Formation of Al-doped Iron Silicides by Ball Milling

S. M. COTES; M. TAYLOR; J. MARTÍNEZ; J. RUNCO; J. DESIMONI

Rio de Janeiro Brasil

Conferencia; 10th Latin American Conference on Applications of the Mössbauer Effect (LACAME '2006); 2006

CBPF-Brasil

Phases obtained in the Fe-Si system are extremely depending on the experimental conditions of synthesis. Non-equilibrium processing techniques like mechanical alloying allow the formation of stable and metastable phases at room temperature. Among the nine known types of iron silicides, the semiconducting b-FeSi2 disilicide has attracting the attention of the researchers in the last recent years due to its technological potential applications in the field of optoelectronic and as a material for thermoelectric conversion. Doping with Al atoms makes the semiconducting b-FeSi2 disilicide to become n-type semiconductor and consequently some interesting fundamental issues arise. This facts are related to the occurrence of metastable phases and to the impurity location at the two non-equivalent Fe site of the b-FeSi2 lattice structure. In this frame, a study of the sequence of phase formation of stoichiometric Fe1-xAlxSi2 (0.03 £  x £ 0.50) mixtures prepared by mechanical alloying from elemental Fe, Al and Si powders is presented. The milling process was performed at room temperature in Ar atmosphere in a horizontal mill device during 15 h. Mössbauer Spectroscopy and X-ray diffraction were used to identify the phases produced during sample preparation and to follow the relative fraction of the obtained phases as Al concentration is increased. The diffractograms and the Mössbauer patterns are characterized by broad lines indicating the formation of different disordered iron silicides. The observed phase could be associated with stable and metastable room temperature phases like b-FeSi2, a-FeSi2 and e-FeSi. No traces of the pure elements were detected. The present results are compared with those obtained on Pt and Mn doped b-FeSi2 prepared by the same method, where chemical driving forces predominate over the diffusion process.