Field Gradient In Dilute Alloys Research Articles

Electronic contribution to electric field gradient in dilute alloys

A simple relation for calculating the electronic contribution to the electric field gradient in dilute alloys of transition metals is reported and is compared with the conduction electron charge shift model. The dependence of the field gradient on thes andd electrons and the difference in radii between the host and the probe atoms is considered for calculating the field gradient. It is found that thed electrons are the major contributors to the field gradient.

Effect of higher-order terms in the free-electron screening-charge distribution on the electric field gradient in dilute alloys of cubic host metals

It is shown for the first time that within the free-electron model of the screening-charge distribution, the accuracy of the electric field gradient calculated at the nearest-neighbor host site from an impurity in a cubic host metal can improve considerably if terms of higher order than two are retained in the charge-density expression and the coefficients of the charge distribution are determined in a more realistic scattering potential than square well.

Electric field gradient in dilute alloys of aluminum

The electric field gradient $q$ and asymmetry parameter $\ensuremath{\eta}$ are calculated for $\mathrm{Al}\mathrm{Mg}$, $\mathrm{Al}\mathrm{Si}$, $\mathrm{Al}\mathrm{Cu}$, $\mathrm{Al}\mathrm{Zn}$, $\mathrm{Al}\mathrm{Ga}$, $\mathrm{Al}\mathrm{Ge}$, $\mathrm{Al}\mathrm{Ag}$, and $\mathrm{Al}\mathrm{Cd}$ alloys. The Alfred and Van Ostenburg charge perturbation, which accounts for both the asymptotic and preasymptotic regions, is used to evaluate the valence-effect contribution. The size-effect contribution is calculated in the elastic continuum model proposed by Sagalyn and Alexander. It is found that the valence effect alone cannot explain the observed $q$ and $\ensuremath{\eta}$. The size-effect contribution is found larger than the valence-effect contribution for all the alloys except for $\mathrm{Al}\mathrm{Ag}$ for which the valence-effect contribution is found larger than the size-effect contribution. The calculated values of $q$ and $\ensuremath{\eta}$ are found to be in close agreement with the experimental values and exhibit an improvement over other available theoretical results.

Electric field gradient in dilute alloys of copper

The electric field gradients for dilute alloys of copper with fourth- and fifth-row impurities are calculated. The change in the charge distribution proposed by Alfred and Van Ostenburg, which includes preasymptotic contribution, is used to evaluate the valence-effect contribution. The size-effect contribution is adopted from Sagalyn and Alexander. The calculated values for electric field gradients (EFG's) and asymmetry parameters ($\ensuremath{\eta}'\mathrm{s}$) are found in close agreement with experimental values for almost all the alloys. The results are also compared with other available theoretical results. An attempt is also made to correlate the magnitudes of EFG and $\ensuremath{\eta}$ with the magnitudes of the impurity effective charges which are estimated with consideration of the bound state and size effect.

Electric field gradients in dilute alloys of Cu, Ag and Au

In this paper we present perturbed angular correlation (PAC) measurements on100Rh and111Cd in a number of dilute alloys of Cu, Ag and Au. We discuss the electric field gradient (EFG) values derived from these and other experiments in the framework of a theory of the EFG at nearest neighbours of point defects in metals, essentially based on the screening of a point charge in a free electron gas. We include in our discussion the EFG due to a neighbour monovacancy for a number of fcc metals.

An anisotropic screening effect in the theory of electric field gradients in dilute alloys of simple metals

The Kohn-Vosko formula for electric field gradients associated with point defects is modified to account for the effect of anisotropic screening charge density on the core enhancement factor.

Single crystal studies of electric field gradients in dilute alloys. III. Non transition metal impurities in aluminium and copper

For pt.II see abstr. A16667 of 1972. The electric field gradients (EFG) at host nuclei being neighbours to impurity atoms have been determined in several Al and Cu alloys by the quadrupole effects in nuclear magnetic resonance. The work supplements previous studies by several workers so that neighbour field gradients due to almost all nontransition metal impurities soluble in the two host materials are now available. This body of results has been compared to present theories of impurity scattering and seems to indicate that these are inadequate to describe the symmetries and sizes of the charge distributions close to the impurities.

Single crystal studies of electric field gradients in dilute alloys. II. Copper based crystals

For Pt. I see abstr. A1732 of 1972. The electric field gradients at nearest and in some cases next nearest host Cu nuclei to various impurities in dilute Cu alloy single crystals have been determined by the quadrupole effects in nuclear magnetic resonance. The impurities are In, Sn, Sb and Ge. The field gradients at nearest neighbour sites are far from rotational symmetric around the direction towards the impurity and in the case of CuGe it does not even have the main component in that direction. These results question the validity of the theoretical models assuming spherical symmetry for the charge density around the impurity, at least in host metals like copper.

Single crystal studies of electric field gradients in dilute alloys I. Aluminium based crystals

A study of the nuclear magnetic resonance spectrum of single crystals of three alloys of aluminium containing 0.5 at% Mg, Ga and Ge impurities respectively has revealed the presence of weak satellite lines whose dependence upon the orientation of the crystal in the magnetic field establishes that they originate at host sites which are nearest neighbours to the impurity. The Ga and Ge results contradict the earlier interpretation of Minier based upon pure quadrupole resonance studies and the new assignment is in greatly improved agreement with the theoretical calculations of Fukai and Watanabe.

Electric Field Gradients in Dilute Alloys of Copper with Nonmagnetic Transition Impurities,

Electric Field Gradients in Dilute Alloys of Copper with Nonmagnetic Transition Impurities,

Electric Field Gradients in Dilute Alloys of Copper with Nonmagnetic Transition Impurities

Recent NMR experiments on dilute alloys of copper with nonmagnetic transition impurities can be explained if one assumes a nearly, but not completely, filled $d$ shell on the impurity. This model gives, for the resistivities and the field gradients, theoretical results in good agreement with the experiments. The field gradients are calculated taking into account both the valency and the size differences between the impurity and the copper.

Electric Field Gradients in Dilute Alloys of Silver

BS>The directional correlation of the gamma rays emitted in the decay of Cd/sup 111/ was measured with the cadmium embedded in the cubic silver lattice in order to observe the electric field gradients produced by various solute atoms. The alloys atudied contain small concentnations of Cd, In, Sn, Sb, or Ge. The results are compared to various theories of screening and are found to be in agreement with a cos (2kr + Phi)/r/sup 3/ fail off of shielding charge, where k is the wave number at the Fermi surface. (auth)