Temperature dependence of the crystal structures and phase fractions of secondary phases in a Nd-Fe-B sintered magnet

Naruki Tsuji, Hiroyuki Okazaki, Wakana Ueno, Yoshinori Kotani, David Billington, Akira Yasui, Shogo Kawaguchi, Kunihisa Sugimoto, Kentaro Toyoki, Tomoki Fukagawa, Takeshi Nishiuchi, Yoshihiro Gohda, Satoshi Hirosawa, Kazuhiro Hono, Tetsuya Nakamura

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

The constituent phases of a Nd14.2Fe79.4B6.3Cu0.1 sintered magnet and their crystal structures at ambient and elevated temperatures have been determined by synchrotron X-ray diffraction. At room temperature, dhcp-Nd, NdOx, hcp-Nd2O3, and Nd5Fe18B18 (Nd1.1Fe4B4) secondary phases have been identified in addition to the Nd2Fe14B main phase. The dhcp-Nd phase melts around 600 °C, corresponding to the eutectic temperature for the ternary Nd2Fe14B, Nd and Nd5Fe18B18 system. Below 600 °C, the variation of the lattice constants of the dhcp-Nd phase with temperature is strongly influenced by an internal stress from the spontaneous magnetostriction of the Nd2Fe14B phase. The difference of the lattice constants of the dhcp-Nd phase compared to those of pristine Nd metal is also significant, which is possibly associated with the inclusion of interstitial oxygen atoms at the 4f Wyckoff positions in the dhcp-Nd crystal. The validity of this scenario is confirmed by first-principles calculations of the equilibrium lattice constants of three-, four-, and nine-unit-cell supercells, in which different numbers of oxygen atoms quasi-randomly occupy some of the unoccupied 4f-sites.

Original languageEnglish
Pages (from-to)25-32
Number of pages8
JournalActa Materialia
Volume154
DOIs
Publication statusPublished - 2018 Aug 1
Externally publishedYes

Keywords

  • Crystal structure
  • Intergranular phases
  • Nd-Fe-B sintered magnet
  • Synchrotron X-ray diffraction

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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    Tsuji, N., Okazaki, H., Ueno, W., Kotani, Y., Billington, D., Yasui, A., Kawaguchi, S., Sugimoto, K., Toyoki, K., Fukagawa, T., Nishiuchi, T., Gohda, Y., Hirosawa, S., Hono, K., & Nakamura, T. (2018). Temperature dependence of the crystal structures and phase fractions of secondary phases in a Nd-Fe-B sintered magnet. Acta Materialia, 154, 25-32. https://doi.org/10.1016/j.actamat.2018.05.020