Structure and properties of fiber-reinforced LiZn ferrite ceramics prepared via spark plasma sintering

Abstract

In order to improve the matrix cracking of LiZn ferrite (LZF) ceramics during spark plasma sintering, fiber-reinforced LZF materials were prepared using silicon carbide nanofibers (SCFs) and alumina whiskers (AWs) as reinforcement phases. The effect of fiber reinforcement on the microstructure and mechanical, electrical, and magnetic properties of LZF was systematically studied. The results reveal that SCFs lead to an increase in grain size of SCF-reinforced LiZn ferrites (LZF-S) and a deterioration of grain morphology due to the transgranular behavior of SCFs. The increase in complex dielectric constant and dielectric loss, as well as the decrease in resistance of LZF-S, is due to the increase in Fe2+ concentration in ceramics and low resistance of SCFs. AW-reinforced LiZn ferrites (LZF-A) show the opposite effect due to the high porosity caused by AWs and the high resistance of AWs. LZF-S exhibits high fiber/matrix bonding strength, which permits the transfer of the load from the matrix to the fiber to be more effective, leading to a high fracture toughness (KIC) of 5.1 MPa m1/2. The bonding strength between fiber and matrix of LZF-A is low, but a large number of pores passivate the crack tip. At an SCF content of less than 2.5 wt%, the saturation magnetization (Ms) of LZF does not decrease obviously, but a small amount of AWs leads to a significant decrease in Ms (pure LZF: 83 emu·g−1; 1.0 wt% SCFs: 80 emu·g−1; 1.0 wt% AWs: 62 emu·g−1), which can be ascribed to the partial substitution of Fe3+ by nonmagnetic Al3+ ions. When the content of reinforcement phases is 1 wt%, the ferroresonance linewidth increases significantly due to the high porosity caused by the secondary phases (pure LZF: 234 Oe; 1.0 wt% SCFs: 2161 Oe; 1.0 wt% AWs: 1020 Oe).