The entropy effect on the structure and microwave dielectric properties of high-entropy Lix(MgZnCoNi)(1-x)/4Al2O4-δ ceramics

In present study, high-entropy Lix(MgZnCoNi)(1-x)/4Al2O4-delta x (MgZnCoNi) (1- x )/4 Al 2 O 4- delta ceramics (x x = 0.00-0.45) were synthesized using solid-state reaction route, which formed a single-phase spinel structure with a Fd-3m space group. The reduction in unit cell volume and lattice parameters were attributed to the compression of polyhedral structures. A moderate content of Li+ + ions promoted the grain growth and improved the densification of ceramics. The internal connection among the conformational entropy ( Delta S config ), structure, and microwave dielectric properties in high- entropy Lix(MgZnCoNi)(1-x)/4Al2O4-delta x (MgZnCoNi) (1- x )/4 Al 2 O 4- delta ceramics was systematically studied. The dielectric constant (epsilon r) epsilon r ) was largely affected by the polarizability, and relatively high conformational entropy helped to increase the phonon vibrational energy and enhance the bond strength, resulting in low epsilon r values. Additionally, the high concentration of oxygen vacancies, high packing fraction, low internal strain/fluctuation and suppressed damping behavior were closely related to relatively low conformational entropy. Notably, the introduction of oxygen vacancy leaded to the Al3+ 3+ ions preferentially occupy tetrahedral sites enhancing the covalency. These factors collectively reduced the intrinsic losses and improved the quality factor (Qxf). Q x f ). Moreover, relatively high conformational entropy conduced to the structural stability by improving the M-O (M M = Li, Mg, Zn, Co, and Ni) bond strength and valence, which contributes to achieve near-zero temperature coefficient of resonant frequency (tau f). tau f ). As Delta S config changes, high-entropy Lix(MgZnCoNi)(1-x)/4Al2O4-delta x (MgZnCoNi) (1- x )/4 Al 2 O 4- delta ceramics presented great microwave dielectric properties: epsilon r values of 5.46 8.49, Q x f values of 3,540 GHz (f f = 14.84 GHz) 56,950 GHz (f f = 12.99 GHz), and tau f f values of-58 ppm/degrees C degrees C-14 ppm/degrees C. degrees C. Our study demonstrates that the high-entropy strategy effectively enhances microwave dielectric properties. This approach has potential applications across a broad spectrum of microwave dielectrics ceramics.