Electronic devices, designed to be long lasting, are commonly made with rigid, nondegradable materials. This, together with the presence of rare and toxic elements, creates significant issues for their waste management. The production of electronic devices, made with biodegradable materials that are sourced from waste streams of the agricultural sector, will create the premises for circular economy systems in the electronics sector that will increase its sustainability. Here, this new approach has been demonstrated by using keratin, the protein extracted from waste wool clips, combined with graphene to produce protein-based electronic materials. Resistors plane capacitors and inductors were fabricated, characterized and then assembled together to obtain analogue electrical circuits, such as, high-pass filters or resonators. Morphological structures, electrical characteristics, thermal stability and mechanical properties were fully investigated. Finally, a water-based ink of keratin and graphene was used to functionalize cellulose, obtaining flexible electrodes with remarkable sheet resistances (≈ 10 Ω/sq), ohmic I-V curves were obtained and the electrical conductivity after folding/unfolding cycles was measured. All the processing and fabrication methods used water as the only solvent. The described approach produced easily disposable electronics materials with reduced fingerprint on the environment, demonstrating that keratin from wool waste is an excellent candidate for the creation of circular economy systems in the electronics sector. The proposed valorization of waste materials for electronics applications is named "wastetronics".
In this work, we demonstrate an approach for improving ferroelectric properties of La:HfO2 thin films by shifting the grain growth regime toward heterogeneous nucleation. A dilute 0.083 M instead of a 0.25 M solution together with an annealing step after every spin-coating cycle film gives rise to a significant improvement of ferroelectric properties. While a remanent polarization of 7 μC/cm2 was found for randomly oriented conventional films, the value of 15 μC/cm2 for the dilute solution is a result of a mixed 111 and 002 preferential orientation. A more than 50% improved breakdown voltage stems from a global density improvement from 8.0 to 8.4 g/cm3 as obtained from x-ray reflectivity (XRR). We also find superstructure peaks in XRR hinting on periodic alternations of the local density throughout the film thickness. Scanning transmission electron microscopy and secondary ion mass spectrometry confirm this periodicity. The sensitivity of XRR for this periodicity was leveraged to gain further insights in the origin of this superstructure with additional experiments. We conclude that both orientation and the superstructure are caused by a “layered structure” according to Schuler's microstructural zone model. However, our data also provide evidence for parallel chemical effects of cap formation in each stacked sub-layer. While this work shows a significant enhancement of ferroelectric properties, it also provides insights into further optimization potential of solution deposition of HfO2/ZrO2 thin films. Our XRR-based approach supplemented with suitable additional analysis can be of great value for the optimization of other solution-derived thin films beyond the material class studied here.
The ability to tune and enhance the properties of luminescent materials is essential for enlarging their application potential. Recently, the modulation of the photoluminescence emission of lanthanide-doped ferroelectric perovskites by applying an electric field has been reported. Herein, we show that the ferroelectric order and, more generally the polar order, has a direct effect on the photoluminescence of Eu 3+ in the model BaZr x Ti 1−x O 3 perovskite even in the absence of an external field. The dipole arrangement evolves with increasing x from long-range ferroelectric order to short-range order typical of relaxors until the non-polar paraelectric BaZrO 3 is achieved. The cooperative polar interactions existing in the lattice ( x < 1) promote the off-center displacement of the Eu 3+ ion determining a change of the lanthanide site symmetry and, consequently, an abrupt variation of the photoluminescence emission with temperature. Each type of polar order is characterized by a distinct photoluminescence behaviour.
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