Study of hyperfine interactions in pure and Mn-doped CeO2 nanoparticles by perturbed gamma-gamma angular perturbed spectroscopy using 111Cd and 140Ce as nuclei probe

Full text: Cerium dioxide (CeO2) or ceria has played a crucial role in scientific research due to its extreme importance for the high-technology industry, so it has been widely studied and applied in various applications such as in automotive industry, medicine, oxygen sensors, protectors of the radiation and so on. A special case of our interest is that ceria is a good candidate to substitute SiO2 at electronic devices. In this work, a nuclear technique called Perturbed gamma-gamma Angular Correlation (PAC) was used to measure hyperfine interactions in nanostructured insulating CeO2 oxide doped with 3d transition metals that present magnetic moment. Ceria was doped with around 5 at. % Manganese (Mn), which introduce spin property for the charge carriers. It is important to remark that PAC spectroscopy uses a nuclear probe, which decays in gamma-gamma ray cascade. Here it was used 140La (140Ce) which decays through the gamma cascade 329-487 keV and 111In (111Cd) (171-245 keV) probe, both nuclear properties of the intermediate level are well known. 111Cd: t1/2 = 84.5 ns, quadrupolar moment (Q) is 0.83 b and dipolar moment μ 0.76 μN. And 140Ce: t1/2 = 3.4 ns, Q = 0.3 b and μ = 4.68 μN. Doped ceria samples were prepared by the Pechini sol-gel method from pure Ce and Mn elements. In this methodology metallic Ce and Mn are separately dissolved in nitric acid and then mixed. The obtained gel is then heated in air in a muffle furnace at 380 deg C during 10h. Radioactive probe nuclei 140La (140Ce) or 111In (111Cd) were introduced during the sample preparation. The obtained pure and doped CeO2 were annealed at 1100 deg C for 5h in N2. The PAC measurements were carried out in the temperature range from 15 K to 1175 K with a conventional slow-fast coincidence set-up with four conical Baf2 detectors. A small tubular furnace was used for heating the sample while a cryogenic system was used to cool. A comparative analysis was made for two probes nuclei used which showed that to both nuclei PAC spectroscopy is a good technique to investigate hyperfine parameters as electric field gradient (EFG) and magnetic field which are respectively characterized by quadrupole frequency and Larmor frequency. (author)