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Choi, N.,Lim, K.R.,Na, Y.S.,Glatzel, U.,Park, J.H. Elsevier 2018 Journal of alloys and compounds Vol.763 No.-
<P><B>Abstract</B></P> <P>The characteristics of non-metallic inclusions (NMI) that precipitated in an equiatomic CoCrFeMnNi high-entropy alloy (HEA) were investigated in order to understand their effect on the mechanical properties of the HEA. As the existence of NMI could degrade the mechanical properties, improved information concerning NMI could hold key importance in controlling the promising applications of HEA. An equiatomic HEA composed of CoCrFeMnNi was manufactured using vacuum induction melting (VIM) method. A thermodynamic computation program (FactSage™7.0) was used to investigate the solidification process of the HEA at both equilibrium and non-equilibrium states. Furthermore, the computational program also predicted the type of inclusions that would precipitate. Through an electrolytic extraction process and scanning electron microscopy - energy dispersive spectroscopy (SEM-EDS) observations, the actual compositions of the precipitated inclusions were observed and classified as (a) Mn-Cr-Al oxide, (b) Mn(S,Se), and (c) mixed type; a Mn-Cr-Al oxide core with a Mn(S,Se) shell. Mn-Cr-Al oxide, in a brittle spinel-structured phase with high melting temperature, was also observed in dimples on the fracture surface. The relationship between the tensile properties of HEA and the characteristics of NMI were discussed by comparing two CoCrFeMnNi specimens with the same structure and composition. Overall, the present results indicate that the tensile properties of the HEA were significantly degraded as the area fraction (AF) and number density (ND) of NMI increased.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Qualitative and quantitative characterization of non-metallic particles in HEA was performed. </LI> <LI> Effect of impurity on non-metallic particle in HEA was thermodynamically simulated. </LI> <LI> Fracture mechanics of HEA with crack initiation under load condition was revealed. </LI> <LI> Importance of manufacturing (impurity, casting) conditions of HEA was highlighted. </LI> <LI> Necessity of refining non-metallic particles in HEA was highlighted. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Agrestini, S.,Kuo, C.-Y.,Moretti Sala, M.,Hu, Z.,Kasinathan, D.,Ko, K.-T.,Glatzel, P.,Rossi, M.,Cafun, J.-D.,Kvashnina, K. O.,Matsumoto, A.,Takayama, T.,Takagi, H.,Tjeng, L. H.,Haverkort, M. W. American Physical Society 2017 Physical review. B Vol.95 No.20
<P>We have investigated the electronic structure of Sr2IrO4 using core-to-core resonant inelastic x-ray scattering. The experimental spectra can be well reproduced using ab initio density functional theory based multiplet ligand field theory calculations, thereby validating these calculations. We found that the low-energy, effective Ir t(2g) orbitals are practically degenerate in their crystal-field energy. We uncovered that Sr2IrO4 and iridates in general are negative charge transfer systems with large covalency and a substantial oxygen ligand hole character in the Ir t(2g) Wannier orbitals. This has far reaching consequences, as not only the on-site crystal-field energies are determined by the long-range crystal structure, but, more significantly, magnetic exchange interactions will have long-range distance dependent anisotropies in the spin direction. These findings set constraints and show pathways for the design of d(5) materials that can host compasslike magnetic interactions.</P>