Nanocrystalline LiFePO 4 and doped LiTi 0.01 Fe 0.99 PO 4 powders were synthesized via a sol-gel preparation route. High-resolution tunneling electron microscopy observation and energy dispersive spectroscopy, mapping show the homogeneous distribution of dopant Ti cations in the crystals. Fe and O K-edge X-ray absorption near-edge structure ͑XANES͒ measurements show that Ti 4+ doping induces an increased unoccupied d-state in LiFePO 4 , resulting in an enhanced p-type semiconductivity. In situ Fe K-edge XANES measurements of Ti-doped and undoped LiFePO 4 electrodes have been performed to determine the change of Fe valence during the lithium intercalation and de-intercalation processes. Both LiFePO 4 and doped LiTi 0.01 Fe 0.99 PO 4 cathodes demonstrate good electrochemical performance.

In the present investigation, we report the transformation of alpha-LiVOPO 4 to alpha-Li 3V 2(PO 4) 3, leading to an enhancement of capacity. The alpha-LiVOPO 4 sample was synthesized by a sol-gel method, followed by sintering at 550-650 degrees C in a flow of 5% H 2/Ar. The structural transformation of a triclinic alpha-LiVOPO 4 structure to a monoclinic alpha-Li 3V 2(PO 4) 3 structure was observed at higher sintering temperatures (700-800 degrees C in a flow of 5% H 2/Ar). The alpha-Li 3V 2(PO 4) 3 phase was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, and X-ray absorption near edge spectrum (XANES) techniques. The valence shift of vanadium ions from +4 to +3 states was observed using in situ XANES experiments at V K-edge. The structural transformation is ascertained by the shape changes in pre-edge and near edge area of X-ray absorption spectrum. It was observed that the capacity was enhanced from 140 mAh/g to 164 mAh/g via structural transformation process of LiVOPO 4 to Li 3V 2(PO 4) 3.

We present a pressure study of the electrical resistivity, ac magnetic susceptibility and powder x-ray diffraction (XRD) of the recently discovered BiS2-based superconductor EuBiS2F. At ambient pressure, EuBiS2F shows an anomaly in the resistivity at around T0 ≈ 280 K and a superconducting transition at Tc ≈ 0.3 K. Upon applying hydrostatic pressure, there is little change in T0 but the amplitude of the resistive anomaly is suppressed, whereas there is a dramatic enhancement of Tc from 0.3 K to about 8.6 K at a critical pressure of pc ≈ 1.4 GPa. XRD measurements confirm that this enhancement of Tc coincides with a structural phase transition from a tetragonal phase (P 4/nmm) to a monoclinic phase (P 21/m), which is similar to that observed in isostructural LaO0.5F0.5BiS2. Our results suggest the presence of two different superconducting phases with distinct crystal structures in EuBiS2F, which may be a general property of this family of BiS2-based superconductors.

Induction of holes not only in the superconductive CuO 2 plane but also in the Bi 2 O 2+δ charge reservoir of the Bi 2 Sr 2 (Y 1-x Ca x )Cu 2 O 8+δ superconductor upon Ca II -for-Y III substitution is evidenced by means of two independent techniques, i.e., high-resolution x-ray-absorption near-edge structure (XANES) spectroscopy measurements and coulometric redox titrations. The absolute values derived for the CuO 2 -plane hole concentration from the Cu L 2,3 -edge XANES spectra are in good agreement with those obtained from the coulometric redox analysis. The CuO 2 -plane hole concentration is found to increase from 0.03 to 0.14 concomitantly with the increase in the BiO 1+δ/2 -layer hole concentration from 0.00 to 0.13 as the Ca-substitution level, x, increases from 0 to 1. The threshold CuO 2 -plane hole concentration for the appearance of superconductivity is determined at 0.06, while the highest T c is obtained at the hole concentration of 0.12. In the O K-edge XANES spectrum, the increases in the CuO 2 -plane and BiO 1+δ/2 -layer hole concentrations with increasing x are seen as enhancement in the relative intensities of the pre-edge peaks at ∼528.3 and ∼530.5 eV, respectively. : 61.10.Ht; 74.62.Dh; 74.72.Hs The high-T c superconductive copper oxide, M m A 2 Q n-1 Cu n O m+2+2n±δ or M-m2(n-1)n, is believed to possess an antiferromagnetic insulating ground state related to its "undoped parent phase". By increasing the CuO 2 -plane hole concentration the phase undergoes an insulatormetal transition and starts to show superconductivity with a transition temperature, T c , that strongly depends on the concentration of induced holes. In the multi-layered structure of an Mm2(n-1)n phase the superconductive Q n-1 Cu n O 2n block containing the CuO 2 plane(s) is sandwiched with two AO layers and an M m O m±δ "charge reservoir" block with a layer sequence of AO-CuO 2 -(Q-CuO 2 ) n-1 -AO-(MO 1±δ/m ) m . 1 Among the variety of known M-m2(n-1)n phases (M = e.g. Cu, Bi, Pb, Tl, Hg, Al, Ga, B; m = 0 -3; A = e.g. Ba, Sr, La; Q = e.g. Ca, rare-earth element R; n = 1 -9), 1 only a limited number of phases, e.g. (La,Sr) ((Tl,Pb)-1212), 2-6 allow us to experimentally observe the actual appearance of superconductivity adjacent to the insulator-metal boundary. This is because many of these phases are structurally rather weak to sustain doping within a sufficiently wide range. Another difficulty arises from the fact that no universal experimental tool to accurately probe the local The accurate oxygen contents were determined by coulometric Cu + /Cu 2+ redox titration. 1,7 This experiment yields the total amount of high-valent copper and bismuth species, i.e., Cu III and Bi V , and thus the oxygen content of the sample. Upon dissolving the sample in 1 M HCl containing a known amount of Cu + ions both Cu III and Bi V oxidize Cu + to Cu 2+ according to reactions, PACSandOnce the reactions given by Eqs.(1) and (2) are completed the amount of remaining Cu + ions is accurately analyzed through coulometric titration, i.e., anodic...