Water-Assisted Densification and Broadband Dielectric Response of Cold-Sintered Gd₃Fe₅O₁₂-SnF₂ Composites

Technological breakthroughs in this era of 5G and IoT entail the sustainable fabrication of integrable and multifunctional compact devices using low-loss microwave dielectric materials. Nowadays, the miniaturization of devices using magnetodielectric materials fabricated through a green and sustainable cold sintering process has expanded the scope of applications in various fields of modern communication. Cold sintering, a novel ultra-low-energy sintering technique based on pressure solution creep mechanisms, is a potential strategy with impressive savings in energy, time, and cost. This present work highlights the dielectric response and microstructure of (1−x) Gd₃Fe₅O₁₂-x SnF₂ (x = 0.2, 0.3, 0.4, 0.5 volume fraction) ceramic composites fabricated via a water-assisted cold-sintering process at a temperature of 150 °C under 300 MPa pressure for 30 min. The novelty of using SnF₂ with Gd₃Fe₅O₁₂ in a cold sintering process lies in its ability to enhance densification, lower hygroscopicity, moderate relative permittivity (18.6 at 900 MHz), low loss (∼10⁻²), and its low melting temperature of 216 °C. This innovative approach improves the properties of ceramic composites at significantly low temperatures, showing the potential for sustainable and efficient fabrication. Microstructural studies of these composites indicate that, as the volume fraction of SnF₂ increases, the densification of the composites rises to 94.6% due to consecutive mechanisms of particle rearrangement, compaction, dissolution, and diffusion of SnF₂ through the liquid phase at the initial stage, followed by the evaporation of the liquid phase, resulting in the precipitation of the supersaturated phase at pores and interfaces, and, finally, the melting of SnF₂ forms a glassy phase around the grain boundaries. After cold sintering, the relative density of (1−x) Gd₃Fe₅O₁₂-x SnF₂ composites ranges from 82.4% to 94.6% as x changes from 0.2 to 0.5. The relative permittivity (ε_r) of these (1−x) Gd₃Fe₅O₁₂-x SnF₂ ceramic composites ranges from 10.1 to 12.6 with a dielectric loss (tan δ) of the order of 10⁻² at 900 MHz. Hence, water and SnF₂-assisted cold sintering is an efficient fabrication route for compact and densified magneto-dielectric ceramic GdIG-SnF₂ composites with electromagnetic parameter suitable for microwave applications like miniaturized antennae.