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Funding Information: 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. C.S.B.G. acknowledges funding from Fundação para a Ciência e Tecnologia FCT/MCTES through projects UIDB/50006/2020, UIDP/50006/2020 and LA/P/0008/2020 of the Associate Laboratory for Green Chemistry—LAQV, UIDB/04378/2020, UIDP/04378/2020 and LA/P/0140/2020 of UCIBIO and Associate Laboratory i4HB, respectively. Funding Information: We acknowledge national funds (OE), through FCT − Fundação para a Ciência e a Tecnologia, I.P., in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of article 23 of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19. Publisher Copyright: © 2023 by the authors. A polymorph of glycyl-L-alanine HI.H2O is synthesized from chiral cyclo-glycyl-L-alanine dipeptide. The dipeptide is known to show molecular flexibility in different environments, which leads to polymorphism. The crystal structure of the glycyl-L-alanine HI.H2O polymorph is determined at room temperature and indicates that the space group is polar (P21), with two molecules per unit cell and unit cell parameters a = 7.747 Å, b = 6.435 Å, c = 10.941 Å, α = 90°, β = 107.53(3)°, γ = 90° and V = 520.1(7) Å3. Crystallization in the polar point group 2, with one polar axis parallel to the b axis, allows pyroelectricity and optical second harmonic generation. Thermal melting of the glycyl-L-alanine HI.H2O polymorph starts at 533 K, close to the melting temperature reported for cyclo-glycyl-L-alanine (531 K) and 32 K lower than that reported for linear glycyl-L-alanine dipeptide (563 K), suggesting that although the dipeptide, when crystallized in the polymorphic form, is not anymore in its cyclic form, it keeps a memory of its initial closed chain and therefore shows a thermal memory effect. Here, we report a pyroelectric coefficient as high as 45 µC/m2K occurring at 345 K, one order of magnitude smaller than that of semi-organic ferroelectric triglycine sulphate (TGS) crystal. Moreover, the glycyl-L-alanine HI.H2O polymorph displays a nonlinear optical effective coefficient of 0.14 pm/V, around 14 times smaller than the value from a phase-matched inorganic barium borate (BBO) single crystal. The new polymorph displays an effective piezoelectric coefficient equal to (Formula presented.), when embedded into electrospun polymer fibers, indicating its suitability as an active system for energy harvesting. publishersversion published

In this work, we introduce lead-free organic ferroelectric perovskite N-methyl-N′-diazabicyclo [2.2.2]octonium)–ammonium triiodide (MDABCO-NH4I3) nanocrystals embedded in three different polymer fibers fabricated by the electrospinning technique, as mechanical energy harvesters. Molecular ferroelectrics offer the advantage of structural diversity and tunability, easy fabrication, and mechanical flexibility. Organic–inorganic hybrid materials are new low-symmetry emerging materials that may be used as energy harvesters because of their piezoelectric or ferroelectric properties. Among these, ferroelectric metal-free perovskites are a class of recently discovered multifunctional materials. The doped nanofibers, which are very flexible and have a high Young modulus, behave as active piezoelectric energy harvesting sources that produce a piezoelectric voltage coefficient up to geff = 3.6 VmN−1 and show a blue intense luminescence band at 325 nm. In this work, the pyroelectric coefficient is reported for the MDABCO-NH4I3 perovskite inserted in electrospun fibers. At the ferroelectric–paraelectric phase transition, the embedded nanocrystals display a pyroelectric coefficient as high as 194 × 10−6 Cm−2k−1, within the same order of magnitude as that reported for the state-of-the-art bulk ferroelectric triglycine sulfate (TGS). The perovskite nanocrystals embedded into the polymer fibers remain stable in their piezoelectric output response, and no degradation is caused by oxidation, making the piezoelectric perovskite nanofibers suitable to be used as flexible energy harvesters., 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.

Self-assembly of two N-tert-butoxycarbonyl (Boc) protected analogues of diphenylalanine dipeptide, Boc-p-nitro-l-phenylalanyl-p-nitro-l-phenylalanine and Boc-l-phenylalanyl-l-tyrosine, respectively, Boc-pNPhepNPhe and Boc-PheTyr, in 1,1,1,3,3,3-hexafluoro-2-propanol/ethanol(water) solvents and into electrospun fibers is studied. Uncommon dual self-assembly is found for Boc-pNPhepNPhe, with the formation of nanotubes which in turn self-assemble themselves into microtapes. Boc-PheTyr self-assembles into microspheres or microtapes depending on the solvent. Optical absorption and photoluminescence exhibit step-like peaks in the spectral region of 240290 nm indicating quantum confinement due to nanostructure formation. The dipeptides were further embedded into electrospun fibers, generating high output voltages through the piezoelectric effect. For Boc-pNPhepNPhe a maximum output voltage of 58 V, a power density of 9 W cm2 and effective piezoelectric voltage coefficients geff 0.6 Vm N1 were measured under a 1.5 N applied periodical force. Its estimated effective piezoelectric coefficient is twice that of diphenylalanine dipeptide., We acknowledge FEDER (European Fund for Regional Develop ment)-COMPETE-QREN-EU for financial support through the Phy sics Centers of the Universities of Minho and Porto (Ref. UID/FIS/ 04650/2013 and UID/FIS/04650/2019). We also acknowledge funding from the project PTDC/NAN-OPT/29265/2017. Part of this work was funded by national funds (OE), through FCT – Fundaça˜o para a Cieˆncia e a Tecnologia, I. P., in the scope of the framework contract foreseen in the numbers 4, 5, and 6 of the article 23, of the Decree Law 57/2016, of August 29, changed by Law 57/2017, of July 19, info:eu-repo/semantics/publishedVersion

Ferroelectric nanofibers, based on the insertion of ferroelectric compounds into a polymer matrix, have been attracting strong interest due to their potential for technological applications, namely in sensors/actuators where their dielectric, pyroelectric and piezoelectric characteristics can be exploited. In this respect, nanofibers prepared by the versatile electrospinning technique present a high surface to- volume ratio and unique structure, allowing to tailor the fiber diameter down to the nanometer scale. Phenanthrene is an organic ferroelectric material that has been studied mainly in its bulk form and it has not been explored for the incorporation in functionalized nanostructures. As such, in this work we have studied the synthesis of phenanthrene nanofibers by electrospinning and their structural, dielectric and pyroelectric properties were characterized. The X-ray diffraction and Raman studies show that the prepared fibers are polycrystalline presenting the monoclinic ferroelectric structure. Scanning electron microscopy (SEM) measurements show that the fiber diameters are in the range 198-305 nm, being composed by phenanthrene inclusions embedded inside the polymer matrix. The temperature dependent permittivity studies indicate that the ferroelectric transition temperature (Tc) is ~ 75 ºC, similar to its bulk value (Tc,bulk = 72 ºC), with some hysteresis under temperature cycling. Pyroelectric measurements allowed to determine the pyroelectric coefficient, which similar to the bulk value. The observed behaviors were correlated with the nanosized character of the polar ferroelectric inclusions inside the synthesized nanofibers.

Dissertação de mestrado em Física, O estudo de nanofibras com diâmetros sub-micrométricos tem atraído, recentemente, grande interesse dada a sua baixa dimensionalidade, que permite criar dispositivos com resolução nanométrica. O conceito de nanofibras magnetoelétricas baseia-se na inserção de compostos ferroelétricos e magnetostritivos, que irão acoplar-se mecanicamente, numa matriz polimérica a partir de uma solução percursora. A técnica de electrospinning apresenta uma grande versatilidade que permite um controlo efetivo da morfologia das nanofibras, sendo possível obter diâmetros inferiores ao mícron e comprimentos muito longos. Assim, neste trabalho são preparadas nanofibras magnetoelétricas compósitas a partir de um acoplamento mecânico de 1 fase de niobato de lítio com 1 fase de ferrite de cobalto, com diferentes percentagens estequiométricas das 2, sendo depois as fibras sujeitas a recozimento. O niobato de lítio (LNO) é um material ferroelétrico que apresenta elevadas propriedades piezoelétricas, piroelétricas, eletro-ópticas, birrefringentes, fotorrefrativas e fotoelásticas. Por outro lado, a ferrite de cobalto (CFO) apresenta uma anisotropia magnetocristalina alta e magnetostricção elevada. Medidas de difração de raios-X mostram que as fibras são policristalinas, com a estrutura cristalina pretendida para as fases de LNO e CFO. A microscopia eletrónica de varrimento, mostrou que grande parte das amostras apresenta estrutura de nanofibras com diâmetros na ordem das centenas de nanómetros, sendo que a temperatura de recozimento selecionada (650°C) terá sido excessiva para amostras com fase de LNO muito predominante. Utilizando o modelo de Havriliak-Negami e incluindo uma contribuição de condutividade, modelizou-se e ajustou-se a componente imaginária do módulo elétrico, obtido com espetroscopia de impedâncias, para obter os tempos de relaxação e energias de ativação. É, então, apresentada a influência da quantidade da fase de LNO e CFO nas propriedades dielétricas das amostras., The study of nanofibers with sub-micrometer diameters has recently attracted great interest given their low dimensionality which allows the creation of devices with nanometric resolution. The concept of magnetoelectric nanofibers is based on the insertion of ferroelectric and magnetostrictive compounds, that will mechanically couple together, in a polymer matrix through a precursor solution. The electrospinning technique has great versatility, which allows an effective control of the morphology of the nanofibers, being possible to obtain diameters smaller than the micron and with long lengths. Thus, in this work, composite magnetoelectric nanofibers are prepared from a mechanical coupling of a lithium niobate phase with a cobalt ferrite phase, with different stoichiometric percentages of the 2, after which the fibers are subjected to annealing. Lithium niobate (LNO) is a ferroelectric material that has high piezoelectric, pyroelectric, electro-optical, birefringent, photorefractive and photoelastic properties. On the other hand, cobalt ferrite (CFO) has a high magnetocrystalline anisotropy and high magnetostriction. X-ray diffraction measurements show that the fibers are polycrystalline, with the desired crystal structure for the LNO and CFO phases. Scanning electron microscopy showed that most samples have a nanofiber structure with diameters in the hundreds of nanometers, and the selected annealing temperature (650°C) was excessive for samples with a very predominant LNO phase. Using the Havriliak-Negami model and including a contribution of conductivity, the imaginary component of the electrical modulus, obtained with impedance spectroscopy, was modeled and adjusted to obtain relaxation times and activation energies. The influence of the amount of the LNO and CFO phase on the dielectric properties of the samples is then presented.