Transparent, flexible and efficient ferroelectric composite films were fabricated by a simple ultrasonication approach followed by thermal treatment. The enhanced electroactive β‐phase and stabilization of the ferroelectric poly(vinylidene fluoride) (PVDF) polymer were analyzed by the substitution of various cations with different oxidation states (Li1+, Al3+) as fillers. The electroactive β‐phase was obtained due to the stretching of −CH2−/−CF2− molecular chains, stress‐induced effects during the sonication process and the interfacial interaction between the molecular chains and the surface charge of foreign elements. Further, a flexible ferroelectric nanogenerator was implemented and subjected to harness the waste biomechanical energy. The PVDF/Al3+ composite film‐based device gave the maximum amount of voltage and current of 189 V and 0.97 μA respectively at 2 N force. This high electrical output is caused by the electrostatic interaction between electronegative fluorine atoms and the surface active, positive charged ions of the fillers. The obtained maximum instantaneous power density of the FF‐CNG device at 20 MΩ load resistance is 1.92 mW/m2. The generated output is used to power up commercial light‐emitting diodes and display devices without using storage components. The proposed approach for enhancing the throughput of ferroelectric polymers can pave the way to develop new smart composite films for efficient energy conversion.
Ferromagnetic oxide semiconductors exhibiting efficient luminescent properties together with robust ferromagnetism above room temperature form an exclusive class of spintronic materials endowed with both charge and spin degrees of freedom.
We have synthesized FINEMET alloy by a melt spinning technique and studied in detail its crystallization behavior and low-temperature magnetic properties. The crystallization behavior is characterized by transmission electron microscopy and Mössbauer spectroscopy. At early stages bcc solid solution precipitates from the amorphous matrix. At later stages, they order to yield DO3 ordered Fe3Si coexisting with a small amount of Fe2B. The analysis of Mössbauer spectra supports this observation. The temperature dependence of the magnetization in the temperature range 10–300 K of the FINEMET alloy in its as-quenched state follows the relation M(T)=M0(T) (1−B T3/2−C T5/2−⋅⋅⋅), which is indicative of the presence of spin wave excitations in the alloy. The value of the C/B ratio and the mean-square value of the range of exchange interaction 〈r2〉 are found to be characteristic of the noncrystalline ferromagnets. The small value obtained for the exchange stiffness constant D is an indication of the softening of the exchange interaction.
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