Improvement of microwave dielectric properties of the LiNb _0.6 Ti _0.5 O ₃ M‐phase by doping with (Co _1/3 Nb _2/3 ) ⁴⁺

Abstract Structural evolution and microwave dielectric properties of LiNb _0.6 (Ti _1‐x [Co _1/3 Nb _2/3 ] _x ) _0.5 O ₃ (.05≤x≤.2) ceramics have been studied in this paper. Although the doped compositions maintain the M‐phase solid solutions, compositional fluctuation due to nonuniform dispersion of minor dopants could be observed as x < .05, and trace amount of Li ₂ TiO ₃ ‐based solid solution (Li ₂ TiO ₃ ss) secondary phase presents in the x > .05 compositions. The microwave dielectric properties could be remarkably improved by the doping of (Co _1/2 Nb _1/2 ) ⁴⁺ in comparison to the undoped counterpart. Optimized microwave dielectric properties with Q × f = ∼6500 GHz, ε _r = ∼74 and τ _f = +8.2 ppm/°C could be obtained at x = .10 after sintering at 1050°C/2 h. The sintering temperature could be further reduced to 900°C/2 h by adding .2 wt% B ₂ O ₃ without affecting significantly its microwave dielectric properties: ε _r = 73, Q × f = 6000 GHz, τ _f = +8.5 ppm/°C. The LiNb _0.6 (Ti _1‐x [Co _1/3 Nb _2/3 ] _x ) _0.5 O ₃ ceramics obtained in this case exhibit large dielectric permittivity coupled with much improved Q × f values, near zero τ _f , and low sintering temperature simultaneously, which makes it a promising high‐k microwave dielectric material for low temperature cofired ceramic applications.