Search

Cadmium sulfide (CdS) crystal is a representative of AIIBVI crystal group and exhibits typical semiconductor behavior. CdS crystal can exist in either zinc-blende or hexagonal (wurtzite) structures under normal conditions, depending on the growth conditions. These crystals remain an important research Field because of their wide application in various Fields of optoelectronic devices. From this point of view, the study of structural properties and the dynamics of electronic spectra of CdS crystal under the action of external pressures is of fundamental interest for studying the process of stabilization in compounds. We have investigated the effect of pressure on the electronic band structure of CdS crystal using the density functional theory. In this approach, the generalized gradient approximation (GGA) and the Purdue-Burke-Ernzerh of (PBEsol) parameterization were used for the exchange-correlation potential calculation. The ground-state properties were determined for the bulk material (CdS) in zinc blende structure. Structural and electronic properties were studied in the range of hydrostatic pressures between 0 and 90 GPa. The electron band-energy structure and density of states were calculated at different pressures. The equilibrium structural parameters, bulk modules and bandgaps were calculated and compared with the available experimental data and other theoretical results. The effect of pressure on the energy gap, total energy, and lattice parameters of CdS crystal has been determined and compared with other known data. [ABSTRACT FROM AUTHOR]

Endohedral fullerenes (EEFs) are of particular interest for researchers because their molecules have a unique structure and, so, physicochemical properties. The chemical elements used to alloy the electrodes give new properties to the spherical molecules formed during the synthesis process. In this direction, there are still many unsolved problems related to the understanding of the processes that take place in the carbon plasma containing impurities of different chemical composition, as well as the processes of extraction, isolation, separation and identification of products. The research focused on optimizing the conditions for the synthesis of EEF-containing carbon black (a mixture of products formed during the arc synthesis of endometallofullerenes), the development of new approaches to the synthesis of EEF derivatives and of effective methods for extracting EEF from synthesis products. Quick identification of the resulting product will accelerate research in this area. The aim of the study was to examine the electronic absorption spectra of the extracts obtained by isolating endometallofullerenes and fullerenes from carbon black obtained in the experiments. This is necessary to identify the characteristics of their absorption spectra for further use to determine the synthesized products by spectrophotometric method. Endohedral fullerenes were obtained by the most common and productive method of electric arc synthesis. The paper describes the study of materials formed by the joint arc evaporation of graphite and metals. The scheme of two-stage extraction of EEF from fullerene-containing carbon black was used, which made it possible to obtain dimethylformamide (DMF) solutions of practically pure endometallofullerenes. A possibility of using spectrometry for the identification of endometallofullerenes has been shown and it is proposed to use the spectrophotometric method for their detection. It has been found that the purest fullerites are formed under conditions if extraction and crystallization are carried out at the lowest possible temperatures. [ABSTRACT FROM AUTHOR]

The purpose of this work is to determine the influence of spin-orbital interaction on the electronic energy spectrum of CsPbBr3 and CsPbI3 crystals. The goal was achieved in the following sequence. At the first stage, partial densities of electronic states were calculated and a symmetrical analysis of the electronic structure of the crystals was performed. The calculations were made from the first principles in the formalism of the density functional theory in the basis of the projector augmented waves (PAW). The semilocal exchange-correlation potential derived within the generalized gradient approximation (GGA) was used in the calculations. At the second stage, the electronic energy bands were obtained without taking into account the spin-orbital interaction. The third stage consisted in obtaining the electron energy spectrum of the crystals including the spin-orbital interaction in the calculation scheme. A significant influence of the spin-orbit interaction on the values of the interband gaps ∆E(k) of both crystals has been revealed. In particular, it has been found that the spin-orbit interaction reduces interband gaps in the CsPbBr3 crystal at the points Γ, X, M and R of the first Brillouin zone by 0.17, 0.22, 0.66 and 1.01 eV, respectively. In the CsPbI3 crystal, the reduction of interband gaps at the same points was found to be 0.31, 0.25, 0.73 and 1.08 eV, respectively. Such significant dependence of the parameter ∆E(k) on the momentum indicates a strong non-locality of the spin-orbital interaction operator of CsPbBr3 and CsPbI3 crystals. Consequently, it is not justified to compare the calculated parameters of the electron energy spectrum obtained without the spin-orbital interaction for CsPbBr3 and CsPbI3 crystals with the experiment. Neglecting the spin-orbit interaction can lead to significant errors in the calculation of the optical constants of crystals containing heavy elements. The obtained parameters ∆E(k) can be used to correct the values of the interband gaps of CsPbBr3 and CsPbI3 crystals found without taking into account the spin-orbital interaction on the basis of other theoretical methods. [ABSTRACT FROM AUTHOR]