A method with ultra-high angular resolution for X-ray diffraction experiments.

In X-ray diffraction measurements, the angular resolution has a detection limit due to the receiving size of the detector. In many cases this detection limit is too large and must be breached to obtain the desired information. A novel method is proposed here by making the detector simultaneously measuring and moving. Using the deconvolution algorithm to remove the convolution effect, the pixel size limitation is finally broken. The algorithm used is not a common one, and suppresses signals at high frequencies, ensuring the reliability of the peak shape after restoration. The feasibility of this method is verified by successfully measuring the crystal truncation rod signal of SrTiO3 single crystal, and the resolution is nearly ten times higher than that of a single pixel. Moreover, this method greatly reduces the noise and improves the signal-to-noise ratio.

Y(III) Sorption at the Orthoclase (001) Surface Measured by X-ray Reflectivity.

Interactions of heavy metals with charged mineral surfaces control their mobility in the environment. Here, we investigate the adsorption of Y(III) onto the orthoclase (001) basal plane, the former as a representative of rare earth elements and an analogue of trivalent actinides and the latter as a representative of naturally abundant K-feldspar minerals. We apply in situ high-resolution X-ray reflectivity to determine the sorption capacity and molecular distribution of adsorbed Y species as a function of the Y3+ concentration, [Y3+], at pH 7 and 5. With [Y3+] ≥ 1 mM at pH 7, we observe an inner-sphere (IS) sorption complex at a distance of ∼1.5 Å from the surface and an outer-sphere (OS) complex at 3-4 Å. Based on the adsorption height of the IS complex, a bidentate, binuclear binding mode, in which Y3+ binds to two terminal oxygens, is proposed. In contrast, mostly OS sorption is observed at pH 5. The observed maximum Y coverage is ∼1.3 Y3+/AUC (AUC: area of the unit cell = 111.4 Å2) for all the investigated pH values and Y concentrations, which is in the expected range based on the estimated surface charge of orthoclase (001).

Drastic Reduction of the Solid Electrolyte-Electrode Interface Resistance via Annealing in Battery Form.

The origin of electrical resistance at the interface between the positive electrode and solid electrolyte of an all-solid-state Li battery has not been fully determined. It is well known that the interface resistance increases when the electrode surface is exposed to air. However, an effective method of reducing this resistance has not been developed. This report demonstrates that drastic reduction of the resistance is achievable by annealing the entire battery cell. Exposing the LiCoO2 positive electrode surface to H2O vapor increases the resistance by more than 10 times (to greater than 136 Ω cm2). The magnitude can be reduced to the initial value (10.3 Ω cm2) by annealing the sample in a battery form. First-principles calculations reveal that the protons incorporated into the LiCoO2 structure are spontaneously deintercalated during annealing to restore the low-resistance interface. These results provide fundamental insights into the fabrication of high-performance all-solid-state Li batteries.

Tuning the Schottky Barrier Height at the Interfaces of Metals and Mixed Conductors.

Understanding electronic and ionic transport across interfaces is crucial for designing high-performance electric devices. The adjustment of work functions is critical for band alignment at the interfaces of metals and semiconductors. However, the electronic structures at the interfaces of metals and mixed conductors, which conduct both electrons and ions, remain poorly understood. This study reveals that a Schottky barrier is present at the interface of the Nb-doped SrTiO3 metal and a LiCoO2 mixed conductor and that the interfacial resistance can be tuned by inserting an electric dipole layer. The interfacial resistance significantly decreased (by more than 5 orders of magnitude) upon the insertion of a 1 nm thick insulating LaAlO3 layer at the interface. We apply these techniques to solid-state lithium batteries and demonstrate that tuning the electronic energy band alignment by interfacial engineering is applicable to the interfaces of metals and mixed conductors. These results highlight the importance of designing positive electrode and current collector interfaces for solid-state lithium batteries with high power density.

In situ structural study of the surface complexation of lead(II) on the chemically mechanically polished hematite (11¯02) surface.

A structural study of the surface complexation of Pb(II) on the (11¯02) surface of hematite was undertaken using crystal truncation rod (CTR) X-ray diffraction measurements under in situ conditions. The sorbed Pb was found to form inner sphere (IS) complexes at two types of edge-sharing sites on the half layer termination of the hematite (11¯02) surface. The best fit model contains Pb in distorted trigonal pyramids with an average PbO bond length of 2.27(4) Å and two characteristic Pb-Fe distances of 3.19(1) Å and 3.59(1) Å. In addition, a site coverage model was developed to simulate coverage as a function of sorbate-sorbate distance. The simulation results suggest a plausible Pb-Pb distance of 5.42 Å, which is slightly larger than the diameter of Pb's first hydration shell. This relates the best fit surface coverage of 0.59(4) Pb per unit cell at monolayer saturation to steric constraints as well as electrostatic repulsion imposed by the hydrated Pb complex. Based on the structural results we propose a stoichiometry of the surface complexation reaction of Pb(II) on the hematite (11¯02) surface and use bond valence analysis to assign the protonation schemes of surface oxygens. Surface reaction stoichiometry suggests that the proton release in the course of surface complexation occurs from the Pb-bound surface O atoms at pH 5.5.

Atomically Well-Ordered Structure at Solid Electrolyte and Electrode Interface Reduces the Interfacial Resistance.

Using synchrotron surface X-ray diffraction, we investigated the atomic structures of the interfaces of a solid electrolyte (Li3PO4) and electrode (LiCoO2). We prepared two types of interfaces with high and low interface resistances; the low-resistance interface exhibited a flat and well-ordered atomic arrangement at the electrode surface, whereas the high-resistance interface showed a disordered interface. These results indicate that the crystallinity of LiCoO2 at the interface has a significant impact on interface resistance. Furthermore, we reveal that the migration of Li ions along the interface and into grain boundaries and antiphase domain boundaries is a critical factor reducing interface resistance.