Investigation On The Structure-properties Relationship Of NdNbO₄ Microwave Dielectric Ceramics

In recent years,many researchers pay their attentions on the multifunctional materials of Nd NbO₄ ceramics.In this paper,the NdNbO₄ ceramics were prepared via conventional solid-state reaction method.Based on the XRD data,the Rietveld refinement was used to investigate the structural properties and chemical bond characterizations of Nd NbO₄ ceramics.The intrinsic factors on microwave dielectric properties were also discussed.Besides,a series of NdNbO₄-based materials with high performance were prepared.1.Based on the refined results of pure NdNbO₄ ceramics,sintered samples are indexed as monoclinic fergusonite phase,belonged to the space group of I12/c,and its lattice parameters were a=4.7022?,b=17.0801?,c=5.0683?,?=94.47°and V=317.31?³.According to the complex chemical bond theory,chemical bond characterizations?bond ionicity,lattice energy,bond energy?were calculated and its relationship with microwave dielectric properties?dielectric constant,quality factor,temperature coefficient?were also studied.2.A series of different trivalent ions(Y³⁺,La³⁺,Ce³⁺,Sm³⁺,Gd³⁺,Dy³⁺,Ho³⁺,Er³⁺and Yb³⁺)were chosen to substitute Nd³⁺ion of NdNbO₄ ceramics.The effects of different trivalent ions on the structure properties and dielectric properties were systematically investigated.The obtained results indicate that(Nd_0.92Y_0.08)NbO₄ceramics possess highest quality factor?81100 GHz?and(Nd_0.94La_0.06)NbO₄ ceramics have a stable temperature coefficient?0 ppm/^??.3.The Nd(Nb_1-xB_x)O₄(B=Ta⁵⁺,Sb⁵⁺)ceramics were prepared and the effects of pentavalent ion substitution on structure,chemical bond characterization and microwave dielectric properties were studied.Based on the obtained results,partial Nb⁵⁺ions were substituted by Ta⁵⁺or Sb⁵⁺ions,the lattice energy of NdNbO₄ceramics would increase and the Nb-site bond energy of NdNbO₄ ceramics would decrease.However,the quality factor would be enhanced and the stability would be destroyed in NdNbO₄ ceramics due to the change of lattice energy and bond energy.3.In order to meet the requirement about the LTCC application,Al₂O₃,LiF,MgF₂ and Li₂WO₄ were added NdNbO₄ ceramics as sintering aids and lowered its sintering temperature.The sintering characterization,structural properties and microwave dielectric properties of the sintered ceramics were investigated systematically.Based on the experimental results,it is indicated that Al₂O₃ and Li₂WO₄ were suitable for NdNbO₄ ceramics as sintering aids.NdNbO₄-3 wt.%Al₂O₃ceramics exhibited excellent microwave dielectric properties??_r=18.10,Q×f=54700GHz and t_f=-0.51ppm/^??sintered at 1150^? and NdNbO₄-2wt.%Li₂WO₄ ceramics with high performance??_r=16.72,Q×f=21820GHz,t_f=-35.90 ppm/^??ceramics were obtained at 1050 ^?.