Correlation between crystal structure and properties of ultra-high dielectric constant ceramics x SrCO₃-Bi₂O₃-Ag(Nb,Ta)O₃

The correlation between crystal structure and properties of x wt% SrCO₃-4.5 wt.%Bi₂O₃-Ag(Nb_0.8Ta_0.2)O₃ (x SrCO₃-Bi₂O₃-ANT) (x = 0.5 ~ 3.0) dielectric ceramics was investigated. The permittivity was significantly influenced by the redshift of three typical vibration modes of A_1g(Ag), F_2g(Nb/Ta) and A_1g(O). The dielectric loss was optimized by the restraint of the second phase AgNbO₃, and a minimum value was obtained when x = 2.0. Changes of c/a value, which indicate the degree of lattice distortion, reflected the temperature coefficient of relative permittivity (τ_ε) was highly correlated with the crystal structure and a near zero τ_ε value was achieved with 2.0 wt.% Sr concentration. The Bi₂O₃-doped ANT ceramics containing 2.0 wt.% SrCO₃ sintered at 1150°C showed excellent dielectric properties: an ε_r value of 841, a tan δ value of 0.00119 and a near zero (−23.7 ppm/°C) τ_ε value.