Here we show that the B-site cation (Fe/Mo) ordering in the double-perovskite magnetoresistor, Sr 2 FeMoO 6 , is controlled by either kinetics or thermal equilibrium depending on the temperature range. In order to enhance the ordering, long synthesis periods at moderate temperatures are thus required. Employment of a special oxygen-getter-controlled low-O 2 -pressure encapsulation technique for the sample synthesis enabled us to use long heating periods without evident evaporation of Mo, and thereby reach the thermal equilibrium state and a high degree of B-site cation order. For samples fired at 1150 o C for long periods (≥ 36 hours), record-high M S values of 3.7 ∼ 3.9 µ B were obtained.

In situ X-ray and neutron powder diffraction were carried out for the La 4 MgNi 19 alloy sample, which was obtained by annealing under controlled Mg-vapor pressure and temperature. The sample contained five phases:

Carbon-and boron-2p states of superconducting and non-superconducting boron-doped diamond samples are measured using soft X-ray emission and absorption spectroscopy. For the superconducting sample, a large density of hole states is observed in the valence band in addition to the states in the impurity band. The hole states in the valence band is located at about 1.3 eV below the valence band maximum regardless of the doping level, which cannot be interpreted within a simple rigid band model. Present experimental results, combined with the first principles calculations, suggest that superconductivity is to be attributed to the holes in the valence band.

X-ray absorption (XAS) and emission (XES) spectroscopy near B K and C K edges have been performed on metallic (ϳ0.1 at. % B, B-diamond) and semiconducting (ϳ0.03 at. % B and N, BN-diamond) doped diamond films. Both B K XAS and XES spectra show a metallic partial density of states (PDOS) with the Fermi energy of 185.3 eV, and there is no apparent boron-concentration dependence in contrast to the different electric property. In C K XAS spectrum of B-diamond, the impurity state ascribed to boron is clearly observed near the Fermi level. The Fermi energy is found to be almost same with the top of the valence band of nondoped diamond: E V = 283.9 eV. C K XAS of BN-diamond shows both the B-induced shallow level and N-induced deep and broad levels as the in-gap states, in which the shallow level is in good agreement with the activation energy ͑E a = 0.37 eV͒ estimated from the temperature dependence of the conductivity; namely, the change in C 2p PDOS of impurity-induced metallization is directly observed. The electric property of this diamond is ascribed mainly to the electronic structure of C 2p near the Fermi level. The observed XES spectra are compared with the discrete variational X␣ (DVX␣) cluster calculation. The DVX␣ result supports the strong hybridization between B 2p and C 2p observed in XAS and XES spectra, and suggests that the small amount of boron ͑ഛ0.1 at. % ͒ in diamond occupies the substitutional site rather than interstitial site.

High-purity Sr 2 Fe(Mo 1Ϫx T x )O 6 samples with TϭW, Ta and 0рxр1 were obtained by means of encapsulation synthesis. For the nonsubstituted samples earlier 57 Fe Mössbauer spectroscopy measurements indicate that the Fe ions occupy a fluctuating mixed-valence state of ϩ2.5. ͓J. Lindén et al. Appl. Phys. Lett. 76 ͑2000͒ 2925.͔ W VI substitution causes increasing amounts of Fe to enter the II state, whereas Ta V substitution yields increasing amounts of Fe III . Both substitution schemes lead to a decrease in the intensity of the component assigned to Fe 2.5ϩ . Nonsubstituted samples exhibit a characteristic tunneling-type magnetoresistance below T C . Both W and Ta substitution were found to enhance the low-temperature magnetoresistance around the Néel temperature of the pure Sr 2 FeWO 6 and Sr 2 FeTaO 6 phases, respectively. The enhancement appears to be related to the colossal magnetoresistance ͑CMR͒ effect at the paramagnetic to antiferromagnetic transitions in the areas rich in W or Ta. The transition and consequently the region of non-zero CMR effect are rather broad due to the glass-like behavior of the highly-substituted samples within the low-temperature region. Ta substitution had a stronger influence on the transport properties, magnetization and mixed valency than W substitution had. It is suggested that Ta V disrupts the double-exchange interaction responsible for the magnetism in the Sr 2 FeMoO 6 more efficiently than W VI .

In this report, we established a new electrochemical method for the detection of conformational changes in large, non-metalloproteins such as bovine serum albumin, using flow injection analysis coupled with hydrogen-terminated, boron-doped diamond electrodes. The oxidation current was used as a signal reporter in the monitoring of urea-induced BSA denaturation. In the denatured state at high urea concentrations, the electrochemical signal increased, and the amperometric responses for the oxidation potential at 1300 mV were consistent with the results of conventional methods of denaturation monitoring using fluorescence spectroscopy. The oxidation involved at least five redox-active species (cysteine, tryptophan, tyrosine, methionine, and disulfide bonds). Furthermore, the method also showed high sensitivity for quantitative analysis of protein. A linear dynamic in the concentration range 50-400 microg/mL (r(2) = 0.977) with a lower detection limit of 190 ng/mL was achieved for BSA. Direct electrochemical detection of conformation changes of proteins using BDD electrodes can be performed with advantages in terms of simplicity and sensitivity.

Reduction in reversible hydrogen storage capacity with increasing hydrogenation and dehydrogenation cycle number is observed in numerous hydrogen storage materials, but the mechanism behind this unfavorable change has not been elucidated yet. In this study, we have investigated the development of structural defects or disorders in V1–x Ti x H2, x = 0, 0.2, and 0.5, during the first 15 hydrogen absorption and desorption cycles using the atomic pair distribution function (PDF) analysis of synchrotron X-ray total scattering data to find out the possible structural origin of the poor cyclic stability of V1–x Ti x alloys. While pure vanadium shows no significant change in the PDF, alloy samples subject to several hydrogenation and dehydrogenation cycles display fast decaying of the PDF profile due to a progressive increase in the PDF peak width with increasing r. This r-dependent PDF peak broadening effect becomes stronger with cycle number. Molecular dynamics (MD) simulations demonstrated that dislocation defects explain characteristic features in our experimental PDFs very well and suggested that a large number of dislocations are formed during hydrogen cycling. We found there is a close relation between the reduced amount of the reversible hydrogen content of V0.8Ti0.2 and the amount of generated dislocations. On the basis of the PDF analysis results, a possible mechanism behind degradation in the reversible hydrogen storage capacity of V1–x Ti x is discussed.

Magnetization vs temperature behavior of RuSr2GdCu2O8−δ (Ru-1212) measured in an field of 5 Oe, shows a clear branching of zero-field-cooled (ZFC) and field-cooled (FC) curves around 140 K, a cusp at 135 K, and a diamagnetic transition around 20 K (in the ZFC branch). The cusp at 135 K is due to the antiferromagnetic ordering of the Ru moments. The magnetization-field isotherms, below 50 K, show a nonlinear contribution from a ferromagnetic component. The resistance vs temperature behavior of the compound, in applied fields of 0, 3, and 7 T, confirms that the sample is superconducting at around 20 K. The superconducting transition exhibits field broadening of a type different than that known for conventional high Tc superconductors. The magnetoresistance (MR) is negative above the Ru magnetic ordering temperature of 135 K, while below this temperature, MR displays a positive peak in low fields and becomes negative in higher fields. A maximum of 2% is observed for the negative MR value at the Ru magnetic ordering temperature. An electron diffraction pattern obtained for this Ru-1212 sample shows two types of superstructure; one with a weak spot at the center of the a–b rectangle and the other only along the b direction. It is possible that either Ru/Cu or Ru4+/Ru5+ ordering of 2b periodicity takes place along the b direction.