New superconductor Li_xFe_1+δSe (x ≤ 0.07, T_c up to 44 K) by an electrochemical route

The superconducting transition temperature (T(c)) of tetragonal Fe(1+δ)Se was enhanced from 8.5 K to 44 K by chemical structure modification. While insertion of large alkaline cations like K or solvated lithium and iron cations in the interlayer space, the [Fe(2)Se(2)] interlayer separation increases significantly from 5.5 Å in native Fe(1+δ)Se to >7 Å in K(x)Fe(1−y)Se and to >9 Å in Li(1−x)Fe(x)(OH)Fe(1−y)Se, we report on an electrochemical route to modify the superconducting properties of Fe(1+δ)Se. In contrast to conventional chemical (solution) techniques, the electrochemical approach allows to insert non-solvated Li(+) into the Fe(1+δ)Se structure which preserves the native arrangement of [Fe(2)Se(2)] layers and their small separation. The amount of intercalated lithium is extremely small (about 0.07 Li(+) per f.u.), however, its incorporation results in the enhancement of T(c) up to ∼44 K. The quantum-mechanical calculations show that Li occupies the octahedrally coordinated position, while the [Fe(2)Se(2)] layers remain basically unmodified. The obtained enhancement of the electronic density of states at the Fermi level clearly exceeds the effect expected on basis of rigid band behavior

Structure and high-temperature properties of the (Sr,Ca,Y)(Co, Mn)O3-y perovskites - perspective cathode materials for IT-SOFC

Oxygen deficient perovskites Sr0.75Y0.25Co1-xMnxO3-y, x=0.5 and 0.75, were prepared by using the citrate route at 1373-1573 K for 48 h. The cubic Pm-3m perovskite structure for x=0.5 was confirmed by electron diffraction study and refined using neutron powder diffraction (NPD) data. For x=0.75, the superstructure corresponding to a=root 2 x a(per), b=2 x a(per), c=root 2 x a(per) (a(0)b(-)b(-) tilt system, space group Imma) was revealed by electron diffraction. The solid solution Sr0.75-xCaxY0.25Co0.25Mn0.75O3-y, 0.1 &lt;= x &lt;= 0.6 and compound Ca0.75Y0.25Mn0.85Co0.15O2.92 were prepared in air at 1573 K for 48 h. The crystal structure of Ca0.75Y0.25Mn0.85Co0.15O2.92 was refined using NPD data (S.G. Pnma, a=5.36595(4), b=7.5091(6), c=5.2992(4) angstrom, R-p=0.057, R-wp=0.056, chi(2)=4.26). High-temperature thermal expansion properties of the prepared compounds were studied in air using both dilatometry and high-temperature X-ray powder diffraction data (HTXRPD). They expanding non-linearly at 298-1073 K due to the loss of oxygen at high temperatures. Calculated average thermal expansion coefficients (TECs) for Sr0.75Y0.25Co1-xMnxO3-y, x=0.5, 0.75 and Ca0.75Y0.25Mn0.85Co0.15O2.92(1) are 15.5, 15.1, and 13.8 ppm K-1, respectively. Anisotropy of the thermal expansion along different unit cell axes was observed for Sr0.15Ca0.6Y0.25Co0.25Mn0.75O3-y, and Ca0.75Y0.25Mn0.85Co0.15O2.92. Conductivity of Sr0.75Y0.25Co1-xMnxO3-y, x=0.5 and 0.75 increases with the temperature reaching 110 S/cm for x=0.5 and 44 S/cm for x=0.75 at 1173 K. Samples of Sr0.75-xCaxY0.25Co0.25Mn0.75O3-y, 0.1 &lt;= y &lt;= 0.6 were found to be n-type conductors at room temperature with the similar temperature dependence of the conductivity and demonstrated the increase of the sigma value from similar to 1 to similar to 50 S/cm as the temperature increases from 300 to 1173 K. Their conductivity is described in terms of the small polaron charge transport with the activation energy (E-p) increasing from 340 to 430 meV with an increase of the calcium content from x=0 to x=0.6.AuthorCount:10;</p

Sosnowskyi Hogweed-Based Hard Carbons for Sodium-Ion Batteries

Sodium-ion battery technology rapidly develops in the post-lithium-ion landscape. Among the variety of studied anode materials, hard carbons appear to be the realistic candidates because of their electrochemical performance and relative ease of production. This class of materials can be obtained from a variety of precursors, and the most ecologically important and interesting route is the synthesis from biomass. In the present work, for the first time, hard carbons were obtained from Heracleum sosnowskyi, a highly invasive plant, which is dangerous for humans and can cause skin burns but produces a large amount of green biomass in a short time. We proposed a simple synthesis method that includes the pretreatment stage and further carbonization at 1300 &deg;C. The effect of the pretreatment of giant hogweed on the hard carbon electrochemical properties was studied. Obtained materials demonstrate &gt;220 mAh g&minus;1 of the discharge capacity, high values of the initial Coulombic efficiency reaching 87% and capacity retention of 95% after 100 charge-discharge cycles in sodium half-cells. Key parameters of the materials were examined by means of different analytical, spectroscopic and microscopic techniques. The possibility of using the giant hogweed-based hard carbons in real batteries is demonstrated with full sodium-ion cells with NASICON-type Na3V2(PO4)3 cathode material

Sosnowskyi Hogweed-Based Hard Carbons for Sodium-Ion Batteries

Sodium-ion battery technology rapidly develops in the post-lithium-ion landscape. Among the variety of studied anode materials, hard carbons appear to be the realistic candidates because of their electrochemical performance and relative ease of production. This class of materials can be obtained from a variety of precursors, and the most ecologically important and interesting route is the synthesis from biomass. In the present work, for the first time, hard carbons were obtained from Heracleum sosnowskyi, a highly invasive plant, which is dangerous for humans and can cause skin burns but produces a large amount of green biomass in a short time. We proposed a simple synthesis method that includes the pretreatment stage and further carbonization at 1300 °C. The effect of the pretreatment of giant hogweed on the hard carbon electrochemical properties was studied. Obtained materials demonstrate >220 mAh g−1 of the discharge capacity, high values of the initial Coulombic efficiency reaching 87% and capacity retention of 95% after 100 charge-discharge cycles in sodium half-cells. Key parameters of the materials were examined by means of different analytical, spectroscopic and microscopic techniques. The possibility of using the giant hogweed-based hard carbons in real batteries is demonstrated with full sodium-ion cells with NASICON-type Na3V2(PO4)3 cathode material