Water and SnF2 Assisted Ultralow-Temperature Sintering of Mechanically Tough Y3Fe5O12 Composites for Magneto-Dielectric Antennas

Abstract

Recently, the cold sintering process (CSP) has gained worldwide recognition from the scientific community as a green and innovative fabrication technique due to the substantial reduction of processing energy, time, and cost. The present work reports the preparation, fabrication, and properties of (1 – x)Y3Fe5O12–xSnF2 (x = 0.2, 0.3, 0.4, 0.5 volume fraction) ceramic composites for the first time through the cold sintering process under 150 °C, by applying 300 MPa uniaxial pressure for 30 min. The evolved microstructures of the cold-sintered composites suggest enhanced densification with increasing SnF2 concentration. The evolution of the microstructure, consequent densification, and hardness of the composites can be due to the combined effect of water as a transient solvent and the relatively low melting point of SnF2. The main mechanism behind the densification in the SnF2-based system can be the liquid phase formation followed by pressure solution creep and plastic deformation. At the optimum additive concentration, the measured microhardness of the composite is around 4.7 GPa and its moisture absorption lies below 0.1%. The (1 – x)YIG–xSnF2 ceramics have relative permittivity (εr) in the range of 7.1–11.3 and loss tangent of the order of 10–2 at a frequency of 900 MHz. Further, the real part of permeability and the corresponding loss tangent lie below 2 and 10–1, respectively, at 900 MHz. Herein, a microstrip patch antenna (MPA) is designed, simulated, and fabricated using the 0.5YIG–0.5SnF2 composite, which shows excellent performance at 5.29 GHz with a return loss of −17.9 dB and an impedance bandwidth of 780 MHz. Hence, cold sintering using SnF2-based additives is considered a sustainable, energy-efficient, and cost-effective tool for the densification of magneto-dielectric materials.