Interaction of sulfur with impurities in bcc iron

In this work, the modeling of the sulfur interaction with substitutional impurities (Mn, P) and interstitial (C) has been carried out. All calculations were performed using the density functional theory in the WIEN2k software package. For the first two coordination spheres, there is a strong repulsion between carbon and sulfur, but in the third relative position, a slight attraction arises between the atoms. When sulfur interacts with manganese, attraction occurs only for the first coordination sphere, while the dissolution energy of both manganese and sulfur decreases. In the case of the S-P interaction, the binding energy is negative, and the dissolution energy of both sulfur and phosphorus decreases for all configurations, although the distance between phosphorus and sulfur increases. It can be assumed that the presence of phosphorus leads to the accumulation of sulfur in the material.

Ab initio моделирование энергии растворения и энергии связи водорода с 3sp-, 3d- и 4d-примесями в ОЦК-железе

A fundamental understanding of the localization of H atoms in steel is an important step towards a theoretical description of the mechanisms of hydrogen embrittlement at the atomic level. Ab initio calculations within the framework of density functional theory (DFT) is used to investigate the effect of various substitutional impurities Mg, Al, Si, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo , Pd and Cd on the energy of hydrogen dissolution in the lattice of bcc iron. The electronic and elastic contributions of various impurities to the dissolution energy are distinguished, and their influence on the binding energy of hydrogen and impurities is analyzed. The existence of a linear dependence of the energy of hydrogen dissolution on the magnitude of the change in the electron density of the intra-tetrahedral pore after the introduction of a hydrogen atom into it is shown. The results obtained made it possible to formulate the key mechanisms for controlling the localization of hydrogen in bcc iron by substitution impurities.

Оптические сечения поглощения и силы осцилляторов двойного донора магния в кремнии

The optical properties of magnesium impurity in silicon, whose atoms at interstitial positions in the lattice are deep double donors with an ionization energy of 107.56 meV in the neutral state, were studied. For optical transitions from the ground state of a neutral center to the excited levels 2p0 and 2p, the absorption cross sections and oscillator strengths were determined. These parameters were calculated from the impurity absorption spectra that were measured at T  K in samples with different magnesium concentrations. The deep donor content in the samples was determined using Hall effect measurements in the temperature range 78–300 K. The obtained characteristics of intracenter transitions in magnesium were compared with the corresponding literature data for shallow Group V donors in silicon, which are substitutional impurities. It was found that the optical characteristics of the investigated transitions in magnesium are consistent with the dependences of the corresponding parameters on the ionization energy for shallow donors, extrapolated to the region of larger electron binding energies.

Substitutional impurities in monolayer hexagonal boron nitride as single-photon emitters

Single-photon emitters in hexagonal boron nitride have attracted great attention over the last few years due to their excellent optoelectronical properties. Despite the vast range of results reported in the literature, studies on substitutional impurities belonging to the 13th and 15th groups have not been reported yet. Here, through theoretical modeling, we provide direct evidence that hexagonal boron nitride can be opportunely modified by introducing impurity atoms such as aluminum or phosphorus that may work as color centers for single-photon emission. By means of density functional theory, we focus on determining the structural stability, induced strain, and charge states of such defects and discuss their electronic properties. Nitrogen substitutions with heteroatoms of group 15 are shown to provide attractive features (e.g. deep defect levels and localized defect states) for single-photon emission. These results may open up new possibilities for employing innovative quantum emitters based on hexagonal boron nitride for emerging applications in nanophotonics and nanoscale sensing devices.

Impurity elements in quartz from gold deposits of the Darasun ore field (Eastern Transbaikalia, Russia): electron paramagnetic resonance data.

The distribution of substitutional Al, Ti, and Ge impurities in quartz samples from the Darasun, Teremkinskoe and Talatui gold deposits, located in the Darasun orefield, were studied using the electron paramagnetic resonance method. Relationship between the isomorphic substitution and the dynamic recrystallization of quartz was studied by optical and scanning electron microscopy. Analysis of the plots of interdependency between the concentrations of various substitutional impurities in quartz (isogens) provided an opportunity to detect isomorphic substitution development trends. Two isomorphic substitution stages were recognized, one associated with mineral crystallization and the other, with its subsequent dynamic recrystallization. The first stage leads to Al impurity incorporation into the quartz crystal lattice, and the second, to Ti impurity incorporation. The Ge impurity is the isomorphic substitution catalyst, and its concentrations vary widely. It is noted that the second stage plays a decisive role, because it accounts for the incorporation of the larger part of substitutional impurities. This process is facilitated by the dynamic recrystallization of quartz. Four quartz genetic groups, which are described by individual isogens, have been recognized in the Darasun orefield. Two of them correspond to the quartz crystallized from a magmatogenic fluid directly or redeposited with its participation, and the other two correspond to the quartz crystallized from an altered fluid. The facts that substitutional Al concentrations are retained in quartz after redeposition, whereas substitutional Ti impurity concentrations fall dramatically, are demonstrated. Mineral formation processes at each gold deposit are discussed. Two types of temperature zoning, the normal and the reverse, have been recognized at the Darasun deposit. Each zoning is characterized by an individual quartz genetic group and the extent of mineralization system closedness. The genetically similar magmatogenic quartz samples found at the Darasun and Talatui deposits attest to the uniformity of mineralization process in the Darasun orefield. The established trends of isomorphic substitution in quartz are applicable in the studies of ore formation histories of gold and other ore deposits. Keywords: Darasun; Teremkinskoe; and Talatui deposits of the Darasun orefield; mineral formation; auriferous quartz; dynamic recrystallization; substitutional impurities; genetic analysis; isogens; isomorphic substitution stages; quartz redeposition; temperature zoning; EPR method; scanning electron microscopy