High Piezoelectric Output Voltage from Blue Fluorescent N,N-Dimethyl-4-nitroaniline Nano Crystals in Poly-L-Lactic Acid Electrospun Fibers

N,N-dimethyl-4-nitroaniline is a piezoelectric organic superplastic and superelastic charge transfer molecular crystal that crystallizes in an acentric structure. Organic mechanical flexible crystals are of great importance as they stand between soft matter and inorganic crystals. Highly aligned poly-l-lactic acid polymer microfibers with embedded N,N-dimethyl-4-nitroaniline nanocrystals are fabricated using the electrospinning technique, and their piezoelectric and optical properties are explored as hybrid systems. The composite fibers display an extraordinarily high piezoelectric output response, where for a small stress of 5.0 × 103 Nm−2, an effective piezoelectric voltage coefficient of geff = 4.1 VmN−1 is obtained, which is one of the highest among piezoelectric polymers and organic lead perovskites. Mechanically, they exhibit an average increase of 67% in the Young modulus compared to polymer microfibers alone, reaching 55 MPa, while the tensile strength reaches 2.8 MPa. Furthermore, the fibers show solid-state blue fluorescence, important for emission applications, with a long lifetime decay (147 ns) lifetime decay. The present results show that nanocrystals from small organic molecules with luminescent, elastic and piezoelectric properties form a mechanically strong hybrid functional 2-dimensional array, promising for applications in energy harvesting through the piezoelectric effect and as solid-state blue emitters.This research was funded by Fundação para a Ciência e Tecnologia through FEDER (European Fund for Regional Development)-COMPETE-QREN-EU (ref. UID/FIS/04650/2013 and UID/FIS/04650/2019) and E-Field - "Electric-Field Engineered Lattice Distortions (E-FiELD) for optoelectronic devices", ref. PTDC/NAN-MAT/0098/2020

Functionalized magnetic composite nano/ microfibres with highly oriented van der Waals CrI3 inclusions by electrospinning

This study reports on the synthesis of highly oriented chromium triiodide (CrI3) magnetic inclusions inside nano/microfibres with a polyethylene oxide matrix, prepared by the electrospinning technique. The structural, microstructural and spectroscopic analysis shows uniformly dispersed CrI3 nanosized inclusions inside the fibres, presenting a C2/m monoclinic structure at room temperature, where their c-axis is perpendicular to the fibre mat plane and the ab layers are in-plane. Analysis of the magnetic properties show that the samples have a ferromagnetic-paramagnetic phase transition at ∼55-56 K, lower than that of bulk CrI3. Noticeably, a field-driven metamagnetic transition is observed below ∼45 K, from M versus H curves, when the applied magnetic field is perpendicular to the fibre mat plane, while it is strongly reduced when the field is in-plane. This anisotropic behaviour is attributed to the field-induced changes from antiferromagnetic to ferromagnetic interlayer magnetic moment alignment along the CrI3 c-axis stacked layers. These CrI3 electrospun fibres then show an efficient cost-effective route to synthesize magnetic composite fibres with highly oriented van der Walls inclusions, for spintronic applications, taking advantage of their anisotropic 2D layered materials properties.We are grateful to the Fundacao Para a Ciencia e a Tecnologia (FCT) for the financial support through the Physics Centers of the Universities of Minho and Porto (Ref. UIDB/04650/2020) and projects UTAPEXPL/NTec/0046/2017, NORTE-01-0145-FEDER-028538 and PTDC/FIS-MAC/29454/2017. J H Belo thanks FCT for the Grant SFRH/BD/88440/2012, the project PTDC/FIS-MAC/31302/2017 and his contract DL57/2016 reference SFRH-BPD-87430/2012. J P Araujo and J H Belo thank the funding from the project, with reference POCI-01-0145-FEDER-032527. V B Isfahani acknowledges a Post-Doc grant from the project NORTE-01-0145-FEDER-028538. L Boddapati acknowledges the Nano TRAIN for Growth II program by the European Commission through the Horizon 2020 Marie Sklodowska-Curie COFUND Programme and support provided by the International Iberian Nanotechnology Laboratory. We are gratefull to Professor Michael Belsley, of the Physics Department at Minho University, for the fruitfull discussions on the manuscript

Comparison of physical/chemical properties of Prussian Blue thin films prepared by different pulse and DC electrodeposition methods

Prussian Blue (PB) thin films were prepared by DC chronoamperometry (CHA), symmetric pulse, and non-symmetric pulse electrodeposition techniques. The formation of PB was confirmed by infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX) and UV-Vis transmission measurements. X-ray diffraction (XRD) shows the stabilization of the insoluble form of PB. From scanning electron microscopy (SEM) studies, an increase in porosity is obtained for the shorter pulse widths, which tends to improve the total charge exchange and electrochemical stability of the films. While the film prepared by CHA suffered a degradation of 82% after 260 cycles, the degradation reduced to 24% and 34% for the samples prepared by the symmetric and non-symmetric pulse methods, respectively. Additionally, in the non-symmetric pulse film, the improvement in the charge exchange reached ~522% after 260 cycles. According to this study, the deposition time distribution affects the physical/chemical properties of PB films. These results then render pulse electrodeposition methods especially suitable to produce high-quality thin films for electrochemical devices, based on PB.This work was supported by the Portuguese Foundation for Science and Technology (FCT), through the projects POCI-01-0145-FEDER-029454, NORTE-01-0145-FEDER-028538, PTDC/NANMAT/0098/2020 and UID/QUI/0686/2020. It was also funded by the R&D project “SOLPOWINS”, with reference PTDC/CTM-REF/4304/2020, and E-Field- “Electric-Field Engineered Lattice Distortions (E-FiELD) for optoelectronic devices”, ref. PTDC/NAN-MAT/0098/2020, financed by the FCT

Comparison of Physical/Chemical Properties of Prussian Blue Thin Films Prepared by Different Pulse and DC Electrodeposition Methods

Prussian Blue (PB) thin films were prepared by DC chronoamperometry (CHA), symmetric pulse, and non-symmetric pulse electrodeposition techniques. The formation of PB was confirmed by infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX) and UV-Vis transmission measurements. X-ray diffraction (XRD) shows the stabilization of the insoluble form of PB. From scanning electron microscopy (SEM) studies, an increase in porosity is obtained for the shorter pulse widths, which tends to improve the total charge exchange and electrochemical stability of the films. While the film prepared by CHA suffered a degradation of 82% after 260 cycles, the degradation reduced to 24% and 34% for the samples prepared by the symmetric and non-symmetric pulse methods, respectively. Additionally, in the non-symmetric pulse film, the improvement in the charge exchange reached ~522% after 260 cycles. According to this study, the deposition time distribution affects the physical/chemical properties of PB films. These results then render pulse electrodeposition methods especially suitable to produce high-quality thin films for electrochemical devices, based on PB

Gellan-gum and LiTFSI-Based solid polymer electrolytes for electrochromic devices

It has been long recognized that solid polymer electrolytes (SPEs) are potentially interesting for solid-state electrochemical devices. Gellan gum (Ge)-based SPEs, plasticized with glycerol (Gly) and doped with lithium bis(trifluoromethanesulfone)imide (LiTFSI) were prepared by the solvent casting technique, and their properties were evaluated. LiTFSI-based SPE systems exhibit, on the average, higher conductivities than similar systems with other lithium salts. The structure, morphology, complex impedance spectroscopy, cyclic voltammetry and thermal stability of the new electrolyte system were characterized. Electrochromic devices (ECDs) were built with optimized electrolyte samples and their performance was analyzed. The samples were applied in small ECDs with glass/ITO/CeO2-TiO2/SPE/Prussian blue/ITO/glass configuration. The devices presented a two-modulation operation: a semi-bright mode (-2.5 V) and a dark mode (+0.5 V). The best results were obtained with the ECD containing the GeGly(1)Li(2.4) electrolyte, for which the transmittance (T) values in the bleached and colored states were ca. 33.4/43.0 % and 5.4/8.8 % at 555/1000 nm, respectively. These results correspond to Delta T and Delta OD values of 28.0/34.2 % and 0.79/0.69, respectively, which give quite high CEin and CEout values of -4925 cm(2) C-1 for bleaching (Q(in)=-272.1 mu C cm(-2)), and 2062 cm(2) C-1 for coloring (Q(out)=650.0 mu C cm(-2)), at 630 nm. This electro-optical performance suggests that the proposed SPE systems are promising materials to be further investigated and applied in ECDs.The authors are grateful to FundacAo para a Ciencia e a Tecnologia (FCT) under contracts, UID/QUI/00686/2020, UIDB/00616/2020 and UIDP/00616/2020. V. B. Isfahani acknowledges a Post-Doc grant from the project NORTE-01-0145-FEDER-028538. R.F.P. Pereira thanks FCT-UM for the contracts in the scope of Decreto-Lei 57/2016 and 57/2017. M. Fernandes acknowledges FCT-UTAD for the contract in the scope of Decreto-Lei 57/2016 and Lei 57/2017. A. Pawlicka acknowledges The Brazilian National Council for Scientific and Technological Development (CNPq) for grant 307429/2017-2 and R. C. Sabadini acknowledges "CoordenacAo de Aperfeicoamento de Pessoal de Nivel Superior" (CAPES) for grant 88881.172281/2018-01

Synthesis, structural and dielectric properties of Ca3Mn2O7 thin films prepared by pulsed laser deposition

Multiferroic Ruddlesden-Popper Ca3Mn2O7 thin films were prepared by laser ablation on SrTiO3 substrates. For low laser fluences and high oxygen pressures, the films assumed the CaMnO3 Pnma orthorhombic structure. However, by increasing fluence and decreasing the oxygen pressure, the Ca3Mn2O7 phase is achieved through a post-deposition annealing treatment. Furthermore, the ferroelectric phase A21am was observed in the films, along with the orthorhombic Acaa phase, with a preferential [111] growth orientation and substrate-induced enhancement of the polar ferroelectric distortion. The dielectric permittivity shows dispersion described by the Havriliak-Negami function, and from fits to the curves, a different behavior was observed in the antiferromagnetic region. Also, the Kohlrausch-Williams-Watts stretched exponential parameter showed an abrupt decrease below ~110 K, near the Néel temperature. This indicates the presence of magnetoelectric interactions and magnetically induced enhancement of dipolar correlations in the samples, favoring substrate-induced strain to enhance multiferroicity in these films.This work was supported by the Portuguese Foundation for Science and Technology (FCT), through the projects POCI-01-0145- FEDER-029454, NORTE-01-0145-FEDER-028538, PTDC/NAN-MAT/ 0098/2020, NORTE-01-0145-FEDER-022096, and POCI-01-0145- FEDER-032527. V. B. Isfahani acknowledges a post-doc grant from the project NORTE-01-0145-FEDER-028538. B. M. Silva and J. Oliveira acknowledge their Ph.D. grants from FCT, with references 2021.07277. BD and SFRH/BD/146886/2019, respectively. F. L. Deepak acknowledges the CASOLEM project (028917) “Correlated Analysis of Inorganic Solar Cells in and outside an Electron Microscope”, co-funded by FCT and ERDF through COMPETE2020