Sílvia Soreto

By Sílvia Soreto, Manuel Graça, Manuel Valente and Luís Costa

Lithium ferrite (LiFe5O8) is a cubic ferrite, belongs to the group of soft ferrite materials with a square hysteresis loop, with high Curie temperature and magnetization. The spinel structure of LiFe5O8 has two crystalline forms: ordered, β-LiFe5O8 (Fd3m space group) and disordered, α-LiFe5O8 (P4132/P4332 space group). It has numerous technological applications in microwave devices, computer memory chip, magnetic recording, radio frequency coil fabrication, transformer cores, rod antennas, magnetic liquids among others. It is also a promising candidate for cathode in rechargeable lithium batteries. In this work, the dc electrical conductivity, the impedance spectroscopy and the magnetization of Li2O-Fe2O3 powders, with [Li]/[Fe]=1/5 (mol), heat-treated at several temperatures, are studied and related to their structure and morphology. The structural data were obtained by X-ray diffraction and Raman spectroscopy, and the morphology by scanning electron microscopy. The impedance spectroscopy was analysed in function of temperature and frequency, and it was observed that the dielectric properties are highly dependent on the microstructure of the samples. The dc magnetic susceptibility was recorded with a vibrating sample magnetometer, under zero field cooled and field cooled sequences, between 5-300 K. Typical hysteresis curves were obtained and the saturation magnetization increases with increase in heat-treatment temperature.

Part of the book: Magnetic Spinels

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