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Density-functional supercell calculations are employed to follow the location of the donor levels arising from interstitial carbon and interstitial carbon–oxygen complexes in SiGe alloys. We show that these complexes interact weakly with neighboring Ge atoms, and that energetics rules out the existence of defect-Ge complexes involving direct Ge C or Ge O bonds. The C i O i defect is predicted to produce a hole trap that varies as E (0/+) − E v = 0.41 − 0.76 x eV, implying its disappearance for Ge fractions x greater than 0.5.

In this paper, a H-doped Gd ribbon was prepared by annealing a melt-spun Gd ribbon at 600 °C and then exposing it to a H 2 atmosphere at 300 °C. The Curie temperature of the GdH x ribbon increases after hydrogenation and the magnetic entropy change is a little higher than that of Gd. The refrigerant capacity of this material is also significantly higher than that of Gd. The limitation of this GdH x ribbon is that the hydrogen can easily diffuse out.

Structure and magnetic properties of La(Fe0.88Al0.12)13Cx interstitial compounds with x=0–0.8, were studied by x-ray diffraction and magnetic measurements. The interstitial compounds retain the NaZn13-type structure and the lattice constant increases with carbon content. The Wigner–Seitz cell volume and void calculations show there are seven different voids in the NaZn13 structure with the void at the 24d site (0, 0.25, 0.25) having the largest volume and the largest number of La neighbors. It is highly likely that the carbon atoms enter the 24d site. The small carbon doping collapses the antiferromagnetic state in La(Fe0.88Al0.12)13 and forms a ferromagnetic state. The magnetic transition temperature increases from 198 K to 280 K and the spontaneous magnetization (5 K) decreases from 22.9 μB to 21.3 μB per formula unit with increasing carbon content from x=0 to 0.8. The change in magnetic properties on carbon addition is attributed to cell volume expansion and Fe–Fe distance variations.

Atomic ordering of strongly nonstoichiometric compounds like carbides of transition metals is a very widespread phenomenon. The lower tungsten carbide \(\mathrm{W}_{2}\mathrm{C}_{y}\) is a strongly nonstoichiometric interstitial compound and has a wide homogeneity interval \(\mathrm{WC}_{0.34}-\mathrm{WC}_{0.52}\) at a temperature \(\sim \)3000 K. The literature data on the crystal structure of disordered and different ordered phases of \(\mathrm{W}_{2}\mathrm{C}_{y}\) carbide are contradictory. In this chapter the symmetry analysis of all possible superstructures of \(\mathrm{W}_{2}\mathrm{C}_{y}\) is performed and the physically possible sequence of phase transformations in this carbide is established. Also an analytical method is proposed for calculating the probabilities of existence of different pair interactions in the nonmetal sublattice of superstructures formed in strongly nonstoichiometric compounds \(\mathrm{MX}_{y}\) and \(\mathrm{M}_{2} \mathrm{X}_{y^{\prime }}\) with a high content of structural vacancies \(\square \).

Ordering of binary interstitial solid solutions in a crystal with a BCC lattice is investigated. Two cases are considered: 1) interstitial atoms occupy interstices of only one type, 2) interstitial atoms occupy interstices of two types. It is demonstrated that in the second case, the order-disorder phase transformation is absent, and the solution remains ordered at all temperatures. © 2013 Springer Science+Business Media New York.

The effects of boron and carbon on the structural, elastic, and electronic properties of both Ni solution and Ni3Al intermetallics are investigated using first-principles calculations. The results agree well with theoretical and experimental data from previous studies and are analyzed based on the density of states and charge density. It is found that both boron and carbon are inclined to occupy the Ni-rich interstices in Ni3Al, which gives rise to a cubic interstitial phase. In addition, the interstitial boron and carbon have different effects on the elastic moduli of Ni and Ni3Al. The calculation results for the G/B and Poisson's ratios further demonstrate that interstitial boron and carbon can both reduce the brittleness of Ni, thereby increasing its ductility. Meanwhile, boron can also enhance the ductility of the Ni3Al while carbon hardly has an effect on its brittleness or ductility.

Fundamental understanding of impurity diffusion in crystals remains a challenge due to lack of experimental capabilities for measuring the diffusion properties of atoms according to their substitutional and interstitial lattice locations. With examples of indium and silver in ZnO crystals, we demonstrate an ion beam based method to experimentally determine the energetics and entropy changes in diffusion of substitutional and interstitial impurity atoms. While the interstitial Ag diffuses much faster than the substitutional Ag, as normally expected, the interstitial In migrates slower than the substitutional In, which is attributed to a large negative entropy change (∼−10 kB), possibly caused by the large atomic size of In. The activation energy and the diffusivity pre-exponential factor for the interstitial Ag are significantly enhanced, being more than a factor of two and ∼13 orders of magnitude, respectively, relative to the case for the interstitial In. This implies two different diffusion mechanisms b...

In the present paper the diffusion behavior of nitrogen in Sm 2 Fe 17 has been investigated. The Curie temperatures of nitrides are experimentally found to vary in a very narrow temperature range. No other intermediate nitride with a small Curie temperature has been found. After the further annealing of non-fully nitrided powder in an Ar atmosphere, some of the nitrogen atoms, which have weak interactions with the interstitial site, can be excited from interstitial sites of Sm 2 Fe 17 molecule by thermal energy and migrate again. However, some of nitrogen atoms are still located at interstitial sites of Sm 2 Fe 17 molecule owing to the strong interaction between gas atoms and the interstitial site. In the nitrogen diffusion process, with increasing occupation of the interstitial site in Sm 2 Fe 17 by nitrogen atoms, the diffuse force for nitrogen atom decreases owing to the change in the chemical potential of system, which results in different diffusive activities of nitrogen atoms under different nitrogen absorption contents x in Sm 2 Fe 17 N x . Meanwhile the particle size dependence of the diffusion behavior has also been discussed. The surface and the grain boundary diffusion modes play important roles in the diffusion process of nitrogen atoms into Sm 2 Fe 17 particles especially for small particles.

The possible interstitial sites for hydrogen occupation in the intermetallic lattices of ZrPd 2 (MoSi 2 tetragonal structure type) and UPd 3 (Ni 3 Ti hexagonal structure type) were identified by their Wyckoff notation and characterized by the metal atoms on the polyhedron vertices. Interstitial hole sizes and intersite distances were also calculated utilizing lattice constants and estimated atomic metal radii. It is concluded that hydrogen absorption is not restricted by geometrical factors imposed by empirical and theoretical criteria for the minimum hole size and intersite distance. The hydrogen inertness of the ZrPd 2 and UPd 3 compounds is discussed from the point of view of their large stabilities and the recently found correlations between bonding strengths and hydrogen absorption.

A sample with nominal composition YFe10.5TiB0.5 has been prepared through careful processing. X-ray diffraction analysis revealed that the main phase in the sample is in the tetragonal ThMn12-type structure (space group, I4/mmm),-and a small amount (less than 3%) of alpha-Fe exists as a second phase. Neutron diffraction measurements indicated that, in the tetragonal structure, the boron atoms occupy the 8i sites, substituting for a few Ti atoms, while the substituted Ti atoms enter the interstitial 2b sites. The real composition of the main phase was determined to be Y(Fe11.04Ti0.52B0.43)Ti-0.39.

Surface analysis of Pd thin foil is done by Auger electron spectroscopy after various treatments. The results are related to hydrogen gas permeation through Pd membrane on the ranges of low pressure and medium temperature.

Carbon–vacancy ordering in the rhenium-based solid solution (Cr1−xRex)2C1−y was investigated by X-ray and neutron diffraction for the alloy (Cr0.7Re0.3)2C0.9 quenched from the as-cast state as well as from 800 °C. A structural order–disorder transformation is observed with substitution of rhenium for chromium. The type of carbon–vacancy order for (Cr0.7Re0.3)2C0.9 [a=0.49281(3), c=0.44774(3) nm] corresponds to the e′W2C-type with space group P 3 1m .

Basic equations of diffusional kinetics in alloys are statistically derived using the master equation approach. To describe diffusional transformations in substitution alloys, we derive the "quasi-equilibrium" kinetic equation which generalizes its earlier versions by taking into account possible "interaction renormalization" effects. For the interstitial alloys Me-X, we derive the explicit expression for the diffusivity D of an interstitial atom X which notably differs from those used in previous phenomenological treatments. This microscopic expression for D is applied to describe the diffusion of carbon in austenite basing on some simple models of carbon-carbon interaction. The results obtained enable us to make certain conclusions about the real form of these interactions, and about the scale of the "transition state entropy" for diffusion of carbon in austenite., Comment: 26 pages, 5 postscript figures, LaTeX

The solubility of a substitutional impurity in homogeneously deformed solid interstitial bcc- and fcc-solutions is calculated. It is shown that due to deformation in bcc-crystals both octa- and tetra-interstices are split into three types; no such effect is observed in fcc-crystals. The conditions of increased or decreased solubility under deformation are discussed. © 2012 Springer Science+Business Media, Inc.

The distribution of interstitial impurities between liquid lithium and solid titanium-alloyed vanadium is investigated. It is shown that titanium alloying of vandium intensifies nitrogen and carbon transport from lithium into the solid metal. At the same time, the concentration of oxygen in the surface layers of the specimens increases as a result of penetration of lithium and formation of complex oxides of the Me x Li y O z type. Increase in the titanium content leads to an increase in the carbon concentration on the surface and to the formation of protective carbon films that inhibit the diffusion of interstitial impurities into deep-seated layers.

Segregation effects which appear because of interstitial element interaction with austenite structural imperfections have a significant influence on the austenite crystal lattice energy. It has been shown that, for FCC-crystals which show a tendency to split perfect dislocations into partial dislocations, the thermochemical nature is typical for interaction between planar defects and interstitial atoms in spite of the relatively low interaction energy (about 0.1 eV). Electron microscope investigations of stacking fault (SF) aging done at relative later aging stage when dispersive carbide particles have formed at these imperfections. But the internal friction and austenite yield stress measurements have shown changes in solid solution state and dislocation pinning by interstitial solute atoms at 200--400 C. As regards the interstitial atom atmosphere formation at room temperature, there are no publications in the literature on this subject. The carbon atom distribution at different imperfections in manganese austenite was studied in this work by means of analytical electron microscopy (AEM).

Different experimental measurements show that transformations of martensite occur from very low temperature, often below 77K. In order to understand the redistribution of interstitial atoms which is studied by Mössbauer spectrosopy near room temperature the previous low temperature changes are briefly discussed. The Mössbauer data related to cubic [MATH] and [MATH] Fe-N alloys are presented. It is shown that the interstitial atom distribution and redistribution of interstitial atoms is partially inherited from austenite and that [MATH] nuclei corresponds in [MATH] and [MATH] to N-Fe-N chains oriented along [MATH] in [MATH] and along [MATH] in [MATH].

The ordering mechanism in the excess-hydrogen system of the interstitial alloy CeH2 + x is described based on the mean-field approximation of the static-concentration-waves theory and using the results of neutron-diffraction experiments. The computed order-disorder transition temperatures (normalized at c = 0.25) agree with the various available experimental data quite satisfactorily, in the concentration range 0.13 ≲ c ≲ 0.5, but seem to be overestimated for c > 0.5, probably due to the increasing role of the lattice contraction with increasing c. The character of the transition changes progressively from first to second order above a critical concentration co ~ 0.3.

The ordering process in the hydrogen subsystem of the interstitial alloy TbD 2+x is described with the mean-field approximation to static-concentration wave theory and with the results of neutron-diffraction experiments. It is shown that the measured temperature dependence of the intensity for the superstructure reflections in the alloy with composition TbD 2.18 is well represented by the calculated temperature dependence of the square of the order parameter. Furthermore, the computed transition temperatures for alloys with different concentrations x in the range 0≤x≤0.25 are close to those determined from resistivity and neutron-scattering experiments

We investigate the microscopic structures of interstitial and substitutional hydrogen impurities in LiNbO3 through the first-principles pseudopotential total-energy calculations. The interstitial hydrogen is located between two O atoms and bonds to one of the oxygen atoms. The hydrogen impurity substituting Li is significantly displaced from the Li-site and strongly bonds to an oxygen atom and is located on a biaxial axis of an O triangle. We discuss the effect of hydrogen to the ferroelectric polarization and the energetics for the trap of the interstitial hydrogen at a Li vacancy.

Understanding the behavior of hydrogen in hexagonal tungsten carbide (WC) is of particular interest for fusion reactor design due to the presence of WC in the divertor of fusion reactors. Therefore, we use first-principles calculations to study the hydrogen behavior in WC. The most stable interstitial site for the hydrogen atom is the projection of the octahedral interstitial site on tungsten basal plane, followed by the site near the projection of the octahedral interstitial site on carbon basal plane. The binding energy between two interstitial hydrogen atoms is negative, suggesting that hydrogen itself is not capable of trapping other hydrogen atoms to form a hydrogen molecule. The calculated results on the interaction between hydrogen and vacancy indicate that the hydrogen atom is energetically trapped by vacancy and the hydrogen molecule can not be formed in mono-vacancy. In addition, the hydrogen atom bound to carbon is only found in tungsten vacancy. We also study the migrations of hydrogen in WC and find that the interstitial hydrogen atom prefers to diffusion along the c axis. Our studies on the hydrogen behavior in WC provide some explanations for the experimental results of the thermal desorption process of energetic hydrogen ion implanted into WC., 29 pages and 7 figures, submitted to Journal of Nuclear Materials, under review

The results of electrical resistivity measurements in the temperature internal 1.4–300 K on the alloys, CeMXGe2 (M = Fe, Co, Ni and Cu; 0

Interstitial alloys are formed by the incorporation of carbon, nitrogen and oxygen into the lattices of early transition metals to produce a class of compounds with metallic character. The crystal structure of the materials is similar to that of the metals, with the metal atoms usually forming closed-packed lattices. The compounds can now be prepared in very high surface area form by a number of methods. They have excellent catalytic activity in a wide variety of reactions: ammonia synthesis and decomposition, hydrogenolysis, isomerization, methanation, and hydroprocessing. In particular, for hydrogenation type reactions they display activity approaching or surpassing those of the best Group 8 metals. Although their activity is similar to those of the noble metals, kinetics and product selectivities are often different and indicate that the carbides and nitrides provide unique catalytic pathways.

Rapidly solidified Sm11Fe89 was observed to form partially ordered Sm2Fe17. The ordering increased systematically with annealing temperature, reaching an order parameter of 0.8 after annealing at 950 °C for 15 min. The coercivity of the corresponding interstitial compound Sm2Fe17Nx varied with annealing temperature and thus order parameter. The coercivity reached a maximum for an order parameter of 0.45–5, then dramatically decreased as the order increased. This behavior is characteristic of demagnetization controlled by domain wall pinning by antiphase boundaries.

First principles calculations suggest that mobility of H in solid borohydrides is dominated by neutral interstitial H(2), not charged defects.

Using the Onsager-type kinetics equation, the differential equation for the kinetics of orientational long-range order (LRO) parameter for the interstitial H-atoms' distribution within the hexagonal close-packed (h.c.p.) lattice of a metal (Me) is firstly derived. The numerical solutions of this equation enable to analyze the orientational ordering of H atoms. The decreasing of H concentration results in a decelerating of the orientational-LRO parameter change and in an increasing of its relaxation time. Temperature influence on the orientational-ordering process is more appreciable for lower hydrogen concentrations because of the open-chain (two by two) distribution of H atoms in h.c.p. metals.

Low-concentration α-phases of rare-earth metal hydrides are considered. A system of simple mathematical models aimed to describe equilibrium states of the subsystem of interstitial hydrogen atoms is presented. Description is based on the assumption that in the low-concentration interstitial metal-hydrogen systems atomic Me a H b complexes are formed and the interstitial alloy MeH x can be considered as a dilute solution of these complexes in the metallic matrix. It is shown that in the suitable conditions the distribution of these complexes in lattices becomes spatially correlated that provides formation of some ordered structures. Consideration is applied particularly to the low-concentration rare-earth hydrides.

In this paper interaction of hydrogen with interstitial impurities and their mutual influence on the structure of titanium powders is considered.

We improved an embedded atom (EAM) interatomic potential for the description of defective body-centered cubic α-Fe containing C interstitials. Guided by first principles calculations results the potential was developed to reproduce experimental information such as the dilute heat of solution of carbon, the vacancy-carbon binding energy and its configuration, the location of interstitial carbon atoms and the migration energy of carbon atoms in body-centered cubic (bcc) Fe. The potential reproduces the known physical properties of carbon as an interstitial solute element both in ferrite and austenite. It also successfully calculates energetically favored defect configurations and predicts the formation energy and configurations of multicarbon-vacancy defect clusters. The potential performs well for the atomistic study of the interactions between carbon interstitial solute atoms and extended defects in ferrite, such as free surfaces, dislocations and grain boundaries. Since C–C interactions are taken into account, this potential is applicable to the study of cementite and we present results for a ferrite/cementite interface.

The lattice dynamics of the interstitial solid solutions VOx and VNx has been studied. The deformation of the vanadium atom frequency distribution caused by interstitials is observed. The local vibration frequencies of O and N atoms are reported. A computer simulation of the frequency spectra of these compounds were performed.

A new derivation for the driving force on an impurity in the electron-impurity model system is given which results in an exact cancellation of the direct force for the electron-impurity system unambiguously, in accordance with an independent derivation by others in the past. However, the conclusion becomes much different if electron-phonon interaction is accounted for. Then the screening of the direct force appears to be much less effective. Since at the temperatures, at which electromigration experiments on dilute interstitial alloys are done, the electron-phonon interaction is predominant, the direct force valence is expected to lie in practice closer to the bare ion valency than to the completely screened value of zero. The theory predicts a resistivity-dependent direct force in contrast with the constant value used in the past.

The displacement of boron atoms from silicon lattice sites by silicon interstitial atoms was studied, by galvanomagnetic and x-ray methods. The substitution is controlled by the charge state of the interstitial defects. The charge transfer was effected by a change in the level of ionization during implantation by varying the ion-beam density and during annealing by additional electron bombardment.

The energy of formation of self-interstitial atoms has been experimentally determined using an energy analysis of low-temperature field evaporation of tungsten in a field-ion microscope. An experimental approach, based on the strong dependence of the threshold field for evaporation on the total energy of the surface atoms, is used. It was found that the excited atomic states can be produced by the release of the formation energy of self-interstitial atoms emerging at the surface. The experimental results are discussed in the framework of the image-hump model of field evaporation and compared with theoretical data on the energy of formation of interstitial atoms.

The H mass density of the bcc Ti 35 Cr 65− x V x alloys ( x = 18, 22) has been investigated as a function of pressure at various temperatures by tracing P – C isotherms from which the formation enthalpy of the γ hydride has been derived (Δ H = −39 ± 2 kJ/mol for the Ti 35 Cr 43 V 22 alloy and Δ H = −35 ± 6 kJ/mol for the Ti 35 Cr 47 V 18 alloy) . Internal friction measurements have revealed the existence of a broad H Snoek-type of relaxation at around 150 K ( f ≅ 1 kHz), which has been used to deduce information on H mobility. Combined Snoek and high-temperature absorption data have provided the following values for the H diffusion parameters W and D 0 : W = 0.32 ±0.01 eV; D 0 = (4 ± 2) × 10 −7 m 2 /s (Ti 35 Cr 47 V 18 alloy) and W = 0.34 ± 0.01 eV; D 0 = (2 ± 0.5) × 10 −7 m 2 /s (Ti 35 Cr 43 V 22 alloy). X-ray diffraction patterns have confirmed the fcc lattice structure of the hydride while differential scanning calorimetry and thermal desorption spectroscopy data exhibited peaks along the temperature scale which could be attributed to structural transitions of the hydrides. The occurrence of these transitions is accounted for in terms of a previously proposed atomistic model.

Made available in DSpace on 2022-04-29T08:47:51Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-01-01 Metals with a bcc crystalline structure such as Ti-13V-11Cr-3Al alloys have their physical properties significantly changed through the addition of interstitial elements such as oxygen and nitrogen. These metals can dissolve substantial amounts of interstitial elements forming solid solutions. Mechanical spectroscopy measurements constitute a powerful tool for studying interactions of these interstitial elements with other elements that make up the alloy. From these measurements, it is possible to obtain information regarding diffusion, interstitial concentration, interaction between interstitials, and other imperfections of the crystalline lattice. In this paper, Ti-13V-11Cr-3Al alloys with several amount of nitrogen, in a solid solution, were studied using mechanical spectroscopy (internal friction) measurements. The results presented complex internal friction spectra which were resolved in a series of constituent Debye peaks corresponding to different interactions and interstitial diffusion coefficients. Pre-exponential factors and activation energies were calculated for nitrogen in theses alloys. UNESP Grupo de Relaxações Anelásticas, 17.033-360, Bauru, SP USP Escola de Engenharia de Lorena, 12.602-810, Lorena, SP UFSCar Departamento de Física, 13.565-905, São Carlos, SP UNESP Grupo de Relaxações Anelásticas, 17.033-360, Bauru, SP

Statistical thermodynamic analysis was applied to the available phosphorus solubility data set for molten Fe1 – y Cr y P x given as functions of Cr composition y, temperature T and phosphorus activity a(P) under the assumption that the solubility limit x of P in the molten Fe1-y Cr y was 0.50 irrespective of y. The evaluated values of the energy parameter representing the extent of stability of P atoms in the molten Fe1 – y Cr y P x showed an apparently realistic variation pattern with y for the level of y up to 0.465. Further, it was demonstrated by an interpolating estimation using the obtained statistical thermodynamic parameter values at two known levels of y that a(P) vs. x relationships for arbitrary y at specified T could be derived with acceptable accuracy.

The dislocation structure developed in an α-type Ti5Al2.5Sn extra-low interstitial alloy under various cyclic stresses at cryogenic temperatures was investigated by transmission electron microscopy. When the maximum stress was above the yield strength, coplanar dislocation arrays were distributed over α grains. Prism slip occurred predominantly and a pyramidal slip system was also activated. As the maximum stress was decreased, dislocation pile-ups became less homogeneously distributed. The dislocation arrays on the prism plane passed through grain boundaries. When the maximum stress was below about 75% of the yield strength, where the present alloy showed subsurface fatigue crack initiation, dislocations were piled up and blocked at grain boundaries in the small α grain region. Slip occurred predominantly along prism planes and the Burgers vector of the dislocation was .

The relations between the thermodynamic properties of the unary lattice gas and the equivalent binary substitutional and interstitial alloys are discussed. New methods for the estimation of the partial particle energy in a lattice gas from Monte Carlo simulations in both the petit and grand canonical ensembles are presented and evaluated. Taken together with well established procedures for estimating the particle chemical potential and more recent procedures for estimating the lattice gas pressure, it becomes possible, for the first time, to obtain reliable determinations of both the partial and integral quantities for internal energy, entropy and free energy at a given temperature and composition in a rigid binary alloy from the one Monte Carlo experiment in either ensemble. Some illustrative results are given for the square lattice with nearest neighbour interactions.

A self-consistent formulation for the force field and the associated dipole force tensor is presented. In the tight-binding approximation of the Hartree-Fock scheme, the variation of the total energy of the solids-up to first order in the atomic displacement-is obtained in terms of neutral quantities with respect to the frozen crystal. Improvements from previous estimations concerning dilute substitutional and interstitial alloys are reported. Also, the authors present-for the first time-a derivation of the force field arising from the presence of the surface of a transition metal.

The interstitial metal clusters form a fascinating class of complexes of the transition metals, where a non-metallic atom X is uniquely bonded to the metal atoms of the core. From the structural point of view, two subclasses might be distinguished, the properly called “interstitial” clusters, where the heteroatom is completely surrounded by the metal atoms of the cage in which it is inserted, and the “semi-interstitial” or “exposed” clusters, where the heteroatom is placed on, or nearby, a face or an edge of a metal polihedron. Moreover, even if the carbon atom remains the first reported and the most commonly encountered heteroatom, one example at least has appeared with hydrogen1, nitrogen,2 boron,3 phosphorous,4 sulphur,5 silicium,6 arsenic7 and antimony8 interstitial atoms. Together with these more common systems, there is an increasing number of policarbido and polihydrido complexes, containing several interstitial heteroatoms9; recently, an example of a cluster with carbon and hydrogen toget...

Coatings based on interstitial alloys of transition metals have acquired a wide application range. However, interest in synthesizing coatings from new materials with requisite service properties is limited by the scarceness of data on their melting temperature. The present paper concerns calculation of the melting temperature of interstitial alloys of transition metals based on the characteristics of intermolecular interaction.

First-principles method based on the density-functional theory is used to study the diffusion of the single carbon interstitial in graphite. Possible diffusion processes in directions both parallel and perpendicular to the basal plane are analyzed. A different path for the interstitial to penetrate the graphitic layer is proposed. Along this path, the migration is carried out through atom exchange between the interstitial and the lattice atom, with a barrier lower than $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. Introducing shear into the graphite may reduce the interstitial migration energy.

The cubic anti-perovskite Mn 3.1 Sn 0.9 N compound is prepared via nitrogenation of the hexagonal Mn 3.1 Sn 0.9 compound. A magnetic phase diagram of Mn 3.1 Sn 0.9 compound is constructed by analysis of data of its magnetic properties. For Mn 3.1 Sn 0.9 N compound, parasitic ferromagnetism exists in the temperature range of 5–370 K, besides a spin-reorientation at about 280 K. Mn 3.1 Sn 0.9 compound exhibits a metallic conducting behavior, while Mn 3.1 Sn 0.9 N displays a metal–nonmetal transition due to the electron localization caused by the static disorder. The differences of the physical properties between the both compounds, are discussed, in terms of the correlation of the hexagonal DO 19 and the cubic anti-perovskite structures, the reduction of the distances between Mn atoms, and the spin-pairing or charge transfer effect due to the electron donation by N 2p to Mn 3d states after introduction of N atoms into the interstitial sites of Mn 3.1 Sn 0.9 compound.

We have studied the formation of yttrium nitride in which the Y-atoms were arranged in two common close-packed stacking: The AB-stacking (hcp-symmetry) is the ground state of metallic yttrium; while the ABC-stacking (fcc-symmetry) is the ground state of yttrium nitride. Given the different symmetries between YN and Y, there must be a phase transition (hcp->fcc) as N is incorporated in the Y-lattice. By means of first principles calculations we have made a systematical investigation where N was gradually incorporated in octahedral interstices in AB and ABC stacking of Y. We report the heat of formation, bulk modulus, lattice parameter and electronic structure of the resultant nitrides. We found that both metal arrangements are physically achievable. Furthermore, for low nitrogen incorporation the two phases may coexist. However for high nitrogen concentration the cubic phases are favored by a 30 kJ mol-1 margin. These results are important since fcc-YN is semiconducting and could be utilized as active layer in electronic devices., One document 18 pages

A theoretical modeling and comparative analysis of the process of diffusion of the interstitial oxygen atoms and interstitial hydrogen molecules (H2) in silicon and germanium crystals at normal and hydrostatic pressure (HP) have been performed. The process of diffusion of particle with a strong interaction with a crystal lattice (interstitial oxygen atom) is a cooperative process. Three nearest Si (Ge) atoms of crystal lattice are involved in an elementary oxygen jump from a bond-center site to another bond-center site along a path in the (110) plane. It is precisely their optimum position (corresponding to a local minimum of the crystal total energy) determines the value of the diffusion parameters of an interstitial oxygen atom in silicon and germanium crystals. In a sense, the diffusion process may be considered as a diffusion process of qwasiparticle – (Oi+3Si). In the case of a particle weakly interacting with a crystal lattice (interstitial hydrogen molecules) we come up against the opposite case – the diffusion of H2 is not a cooperative process. The calculated values of the activation energy and pre-exponential factor for an interstitial oxygen atom δE(Si) = 2.59 eV, δE(Ge) = 2.05 eV, D0 (Si)= 0.28 cm2 s−1, D0 (Ge)= 0.39 cm2 s−1 and interstitial hydrogen molecule δE(Si) = 0.79 – 0.83 eV, δE(Ge) = 0.58 – 0.62 eV D0 (Si)= 7.4 10−4 cm2 s−1, D0 (Ge)= 6.510−4 cm2 s−1 are in an excellent agreement with experimental ones and for the first time describe perfectly an experimental temperature dependence of an interstitial oxygen atom and hydrogen molecules diffusion constant in Si crystals.

The effect of Co substitution for Fe in Nd3(Fe1−xCox)27.7Ti1.3Ny (x = 0.1 – 0.4) compounds on the magnetocrystalline anisotropy has been investigated. The materials were prepared by heating the parent compounds in 5 atm of high purity N2 at 743–773 K for 4h. The nitrogenation was full as confirmed by X‐ray diffraction analysis (Rietveld). The anisotropy constants and the anisotropy field HA have been deduced from the magnetization curves measured on magnetically aligned powder (4–7 μm) samples by using the Sucksmith‐Thompson method. At room temperature the magnetic anisotropy is uniaxial one, HA ≈ 10 T and it practically doesn’t change upon the Fe‐substitution. At 5 K the obtained values of the anisotropy constants give evidence for the presence of easy‐cone‐type magnetic anisotropy. The cone angle and the anisotropy field decrease substantially upon Fe‐substitution from 21.6 to 11.8 degrees and from 22.8 to 18.6 T respectively.

The energy changes in the formation of interstitially doped BaSi2, caused by doping with Na, Mg, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, B, C, N, O, F, and Ne, are calculated using the Perdew–Wang generalized gradient approximations of the density functional theory. It is predicted that the majority of the elements, apart from Na, Mg, Zn, and Ne, are capable of forming interstitially doped compounds with BaSi2, if these elements are provided as an isolated atom. However, the energetic stabilities of the standard states of these elements (metals, diatomic gases, etc.) exceed the energy gain accompanying the formation of the interstitial compounds and, therefore, the conventional diffusion method using metals or gaseous source materials cannot produce the interstitial compounds. From the energetic perspective, B, C, N, O, and F appear to be favorably inserted into the BaSi2 lattice, but the observed behavior of B-implanted BaSi2 suggests that substitution of B for Si may occur.