Powder X-ray diffraction experiments under pressure up to ∼10 GPa were performed on tetragonal CeFeSi-type RMnSi (R = La, Ce, Pr, Nd). A structural phase transition was observed in CeMnSi at a critical pressure of Ps∼ 5.7 GPa. In contrast, LaMnSi, PrMnSi, and NdMnSi do not exhibit any structural transitions within the same pressure range. The lattice parameter ratio c/a of CeMnSi decreases rapidly as pressure approaches Ps, whereas the c/a ratios of the other RMnSi increase monotonically with pressure. CeMnSi also shows a relatively small bulk modulus: B0∼ 41.4(4) GPa in the 0--2 GPa range and B0∼ 32.8(2) GPa in the 4--5 GPa range, suggesting valence instability under pressure. The structural transition in CeMnSi is attributed to the pressure-induced decrease in c/a and its low bulk modulus. Above Ps, the X-ray diffraction pattern indicates a transition to a monoclinic structure with space group No. 11, P21/m. These findings highlight the unique pressure response of CeMnSi and provide insight into the coupling between lattice and electronic degrees of freedom in Ce-based intermetallic systems.
@article{arxiv.2509.07210,
title = {Structural Phase Transition in CeMnSi under Pressure and Comparative Structural Properties of $R$MnSi ($R$ = La, Ce, Pr, Nd)},
author = {Yukihiro Kawamura and Sae Nishiyama and Jun-ichi Hayashi and Keiki Takeda and Chihiro Sekine and Hiroshi Tanida},
journal= {arXiv preprint arXiv:2509.07210},
year = {2025}
}