Structure Solution of NaYO2 Compound Prepared by Soft Chemistry from X-Ray Diffraction Powder Data

In this work we reveal the structure of a NaYO2 compound solved from the X-ray diffraction powder pattern using the “ab-initio” structure solution approach. The compound turned out to be of trigonal structure, S. G. R-3m isomorphous with α-NaFeO2 layered compound. The lattice parameters are a = 3.404 and c = 16.602 Å, respectively, the atoms being located in Wickoff sites (cba) for O, Na and Y, respectively, leading to a calculated density of 4.31 g/cm3. The ordering of sodium and yttrium atoms into alternate (111) planes of the cubic close-packed oxygen lattice of NaYO2 is very regular. The octahedra are slightly distorted, the positive deviation of the Oz parameter from 0.25 elongates the NaO6 octahedra while compressing the YO6 octahedra. Actually the Na-O and Y-O bond distances are 2.58 (1) and 2.25 (1) Å, respectively, as it is expected from their ionic radii values reported (1.16 vs 1.04 radii for both ion-species octahedral coordination). Finally, the Na-Y, Y-Y, and Na-Na next neighbor distances are close to 3.40 Å.JRC.F.2-Energy Conversion and Storage Technologie

Machine learning techniques for the ab initio Bravais lattice determination

Machine learning-based algorithms have been widely applied recently in different areas due to its ability to solve problems in all fields. In this research, machine learning techniques classifying the Bravais lattices from a conventional X-ray diffraction diagram have been applied. Indexing algorithms are an essential tool of the preliminary protocol for the structural determination problem in crystallography. The task of reverting the obtained information in reciprocal lattice to direct space is a complex issue. As an alternative way to afford this problem, different machine learning algorithms have been applied and a comparison between them has been conducted. The obtained accuracy was 95.9% using 10-fold cross-validation (while the best result obtained so far has been 84%). A model based on Bragg positions was our unique predictor, allowing us to obtain the set of the interplanar lattice distances. Our model was successfully checked with a complex example. In addition, our procedure incorporates the following advantages: robustness versus imprecision in data acquisition and reduction of the amount of necessary input data. This is the first time so far that such classification has been carried out in true ab initio condition

Crystalline Forms of 4,4'-Methylenediantipyrine: Crystallographic Unit Cell for the Anhydrous Form, from Laboratory Powder XRD Pattern by DASH Program Package

Crystalline unit cell structure of anhydrous title compound, diantipyrinylmethane (CAS Registry No. 1251-85-0), a substance usually obtained as a by-product in Mannich type reactions of antipyrine, has been modelled by the help of powder X-ray diffraction, applying the DASH software package and crystal coordinates coming from former single crystal X-ray structure determinations (CSD codes FADDIY and FADDIY01) of its monohydrate. The unit cell of the anhydrate compound belongs to the monoclinic space group P21/a, with unit cell parameters of a = 14.604, b = 9.858, c = 14.509 Å, β = 95.56 °, V = 2078.9 Å3, Z = 4, Z ' = 1. Comparisons of FT-IR spectrum and thermal behavior of the anhydrous and monohydrated forms confirm differences in degree of hydration and solid state structure, while those of 1H- and 13C NMR-spectra show their molecular identity

Observation of superconductivity at 30 K~46 K in AxFe2Se2 (A = Li, Na, Ba, Sr, Ca, Yb, and Eu)

New iron selenide superconductors by intercalating smaller-sized alkali metals (Li, Na) and alkaline earths using high-temperature routes have been pursued ever since the discovery of superconductivity at about 30 K in KFe2Se2, but all have failed so far. Here we demonstrate that a series of superconductors with enhanced Tc=30~46 K can be obtained by intercalating metals, Li, Na, Ba, Sr, Ca, Yb, and Eu in between FeSe layers by the ammonothermal method at room temperature. Analysis on their powder X-ray diffraction patterns reveals that all the main phases can be indexed based on body-centered tetragonal lattices with a~3.755-3.831 {\AA} while c~15.99-20.54 {\AA}. Resistivities show the corresponding sharp transitions at 45 K and 39 K for NaFe2Se2 and Ba0.8Fe2Se2, respectively, confirming their bulk superconductivity. These findings provide a new starting point for studying the properties of these superconductors and an effective synthetic route for the exploration of new superconductors as well.Comment: 22 pages, 5 figure

Tenth European Powder Diffraction Conference – Geneva, September 1-4, 2006

Zeitschrift für Kristallographie. Supplement Volume 26 presents the complete Proceedings of all contributions to the X European Powder Diffraction Conference in Geneva 2006: Method Development and Application, Instrumental Software Development, Materials Supplement Series of Zeitschrift für Kristallographie publishes Proceedings and Abstracts of international conferences on the interdisciplinary field of crystallography