Crystallographic characterization of U2CrN3: A neutron diffraction and transmission electron microscopy approach

• Published in: Nuclear materials and energy 2023-06, Vol.35, p.101441, Article 101441
• Main Authors: Patnaik, Sobhan, Mishchenko, Yulia, Stansby, Jennifer H., Fazi, Andrea, Peterson, Vanessa K., Jädernäs, Daniel, Thuvander, Mattias, Johnson, Kyle D., Obbard, Edward G., Lopes, Denise A.
• Format: Article
• Language: English
• ISSN: 2352-1791; 2352-1791
• DOI: 10.1016/j.nme.2023.101441

•Neutron diffraction and transmission electron microscopy (TEM) have been implemented to study the crystallographic structure of the ternary phase U2CrN3 from pellet to nano scale respectively.•For the first time, the crystallographic structure of the ordered ternary U2CrN3 phase, stabilized in pellet condition, has been obtained by implementing neutron diffraction.•TEM and selected area electron diffraction rendered nano-level information and revealed the formation mechanism of the ternary phase via nano domains by grain boundary nucleation.•CIF file for the U2CrN3 ternary phase has been created and submitted to be included in the open crystallographic database. In this study, neutron diffraction and transmission electron microscopy (TEM) have been implemented to study the crystallographic structure of the ternary phase U2CrN3 from pellet to nano scale respectively. Recently microstructural evaluation of this ternary phase has been performed for the first time in pellet condition, overcoming the Cr evaporation issue during the conventional sintering process. In this work for the first time, the crystallographic structure of the ordered ternary U2CrN3 phase, stabilized in pellet condition, has been obtained by implementing neutron diffraction. For this study, pellets of the composite material UN with 20 vol% CrN were fabricated by powder metallurgy by mixing UN and CrN powders followed by Spark Plasma Sintering (SPS). TEM was used to investigate the nanoscale structure with a thin lamella of the order of 100–140 nm produced by focused ion beam (FIB). The neutron data revealed the phase composition of the pellet to be primarily 54(8) wt.% U2CrN3, in good agreement with the stoichiometry of starting reagents (UN and CrN powder) and metallographic analysis. Neutron data analysis confirms that all the crystallographic sites in U2CrN3 phase are fully occupied reinforcing the fully stoichiometric composition of this phase, however, the position of the N at the 4i site was found to be closer to the Cr than previously thought. TEM and selected area electron diffraction rendered nano-level information and revealed the presence of nano domains along grain boundaries of UN and U2CrN3, indicating a formation mechanism of the ternary phase, where the phase likely nucleates as nano domains in UN grains from migration of Cr.