Progress in Crystal Growth and Characterization of Materials最新文献

III/V semiconductors with cubic zinc-blende crystal structure, for example GaAs, GaP or InP, become metastable if atoms with significantly smaller or larger covalent radius than the matrix atoms are alloyed. Examples are the incorporation of Boron, Nitrogen and Bismuth in the above-mentioned materials. The resulting multinary compound semiconductors, like for example (Ga,In)(N,As), Ga(N,As,P) and Ga(As,Bi), are extremely interesting for several novel applications. The growth conditions, however, have to be adopted to the metastability of the material systems. In addition, structure formation can occur which is different from stable materials. This paper summarizes our current knowledge on growth characteristics of several metastable materials. Mainly examples for Metal Organic Vapor Phase Epitaxy (MOVPE) are given. The MOVPE growth characteristics are compared to selected examples using Molecular Beam Epitaxy growth to highlight that the observed growth characteristics are intrinsic for the studied metastable material systems. Furthermore, structural peculiarities of dilute borides, nitrides and bismides occurring during growth as well as in growth interruptions are summarized and correlated to the growth conditions.

This report centers on different modern chemical synthesis methods suitable for production with which low-dimensional crystalline structures are attainable in the Ge–Sb–Te material system. The general characteristics of the methods are described first. The special challenges are discussed for the Ge–Sb–Te material system. Growth optimization is studied, and the resulting nanostructures are presented. At last a comparison of the methods is given with respect to research scale vapor transport approach on the one hand and the potential described for future application in technology on the other hand.

The rapid advance in superconducting magnet technology enables more and more applications for the use of high magnetic fields in scientific researches and industrial manufacturing. These applications include material processing, separation, chemical reaction, nuclear fusion, high energy physics, and many more. Generally, a superconducting magnet provides both homogeneous and inhomogeneous magnetic fields simultaneously, and both can affect the samples in the field so that the magnetic field can be utilized for various purposes. A homogeneous or inhomogeneous magnetic field will exert a torque on suspending particles in a solution if the particles have anisotropic magnetic susceptibility, which will further influence the properties of the solution; in an inhomogeneous magnetic field, a repulsive force will act on a diamagnetic solution so that the levels of apparent or effective gravity of the solution can be tuned in a vertical magnetic field. These effects can be utilized to govern the physical and chemical processes in solution like crystallization. In recent years, high magnetic fields have been applied in protein crystallization. It was found that a magnetic field can align the crystals along the field direction, decrease the diffusivity of macromolecules in the solution, and increase the viscosity of the solution; a suitable inhomogeneous magnetic field can damp the natural convection substantially, which resembles the case in a space environment. Both homogeneous and inhomogeneous magnetic fields have been found to improve the quality of some protein crystals. These discoveries showed that the researches on protein crystallization in high magnetic field is potentially valuable, because obtaining high quality protein crystals is important for 3-dimensional structure determination of proteins using X ray crystallography. This paper will review the background and more recent progress and discuss the future perspectives in this research field.

A powder-bed 3D printer (3DP) is investigated to fabricate porous titanium components. The titanium material was 3D printed and subsequently post-processed by thermal debinding and sintering. Characterization work was carried out to investigate the effects of sintering temperature on the internal porosity profile and shrinkage of 3D printed titanium components, the effects of different binder content on the overall shape of the pre-designed porous components and the effects of post-processing debinding profiles on the titanium components.

In the present work, PVA and various concentrations of FeCl₃ doped PVA polymer were prepared and optical studies like IR and UV/Visible analysis were carried out on them in solution form also the cast films were examined for their conductance. The variation of optical band gap of PVA polymer with the addition of Fe³⁺ transition metal ion has been determined by the Tauc plot method. It is found that the optical band gap and the transmittance of the polymer solutions being decreased with the increase in the concentration of Fe³⁺ ion, and thus obeys Beer's Law. This is supported by conductivity obtained for these polymers and FT-IR spectra which shows the stretching of the various bonds of the polymer due to the addition of transition metal (Fe³⁺) ions.

Calcium copper titanate, CaCu₃Ti₄O₁₂, (CCTO), a potential electro-ceramic is a member of a very important perovskite family and has been found to a show dielectric constant of the order of 10⁴–10⁵. It has a remarkable ability to undergo a series of cationic exchange reactions resulting in corresponding isomorphs. In the past decade there has been immense activity in the search of an isomorph of CCTO with high dielectric constant and low loss which enables its use as capacitor material for the storage of energy and miniaturization of electronic based equipment. Despite intensive research in the area there is no source of any literature that gives all the possible relevant information regarding various synthetic methods, characterizations, effect of sintering parameters (temperature, duration, and atmosphere). This review article is an effort to review the synthesis, grain growth, morphological evolution, effect of impurities, substitution and interface anisotropy on the dielectric constant, resistivity and other materials parameters.