Crystallochemistry of Thortveitite-Like and Thortveitite-Type Compounds

2004 ◽  
Vol 848 ◽  
Author(s):  
E. A. Juarez-Arellano ◽  
J. Campa-Molina ◽  
S. Ulloa-Godínez ◽  
L. Bucio ◽  
E. Orozco
Keyword(s):  
Crystal Structure ◽  
Crystal Structures ◽  
Bond Valence ◽  
Structure Stability ◽  
Structural Relationships ◽  
Distortion Analysis ◽  
The Difference ◽  
Stability Ranges

ABSTRACTIn this article we present the main features and structural relationships between thortveitite-type and thortveitite-like germanates compounds. We describe in detail the crystal structures, how they are built and the difference between them. Bond-valence and polyhedra distortion analysis are made and crystal structure stability ranges are given.

Concerning inorganic crystal structure types

1999 ◽  
Vol 55 (2) ◽  
pp. 147-156 ◽  
Author(s):  
G. Bergerhoff ◽  
M. Berndt ◽  
K. Brandenburg ◽  
T. Degen
Keyword(s):  
Crystal Structure ◽  
Crystal Structures ◽  
Structure Type ◽  
Inorganic Crystal Structure Database ◽  
Full Information ◽  
Structure Database ◽  
Inorganic Crystal ◽  
The Difference ◽  
Crystal Structure Database

All representatives of an inorganic crystal structure type can be found systematically in the new database SICS (Standardized Inorganic Crystal Structures). It is derived from the Inorganic Crystal Structure Database (ICSD) by selecting the best determination of each phase. In addition, each entry is given in a standardized description and complemented by searchable descriptors \Delta, which give the difference between all structures of an isopointal set. Because of the large number of structures the full information on relationships present can only be found by means of the new database itself. Some examples are given here in printed form. The limitations and the possibilities of expansion of SICS in terms of the concept of `structure types' are demonstrated.

scholarly journals Explainable machine learning for materials discovery: predicting the potentially formable Nd–Fe–B crystal structures and extracting the structure–stability relationship

IUCrJ ◽  
2020 ◽  
Vol 7 (6) ◽  
pp. 1036-1047
Author(s):  
Tien-Lam Pham ◽  
Duong-Nguyen Nguyen ◽  
Minh-Quyet Ha ◽  
Hiori Kino ◽  
Takashi Miyake ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Unsupervised Learning ◽  
Crystal Structures ◽  
Coordination Number ◽  
Phase Stability ◽  
Learning Model ◽  
Structure Stability ◽  
Host Crystal ◽  
The Stability ◽  
Relationship Of

New Nd–Fe–B crystal structures can be formed via the elemental substitution of LA–T–X host structures, including lanthanides (LA), transition metals (T) and light elements, X = B, C, N and O. The 5967 samples of ternary LA–T–X materials that are collected are then used as the host structures. For each host crystal structure, a substituted crystal structure is created by substituting all lanthanide sites with Nd, all transition metal sites with Fe and all light-element sites with B. High-throughput first-principles calculations are applied to evaluate the phase stability of the newly created crystal structures, and 20 of them are found to be potentially formable. A data-driven approach based on supervised and unsupervised learning techniques is applied to estimate the stability and analyze the structure–stability relationship of the newly created Nd–Fe–B crystal structures. For predicting the stability for the newly created Nd–Fe–B structures, three supervised learning models: kernel ridge regression, logistic classification and decision tree model, are learned from the LA–T–X host crystal structures; the models achieved maximum accuracy and recall scores of 70.4 and 68.7%, respectively. On the other hand, our proposed unsupervised learning model based on the integration of descriptor-relevance analysis and a Gaussian mixture model achieved an accuracy and recall score of 72.9 and 82.1%, respectively, which are significantly better than those of the supervised models. While capturing and interpreting the structure–stability relationship of the Nd–Fe–B crystal structures, the unsupervised learning model indicates that the average atomic coordination number and coordination number of the Fe sites are the most important factors in determining the phase stability of the new substituted Nd–Fe–B crystal structures.

Betpakdalite Unmasked, and a Comment on Bond Valences

1992 ◽  
Vol 45 (9) ◽  
pp. 1335 ◽  
Author(s):  
PB Moore
Keyword(s):  
Crystal Structure ◽  
Bond Strength ◽  
Close Packing ◽  
Transformation Matrix ◽  
Bond Valence ◽  
Real Structure ◽  
Remarkable Case ◽  
Octahedral Cation ◽  
The Difference ◽  
Packing Efficiency

A new representation of the crystal structure of complex betpakdalite reported in 1984 (R ≈ 0.08) reveals a remarkable case of . hccchhccch 10-layer anion (O2-)/void ( ) close-packing. The transformation matrix from earlier C12/m 1 cell to new F 2/m 11 cell is [010/100/102], new a = 11.10, b = 19.44, c = 22. 93 �, α)/10 = 2.29 Ǻ. The packing efficiency is Ve = 15.45 � α3 for 10 layers of 32(O2-+ ) per layer. For Pauling r(O2-) = 1.40 �, Ve = 15.52 �3. Oxide anions populate only 46.25% of the close-packed slots; the rest are voids. The difference, Δ, between real structure and ideal (perfect) structure is (0.13 �) for O2-, (0.20 �) for cations and (0.15 A) for all atoms in the close-packed frame, range 0.00-0.43 �. The cell formula for x = 2 is H8 [K(H2O)6]4 [Ca(H20)6]8 [MO6+32 As5+8O148]28-.8H2O. It is suggested that H8 bonds with 8O(10) in the cell, the only anion bonded to only one Mo6+. The cell formula gives D(calc) = 2.90 g cm-3, close to reported D( obs ) = 2.98, 3.05; and 2.92 g cm-3. Bond strength/bond valence calculations for assorted Mp+6 � q- (M = octahedral cation linked to generalized anion �) often show extreme deviations. This is shown to be a consequence of Pauling's third rule of cation-cation repulsions across shared polyhedral edges and faces.

Hydrogen order in hydrides of Laves phases

2020 ◽  
Vol 235 (8-9) ◽  
pp. 319-332 ◽  
Author(s):  
Holger Kohlmann
Keyword(s):  
Crystal Structure ◽  
Phase Transitions ◽  
Crystal Structures ◽  
Laves Phase ◽  
Crystallographic Group ◽  
Crystal Chemical ◽  
Hydrogen Atoms ◽  
Laves Phases ◽  
Structural Relationships ◽  
Chemical Description

AbstractMany Laves phases AM2 takes up hydrogen to form interstitial hydrides in which hydrogen atoms partially occupy A2M2, AM3, and/or M4 tetrahedral interstices. They often exhibit temperature-driven order-disorder phase transitions, which are triggered by repulsion of hydrogen atoms occupying neighboring tetrahedral interstices. Because of the phase widths with respect to hydrogen a complete ordering, i.e., full occupation of all hydrogen positions is usually not achieved. Order-disorder transitions in Laves phase hydrides are thus phase transitions between crystal structures with different degrees of hydrogen order. Comparing the crystal structures of ordered and disordered phases reveals close symmetry relationships in all known cases. This allows new insights into the crystal chemical description of such phases and into the nature of the phase transitions. Structural relationships for over 40 hydrides of cubic and hexagonal Laves phases ZrV2, HfV2, ZrCr2, ZrCo2, LaMg2, CeMg2, PrMg2, NdMg2, SmMg2, YMn2, ErMn2, TmMn2, LuMn2, Lu0.4Y0.6Mn2 YFe2, and ErFe2 are concisely described in terms of crystallographic group-subgroup schemes (Bärnighausen trees) covering 32 different crystal structure types, 26 of which represent hydrogen-ordered crystal structures.

scholarly journals Bond softness sensitive bond-valence parameters for crystal structure plausibility tests

IUCrJ ◽  
2017 ◽  
Vol 4 (5) ◽  
pp. 614-625 ◽  
Author(s):  
Haomin Chen ◽  
Stefan Adams
Keyword(s):  
Crystal Structure ◽  
Crystal Structures ◽  
Electron Density ◽  
Valence Electron ◽  
Coordination Shell ◽  
Bond Valence ◽  
Coordination Numbers ◽  
Valence Electron Density ◽  
Bond Valence Parameter

Based on a description of bond valence as a function of valence electron density, a systematic bond softness sensitive approach to determine bond-valence parameters and related quantities such as coordination numbers is elaborated and applied to determine bond-valence parameters for 706 cation–anion pairs. While the approach is closely related to the earliersoftBVparameter set, the newsoftNC1parameters proposed in this work may be simpler to apply in plausibility checks of crystal structures, as they follow the first coordination shell convention. The performance of thissoftNC1bond-valence parameter set is compared with that of the previously derivedsoftBVparameter set that also factors in contributions from higher coordination shells, and with a benchmarking parameter set that has been optimized following the conventional choice of a universal value of the bond-valence parameterb. The results show that a systematic adaptation of the bond-valence parameters to the bond softness leads to a significant improvement in the bond-valence parameters, particularly for bonds involving soft anions, and is safer than individual free refinements of bothR0andbfrom a limited number of reference cation environments.

Crystallochemical analysis of the crystal structure of PbGa2S4: the bond valence model

2016 ◽  
Vol 39 (0) ◽  
pp. 7-11
Author(s):  
А. Я. Штейфан ◽  
В. І. Сідей ◽  
І. І. Небола ◽  
І. П. Студеняк
Keyword(s):  
Crystal Structure ◽  
Bond Valence ◽  
Bond Valence Model ◽  
Crystallochemical Analysis

Effect of solution acidity on the crystallization of polychromates in uranyl-bearing systems: synthesis and crystal structures of Rb2[(UO2)(Cr2O7)(NO3)2] and two new polymorphs of Rb2Cr3O10

2021 ◽  
Vol 236 (1-2) ◽  
pp. 11-21
Author(s):  
Evgeny V. Nazarchuk ◽  
Oleg I. Siidra ◽  
Dmitry O. Charkin ◽  
Stepan N. Kalmykov ◽  
Elena L. Kotova
Keyword(s):  
Crystal Structure ◽  
Aqueous Solutions ◽  
Crystal Structures ◽  
Hydrothermal Treatment ◽  
Ambient Conditions ◽  
Screw Axis ◽  
3D Framework ◽  
Solution Acidity

Abstract Three new rubidium polychromates, Rb2[(UO2)(Cr2O7)(NO3)2] (1), γ-Rb2Cr3O10 (2) and δ-Rb2Cr3O10 (3) were prepared by combination of hydrothermal treatment at 220 °C and evaporation of aqueous solutions under ambient conditions. Compound 1 is monoclinic, P 2 1 / c $P{2}_{1}/c$ , a = 13.6542(19), b = 19.698(3), c = 11.6984(17) Å, β = 114.326(2)°, V = 2867.0(7) Å3, R 1 = 0.040; 2 is hexagonal, P 6 3 / m $P{6}_{3}/m$ , a = 11.991(2), c = 12.828(3) Å, γ = 120°, V = 1597.3(5) Å3, R 1 = 0.031; 3 is monoclinic, P 2 1 / n $P{2}_{1}/n$ , a = 7.446(3), b = 18.194(6), c = 7.848(3) Å, β = 99.953(9)°, V = 1047.3(7) Å3, R 1 = 0.037. In the crystal structure of 1, UO8 bipyramids and NO3 groups share edges to form [(UO2)(NO3)2] species which share common corners with dichromate Cr2O7 groups producing novel type of uranyl dichromate chains [(UO2)(Cr2O7)(NO3)2]2−. In the structures of new Rb2Cr3O10 polymorphs, CrO4 tetrahedra share vertices to form Cr3O10 2− species. The trichromate groups are aligned along the 63 screw axis forming channels running in the ab plane in the structure of 2. The Rb cations reside between the channels and in their centers completing the structure. The trichromate anions are linked by the Rb+ cations into a 3D framework in the structure of 3. Effect of solution acidity on the crystallization of polychromates in uranyl-bearing systems is discussed.

scholarly journals Crystal Chemical Relations in the Shchurovskyite Family: Synthesis and Crystal Structures of K2Cu[Cu3O]2(PO4)4 and K2.35Cu0.825[Cu3O]2(PO4)4

Crystals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 807
Author(s):  
Ilya V. Kornyakov ◽  
Sergey V. Krivovichev
Keyword(s):  
Crystal Structure ◽  
Crystal Structures ◽  
Structural Complexity ◽  
Crystal Chemical ◽  
X Ray Diffraction ◽  
Complexity Measures ◽  
X Ray ◽  
The Family ◽  
Similarities And Differences ◽  
Related Compounds

Single crystals of two novel shchurovskyite-related compounds, K2Cu[Cu3O]2(PO4)4 (1) and K2.35Cu0.825[Cu3O]2(PO4)4 (2), were synthesized by crystallization from gaseous phase and structurally characterized using single-crystal X-ray diffraction analysis. The crystal structures of both compounds are based upon similar Cu-based layers, formed by rods of the [O2Cu6] dimers of oxocentered (OCu4) tetrahedra. The topologies of the layers show both similarities and differences from the shchurovskyite-type layers. The layers are connected in different fashions via additional Cu atoms located in the interlayer, in contrast to shchurovskyite, where the layers are linked by Ca2+ cations. The structures of the shchurovskyite family are characterized using information-based structural complexity measures, which demonstrate that the crystal structure of 1 is the simplest one, whereas that of 2 is the most complex in the family.

scholarly journals On the Proton-Bound Noble Gas Dimers (Ng-H-Ng)+ and (Ng-H-Ng')+ (Ng, Ng'= He-Xe): Relationships betweenStructure, Stability, and Bonding Character

Molecules ◽  
2021 ◽  
Vol 26 (5) ◽  
pp. 1305
Author(s):  
Stefano Borocci ◽  
Felice Grandinetti ◽  
Nico Sanna
Keyword(s):  
Theoretical Calculations ◽  
Noble Gas ◽  
Structure Stability ◽  
Covalent Bonds ◽  
Dissociation Energies ◽  
Non Covalent Interactions ◽  
The Difference ◽  
Noble Gas Dimers ◽  
Covalent Interactions ◽  
Cluster Level

The structure, stability, and bonding character of fifteen (Ng-H-Ng)+ and (Ng-H-Ng')+ (Ng, Ng' = He-Xe) compounds were explored by theoretical calculations performed at the coupled cluster level of theory. The nature of the stabilizing interactions was, in particular, assayed using a method recently proposed by the authors to classify the chemical bonds involving the noble-gas atoms. The bond distances and dissociation energies of the investigated ions fall in rather large intervals, and follow regular periodic trends, clearly referable to the difference between the proton affinity (PA) of the various Ng and Ng'. These variations are nicely correlated with the bonding situation of the (Ng-H-Ng)+ and (Ng-H-Ng')+. The Ng-H and Ng'-H contacts range, in fact, between strong covalent bonds to weak, non-covalent interactions, and their regular variability clearly illustrates the peculiar capability of the noble gases to undergo interactions covering the entire spectrum of the chemical bond.

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