Controlling the crystal structure of precisely spaced polyethylene-like polyphosphoesters

Understanding polymer crystallization is important for polyethylene-like materials. A small fraction of monomers with functional groups within the polyethylene chain can act as crystallization “defects”. Such defects can be used to control the crystallization behavior in bulk and to generate functional anisotropic polymer crystals if crystallized from a dilute solution. Due to their geometry, phosphate groups cannot be incorporated in the polyethylene lamellae and thus control chain folding and crystal morphology. Herein, the synthesis and crystallization behavior for three different long-chain polyphosphates with a precise spacing of 20, 30, and 40 CH2-groups between each phosphate group are reported. Monomers were prepared by esterification of ethyl dichlorophosphate with respective tailor-made unsaturated alcohols. Acyclic diene metathesis (ADMET) polymerization and subsequent hydrogenation were used to receive polyethylene-like polyphosphoesters with molecular weights up 23 100 g mol−1. Polymer crystallization was studied from the melt and dilute solution. Samples were characterized by differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). A change in crystal structure from pseudo-hexagonal to orthorhombic was observed from the “C20” to the “C40” polymer. Melting points and lamellar thicknesses increased with the length of the aliphatic spacer from 51 °C (“C20”) to 62 °C (“C30”) and 91 °C (“C40”). Values for the long periods in bulk (3.1 nm for C20, 4.8 nm for C30, and 7.2 nm for C40) obtained by SAXS and TEM are in qualitative agreement. The thickness of the crystalline part obtained by AFM and TEM increased from about 1.0 nm (C20) to 2.0 nm (C30) to 2.9 nm (C40). Our systematic library of long-chain polyphosphates will allow designing anisotropic polymer colloids by crystallization from solution as functional and versatile colloid platform

Single crystal growth, structure and magnetic properties of Pr2Hf2O7 pyrochlore

Large single crystals of the pyrochlore Pr2Hf2O7 have been successfully grown by the floating zone technique using an optical furnace equipped with high power Xenon arc lamps. Structural investigations have been carried out by both synchrotron X-ray and neutron powder diffraction to establish the crystallographic structure of the materials produced. The magnetic properties of the single crystals have been determined for magnetic fields applied along different crystallographic axes. The results reveal that Pr2Hf2O7 is an interesting material for further investigations as a frustrated magnet. The high quality of the crystals produced make them ideal for detailed investigations, especially those using neutron scattering techniques.Comment: Accepted for publication in J. Phys.: Condens. Matte

Preparation and Crystal Structure Characterization of Li(1+x)mn2o4

Li(1+x)Mn2O4 powder has been prepared with starting material of Li2CO3 as lithium source and MnO2 as manganese source. The preparation was done by powder metallurgy with varying Li addition in weight% of 5%, 10%, 15% and 30%. From Differential Thermal Analisys (DTA) data , it is revealed that calcination andsintering temperature are at 700 °C and 800 °C respectively. The characterisation results showed that all XRD patterns are similar for all composition of Li addition, but different in intensity. The diffraction data was analyzed by Rietveld method to get lattice parameter unit cell volume and crystal density. The lattice parameters reach optimum at 15% of Li addition. The cell volume increased could lead to better intercalation properties ofthis powder. Li ion can intercalate easier in this unit cell which make Li(1+x)Mn2O4 can be used as a cathodematerial

Predicting the Volumes of Crystals

New crystal structures are frequently derived by performing ionic substitutions on known crystal structures. These derived structures are then used in further experimental analysis, or as the initial guess for structural optimization in electronic structure calculations, both of which usually require a reasonable guess of the lattice parameters. In this work, we propose two lattice prediction schemes to improve the initial guess of a candidate crystal structure. The first scheme relies on a one-to-one mapping of species in the candidate crystal structure to a known crystal structure, while the second scheme relies on data-mined minimum atom pair distances to predict the crystal volume of the candidate crystal structure and does not require a reference structure. We demonstrate that the two schemes can effectively predict the volumes within mean absolute errors (MAE) as low as 3.8% and 8.2%. We also discuss the various factors that may impact the performance of the schemes. Implementations for both schemes are available in the open-source pymatgen software.Comment: 8 figures, 2 table

Analysis of Crystal Structure and Dielectric of Zn2+ Ion Doped Nanoparticle Magnetite Based on Iron Sand Synthesized by Coprecipitation Method

Zn2+ ion doped Fe3O4 nanoparticles based on iron sand have been successfully synthesized by coprecipitation method at low temperature. The starting materials were iron sand, ZnCl2, HCl, and NH4OH. Characterizations were conducted by means of X-Ray Flourescence (XRF), X-Ray Diffraction (XRD) and digital capacitance meter AD5822. XRF identification confirms that the elemental composition of all samples is appropriate with the stoichiometry calculation. Phase formation identification by using High Score Plus and DDView+PDF2 software reveals that all samples crystallize in cubic spinel structure. Rietveld refinement analysis bymeans of Reitica yields the doping of Zn2+ ion on Fe3O4 increases the lattice parameter with crystal size in the order of nanometer. This is in line with theoretical predictions as a consequence of the influence of Zn2+ ionic radii that replace Fe2+. Furthermore, dielectricity analysis shows that the higher the amount of Zn2+ doped Fe3O4 nanoparticles the higher the dielectric constant. This mechanism is ionic polarization phenomenom as consequence of the decreasing in the crystal volume and the atomic distance that lead to increase the moment of dipole

Crystal Structure Transformation of Ba-sr Hexaferrite and Its Effect on Particle Orientation in Recycle Process

CRYSTAL STRUCTURE TRANSFORMATION OF Ba-Sr HEXAFERRITE AND ITS EFFECT ON PARTICLE ORIENTATION IN RECYCLE PROCESS. In general, during its fabrication, 2-5%of total products of Ba-Sr hexaferrite permanent magnet will be rejected.Accordingly, an increase in rejected product of permanent magnet needs to be considered. It is expected that the re-utilization of rejected product can increase the production efficiency in order to achieve zero waste-production. In the present work, the recycling process of Ba-Sr hexaferrite permanent magnet was studied by applying 1 T magnetic field (anisotropic) to align the powder. The rejected products were milled using shaker mill PPF-UG for 10-40 min and then sintered at 1200 ºC for 60 min. The results show that the remanence of original powder was increased by 50% after the particle orientation. However, the recycled sample doesn't show a significant different. SEM and XRD analysis show the crystalline structure transformation from symmetrical hexagonal to asymmetrical hexagonal structure with crystalline growth in a-b axis direction. This transformation leads to lost in its magneto crystalline anisotropy. Therefore, it was difficult to align the particle

Nanoscale mosaicity revealed in peptide microcrystals by scanning electron nanodiffraction.

Changes in lattice structure across sub-regions of protein crystals are challenging to assess when relying on whole crystal measurements. Because of this difficulty, macromolecular structure determination from protein micro and nanocrystals requires assumptions of bulk crystallinity and domain block substructure. Here we map lattice structure across micron size areas of cryogenically preserved three-dimensional peptide crystals using a nano-focused electron beam. This approach produces diffraction from as few as 1500 molecules in a crystal, is sensitive to crystal thickness and three-dimensional lattice orientation. Real-space maps reconstructed from unsupervised classification of diffraction patterns across a crystal reveal regions of crystal order/disorder and three-dimensional lattice tilts on the sub-100nm scale. The nanoscale lattice reorientation observed in the micron-sized peptide crystal lattices studied here provides a direct view of their plasticity. Knowledge of these features facilitates an improved understanding of peptide assemblies that could aid in the determination of structures from nano- and microcrystals by single or serial crystal electron diffraction