Hexagonal CoSe formation in mechanical alloyed Co75Se25 mixture

A hexagonal CoSe alloy with NiAs-type structure was obtained by mechanical alloying starting from a mixture of pure crystalline powders with nominal composition Co75Se25. X-ray diffraction (XRD), differential scanning calorimetry (DSC), Mössbauer spectroscopy (MS) and Raman scattering (RS) techniques were used to follow the structural, thermal, magnetic and optical properties of the binary mixture as a function of milling time. XRD results show the formation of a nanometric hexagonal CoSe phase between 3 and 70 h of milling coexisting with non-reacted Co phases, also in nanometric scale. DSC and RS results showed some changes in the thermal and optical properties of the crystalline phases when the milling time increases. The Raman active modes of the CoSe and Co oxide phases were observed. MS results showed practically no iron in the samples milled up to 15 h, while for extended milling times (70 h), they showed the presence of some α-Fe and the formation of other iron alloys due to the contamination by the milling media.