TY - JOUR
T1 - Temperature dependence of the crystal structures and phase fractions of secondary phases in a Nd-Fe-B sintered magnet
AU - Tsuji, Naruki
AU - Okazaki, Hiroyuki
AU - Ueno, Wakana
AU - Kotani, Yoshinori
AU - Billington, David
AU - Yasui, Akira
AU - Kawaguchi, Shogo
AU - Sugimoto, Kunihisa
AU - Toyoki, Kentaro
AU - Fukagawa, Tomoki
AU - Nishiuchi, Takeshi
AU - Gohda, Yoshihiro
AU - Hirosawa, Satoshi
AU - Hono, Kazuhiro
AU - Nakamura, Tetsuya
N1 - Funding Information:
We thank M. Takata and A. Fujiwara for providing useful comments in synchrotron studies, and J. Kim for experimental support. This work has been performed with the approval of the SPring-8 Program Advisory Committee (Proposal No. 2011B1333 , 2013A1011 , 2013A1894 , 2013B1012 , 2014A1017 , 2014B1009 , 2015A1225 , and 2015A1007 ). Elements Strategy Initiative Center for Magnetic Materials (ESICMM) is funded by MEXT . N.T. and H.O. contributed equally to this work.
Publisher Copyright:
© 2018 Acta Materialia Inc.
PY - 2018/8/1
Y1 - 2018/8/1
N2 - 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.
AB - 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.
KW - Crystal structure
KW - Intergranular phases
KW - Nd-Fe-B sintered magnet
KW - Synchrotron X-ray diffraction
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U2 - 10.1016/j.actamat.2018.05.020
DO - 10.1016/j.actamat.2018.05.020
M3 - Article
AN - SCOPUS:85047259395
SN - 1359-6454
VL - 154
SP - 25
EP - 32
JO - Acta Materialia
JF - Acta Materialia
ER -