Electrostatic screening contributions to the vacancy binding energy in doped oxides

Linear Response Theory is used to estimate the relative magnitudes of the electrostatic contributions to the binding energy of an oxygen vacancy to a dopant ion in mixed oxides. The theory is further developed to yield the electrical conductivity activation enthalpy and pre-exponential factor in the ionic conduction regime. Experimentally observed trends in these quantities are not reproduced. The discrepancy is not removed by inclusion of polarization effects associated with the field-induced displacement of the screening cloud around the mobile vacancy or ionized dopant. Both of these are estimated to produce negligible changes. The same applies to the enhancement of the local field at the vacancy due to nearby vacancy—dopant pairs. It is concluded that some other physical mechanism is required to account for the variation in the conductivity activation enthalpy with dopant concentration.     

Non-spherical contributions to the vacancy formation energy

A linear response formalism is presented which allows the calculation of the non-spherically symmetric (angular momentum index, l ≠ 0) response to a random external charge perturbation when the spherically symmetric response is available. This procedure is applied to the problem of the energy of vacancy formation so that the electron charge depletion in the vicinity of vacancy is taken into account. The non-spherical contribution to the energy formation for the alkali metals is estimated and found to be non-negligible.     

Third-order contributions to the binding energy of oxygen

Binding energy calculations reported in earlier papers using matrix elements deduced from phase shifts are continued to third order in a perturbative treatment. The total third-order contribution is small due to a cancellation between diagrams and there are indications that higher order terms are also small.     

Anion vacancy centers in alkaline earth oxides

For many years, study of the defect state of oxide crystals was overshadowed by activity in the alkali halides. However, during the last decade, work on oxides has emerged as an important field of study in its. own right. This burgeoning of interest came about for many reasons. First the properties of defects in the alkali halides became well understood, and it was natural for workers in this field, to search for new pastures. Secondly, reliable supplies of good? quality single crystals became more readily available. Furthermore, a greater understanding of band structure, lattice dynamics, and mass transport became apparent, and concerted efforts were made by various researchers to introduce defects into oxides in a controlled manner.     

Nucleon-nucleon on-shell and off-shell contributions to the triton binding energy in an energy-dependent potential model formulation

An energy-dependent nucleon-nucleon (NN) potential model is presented which allows an unambiguous separation of NN on-shell and off-shell contributions to trinucleon observables. A potential of the form $\text{V(E; p, p′) = λ (E)}\text{V}\text{(p, p′)}$ is constructed at negative energies by comparison with various hermitian potentials. The latter comparison suggests a symmetric choice of λ(E) with respect to E = 0. It is shown that the force model constructed according to the present study is more reasonable and less ambiguous than the hermitian potential model, for which the negative-energy dependence of the corresponding t-matrix is generated in an arbitrary way by the accidental choice of the off-shell behavior of the potential. The pertinent shortcomings of the conventional potential model are elucidated by their inconsistent predictions for two- and three-nucleon systems. In the case of the proposed energy-dependent potential model the on-shell information is decoupled from the off-shell behavior at positive and negative energies. This allows one to eliminate the two-body off-shell contributions within the three-body equations in a continuous process by taking the range of forces to zero while keeping at each step the two-body on-shell information unaltered.     

Polarization contributions to the spin dependence of the effective interaction in neutron matter

We calculate the modification of the effective interaction of particles on the Fermi surface due to polarization contributions, with particular attention to spin-dependent forces. In addition to the standard spin-spin, tensor, and spin-orbit forces, spin nonconserving effective interactions are induced by screening in the particle-hole channels. Furthermore, a novel long-wavelength tensor force is generated. We compute the polarization contributions to second order in the low-momentum interaction V(low k) and find that the medium-induced spin-orbit interaction leads to a reduction of the 3P2 pairing gap for neutrons in the interior of neutron stars.     

Hydrogen binding in vacancy clusters in platinum

The binding of hydrogen in different vacancy complexes in platinum metal was investigated with atomic-scale sensitivity using perturbed angular correlations of gamma rays (PAC). Hydrogen was introduced by cathodic charging. Detrapping was monitored microscopically during desorption at 294 K by changes in site fractions of hydrogen-decorated and undecorated complexes. Analysis of desorption includes effects of retrapping of hydrogen at other sites. Assuming a trap concentration of 10^–3, binding enthalpies of 0.23(2), 0.28(1), 0.24(1) and >0.20 eV are obtained for hydrogen atoms in 1V to 4V complexes, respectively. The small differences between the binding enthalpies demonstrate that hydrogen binding is insensitive to the detailed geometrical structure of small vacancy complexes. However, the magnitudes found here are a factor of two smaller than in the literature.     

Relaxation energy for single vacancy in Na

Using a new method, the qualitative corrections to the relaxation energies in the discrete lattice theory, including displacements of a limited number of neighbouring ions around single vacancy in Na, are calculated. The long-range effect of the relaxation is important and brings about the increase of the relaxation energy, i.e. the decrease of the formation energy.     

Nitrogen vacancy effects on the ferromagnetism of Mn doped GaN films

The amorphous gallium nitride thin films doped with Mn were deposited by Laser assisted Molecular Beam Epitaxy (LMBE). After annealing at different NH₃ flow rates, the high-quality GaMnN crystalline films with different concentration of nitrogen vacancies (V _N) were obtained, which were confirmed by the X-ray diffraction spectroscopy and Raman measurements. The magnetic behaviors of these films were also obtained to investigate the effects of nitrogen vacancies. It indicates that V _N play a significant role in the origin of ferromagnetism. The stronger room-temperature ferromagnetism is given with the higher V _N concentration when it is not beyond a critical concentration. Moreover, from our M(T) curves and Raman analysis, the films present high resistivity. The magnetism of films with high resistivity varies with concentration of nitrogen vacancies, which can be explained by the bound magnetic polarons (BMP) theory.     

Mesonic and binding contributions to the nuclear Drell-Yan process

We have evaluated the Drell-Yan cross section in nuclei paying special attention to the meson cloud contribution from pions and ϱ-mesons, for which an accurate calculation using the meson nuclear spectral functions is used. Similarly, the nucleonic contribution is evaluated in terms of a relativistic nucleon spectral function. Fair agreement with experiment is found for different nuclei and the results show a sizeable contribution from the renormalized meson cloud. In order to reproduce the experiment a novel element is introduced, consisting of a gradual energy loss of the incoming proton in its pass through the nucleus which produces a strong A dependence at x₁ large.     

Kinetic energy contributions to heavy ion potentials

It is shown that the change in the intrinsic kinetic energies of two interacting heavy ions gives a repulsive contribution to the heavy ion interaction potential. It is proposed that this effect explains a major part of the discrepancy between folded and experimentally determined HI potentials.     

Pseudopotential calculation of the vacancy formation energy in polyvalent metals

Values of the vacancy formation energy have been calculated in polyvalent metals Be, Mg, Zn, Tl, and Sc, without taking into account lattice relaxation energy. Parameters of the model pseudopotential used in the calculations were determined from experimental phonon spectra. Sensitivity of the quantities calculated to the choice of the approximation for exchange-correlation corrections in the dieletric function has been studied.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 7–10, March, 1982.     

Perturbative analysis of the divergent contributions to the Casimir energy

We investigate the divergence structure of the Casimir energy for the case that ?(x) and μ(x) are general functions ofx and of the frequency. The analysis is done in perturbation theory up to second order. The degree of divergence is found to be lowered by one unit if the usual approximation of sharp boundaries is relaxed. This introduces the inverse width of the boundary layer as another physical cutoff for the divergent integrals, besides the cutoffs related to retardation and spatial nonlocality of the dielectric response.     

Binding energy of hydrogen-Cd vacancy complex in CdTe

The structural and electronic properties of hydrogen-Cd vacancy complex in CdTe have been studied by using density functional theory. Three typical complexes between hydrogen and Cd vacancy were found in our present study. The stablest complex P₂ was predicted by using the formation energy and the binding energy. We found that the formation of the complex is exothermic and its binding energy is extremely large. The analysis of the transition energy level indicates that the forming of the complex turns the double acceptors caused by Cd vacancy to be a single one. The position of the single acceptor deeper than the shallow acceptor derived from the cation vacancy. At the same time, the forming of the complex directly increases the lifetime of the minority carrier from decreasing its concentration. The mechanism of the hydrogen passivation effect was also briefly discussed in our present study.     

Behaviour of up to 25% iron doped BSCCO ceramic oxides

XRD analysis and Mössbauer Spectroscopy studies were performed on samples of the ceramic oxide of nominal composition Bi₂Sr₂CaCu₂O₈ doped with iron substituting copper up to 25%. XRD results point out that increased doping favors the growth of the n=1 phase relative to the n=2 phase. RT Mössbauer spectra were fitted with three doublets D₁, D₂, and D₃, corresponding D₁ and D₂ to Fe in the n=2 phase, and D₃ to Fe in the n=1 phase. The Fe ions localization, in the Cu₂O planes, and their effect on structural and electronic properties, are discussed.     

Second-neighbours contribution to the repulsive energy of crystalline alkaline-earth oxides

The Born-Mayer model in the alkaline-earth oxides is reconsidered, using new compressibility data. All four oxides cannot share a unique hardness parameter ?. An exact solution is found by assuming that ?(MgO) = ?(CaO) and ?(SrO) = ?(BaO); another solution is proposed, which involves three distinct ? values in the family of salts. Results are tested by calculating the electron affinity of O^2- from each salt.     

Magnetic contributions to high energy inverse bremsstrahlung process

Magnetic contribution to inverse bremsstrahlung is estimated at high energies. It begins to dominate over the Coulomb contribution in the ratioCE ₂ ² tan² (θ ₂/2) (1+sin² (θ ₂/2)) whereE ₂ andθ ₂ denote the energy and angle of the accelerated electron andC is essentially a nuclear constant.     

Quantum mechanical activation energy of vacancy diffusion in crystals

This report examines the quantum mechanical mobility of vacancies in cubic crystals using the Morse potential. Nonadiahatic effects in vacancy diffusion are considered. Analytic expressions for the probability of a diffusive jump and for the activation energy are derived.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 29–32, April, 1988.     

Mechanism of dissipation of the excitation energy in garnet oxides doped with rare-earth ions with 4f-5d transitions

Mechanisms of dissipation of the excitation energy in garnet crystal phosphors Y₃Al₅O₁₂ and Y₃Ga₅O₁₂ doped with rare-earth ions with interconfiguration transitions are studied depending on the Ga concentration.