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Many technological applications demand large amount of nanoparticles with well-defined properties, which is feasible only by using large-scale production methods. In this framework, we have performed structural and local geometric investigations of cobalt oxide nanoparticles synthesized by high temperature arc plasma route in helium and in air atmosphere with different arc currents, a competitive and low cost technological approach to synthesize large quantity of different types of nanoparticles. The complex scenario of phase fraction, shape, size distribution and hysteresis loop features of high temperature arc plasma synthesis of nanoparticles can be determined by the arc current and the selected gas. X-ray diffraction patterns reveal a multicomponent phase formation containing cubic cobaltous oxide (CoO), cobaltic oxide (Co3O4) and metallic cobalt phases. The synthesis of different phases is confirmed by x-ray absorption spectroscopy measurements at the Co K-edge. Both extended x-ray absorption fine structure and x-ray absorption near edge structure analyses show the presence of metallic nanoparticles in He ambient at high arc current. Moreover, high-resolution transmission electron microscopy images and magnetic hysteresis loop measurements show that the mean particle size increases and the coercivity decreases with increasing arc current in air ambient due to the intense particle–particle interaction. At variance, in He ambient synthesized samples due to the high quenching rate and the high thermal conductivity, a multi-domain formation in which the nanoparticles’ crystalline fraction decreases and a fluctuating coercivity due to core–shell structure is observed.

The local structure of La(Fe1−x Mn x )AsO has been investigated using temperature dependent Fe K-edge extended x-ray absorption fine structure (EXAFS) measurements. The EXAFS data reveal distinct behavior of Fe–As and Fe–Fe atomic displacements with a clear boundary between x ⩽ 0.02 and x > 0.02. The Fe–As bondlength shows a gradual thermal expansion while the Fe–Fe bond manifests a temperature dependent anomaly at ∼180 K for x > 0.02. It is interesting to find characteristically different nature of Fe–As and Fe–Fe bondlengths shown by the temperature dependent mean square relative displacements. Indeed, the Fe–As bond, stiffer than that of the Fe–Fe, gets softer for x ⩽ 0.02 and hardly shows any change for x > 0.02. On the other hand, Fe–Fe bond tends to be stiffer for x ⩽ 0.02 followed by a substantial softening for x > 0.02. Such a distinction has been seen also in the As K-edge x-ray absorption near edge structure, probing local geometry around As atom together with the valence electronic structure. The results suggest that local atomic displacements by Mn substitution inducing increased iron local magnetic moment that should be the main reason for its dramatic effect in iron-based superconductors.

Isovalent substitution of S by Se in LaOBiS2-x Se x has a substantial effect on its electronic structure and thermoelectric properties. To investigate the possible role of BiS2 structural instability, we have studied the local structure of LaOBiS2-x Se x ([Formula: see text]) using temperature dependent Bi L3-edge extended x-ray absorption fine structure measurements. The results reveal that the local structure of the two compounds is significantly different. The BiS2 sub-lattice is largely distorted in LaOBiS2 (x = 0.0), with two in-plane Bi-S1 distances separated by ∼0.4 A instead LaOBiSSe (x = 1.0) showing much smaller local disorder with two in-plane Bi-Se distances in the plane being separated by ∼0.2 A. Temperature dependent study shows that the two Bi-S1 distances are characterized by different bond strength in LaOBiS2 (x = 0.0) while it is similar for the Bi-Se distances in LaOBiSSe (x = 1.0). The out of plane Bi-S2 bond is harder in LaOBiSSe indicating that the structural instability of BiS2 layer has large effect on the out-of-plane atomic correlations. The results suggest that the local structure of LaOBiS2-x Se x is an important factor to describe differing electronic and thermal transport of the two compounds.

Cu K-edge extended X-ray absorption fine-structure (EXAFS) measurements have been used to study the temperature-dependent local structure of the underdoped and overdoped superconducting La2 − xSrxCuO4 system. The Debye-Waller factor of the in-plane Cu-O bonds has been used as an order parameter to measure the local displacements, revealing an anomalous behavior for the underdoped case while the overdoped system shows a negligible change as a function of temperature. The results provide an evidence for a close relationship between local Cu-O displacements, electron-lattice interaction and charge inhomogeneity in the copper oxide superconductors.

The local structure of Nb3Ge intermetallic superconductor has been studied by Ge K-edge absorption spectroscopy. Extended x-ray absorption fine structure (EXAFS) experiments show two Ge–Nb distances. In addition to the crystallographic distance of ~2.87 A, there exists a second Ge–Nb distance, shorter than the first by ~0.2 A, assigned to a phase with short-range symmetry related to local displacements in the Nb–Nb chains. The x-ray absorption near-edge structure (XANES) spectrum has been simulated by full multiple-scattering calculations considering the local displacements determined by the EXAFS analysis. The XANES spectrum has been well reproduced by considering a cluster of 99 atoms within a radius of about 7 A from the central Ge atom and introducing determined local displacements.

The increase of Tc with x in Al 1 − x Mg x B 2 is controlled by the Fermi level tuning at a "shape resonance" (i.e., the 2D-3D cross-over, at x = 0.66, of the topology of the Fermi surface of σ holes in the superlattice of boron mono-layers intercalated by Al 1 − x Mg x ions) and by the tensile "micro-strain" in the boron sub-lattice (due to the lattice misfit between the boron and the intercalated layers). The softening of the E2g phonon frequency with increasing boron tensile micro-strain e in the range 3% < e < 6% shows the increasing electron-lattice interaction. The linear scaling, for 0.66 < x < 1, of Tc vs. the Fermi temperature TF of the σ holes shows a constant coupling strength with kFξ0 = 90 (where kF is the Fermi wave vector and ξ0 is the Pippard coherence length) that points toward a vibronic pairing mechanism.

We have used x-ray absorption spectroscopy as a tool to study instantaneous local lattice distortions of the CuO2 plane in high Tc superconductors and we have investigated the inhomogeneous charge states of these materials. The temperature-dependent Cu K-edge extended x-ray absorption fine structure (EXAFS) has been used to determine the correlated Debye–Waller factor of the Cu–O bonds, measuring local lattice fluctuations. The Debye–Waller factor of the Cu–O bonds shows an order-parameter-like behaviour across the charge stripe ordering temperature. The EXAFS results are supported by a temperature-dependent Cu K-edge x-ray absorption near edge structure (XANES) revealing a particular change in the local lattice displacements at the charge stripe ordering. The experimental Cu K-edge XANES results are well reproduced by full multiple scattering calculations including different distortions of the CuO2 plane showing particular lattice displacements which are consistent with the EXAFS results. The particular distortion mode as a response function to the charge stripe ordering has been discussed with several examples. The results are consistent with an inhomogeneous charge distribution in the high Tc cuprates suggesting an intimate relationship between the charge stripe ordering, local lattice fluctuations and high Tc superconductivity in the cuprates.

The effect of delithiation in Li x CoO2 is studied by high resolution Co K-edge x-ray absorption and x-ray emission spectroscopy. Polarization dependence of the x-ray absorption spectra on single crystal samples is exploited to reveal information on the anisotropic electronic structure. We find that the electronic structure of Li x CoO2 is significantly affected by delithiation in which the Co ions oxidation state tending to change from 3+ to 4+. The Co intersite (intrasite) 4p-3d hybridization suffers a decrease (increase) by delithiation. The unoccupied 3d t 2g orbitals with a 1g symmetry, containing substantial O 2p character, hybridize isotropically with Co 4p orbitals and likely to have itinerant character unlike anisotropically hybridized 3d e g orbitals. Such a peculiar electronic structure could have significant effect on the mobility of Li in Li x CoO2 cathode and hence the battery characteristics.

Polarized x-ray absorption spectroscopic (XAS) measurements have been made on Cu L3 and O K edges on four superconducting thin films of NdBCO with different Tc values to study the relative importance of the in-plane (Cu 3dx2-y2 and O 2px,y orbitals) and the out-of-plane (Cu 3dz2 and O2pz) orbitals in the mechanism of superconductivity. Our results clearly show that a significant number of out-of plane O 2pz and Cu 3dz2-r2 do exist in these films, still hardly affecting their Tc. Tc is found to depend more upon number of itinerant holes rather than the orientation or substrate of the film. However the out-of-plane holes perhaps do affect the superconducting fraction in the film. O K-edge spectra recorded for E∥ab to measure the density of itinerant holes in plane show a good agreement with the conclusion drawn from Cu L3 data. The results have been compared with the XRD and the magnetic susceptibility measurements reported on these films earlier and a good qualitative agreement found. From the present study we can confidently state that no direct correlation exists between Tc and out-of-plane covalent and doping hole densities and the models based on the premise that out-of-plane orbitals, if present, will destroy superconductivity also do not seem to be valid in these systems.

We have measured high-resolution Ru K-edge x-ray absorption spectra for the intermetallic La1-xCexRu2 system. Multiple-scattering calculations are made to explore the origins of different features observed in the experimental x-ray absorption near-edge structure (XANES) and their variation with Ce doping. The experiments and theoretical analysis demonstrate that the Ce doping in La1-xCexRu2 has a direct influence on the states at the Fermi level and hence the hybridization between the f and d states induced by doping.

A very large oxygen-isotope shift of the charge-stripe ordering temperature in the high-temperature superconductors La2-xSrxCuO4 has been observed using x-ray absorption spectroscopy, a fast (~10-15 seconds) and local probe (~5 A). Upon replacing 16O with 18O, the charge-stripe ordering temperature in La1.94Sr0.06CuO4 increases from about 110 K to 180 K. The present results provide compelling evidence for a strong electron-phonon interaction in this compound, and thus place important constraints on the microscopic origin of the stripe formation.

X-ray absorption spectroscopy has been used to investigate the environment of all four cations in a series of six samples of (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0). Interatomic distances and their mean square variations, together with some coordination numbers, have been obtained from an analysis of the EXAFS using the multiple-scattering fast curved-wave theory. The environments of the Ba, Cu and Y atoms were found to be invariant with changing composition, the structural parameters being in good agreement with crystallographic data for the end-point materials. The environment of the Pr atom was found to change with composition, both the mean Pr-O distance and its mean square variation varying in a characteristic way. The variations with composition may be closely modelled by the forms and . These results have been interpreted in terms of a combination of two Pr-O distances, each invariant with composition, the proportions of these varying linearly with praseodymium content. The consequences of this variation, both for the praseodymium valence and the superconducting properties of the material, are considered.

A study of the electronic states near the Fermi level in high- superconductors, which is so important to understanding the mechanism of superconductivity, has been carried out on well characterized single crystals of superconducting . A large number of polarized x-ray absorption spectra have been recorded with the E vector parallel to the a - b plane and perpendicular to it at the Dragon beam line at the Brookhaven Light Source using the fluorescence mode of detection. These bulk spectra of and O K are then analysed to obtain the density of the unoccupied and orbitals from the spectra and the density of the and orbitals from the O K spectra. The results clearly show the presence of orbitals in a substantial amount although the same cannot be said of the orbitals. Tight-binding calculations of the holes are also reported and compared with experimental results.

X-ray photoemission measurements were performed on Au deposited on a Bi(2212) single crystal after progressively sputtering it with Ar ions. This was to see whether changes such as diffusion of Au, segregation of a particular element or clustering effects take place at the interface. Spectra of different core levels reveal no elemental diffusion at the interface and an absence of Au interaction with the crystal at room temperature.

We have studied the effect of chemical pressure on the local structure of LaSmxFeAsO oxypnictides. The combination of arsenic K-edge and rare-earth (RE = La, Sm) L3-edge x-ray absorption spectra has permitted us to determine local bondlengths and unoccupied electronic states with varying chemical pressure controlled by the size difference of La and Sm. The Fe–As distance is hardly affected by the chemical pressure, and remains covalent as shown by As K-edge extended x-ray absorption fine structure (EXAFS) analysis. On the other hand, the As–RE and As–As distances show a gradual change. The changes indicate a larger effect of chemical pressure in the REO spacer layer and on the interlayer interactions, consistent with x-ray absorption near edge structure (XANES) data. The results suggest that interlayer atomic correlations are likely to have an important role in the physical properties of the LaSmxFeAsO parent phases of the superconducting oxypnictides.

We have used Bi and Ce L3-edges extended x-ray absorption fine structure measurements to study local structure of CeO(1-x)F(x)BiS2 system as a function of F-substitution. The local structure of both BiS2 active layer and CeO1-xFx spacer layer changes systematically. The in-plane Bi-S1 distance decreases (ΔRmax ∼ 0.08 Å) and the out-of-plane Bi-S2 distance increases (ΔRmax ∼ 0.12 Å) with increasing F-content. On the other hand, the Ce-O/F distance increases (ΔRmax ∼ 0.2 Å) with a concomitant decrease of the Ce-S2 distance (ΔRmax ∼ 0.15 Å). Interestingly, the Bi-S1 distance is characterized by a large disorder that increases with F-content. The results provide useful information on the local atomic displacements in CeO(1-x)F(x)BiS2, that should be important for the understanding of the coexistence of superconductivity and low temperature ferromagnetism in this system.

X-ray absorption near-edge structure (XANES) spectroscopy has been used to investigate the unoccupied electronic states and local geometry of Ir1-xPtxTe2(x = 0.0, 0.03 and 0.04) as a function of temperature. The Ir L3-edge absorption white line, as well as high energy XANES features due to the photoelectron multiple scatterings with near neighbours, reveal clear changes in the unoccupied 5d-electronic states and the local geometry with Pt substitution. We find an anomalous spectral weight transfer across the known first-order structural phase transition from the trigonal to monoclinic phase in IrTe2, which characterizes the reduced atomic structure symmetry below the transition temperature. No such changes with temperature are seen in the Pt substituted superconducting samples. In addition, a gradual increase of the spectral weight transfer is observed in IrTe2 with a further decrease in temperature below the transition, indicating that the low temperature phase is likely to have a symmetry lower than the monoclinic one. The results suggest that the interplay between inter-layer and intra-layer atomic correlations should have a significant role in the properties of an Ir1-xPtxTe2 system.

We have studied the local structure of LiCoO(2) nanoparticles by Co K-edge x-ray absorption spectroscopy as a function of particle size. Extended x-ray absorption fine structure data reveal substantial changes in the near neighbor distances and the associated mean square relative displacements with decreasing particle size. X-ray absorption near edge structure spectra show clear local geometrical changes with decreasing particle size, similar to those that appear in the charging (delithiation) process. The results suggest that the LiCoO(2) nanoparticles are characterized by a large atomic disorder confined to the Co-O octahedra, similar to the distortions generated during the delithiation, and this disorder should be the primary limiting factor for a reversible diffusion of Li ions when nanoparticles of LiCoO(2) are used as cathode material in rechargeable Li ion batteries.

We have measured local structure of superconducting K_{0.8}Fe_{1.6}Se_{2} chalcogenide (T_{c}=31.8 K) by temperature dependent polarized extended x-ray absorption fine structure (EXAFS) at the Fe and Se K-edges. We find that the system is characterized by a large local disorder. The Fe-Se and Fe-Fe distances are found to be shorter than the distances measured by diffraction, while the corresponding mean square relative displacements reveal large Fe-site disorder and relatively large c-axis disorder. The local force constant for Fe-Se bondlength (k ~ 5.8 eV/\AA^{2}) is similar to the one found in the binary FeSe superconductor, however, the Fe-Fe bondlength appears to get flexible (k ~ 2.1 eV/\AA^{2}) in comparison to the binary FeSe (k ~ 3.5 eV/\AA^{2}), an indication of partly relaxed Fe-Fe networks in K_{0.8}Fe_{1.6}Se_{2}. The results suggest glassy nature of the title system, with the superconductivity being similar to the one in the granular materials.

Temperature-dependent polarized extended X-ray absorption fine-structure (EXAFS) measurements are made on the superconducting FeSe0.25Te0.75 single crystal. The Fe-Se bond length is found to be significantly shorter than the average crystallographic Fe-Se/Te distance, and almost equal to the one for the system without Te. On the other hand, the Fe-Te bond length is nearly equal to the one known for a binary FeTe system. This suggests that the Se and Te occupy distinct sites in the ternary FeSe0.25Te0.75, indicating the breaking of the average crystal symmetry with locally inhomogeneous atomic distribution.

Here we provide the material design of a possible high temperature multiband superconductor (HTMS) made of a 'heterostructure at the atomic limit' formed by alternate layers of electron doped FeAs and CuO2 separated by intercalated NdO spacers. This new class of materials is derived from the two well known electron doped superconductors Nd2CuO4 and NdOFeAs belonging to the cuprate and the pnictide families, respectively. The calculated local electronic density of states show that both the Cu and Fe bands cross the Fermi surface. This will provide (i) superconducting Fermi arcs made by charges from the CuO2 plane, and (ii) tubular Fermi surfaces, as in pnictides, by itinerant charges from the Fe atomic layer. The electronic properties of this new class of materials are presented to highlight the possibility of material design of a HTMS tuned at a shape resonance in the energy gap parameters belonging to the class of Fano–Feshbach resonances called superstripes. The Nd L3-edge x-ray absorption near edge structure (XANES) of the proposed model system is calculated and compared with the XANES spectra of the Nd2CuO4 and NdOFeAs parent compounds.

The REFeAsO (RE = La, Pr, Nd and Sm) system has been studied by RE L(3) x-ray absorption near edge structure (XANES) spectroscopy to explore the contribution of the REO spacers between the electronically active FeAs slabs in these materials. The XANES spectra have been simulated by full multiple scattering calculations to describe the different experimental features and their evolution with the RE size. The near edge feature just above the L(3) white line is found to be sensitive to the ordering/disordering of oxygen atoms in the REO layers. In addition, shape resonance peaks due to As and O scattering change systematically, indicating local structural changes in the FeAs slabs and the REO spacers due to RE size. The results suggest that interlayer coupling and oxygen order/disorder in the REO spacers may have an important role in the superconductivity and itinerant magnetism of the oxypnictides.

It was shown by the present authors group that tardigrade can survive under high pressure of 7.5 GPa. In the case of land plants, however, no result of such experiment has been reported. We have extended our experiments to moss searching for lives under very high pressure. Spore placentas of moss Venturiella were sealed in a small Teflon capsule together with a liquid pressure medium. The capsule was put in the center of a pyrophillite cube, and the maximum pressure of 7.5 GPa was applied using a two-stage cubic anvil press. The pressure was kept constant at the maximum pressure for12, 24, 72 and 144 hours. After the pressure was released, the spores were seeded on a ager medium, and incubated for one week and more longer at 25°C with white light of 2000 lux. It was proved that 70-90% of the spores were alive and germinated after exposed to the maximum pressure of 7.5 GPa for up to 72 hours. However, after exposed to 7.5 GPa for 6 days, only 4 individuals in a hundred were germinated. The pressure tolerance of moss Venturiella is found to be stronger than a small animal, tardigrade.