The case of meneghinite, CuPb13Sb7S24

2017 ◽  
Vol 73 (3) ◽  
pp. 369-376 ◽  
Author(s):  
Luca Bindi ◽  
Václav Petříček ◽  
Cristian Biagioni ◽  
Jakub Plášil ◽  
Yves Moëlo
Keyword(s):  
Driving Forces ◽  
Bimodal Distribution ◽  
Modulated Structure ◽  
Cell Parameters ◽  
Incommensurate Structure ◽  
Incommensurate Modulation ◽  
Coupled Substitution ◽  
Modulation Vector ◽  
Different Parts ◽  
Apuan Alps

The structure of meneghinite (CuPb13Sb7S24), from the Bottino mine in the Apuan Alps (Italy), has been solved and refined as an incommensurate structure in four-dimensional superspace. The structure is orthorhombic, superspace groupPnma(0β0)00s, cell parametersa =24.0549 (3),b =4.1291 (6),c =11.3361 (16) Å, modulation vectorq= 0.5433 (4)b*. The structure was refined from 6604 reflections to a finalR= 0.0479. The model includes modulation of both atomic positions and displacement parameters, as well as occupational waves. The driving forces stabilizing the modulated structure of meneghinite are linked to the occupation modulation of Cu and some of the Pb atoms. As a consequence of the Cu/[] and Pb/Sb modulations, three- to sevenfold coordinations of theMcations (Pb/Sb) occur in different parts of the structure. The almost bimodal distribution of the occupation of Cu/[] and Pb/Sb atM5 conforms with the coupled substitution Sb3++ [] → Pb2++ Cu+, thus corroborating the hypothesis deduced previously for the incorporation of copper in the meneghinite structure. The very small departure (∼0.54versus0.50) from the commensurate value of the modulation raises the question of whether other sulfosalts considered superstructures have been properly described, and, in this light, if incommensurate modulation in sulfosalts could be much more common than thought.

scholarly journals The modulated structure of Ba0.39Sr0.61Nb2O6. I. Harmonic solution

2003 ◽  
Vol 59 (1) ◽  
pp. 28-35 ◽  
Author(s):  
Theo Woike ◽  
Václav Petříček ◽  
Michal Dušek ◽  
Niels K. Hansen ◽  
Pierre Fertey ◽  
...  
Keyword(s):  
Complete Solution ◽  
Atomic Position ◽  
Unit Cell Parameters ◽  
Data Set ◽  
Modulated Structure ◽  
Cell Parameters ◽  
First Order ◽  
Harmonic Solution ◽  
Incommensurate Structure ◽  
Complicated Model

The structure of a crystal of Sr0.61Ba0.39Nb2O6 has been solved and refined as an incommensurate structure in five-dimensional superspace. The structure is tetragonal, superspace group P4bm(\,pp1/2,p - p1/2), unit-cell parameters a = 12.4566 (9), c = 7.8698 (6) Å, modulation vectors q 1 = 0.3075 (6) (a* + b*), q 2 = 0.3075 (6) (a* − b*). The data collection was performed on a KUMA-CCD diffractometer and allowed the integration of weak first-order satellite reflections. The structure was refined from 2569 reflections to a final value of R = 0.0479. The modulation affects mainly the positions of the O atoms, which are displaced by as much as 0.5 Å, and the site 4c that is occupied by Sr and Ba atoms. Only a simplified model, in which this atomic position is occupied by an effective atom Sr/Ba, could be refined from the data set. The modulation of displacement parameters has been used to account for the modulated distribution of Sr and Ba. The whole refinement uses only first-order modulation waves, but there are strong indications that for a complete solution the use of higher-order satellites and a more complicated model is necessary.

Structure of Mn8Sn5

1997 ◽  
Vol 53 (3) ◽  
pp. 364-372 ◽  
Author(s):  
M. Elding-Pontén ◽  
L. Stenberg ◽  
S. Lidin ◽  
G. Madariaga ◽  
J.-M. Pérez-Mato
Keyword(s):  
Electron Diffraction ◽  
Title Compound ◽  
Type Structure ◽  
Space Group ◽  
Cell Parameters ◽  
Incommensurate Structure ◽  
Incommensurate Modulation ◽  
Fifth Order

The title compound crystallizes as a slightly incommensurate modulation of the B8-type structure. In a basic NiAs structure, ∼60% of the trigonal pyramidal interstices are filled with Mn atoms in an ordered manner. The highest corresponding commensurate space group is Pbnm (Pnma, No. 62) with the cell parameters a = 21.9114 (4), b: 7.6003 (5), c = 5.5247  (5) Å. The four-dimensional superspace group of the incommensurate structure is Cmcm(α00)0s0 (No. 63.8), with the conventional setting Amam(00γ)0s0. The cell parameters for this incommensurate cell are a = 382 (1), b = 7.600 (2), c = 5.525 (2) Å, q = [0.616 (5), 0, 0]. The structural refinements were carried out on a multiply twinned specimen. The R-factors were 0.037 for the incommensurate refinement and 0.046 for one commensurate approximation. The refinements unambiguously show that the modulation is caused by the step-like modulation of one Mn site, which is accompanied by small displacive modulations of the basic lattice. The incommensurate nature of the modulation is manifested in a slight splitting of fifth-order satellites, visible in electron diffraction.

Superspace-symmetry determination and multidimensional refinement of the incommensurately modulated structure of natural fresnoite

2006 ◽  
Vol 62 (6) ◽  
pp. 1031-1037 ◽  
Author(s):  
Luca Bindi ◽  
Michal Dusek ◽  
Vaclav Petricek ◽  
Paola Bonazzi
Keyword(s):  
Data Collection ◽  
Modulated Structure ◽  
Fresno County ◽  
Cell Parameters ◽  
Incommensurate Structure

The structure of natural fresnoite, Ba2TiSi2O8, from the sanbornite deposits of eastern Fresno County, California, has been solved and refined as an incommensurate structure in five-dimensional superspace. The structure is tetragonal, superspace group P4bm\left({\alpha, \alpha, 1/2} \right)\left({ - \alpha, \alpha, 1/2} \right)0gg, cell parameters a = 8.5353 (6), c = 10.4128 (7) Å, modulation vectors {\bf q}_1 = 0.3020\,\left(3 \right)\,\left({{\bf a}^* + {\bf b}^* } \right), {\bf q}_2 = 0.3020\,\left(3 \right)\,\left({ - {\bf a}^* + {\bf b}^* } \right). Data collection was performed on an Xcalibur CCD diffractometer at 110 K. The structure was refined from 3452 reflections to final R = 0.0123. The model includes modulation of both atomic positions and displacement parameters. As a consequence of the Ba and O positional modulation, eight-, nine- and tenfold Ba coordinations occur throughout the structure. The change of coordination around the Ba atom is clearly represented by the deformation of the pentagonal rings, as seen from a projection along [001]. The deformed pentagonal rings correspond to Ba atoms with eight- and ninefold coordinations and form octagonal clusters closely resembling those observed in the incommensurate structure of melilite-type compounds.

scholarly journals The incommensurate structure of K3In(PO4)2

2003 ◽  
Vol 59 (1) ◽  
pp. 17-27 ◽  
Author(s):  
Alla Arakcheeva ◽  
Gervais Chapuis ◽  
Vaclav Petříček ◽  
Michal Dušek ◽  
Andreas Schönleber
Keyword(s):  
Room Temperature ◽  
Driving Forces ◽  
Three Dimensional ◽  
Close Packing ◽  
The Other ◽  
Dimensional Structure ◽  
Powder Diffraction Data ◽  
Modulated Structure ◽  
Incommensurate Structure ◽  
Modulated Phase

The incommensurately modulated structure of K3In(PO4)2 has been solved and refined. The origin of the modulation relates to the ordering of K cations within the hexagonal close packing of the PO4 anions. The driving forces for the modulation of the other cations are In—P and K—P interactions. The modulation of O atoms of rigid PO4 units follows the cations in order to stabilize the InO6 octahedron. It is shown that the previously published three-dimensional structure refined from powder diffraction data obtained at room temperature is an average structure. Therefore the incommensurately modulated phase of K3In(PO4)2 is the only one that has been unequivocally identified at room temperature. The origin of the modulation is discussed in comparison with the structures of Na3InP2, α- and β-Na3In(PO4)2, Na3Fe(PO4)2 and Rb3In(PO4)2.

Meieranite, Na2Sr3MgSi6O17, a New Mineral from the Wessels Mine, Kalahari Manganese Fields, South Africa

2019 ◽  
Vol 57 (4) ◽  
pp. 457-466 ◽  
Author(s):  
Hexiong Yang ◽  
Xiangping Gu ◽  
Robert T. Downs ◽  
Stanley H. Evans ◽  
Jaco J. Van Nieuwenhuizen ◽  
...  
Keyword(s):  
South Africa ◽  
Empirical Formula ◽  
Microprobe Analysis ◽  
New Mineral ◽  
Cell Parameters ◽  
New Mineral Species ◽  
General Chemical ◽  
Northern Cape ◽  
Coupled Substitution ◽  
Mohs Hardness

Abstract A new mineral species, meieranite, ideally Na2Sr3MgSi6O17, has been found in the Wessels mine, Kalahari Manganese Fields, Northern Cape Province, South Africa. It occurs in isolated aggregates embedded in a matrix mainly of sugilite, along with minor aegirine and pectolite. Crystals of meieranite are up to 0.5 × 0.5 × 0.4 mm in size. No twinning is observed. The mineral is light blue to blue in transmitted and under incident lights, transparent with white streak, and has vitreous luster. It is brittle and has a Mohs hardness of 5.5; cleavage is good on {010} and no parting was observed. The measured and calculated densities are 3.41(3) and 3.410 g/cm3, respectively. Optically, meieranite is biaxial (–), with α = 1.610(1), β = 1.623(1), γ = 1.630(1) (white light), 2V (meas.) = 70(1)°, 2V (calc.) = 72°. The calculated compatibility index based on the empirical formula is –0.007 (superior). An electron microprobe analysis yields an empirical formula (based on 17 O apfu) of Na1.96(Sr2.91Ba0.03Ca0.03Pb0.02)Σ2.99(Mg0.62Mn0.28Co0.07Fe0.01)Σ0.98Si6.03O17, which can be simplified to Na2Sr3MgSi6O17. Meieranite is orthorhombic, with space group P21nb and unit-cell parameters a 7.9380(2), b 10.4923(3), c 18.2560(6) Å, and V 1520.50(8) Å3. Its crystal structure is characterized by two kinds of layers that alternate along [010]: layers of corner-sharing SiO4 and M2+O4 tetrahedra (M2+ = Mg, Mn, Co, Fe) and layers of NaO6 and SrO8 polyhedra. The tetrahedral layers consist of eight-, five-, and four-membered rings and are composed of [Si6O17] ribbons (parallel to [101]) linked together by MO4 tetrahedra. Most remarkably, the structure of meieranite is topologically identical to that of the nordite group of minerals, which has the general chemical formula Na3SrR3+M2+Si6O17, where R = Ce and La and M = Zn, Fe, and Mn. Accordingly, chemically, meieranite may be obtained through the coupled substitution of 2Sr2+ for (Na+ + R3+) in nordite.

Indexing of incommensurate satellite reflections in X-ray powder diffraction pattern of (Bi, Pb)2Sr2Ca2Cu3Ox (2223) phase

1997 ◽  
Vol 12 (3) ◽  
pp. 141-144 ◽  
Author(s):  
D. Y. Li ◽  
C. W. MacKinnon
Keyword(s):  
Powder Diffraction ◽  
Wave Vector ◽  
Diffraction Data ◽  
Powder Diffraction Data ◽  
X Ray ◽  
Cell Parameters ◽  
Modulation Wave ◽  
Two Component ◽  
Incommensurate Modulation ◽  
Comparison Of The Results

X-ray powder diffraction data and refined unit cell parameters for the (Bi, Pb)2Sr2Ca2Cu3Ox (2223) superconducting phase, indexed using incommensurate modulation principles, are reported. Comparison of the results obtained with one- and two-component modulation wave vectors showed that the two-component modulation wave vector is superior for indexing the satellite reflections. A two-component wave vector indexing result seems likely when only the powder diffraction data are considered.

scholarly journals Modulated Structures, Microstructures and Subsolidus Phase Relations of Labradorite Feldspars

2021 ◽  
Vol 6 (1) ◽  
pp. 1
Author(s):  
Huifang Xu ◽  
Shiyun Jin ◽  
Seungyeol Lee
Keyword(s):  
Cooling Rate ◽  
Group Symmetry ◽  
Subsolidus Phase ◽  
Plagioclase Feldspar ◽  
Modulated Structure ◽  
Modulated Structures ◽  
Coupled Substitution ◽  
Density Modulation ◽  
Q Vector ◽  
Rich Side

The coupled substitution between Na+Si and Ca+Al, in the plagioclase solid solution, results in a continuous variation in the Al/Si ratio of the composition, which is the reason for the complicated ordering patterns in the intermediate plagioclase feldspars such as labradorite. Both fast-cooled and slow-cooled labradorite feldspars display the incommensurately modulated structures. The ordering pattern in the incommensurately modulated structures of e-plagioclase (characterized by the satellite diffraction peak called e-reflections) is the most complicated and intriguing. The modulated structure has a super-space group symmetry of X(αβγ)0, with a special centering condition of (½ ½ ½ 0), (0 0 ½ ½), (½ ½ 0 ½), and the q-vector has components (i.e., δh, δk, δl) along all three axes in reciprocal space. Displacive modulation, occupational modulation, and density modulation are observed in slowly cooled labradorite feldspars. No density modulation was observed in fast cooled (volcanic) labradorite feldspars. The amplitudes of the modulation waves are new parameters for quantifying the ordering state of labradorite. Iridescent labradorite feldspars display exsolution lamellae with an average periodicity ranging from ~150 nm to ~350 nm. Compositional difference between the lamellae is about 12 mole % in anorthite components. Areas or zones with red (or yellow) iridescent color (i.e., long lamellae periodicity) always contain more Ca (~1 to 3 mole %) than the areas with blue (or green) iridescent color within the same labradorite crystal. We proposed that the solvus for Bøggild intergrowth has a loop-like shape, ranging from ~An44 to ~An63. The Ca-rich side / zone has higher exsolution temperature than the Na-rich side / zone. The shapes of satellite peaks, the distances between e-reflections (modulation periods), and even the intensity of e-reflections may also be used to evaluate the ordering state or cooling rate of the plagioclase feldspar. Both modulated structure and the exsolution lamellae can be used as proxies for quantifying cooling rate of a labradorite and it’s host rock.

scholarly journals The role of hydrogen bonding in the incommensurate modulation of myo-inositol camphor ketal

2021 ◽  
Vol 77 (1) ◽  
pp. 83-92
Author(s):  
Viktor Savic ◽  
Felix Eder ◽  
Christian Göb ◽  
Marko D. Mihovilovic ◽  
Christian Stanetty ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Basic Structure ◽  
Two Dimensions ◽  
Group Symmetry ◽  
Internal Space ◽  
Disorder Phase Transition ◽  
Modulation Wave ◽  
Incommensurate Structure ◽  
Incommensurate Modulation ◽  
Definition Of

myo-Inositol-2,3-D-camphor ketal crystallizes as an incommensurate structure with the C2(0σ2½) superspace group symmetry [σ2 = 0.1486 (3) at 100 K]. The bornane and myo-inositol moieties aggregate in distinct layers extending parallel to (001). The myo-inositol rings are connected by a complex hydrogen-bonding network extending in two dimensions, which is disordered in the basic structure and (mostly) ordered in the actual modulated structure. The domains of definition of the H atoms in internal space were derived by chemical reasoning and modeled with crenel functions. By tracing the hydrogen bonding, distinct chains, which are periodic in the [100] direction, are identified. These chains possess one of two possible orientations with respect to the hydrogen bonding. The incommensurate modulation is characterized by a non-periodic succession of the two chain orientations in the [010] direction. On heating, the σ2-component of the modulation wave vector decreases from σ2 = 0.1486 (3) at 100 K to σ2 = 0.1405 (6) at 430 K, which means that the periodicity of the modulation wave increases. No order–disorder phase transition was evidenced up to the melting point (with decomposition).

scholarly journals International commercial courts as new actors in adjudication business: Collaborators or competitors?

2021 ◽  
Vol 59 (1) ◽  
pp. 52-71
Author(s):  
Balša Stevanović
Keyword(s):  
Dispute Resolution ◽  
Driving Forces ◽  
Hybrid Structure ◽  
Definitive Answer ◽  
Financial Centre ◽  
The World ◽  
Geographic Regions ◽  
International Adjudication ◽  
Commercial Courts ◽  
Different Parts

International commercial courts are a relatively new phenomenon that changes the configuration of the international adjudication business. As novel players on the dispute resolution scene, these courts challenge the notion of competition between the existing actors in the business. From the perspective of arbitration, international commercial courts tend to be perceived as both collaborators and competitors. Furthermore, various driving forces influenced the creation of these courts, which gave them a hybrid structure and a quite unique institutional appearance. This article examines three prominent courts in three different parts of the world: the Dubai International Financial Centre Courts (DIFCC), the Singapore International Commercial Court (SICC) and the Netherlands Commercial Court (NCC). The aim is to identify the main features of these adjudication actors that operate within three highly commercially relevant geographic regions in order to outline their character and role on the adjudication business stage. Eventually, through these examples this article addresses the puzzling question of competition versus cooperation in contrast to arbitration. Nevertheless, it is still hard to give a definitive answer - it seems too early for a firm prediction regarding the future of these projects. Jurisprudence must be developed in order to comprehensively test the success of international commercial courts

Training Children for Work in the Nineteenth Century

2018 ◽  
Author(s):  
Vicky Crewe
Keyword(s):  
Nineteenth Century ◽  
Material Culture ◽  
Driving Forces ◽  
Western World ◽  
Work Related ◽  
Decorative Motifs ◽  
Domestic Material Culture ◽  
The Subject ◽  
Different Parts

Material culture in Victorian working-class homes acted as a medium through which messages about the importance of industry, diligence, and obedience could be emphasized to children. This chapter will review the ways in which material culture scholars have approached the subject of child labour in different areas of the Victorian world, as well as elucidating the differences and similarities in children’s experiences of work in different parts of the western world during the nineteenth century. It will consider decorative motifs on mass-produced domestic material culture, the role of toys as objects for training children, and work-related artefacts with which children may have interacted, but which do not bear obvious characteristics suggesting that they were specifically made for children. Labour will be addressed in its broadest sense, including gendered differences in the material culture of labour and the broader historical driving forces behind the existence of work-related material ‘propaganda’.

Sign in / Sign up

Export Citation Format

Share Document