Centrosymmetric LaRh2Ga2

2020 ◽  
Vol 235 (1-2) ◽  
pp. 41-46
Author(s):  
Stefan Seidel ◽  
Lea Schubert ◽  
Rolf-Dieter Hoffmann ◽  
Rainer Pöttgen
Keyword(s):  
Single Crystals ◽  
Induction Furnace ◽  
Atomic Displacement ◽  
Type Structure ◽  
Arc Melting ◽  
Atomic Displacement Parameters ◽  
Centrosymmetric Structure

AbstractPolycrystalline samples of LaRh2Ga2 with the centrosymmetric CaBe2Ge2 type structure were obtained by arc-melting. Small single crystals were grown through a special annealing sequence in an induction furnace. The structures of two different crystals were refined from diffractometer data, confirming the centrosymmetric structure. The 2c Rh sites were refined with anharmonic atomic displacement parameters.

Incommensurate modulation of calcium barium niobate (CBN28 and Ce:CBN28)

2012 ◽  
Vol 68 (2) ◽  
pp. 101-106 ◽  
Author(s):  
Heribert A. Graetsch ◽  
Chandra Shekhar Pandey ◽  
Jürgen Schreuer ◽  
Manfred Burianek ◽  
Manfred Mühlberg
Keyword(s):  
Crystal Structures ◽  
Tungsten Bronze ◽  
Atomic Displacement ◽  
Type Structure ◽  
Formula Unit ◽  
Tetragonal Tungsten Bronze ◽  
First Order ◽  
Oxygen Coordination ◽  
Incommensurate Modulation ◽  
Atomic Displacement Parameters

The incommensurately modulated crystal structures of Ca0.28Ba0.72Nb2O6 (CBN28) and Ce0.02Ca0.25Ba0.72Nb2O6 (Ce:CBN28) were refined in the supercentred setting X4bm(AA0,−AA0) of the 3 + 2-dimensional superspace group P4bm(aa½,−aa½). Both compounds are isostructural with a tetragonal tungsten bronze-type structure. The modulation of CBN28 consists of a wavy distribution of Ba and Ca atoms as well as vacancies on the incompletely occupied Me2 site with 15-fold oxygen coordination. The occupational modulation is coupled with a modulation of the atomic displacement parameters and a very weak modulation of the positional parameters of Me2. The surrounding O atoms show strong displacive modulations with amplitudes up to ca 0.2 Å owing to the cooperative tilting of the rigid NbO6 octahedra. The Me1 site with 12-fold coordination and Nb atoms are hardly affected by the modulations. Only first-order satellites were observed and the modulations are described by first-order harmonics. In Ce:CBN28 cerium appears to be located on both the Me2 and Me1 sites. Wavevectors and structural modulations are only weakly modified upon substitutional incorporation of 0.02 cerium per formula unit of calcium.

Ternary Indides LnRhIn2 (Ln = La, Ce, Pr, Nd, Sm) with MgCuAl2 Type Structure

2002 ◽  
Vol 57 (7) ◽  
pp. 798-802 ◽  
Author(s):  
Vasyl’ I Zaremba ◽  
Vitaliy P Dubenskiy ◽  
Rainer Pöttgena
Keyword(s):  
Single Crystals ◽  
Three Dimensional ◽  
Argon Atmosphere ◽  
Type Structure ◽  
Subsequent Annealing ◽  
X Ray Diffraction ◽  
Interatomic Distances ◽  
X Ray ◽  
Arc Melting ◽  
Trigonal Prisms

The ternary indides LnRhIn2 (Ln = La, Ce, Pr, Nd, Sm) were synthesized by arc-melting of the elements under an argon atmosphere and subsequent annealing at 870 K. The samples have been investigated by X-ray diffraction on powders and single crystals: MgCuAl2 type, Cmcm, a = 448.2(1), b = 1025.7(1), c = 795.1(1) pm, wR2 = 0.0372, 228 F2 values, 16 variables for LaRhIn2, a = 446.0(1), b = 1017.3(2), c = 792.7(1) pm for CeRhIn2, a = 444.03(6), b = 1013.1(1), c = 792.5(1) pm for PrRhIn2, a = 442.49(5), b = 1012.7(1), c = 789.3(1) pm for NdRhIn2, and a = 438.1(1), b = 1009.3(1), c = 788.3(1) pm, wR2= 0.0414, 304 F2 values, 16 variables for SmRhIn2. Geometrical motifs of these structures are tricapped trigonal prisms around the rhodium atoms. The shortest interatomic distances were observed for the Rh-In contacts: 280-282 pm for LaRhIn2 and 276-279 pm for SmRhIn2. Together, the rhodium and indium atoms build a three-dimensional [RhIn2] polyanion in which the lanthanoid atoms fill distorted pentagonal channels. According to one short La-Rh (282 pm) and Sm-Rh (284 pm) distance one can assume strong bonding of the lanthanoid atoms to the polyanion.

The Stannide Zr5CuSn3

1997 ◽  
Vol 52 (1) ◽  
pp. 141-144 ◽  
Author(s):  
Rainer Pöttgen
Keyword(s):  
Crystal Structure ◽  
Single Crystals ◽  
Melting Furnace ◽  
Type Structure ◽  
X Ray Diffraction ◽  
X Ray ◽  
Arc Melting

Zr5CuSn3 was prepared from the elements in an arc-melting furnace and investigated by X-ray diffraction of powders as well as of single crystals. The crystal structure was refined from four-circle diffractometer data: P63/mcm, a = 860.04(7) pm, c = 586.80(5) pm, V = 0.3759(1) nm3, Z = 2, wR2 = 0.0402 for 371 F2 values and 15 variables. A refinement of the occupancy parameters re­vealed that the copper position is occupied to only 95.3(8)% in the crystal used for the X-ray investigation. Zr5CuSn3 crystallizes in the Hf5CuSn3 type structure, a filled variant of the Mn5Si3 type. The main features of the Zr5CuSn3 structure are condensed Zr6 octahedra that are centered by copper atoms

U3TiSb5, U3VSb5, U3CrSb5, and U3MnSb5 with "Anti"-Hf5Sn3Cu Type Structure

1994 ◽  
Vol 49 (6) ◽  
pp. 747-752 ◽  
Author(s):  
Markus Brylak ◽  
Wolfgang Jeitschko
Keyword(s):  
Transition Metal ◽  
Single Crystals ◽  
Type Structure ◽  
Interatomic Distances ◽  
X Ray ◽  
Lattice Constants ◽  
Arc Melting ◽  
Metal Atoms ◽  
Transition Metal Atoms ◽  
Structure Factors

The title compounds have been prepared from the elemental components by arc-melting and subsequent annealing. Single crystals of U3TiSb5 and U3MnSb5 were obtained from a tin flux and their structures were determined from single-crystal X-ray data: P63/mcm, Z = 2; a = 913.9(2), c = 611.2(1) pm, R = 0.011 (233 structure factors, 14 variables) for U3TiSb5 and a = 916.8(2), c = 613.2(1) pm, R = 0.015 (427 structure factors, 14 variables) for U3MnSb5. The lattice constants of the isotypic compounds are: a = 908.2(2), c = 608.3(2) pm for U3VSb5 and a = 911.0(1), c = 611.5(1) pm for U3CrSb5. The structure of these antimonides may be regarded as an “anti”-type structure of Hf5Sn3Cu with the antimony atoms on the hafnium sites, while the positions of the uranium and transition metal atoms correspond to the positions of the tin and copper atoms. A comparison of the interatomic distances of U3TiSb5 with those of U3Sb4, USb2, and a-antimony suggests oxidation numbers according to (U+III)3Ti+IV(Sb1-III)3(Sb2-II)2, where the Sb2 atoms form weakly bonded chains

La5Ir1.73In4.27 with Lu5Ni2In4-type structure

2020 ◽  
Vol 75 (6-7) ◽  
pp. 709-713
Author(s):  
Nataliya Dominyuk ◽  
Vasyl’ I. Zaremba ◽  
Rainer Pöttgen
Keyword(s):  
Single Crystal ◽  
Single Crystals ◽  
Small Degree ◽  
Type Structure ◽  
Muffle Furnace ◽  
Space Group ◽  
One Dimensional ◽  
X Ray ◽  
Structure Space ◽  
Arc Melting

AbstractSingle crystals of La5Ir1.73In4.27 were grown from a sample of the starting composition 47La: 17Ir: 36 In by arc-melting, followed by a long annealing sequence in a muffle furnace. La5Ir1.73In4.27 crystallizes with the Lu5Ni2In4-type structure, space group Pbam, which was refined from single-crystal X-ray diffractometer data: a = 834.0(2), b = 1862.2(4), c = 385.31(8) pm, wR2 = 0.0278, 1165 F2 values and 37 variables. The 4h iridium site shows a small degree of Ir/In mixing. Geometrically one can describe the La5Ir1.73In4.27 structure as a simple 4:1 intergrowth variant of CsCl and AlB2-related slabs. The iridium and indium atoms form a one-dimensional meandering [Ir1.73In4.27]δ– polyanion (292 pm Ir–In and 327 pm In–In) which is embedded in a lanthanum matrix.

scholarly journals Crystal Structure of Moganite and Its Anisotropic Atomic Displacement Parameters Determined by Synchrotron X-ray Diffraction and X-ray/Neutron Pair Distribution Function Analyses

Minerals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 272
Author(s):  
Seungyeol Lee ◽  
Huifang Xu ◽  
Hongwu Xu ◽  
Joerg Neuefeind
Keyword(s):  
Crystal Structure ◽  
Distribution Function ◽  
Single Crystal ◽  
Pair Distribution Function ◽  
Atomic Displacement ◽  
Single Crystal Xrd ◽  
X Ray Diffraction ◽  
X Ray ◽  
Neutron Pair ◽  
Atomic Displacement Parameters

The crystal structure of moganite from the Mogán formation on Gran Canaria has been re-investigated using high-resolution synchrotron X-ray diffraction (XRD) and X-ray/neutron pair distribution function (PDF) analyses. Our study for the first time reports the anisotropic atomic displacement parameters (ADPs) of a natural moganite. Rietveld analysis of synchrotron XRD data determined the crystal structure of moganite with the space group I2/a. The refined unit-cell parameters are a = 8.7363(8), b = 4.8688(5), c = 10.7203(9) Å, and β = 90.212(4)°. The ADPs of Si and O in moganite were obtained from X-ray and neutron PDF analyses. The shapes and orientations of the anisotropic ellipsoids determined from X-ray and neutron measurements are similar. The anisotropic ellipsoids for O extend along planes perpendicular to the Si-Si axis of corner-sharing SiO4 tetrahedra, suggesting precession-like movement. Neutron PDF result confirms the occurrence of OH over some of the tetrahedral sites. We postulate that moganite nanomineral is stable with respect to quartz in hypersaline water. The ADPs of moganite show a similar trend as those of quartz determined by single-crystal XRD. In short, the combined methods can provide high-quality structural parameters of moganite nanomineral, including its ADPs and extra OH position at the surface. This approach can be used as an alternative means for solving the structures of crystals that are not large enough for single-crystal XRD measurements, such as fine-grained and nanocrystalline minerals formed in various geological environments.

scholarly journals Reproducibility of protein x-ray diffuse scattering and potential utility for modeling atomic displacement parameters

2021 ◽  
Vol 8 (4) ◽  
pp. 044701
Author(s):  
Zhen Su ◽  
Medhanjali Dasgupta ◽  
Frédéric Poitevin ◽  
Irimpan I. Mathews ◽  
Henry van den Bedem ◽  
...  
Keyword(s):  
Diffuse Scattering ◽  
Atomic Displacement ◽  
Potential Utility ◽  
X Ray ◽  
Protein X ◽  
Atomic Displacement Parameters

Ternary Antimonides RE4T7Sb6 (RE=Gd–Lu; T =Ru, Rh) with Cubic U4Re7Si6-type Structure

2013 ◽  
Vol 68 (9) ◽  
pp. 971-978 ◽  
Author(s):  
Inga Schellenberg ◽  
Ute Ch. Rodewald ◽  
Christian Schwickert ◽  
Matthias Eul ◽  
Rainer Pöttgen
Keyword(s):  
Magnetic Susceptibility ◽  
Single Crystal ◽  
Magnetic Moment ◽  
Induction Furnace ◽  
X Ray Diffraction ◽  
Temperature Dependent ◽  
X Ray ◽  
Antiferromagnetic Ordering ◽  
Arc Melting ◽  
Intermediate Valent

The ternary antimonides RE4T7Sb6 (RE=Gd-Lu; T =Ru, Rh) have been synthesized from the elements by arc-melting and subsequent annealing in an induction furnace. The samples have been characterized by powder X-ray diffraction. Four structures were refined on the basis of single-crystal X-ray diffractometer data: U4Re7Si6 type, space group Im3m with a=862.9(2) pm, wR2=0.0296, 163 F2 values for Er4Ru7Sb6; a=864.1(1) pm, wR2=0.1423, 153 F2 values for Yb4Ru7Sb6; a=872.0(2) pm, wR2=0.0427, 172 F2 values for Tb4Rh7Sb6; and a=868.0(2) pm, wR2=0.0529, 154 F2 values for Er4Rh7Sb6, with 10 variables per refinement. The structures have T1@Sb6 octahedra and slightly distorted RE@T26Sb6 cuboctahedra as building units. The distorted cuboctahedra are condensed via all trapezoidal faces, and this network leaves octahedral voids for the T1 atoms. The ruthenium-based series of compounds was studied by temperature-dependent magnetic susceptibility measurements. Lu4Ru7Sb6 is Pauli-paramagnetic. The antimonides RE4Ru7Sb6 with RE=Dy, Ho, Er, and Tm show Curie-Weiss paramagnetism. Antiferromagnetic ordering occurs at 10.0(5), 5.1(5) and 4.0(5) K for Dy4Ru7Sb6, Ho4Ru7Sb6 and Er4Ru7Sb6, respectively, while Tm4Ru7Sb6 remains paramagnetic. Yb4Ru7Sb6 is an intermediate-valent compound with a reduced magnetic moment of 3.71(1) μB per Yb as compared to 4.54 μB for a free Yb3+ ion

scholarly journals Structural analysis and multipole modelling of quercetin monohydrate – a quantitative and comparative study

2010 ◽  
Vol 67 (1) ◽  
pp. 63-78 ◽  
Author(s):  
Sławomir Domagała ◽  
Parthapratim Munshi ◽  
Maqsood Ahmed ◽  
Benoît Guillot ◽  
Christian Jelsch
Keyword(s):  
Comparative Study ◽  
Charge Density ◽  
Topological Analysis ◽  
Atomic Displacement ◽  
X Ray Diffraction ◽  
Experimental Database ◽  
Figures Of Merit ◽  
Atom Model ◽  
Atomic Displacement Parameters ◽  
Model Approach

The multipolar atom model, constructed by transferring the charge-density parameters from an experimental or theoretical database, is considered to be an easy replacement of the widely used independent atom model. The present study on a new crystal structure of quercetin monohydrate [2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxy-4H-chromen-4-one monohydrate], a plant flavonoid, determined by X-ray diffraction, demonstrates that the transferred multipolar atom model approach greatly improves several factors: the accuracy of atomic positions and the magnitudes of atomic displacement parameters, the residual electron densities and the crystallographic figures of merit. The charge-density features, topological analysis and electrostatic interaction energies obtained from the multipole models based on experimental database transfer and periodic quantum mechanical calculations are found to compare well. This quantitative and comparative study shows that in the absence of high-resolution diffraction data, the database transfer approach can be applied to the multipolar electron density features very accurately.

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