R. Bensalem

Structural study of the mechanically alloyed Fe-P

Elemental Fe and red phosphorus powders with a composition close to Fe-xP (x = 10, 15 and 20 wt. %) were mechanically alloyed in a planetary ball mill under an argon atmosphere. Structural changes were studied by X-ray diffraction. The complete dissolution of the elemental powders is achieved within 3 h of milling. Detailed analysis of the X-ray diffraction patterns reveal the formation of a Fe(P) solid solution with two structures (α-Fe1 and α-Fe2) having different lattice parameters, crystallite size and microstrains in addition to FeP, Fe2P and Fe3P phosphides. The structural parameters and phase percentages are P content dependent.

Structural characterisation of the mechanically alloyed Fe57Co21Nb7B15 powders

X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to investigate the phase identification and the thermal behaviour of the mechanically alloyed Fe57Co21Nb7B15 powders. The diffusion of B into the Nb lattice leads, after 1 h of milling, to the formation of a bcc Nb(B) solid solution with a lattice parameter close to a = 0.3425 nm. The solid state reaction between Fe and B gives rise to the formation of Fe23B6 and Fe2B boride phases after 3 and 6 h of milling, respectively. On further milling (96 h), an amorphous matrix (∼80%), where nanocrystalline bcc α-Fe, bcc Nb(B), Fe2B and Fe3B phases were embedded, is obtained. The broad exothermic reaction in the DSC scans consists of several exothermic peaks and spreads over the entire temperature range 100-700°C. The enthalpy release at temperatures below 300°C can be attributed to recovery and strain relaxation. Crystallisation and grain growth are the dominating processes at high temperatures.

Solid state amorphisation of mechanically alloyed Fe-Co-Nb-B alloys

Fe 61 Co 21 Nb 3 B 15 powder mixture was prepared by mechanical alloying process in a high energy planetary ball mill. Structural and thermal changes of the milled powders were followed by X-ray diffraction (XRD), Mossbauer spectrometry and differential scanning calorimetry (DSC). Both XRD and Mossbauer spectrometry results reveal the formation, after 48 h of milling, of a highly disordered amorphous-like structure where nanometer-sized iron borides were embedded. A mechanical recrystallisation process gives rise to the formation of α-Fe and α-FeCo nanograins on further milling. The occurrence of structural disorder in the milled powders might be confirmed by broad exothermic reaction in the DSC scans which consists of several overlapping exothermic peaks. Such behaviour originates from recovery, strain relaxation, grain growth and crystallisation.

Microstructural properties of Fe-doped ZnO thin films and first-principals calculations

Microstructural, and morphological properties of Fe-doped nanostructured ZnO semiconducting thin films have been investigated by optical, SEM, XRD, and first-principals computing. ZnO thin films grown on glass and Si substrates by the spray pyrolysis method at 300°C, and under ambient atmosphere, have initial preferred (002) orientation. XRD peak intensity changed rapidly as the Fe-concentration is increased from 1 to 5 mol.%, despite the fact that lattice parameters changed monotonously. Fe ions occupied the Zn sites without changing the original hexagonal wurtzite structure. All Fe-doped ZnO films are polycrystalline with an average grain size of 23 nm. Band structure and density of states of the possible phases of crystal ZnO computed using first principal methods, confirmed that pure ZnO is a direct band gap semiconductor when obtained in the B3 or B4 type structure phase. However, the B1 phase turned out to be an indirect band gap semiconductor.

Structural, microstructural and magnetic properties of 1% Fe-doped ZnO powder nanostructures prepared by mechanical alloying

ZnO powder nanoparticles were doped with iron (mixing produced by mechanical alloying). Their structure, microstructure and magnetic properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). ZnO starting pure powder exhibits a hexagonal crystal structure with space group P63mc. Otherwise, with the addition of 1% Fe in the ZnO milled powder, the hexagonal ZnO phase remained unchanged, whereas the microstructural parameters were subject to significant variations due to the introduction of Fe atoms into the ZnO hexagonal matrix to replace oxygen ones. The size of crystallites and microstrains were milling time-dependent.