On the formation of pure and Pt-doped iron silicides using ball milling

Abstract

The sequence of phase formations for elemental powders of stoichiometric FeSi2 and Fe1-xPtxSi2 (0.03⩽x⩽0.50) mixtures prepared by mechanical alloying at room temperature in an Ar atmosphere in a horizontal mill is presented. Sample evolution was followed by means of Mössbauer spectroscopy and x-ray diffraction. After the milling, the results indicate the formation of different disordered iron silicides, depending on milling time. The kinetics of iron silicide formation was also studied; a diffusion-controlled process with decreasing nucleation rate was found. In the case of Pt-doped samples, the segregation of Pt silicides was observed even for the smallest concentration, and no noticeable incorporation of Pt into the β-FeSi2 lattice could be inferred. Samples were also subjected to annealing at 1123 K for 4 h to produce ordering in the structures.

Phase stabilization in the Fe1−xMnxSi2 system induced by ball milling

“…3(a)). All these results agreed with the previous ones obtained on Pt doped bFeSi 2 milled in similar conditions [13]. The relative fraction of interaction I 3 remained lower than 10% in A-type samples while a higher contribution was observed in B-type samples.…”

“…Non-equilibrium preparation methods, like mechanical alloying, allow the formation of compounds and metastable phases which are not accessible by conventional techniques. For instance, when mechanical alloying is used to prepare Pt-doped iron silicides from the pure elements [13], the segregation of Pt silicides and Si was observed together with the formation of a lower amount of stoichiometry iron silicides, then suggesting that chemical driving forces dominate the process. It is interesting to find alternative routes of sample preparation to avoid the presence of such undesirable phases, when formation heat of silicides is highly negative.…”

Formation of Mn-doped iron silicides by ball milling

“…In agreement with previous results obtained on Pt doped β-FeSi 2 milled under the same conditions [5], the main contribution to the spectra comes from the ɛ-FeSi phase (I 1 , see Table 1). The isomer shift of the second interaction (I 2 ) is close to the average value of the isomer shift of both Fe sites of the β-FeSi 2 phase [4].…”

The effect of Mn and Al dopants on the β-FeSi2 stabilization by a two-step route: Mechanical alloying and annealing

“…For such applications, controlling the electrical conductivity of the system is critical, and the semiconductor needs to be doped to form either n-or p-type ␤-FeSi 2 . Additives like Pt [1,2], Mn [3][4][5] and Al [6][7][8] turn the material into a p-type semiconductor.…”

“…Moreover, it is well known that phases obtained in the Fe-Si system are extremely depending on the synthesis conditions. As an example, an admixture of highly disordered ␤-FeSi 2 , ␣-FeSi 2 and -FeSi phases is obtained after ball-milling together with segregated Si, Fe, atomic dopant and dopant silicide [2,4,9]. Even ordered doped iron disilicides are obtained after a subsequent annealing, phase segregation often occurs giving rise to a multiphase sample [2,4,[9][10][11][12][13][14][15].…”