SINTERING FORMATION OF LOW-TEMPERATURE PHASE MNBI AND ITS DISORDERINGIN MECHANICAL MILLING

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 lo w-temperature phase (LTP) MnBi. The c/a of the fabricated LTP MnBi is 1.4286. Metastable phase MnBip formed in primary sintering stage of LT P MnBi has the similar crystal structure and lattice constant with the quenched high-temperature phase (HTP) Mn1.08Bi. The structural differ ences between MnBip phase and Mn1.08Bi phase are discussed. The LTP Mn Bi 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 cr ystals, and the crystal size of the milled MnBi is only 30 nm before t he presence of grains coalescence. The whole milling process can be cl assified into 3 stages indicated by the structural changes. Based on t he structural parameter calculation, the changes of atomic configurati ons in every stage have been discussed. The existence of Bi equivalent vacancy site is considered to play an important role in the disorderi ng processes of Mn and Bi atoms.