The structural and magnetic phase transitions of the ternary iron arsenides SrFe 2 As 2 and EuFe 2 As 2 were studied by temperature-dependent x-ray powder diffraction and 57 Fe Mössbauer spectroscopy. Both compounds crystallize in the tetragonal ThCr 2 Si 2 -type structure at room temperature and exhibit displacive structural transitions at 203 K (SrFe 2 As 2 ) or 190 K (EuFe 2 As 2 ) to orthorhombic lattice symmetry in agreement with the group-subgroup relationship between I4/mmm and F mmm. 57 Fe Mössbauer spectroscopy experiments with SrFe 2 As 2 show full hyperfine field splitting below the phase transition temperature (8.91(1) T at 4.2 K). Order parameters were extracted from detailed measurements of the lattice parameters and fitted to a simple power law. We find a relation between the critical exponents and the transition temperatures for AFe 2 As 2 compounds, which shows that the transition of BaFe 2 As 2 is indeed more continuous than the transition of SrFe 2 As 2 but it remains second order even in the latter case.
The stringent environmental requirements regarding the mobility energy usage are forcing most automakers to develop hybrid electric vehicles, which allows for a more efficient and thus less polluting use of fossil combustibles. A vast deployment of such vehicles involves producing and recycling of batteries on the thousand tons per year scale. Present Li-ion technologies involve the use of fluorinated binders, which are costly, and the use of environmentally unfriendly volatile organic compounds for the processing, which are difficult to recycle. In this paper, it is shown that the fluorinated binders can be replaced with greener and cost-effective polymers derived from cellulose.
Single crystalline Sn 2 Co 3 S 2 with the shandite-type structure was investigated by magnetization, magnetoresistance, Hall effect, and heat capacity measurements and by 119 Sn Mößbauer spectroscopy. Sn 2 Co 3 S 2 orders ferromagnetically at 172 K with an easy-axis magnetization of ≈1 μ B along the hexagonal c axis. The half-metallic ferromagnetic state is investigated by detailed band-structure calculations by density functional theory (DFT) methods. The magnetoresistance and the Hall effect as well as the DFT results show that ferromagnetic Sn 2 Co 3 S 2 is a compensated metal. The 119 Sn Mößbauer spectroscopic data confirm these findings. Large transferred hyperfine fields B hf up to 34.2 T are observed.
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