Study On Modification Of CaTiO₃ Based Microwave Ceramics Sintered In Nitrogen Atmosphere

With the development of modern communication technology,especially the development of 5G technology,the volume of electronic products is becoming smaller and smaller,and the trend of higher and higher working frequencies is irreversible.To meet the need of the current miniaturization of electronic equipment and reduce costs,the demand for base metal multilayer ceramic capacitors?BME MLCC?is becoming more and more urgent.Therefore,the anti-reduction microwave dielectric material with high dielectric constant,which can be co-fired with base metals in a neutral atmosphere has become a research hotspot.CaTiO₃ has attracted attention for its high dielectric constant.In this paper,CaTiO₃ based microwave dielectric ceramics was studied and the effect of the substitution of A-site by Ce on the phase composition,structures and microwave dielectric properties of Ca_?1-3x/2?Ce_x TiO₃?CCT?was studied.Based on Ca_?1-3x/2?Ce_xTiO₃,the effects of combination with compounds and B-site substitution on microwave dielectric properties and phase structure were investigated.Firstly,the phase composition,structures and microwave dielectric properties of Ca_?1-3x/2?Ce_xTiO₃ ceramics sintered in nitrogen atmosphere were studied.The results showed that the sintering environment of nitrogen contributed to the formation of Ce³⁺and the solid solubility of Ce in CaTiO₃ was significantly improved compared with the sintered sample in air.Through XRD and Raman analysis,with the increasing of x,the perovskite structure of the ceramics transformed from Pbnm into I4/mcm.Q×f value of ceramics sintered in nitrogen increased with increasing amount of cerium and then decrease,?_f value gradually decreased.The results showed the substitution of A-site of CCT ceramics by Ce improved the anti-reduction and the XPS analysis showed the amount of oxygen vacancies and the content of Ti³⁺reduced,which was studied by the internal strain and defects.The optimum combination of microwave dielectric properties:?_r¹30.6,Q×f¹1705 GHz,and?_f⁺352 ppm/oC were obtained at x=0.14 in CCT ceramics sintered in nitrogen atmosphere.The effects of microwave dielectric properties of CCT ceramics combining with negative?_f value ceramics compounds(NdAlO₃ and Li_1/2Nd_1/2O₃)to further improve the temperature stability of CCT ceramics sintered in nitrogen.The results showed?_f value of CCT ceramics decreased with the increasing of the content of NdAlO₃,when n=0.3?_f value was near zero.The?_r gradually decreased,Q×f value decreased at first then increased and finally decreased with the increasing of the content of NdAlO₃.The perovskite structure of Li_1/2Ce_1/2O₃ sintered in air and nitrogen atmosphere was unstable.When CCT ceramics combined with Li_1/2Nd_1/2O₃,the?_r,Q×f and?_f value decreased with the increasing of the content of Li_1/2Nd_1/2O₃,when l=0.3?_f value was near zero and the Q×f value was small.To reduce the ?_f value and simultaneously keep high dielectric constant and Q×f value,the property of the B-site substitution of CCT ceramics was investigated.The results showed that the solid solubility of CrNb in Ca_0.79Ce_0.14Ti_1-c(Cr_0.5Nb_0.5)_cO₃?CCTCN?ceramics sintered in nitrogen was significantly improved compared with the samples sintered in air.With the increasing of the content of CrNb,the?_r,Q×f and?_f value gradually decreased.The investigation of the substitution of B-site by Al³⁺showed that when Ca_0.79Ce_0.14Ti_1-3a/4Al_aO₃?CCTA?ceramics sintered in nitrogen,with increasing amount of Al,the grain size,?_r,and?_f value decreased.With the increase amount of Al³⁺,the Q×f value increased at 0.067?a?0.20,at a>0.2 the Q×f value decreased.The optimum combination of microwave dielectric properties:?_r⁸3.97,Q×f¹8431 GHz,and?_f⁺159 ppm/oC were obtained at a=0.2 in CCTA ceramics sintered in nitrogen atmosphere.