Microstructure and magnetic properties evolution of Al/CoCrFeNi nanocrystalline high-entropy alloy composite

A systematic microstructure-oriented magnetic property investigation for Al/CoCrFeNi nanocrystalline high-entropy alloys composite(nc-HEAC)is presented.In the initial state,the Al/CoCrFeNi nc-HEAC is composed of face-centered cubic(FCC)-Al,FCC-CoCrFeNi and hexagonal close-packed(HCP)-CoNi phases.High energy synchrotron radiation X-ray diffraction and high-resolution transmission electron microscopy were used to reveal the relationship between microstructure evolution and mag-netic mechanism of Al/CoCrFeNi nc-HEAC during heat treatment.At low-temperature annealing stage,the mag-netic properties are mainly contributed by the HCP-CoNi phase.With the increase of temperature,the diffusion-in-duced phase transition process including the transformation of AlCoCrFeNi HEA from FCC to BCC structure and the growth of B2 phase plays a dominant role in the magnetic properties.It was found that the magnetic properties can be effectively regulated through the control of the thermal diffusion process.The nano dual-phase thermal diffusion-induced phase transition behavior of nanocomposites pre-pared based on laser-IGC technology provides guidance for the diffusion process and microstructure evolution of two phases in composites.

Controlled synthesis and optical properties of Ce^(3+)/Tb^(3+) co-doped BaGdF_5 nanocrystals

Based on a hydrothermal method, the Ce3+/Tb3+ co-doped Ba Gd F5 nanocrystals were synthesized by controlling the introduction concentration of Ba2+ and Gd3+. The samples were characterized by X-ray diffraction(XRD), field emission scanning electron microscopy(FESEM) images, photoluminescence(PL) excitation, and emission spectra, as well as the photoluminescence dynamic decay curves. With the increase of the Ba2+ concentration in the synthesis procedure, the positions of diffraction peaks of XRD patterns move toward lower degree, and the case of the samples synthesized with the increase of the Gd3+ concentration is contrary, which consists well with each other. The FE-SEM images suggest that the BaGdF5 nanocrystals are in spherical morphology,and the average diameters decrease with the increase of Ba2+ or Gd3+ concentration. For the 4f–5d transition of Ce3+ is sensitive to the environment of local lattice, the PL excitation and emission spectra of the samples are different. The 4f–4f transition of Tb3+ also presents different optical properties in different host lattices. The variations of the optical properties of Ce3+ and Tb3+ as well as the lifetime of the 5D4+7F5 emission of Tb3+ are also consistent well with each other in the two series of samples.