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1.
The strain field due to body centered substitutional transition metal impurities in Ni and Pd metals are investigated. The
calculations are carried out in the discrete lattice model of the metal using Kanzaki lattice static method. The effective
ion-ion interaction potential due to Wills and Harrison is used to evaluate dynamical matrix and the impurity-induced forces.
The results for atomic displacements due to 3d, 4d and 5d impurities (Fe, Co, Cu, Nb, Mo, Pd, Pt and Au) in Ni and (Fe, Co,
Cu, Ni, Nb, Mo, Pt and Au) impurities in Pd are given up to 25 NN’s of impurity and these are compared with the available
experimental data. The maximum displacements of 4.6% and 3.8% of 1NN distance are found for NiNb and PdNb alloys respectively,
while the minimum displacements of 0.63% and 0.23% of 1NN distance are found for NiFe and PdFe alloys respectively. Except
for Cu, the atomic displacements are found to be proportional to the core radii and d state radius. The relaxation energies
for 3d impurities are found less than those for 4d and 5d impurities in Ni and Pd metals. Therefore, 3d impurities may easily
be solvable in these metals. 相似文献
2.
B. Lengeler 《Solid State Communications》1985,55(8):679-682
The local lattice structure around B atoms in Pd was determined from the EXAFS at the K-edge of' Pd in to alloys with B/Pd = 16 and 11.4 %. It was confirmed that B occupies octahedral interstices in the fcc lattice of Pd. The lattice expansion of the Pd matrix by the dissolved B is da/a = (0.169±0.003) for B/Pd = 1. Boron displaces its 6 nearest Pd neighbors outwards by (0.106 ± 0.005)Å relative to pure Pd and by (0.061 ± 0.005)Å relative to the average lattice. The local lattice distortion has practically vanished beyond the second Pd neighbors. 相似文献
3.
The embedded-atom method have been applied to study the strain field produced by the self-interstitial impurity at the octahedral
site in Ni. The calculation have been carried out consistently on the basis of discrete lattice theory, using Kanzaki method.
The atomic force constants are evaluated using Wills and Harrison interatomic potential. The dynamical matrix and external
force are evaluated considering the interaction up to first nearest neighbors. The atomic displacements are tabulated up to
20NN’s. These displacements are of oscillatory nature and of decreasing magnitude with NN’s distance. The physical properties
such as self-interstitial formation energy and volume change calculated using atomic displacements are in accordance with
the earlier studies. 相似文献
4.
A. A. Klopotov A. I. Potekaev É. V. Kozlov V. V. Kulagina 《Russian Physics Journal》2012,54(9):1012-1023
Low-stability states and peculiarities of structural changes in the region of phase transitions are investigated using the
Cu–Pd ~40 at.% Pd alloys as an example. To this end, the crystal lattice and long-range atomic order parameters and the Debye-Waller
factors were determined in situ directly in the temperature range of the B2–A1 phases and the order – disorder phase transition using X-ray structural analysis. Based on the data obtained, peculiarities
of the B2 and A1 phases in the CuPd alloys were analyzed near the structure-phase transitions and the behavior pattern of atomic vibrations
in the crystal lattice was discussed. It is shown that in the CuPd alloys with ~40 at.% Pd, low-stability states are observed,
which exhibit a number of anomalous phenomena (such as anisotropy of atomic displacements, splitting, heterophase fluctuations,
nonlinearity of the lattice parameter and long-range order parameter dependences, etc.), which precede transformation of the
alloy. 相似文献
5.
I. V. Bodnar 《Technical Physics》2003,48(5):587-591
The thermal expansion coefficients and the thermal conductivity of Bridgman-grown crystals of CuGa1−x
InxTe2 solid solutions are investigated. It is found that the thermal expansion coefficient varies with x linearly, while the thermal conductivity is minimal when x=0.5. The Debye temperature and the rms dynamic atomic displacements are calculated from experimental data. It is shown that
the Debye temperature decreases and the rms displacements in the crystal lattice sharply increase as the In content in the
solid solutions grows. 相似文献
6.
7.
Kanzaki lattice static method is used to calculate the atomic displacements due to substitutional impurities in 3d (Cr) and
4d (Nb, Mo) metals. Wills and Harrison interatomic potential is used to calculate dynamical matrix and the impurity-induced
forces up to second nearest neighbors. The calculated atomic displacements for 3d, 4d and 5d impurities in Cr (V, Mn, Fe,
Ni, Nb, Mo, Ta and W), Nb (V, Cr, Mn, Fe, Zr, Mo, Ta and W) and Mo (V, Cr, Mn, Fe, Zr, Nb, Ta and W) are tabulated up to 10
NN’s. The strain field due to 3d impurities is least in Cr metal while it is larger in Nb and Mo metals. For 4d and 5d impurities
the strain is larger in Cr metal than in Nb and Mo hosts. Similar trend is found for relaxation energies also. 相似文献
8.
We have calculated the temperature dependence of the atomic mean-square displacements (MSD's) for a reasonable harmonic lattice dynamical model considered to be appropriate to 2HMoS2. Thermal expansion effects were estimated in a crude way using previous model calculations and thermal expansion data. Our results are shown to obey the Lindeman melting criterion. 相似文献
9.
The effects of symmetric lattice relaxation around the tetrahedral (T) and the hexagonal (H) interstitial sites are calculated
for normal muonium (Mu) in diamond using the non-semiempirical method of Partial Retention of Diatomic Differential Overlap
(PRDDO). We use clusters containing 3 and 4 host atom shells around the T and the H sites (C20H32 and C30H40). The only significant relaxations are the outward displacement of the 6 nearest neighbors (NN) to the H site and, when the
muon is at the T site, the simultaneous outward displacement of the first and second NN to the T site. In the case of diamond,
the effects of these relaxations on the energy profiles and spin densities are small. 相似文献
10.
The electric field gradients at27Al and63Cu nuclei which are nearest neighbors to the muon in the face-centered cubic metals aluminum and copper, with muon at an octahedral
interstitial site, are studied. The electron density fluctuations needed for the evaluation of the electronic, or valence,
contributions to field gradients are taken from earlier investigations involving the spherical solid approximation. The enhancement
factors a that have to be applied to the electric field-gradients obtained from these approximations, due to the departures
of the electronic wave-functions from plane-wave character, and the incorporation of antishielding effects, have been obtained
for both APW and OPW approaches to the conduction electron wave-functions and good agreement is found between the results
by the two approaches. Size effects due to the lattice distortion associated with the presence of the muon are included through
actual point ion summations using available calculated displacements of the ions surrounding the muon. The valence contributions
are the dominant ones but the size effect contributions are also significant. The net field-gradient obtained for the27Al site is significantly smaller than experiment while that for63Cu is substantially larger than experiment. Possible sources that could lead to better agreement with experiment are discussed
and it is concluded that major improvement is needed in the valence effect contributions in both metals. 相似文献
11.
R. E. Félix-Medina M. A. Leyva-Lucero R. A. Guirado-López S. Meza-Aguilar 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,75(4):431-437
We present extensive first principles density functional theory (DFT)
calculations dedicated to analyze the magnetic and electronic properties of
small V
n
clusters (n = 1, 2, 3, 4, 5, 6) embedded in a Cu fcc matrix. We consider
different cluster structures such as: (i) a single V impurity, (ii) several V2
dimers having different interatomic distance and varying local atomic
environment, (iii) V3 and (iv) V4 clusters for which we assume compact as well
as 2- and 1-dimensional atomic configurations and finally, in the case of the
(v) V5 and (vi) V6 structures we consider a square pyramid and a square
bipyramid together with linear arrays, respectively. In all cases, the V atoms
are embedded as substitutional impurities in the Cu network. In general, and
as in the free standing case, we have found that the V clusters tend to form
compact atomic arrays within the cooper matrix. Our calculated non
spin-polarized density of states at the V sites shows a complex peaked
structure around the Fermi level that strongly changes as a function of both
the interatomic distance and local atomic environment, a result that
anticipates a non trivial magnetic behavior. In fact, our DFT calculations
reveal, in each one of our clusters systems, the existence of different
magnetic solutions (ferromagnetic, ferrimagnetic, and antiferromagnetic) with
very small energy differences among them, a result that could lead to the
existence of complex finite-temperature magnetic properties. Finally, we
compare our results with recent experimental measurements. 相似文献
12.
The thermodynamic properties of the cerium dioxide (CeO2) are studied using the statistical moment method, including the anharmonicity effects of thermal lattice vibrations. The free energy, linear thermal expansion coefficient, bulk modulus, specific heats at the constant volume and those at the constant pressure, CV and CP, are derived in closed analytic forms in terms of the power moments of the atomic displacements. The temperature dependence of the thermodynamic quantities of cerium dioxide is calculated using three different interatomic potentials. The influence of dipole polarization effects on the thermodynamic properties and thermodynamic stability of cerium dioxide have been studied in detail. 相似文献
13.
The effect of vacancies and interstitials in the CuO2 layer on the vibrational spectrum in the La2−x
SrxCuO4 system has been calculated by molecular dynamics. It is shown that the excitation probability for local ∼0.4-eV high-frequency
vibrations of nonphonon origin in the vicinity of Sr impurity atoms decreases if copper vacancies are introduced at a concentration
x=0.17, which corresponds to the maximum superconducting transition temperature, this decrease being still more effective (by
about ten times) if interstitial atoms are present. The appearance of interstitials makes a considerable region around them
(five to six nearest neighbors) quasi-amorphous. A comparison with available experimental data is made. It is concluded that
the behavior of the system under irradiation is accounted for primarily by interstitials, which bring about strong perturbation
in the lattice (∼1 nm) up to making it completely amorphous.
Fiz. Tverd. Tela (St. Petersburg) 40, 984–988 (June 1998) 相似文献
14.
We have simulated two-dimensional classical XY-model in a microcanonical ensemble using the Monte Carlo technique. Simulations
were carried out on a square lattice having 25, 100 or 900-spins with periodic boundary conditions. The nearest neighbour
interaction potential was taken to beV(θ)=2J[1−cos100(θ/2)]. The system energy, mean square magnetization and vortex-density were calculated as functions of temperature. A sudden
change in the system energy, vortex density and mean square magnetization was observed at the first-order transition which
is associated with this choice of the nearest neighbour interaction potential. The transition temperature increases with decrease
in the system size. It is found that the creation of a vortex-antivortex pair costs more energy during the first-order transition
than the energy associated with a tightly bound vortex-antivortex pair. 相似文献
15.
In this paper we present an expression relating the lattice thermal expansion coefficient αL (10−6 K−1) for the AIIIBV and AIIBVI semiconductors with the product of ionic charges (Z1Z2), melting temperature (Tm) and nearest neighbor distance d (Å). The lattice thermal expansion coefficient of these compounds exhibit a linear relationship when plotted on a log–log scale against the melting temperature (Tm), but fall on different straight lines according to the ionic charge product of the compounds. A good agreement has been found between the experimental and calculated values of the lattice thermal expansion coefficient for AIIIBV and AIIBVI semiconductors. 相似文献
16.
Hydrogen impurities in f.c.c. lattices, Pd metal for example, can occupy two interstitial sites, with tetrahedral or octahedral symmetries. Using the Husimi cactus to represent the f.c.c. lattice and two clusters to describe the two different interstices, we calculate the densities of states and the occupation numbers at the impurity site and on its nearest neighbours. The binding energies are calculated and plotted against the hopping integral between the hydrogen and its neighbours (ta). We found that the octahedral site is the stable one for values of ta from 0 to 1.5 eV. 相似文献
17.
本文发展文献[1]的方法到两种不同自旋的原子(Sa=1,Sb=1/2)构成的晶格中,计算了简单立方晶格在具有再次近邻反铁磁相互作用下在外磁场中的基态自旋结构、能量和相界。从文中给出的相图可知:这种晶格有两种反铁磁自旋结构,有四种亚铁磁自旋结构。
关键词: 相似文献
18.
Gygax F. N. Schenck A. Barth S. Riesterer T. Schlapbach L. 《Hyperfine Interactions》1986,31(1-4):75-79
The orientation dependence of the inhomogeneously broadened μSR line width has been measured in a single crystal α′-PdH0.74 sample between 20 and 150 K. Protons and muon are thought to occupy octahedral interstitial sites in the Pd lattice. A good
fit to the data is only obtained assuming a decrease in the proton occupancy of the octahedral sites nearest to the μ+ with increasing temperature. The proton occupancy of the remaining octahedral sites at all temperatures as well as the occupancy
of the proton sites nearest to the μ+ at 20 K is compatible with the bulk nominal hydrogen concentration x=0.74. 相似文献
19.
In the context of the density functional theory (DFT), we use the ab-initio electronic structure code, SIESTA, coupled to an economic technique to find activated states (or migration barriers), in order to study atomic defects diffusion through the crystal lattice: The monomer method [V.P. Ramunni, M.A. Alurralde, R.C. Pasianot, Phys. Rev. B 74 (2006) 054113]. We test our technique calculating the activated transition states of interstitial hydrogen (H) between two sites of high symmetry, tetrahedral and octahedral, in the α and β phases of Fe. The results are discussed in the context of experimental data and other available models. 相似文献
20.
Janusz Jędrzejewski 《Zeitschrift für Physik B Condensed Matter》1982,48(3):219-225
The Hubbard model on 3-dimensionalsc lattice with an attractive or repulsive on site interaction, augmented by a renulsive nearest neighbour interaction and its atomic limit are studied using the method of infrared bounds. Conditions upon interactions for the existence of a temperature driven phase transition to so called charge ordered phase are derived. A lower bound in terms of interactions for the corresponding critical temperature is calculated. 相似文献