Degree of inversion of A/B lattice sites and microwave/millimeter wave/terahertz dielectric properties of MgAl_2-x(Zn_0.5Mn_0.5)_xO₄ ceramics

In this work, spinel-structured MgAl_2-x(Zn_0.5Mn_0.5)_xO₄ (0 ≤ x ≤ 0.08) single-phase ceramics were prepared through a solid-state reaction route. The substitution of (Zn_0.5Mn_0.5)³⁺ for Al³⁺ at the octahedral site affected the degree of inversion of A/B lattice sites, bond length/strength/valence, and covalency of metal-oxygen bond in the tetrahedron and hence microwave dielectric properties of MgAl₂O₄. The variation in ε_r and tanδ of ceramics is investigated in the millimeter wave-terahertz frequency band by combining infrared reflection spectrum and terahertz time-domain spectroscopy. A high Q×f value of 111,010 GHz @ 12.01 GHz, low ε_r = 8.3, and slightly lower τ_f = −60 ppm/°C is obtained for MgAl_1.98Zn_0.01Mn_0.01O₄ ceramics, which is tuned by adding a small amount of SrTiO₃. The composite ceramics exhibited a near-zero τ_f (2.8 ppm/°C), high Q×f (55,400 GHz @ 11.15 GHz), and low ε_r (= 8.5), showing a great potential application prospect for 5G/6G wireless communication.