Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Nanostructured Ferritic Alloys (NFA) are considered as promising candidates for the structural materials of future fusion and fission reactors [1]. They consist of a ferritic or ferritic/martensitic Fe-Cr matrix with a high dispersion of nanometer size yttria-based oxide particles. In this research project (started in November 2016) the nature of nanometer-size yttria-based oxide clusters in a bcc Fe matrix are investigated by DFT calculations. The main goal of these studies is the better understanding of the nucleation as well as the structure and composition of the nanoclusters.
The investigations shall clarify the conditions for the formation of nonstoichiometric clusters that are coherent with the bcc lattice and for the formation of oxide phases (in particular Y2O3 and Y2Ti2O7). Three models are considered: (i) clusters consisting of Y, Ti atoms on bcc lattice sites and O on octahedral site [2-4], termed as On-Lattice (OL) model, (ii) cluster consisting of parts of the bixbyite (Y2O3) or pyrochlore (Y2Ti2O7) structure embedded in bcc Fe [5] termed as Structure Matching (SM) model, and (iii) substituting O also on Fe site, termed as OFe model. In all cases vacancies are introduced into the simulation cell in order to provide additional volume for O atoms. We studied clusters of different sizes in the framework of the three models. Our results show that all three models lead to almost the same energy for considered cluster configurations. This revises the statement of Barnard et al. [5] who claimed that clusters with SM configuration are generally favored energetically.
[1] G. R. Odette, JOM-J. Min. Met. Mat. S. 66, 2427 (2014)
[2] D. Murali, B.K. Panigrahi, M.C. Valsakumar, S. Chandra, C.S. Sundar, B. Raj, J. Nucl. Mater. 403,
113 (2010)
[3] A. Claisse, P. Olsson, Nucl. Instr. Meth. B 303, 18 (2013)
[4] M. Posselt, D. Murali, B. K. Panigrahi, Model. Simul. Mater. Sc. 22, 085003 (2014)
[5] L. Barnard, G. R. Odette, I. Szlufarska, D. Morgan. Acta Mater. 60 (2012) 935 (2012)