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

Abstract

Abstract. In this chapter Perturbed Angular Correlation (PAC) experiments on binary oxides are described. These experiments provide local-scale fingerprints about the formation, identification, and lattice environment of defect complexes at the PAC probe site. The potential of the PAC observations in conjunction with ab initio calculations is shown. Measurements of the electric-field gradient at impurity sites using 111 Cd and 181 Ta probes are reviewed. Special attention is paid to oxides with the bixbyite structure. The case of In 2 O 3 is particularly analyzed. Results obtained with HfO 2 , in form of coarse grain or nano particles, are described. The potential results that can be obtained from Density Functional Theory ab initio calculations in doped systems are shown describing the main results observed in many impurity-host systems.

Experimental and First-Principles Theoretical Study of Structural and Electronic Properties in Tantalum-Doped In2O3 Semiconductor: Finding a Definitive Hyperfine Interaction Assignment

“…The two last ratios are larger than the crystallographic relative abundance of sites C and D in the bixbyite structure (3:1). The deviations from the value f C / f D = 3, which would correspond to a homogeneous population of the cationic sites by the TDPAC probe, are consistent with the variations previously observed in other isomorphous oxides. , The present experimental value points to a preference of the 181 Hf atoms for the asymmetric site C, in perfect agreement with the site preference predicted by the FP-APW+lo total energy calculations of Hf atoms localized at each cationic site of In 2 O 3 , presented in section III…”

“…These characteristics predicted by this simple model are in qualitative agreement with the experimental results observed in many bixbyite oxides doped with 111 Cd as probe (see refs and and references therein) and also in other 181 Ta-doped bixbyite sesquioxides with lattice parameter larger than that of In 2 O 3 . This agreement led to think to some researchers in the 90′s that the 111 Cd impurity did not introduce structural and electronic distortions in the host lattice and, afterward, similar conclusions were proposed for 181 Ta in bixbyites …”

“…It is well-known that the thermal annealing treatments following ion implantation remove the radiation damage and favor the replacement of host cations by TDPAC probes. ,, Considering this, the initial interaction assignment was done based on the relative abundance of both inequivalent cations sites of the bixbyite structure and the intensities of the obtained hyperfine interactions. So, the dominant hyperfine interaction was assigned to probes localized at cationic site C, and the minority interaction to probes localized at site D. With these assignments, the axially symmetric interaction is in agreement with the axial symmetry of site D. Even though V 33 D is not twice as large as V 33 C as in the rest of 181 Ta-doped and 111 Cd-doped bixbyites , V 33 D is still larger than V 33 C . According to the values presented in Table , the ratio f C / f D is 2.6, 4.9, and 5.2 after the thermal annealings performed at 673, 1073, and 1273 K, respectively.…”

“…Different hyperfine techniques has been employed in the study of pure and doped In 2 O 3 . Particularly, the time-differential perturbed γ–γ angular correlation (TDPAC) technique have been systematically applied to the study of hyperfine interactions in a very wide group of binary oxides, being In 2 O 3 the first oxide studied with ( 111 In →) 111 Cd impurity probe-atoms. − This technique could give very accurate information about the subnanoscopic environment around a probe nucleus through the determination of the electric-field gradient tensor (EFG) at this site. In this respect, the EFG is a very sensitive observable, which originates from the nonspherical charge distribution surrounding the probe nucleus.…”

Experimental TDPAC and Theoretical DFT Study of Structural, Electronic, and Hyperfine Properties in (111In → )111Cd-Doped SnO2 Semiconductor: Ab Initio Modeling of the Electron-Capture-Decay After-Effects Phenomenon

“…Differently to other proposals that lead to numerical simulations of the R(t) spectrum (see, e.g., Ref. 40), one of the advantages of the BO model consists that it leads to an analytical expression for the perturbation factor that can be used for the spectra fitting. Let´s describe now in more detail the construction of the perturbation factor in the BO model 40 used to analyze the TDPAC results in this work.…”