Ceramic materials have been widely used for structural applications. However, most ceramics have rather limited plasticity at low temperatures and fracture well before the onset of plastic yielding. The brittle nature of ceramics arises from the lack of dislocation activity and the need for high stress to nucleate dislocations. Here, we have investigated the deformability of TiO2 prepared by a flash-sintering technique. Our in situ studies show that the flash-sintered TiO2 can be compressed to ~10% strain under room temperature without noticeable crack formation. The room temperature plasticity in flash-sintered TiO2 is attributed to the formation of nanoscale stacking faults and nanotwins, which may be assisted by the high-density preexisting defects and oxygen vacancies introduced by the flash-sintering process. Distinct deformation behaviors have been observed in flash-sintered TiO2 deformed at different testing temperatures, ranging from room temperature to 600°C. Potential mechanisms that may render ductile ceramic materials are discussed.
Light-weight aluminum (Al) alloys have widespread applications. However, most Al alloys have inherently low mechanical strength. Nanotwins can induce high strength and ductility in metallic materials. Yet, introducing high-density growth twins into Al remains difficult due to its ultrahigh stacking-fault energy. In this study, it is shown that incorporating merely several atomic percent of Fe solutes into Al enables the formation of nanotwinned (nt) columnar grains with high-density 9R phase in Al(Fe) solid solutions. The nt Al-Fe alloy coatings reach a maximum hardness of ≈5.5 GPa, one of the strongest binary Al alloys ever created. In situ uniaxial compressions show that the nt Al-Fe alloys populated with 9R phase have flow stress exceeding 1.5 GPa, comparable to high-strength steels. Molecular dynamics simulations reveal that high strength and hardening ability of Al-Fe alloys arise mainly from the high-density 9R phase and nanoscale grain sizes.
High energy particle radiations induce severe microstructural damage in metallic materials. Nanoporous materials with a giant surface-to-volume ratio may alleviate radiation damage in irradiated metallic materials as free surface are defect sinks. Here we show, by using in situ Kr ion irradiation in a transmission electron microscope at room temperature, that nanoporous Au indeed has significantly improved radiation tolerance comparing with coarse-grained, fully dense Au. In situ studies show that nanopores can absorb and eliminate a large number of radiation-induced defect clusters. Meanwhile, nanopores shrink (self-heal) during radiation, and their shrinkage rate is pore size dependent. Furthermore, the in situ studies show dose-rate-dependent diffusivity of defect clusters. This study sheds light on the design of radiation-tolerant nanoporous metallic materials for advanced nuclear reactor applications.
Recently,
SnO2 has been recognized as a promising electron
transport layer (ETL) for perovskite solar cells (PSCs) due to its
outstanding optoelectronic properties and low-temperature fabricating
process. However, the detrimental defects formed at the SnO2/perovskite interface and within bulk perovskite films cause severe
non-radiative recombination, limiting the further improvement of power
conversion efficiencies (PCEs). Herein, we have demonstrated a facile
surface treatment on SnO2 through KF modification to passivate
defects at both regions simultaneously. F– ions
reduce the detrimental hydroxyl group defects on the SnO2 surface effectively, resulting in improved crystallinity of perovskite
films with a more favorable morphology. Meanwhile, a preferred energy
level alignment between SnO2 and MAPbI3 films
is obtained, improving the carrier transport capability. Moreover,
K+ ions can diffuse into the MAPbI3 film, passivating
the grain boundaries and intrinsic I– vacancy defects.
Consequently, a significant increase in PCE from 18.47 to 20.33% is
achieved for a MAPbI3 PSC based on a SnO2/KF
ETL, with negligible hysteresis and improved stability.
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