Nanoscale polarization switching and magneto–piezoelectric coupling in MgFe2O4–PVDF-HFP nanocomposites for low-field magnetic energy harvesting and self-powered IoT microsystems

Magneto-piezoelectric technology has emerged as a promising multifunctional platform for hybrid and self-powered sensing systems, wearable electronics, and low-power internet-of-things (IoT) applications by harvesting both mechanical vibrations and stray magnetic fields. In this study, we demonstrate a compositionally optimized magneto-piezoelectric composite where the calculated incorporation of MgFe2O4 nanofillers into electroactive PVDF-HFP matrix enables efficient synchronization between magnetic stimulus, mechanical deformation and piezoelectric charge generation. The optimal composition with superior β-phase nucleation, MF-3, shows the highest maximum polarization of 7.3 nC cm−2 with a recoverable energy density of 0.67 µJ cm−3 at a low electric field of 220 V m−1. Nanoscale Switching Spectroscopy-Piezoelectric Force Microscopy measurements reveal a displacement of 1.8 nm and a near-complete phase reversal of 170°, confirming a reversible polarization switching at the domain level. The prototype magneto-piezoelectric nanogenerator fabricated with MF-3 film generates a high peak-to-peak voltage of 97.5 V under dynamic mechanical excitation via human finger tapping motion, higher than widely studied spinel fillers. Most notably, the MF-3 composite exhibits a distinct magneto-piezoelectric response, generating a voltage of ∼40 mV when exposed to a low magnetic field of 320 µT, originating from the coupling of the magnetic and piezoelectric phases that efficiently transfers the magnetic strain as a stimulus to the electroactive composite. The device successfully powers multiple light-emitting diodes and charges a capacitor of 1 µF to 4.5 V under 2.5 s under tactile activation through repetitive finger tapping. This study not only unveils a highly effective design for harvesting energy from stray magnetic fields but also highlights the transformative potential of magneto-piezoelectric technology as an essential multifunctional strategy in next-generation technological advancements.

Piezoelectricity in twisted few-layer graphene composites enabling real-time FFT-resolved rotational motion sensing and biomechanical thumb-grip assessment

Convergence of energy harvesting and multimodal sensing functionalities in a self-powered, flexible composite represents a major step towards self-powered and intelligent systems. Piezoelectricity in twisted few-layer graphene (FLG), an intermediate structure between monolayer graphene and bulk graphite, and their composites with PVDF-HFP, is being investigated in the present study. We demonstrate that twisting-induced structural modification of FLG acts as an effective non-functionalized strategy to enhance interfacial polarization and promote β-phase stabilization in PVDF-HFP composites, resulting in improved piezoelectric performance. Twisting preserves the weak interaction between the layers while inducing distortion and the negative surface charge promotes the Maxwell-Wagner interaction between the filler and polymer phases, facilitating electroactive β-phase nucleation. Investigation of key piezoelectric performance metrics through Ferroelectric loops and Piezoresponse Force Microscopy confirms that the optimized composite, PG-10, delivered a saturation polarization of 15.64 nC/cm2, achieved a remarkable d33⁎ value of 0.35 nm/V and a high recoverable energy density of 15.54 nCJ/cm3 at 220 V/cm, attributed to diluted intragranular interaction and induced dielectric inhomogeneities. The PG-10 piezoelectric nanogenerator (PENG) produced an output of 108.1 V, and finger-tap actuation rapidly charged a 4.7 pF capacitor to ∼2.5 V within 10 s, showcasing its fast response under sustained mechanical excitation. Demonstrating practical applicability beyond energy harvesting, the PG-10 PENG accurately tracked the rotational frequency of a spin coater through FFT-based frequency mapping and resolved nuanced thumb-grip dynamics, establishing FLG-PVDF-HFP composites as promising candidates for non-destructive structural monitoring and biomechanical sensing platforms, accelerating the integration of flexible piezoelectric modules into sustainable MEMS devices.

Metal oxide doping for photodetectors and display device applications

Doped metal oxides have emerged as highly promising materials for a range of optoelectronic applications, attracting significant attention in recent years. Their unique combination of properties, including high carrier mobility, wide band gaps, and low electrical conductivity, positions them as ideal candidates for advanced technological uses. This study delves into the rationale behind doping metal oxides to enhance carrier mobility, elucidating how this process contributes to improved performance in photodiodes, photodetectors, and displays. The analysis explores the mechanisms underpinning the enhanced performance parameters of doped metal oxides within each application category. Specifically, it examines how doping influences the efficiency and sensitivity of photodiodes, the responsiveness of photodetectors across various spectral ranges, and the brightness, color accuracy, and energy efficiency of displays. Furthermore, this study underscores the need for further research in several aspects such as the exploration of novel fabrication techniques, the development of innovative device design, and the commercial integration challenges. In addition, prospective directions for future research are briefly discussed, aiming to guide continued advancements in the field of doped metal oxides for optoelectronic applications.

Deciphering the Role of Strain Effect in the Evolution of the Electronic Structure in Organic Lead Halide Perovskites

Organic lead halide perovskite (OLHP) materials have made notable improvements in their optical and electronic properties, expanding their spectrum of possible applications. However, their long-term stability and performance are often compromised by ion migration within the perovskite structure. One effective solution to address this issue is the stabilization of the perovskite structure through compositional engineering. Nevertheless, such modifications also alter certain perovskite functionalities. The present study delves into the intricate chemical and electronic structure properties of A-site and X-site substituted OLHPs, APbX3 (where A = methylammonium, MA+; and formamidinium, FA+; X = Cl and Br) single crystals using X-ray photoemission spectroscopy in conjunction with UV–vis spectroscopy. The study reveals that the cationic size difference of MA+ and FA+ ions and the electronegativity of Br¯ and Cl¯ influence the binding energy peak shifts due to the insertion of strain effects in the PbX6 octahedral network. The Elliott model fitting of the absorbance spectra yields an exciton binding energy and a continuum energy state at the conduction band edge that marks the onset of the band gap energy and extends to the higher energies within the conduction band. Higher exciton binding energy is recorded in MA-based systems as compared to FA. A closer look at the Pb 4f core level spectra shows the emergence of metallic Pb0 doublets with increased X-ray exposure, which is significantly suppressed in FA-based systems, pointing to their increased stability toward X-ray irradiation. These vital insights into the electronic structures of APbX3 pave the way for the optimization of perovskite materials, ultimately guiding the design of optimal structures from an applications perspective.

Dynamic Structural Evolution and Dual Emission Behavior in Hybrid Organic Lead Bromide Perovskites

The optoelectronic properties of organic lead halide perovskites (OLHPs) strongly depend on their underlying crystal symmetry and dynamics. Here, we exploit temperature-dependent synchrotron powder X-ray diffraction and temperature-dependent photoluminescence to investigate how the subtle structural changes happening in the pure and mixed A-site cation MA1–xFAxPbBr3 (x = 0, 0.5, and 1) systems influences their optoelectronic properties. Diffraction investigations reveal a cubic structure at high temperatures and tetragonal and orthorhombic structures with octahedral distortion at low temperatures. Steady state photoluminescence and time correlated single photon counting study reveals that the dual emission behavior of these OLHPs is due to the direct-indirect band formation. In the orthorhombic phase of MAPbBr3, the indirect band is dominated by self-trapped exciton (STE) emission due to the higher-order lattice distortions of PbBr6 octahedra. Our findings provide a comprehensive explanation of the dual emission behavior of OLHPs while also providing a rationale for previous experimental observations.

Enhanced Performance of Al-Doped ZnO through In Situ Pressure-Controlled Growth: An Alternate Approach for Developing n‑Type Transparent Conducting Materials for Optoelectronic Devices

Transparent conducting materials exhibit a unique combination of high electrical conductivity and high optical transparency within the visible range, two seemingly impossible properties to be present in any solid-state material, simultaneously. This uniqueness makes them the backbone of the whole electronic and optoelectronic industries and is currently dominated by indium-based materials. High-performance aluminum-doped zinc oxide (AZO) nanocrystals could be a viable option for application in transparent electronics. This work focuses on the impact of in situ pressure on the AZO nanoparticles in driving their optoelectronic properties, which is being reported for the first time to the best of our knowledge. Thin film fabricated with AZO nanoparticles synthesized at 100 bar of pressure (AZO-100) has the highest figure of merit, optical transparency (>95%) and lowest sheet resistance (∼103 Ω sq–1), significantly lower than the AZO film fabricated from the nanoparticles synthesized at atmospheric pressure. These modifications could be attributed to the improved crystallinity, lowering of surface roughness, and shifts in band gaps, which facilitate electron transfer, as is evident from the optical and valence-band electronic structure measurements, suggesting a substantial influence of in situ pressure-controlled growth of AZO nanoparticles. The improved properties confirm the possibility of using AZO-100 as an n-type transparent conducting material, replacing indium tin oxide in various optoelectronic devices, as successfully demonstrated in laboratory-fabricated prototype liquid crystal display (LCD) and organic light-emitting diode (OLED) devices using the developed films.

Giant Magnetocaloric Effect in Cr- and Fe-Substituted Frustrated Magnet Gadolinium Gallium Garnets, Gd3Ga5O12, for Magnetic Cooling at Cryogenic Temperatures

The beneficial effects of Cr and Fe substitutions in enhancing the magnetocaloric properties of the frustrated magnetic system gadolinium gallium garnets Gd3Ga5O12, i.e., Gd3CrGa4O12 and Gd3FeGa4O12, are discussed for their potential use as magnetic refrigerant materials. Evaluations of their structural, electronic, magnetic, and thermal properties were carried out to investigate the effect of magnetic ion substitution in the frustrated magnetic lattice and its magnetocaloric properties. For both Cr and Fe substitutions, the cubic Iad structure remains preserved, and antiferromagnetic correlations are observed with very negligible magnetic hysteresis at low temperatures. A maximum isothermal magnetic entropy change, ⁠, adiabatic temperature change, ⁠, and relative cooling power, RCPmax ∼ 645.53 J/kg for Gd3CrGa4O12 and ⁠, ⁠, and RCPmax ∼ 549.72 J/kg for Gd3CrGa4O12 systems are observed, respectively, under a magnetic field change of 9 T. This significant enhancement in the magnetic entropy of the Cr substituted system could be attributed to the changing nature of the magnetic ground state and the considerable change in magnetic frustration that enhances the Gd spin loop. The presence of giant magnetocaloric parameters makes both systems promising competitors in the field of magnetic refrigeration technology for cooling applications at cryogenic temperatures.