We derived revised effective diffusion energy barriers following the Boltzmann distribution assumption for impurity atoms in a bulk material under the impact of various kinds of point defects to reveal the insights of migration mechanisms. The effective diffusion energy barriers of copper impurities in bulk zirconium were calculated through the first principle method under the presented hypothesis. Our results(?E_(||) =1.27 eV, ?E_⊥=1.31 eV) agreed well with the experimental results(?E_(||) =1.54 eV, ?E_⊥=1.60 eV), which validated bulk diffusion as the major mechanism for copper diffusion in zirconium. The effective diffusion energy barriers could be used for estimating whether the defects will accelerate the diffusion or slow them down by acting as traps of the impurity atoms. On the other hand, the first principle results of the impurity diffusion via defects could be further used as inputs of larger scale computational simulations, such as MC(Monte Carlo) or Phase Field calculations.
Based on density function theory(DFT) and the local density approximation(LDA),the formation energy and transition levels of native point defects in LaBr_3 were calculated under Br-rich conditions.From the calculated results,the following conclusions have been obtained:①The dominant defect type is the triply positive lanthanum interstitial under p-type conditions.②The triply negative lanthanum vacancy plays the most important role in n-type LaBr_3.③Neutral and singly positive bromine antisites are more stable in the middle of the band gap.④The singly positive(negative) bromine antisite can be a potential compensation source in n-type(p-type) LaBr_3.⑤All the transition levels in LaBr_3 belong to deep levels.The optimized geometric structures of bromine interstitials and antisites show that there is no formation of Br-Br covalent bond.
SrTi1-xFexO3-δ ceramics were prepared using a traditional solid-state reaction method. From X-ray diffraction(XRD) result, we found that the doped Fe^3+ dissolved in the lattice, and no secondary phase was observed. Cation vacancies in perovskite oxides were identified via positron annihilation lifetime spectroscopy(PALS) measurements. Undoped and Fe-doped SrTiO3 ceramics and single-crystal SrTiO3 were measured by PALS at room temperature. The results show that the main defects in undoped SrTiO3 ceramics are Ti-related defects, and the isolated Ti vacancy lifetime is about 183.4 ps. With the increase of Fe^3+, the concentration of the Ti vacancies decreases accompanied by the appearance of the V^nSr-nV^**O(defect association of Sr vacancies and multiple O vacancies) vacancy defect complexes.
