Effect of particle size on the gamma-ray induced positron annihilation lifetime of CeO

Doshi, Satoru*; Maeda, Kazuki*; Taira, Yoshitaka*; Watanabe, Shinta*; Hirade, Tetsuya  

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 390.81.6 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.