Crystal structure of high-density Fe56 cluster Nd2Fe14B under high pressure

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS

卷:498

Article

Tajiri, Takayuki¹  Mito, Masaki² 

[1] Fukuoka Univ, Fac Sci, Jonan Ku, 8-19-1 Nanakuma, Fukuoka, Fukuoka 8140180, Japan

[2] Kyushu Inst Technol, Grad Sch Engn, Tobata Ku, 1-1 Sensui Cho, Kitakyushu, Fukuoka 8048550, Japan

关键词: Nd2Fe14B;    Crystallographic structure;    X-ray diffraction;    High pressure;    Atomic position;   

DOI  :  10.1016/j.jmmm.2019.166163

来源: Elsevier

【 摘 要 】

Nd2Fe14B is a high-density Fe cluster containing 56 Fe atoms in one unit cell. We investigated the crystallographic structure of an isotropic Nd2Fe14B magnet comprising nanocrystals of a size of similar to 30 nm at pressures up to 2 GPa. The results of X-ray diffraction measurements using Rietveld refinement revealed the displacements of each Fe atomic site in the Fe cluster, Nd, and B atomic sites. The lattice constants, a and c, of tetragonal symmetry decreased proportionally with external pressure, whereas the shrinkage ratio for both a and c changed at approximately 0.5 GPa. However, each atomic position exhibited non-monotonic pressure dependence. The trend of displacement of atomic positions changed at a characteristic pressure of 0.4 +/- 0.1 GPa. When exceeded, most atoms shifted to the direction opposite their displacement at lower pressures. Thus, they exhibited restoration tendencies toward the positions at ambient pressure. The bond angles and bond lengths among Nd, Fe, and B atoms also exhibited characteristic pressure dependences. As pressure increased, the basal triangle of the trigonal prism in the Fe cluster layers distorted up to similar to 0.5 GPa, whereas the strain of the trigonal prism gradually reduced just above 0.5 GPa. The atomic position of the heaviest Nd atoms was a key structural parameter to characterize the change.

【 授权许可】

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