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Abstract: Local structure of optimally doped T-(La,Sr)2CuO4 (LSCO) single-crystal thin films grown by molecular-beam epitaxy on LaSrCuO4 and SrTiO3 substrates was studied by the in-plane polarized Cu K-edge extended X-ray absorption fine structure (EXAFS). The results of data analysis show that the local structure (CuO6 octahedra) of LSCO thin films is strained by ca. 5×10−3 in accordance with the crystallographic data. Although the planar and apical oxygen displacements ΔR CuO are related to the critical temperature in a simple relation, the magnitude of strain-induced oxygen displacements (leading to anti-Jahn–Tell or Jahn–Teller distortion) is less than 0.1% of the equilibrium bond length. This suggests that the strain dependence of electronic states involves a different mechanism than a purely electronic model in a homogeneous conducting plane. The fact that LSCO thin films under tensile strain have a large local distortion of planar oxygens indicates that inhomogeneity may affect the critical temperature rather than the apical oxygen displacement. [Copyright &y& Elsevier]

We have studied local structure of the La2 - xSrxCuO4 system, in the underdoped and overdoped regimes, by polarized Cu K-edge extended X-ray absorption fine structure (EXAFS) measurements. The mean square relative displacements (MSRD), determined by the correlated Debye–Waller factors of the Cu–O bonds, have been measured as a function of temperature. We find that, while the Cu–O MSRD in the underdoped regime shows anomalous temperature dependence, the overdoped regime does not reveal such an anomaly. The results are consistent with decreasing charge heterogeneities in the overdoped regime, revealing importance of the local Cu–O displacements and the electron–lattice interaction in the heterogeneous nature of the cuprate superconductors. [Copyright &y& Elsevier]

We have used a combination of the Cu K-edge extended X-ray absorption fine structure (EXAFS), and the Cu L-edge X-ray absorption measurements, with polarization vector parallel to the two orthogonal Cu–O–Cu bonds, to explore the directional instantaneous atomic displacements and the orbital distribution within the heterogeneaous CuO2 plane of the Bi2Sr2CaCu2O8+δ (Bi2212) system. The results show an anisotropic Cu–O bond distribution, measured by the EXAFS in the two directions, and reveal large anisotropy of the unoccupied Cu 3d orbitals. The outcome of the present measurements is consistent with the nanoscale heterogeneities with coexisting electronic components. [Copyright &y& Elsevier]

Ab initio X-ray absorption near edge structure (XANES) calculations for FeSe x Te 1− x , using a structural model that combines FeSe and FeTe phases at the nanoscale, are compared with Fe K -edge XANES measurements in the “pre-edge” region. The important aspects of this model are (i) magnetic order in the FeTe phase; (ii) Se and Te atoms placed randomly in both FeSe and FeTe crystallographic positions and; (iii) the two distinct distances for Fe–Se and Fe–Te of the bulk phases. The calculated spectra reproduce the observed increase of spectral weight in the experiments on FeSe x Te 1− x with Se concentration. This is consistent with an inhomogeneous local electronic structure of FeSe x Te 1− x . Additionally, we have calculated projected electronic density of d -states for the Fe atom, revealing increased spectral weight in the “pre-edge” region of the XANES spectra, which correlates with the increase in Se concentration. The decrease of calculated Fe d -density of states for the Fermi level, N ( ε F ), for high Te content is consistent with the suppression of superconductivity in the title system. [ABSTRACT FROM AUTHOR]

Cu L3 and O K edge polarised X-ray absorption spectroscopy has been employed to study a three-dimensional oxygen deficient perovskite single crystal of La8-xSrxCu8O20-δ (8820) (x=1.56) for E//a, E//b and E//a^45 polarizations. A careful analysis of the data shows an unmistakable presence of the itinerant eg(x2–y2) holes in it. The density of itinerant holes increases slightly as we move from E//a to the E//b orientation. This behaviour seems to be similar to the charge aggregation taking place along b-direction in an under-doped YBCO crystal in the normal state but it is rather strange as this system does not become superconducting on further cooling. This intriguing behaviour warrants further investigation. [Copyright &y& Elsevier]

A polarised X-ray absorption study is made on an underdoped YBCO substantially detwinned single crystal to study the anomalous temperature dependence of itinerant holes, charge aggregation and pair formation along the E&par;b and E&par;a directions. The measurements were made at the O K and Cu L3 edges varying the temperature from 10 K to room temperature (∼300 K) using a liquid helium cryostat. In earlier reports on the YBCO reported observing the charge aggregation and the Cooper pair formation taking place only once each at temperatures T&ast; and T&ast;&ast;, both greater than Tc we observe these phenomena repeating themselves at two more temperatures, still in the normal state though. We have observed much smaller magnitude of the fluctuations of the itinerant holes in the ‘a’-direction as compared to ‘b’-direction in our experiment. Our results at T<40 K appear to go against the hypothesis that treats stripe formation essential to superconductivity in the cuprate perovskite systems. [Copyright &y& Elsevier]

We have studied the surface electronic structure of AV 10 O 15 (A = Ba, Sr) and Ba 0.9 Sr 0.1 V 13 O 18 by using x-ray photoemission spectroscopy (XPS). The V 2 p XPS shows multiple peaks associated with the charge fluctuation in the system. The relative intensity of each valence component can be extracted by Gaussian and Voigt fittings. The result strongly depends on the number of Gaussians/Voigts. In BaV 10 O 15 and Ba 0.9 Sr 0.1 V 13 O 18, the surface state has more V 3+ than the bulk. In addition to the presence of surface V 3+ , the V 2.5+ in AV 10 O 15 (A = Ba, Sr) and V 2+ in Ba 0.9 Sr 0.1 V 13 O 18 systems are observed even in the surface sensitive XPS. The number of Gaussians/Voigts should be as large as four for the V 2 p 3/2 , in order to obtain the results consistent with the bulk sensitive HAXPES study. [ABSTRACT FROM AUTHOR]

We have studied the local structure of layered Na x (NH 3 ) y MoSe 2 system by Mo K-edge extended X-ray absorption fine structure (EXAFS) measurements performed as a function of temperature. We find that molecular intercalation in MoSe 2 largely affects the Mo-Se network while Mo-Mo seems to sustain small changes. The Einstein temperature ( Θ E ) of Mo-Mo distance hardly changes ( ∼ 264 K) indicating that bond strength of this distance remains unaffected by intercalation. On the other hand, Mo-Se distance suffers a softening, revealed by the decrease of Θ E from ∼ 364 K to ∼ 350 K. The results indicate that Na + ion transported by NH 3 molecules may enter between the two MoSe-layers resulting reduced Se-Se coupling. Therefore, increased hybridization between Se 4p and Mo 4d orbitals due to inter-layer disorder is the likely reason of metallicity in intercalated MoSe 2 and superconductivity at low temperature. [ABSTRACT FROM AUTHOR]

We have used high heat flux plasma synthesis process to grow Co those for the morphology, stoichiometry and the local structure as a function of plasma current. We find that the nanoparticles produced by the thermal plasma method have different shapes and size distribution with the plasma current being a key parameter in controlling the formation of composition, morphology and crystalline structure. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements at Co K-edge have revealed formation of metal and metal oxide nanoparticles with the composition mainly depending on the arc current. While low plasma current appears to produce nanoparticles solely of CoO with a small amount of Co metal, the high plasma current tends to produce nanoparticles of CoO and Co 3 O 4 oxides with increased amount of Co metal. The results are consistent with the morphological and structural analysis, showing nanoparticles of different shapes and size depending on the arc current. [ABSTRACT FROM AUTHOR]

We have investigated the local structure of Tr Zr 2 (Tr = transition metal) superconductor with variable configurational entropy using x-ray absorption spectroscopy. Temperature dependent Zr K-edge extended x-ray absorption fine structure (EXAFS) measurements are carried out on three different samples including the pristine CoZr 2 , medium entropy Co 0.33 Rh 0.34 Ir 0.33 Zr 2 and high entropy Co 0.2 Fe 0.2 Ni 0.2 Rh 0.2 Ir 0.2 Zr 2. We have found that the local bondlengths remain largely temperature independent or tend to show negative thermal expansion, instead the Zr–Zr bondlengths get stiffer with the configurational entropy. The x-ray absorption near edge structure (XANES) spectra at Zr K-edge and Ir L 3 -edge indicate Zr 4 d - Tr n d (n = 2, 3, 4) hybridization to be related with the superconducting transition temperature. The results provide important information on the local structure that can be useful to understand the physical properties of these materials and design new high entropy alloys (HEAs) superconductors. • The effect of mixing entropy in TrZr 2 superconductor has been studied. • The local structure of TrZr 2 changes significantly with the mixing entropy. • The bond lengths are temperature independent or show negative thermal expansion. • The bond lengths are stiffer in presence of an overall increased local disorder. • The Zr 4d – Tr nd hybridization is related with the superconducting transition temperature. [ABSTRACT FROM AUTHOR]

Iron-oxide nanoparticles have been synthesized by high temperature arc plasma route with different plasma currents and characterized for their structure, morphology and local atomic order. Fe K-edge x-ray absorption spectra reveal distinct local structure of the samples grown with different plasma currents. We have shown that the local disorder is higher for the higher plasma current grown samples that also have a larger average particle-size. The results provide useful information to control structural and morphological properties of nanoparticles grown by high temperature plasma synthesis process. [ABSTRACT FROM AUTHOR]

Abstract: We have studied the electronic structure of unoccupied states measured by O K-edge and Cu L-edge x-ray absorption spectroscopy (XAS), combined with crystal structure studied by high resolution powder x-ray diffraction (HRPXRD), of charge-compensated layered superconducting Ca x La1−x Ba1.75−x La0.25+x Cu3O y (0≤x≤0.4 and 6.4≤y≤7.3) cuprate. A detailed analysis shows that, apart from hole doping, chemical pressure on the electronically active CuO2 plane due to the lattice mismatch with the spacer layers greatly influences the superconducting properties of this system. The results suggest chemical pressure to be the most plausible parameter to control the maximum critical temperatures (T c max) in different cuprate families at optimum hole density. [Copyright &y& Elsevier]

Abstract: We have studied local structure of LiMnO2, LiMn0.65Cr0.35O2 and LiMn0.5Ni0.5O2 compounds by Mn K-edge extended X-ray absorption fine structure measurements. The local structure of LiMnO2 is found to be consistent with Jahn–Teller distorted MnO6 octahedra characterized by two different Mn–O bond distances. The Jahn–Teller distortions are suppressed in the Cr and Ni substituted compounds, resulting a single Mn–O distance. However, the Cr atoms tend to occupy a site at a longer distance from Mn in the host lattice (Mn–Cr distance is longer than Mn–Mn distance), unlike the Ni atoms which prefer a site closer to the Mn atoms (Mn–Ni distance is shorter than Mn–Mn distance). Incidentally, Mn–O and Mn–Mn bonds are substantially stiffer in the Cr and Ni substituted compounds. In addition, the static atomic disorder is confined around Cr atoms in the LiMn0.65Cr0.35O2, that is different from the case of LiMn0.5Ni0.5O2 in which larger static disorder appears in the proximity of the Mn atoms. The results suggest that the differences in the local structure of different compounds should be the likely reason for their differing battery characteristics. [Copyright &y& Elsevier]

In our previous studies on the tolerance of living organisms such as planktons and spores of mosses to the high hydrostatic pressure of 7.5 GPa, we showed that all the samples could be borne at this high pressure. These studies have been extended to the extreme high pressure of 20 GPa by using a Kawai-type octahedral anvil press. It was found that the average diameter of the spores ofVenturiellaexposed to 20 GPa for 30 min was 25.5 μm, which is 16.5% smaller (40.0% smaller in volume) than that of the control group which was not exposed to high pressure. The inner organisms showed a further extent of plastic deformation. As a result, a gap appeared between the outer cover and the cytoplasm. A relationship has been obtained between the survival ratio and plastic deformation of spores of mossVenturiellacaused by the application of ultra high pressure. [ABSTRACT FROM PUBLISHER]

Abstract: Temperature dependent Co K-edge extended X-ray absorption fine structure is used to investigate local disorder in LiCoO2 nanoparticles. We find that the nanostructuring has direct influence on the bondlength characteristics. The results reveal a substantial decrease in the force constant of Co–O bonds (the Co–O bonds becoming more flexible), while that for the Co–Co bonds showing hardly any change (or increases slightly) in LiCoO2 nanoparticles with respect to the bulk. Therefore, both random disorder and Co–O bondlength flexibility should be the factors to limit the battery characteristics of the LiCoO2 nanoparticles. [Copyright &y& Elsevier]

Abstract: The experiment on the search for life under very high pressure done for small animal tardigrades has been extended to a plankton, Artemia. It was found that cysts, or dried eggs, of Artemia remain alive after being exposed to a very high hydrostatic pressure of 7.5GPa for 42h. We are convinced that at least two kinds of small animals are still alive after being exposed to such high hydrostatic pressure of 7.5GPa, which corresponds to the pressure at the depth of about 180km below the surface of the Earth, i.e., Mantle pressure. The results of the present investigation suggest the possibility that Artemia, as well as tardigrade may have traveled through outer space in a large meteorite, and reached the Earth alive from another planet or galaxy. [Copyright &y& Elsevier]

Abstract: Measurements of the Fe K-edge X-ray absorption near edge (XANES) spectra of LnOFeAs high T c superconductors exhibit small but measurable changes across the tetragonal to orthorhombic phase structural phase transition. Calculations, based on the local structure centered at the Fe site obtained by crystallographic investigations, reproduce the observed changes in the spectra under the change of the crystal structure, indicating variations in the Fe local unoccupied electronic states. Calculated Fe density of states including stripe spin ordering in the orthorhombic phase show significant modifications with respect to Fe 3d density of states in the tetragonal phase or the density of states in the orthorhombic phase calculated ignoring spin ordering. This implies that the striped spin ordering in the orthorhombic phase is necessary to describe its electronic properties not only in the ground state but also for excited states above the Fermi energy. [Copyright &y& Elsevier]

Abstract: The experiment on the search for life under very high pressure done on small animal, tardigrade, has been extended to the moss Ptychomitrium. Several spore placentas of the moss Ptychomitrium were sealed in a small Teflon capsule together with fluorinate as liquid pressure medium. The capsule was put in the center of a pyrophillite cube. This cube was compressed by six tungsten–carbide second-stage anvils with a front edge length of 4.0mm. These anvils were compressed by a first stage, 250ton press. It was proven that 80–90% of the spores were alive and germinated after being exposed to the maximum pressure of 7.5GPa for up to 48h. Furthermore, a relatively high germination rate of about 35% was retained even after exposure to 7.5GPa for 6 days. The pressure tolerance of moss is found to be much stronger than tardigrades. [Copyright &y& Elsevier]

Abstract: Local structure of the nanostructured LaNi5 alloys, prepared by ball-milling, has been studied using La L3-edge extended X-ray absorption fine structure spectroscopy. The near-neighbor distances tend to decrease with the ball-milling, and the mean square relative displacements (MSRD) show substantial increase suggesting an increased atomic disorder. High temperature annealing helps in partial recovery of atomic order in the ball-milled samples for milling times upto 20h, however, the long-time ball-milled samples seems to gain only a local random order. The results suggest that reduced unit-cell volume together with large atomic-disorder might be causing a higher energy-barrier for the hydride-phase formation in the long time ball-milled LaNi5 powders. [Copyright &y& Elsevier]

Abstract: Local structure of the nanostructured LaNi5 hydrogen storage alloys, prepared by ball-milling, has been studied using Ni K-edge extended X-ray absorption fine structure spectroscopy. Results indicate that the ball-milling up to 100h results in the production of nanoparticles characterized by large atomic disorder and slightly reduced unit-cell volume, compared to the bulk LaNi5. High temperature annealing appears to help in partial recovery of atomic order in the ball-milled samples; however, long-time ball-milled samples retain large disorder even after the high temperature annealing. The results suggest that the large disorder and the reduced unit-cell volume might be causing a higher energy-barrier for the hydride-phase formation in the long time ball-milled LaNi5 powders. [Copyright &y& Elsevier]

Abstract: Terrestrial tardigrade is known to show very strong anti-environmental character at a dehydrated state called “tun” state. It was reported to be alive after exposed to the hydrostatic pressure of 0.6GPa, which was almost twice higher than the limit for most bacteria and multi-organisms. However, the limit of the hydrostatic pressure above which tardigrades cannot survive is unknown. We performed an experiment to put tardigrades into high hydrostatic pressure of 7.5GPa, more than 10-times higher than investigated so far, and convinced that they can survive after exposure to 7.5GPa for up to 12h. [Copyright &y& Elsevier]

Abstract: Lattice vibrational property has been determined in ZrB2 system using the temperature-dependent extended X-ray-absorption fine-structure (EXAFS) technique from room temperature to 28K. The smooth behavior of Debye–Waller factor curve with temperature is slightly abnormal for the first pair Zr–B. In order to reproduce this curve, an improved Einstein mode with two Einstein frequencies has been used. The quantitative analysis of temperature-dependent Debye–Waller factor of Zr–B pair shows one Einstein frequency is very high and the other is small. These frequencies correspond to the vibration of boron layer atoms and transition-metal layer atoms, respectively. Based on the Einstein mode with one frequency, the vibrational frequency for Zr–Zr pair has been also obtained. Zirconium diboride has two types of Zr–Zr interaction. One is in-plane and the other is out-of-plane along the high symmetry axis. Our analysis shows there is a little difference between in-plane Zr–Zr vibration and out-of-plane one. And the smaller Einstein vibrational frequency for the Zr–B shell is just between the two ones of the Zr–Zr shells. Our results show that the lattice vibrational behavior in ZrB2 presents obvious particularity and anisotropy. [Copyright &y& Elsevier]

Abstract: The recent discovery of the magnesium diboride superconductor, a system characterized by a remarkably high transition temperature (), has renewed interest towards experimental and theoretical research of the superconductivity in isostructural systems, such as transition-metal diborides. Here we present an X-ray-absorption fine-structure investigation in AlB2-type 4d transition-metal diborides TMB2 (TM=Y, Zr, Nb) at the transition-metal K-edge. The vibrational behavior of these transition-metal diborides has also been investigated by analyzing the extended X-ray-absorption fine-structure (EXAFS) spectra. The change of the bond length and Debye–Waller factors of TM–B, TM–TM (in-plane) and TM–TM (out-plane) with the covalent radii of the transition-metal atoms has been shown. Data clearly demonstrate that the chemical stability is in the following order for the 4d transition-metal diborides: ZrB2>NbB2>YB2. The chemical stability of YB2 must be much less than that of the two other compounds. It suggests that the species difference of the transition metals influences the vibrational behavior of TM–B and TM–TM bonds. In particular, a clearly different behavior of the vibration is observed for the transition-metal atoms in and out of plane. The results suggest the importance of the metal atoms in the diborides for superconductivity of these compounds and an intimate relationship between the local atomic displacements and the superconductivity. [Copyright &y& Elsevier]

Abstract: The Ce1− x La x Ru2 system has been studied for its superconducting and normal-state properties by high-pressure ac-susceptibility measurements as a function of temperature in the range of 4.3–300K using a cubic anvil pressure cell. The CeRu2 compound shows a sharp transition at the T c that becomes wider with increasing pressure, getting as wide as ∼1.8K at a pressure of 7.5GPa. The transition for the Ce0.91La0.09Ru2 appears with a width of ∼0.7K (about 3 times wider than that for the CeRu2 at 0.5GPa) and gets wider with increasing pressure, similar to the case of the CeRu2 system. The pressure-dependent broadening and anomalous T c behavior of the Ce1− x La x Ru2 could be related to the Fermi surface topological instability that drives the system to get phase separated in the superconducting and weakly antiferromagnetic domains. [Copyright &y& Elsevier]

The normal state of magnesium diboride, the simplest metallic system showing the macroscopic quantum coherence at high temperature (high Tc superconductivity––HTcS) shows some features that are common with the cuprates, shedding light on the pairing mechanism for Tc amplification in HTcS: (1) two or more electronic components associated with multiple Fermi surface portions; (2) crossing of electronic topological transitions (ETT) where the Fermi surface changes its topology and (3) phonon softening in extended Kohn anomalies (EKA) over a large wave-vector range. [Copyright &y& Elsevier]

Precise measurements of the temperature-dependent lattice parameters in a single crystal of La1.85Sr0.15CuO4 are made by X-ray bond method and analyzed comparing the normal thermal expansion term, proportional to T4. A spontaneous lattice contraction of about 2.3×10−5 A˚ was found in the ab-plane, while along the c-axis a small expansion of about 1.5×10−5 A˚ was observed below the superconducting transition temperature of the system, showing some correlation between the structure and the high-Tc superconductivity. A careful search has been made for existence of any extra lattice distortion above the Tc, that might be associated with the stripe inhomogeneities in the title system, however, within the experimental sensitivity we could not find such distortions. [Copyright &y& Elsevier]

We have made the XAFS measurements at the Cr–K-edge on natural Indian ruby single crystals (corundum) and its two irradiated samples with fluence 1×1012 Ni6+ and 5×1012 Ni6+ ions/cm2. Irradiated samples show interesting changes in their physical appearance. XANES measurements show progressive decrease in Δoct value on increase of Ni fluence in irradiated samples. EXAFS measurements on these samples show decrease in Cr–O distance on increase of Ni fluence. Lowering of Δoct value is correlated with the increase of Cr–O distance. [Copyright &y& Elsevier]

A polarised X-ray absorption study is made on a BSCCO single crystal to study the anomalous temperature dependence of itinerant holes, charge aggregation and pair formation. The total yield measurements were made at the CuL3 edges varying the temperature from the 80 K to room temperature (∼300 K) using a liquid nitrogen cryostat. We observe the processes of charge aggregation, pair formation and pair breaking repeating themselves at various temperatures, in the normal state. [Copyright &y& Elsevier]

We have investigated the local structure of layered La 1 − x Ce x OBiSSe system by Bi L 3 -edge extended X-ray absorption fine structure (EXAFS) measurements for different Ce substitutions. Ce L 3 -edge X-ray absorption spectroscopy (XAS) has been used to evaluate the Ce valence responsible for the self-doping in this system. We have found that the local distortion, determined by the separation between two Bi-Ch distances within the BiCh 2 -layer (Ch=S,Se), is quickly suppressed by Ce substitution while the axial Bi-S2 bond elongates. Ce L 3 -edge XAS reveals a coexistence of Ce 3 + and Ce 4 + in which the Ce 4 + weight decreases, an indication of a partial breaking of R E -S-Bi (R E =La/Ce) charge transfer channel with Ce substitution. The results suggest that interaction between R E O spacer layer and BiCh 2 layer, dictated by the out-of-plane Bi-S2 distance, has a significant role in triggering superconductivity in the title system, with the in-plane distortion controlling the charge mobility within the BiCh 2 -layer. • The effect of Ce substitution in BiCh 2 - based superconductor has been studied. • The local structure of BiCh 2 - layer changes significantly by Ce substitution. • The mixed valence of Ce is responsible for the self-doping of the BiCh 2 - layer. • The BiCh 2 distortion is suppressed and the axial Bi-Ch distance elongates. • The axial distance controls the charge transfer to triggers the superconductivity. [ABSTRACT FROM AUTHOR]

Abstract: We report micro-fluorescence (μ-XRF) and micro-XANES (μ-XANES) analysis on the phase-separated samples belonging to the superconducting section Mg1−x Sc x B2 for x >0.27, where we have found a phase separation into a Sc-poor and a Sc-rich region. These phase-separated samples exhibit a critical temperature higher than the pristine MgB2. We have explored the actual Sc distribution along the sample with micro-fluorescence (μ-XRF), with a beam spot size below 1 μm, and we found Sc-poor textures of 100 μm size embedded in a Sc-matrix. With μ-XANES we have studied the chemical state of the Sc in the Sc-poor region, responsible of high T c, and found that Sc does not enter the MgB2 lattice. These results suggest that enhanced T c could be due to the strain, which can be induced by the Sc impurities or by the Sc-rich matrix. [Copyright &y& Elsevier]

Archimedes is an INFN-funded pathfinder experiment aimed at verifying the feasibility of measuring the interaction of vacuum fluctuations with gravity. The final experiment will measure the force exerted by the gravitational field on a Casimir cavity whose vacuum energy is modulated with a superconductive transition, by using a balance as a small force detector. Archimedes is two-year project devoted to test the most critical experimental aspects, in particular the balance resonance frequency and quality factor, the thermal modulation efficiency and the superconductive sample realization. [ABSTRACT FROM AUTHOR]