Structure‐Dependent Microwave Dielectric Properties and Middle‐Temperature Sintering of Forsterite (Mg1–xNix)2SiO4 Ceramics

The crystal structure, microstructure, and microwave dielectric properties of forsterite‐based (Mg_1–xNi_x)₂SiO₄ (x = 0.02–0.20) ceramics were systematically investigated. All samples present a single forsterite phase of an orthorhombic structure with a space group Pbnm except for a little MgSiO₃ secondary phase as x > 0.08. Lattice parameters in all axes decrease linearly with increasing Ni content due to the smaller ionic radius of Ni²⁺ compared to Mg²⁺. The substitution of an appropriate amount of Ni²⁺ could greatly improve the sintering behavior and produce a uniform and closely packed microstructure of the Mg₂SiO₄ ceramics such that a superior Q × f value (152 300 GHz) can be achieved as x = 0.05. The τ_f value was found to increase with increasing A‐site ionic bond valences. In addition, various additives were used as sintering aids to lower the sintering temperature from 1500°C to the middle sintering temperature range. Excellent microwave dielectric properties of ε_r~6.9, Q × f~99800 GHz and τ_f~?50 ppm/°C can be obtained for 12 wt% Li₂CO₃‐V₂O₅‐doped (Mg_0.95Ni_0.05)₂SiO₄ ceramics sintered at 1150°C for 4 h.