scholarly journals A computational–experimental approach for automated crystal structure solution

2014 ◽  
Vol 70 (a1) ◽  
pp. C131-C131
Author(s):  
Chris Wolverton
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Hydrogen Storage ◽  
First Principles ◽  
Materials Science ◽  
Hybrid Approach ◽  
X Rays ◽  
Experimental Conditions ◽  
Algorithmic Optimization ◽  
Structure Solution

Crystal structure solution from diffraction experiments is one of the most fundamental tasks in materials science, chemistry, physics and geology. Unfortunately, numerous factors render this process labour intensive and error prone. Experimental conditions, such as high pressure or structural metastability, often complicate characterization. Furthermore, many materials of great modern interest, such as batteries and hydrogen storage media, contain light elements such as Li and H that only weakly scatter X-rays. Finally, structural refinements generally require significant human input and intuition, as they rely on good initial guesses for the target structure. To address these many challenges, we demonstrate a new hybrid approach, first-principles-assisted structure solution (FPASS), which combines experimental diffraction data, statistical symmetry information and first-principles-based algorithmic optimization to automatically solve crystal structures. We demonstrate the broad utility of FPASS to clarify four important crystal structure debates: the hydrogen storage candidates MgNH and NH3BH3; Li2O2, relevant to Li–air batteries; and high-pressure silane, SiH4.

scholarly journals Combinatorial Approach for solving complex structures from low resolution data

2014 ◽  
Vol 70 (a1) ◽  
pp. C189-C189
Author(s):  
Olivier Gourdon
Keyword(s):  
High Pressure ◽  
High Intensity ◽  
Materials Science ◽  
Energy Storage Materials ◽  
X Rays ◽  
Combinatorial Approach ◽  
Experimental Conditions ◽  
X Ray ◽  
Medium Resolution ◽  
Level Of Understanding

Crystal structure solution from diffraction experiments is an essential step in materials science, chemistry, physics and geology. Unfortunately, numerous factors render this process in some cases quite complex. Experimental conditions, such as high pressure or poor crystallinity, often complicate characterization. Furthermore, many applied materials such as batteries and/or energy storage materials, contain light elements such as Li and H that only weakly scatter X-rays. In that case a combined X-ray /neutron analysis is required. Moreover, the quality of charge-discharge cycling of these materials is at the cost of the crystallinity which brings more complexity to have a good level of understanding of the cycling process. Similar issues could also be raised for the analysis of some minerals which possess numerous phases which could be eventually amorphous. Finally, structural refinements generally require significant human input and intuition, as they rely on good initial guesses for the target structure. To eliminate part of these guesses, we are supporting a more combinatorial approach which uses X-ray and Neutron scattering experiments but also theoretical tools such as DFT and/or Molecular dynamics calculations as well as data mining tools. This presentation will mainly focus on recent experiments performed on two different high intensity/medium resolution T-o-F neutron diffractometers at LANSCE: HIPPO (High Pressure Preferred Orientation) and HIPD (High Intensity Powder Diffractometer). Examples will be used to highlight the level of information which can be achieved using these combined strategies and how we can connect it to the physical properties.

Crystal structure, compressibility and possible phase transitions in \boldvarepsilon-FeSi studied by first-principles pseudopotential calculations

1999 ◽  
Vol 55 (4) ◽  
pp. 484-493 ◽  
Author(s):  
Lidunka Vočadlo ◽  
Geoffrey D. Price ◽  
I. G. Wood
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Phase Transitions ◽  
First Principles ◽  
Stable Phase ◽  
Third Order ◽  
First Derivative ◽  
Pseudopotential Calculations ◽  
Cscl Type ◽  
Murnaghan Equation

An investigation of the relative stability of the FeSi structure and of some hypothetical polymorphs of FeSi has been made by first-principles pseudopotential calculations. It has been shown that the observed distortion from ideal sevenfold coordination is essential in stabilizing the FeSi structure relative to one of the CsCl type. Application of high pressure to FeSi is predicted to produce a structure having nearly perfect sevenfold coordination. However, it appears that FeSi having a CsCl-type structure will be the thermodynamically most stable phase for pressures greater than 13 GPa. Fitting of the calculated internal energy vs volume for the FeSi structure to a third-order Birch–Murnaghan equation of state led to values, at T = 0 K, for the bulk modulus, K 0, and for its first derivative with respect to pressure, K 0′, of 227 GPa and 3.9, respectively.

scholarly journals Crystal Structures of Al2Cu Revisited: Understanding Existing Phases and Exploring Other Potential Phases

Metals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1037 ◽  
Author(s):  
Sai Wang ◽  
Changzeng Fan
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Single Crystal ◽  
First Principles ◽  
First Principles Calculations ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structural Relationships ◽  
Al2cu Phase ◽  
High Pressure Sintering

When processing single crystal X-ray diffraction datasets for twins of Al2Cu sample synthesized by the high-pressure sintering (HPS) method, we have clarified why the crystal structure of Al2Cu was incorrectly solved about a century ago. The structural relationships between all existing Al2Cu phases, including the Owen-, θ-, θ’-, and Ω-Al2Cu phases, were investigated and established based on a proposed pseudo Al2Cu phase. Two potential phases have been built up by adjusting the packing sequences of A/B layers of Al atoms that were inherent in all existing Al2Cu phases. The mechanical, thermal, and dynamical stability of two such novel phases and their electronic properties were investigated by first-principles calculations.

scholarly journals NMR crystallography, diffraction and modeling of small organic molecules

2014 ◽  
Vol 70 (a1) ◽  
pp. C1088-C1088
Author(s):  
Luís Miguel Monteiro Mafra
Keyword(s):  
Crystal Structure ◽  
Solid State ◽  
Crystal Packing ◽  
Computational Study ◽  
Chemical Shifts ◽  
Hybrid Approach ◽  
X Ray Diffraction ◽  
Structure Solution ◽  
Nmr Crystallography

Solid-state NMR (SSNMR) is a powerful atomic-level characterization technique able to study the local chemical environment of a nucleus in crystalline/amorphous solids. Toward a better understanding of how small molecules self-assemble in the solid-state and reorganizes to produce its hydrate/anhydrous forms, an experimental SSNMR, X-ray diffraction (XRD), and computational study of the supramolecular assemblies of selected small pharmaceuticals is presented. The effect of crystal packing on the 1H and 13C chemical shifts including nonconventional hydrogen bonds, pi···pi and CH···pi contacts, is studied through computer simulations. It will be shown that NMR chemical shifts are sensitive detectors of hydration/dehydration states in highly insoluble antibiotics.[1] Recently, SSNMR became an important gadget in the process of crystal structure solution in powders. This is a non-trivial task and using powder XRD methods alone may often lead to the wrong structure solution. In this talk, a new hybrid approach for structure determination of crystalline solids, will be presented, based on the combination of SSNMR, XRD and an ensemble of computational-assisted structure solution tools including a genetic algorithm based on evolution-inspired operators repeatedly applied to populations of possible crystal structure solutions that evolve to eventually produce the best new offspring candidates. Such methodologies are successfully applied to challenging cases involving multiple component crystals composed by flexible molecules such as a trihydrate β-lactamic antibiotic [2] and an azole-based co-crystal featuring an hydrogen bond network of α-helixes involving NH···N/CH···π intermolecular interactions. ACKNOLEDGEMENTS: Supported by Fundação para a Ciência e a Tecnologia (FCT), Portuguese National NMR Network (RNRMN), CICECO (PEst-C/CTM/LA0011/2013), FEDER, COMPETE, and University of Aveiro. FCT is greatly acknowledge for the consolidation grant IF/01401/2013.

Solid-state reactions and hydrogen storage in magnesium mixed with various elements by high-pressure torsion: experiments and first-principles calculations

RSC Advances ◽  
2016 ◽  
Vol 6 (14) ◽  
pp. 11665-11674 ◽  
Author(s):  
Hoda Emami ◽  
Kaveh Edalati ◽  
Aleksandar Staykov ◽  
Toshifumi Hongo ◽  
Hideaki Iwaoka ◽  
...  
Keyword(s):  
High Pressure ◽  
Solid State ◽  
Hydrogen Storage ◽  
First Principles ◽  
High Pressure Torsion ◽  
Solid State Reactions ◽  
First Principles Calculations ◽  
Hydrogen Storage Materials ◽  
Storage Materials

The HPT technique is effective in synthesizing Mg-based hydrogen storage materials and improving the air resistivity and hydrogenation properties.

A new high-pressure strontium germanate, SrGe2O5

2016 ◽  
Vol 72 (10) ◽  
pp. 716-719 ◽  
Author(s):  
Akihiko Nakatsuka ◽  
Kazumasa Sugiyama ◽  
Makio Ohkawa ◽  
Osamu Ohtaka ◽  
Keiko Fujiwara ◽  
...  
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Single Crystals ◽  
Materials Science ◽  
Perovskite Phase ◽  
Structural Response ◽  
Cation Substitution ◽  
Electronic Conductor ◽  
Structural Responses ◽  
Oxygen Framework

The Sr–Ge–O system has an earth-scientific importance as a potentially good low-pressure analog of the Ca–Si–O system, one of the major components in the constituent minerals of the Earth's crust and mantle. However, it is one of the germanate systems that has not yet been fully examined in the phase relations and structural properties. The recent findings that the SrGeO3high-pressure perovskite phase is the first Ge-based transparent electronic conductor make the Sr–Ge–O system interesting in the field of materials science. In the present study, we have revealed the existence of a new high-pressure strontium germanate, SrGe2O5. Single crystals of this compound crystallized as a co-existent phase with SrGeO3perovskite single crystals in the sample recovered in the compression experiment of SrGeO3pseudowollastonite conducted at 6 GPa and 1223 K. The crystal structure consists of germanium–oxygen framework layers stacked along [001], with Sr atoms located at the 12-coordinated cuboctahedral site; the layers are formed by the corner linkages between GeO6octahedra and between GeO6octahedra and GeO4tetrahedra. The present SrGe2O5is thus isostructural with the high-pressure phases of SrSi2O5and BaGe2O5. Comparison of these three compounds leads to the conclusion that the structural responses of the GeO6and GeO4polyhedra to cation substitution at the Sr site are much less than that of the SrO12cuboctahedron to cation substitution at the Ge sites. Such a difference in the structural response is closely related to the bonding nature.

scholarly journals Structural response of α-quartz under plate-impact shock compression

2020 ◽  
Vol 6 (35) ◽  
pp. eabb3913
Author(s):  
Sally June Tracy ◽  
Stefan J. Turneaure ◽  
Thomas S. Duffy
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Shock Compression ◽  
Materials Science ◽  
Metastable Phase ◽  
Dynamic Compression ◽  
Phase Region ◽  
High Pressure Phase ◽  
Gas Gun ◽  
Pressure Phase

Because of its far-reaching applications in geophysics and materials science, quartz has been one of the most extensively examined materials under dynamic compression. Despite 50 years of active research, questions remain concerning the structure and transformation of SiO2 under shock compression. Continuum gas-gun studies have established that under shock loading quartz transforms through an assumed mixed-phase region to a dense high-pressure phase. While it has often been assumed that this high-pressure phase corresponds to the stishovite structure observed in static experiments, there have been no crystal structure data confirming this. In this study, we use gas-gun shock compression coupled with in situ synchrotron x-ray diffraction to interrogate the crystal structure of shock-compressed α-quartz up to 65 GPa. Our results reveal that α-quartz undergoes a phase transformation to a disordered metastable phase as opposed to crystalline stishovite or an amorphous structure, challenging long-standing assumptions about the dynamic response of this fundamental material.

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