A Model for α-Al(Mn,Fe)Si Crystals

Abstract

A series of large crystals of α-Al(Mn,Fe)Si with different content of manganese, iron and silicon have been analyzed using microprobe, X-ray diffraction, pycnometer (density) and electrical devices (electrical resistivity and Seebeck coefficient). The cubic phase α-Al(Mn,Fe)Si had a density varying from 3520 to 3620 kg/m3. When iron was increased from 1.9 to 20.8 wt%, the content of silicon was reduced from 10.7 wt% to 8.6 wt%. The phase had a low electrical resistivity, 2 × 10−6 Ωm. Large crystals of α-AlMnSi had a large Seebeck coefficient, viz. 42 µV/K, the crystal containing some iron gave a slightly lower value, 34 µV/K. All the crystals were n-type semiconductors. A new model for α-AlMnSi has been proposed, where Si-atoms are connected in hexagonal rings around 0,0,0 and ½,½,½. The rings are linked by Mn and Si atoms, all covalently bonded. According to this model, the ideal α-AlMnSi crystals have 24 Mn, 18 Si and 96 Al-atoms in the unit cell. Fe + Al can substitute for Mn + Si atoms in the unit cell. Vacancies can form on Mn-sites.