Susana Devesa

By Susana Devesa, Manuel P.F. Graça and Luís C. Costa

The current progress in communication technologies is leading to extensive studies on the development of miniaturized electronic devices with high electromagnetic performances, reliability, and low cost. Contributing to this purpose, the development and study of new materials, with promising electric properties in radio and microwave ranges, have been subject of our research in particular niobate-based materials. Bismuth niobate, BiNbO4, is a low-firing ceramic that has been studied for a variety of applications in the microelectronic industry. In this work, the microwave dielectric characterization of (Bi1−x Fex )NbO4 (0.00 ≤ x ≤ 1.00) samples, prepared by the sol-gel method and heat treated at specific temperatures, is performed and related with their structure and morphology. The structural data were obtained by X-ray diffraction and Raman spectroscopy and the morphology by scanning electron microscopy. The dielectric characterization in the microwave region was made using the small perturbation theory, with a resonant cavity operating in TE105 mode, at the frequency of 2.7 GHz. The results show that the sol-gel method has the advantage of allowing the formation of α-BiNbO4 phase at lower temperatures when compared with conventional preparation methods, and that the inclusion of iron inhibits the formation of low- and high-temperature β-BiNbO4 phases.

Part of the book: Recent Applications in Sol-Gel Synthesis

By Susana Devesa, Manuel Pedro Fernandes Graça and Luís Cadillon Costa

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.

Part of the book: Bismuth

By Susana Devesa

Nanoparticles are fundamental in nanotechnology, with their applications expanding rapidly due to their unique optical, chemical, electrical, and mechanical properties. Metal oxide nanoparticles are widely studied due to the abundance of their natural precursors, environmental friendliness, affordability, and favorable electrical and optical properties. In some cases, they also exhibit chemical stability. Recent advances in synthesis methods, particularly the sol-gel technique, have enabled precise control over nanoparticle size and shape, offering benefits such as simplicity, low cost, and lower processing temperatures. More recently, eco-friendly biosynthesis of nanoparticles has garnered increasing attention due to its numerous advantages over traditional chemical and physical methods, which often involve hazardous and expensive chemicals. Green synthesis using biological entities like plants, algae, bacteria, fungi, and viruses offers several benefits. The use of plant extracts, in particular, is advantageous because they are readily available, safe to handle, and capable of producing large quantities of nanoparticles. They can act as both reducing and stabilizing agents during synthesis. This mini-review explores both conventional and green sol-gel synthesis approaches for metal oxide nanoparticles, focusing on CuO, Cu₂O, ZnO, TiO₂, MgO, and NiO, with an emphasis on the types of plants used and the procedures employed to obtain the extracts.

Part of the book: Sol-Gel

By Bárbara Costa, Sílvia R. Gavinho, Susana Devesa, Manuel Almeida Valente, Manuel P.F. Graça and Sílvia Soreto

The sol-gel method is a well-established technique for synthesizing metal oxide nanoparticles, widely employed in both research and industrial applications. However, significant drawbacks, such as the use of potentially toxic organic solvents, the lengthy synthesis time, and the high cost of precursors, have driven the scientific community to explore and develop alternative routes to optimize and improve the Sol-Gel method. In this line, the proteic sol-gel route has emerged as a sustainable eco-friendly method that utilizes natural proteins, as both stabilizing and templating agents during the synthesis process. This alternative is already used for the synthesis of magnetic nanoparticles and is recognized in the literate as an efficient method for obtaining magnetic nanoparticles with unique properties, including controlled size distribution, improved thermal stability, and high magnetic response. This chapter provides a comprehensive review of the proteic sol-gel route and presents a case study on the synthesis of an innovative magnetic composite consisting of gadolinium ferrite (Gd₃Fe₅O₁₂) and zinc ferrite (ZnFe₂O₄) using an eco-friendly proteic method using powdered coconut water. The study explores the potential applications of these nanomaterials in nanomedicine. Accordingly, the materials were extensively characterized in terms of their structural properties (thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, and Fourier transform infrared spectroscopy), morphological features (scanning electron microscopy), and magnetic behavior (vibrating-sample magnetometry and magnetic hyperthermia analysis using specific absorption rate). The resulting magnetic composite exhibited ferromagnetic behavior and demonstrated non-cytotoxic properties, highlighting its potential for biomedical applications.

Part of the book: Sol-Gel

By Susana Devesa, Zohra Benzarti, Sílvia Soreto and Sandra Carvalho

Hydroxyapatite (HAp) is a well-known biomaterial that, due to its biocompatibility and bioactivity, has been widely utilized in biomedical applications, including bone tissue engineering and drug delivery systems. Over the years, significant advancements have transformed HAp from a simple biocompatible substance into an advanced functional material with a wide range of applications. The synthesis of HAp is a complex area of study involving numerous techniques, each offering unique benefits and challenges. This chapter discusses different sol-gel synthesis routes, emphasizing the influence of precursor materials and solvent systems on the phase purity and morphology of the resulting materials. In addition to reviewing existing literature, this chapter presents a detailed case study on the synthesis of HAp and its dielectric properties. The case study addresses the challenges encountered during the process, emphasizing the necessity of carefully optimizing precursor concentrations to achieve the desired phase purity. The findings indicate that the highest content of hydroxyapatite (HAp) was obtained after heat treatment at 500°C, although secondary phases such as Ca₂P₂O₇, Ca₃(PO₄)₂, and Ca₃N₂ were also identified. The morphological analysis revealed particles of varying shapes and sizes with signs of agglomeration. Additionally, the electrical characterization showed that the grain and grain boundary resistance values were 46.61 and 245.63 MΩ, respectively. Through this combined review and case study approach, the chapter aims to provide a comprehensive overview of both the theoretical and practical aspects of HAp synthesis, offering valuable insights for researchers in the field of materials science.

Part of the book: Sol-Gel