Dependence of the crystal structure of the Nd-rich phase on oxygen content in an Nd–Fe–B sintered magnet

The crystal structures and composition of the intergranular Nd-rich phase were investigated in a ternary Nd–Fe–B sintered magnet by transmission electron microscopy. The O and Nd contents of the Nd-rich phase of various crystal structures varied greatly, whereas the Fe content was virtually unchanged. The crystal structure of the Nd-rich phase mainly depends on its O content. As the O content increases, the structures of the Nd-rich phase change as follows: double close-packed hexagonal → face-centered cubic → close-packed hexagonal. The corresponding O content of each structure is determined.