Hyperfine Interactions of Sc Impurities in Sapphire

DARRIBA G.N.; RENTERÍA M.

Canberra

Congreso; HFI/NQI2014, 5th Joint Meeting of the 17th International Conference on Hyperfine Interactions & 21th International Symposium on Nuclear Quadrupole Interaction; 2014

HFI/NQI Executive Committee

In this work we present a theoretical study of structural, electronic, and hyperfine properties of a-Al2O3 semiconductor doped with Sc impurities using ab initio Density Functional Theory calculations. In recent years, we have performed similar studies in a-Al2O3 using acceptor or donor impurities, such as Cd and Ta atoms, respectively [1, 2]. These ab initio calculations were compared with Time-Differential γ-γ Perturbed Angular Correlation (PAC) experiments using (111In→)111Cd and (181Hf→)181Ta nuclides as PAC probes.  On the other hand, 44Sc can be used as a non-standard PAC probe using the 44Ti→44Sc decay. In this way, it is interesting to obtain a reliable structural, electronic, and hyperfine theoretical characterization of Sc-doped a-Al2O3 that could be compared with experimental results of 44Sc PAC experiments, now in progress. The ab initio calculations were performed with the Full-Potential Augmented Plane Wave plus Local Orbitals (FP-APW+lo) method using the Wien2K code. We studied different Sc concentrations in order to simulate the isolated impurity condition 44Sc has in PAC experiments. Sc is an isovalent impurity when it replaces the Al atom, nevertheless we performed calculations for different charge states of the impurity. We demonstrate that no magnetic interaction is present at Sc site and therefore a pure quadrupole hyperfine interaction is predicted. The electronic structures and the electric-field gradient are also compared with those obtained for acceptor and donor impurities in a-Al2O3.