In situ TEM study of Nd-rich phase in NdFeB magnet

Hot stage in transmission electron microscope has been used to study the structure and stability of Nd-rich phase in NdFeB magnet. The present observation shows that the so-called complex cubic phase is in fact the prototype of Mn2O3 (space group Ia3¯) with lattice parameter of a=1.08nm. The Nd-rich phase with P3¯m1 structure (h-Nd2O3) was first observed to be transformed from the BCC phase after in situ heating over 400 °C. The orientation relationship between these two structures satisfies as follows: (0 0 0 1)HCP//(2 0 0)BCC, (101¯0)HCP//(020)BCC, [1¯21¯0]HCP//[001]BCC. It is argued that the h-Nd2O3 was arising from the oxidation of the BCC Nd-rich phase rather than from Nd2Fel4B matrix phase as suggested in the literature.