О возможности введения примеси железа в узлы A в SrTiO-=SUB=-3-=/SUB=-

The local environment and oxidation state of the Fe impurity in strontium titanate are studied using XAFS spectroscopy. The influence of annealing temperature and deviation from stoichiometry on the possibility of incorporation of the impurity into the A and B sites of the perovskite structure is studied. The results obtained from the X-ray diffraction, XANES spectra, and EXAFS spectra suggest that at high annealing temperature the iron atoms, at least partially (up to 30%), enter the A sites in SrTiO3. The obtained results agree with results of first-principles calculations, according to which the iron at the A site exhibits strong off-centering (the displacement of ~1 Angstrom), similar to that previously established in SrTiO3 samples doped with Mn and Co.

Resource Recovery of Waste Nd–Fe–B Scrap: Effective Separation of Fe as High-Purity Hematite Nanoparticles

Recycling rare-earth elements from Nd magnet scrap (Nd–Fe–B scrap) is a highly economical process; however, its efficiency is low due to large portions of Fe impurity. In this study, the effective separation of Fe impurity from scrap was performed through an integrated nitric acid dissolution and hydrothermal route with the addition of fructose. Results showed that more than 99% of the scrap was dissolved in nitric acid, and after three dilutions that the Nd, Pr, Dy and Fe concentrations in the diluted acid were 9.01, 2.11, 0.37 and 10.53 g/L, respectively. After the acid was hydrothermally treated in the absence of fructose, only 81.8% Fe was removed as irregular hematite aggregates, whilst more than 98% rare-earth elements were retained. By adding fructose at an Mfructose/Mnitrate ratio of 0.2, 99.94% Fe was precipitated as hematite nanoparticles, and the loss of rare-earth elements was <2%. In the treated acid, the residual Fe was 6.3 mg/L, whilst Nd, Pr and Dy were 8.84, 2.07 and 0.36 g/L, respectively. Such composition was conducive for further recycling of high-purity rare-earth products with low Fe impurity. The generated hematite nanoparticles contained 67.92% Fe with a rare-earth element content of <1%. This value meets the general standard for commercial hematite active pharmaceutical ingredients. In this manner, a green process was developed for separating Fe from Nd–Fe–B scrap without producing secondary waste.

Влияние уровней Ландау на ССТС спектров ЭПР преципитатов Fe-=SUP=-3+-=/SUP=- в дираковском 3D-полуметалле Cd-=SUB=-3-=/SUB=-As-=SUB=-2-=/SUB=-

The influence of d-metal impurities on the magnetic and transport properties of the 3D topological Cd3As2 semimetal is experimentally studied. It was found that when doping with iron, unlike Eu, there is no change in the sign of magneto resistance. There is an increase in the oscillations of the quantities (magnetic susceptibility, contact potential difference, and conductivity) associated with oscillations in the density of states at the Fermi level with temperature and magnetic field. In the temperature range of 10–300 K, EPR signals from Fe2+ ions were not detected, although, most likely, are the main type of Fe impurity in Cd3As2. From Fe3+ ions, weak EPR signals with a super-hyperfine structure (SHFS) were observed, which are obviously effected by Landau levels.