Anion Species Dependence of Local Structures Appearing in RuPn Investigated by 3D-ΔPDF Analysis

In RuP and RuAs with MnP-type structures, it is known that Ru atoms share 3d electrons at low temperatures to form linear Ru₃ trimer^1,2. Such trimer formation phenomena have been observed in many material systems, and in the average structure of the high-temperature phase, the trimers typically disappear and transform into a regular lattice. However, recent studies investigating local structures using 3D-ΔPDF analysis³ revealed that Ru₃ molecules exist locally even at high temperatures in RuP.

In this study, we implemented the 3D-ΔPDF analysis method at BL02B1 of SPring-8, Japan's synchrotron radiation facility, to investigate the local structure of RuP and its analog RuAs. The analysis revealed that, similar to RuP, Ru₃ molecules locally survive at high temperatures in RuAs. However, unlike RuP³, where weak interactions between Ru₃ trimers were reported, correlations were observed between distant Ru₃ trimers in RuAs. This suggests that differences in anion species influence the short-range ordered structure in the high-temperature phase.

1. D. Hirai et al., J. Am. Chem. Soc. 144, 17857 (2022).

2. H. Kotegawa et al., Phys. Rev. Mater. 2, 055001 (2018).

3. R. J. Koch et al., Phys. Rev. B 106, 214516 (2022).