title: Insights into the Phase Relations in a U-N System Using a Cluster Formula.
abstract: Despite the fact that five kinds of uranium nitrides, i.e., uranium mononitrides (UN, R3̅m and Fm3̅m), a uranium dinitride (UN2, Fm3̅m), and uranium sesquinitrides (α-U2N3, Ia3̅; β-U2N3,P3̅m1), have been confirmed, until now the phase relations are not well understood because of the puzzling nonstoichiometric issue. This work reinvestigated the crystallographic structures of these phases using cluster formula theory. The principal clusters (cuboctahedron with six squares and eight triangles) in these phases were determined. N atoms can occupy either six octahedral sites (square face centers) or eight tetrahedral sites (formed by a center atom and a triangle) in the principal cluster of 13 U atoms, resulting in these diversified phases and the nonstoichiometric issue. Also, phase transformations at certain temperatures and pressures (from CaF2-type UN2to Mn2O3-type U2N3, from Mn2O3-type U2N3to NaCl-type UN, and from NaCl-type UN to HgIn-type UN) were deduced by tracking the bond and angle changes of a simplified cluster [U-U6N6]. This investigation provides an in-depth understanding of the phase relations in a U-N system.
authors.affiliation: Science and Technology on Surface Physics and Chemistry Laboratory , P.O. Box Nos. 9-35, Huafengxincun, Jiangyou City, Sichuan Province 621908, P. R. China.
authors.forename: Xin
authors.identifier: http://orcid.org/0000-0002-0147-9485
authors.initials: X
authors.lastname: Wang
authors.affiliation: Science and Technology on Surface Physics and Chemistry Laboratory , P.O. Box Nos. 9-35, Huafengxincun, Jiangyou City, Sichuan Province 621908, P. R. China.
authors.forename: Rui-Zhi
authors.initials: RZ
authors.lastname: Qiu
authors.affiliation: Science and Technology on Surface Physics and Chemistry Laboratory , P.O. Box Nos. 9-35, Huafengxincun, Jiangyou City, Sichuan Province 621908, P. R. China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Science and Technology on Surface Physics and Chemistry Laboratory , P.O. Box Nos. 9-35, Huafengxincun, Jiangyou City, Sichuan Province 621908, P. R. China.
authors.forename: Li-Zhu
authors.initials: LZ
authors.lastname: Luo
authors.affiliation: Science and Technology on Surface Physics and Chemistry Laboratory , P.O. Box Nos. 9-35, Huafengxincun, Jiangyou City, Sichuan Province 621908, P. R. China.
authors.forename: Yin
authors.initials: Y
authors.lastname: Hu
authors.affiliation: Science and Technology on Surface Physics and Chemistry Laboratory , P.O. Box Nos. 9-35, Huafengxincun, Jiangyou City, Sichuan Province 621908, P. R. China.
authors.forename: Ke-Zhao
authors.initials: KZ
authors.lastname: Liu
authors.affiliation: Science and Technology on Surface Physics and Chemistry Laboratory , P.O. Box Nos. 9-35, Huafengxincun, Jiangyou City, Sichuan Province 621908, P. R. China.
authors.forename: Peng-Cheng
authors.initials: PC
authors.lastname: Zhang