Structure‐Dependent Microwave Dielectric Properties and Middle‐Temperature Sintering of Forsterite (Mg 1– x Ni x ) 2 SiO 4 Ceramics

The crystal structure, microstructure, and microwave dielectric properties of forsterite‐based ( Mg 1– x Ni x ) 2 SiO 4 ( 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 MgSiO 3 secondary phase as x  > 0.08. Lattice parameters in all axes decrease linearly with increasing Ni content due to the smaller ionic radius of Ni 2+ compared to Mg 2+ . The substitution of an appropriate amount of Ni 2+ could greatly improve the sintering behavior and produce a uniform and closely packed microstructure of the Mg 2 SiO 4 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% Li 2 CO 3 ‐ V 2 O 5 ‐doped ( Mg 0.95 Ni 0.05 ) 2 SiO 4 ceramics sintered at 1150°C for 4 h.