Electric field gradients at Ta in Zr and Hf inter-metallic compounds

Site localization of Cd impurities in sapphire

“…13,14 In particular, the solid-state nuclear technique time-differential γ -γ perturbedangular correlations (TDPAC) can be employed in order to elucidate the subnanoscopic environment of the impurities or native atoms in solids. [15][16][17][18][19][20][21] In this technique it is necessary to introduce, create, or activate a suitable probe isotope (often an impurity in the system under study), and the local information is imbricated as a product of a nuclear and an extranuclear quantity. For electric quadrupole hyperfine interactions, the nuclear quadrupole moment (Q), characteristic of a given nuclear state with spin I , interacts with the electric-field-gradient (EFG) tensor at the nuclear probe position.…”

“…The EFG can provide very precise information about the local environment of the probe atom and the electronic structure of the doped system since it is very sensitive to the anisotropic charge distribution close to the probe nucleus. Very accurate EFG calculations can nowadays be performed 16,18,19,22,23 through the use of all-electron (AE) ab initio electronic structure calculations in the framework of the density functional theory (DFT). 24 In these calculations, the host charge density, selfconsistently perturbed by the presence of the impurity, is determined.…”

“…These theoretical EFG tensors are then compared to available experimental TDPAC results. 30,31 Although the EFG has already been proved to be a powerful tool to identify impurity sites in metal oxides, 17,19,25,27,28 to our knowledge, a deep study of the Cd localization in Al 2 O 3 through a direct confrontation between measurements and reliable ab initio predictions has not been reported yet. Nevertheless, the situation faced in the present study is complicated by the fact that, in confronting experiments and ab initio EFG results, two possibly equivalent scenarios are found, and to further unravel this issue, we performed energetic studies.…”

Electronic properties of HfXY intermetallic compounds (X = Si, Ge; Y = S, Se, Te)

“…Despite the broad interest in these compounds, their hyperfine electronic properties have not been intensively studied so far by either experimental or theoretical techniques. Hyperfine interactions, initiating from the interaction of the nucleus charge with the surrounding electric and magnetic crystal fields, can be used in such investigations in order to provide structural, chemical and electronic information of solids on the atomic scale [3]. In the case of a pure quadrupole interaction, the nucleus quadrupole moment, arising from the non-spherical nuclear charge distribution, interacts with the electric field gradient (efg), which arises from the non-spherical charge density around it.…”

“…Both of these quantities are tensors, which are usually transformed into a convenient axes system in which all of the I. Yaar (B) · I. Halevy · S. Kahane · A. Beck · Z. Berant Nuclear Research Center-Negev, P.O. Box 9001, Beer-Sheva 84190, Israel e-mail: iyaar@nrcn.org.il Table 1 The tetragonal, a, and, c, lattice parameters [8], the hafnium and Y atoms calculated z coordinate and the V zz value at the hafnium, X and Y sites (the value of η is 0 for all sites) [3].…”