Study of nitrogenation of a NdFe12xMox compound by in situ neutron powder211 diffraction

摘要

The effects on the crystal lattice of a NdFe(sub 12(minus)x)Mo(sub x)(x (approx211u001eequal) 1.7) compound which contained (approximately)12 vol% of bcc-Fe were 211u001estudied by neutron powder diffraction during controlled nitrogenation over the 25-211u001e600 C temperature range. The sample inside the furnace was connected to a closed 211u001evolume of ultra-pure nitrogen gas while neutron data were collected over regular 211u001etime intervals during sequential heating. Substantial nitrogen absorption 211u001eoccurred between 500 to 600 C. During the nitrogenation process the NdFe(sub 211u001e12(minus)x)Mo(sub x)N(sub y) lattice expanded while the bcc-Fe lattice 211u001econtracted. An increasing decomposition of the compound into bcc-Fe at 600 C was 211u001eobserved. The average size of the NdFe(sub 12(minus)x)Mo(sub x)N(sub y) 211u001ecrystalline grains decreased starting at (approximately)300 C, reaching a minimum 211u001eat (approximately)500 C and then increased markedly at higher temperatures. The 211u001edevelopment of lattice strains, on the other hand, showed an opposite trend, 211u001ei.e., a maximum at 500 C. A correlation of structural modification of the 211u001ecrystalline phases and the nitrogenation process is discussed.