RESUMEN

The synthesis of multicomponent and high-entropy compounds has become a rapidly developing field in advanced inorganic chemistry, making it possible to combine the properties of multiple elements in a single phase. This paper reports on the synthesis of a series of novel high-entropy layered rare earth hydroxychlorides, namely, (Sm,Eu,Gd,Y,Er)2(OH)5Cl, (Eu,Gd,Tb,Y,Er)2(OH)5Cl, (Eu,Gd,Dy,Y,Er)2(OH)5Cl, and (Eu,Gd,Y,Er,Yb)2(OH)5Cl, using a homogeneous hydrolysis technique under hydrothermal conditions. Elemental mapping proved the even distribution of rare earth elements, while luminescence spectroscopy confirmed efficient energy transfer between europium and other rare earth cations, thus providing additional evidence of the homogeneous distribution of rare earth elements within the crystal lattice. The average rare earth cation radii correlated linearly with the unit cell parameters (0.868 < R2 < 0.982) of the high-entropy layered rare earth hydroxychlorides. The thermal stability of the high-entropy layered rare earth hydroxychlorides was similar to that of individual hydroxychlorides and their binary solid solutions.

RESUMEN

A significant part of the present and future of optoelectronic devices lies on thin multilayer heterostructures. Their optical properties depend strongly on strain, being essential to the knowledge of the stress level to optimize the growth process. Here the structural and microstructural characteristics of sub-micron a-ZnO epilayers (12 to 770 nm) grown on r-sapphire by metal-organic chemical vapour deposition are studied. Morphological and structural studies have been made using scanning electron microscopy and high-resolution X-ray diffraction. Plastic unit-cell distortion and corresponding strain have been determined as a function of film thickness. A critical thickness has been observed as separating the non-elastic/elastic states with an experimental value of 150-200 nm. This behaviour has been confirmed from ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy measurements. An equation that gives the balance of strains is proposed as an interesting method to experimentally determine this critical thickness. It is concluded that in the thinnest films an elongation of the Zn-O bond takes place and that the plastic strained ZnO films relax through nucleation of misfit dislocations, which is a consequence of three-dimensional surface morphology.

RESUMEN

Electron diffraction enables structure determination of organic small molecules using crystals that are too small for conventional X-ray crystallography. However, because of uncertainties in the experimental parameters, notably the detector distance, the unit-cell parameters and the geometry of the structural models are typically less accurate and precise compared with results obtained by X-ray diffraction. Here, an iterative procedure to optimize the unit-cell parameters obtained from electron diffraction using idealized restraints is proposed. The cell optimization routine has been implemented as part of the structure refinement, and a gradual improvement in lattice parameters and data quality is demonstrated. It is shown that cell optimization, optionally combined with geometrical corrections for any apparent detector distortions, benefits refinement of electron diffraction data in small-molecule crystallography and leads to more accurate structural models.

RESUMEN

A method of ab initio crystal structure determination from powder diffraction data for organic and metal-organic compounds, which does not require prior indexing of the powder pattern, has been developed. Only a reasonable molecular geometry is required, needing knowledge of neither unit-cell parameters nor space group. The structures are solved from scratch by a global fit to the powder data using the new program FIDEL-GO (`FIt with DEviating Lattice parameters - Global Optimization'). FIDEL-GO uses a similarity measure based on cross-correlation functions, which allows the comparison of simulated and experimental powder data even if the unit-cell parameters deviate strongly. The optimization starts from large sets of random structures in various space groups. The unit-cell parameters, molecular position and orientation, and selected internal degrees of freedom are fitted simultaneously to the powder pattern. The optimization proceeds in an elaborate multi-step procedure with built-in clustering of duplicate structures and iterative adaptation of parameter ranges. The best structures are selected for an automatic Rietveld refinement. Finally, a user-controlled Rietveld refinement is performed. The procedure aims for the analysis of a wide range of `problematic' powder patterns, in particular powders of low crystallinity. The method can also be used for the clustering and screening of a large number of possible structure candidates and other application scenarios. Examples are presented for structure determination from unindexed powder data of the previously unknown structures of the nanocrystalline phases of 4,11-difluoro-, 2,9-dichloro- and 2,9-dichloro-6,13-dihydro-quinacridone, which were solved from powder patterns with 14-20 peaks only, and of the coordination polymer dichloro-bis(pyridine-N)copper(II).

Asunto(s)

Cobre , Polímeros , Difracción de Polvo , Polvos

RESUMEN

A method for the self-consistent description of the large variations of unit-cell parameters of crystals with pressure and temperature is presented. It employs linearized versions of equations of state (EoSs) together with constraints to ensure internal consistency. The use of polynomial functions to describe the variation of the unit-cell angles in monoclinic and triclinic crystals is compared with the method of deriving them from linearized EoSs for d spacings. The methods have been implemented in the CrysFML Fortran subroutine library. The unit-cell parameters and the compressibility and thermal expansion tensors of crystals can be calculated from the linearized EoSs in an internally consistent manner in a new utility in the EosFit7c program, which is available as freeware at http://www.rossangel.net.

RESUMEN

This computational study explores a unique modelling approach of the cranial implant, homogenous scaffold algorithm and meshless method, respectively. This meshless method is employed to review the implant underneath intracranial pressure (ICP) conditions with a standard ICP range of 7 mm of Hg to 15 mm of Hg. The algorithm is used to introduce uniform porosity within the implant enabling the implant behaviour with respect to ICP conditions. However, increase in the porosity leads to variation in deformation and equivalent stress, respectively. The meshless approach provides a valuable insight in order to know the effect of total deformation and equivalent stress (von Mises stress) and replaces the standard meshing strategies. The patient CT data (computed tomography) is processed in MIMICS software to get the mesh model. An entirely unique modelling approach is developed to model the cranial implant with the assistance of the Rhinoceros software. This modelling methodology is the easiest one and addressing both the symmetrical and asymmetrical defects. The implant is embedded in a unit cell-based porous structure with the help of an algorithm, and this algorithm is simple to manage the consistency in porosity and pore size of the scaffold. Totally six types of implants are modelled with variation in porosity and replicate the original cranial bone. Among six implants, Type 2 (porosity 82.62%) and Type 5 (porosity 45.73%) implants are analysed with the meshless approach under ICP. The total deformation and equivalent stress (von Mises stress) of porous implants are compared with the solid implant under same ICP conditions. Consequently, distinctive materials are used for structural analysis such as titanium alloy (Ti6Al4V) and polyether-ether-ketone (PEEK), respectively. The deformation and equivalent stress (von Mises stress) results are obtained through the structural analysis. It was observed from the results that the titanium-based solid implant is the best implant in all aspects, while considering weight and osseointegration PEEK-based Type 5 implant is the best one. A novel free-form closed curve network (FCN) technique is successfully developed to model a cranial implant for symmetrical and asymmetrical defects. The porous implant is adequately modelled through the unit cell algorithm and analysed through meshless approach. The implementation of 3D printed component will allow physicians to gain knowledge and successfully plan the preoperative surgery.

Asunto(s)

Cráneo/fisiopatología , Cráneo/cirugía , Algoritmos , Aleaciones , Benzofenonas , Análisis de Elementos Finitos , Humanos , Cetonas/química , Ensayo de Materiales/métodos , Oseointegración/efectos de los fármacos , Polietilenglicoles/química , Polímeros , Porosidad , Prótesis e Implantes , Programas Informáticos , Titanio/química

RESUMEN

Numerous biological and chemical studies involve the use of calcium hydroxyapatite (HA), Ca10(PO4)6(OH)2. In this study detailed physicochemical characterization of HA, prepared from an aqueous solution, was carried out employing different methods and techniques: chemical and thermal analyses, x-ray diffraction, infrared and Raman spectroscopies, scanning and transmission microscopies, and Brunauer, Emmett, and Teller (BET) surface-area method. The contents of calcium (Ca(2+)), phosphate (PO4 (3-)), hydroxide (OH(-)), hydrogenphosphate (HPO4 (2-)), water (H2O), carbonate (CO3 (2-)), and trace constituents, the Ca/P molar ratio, crystal size and morphology, surface area, unit-cell parameters, crystallinity, and solubility of this HA were determined. This highly pure, homogeneous, and highly crystalline HA is certified as a National Institute of Standards and Technology (NIST) standard reference material, SRM 2910.