Structural analysis of sulfuric acid solutions containing Ti and Mn using x-ray diffraction, x-ray absorption fine structure, and molecular dynamics simulation.

Structural analyses have been performed for sulfuric acid (H2SO4) aqueous solutions containing Ti and/or Mn. These solutions are used as the positive electrolyte in the Ti-Mn redox flow (RF) battery, in which it had been found that adding Ti4+ in the positive electrolyte is very effective to reduce the MnO2 precipitation at a high state of charge. X-ray diffraction and x-ray absorption fine structure (XAFS) measurements were employed in order to obtain total correlation functions, T(r)'s, and coordination numbers around Mn and Ti in the solutions, respectively. The T(r)'s showed some peculiar peaks that were assigned to correspond to S-O, O-O, Mn-O, and Ti-O pairs in the solutions. The XAFS analysis demonstrated that both Mn and Ti have 6-coordinating oxygen atoms in the solutions. The classical molecular dynamics simulation was also carried out to obtain structural models of the solutions. By tuning the Born-Mayer type potential parameters, the T(r)'s calculated from the models showed good agreement with the experimental ones. Regarding the coordination number, the 6-coordinated Mn-O was reproduced successfully, while we need further investigation to find parameters that can reproduce the 6-coordinated Ti-O in the solutions. The simulation results also indicated the existence of Ti-SO4 bonds, which should promote the H+ dissociation from HSO4- and increase the H+ concentration in the solutions. This may be effective to suppress the MnO2 precipitation at a high state of charge in the RF battery.

Chemical analysis of impurity boron atoms in diamond using soft X-ray emission spectroscopy.

To analyze the local structure and/or chemical states of boron atoms in boron-doped diamond, which can be synthesized by the microwave plasma-assisted chemical vapor deposition method (CVD-B-diamond) and the temperature gradient method at high pressure and high temperature (HPT-B-diamond), we measured the soft X-ray emission spectra in the CK and BK regions of B-diamonds using synchrotron radiation at the Advanced Light Source (ALS). X-ray spectral analyses using the fingerprint method and molecular orbital calculations confirm that boron atoms in CVD-B-diamond substitute for carbon atoms in the diamond lattice to form covalent B-C bonds, while boron atoms in HPT-B-diamond react with the impurity nitrogen atoms to form hexagonal boron nitride. This suggests that the high purity diamond without nitrogen impurities is necessary to synthesize p-type B-diamond semiconductors.

Local structure analyses around Er(3+) in Er-doped fibers with Al co-doping.

The local structure around Er(3+) in Er-doped optical fiber (EDFs) was explored by X-ray absorption fine structure (XAFS) measurements. Using several new approaches such as a novel sample preparation, we successfully measured the XAFS. The intensities near the 8.36 keV peaks were observed for the first time using X-ray Absorption Near Edge Structure (XANES) analysis. The intensities increased in the order of Er, Er(2)O(3), and EDF samples, indicating that Er(3+) in the EDFs existed as an oxide state. Extend X-ray Absorption Fine Structure (EXAFS) analysis also showed that the oxygen coordination number of Er(3+) increased as the Al concentration increased and that the Er-O distances of EDF with Al co-doping is longer than that of EDF without Al co-doping.