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CuFeS2 (chalcopyrite) is a promising n-type thermoelectric candidate for low-grade waste heat recovery. In this work, chromium-containing CuFeS2 materials of general formula Cu1−xCrxFeS2 (0.0 ≤ x ≤ 0.1) were prepared via solid-state synthesis. Efforts to substitute chromium in CuFeS2 leads to the preferential formation of a composite, in which lamellar precipitates of a Cr-rich, spinel-type [Cu,Fe,Cr]3S4 phase, are embedded in the unsubstituted CuFeS2 matrix. X-ray absorption near-edge spectroscopy (XANES) reveals that the electronic structure of copper, iron and sulfur in the principal CuFeS2 phase remains unaltered by chromium incorporation. However, the formation of [Cu,Fe,Cr]3S4 precipitates alters the Cu : Fe ratio of the CuFeS2 phase, producing a change in the net carrier concentration through reduction of a portion of Fe3+ ions to Fe2+. The chromium content of the spinel precipitates determines the extent of the change in the Cu : Fe ratio of the main CuFeS2 phase, and hence, indirectly affects the electrical properties. The micro/nanometre-sized [Cu,Fe,Cr]3S4 precipitates and nanoscale dislocations enable a broad spectrum of heat-carrying acoustic phonons to be scattered, resulting in a significantly reduced lattice thermal conductivity. Combined with an enhanced power factor, a maximum thermoelectric figure-of-merit, zT of 0.31 at 673 K is achieved for the x = 0.08 sample; a three-fold increase over that of the pristine phase. [ABSTRACT FROM AUTHOR]

We investigated the effect of annealing temperature on magnetic properties of 2% and 10% Fe-doped BaTiO3. To understand the possible structural differences between samples treated at different annealing temperatures, and to correlate them with the magnetic properties, several characterization techniques, such as X-ray diffraction and X-ray absorption spectroscopic methods ( XANES and EXAFS) were employed. We found that the 2% Fe-doped BaTiO3 pseudocubic perovskite is paramagnetic regardless of the heat-treatment conditions. Initially paramagnetic 10% Fe-doped 6H-BaTiO3, treated at 1250°C, became ferromagnetic after additional annealing at higher temperature. We have crystalographically characterized the cation ordering processes in the 6H-BaTiO3 that occurred during the high-temperature annealing. The ferromagnetism that is induced in this stage is most probably associated with the observed diffusion processes but it extrinsic character still cannot be fully disregarded. [ABSTRACT FROM AUTHOR]

We investigated the effect of annealing temperature on magnetic properties of 2% and 10% Fe-doped BaTiO3. To understand the possible structural differences between samples treated at different annealing temperatures, and to correlate them with the magnetic properties, several characterization techniques, such as X-ray diffraction and X-ray absorption spectroscopic methods ( XANES and EXAFS) were employed. We found that the 2% Fe-doped BaTiO3 pseudocubic perovskite is paramagnetic regardless of the heat-treatment conditions. Initially paramagnetic 10% Fe-doped 6H-BaTiO3, treated at 1250°C, became ferromagnetic after additional annealing at higher temperature. We have crystalographically characterized the cation ordering processes in the 6H-BaTiO3 that occurred during the high-temperature annealing. The ferromagnetism that is induced in this stage is most probably associated with the observed diffusion processes but it extrinsic character still cannot be fully disregarded. [ABSTRACT FROM AUTHOR]

We investigate magnesium-iron pyroborate MgFeB 2 O 5 as a potential cathode material for rechargeable magnesium-ion batteries. Synchrotron powder X-ray diffraction and Mössbauer spectroscopy confirm its successful synthesis and iron stabilization in the high-spin Fe(II) state. Initial electrochemical testing against a lithium metal anode yields a first charge capacity near the theoretical value (147.45 mAh·g -1 ), suggesting MgFeB 2 O 5 as a promising cathode candidate. However, multimodal analyses, including scanning electron microscopy energy-dispersive X-ray (SEM-EDS) analysis, operando X-ray absorption near edge spectroscopy (XANES), and Mössbauer spectroscopy, reveal the absence of any Fe redox reactions. Instead, we propose that the source of the observed capacity involves the irreversible reaction of a small (4-7 wt%) Fe metal impurity. These findings highlight the need for diverse characterization techniques in evaluating the performance of new Mg cathode materials, since promising initial cycling may be caused by competing side reactions rather than Mg (de)intercalation., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)