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Doshi, Satoru*; Maeda, Kazuki*; Taira, Yoshitaka*; Watanabe, Shinta*; Hirade, Tetsuya
no journal, ,
It has been reported that oxygen vacancies in cerium oxide (CeO
) affect catalytic activity. There is a need for highly sensitive in-situ measurements of the state and concentration of oxygen vacancies during catalytic reactions, and we are considering using the positron annihilation method. This time, we measured samples with different particle sizes to clarify the sites where positrons are trapped. From the lifetime spectrum of a particle size of 2 nm, which has a high intensity of the long-lived component, we first determined the lifetime value of the longest-lived component to be 390.8
1.6 ps. Next, in the lifetime spectrum of a particle size of 60 nm, where the longest lifetime component is the smallest, the longest lifetime component was fixed at 390.8 ps, and the lifetime value of the other positron trap site was determined to be 199.47.4 ps. These values are close to the lifetimes of positrons trapped in surface and neutral oxygen defects in first-principles calculations.
by using gamma-ray induced positron annihilation lifetime measurementDoshi, Satoru*; Maeda, Kazuki*; Taira, Yoshitaka*; Watanabe, Shinta*; Hirade, Tetsuya
no journal, ,
Gamma-ray-induced positron annihilation lifetime measurement (GiPALS), which utilizes the generation of positrons inside a sample by pair generation with gamma rays, has a significantly smaller background component than conventional measurement methods. It can perform measurements in harsh environments such as high temperature and high pressure because there is no positron source inside the sample. It has been reported that the positron annihilation lifetime spectrum of CeO can be fitted with two components. However, in reality, it is thought that there are at least three components: a component of annihilation in the bulk, a component of annihilation trapped in lattice defects, a component of annihilation trapped on the surface. Therefore, in this study, we tried to fit three components and assigned each by changing the particle size. In addition, we theoretically investigated the bulk, defect, and surface components in the positron annihilation lifetime of CeO using first-principles calculations.