Recent nanomedical applications have again highlighted the significance of silica surface chemistry in solution. Here, we report in situ electronic structure measurements at the silica–aqueous interface as a function of pH for nanoparticles (NPs) of 7, 12, and 22 nm using a liquid microjet in combination with synchrotron radiation. The Si K-edge X-ray absorption near-edge spectroscopy (XANES) spectra reveal a change in shape of the Si 1s → t2 (Si 2p-3s) absorption brought about by changes in the silanol protonation state at the interface of the NPs as a result of changes in solution pH. Our results are consistent with the number of silanol groups changing the protonation state being inversely correlated with the SiO2 NP size. The importance of in situ studies is also demonstrated by comparing the XANES spectra of aqueous 7 nm SiO2 with the same dehydrated sample in vacuum.
A comparative study of ex-situ and in-operando X-ray diffraction experiments using the fast lithium ion conductor Li 0.18 Sr 0.66 Ti 0.5 Nb 0.5 O 3 will be presented.Ex-situ analysis of synchrotron X-ray diffraction data suggests that a single phase material exists for all discharges to as low as 0.422 V.For samples with higher lithium content, it is possible to determine the lithium position from the X-ray data.However, in-operando X-ray diffraction reveals a kinetically driven two phase region on cycling below 1 V. Monitoring the change in unit cell dimension during electrochemical cycling showed a reduction in the rate of unit cell expansion part way through the first discharge and during the second discharge, caused by a drop in lithium diffusion into the bulk material for higher lithium contents.A more significant change is a jump in the unit cell expansion once the lithium content exceeds one lithium ion per vacant site, caused by damping of octahedral rotations.This provides a link between lithium content and octahedral rotations.Using in-operando diffraction may therefore enable to determine the strength of octahedral rotations in defect perovskites and allow correlations with the large variance of ionic conductivities in these materials. References[1] W. R. Brant, D. Li, Q. Gu & S. Schmid, J. Power Sources 302, 126 -134 (2016).Comparison of ex-situ and operando X-ray diffraction techniques for investigating lithium insertion defect perovskite Li 0.18 Sr 0.66 Ti 0.5 Nb 0.5 O 3 .[2
The resistive switching state in Cr-doped SrTiO3 was induced by applying an electric field. This was done in ambient air and in an atmosphere of H2/Ar. The distribution of the thereby introduced oxygen vacancies was studied by spatially resolved X-ray fluorescence images. It was concluded that the oxygen vacancies were introduced in the interface between the SrTiO3 and the positively biased electrode.
High precision measurements of two Zeeman hyperfine transitions in the ground state of muonium in a strong magnetic field have been made at LAMPF using microwave magnetic resonance spectroscopy and a resonance line narrowing technique. These determine the most precise values of the ground state hyperfine structure interval of muonium $\ensuremath{\Delta}\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}4463302765(53)\mathrm{Hz}$ $(12\mathrm{ppb})$, and of the ratio of magnetic moments ${\ensuremath{\mu}}_{\ensuremath{\mu}}/{\ensuremath{\mu}}_{p}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3.18334513(39)$ $(120\mathrm{ppb})$, representing a factor of 3 improvement. Values of the mass ratio ${m}_{\ensuremath{\mu}}/{m}_{e}$ and the fine structure constant $\ensuremath{\alpha}$ are derived from these results.
