TDPAC study of a solid-state reaction doping process of 181Hf(→181Ta) impurities in the Ho2O3 semiconductor

D. RICHARD, E.L. MUÑOZ, G.N. DARRIBA, L.A. ERRICO, AND M. RENTERÍA

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Conferencia; HFI/NQI2010, 15th International Conference on Hyperfine Interactions & 19th International Symposium on Nuclear Quadrupole Interaction; 2010

Executive Committee del 3th HFI/NQI International Conference

Nuclear methods and, in particular, the time-differential perturbed-angularcorrelation (TDPAC) spectroscopy have been extensively applied to study materials toelucidate at a subnanoscopic scale the environment of impurities or constituent atomsof solids (see, e.g., Ref. 1). In the case of TDPAC, a suitable probe isotope,generally an impurity in the system under study, is used and the informationprovided, at this probe site, is given as a product of a nuclear and an extra nuclearquantity. In the case of electric-quadrupole interactions, the nuclear quantity isthe nuclear quadrupole moment (Q), characteristic of a given nuclear state, whichinteracts with the electric-field gradient (EFG) acting on the site of the probeatom. Since the EFG mostly originates in the non-spherical electronic charge densityclose to the impurity nucleus, the TDPAC technique can be used as a powerful tool inorder to study the electronic structure (and related structural, electronic ormagnetic properties) in the close neighborhood of the probe. The probe can beintroduced in the host material by different methods: thermal diffusion, chemicalmethods, neutron activation, or ionic implantation. In this work we study analternative doping method: ball-milling-assisted solid-state reaction betweenneutron-activated m-HfO2 and the system under study (in the present case, thebixbyite Ho2O3). In order to follow the doping process of 181Hf donor impurities inthe semiconductor Ho2O3 and to elucidate the effect of each variable involved in theprocess (milling time, temperature, ball to powder ratio, etc.), TDPAC experimentswere carried out after each step of the doping process. The obtained hyperfineparameters were compared to those of m-HfO2, to those expected for Ho2O3 using a wellestablished EFG systematics for 181Ta in bixbyte sesquioxides, and to TDPAC resultsobtained in Ho2O3 samples doped by ion implantation of 181Hf-->181Ta). As we willshow, we can determine the effect played by the milling and the thermal treatments,showing the capability of the TDPAC technique to follow the doping process and togive information about the inter-diffusion processes. We also demonstrate theexcellent efficiency of the ball-milling-assisted solid-state reaction process tolocate Hf donor impurities at the defect-free cationic sites of the Ho2O3semiconductor, quantifying directly the amount of impurities doped after each step of the process.References[1] L.A. Errico, G. Fabricius, M. Rentería, P. de la Presa, M. Forker, Phys. Rev.Lett. 89 (2002) 55503; L.A. Errico, G. Fabricius, M. Rentería, Phys. Rev. B 67(2003) 144104, and references therein.