No abstract

Cubic garnet phases based on Al-substituted Li7La3Zr2O12 (LLZO) have high ionic conductivities and exhibit good stability versus metallic lithium, making them of particular interest for use in next-generation rechargeable battery systems. However, high interfacial impedances have precluded their successful utilization in such devices until the present. Careful engineering of the surface microstructure, especially the grain boundaries, is critical to achieving low interfacial resistances and enabling long-term stable cycling with lithium metal. This study presents the fabrication of LLZO heterostructured solid electrolytes, which allowed direct correlation of surface microstructure with the electrochemical characteristics of the interface. Grain orientations and grain boundary distributions of samples with differing microstructures were mapped using high-resolution synchrotron polychromatic X-ray Laue microdiffraction. The electrochemical characteristics are strongly dependent upon surface microstructure, with small grained samples exhibiting much lower interfacial resistances and better cycling behavior than those with larger grain sizes. Low area specific resistances of 37 Ω cm(2) were achieved; low enough to ensure stable cycling with minimal polarization losses, thus removing a significant obstacle toward practical implementation of solid electrolytes in high energy density batteries.

Single-crystal micro- and nanomaterials often exhibit higher yield strength than their bulk counterparts. This enhancement is widely recognized in structural materials but is rarely exploited to probe fundamental physics of electronic materials. Vanadium dioxide exhibits coupled electronic and structural phase transitions that involve different structures existing at different strain states. Full understanding of the driving mechanism of these coupled transitions necessitates concurrent structural and electrical measurements over a wide phase space. Taking advantages of the superior mechanical property of micro/nanocrystals of VO(2), we map and explore its stress-temperature phase diagram over a phase space that is more than an order of magnitude broader than previously attained. New structural and electronic aspects were observed crossing phase boundaries at high-strain states. Our work shows that the actively tuning strain in micro/nanoscale electronic materials provides an effective route to investigate their fundamental properties beyond what can be accessed in their bulk counterpart.

Abstract. A new synchrotron X-ray diffraction study of MgSiO3 perovskite at high-pressure and high-temperature has been carried out in a laser-heated diamond-anvil cell to 94 GPa and temperatures above 2500 K. MgSiO3 perovskite is shown to be stable in this P-T range and adopts an orthorhombic structure (space group Pbnm), thus ruling out any phase transition or decomposition to an assemblage of denser oxides. Structural refinements show an increase of the orthorhombic distortion with increasing pressure, counterbalanced by a decrease of this distortion at high temperature, as evidenced by the Si-O-Si angle evolution. In addition, thermoelastic parameters identified from this new pressure-volume-temperature data set indicate that a significant amount of magnesiowtistite is required to match PREM bulk modulus profile, thus making a pure perovskite lower mantle unlikely.