Inducing formation of L10-phase in concave-cube FePt nanoparticles by annealing under high magnetic field

Concave-cube FePt nanoparticles (NPs) with anisotropy of shape and element were annealed under high magnetic field (HMF). The high temperature sphered the FePt NPs, and Pt content and grain size of the NPs were decreased during annealing process. The HMF strength didn’t affect the shape, size and composition of the FePt NPs, but induced the formation of L 1 0 -phase in the annealed NPs. The content and ordering degree of L 1 0 -phase increased with enhancing the HMF strength, which leaded to the increasing of coercivity in the annealed FePt NPs. This work suggests that application of the HMF annealing is an effective strategy to tune the microstructure and property of anisotropic FePt NPs.

Evaluation of crystallographic ordering degree of magnetically active ions in Sr 2FeMoO 6-δ by means of the (101) X-ray peak intensity

Strontium ferromolybdate double perovskite is a promising candidate for room-temperature spintronic applications. Nevertheless, SFMO has not yet found wide application in spintronics. This is attributed to the low reproducibility of its magnetic properties which partially originates from their strong dependence on the ordering degree of Fe and Mo ions in the Bʹ and Bʺ sublattices of double perovskite A2BʹBʺO6. In this work, we have considered an express method of determining the degree of disorder in strontium ferromolybdate. The sublattice occupation with Fe and Mo ions has been estimated for stoichiometric and nonstoichiometric Sr2FeMoO6-δ with a 5% Fe and Mo excess, respectively. We have calculated the intensity ratio between the superstructure (101) XRD peak and the most intense (112 + 200) peak. The calculated curves have been fitted to an analytical expression of a similar case known from literature. The calculation results obtained using the proposed method are within a ± 25 % agreement with Rietveld analysis of experimental data. Thus, this method can be used as an alternative to Rietveld analysis if the exposure time during X-ray diffraction experiment was insufficient. We have discussed the dependence of the I (101)/I (112 + 200) peak intensity ratio on various factors including instrumental broadening of diffraction peaks, peak twinning due to grain size reduction, thin film lattice parameter variation due to substrate lattice mismatch and lattice parameter variation due to oxygen vacancies. The relevance of the method is the evaluation of the degree of superstructure ordering in Sr2FeMoO6-δ without large time consumption for X-ray diffraction pattern recording and Rietveld data processing which may be essential when dealing with large amounts of experimental data.

Rational Development of Structurally Ordered Platinum Ternary Intermetallic Electrocatalysts for Oxygen Reduction Reaction

Structurally ordered intermetallic structure is an efficient catalyst design strategy to significantly improve the catalytic performance of Pt alloy electrocatalysts for oxygen reduction reaction in fuel cells. However, a high structural ordering degree generally relies on high-temperature annealing, which results in detrimental catalyst particle sintering. Herein, we reveal that the incompatibility between high ordering degree and minimum particle sintering during thermal annealing can be resolved through rational development of structurally ordered Pt ternary alloys. Ordering transformation mediated by high-temperature annealing of three representative Pt ternary alloys (Pt–Fe–Co, Pt–Ni–Co and Pt–Fe–Ni) at a similar Pt composition was systematically studied. It was found that Fe can significantly promote the structural ordering due to a faster atomic diffusion, whereas Co can effectively inhibit the particle sintering. As a result of the synergy between Co and Fe, the ordered PtCoFe catalyst exhibited the highest ordering degree after thermal annealing at 600 °C with the minimum nanoparticle growth, leading to the highest catalytic activity (0.65 A/mgPt at 0.9 V, 4 times that of pure Pt catalyst) and best stability (16% drop after 10,000 potential cycles). This study provides important clues for the rational design of high-performance structurally ordered ternary Pt alloys.

Qualitative Analysis of Clustering in Aqueous Alcohol Solutions. II

Specific features of the clustering in aqueous solutions of monoatomic alcohols have been discussed. Main attention is focused on details of the clustering in water-ethanol solutions. The clustering degree is supposed to depend on the nteraction between ethanol and water molecules, as well as on the ordering degree of the H-bond network in water, which changes with the temperature and concentration of the alcohol. The elementary cluster volume is assumed to be smaller than the sum of the molecular volumes of components that form this cluster. The clustering degree in aqueous solutions of methanol and ethanol and its concentration and temperature dependences are determined.