| This article first studied the influence of B-site substitution with different sintering temperature and different Nb5+and Ta5+content on the micro structure and crystal structure of MgTiO3 materials,and systematically studied the internal relationship between the microstructure,crystal structure and microwave dielectric properties.It is further focused on the adjustment of the temperature coefficient of the resonance frequency,and it is expected to obtain a microwave dielectric ceramic system with practical application value.The main findings are as follows:(1)Analyzing the crystal structure of MgTiO3 samples doped with Nb5+/Ta5+by refining the XRD pattern,and both are ilmenite structures.And drew a diagram of its substitution mechanism,confirming that both are B-site substitutions.(2)By analyzing the change law of density and dielectric properties of the sample after Nb5+/Ta5+doping,the density,dielectric constant and quality factor of the sample show the same change law.Therefore,the pores in the sample are the determinants of electrical constant and quality factor.In addition,both elements can compensate to a certain extent for the bound electrons generated due to oxygen deficiency at high temperatures,and inhibit the reduction process of Ti4+to Ti3+to a certain extent,thereby improving the quality factor of the material.The polarizability of the main crystal phase unit cell will affect the change of the temperature coefficient of the resonance frequency,When the sintering temperature is 1350℃ and x=0.05,the microwave dielectric properties of the sample Mg(Ti1-xNbx)O3 are:εr=18.12,Q×f=163618 GHz,τf=-40.1 ppm/℃;When x=0.04,the microwave dielectric properties of sample Mg(Ti1-xTax)O3 are:εr=18.10,Q×f=146457 GHz,τf=-46.3 ppm/℃.(3)By analyzing the Raman spectrum of MgTiO3 samples substituted with Nb5+,it can be seen that the Raman characteristic peaks of the samples are closely related to their dielectric properties,and it is further confirmed that the samples will exhibit high quality factors at the appropriate temperature and appropriate Nb5+content.The value of Q×f is related to the strong Ti-O bond strength,and the temperature coefficient of resonance frequency(τf)is related to the twisting degree of the[TiO6]octahedron.And it is confirmed by XPS that Nb5+can reduce the content of Ti3+in the sample and increase its Qxf value.(4)The influence of different Ca0.6-Nd0.26TiO3 content on the microwave dielectric properties of MgTiO3 was studied.It was confirmed that(1-x)MgTiO3-xCa0.6-Nd0.26TiO3 was compared with the traditional(1-x)MgTiO3-xCaTiO3 sintering temperature has decreased,but its dielectric properties are poor.When the sintering temperature is 1300℃,the dielectric properties of 0.15Ca0.61Nd0.26TiO3-0.85MgTiO3 are:εr=25.12,Q×f=28931 GHz,τf=-3.88 ppm/℃.(5)In order to further explore the high-Q material system with a dielectric constant in the range of 10-20,and improve the performance of 0.15Ca0.61Nd0.26TiO3-0.85MgTiO3,select Mg2.05SiO4.05 to form(0.85-x)MgTiO3-XMg2.05SiO4.05-0.15Ca0.6-Nd0.26TiO3(hereinafter referred to as MCNST),it is confirmed that the dielectric constant(εr)of the sample MCNST is between 9.74～17.82,and the quality factor(Q×f)is between 36992 GHz-63899 GHz,the temperature coefficient of resonance frequency(τf)is between-34.06 ppm/℃ and-22.90 ppm/℃.When the sintering temperature is 1380℃ and x=0.35,the microwave dielectric properties of the system are:εr=15.63,Q×f=60646 GHz,τf=-25.24 ppm/℃. |
