Deflecting Dendrites by Introducing Compressive Stress in Li7La3Zr2O12 Using Ion Implantation.

Lithium dendrites belong to the key challenges of solid-state battery research. They are unavoidable due to the imperfect nature of surfaces containing defects of a critical size that can be filled by lithium until fracturing the solid electrolyte. The penetration of Li metal occurs along the propagating crack until a short circuit takes place. It is hypothesized that ion implantation can be used to introduce stress states into Li6.4La3Zr1.4Ta0.6O12 which enables an effective deflection and arrest of dendrites. The compositional and microstructural changes associated with the implantation of Ag-ions are studied via atom probe tomography, electron microscopy, and nano X-ray diffraction indicating that Ag-ions can be implanted up to 1 µm deep and amorphization takes place down to 650-700 nm, in good agreement with kinetic Monte Carlo simulations. Based on diffraction results pronounced stress states up to -700 MPa are generated in the near-surface region. Such a stress zone and the associated microstructural alterations exhibit the ability to not only deflect mechanically introduced cracks but also dendrites, as demonstrated by nano-indentation and galvanostatic cycling experiments with subsequent electron microscopy observations. These results demonstrate ion implantation as a viable technique to design "dendrite-free" solid-state electrolytes for high-power and energy-dense solid-state batteries.

Enhanced Photoconductivity at Dislocations in SrTiO3.

Dislocations are 1D crystallographic line defects and are usually seen as detrimental to the functional properties of classic semiconductors. It is shown here that this not necessarily accounts for oxide semiconductors in which dislocations are capable of boosting the photoconductivity. Strontium titanate single crystals are controllably deformed to generate a high density of ordered dislocations of two slip systems possessing different mesoscopic arrangements. For both slip systems, nanoscale conductive atomic force microscope investigations reveal a strong enhancement of the photoconductivity around the dislocation cores. Macroscopic in-plane measurements indicate that the two dislocation systems result in different global photoconductivity behavior despite the similar local enhancement. Depending on the arrangement, the global photoresponse can be increased by orders of magnitude. Additionally, indications for a bulk photovoltaic effect enabled by dislocation-surrounding strain fields are observed for the first time. This proves that dislocations in oxide semiconductors can be of large interest for tailoring photoelectric functionalities. Direct evidence that electronic transport is confined to the dislocation core points to a new emerging research field.

Blacklight sintering of ceramics.

For millennia, ceramics have been densified via sintering in a furnace, a time-consuming and energy-intensive process. The need to minimize environmental impact calls for new physical concepts beyond large kilns relying on thermal radiation and insulation. Here, we realize ultrarapid heating with intense blue and UV-light. Thermal management is quantified in experiment and finite element modelling and features a balance between absorbed and radiated energy. With photon energy above the band gap to optimize absorption, bulk ceramics are sintered within seconds and with outstanding efficiency (≈2 kWh kg-1) independent of batch size. Sintering on-the-spot with blacklight as a versatile and widely applicable power source is demonstrated on ceramics needed for energy storage and conversion and in electronic and structural applications foreshadowing economic scalability.

Dislocation-toughened ceramics.

Functional and structural ceramics have become irreplaceable in countless high-tech applications. However, their inherent brittleness tremendously limits the application range and, despite extensive research efforts, particularly short cracks are hard to combat. While local plasticity carried by mobile dislocations allows desirable toughness in metals, high bond strength is widely believed to hinder dislocation-based toughening of ceramics. Here, we demonstrate the possibility to induce and engineer a dislocation microstructure in ceramics that improves the crack tip toughness even though such toughening does not occur naturally after conventional processing. With modern microscopy and simulation techniques, we reveal key ingredients for successful engineering of dislocation-based toughness at ambient temperature. For many ceramics a dislocation-based plastic zone is not impossible due to some intrinsic property (e.g. bond strength) but limited by an engineerable quantity, i.e. the dislocation density. The impact of dislocation density is demonstrated in a surface near region and suggested to be transferrable to bulk ceramics. Unexpected potential in improving mechanical performance of ceramics could be realized with novel synthesis strategies.

Conceptual Framework for Dislocation-Modified Conductivity in Oxide Ceramics Deconvoluting Mesoscopic Structure, Core, and Space Charge Exemplified for SrTiO3.

The introduction of dislocations is a recently proposed strategy to tailor the functional and especially the electrical properties of ceramics. While several works confirm a clear impact of dislocations on electrical conductivity, some studies raise concern in particular when expanding to dislocation arrangements beyond a geometrically tractable bicrystal interface. Moreover, the lack of a complete classification on pertinent dislocation characteristics complicates a systematic discussion and hampers the design of dislocation-modified electrical conductivity. We proceed by mechanically introducing dislocations with three different mesoscopic structures into the model material single-crystal SrTiO3 and extensively characterizing them from both a mechanical as well as an electrical perspective. As a final result, a deconvolution of mesoscopic structure, core structure, and space charge enables us to obtain the complete picture of the effect of dislocations on functional properties, focusing here on electric properties.

Low-profile self-sealing sample transfer flexure box.

A flexural bearing mechanism has enabled the development of a self-sealing box for protecting air sensitive samples during transfer between glove boxes, micro-machining equipment, and microscopy equipment. The simplicity and self-actuating feature of this design makes it applicable to many devices that operate under vacuum conditions. The models used to design the flexural mechanism are presented in detail. The device has been tested in a Zeiss Merlin GEMINI II scanning electron microscope with Li3PS4 samples, showing effective isolation from air and corrosion prevention.