Electric-field gradients at theTa181impurity site in Yb, Y, and Dy sesquioxides

Abstract

The perturbed-angular-correlation (PAC) technique has been applied to the study of the internal electric-field gradients (EFG) in Yb, Y, and Dy sesquioxides. The Ta PAC probes were introduced in the oxide lattices by means of Hf implantation, which decays to the Ta impurity by P emission. The tracer Ta was used and the results were compared to those obtained in bixbyite-structure compounds usingCd as a probe. The measured EFG are essentially independent from the probe, reQecting the structure characteristics of both crystalline sites in these compounds. In the case of Hf'+ and ' 'Ta +, charge compensation (the cations are 3+) seems to be accomplished through a uniform distribution of the probe s extra electrons in the neighboring oxygen anions. Comparisons of the results to point-charge model predictions are also discussed.

Impurity Centers in Oxides Investigated by γ-γ Perturbed Angular Correlation Spectroscopy and <i>Ab Initio</i> Calculations

“…7). This observation is also valid for the rest of the bixbyites studied with the 181 Hf probe [29,35,[92][93][94][95][96] Cd are equal, reflecting the same electron density in the neighborhood of the probe-atom. This fact is in excellent agreement with the results obtained in the ab initio calculations in Cd-doped In 2 O 3 performed almost 20 years later than the first experiments.…”

“…This second probe, introduced in the same systems studied with 111 Cd, allows to study the influence of the electronic configuration of the impurity probe atom itself on the EFG. From the early nineties, many crystal structures have been implanted with 181 Hf probes [29,35,37,[91][92][93][94][95][96]101,102], especially the class of bixbyite oxides. Among this group, twelve oxides with the same crystalline structure have been compared and the data show that in all these oxides, Recent data obtained at IPEN using 111 In-diffused in In 2 O 3 powder samples are shown for comparison [90].…”

Ionic exchange of Hf donor impurities in the wide-gap semiconductor Tm2O3

“…Experimental ratio fC/fD as a function of the lattice parameter a for 181 Ta in cubic bixbyite sesquioxides (data taken from Refs. [10][11][12][13][14][15]). The black triangle corresponds to Tm2O3.…”

“…Experimental quadrupole frequency and asymmetry parameter Á for substitutional 181 Ta impurities at sites C (filled circles) and D (hollow circles) in bixbyites plotted as a function of the lattice parameter a (data taken from Refs. [10][11][12][13][14][15]). Back and hollow triangles correspond to results at sites C and D in Tm2O3, respectively.…”

Site localization of Cd impurities in sapphire

“…Hence, by confronting the theoretical calculations with the EFG inferred from measurements at a given site, we can investigate local characteristics as impurity energy levels, localization of impurities and defects, structural distortions, charge state of defect centers, etc. 33 based on the RBS/C measurements of Farlow et al 32 and on semiempirical point charge model predictions, 34,35 suggested that the 111 Cd probes could not be located at the substitutional Al sites. It should be noted that, as it is well known presently, the point charge model, and the use of the Sternheimer antishielding factor, 36 which only depends on the given probe atom, are not adequate to reproduce the EFG at impurity sites in semiconductor oxides.…”