Effects of MnO₂ doping on microstructure and microwave dielectric properties of Ba_4.2Nd_9.2Ti₁₈O₅₄–NdAlO₃ ceramics

MnO₂ doped Ba_4.2Nd_9.2Ti₁₈O₅₄–NdAlO₃(13 wt%) (BNT–NA) microwave dielectric ceramics with the near zero τ_f and the wide range of sintering temperature were prepared by conventional solid state method. The effects of Mn⁴⁺ doping on the microstructures and microwave dielectric properties of BNT–NA ceramics were investigated. XRD patterns showed only a single BaNd₂Ti₅O₁₄ phase was identified in all samples and there was no second phase. The sintering temperature decreased from 1,380 to 1,320 °C as MnO₂ content increased from 0.1 to 0.9 wt%. The MnO₂ doped BNT–NA ceramics could be densified at a lower sintering temperature. The MnO₂ additive had a positive effect on lowing sintering temperature of BNT–NA ceramics. The τ_f varied from negative to positive with the increase of MnO₂. Excellent microwave dielectric properties were achieved in Ba_4.2Nd_9.2Ti₁₈O₅₄–NdAlO₃ ceramics doped with 0.3 wt% MnO₂ and sintered at 1,380 °C for 2 h: ε_r = 66.5, Q × f = 13,948 GHz, τ_f = 0.4 ppm/°C.