Unveiling the anomalous atomic stacking and formation mechanism of 1:3R Z-plates in Sm2Co17-type magnets

• Published in: Journal of alloys and compounds 2023-02, Vol.934, p.167890, Article 167890
• Main Authors: Zhang, Yong, Wu, Pengfei, Lu, Yu, Cao, Xun, Huang, Yizhong, Gill, Vincent, Li, Zhiming
• Format: Article
• Language: English
• Subjects: Atomic stacking; Permanent magnets; Precipitation; Sm-Co alloys; TEM
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2022.167890

Sm2Co17-type permanent magnets are the favorable choice for applications above 200 °C. Their performance can be enhanced by Zr alloying, mainly due to the formation of Zr-rich 1:3R Z-plates. Herein, the atomic-scale structures of the Z-plates in an 1.7 at% Zr alloyed Sm2Co17-type magnet are unveiled using aberration-corrected STEM. Zr is observed to preferably replace the dumbbell Sm to form (Sm1/3Zr2/3)Co3 Z-plates, which have a number density of 37.6 µm−1 along c-axis. The Z-plate with thickness of the reported one-unit cell is rarely seen, instead several anomalously stacked types are detected. Most of the Z-plates have a two-third stacking (2/3-stacked) of one-unit cell, some of them are lacking one Sm+Co layer while others have additional Sm+Co layers. Totally four types of single 2/3-stacked Z-plates are identified, acting as the basic units for thick Z-plates. A few Z-plates (number density 2.73 µm−1) have thickness of more than double 2/3-stacking, which deteriorate the oxidation-resistance of the magnet. Further, by analyzing the end regions of Z-plates, the diffusion-controlled mechanisms for the phase transformation from the 2:17R matrix to the 1:3R Z-plates are unraveled. [Display omitted] •Most of the 1:3R Z-plates have a two-thirds stacking (2/3-stacked) of one-unit cell.•Four types of single 2/3-stacked Z-plates are identified and they act as the basic units for thick 1:3R.•The Z-plates with thickness > 5 nm are found to deteriorate the oxidation-resistance of the magnet.•1:3R is formed via the diffusion-controlled phase transformation from 2:17R.