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.

Enhanced Conductivity and Microstructure in Highly Textured TiN1-x /c-Al2O3 Thin Films.

Titanium nitride thin films are used as an electrode material in superconducting (SC) applications and in oxide electronics. By controlling the defect density in the TiN thin film, the electrical properties of the film can achieve low resistivities and a high critical temperature (T c) close to bulk values. Generally, low defect densities are achieved by stoichiometric growth and a low grain boundary density. Due to the low lattice mismatch of 0.7%, the best performing TiN layers are grown epitaxially on MgO substrates. Here, we report for the first time a T c of 4.9 K for ultrathin (23 nm), highly textured (111), and stoichiometric TiN films grown on 8.75% lattice mismatch c-cut Al2O3 (sapphire) substrates. We demonstrate that with the increasing nitrogen deficiency, the (111) lattice constant increases, which is accompanied by a decrease in T c. For highly N deficient TiN thin films, no superconductivity could be observed. In addition, a dissociation of grain boundaries (GBs) by the emission of stacking faults could be observed, indicating a combination of two sources for electron scattering defects in the system: (a) volume defects created by nitrogen deficiency and (b) defects created by the presence of GBs. For all samples, the average grain boundary distance is kept constant by a miscut of the c-cut sapphire substrate, which allows us to distinguish the effect of nitrogen deficiency and grain boundary density. These properties and surface roughness govern the electrical performance of the films and influence the compatibility as an electrode material in the respective application. This study aims to provide detailed and scale-bridging insights into the structural and microstructural response to nitrogen deficiency in the c-Al2O3/TiN system, as it is a promising candidate for applications in state-of-the-art systems such as oxide electronic thin film stacks or SC applications.

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.

Control of polarization in bulk ferroelectrics by mechanical dislocation imprint.

Defects are essential to engineering the properties of functional materials ranging from semiconductors and superconductors to ferroics. Whereas point defects have been widely exploited, dislocations are commonly viewed as problematic for functional materials and not as a microstructural tool. We developed a method for mechanically imprinting dislocation networks that favorably skew the domain structure in bulk ferroelectrics and thereby tame the large switching polarization and make it available for functional harvesting. The resulting microstructure yields a strong mechanical restoring force to revert electric field-induced domain wall displacement on the macroscopic level and high pinning force on the local level. This induces a giant increase of the dielectric and electromechanical response at intermediate electric fields in barium titanate [electric field-dependent permittivity (ε33) ≈ 5800 and large-signal piezoelectric coefficient (d 33*) ≈ 1890 picometers/volt]. Dislocation-based anisotropy delivers a different suite of tools with which to tailor functional materials.

Towards a Greener and Scalable Synthesis of Na2Ti6O13 Nanorods and Their Application as Anodes in Batteries for Grid-Level Energy Storage.

Grid applications require high power density (for frequency regulation, load leveling, and renewable energy integration), achievable by combining multiple batteries in a system without strict high capacity requirements. For these applications however, safety, cost efficiency, and the lifespan of electrode materials are crucial. Titanates, safe and longevous anode materials providing much lower energy density than graphite, are excellent candidates for this application. The innovative molten salt synthesis approach proposed in this work provides exceptionally pure Na2Ti6O13 nanorods generated at 900-1100 °C in a yield ≥80 wt%. It is fast, cost-efficient, and suitable for industrial upscaling. Electrochemical tests reveal stable performance providing capacities of ≈100 mA h g-1 (Li) and 40 mA h g-1 (Na). Increasing the synthesis temperature to 1100 °C leads to a capacity decrease, most likely resulting from 1) the morphology/volume change with the synthesis temperature and 2) distortion of the Na2Ti6O13 tunnel structure indicated by electron energy-loss and Raman spectroscopy. The suitability of pristine Na2Ti6O13 as the anode for grid-level energy storage systems has been proven a priori, without any performance-boosting treatment, indicating considerable application potential especially due to the high yield and low cost of the synthesis route.

Strain-rate sensitive ductility in a low-alloy carbon steel after quenching and partitioning treatment.

We investigate an extraordinarily high ductility in a low alloy carbon steel at an elevated temperature after a quenching and partitioning (Q&P) treatment. The conventional (quenched and tempered) reference material does not show similar behavior. Interestingly, the Q&P treated material's ductility is considerably reduced at increasing strain rates while strength remains almost constant. These results indicate the presence of a diffusion-controlled deformation mechanism at elevated temperatures. Our research shows that interlath retained austenite is more stable during deformation at higher temperatures, resulting in a delayed transformation to martensite and therefore to a more pronounced contribution to plastic deformation at (and in the vicinity of) the many interfaces inherently present in this multi-phase steel.