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• Electron, X-ray and neutron scattering reviled that gas atomized AlCoCrFeNi crystallizes in a single phase B2 structure. • In the B2 structure, Co and Ni occupies the (0 0 0) site, with Al and Fe in (½ ½ ½), established for the first time. • B2 phase partly decomposes into fcc and σ phases upon thermal treatment, the onset is highly dependent on the heating rate. • σ phase forms at particle surfaces, giving larger amount of σ phase in powders with a smaller particle size distribution. • Pre-annealing can be utilized to design the microstructure of the sintered components, and reduce the amount of σ phase. [Display omitted] In this study, the crystal structure and phase stability of gas atomized equiatomic AlCoCrFeNi powder was investigated. This alloy is usually described as a high entropy alloy forming a solid solution phase stabilized by a high mixing entropy. However, thermodynamic calculations show that the high entropy phase is stable only at very high temperatures close to the melting point and that a mixture of several phases are the most stable state at lower temperatures. This suggest that kinetic effects may influence the phase composition of atomized powder. The unique features of X-ray diffraction, neutron diffraction as well as transmission electron microscopy were used to study the atomic structure of the atomized powder in detail. The results show that the powder crystallises in an ordered B2 (CsCl-type) structure with a preferred site occupation of Al and Fe on the (½ ½ ½) position and Co and Ni on the (0 0 0) position. During heat-treatment of the powder, the B2 phase decomposes into fcc and σ phases and the final phase composition is highly dependent on the heating rate. The effect of heat-treatment on the atomized powder was also investigated and revealed a significant phase transformation with e.g. the formation of σ phase preferably at the surface of the powder particles. The phase content was also dependent on the size fraction of the powder particles. Sintering of green bodies made with different heat cycles showed that the phase composition of the starting material had a significant impact on the final phase composition and microstructure of the sintered components. The results illustrate the importance of well-defined powder materials for powder consolidation, especially additive manufacturing (binder jetting) of high entropy alloys. [ABSTRACT FROM AUTHOR]

Abstract: This paper introduces a new cell design for the construction of lithium ion batteries with conventional electrochemical performance whilst allowing in situ neutron diffraction measurement. A cell comprising of a wound cathode, electrolyte and anode stack has been prepared. The conventional hydrogen-containing components of the cell have been replaced by hydrogen-free equivalents. The electrodes are fabricated using a PTFE binder, the electrolyte consists of deuterated solvents which are supported in a quartz glass fibre separator. Typical battery performance is reported using the hydrogen-free components with a specific capacity of 140 mA h g−1 being observed for LiFePO4 at a rate of 0.2 C. Neutron diffraction patterns of full cells were recorded with phase change reactions monitored. When aluminium packaging was used a better signal to noise ratio was obtained. The obtained atomic positions and lattice parameters for all cells investigated were found to be consistent with parameters refined from the diffraction pattern of a powder of the pure electrode material. This paper highlights the pertinent points in designing cells for these measurements and addresses some of the problems. [Copyright &y& Elsevier]

Entropy stabilised materials have possibilities for tailoring functionalities to overcome challenges in materials science. The concept of configurational entropy can also be applied to metal oxides, but it is unclear whether these could be considered as solid solutions in the case of perovskite-structured oxides and if the configurational entropy plays a stabilising role. In this study, compositionally complex perovskite oxides, LnMO 3 (Ln ​= ​La, Nd, Sm, Ca and Sr, M ​= ​Ti, Cr, Mn, Fe, Co, Ni, and Cu), are investigated for their phase stability and magnetic behaviour. Phase-pure samples were synthesised, and the room temperature structures were found to crystallise in either Pnma or R 3 ¯ c space groups, depending on the composition and the resulting tolerance factor, while the structural transition temperatures correlate with the pseudo cubic unit cell volume. The techniques used included diffraction with X-rays and neutrons, both ex- and in-situ , X-ray photoelectron spectroscopy, magnetometry as well as electron microscopy. Neutron diffraction studies on one sample reveal that no oxygen vacancies are found in the structure and that the magnetic properties are ferrimagnetic-like with magnetic moments mainly coupled antiferromagnetically along the crystallographic c -direction. X-ray photoelectron spectroscopy gave indications of the oxidation states of the constituting ions where several mixed oxidation states are observed in these valence-compensated perovskites. [Display omitted] • Compositionally complex perovskites are investigated for their phase stability. • They crystallise in either the Pnma or R 3 ¯ c space groups. • Neutron diffraction shows no oxygen vacancies. • The magnetic properties are ferrimagnetic-like. • Magnetic structure can be explained with the magnetic space group Pn'ma'. [ABSTRACT FROM AUTHOR]