Papers by Keyword: Atomic Defects

Abstract: Research in the field of modern battery materials demands characterization techniques which allow an inspection of atomistic processes during battery charging and discharging. Two powerful tools for this purpose are magnetometry and positron-electron annihilation. The magnetic moment serves as highly sensitive fingerprint for the oxidation state of the transition metal ions, thus enabling to identify the electrochemical ”active” ions. The positron lifetime on the other hand, is sensitive to open volume defects of the size of a few missing atoms down to single vacancies providing an unique insight into lattice defects induced by charging and discharging. An overview will be given on operando magnetometry studies of the important class of LiNiCoMn-oxide cathode materials (so-called NMC with Ni:Co:Mn ratios of 1:1:1 and 3:1:1) as well as of sodium vanadium phosphate cathodes. First operando positron annihilation studies on a battery cathode material (NMC 1:1:1) demonstrate the capability of this technique for battery research.

Abstract: The formation and characteristics of atomic defects in Fe-Al alloys and their influences on order-disorder and vacancy-hardening are investigated and discussed in this paper.

Abstract: Atomistic modeling based on Density Functional Theory (DFT) within the framework of the Generalized Gradient Approximation (GGA) is used to show the effects of defects such as vacancy, boron, carbon, nitrogen and oxygen substituting Fe or Al atoms in the B2-FeAl structure. The site preference of each type of defect is determined from a comparison of total energycalculations using a supercell structure, consisting of 16-atoms, within which each the various defects are introduced. The changes in lattice parameter and bulk modulus associated to the presence of the defects in the FeAl matrix are also studied.