Sintering Formation of Low Temperature Phase MnBi and Its Disordering in Mechanical Milling

摘要

With X-ray diffraction and DSC analysis, it is found that 4 cycles of sintering at 593 K are necessary for the complete production of the low-temperature phase (LTP) MnBi. The c/a of the fabricated LTP MnBi is 1.4286. Metastable phase MnBip formed in primary sintering stage of LTP MnBi has the similar crystal structure and lattice constant with the quenched high-temperature phase (HTP) Mn1.08Bi. The structural differences between MnBip phase and Mn1.08Bi phase are discussed. The LTP MnBi phase is unstable for strong mechanical milling as Bi appears after milling over 7200 s in the present milling condition. Strains caused by the mechanical attrition are difficult to accumulate in the MnBi crystaIs, and the crystal size of the milled MnBi is only 30 nm before the presence of grains coalescence. The whole milling process can be classified into 3 stages indicated by the structural changes. Based on the structural parameter calculation, the changes of atomic configurations in every stage have been discussed. The existence of Bi equivalent vacancy site is considered to play an important role in the disordering processes of Mn and Bi