Local Atomic Arrangements and Band Structure of Boron Carbide.
Boron carbide, the simple chemical combination of boron and carbon, is one of the best-known binary ceramic materials. Despite that, a coherent description of its crystal structure and physical properties resembles one of the most challenging problems in materials science. By combining ab initio computational studies, precise crystal structure determination from diffraction experiments, and state-of-the-art high-resolution transmission electron microscopy imaging, this concerted investigation reveals hitherto unknown local structure modifications together with the known structural alterations. The mixture of different local atomic arrangements within the real crystal structure reduces the electron deficiency of the pristine structure CBC+B12 , answering the question about electron precise character of boron carbide and introducing new electronic states within the band gap, which allow a better understanding of physical properties.
Assignment of the electronic transitions in B4.3C boron carbide implies a specifically distorted crystal structure
Abstract The reversible high-pressure phase transition in boron carbide, making this opaque solid glasslike transparent, the visualization of actual structural distortions in the form of atomic arrangements replacing the three-atomic chain in the unit cell, and the electronic DOS calculated for realistic structure models require re-interpretation of the well-known electronic transitions. – The excellent correlation with a selected distorted structure model, proposed by Ektarawong, assuming that the polar C atoms are randomly distributed over all polar sites of the icosahedra, suggests this model to be close to the actual structure. Assignment between electronic properties and structural peculiarities enables solving some open problems, for example, the nature of the high-pressure phase transition. According to Rasim, some boron-rich components replacing a certain share of three-atomic exhibit negative energies; thus they reduce the total energy and make B4.3C the most stable structure.
Electrochemical detection of copper(II) at a gold electrode modified with a self-assembled monolayer of penicillamine
A penicillamine (PCA) self-assembled monolayer (SAM) was prepared on a gold electrode. It has been found that the modified electrode exhibited a selective response to copper ions. As demonstrated by cyclic voltammetric experiments, the SAM-based electrode showed an attractive ability to preconcentrate efficiently traces of copper(II) from solutions. Under optimum conditions, the anodic peak current was proportional to the concentration of Cu(II) in the range from 8.0 × 10−7 to 1.0 × 10−4 M with a detection limit of 4.0 × 10−7 M. Moreover, this modified gold electrode is also characterized by excellent repeatability, showing a relative standard deviation of 3.2% for nine successive measurements of 1.0 × 10−5 M Cu(II). The PCA/Au SAM gold electrode was used for the determination of Cu(II) in a tap water sample and the results showed a good agreement with the data obtained by atomic emission spectrometry.