Preparação e caracterização física de vidros com LiNbO3 e NaNbO3

Doutoramento em FísicaForam preparados pelos métodos de fusão e sol-gel vidros e vidros cerâmicos com nanocristais de LiNbO3 e de NaNbO3. As amostras obtidas foram caracterizadas quanto à sua microestrutura, analisando o efeito do óxido formador de rede vítrea, do método de preparação, das condições de tratamento térmico (temperatura, tempo e amplitude de campo eléctrico externo aplicado durante o tratamento). Foram desenvolvidos modelos físicos para interpretar os resultados experimentais. Na caracterização estrutural usaram-se as técnicas: análise térmica diferencial, difracção de raios X, microscopia electrónica de varrimento e espectroscopia Raman. Foram medidas a condutividade dc e ac, a impedância complexa (Z*) e constante dieléctrica em função da temperatura e frequência e as correntes de despolarização termicamente estimuladas (TSDC). Por fusão foram preparadas as composições 60M-30Li2O-10Nb2O5 (% mole), com M= SiO2, B2O3, P2O5 e TeO2. O sistema com SiO2 é o mais favorável para obter vidros cerâmicos onde a fase de LiNbO3 é a única ou a principal. Verifica-se que o aumento da temperatura de tratamento conduz a um aumento na quantidade de LiNbO3 e que a presença de um campo eléctrico durante o tratamento térmico conduz à diminuição da temperatura necessária para a formação do LiNbO3 e favorece uma cristalização localizada. O ajuste dos espectros de Z* foi realizado com base num método numérico, desenvolvido para esse fim em linguagem Matlab, associado a um modelo de circuito equivalente constituído pelo paralelo R//CPE. Foram preparados pelo método de sol-gel vidros de composição molar (100-2x)SiO2-xLi2O-xNb2O5, com x=4 e 6, que através do método de fusão são de extrema dificuldade de preparar. Nas duas composições a fase de LiNbO3, precipitada por tratamentos térmicos, é superficial. A análise eléctrica permitiu verificar a presença de mecanismos de condução, relaxação e polarização associados aos iões inseridos estruturalmente na matriz vítrea e a fenómenos interfaciais eléctrodos-superfícies da amostra. Os mecanismos de relaxação foram ajustados a um modelo de circuito equivalente constituindo por dois circuitos R//CPE associados em série. Da análise dieléctrica e de TSDC mostra-se a existência de uma distribuição de tempos de relaxação. Foram preparados por fusão vidros com NaNbO3, de composição molar 60M-30Na2O-10Nb2O5, onde M= SiO2, B2O3. Na composição com SiO2, a cristalização é superficial e o comportamento eléctrico correlaciona-se com as características do interior das amostras. Os espectros de Z* ajustam-se ao modelo de circuito equivalente R//CPE. Nas amostras com B2O3 a cristalização ocorre em volume e não se observou a presença de mecanismos de relaxação dieléctrica. Contudo, as medidas de TSDC revelaram a presença de mecanismos de despolarização. Na gama de temperatura de medição usada o valor de ε´ permanece praticamente constante indicando que o NaNbO3 não sofre alterações estruturais.The melt-quenching and the sol-gel methods had been used to prepare glasses and glass-ceramics with LiNbO3 or NaNbO3 nanocrystals. The microstructure of the prepared samples was characterized, analysing the network former oxide effect, the preparation method and the conditions of the thermal treatment (temperature, time and amplitude of the external applied electric field). Physical models had been developed to interpret the experimental results. The structural characterization was made using the techniques of differential thermal analysis, X-ray diffraction, scanning electronic microscopy and Raman spectroscopy. It was measured the dc and ac conductivity, thermally stimulated depolarization current (TSDC), complex impedance (Z*) and dielectric constant in function of temperature and frequency. The 60M-30Li2O-10Nb2O5, with M = SiO2, B2O3, P2O5 and TeO2 molar compositions had been prepared by melt-quenching. The SiO2 system is the most suitable to obtain glass-ceramics where the LiNbO3 is the only one or is the main crystal phase. The increase of the treatment temperature leads to an increase in the amount of LiNbO3. The presence of an electric field during the thermal treatment leads to a decrease in the temperature needed for the LiNbO3 formation and favors a localized superficial crystallization. The Z* spectra was adjust through a numerical method developed for this purpose in Matlab language, associated to an equivalent circuit model consisting in the R//CPE parallel. The sol-gel method allowed to prepare glasses of molar composition (100-2x)SiO2-xLi2O-xNb2O5, with x=4 and 6, that through the melt-quenching method are of extreme difficulty to prepare. In both compositions the LiNbO3 particles, precipitated due to thermal treatments, are observed in the samples surfaces. The electric analysis of these samples show the presence of conduction, relaxation and polarization mechanisms associated with the glass matrix structurally inserted ions and to electrode-sample interface phenomena. The relaxation mechanisms, adjusted to the R//CPE equivalent circuit, and the TSDC data showed the existence of a relaxation times distribution. Glasses with NaNbO3, of molar composition 60M-30Na2O-10Nb2O5, with M = SiO2, B2O3, were prepared by melt-quenching. In the SiO2 matrix the crystallization occurs only in the surface and the dielectric behavior is correlated with the samples bulk characteristics. The Z* spectra were adjusted to the R//CPE equivalent circuit model. In the samples with B2O3 the crystallization occurs in volume. The dielectric results had not showed the presence of relaxation mechanisms. However, the TSDC results show the presence of depolarization mechanisms. In the measurement temperature range the ε´ behaviour, of all samples, is practically constant showing that the NaNbO3 does not suffer structural modifications

Calcium Phosphate Cements in Tissue Engineering

Calcium phosphate cements (CPCs) consist of a combination of calcium phosphates and a liquid phase, allowing it to fit into the body where it was inserted. Several chemical compositions have been synthesized, promoting specific characteristics to the cements for applications such as bone augmentation and reinforcement and metal implant fixation. The hardening reaction mechanism is at low temperatures and makes it capable of incorporating different drugs and other biological molecules. In addition to the abovementioned advantages, CPCs have excellent bioactivity and osteoconductivity and the ability to form a bone bond. Its function as osteoconductor can be improved by insertion of growth factors. In addition, it is possible to functionalize it with silver ions and use it as a coating of implants, conferring antibacterial properties. In this chapter the physical, mechanical, chemical, and biological properties and the possibility of using these cements as drug carriers or biomolecules will be discussed

Synthesis, structural characterization and broadband ferromagnetic resonance in Li ferrite nanoparticles

Producción CientíficaLithium ferrites are well known materials due to its numerous technological applications especially in microwave devices. Lithium ferrite nanoparticles were prepared by sol-gel technique by means of Pechini method, and then annealed at different temperatures in 250–1000 °C range. XRD confirms spinel formation with particles sizes in 15–700 nm range, with increased size with annealing temperature, whereas FTIR and Raman measurement confirm that single phase lithium ferrite with ordered cationic structure is obtained. Microwave magnetoabsorption data of the annealed lithium ferrite nanoparticles were obtained with a broadband system based on a network analyzer that operates up to 8.5 GHz. At fields up to 200 mT we can observe a broad absorption peak that shifts to higher frequencies with magnetic field according to ferromagnetic resonance theory. The amplitude of absorption, up to 85%, together with the frequency width of about 5.5 GHz makes this material suitable as wave absorber. FMR parameters like resonance field, linewidth and broadening are analyzed in order to obtain the characteristic parameters and analyze the microwave behaviour.Ministerio de Economía, Industria y Competitividad ( project MAT2016-80784-P

Dielectric Properties of Bismuth Niobate Ceramics

The development of new dielectric materials that allow the reduction of size and weight of electronic components has been in the scope of the researchers. The bismuth-based dielectric ceramics are extensively studied for this purpose, namely, the bismuth niobate (BiNbO4). The first attempt to improve BiNbO4 occurred in 1992 when Kagata reported the microwave dielectric properties of bismuth niobate doped with the addition of oxides. This chapter will present a brief review of the several attempts that have been carried out to enhance the dielectric properties of BiNbO4 by modifying their structure through addition, doping, or atom(s) substitution. This manuscript focuses on a case study that involves bismuth substitution by europium ions. To investigate the inclusion of europium in BiNbO4 ceramics, (Bi1–xEux)NbO4 samples were prepared using the sol-gel method, in particular, the citrate route. The structure of the prepared samples was studied by X-ray diffraction (XRD) and Raman spectroscopy and the morphology by scanning electron microscopy (SEM). The dielectric properties were studied, in the microwave frequency range (MW), using the resonant cavity method, and in the radio frequency range (RF), with the impedance spectroscopy technique

Broadband ferromagnetic resonance in Mn-doped Li ferrite nanoparticles

Producción CientíficaLithium ferrites are well known materials due to their numerous technological applications especially in microwave devices. Mn-doped lithium ferrite nanoparticles were prepared by sol-gel technique by means of Pechini method, and then annealed at different temperatures in 250–1000 °C range. XRD confirms spinel formation with particle size in the 15–200 nm range, with increased size with annealing temperature. Microwave magnetoabsorption data of annealed lithium ferrite nanoparticles, obtained with a broadband system based on a network analyzer operating up to 8.5 GHz are presented. At fields up to 200 m T we can observe a broad absorption peak that shifts to higher frequencies with magnetic field according to ferromagnetic resonance theory. The amplitude of absorption, up to 85%, together with the frequency width of about 4.5 GHz makes this material suitable as wave absorber. Samples annealed at higher temperatures show a behaviour similar to polycrystalline samples, thus suggesting their multidomain character.Ministerio de Economía, Industria y Competitividad, Agencia Estatal de Investigación with FEDER (project MAT2016-80784-P

The Effect of Iron Oxide Insertion on the In Vitro Bioactivity, and Antibacterial Properties of the 45S5 Bioactive Glass

Funding Information: This research was funded by FEDER funds through the COMPETE 2020 Program and National Funds through the FCT—Portuguese Foundation for Science and Technology under the projects LISBOA-01-0247-FEDER-039985/POCI-01-0247-FEDER-039985, LA/P/0037/2020, UIDP/50025/2020, and UIDB/50025/2020 of the Associate Laboratory Institute of Nanostructures, Nanomodelling and Nanofabrication—i3N, UIDP/04378/2020 and UIDB/04378/2020 of the Research Unit on Applied Molecular Biosciences—UCIBIO, and LA/P/0140/2020 of the Associate Laboratory Institute for Health and Bioeconomy—i4HB. S.K. Jakka acknowledges FCT—Fundação para a Ciência e a Tecnologia, Portugal, 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 29 August, changed by Law 57/2017 of 19 July. Publisher Copyright: © 2024 by the authors.The aging population and increasing incidence of trauma among younger age groups have heightened the increasing demand for reliable implant materials. Effective implant materials must demonstrate rapid osseointegration and strong antibacterial properties to ensure optimal patient outcomes and decrease the chance of implant rejection. This study aims to enhance the bone–implant interface by utilizing 45S5 bioglass modified with various concentrations of Fe3O4 as a coating material. The effect of the insertion of Fe3O4 into the bioglass structure was studied using Raman spectroscopy which shows that with the increase in Fe3O4 concentration, new vibration bands associated with Fe-related structural units appeared within the sample. The bioactivity of the prepared glasses was evaluated using immersion tests in simulated body fluid, revealing the formation of a calcium phosphate-rich layer within 24 h on the samples, indicating their potential for enhanced tissue integration. However, the sample modified with 8 mol% of Fe3O4 showed low reactivity, developing a calcium phosphate-rich layer within 96 h. All the bioglasses showed antibacterial activity against the Gram-positive and Gram-negative bacteria. The modified bioglass did not present significant antibacterial properties compared to the bioglass base.publishersversionpublishe

Magnetic After-effects in Ni Ferrite Nanoparticles

Producción CientíficaMagnetic after-effects in ferrite nanoparticles have been measured with magnetic disaccommodation technique. For higher annealing temperature multidomain formation is detected with low temperature relaxation process similar to single crystal and polycrystalline NiFe2O4. As expected, no room temperature processes are observed due to low vacancy content. On the other hand, logarithmic relaxations are observed at lower annealing temperatures, revealing monodomain character.Ministerio de Economía, Industria y Competitividad (project MAT2016-80784-P

In Vitro Characterization of Doped Bioglass 45S5/HAp Coatings Obtained by CoBlastTM Deposition

Funding Information: FEDER funds through the COMPETE 2020 Program and National Funds through FCT—Portuguese Foundation for Science and Technology under the project LIS-BOA-01-0247-FEDER-039985/POCI-01-0247-FEDER-039985. Publisher Copyright: © 2023 by the authors.Bone replacement is one of the major medical procedures in the oral surgery field due to the progressive ageing population and to illness or trauma in younger age groups. The use of implants without biological activity and effective osseointegration increases the chances of implant failure. This work aims to improve the interaction between implants and bone by using Bioglass 45S5 (BG)/hydroxyapatite (HAp) mixtures, including copper-, zinc-, and cerium-doped BG, as well as co-doping by the mentioned metals, as coatings produced by the CoBlastTM technique. All coatings present a uniform coverage of the Ti-6Al-4V substrate. Furthermore, in vitro testing using human osteosarcoma Saos-2 cells indicated that BG/HAp coatings have no cytotoxic effect, and the used of doping agents did not alter cell adhesion, proliferation, or alkaline phosphatase (ALP) expression when compared to undoped coating. These results demonstrate that BG/HAp by CoBlastTM can be a solution to improve implants’ osseointegration.publishersversionpublishe

Fabrication, Structural, Electrical, and Biological Analysis

This research was funded by FEDER funds through the COMPETE 2020 Program and National Funds through the FCT—Portuguese Foundation for Science and Technology under the projects LISBOA-01-0247-FEDER-039985/POCI-01-0247-FEDER-039985. S.R. Gavinho and A. Sofia Pádua acknowledge the FCT—Portuguese Foundation for Science and Technology for the Ph.D. grant ( UI/DB/151287/2021). Publisher Copyright: © 2023 by the authors.Implantology is crucial for restoring aesthetics and masticatory function in oral rehabilitation. Despite its advantages, certain issues, such as bacterial infection, may still arise that hinder osseointegration and result in implant rejection. This work aims to address these challenges by developing a biomaterial for dental implant coating based on 45S5 Bioglass® modified by zirconium insertion. The structural characterization of the glasses, by XRD, showed that the introduction of zirconium in the Bioglass network at a concentration higher than 2 mol% promotes phase separation, with crystal phase formation. Impedance spectroscopy was used, in the frequency range of 102–106 Hz and the temperature range of 200–400 K, to investigate the electrical properties of these Bioglasses, due to their ability to store electrical charges and therefore enhance the osseointegration capacity. The electrical study showed that the presence of crystal phases, in the glass ceramic with 8 mol% of zirconium, led to a significant increase in conductivity. In terms of biological properties, the Bioglasses exhibited an antibacterial effect against Gram-positive and Gram-negative bacteria and did not show cytotoxicity for the Saos-2 cell line at extract concentrations up to 25 mg/mL. Furthermore, the results of the bioactivity test revealed that within 24 h, a CaP-rich layer began to form on the surface of all the samples. According to our results, the incorporation of 2 mol% of ZrO2 into the Bioglass significantly improves its potential as a coating material for dental implants, enhancing both its antibacterial and osteointegration properties.publishersversionpublishe