Quantification of the crystallographic anisotropy and thermal dependence of Tb diffusion coefficients in the Nd2Fe14B phase through single-crystal diffusion couples
Abstract
Core–shell microstructures in Nd-HREE-Fe-B magnets have been shown to enhance coercivity while reducing the required content of heavy rare-earth elements (HREE). However, the mechanisms governing shell formation remain poorly understood, and key physical parameters are still lacking.The study's primary focus was the anisotropic diffusion of Tb in the τ1 phase. This was conducted using single-crystal diffusion couples. The composition of these samples was characterized at the diffusion interfaces for various Tb concentration gradients and crystal alignments using energy-dispersive X-ray spectroscopy (EDS) with high spatial resolution.At the initial stages of diffusion treatments, as observed for most diffusion couples, a liquid film is formed at the interface between crystals and migrates. A migration zone has been observed to form epitaxially behind the advancing liquid film on one of the crystals. The interface between this zone and the underlying crystal is well-suited for investigating the crystallographic anisotropy of diffusion. This finding was validated through measurements obtained from diffusion couples, in the absence of liquid film formation at the interface.The composition profiles obtained along this interface were used to determine diffusion coefficients as a function of both temperature and crystallographic orientation. The activation energy for Tb diffusion was determined to be 210 ± 30 kJ mol−1 perpendicular to the c-axis and 360 ± 20 kJ mol−1 along the c-axis. An examination of the data reveals no discernible correlation between the diffusion coefficient and the local Tb concentration. This observation suggests that the measured anisotropy is predominantly attributable to crystallographic effects rather than compositional variations.
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BibTeX
@article{mouron2026quantification,
title = {{Quantification of the crystallographic anisotropy and thermal dependence of Tb diffusion coefficients in the Nd2Fe14B phase through single-crystal diffusion couples}},
author = {Raphaël Mouron and Cyril Rado and Eric Robin},
journal = {Journal of Alloys and Compounds},
year = {2026},
month = sep,
doi = {10.1016/j.jallcom.2026.190790},
url = {https://cea.hal.science/cea-05739353v1},
note = {CC BY},
}
RIS
TY - JOUR
TI - Quantification of the crystallographic anisotropy and thermal dependence of Tb diffusion coefficients in the Nd2Fe14B phase through single-crystal diffusion couples
AU - Raphaël Mouron
AU - Cyril Rado
AU - Eric Robin
PY - 2026
DA - 2026/09/04
JO - Journal of Alloys and Compounds
DO - 10.1016/j.jallcom.2026.190790
UR - https://cea.hal.science/cea-05739353v1
AB - Core–shell microstructures in Nd-HREE-Fe-B magnets have been shown to enhance coercivity while reducing the required content of heavy rare-earth elements (HREE). However, the mechanisms governing shell formation remain poorly understood, and key physical parameters are still lacking.The study's primary focus was the anisotropic diffusion of Tb in the τ1 phase. This was conducted using single-crystal diffusion couples. The composition of these samples was characterized at the diffusion interfaces for various Tb concentration gradients and crystal alignments using energy-dispersive X-ray spectroscopy (EDS) with high spatial resolution.At the initial stages of diffusion treatments, as observed for most diffusion couples, a liquid film is formed at the interface between crystals and migrates. A migration zone has been observed to form epitaxially behind the advancing liquid film on one of the crystals. The interface between this zone and the underlying crystal is well-suited for investigating the crystallographic anisotropy of diffusion. This finding was validated through measurements obtained from diffusion couples, in the absence of liquid film formation at the interface.The composition profiles obtained along this interface were used to determine diffusion coefficients as a function of both temperature and crystallographic orientation. The activation energy for Tb diffusion was determined to be 210 ± 30 kJ mol−1 perpendicular to the c-axis and 360 ± 20 kJ mol−1 along the c-axis. An examination of the data reveals no discernible correlation between the diffusion coefficient and the local Tb concentration. This observation suggests that the measured anisotropy is predominantly attributable to crystallographic effects rather than compositional variations.
SN - 0925-8388
ER -