Studying On CaTiO₃-LnAlO₃（Ln=Nd、La） Microwave Dielectric Ceramics Of High-Q Value And Medium Permittivity

Combined with the development of modern communications technology andmicroelectronics technology, as a theoretical support for the research status andachievements of high-Q intermediary microwave dielectric ceramics both at domestic andabroad, CaTiO₃-LnAlO₃（Ln=Nd、La） ceramics are chosen as research system in thisdissertation. The relationships between the component formulations, process of preparation,microstructure and microwave dielectric properties of samples were discussed in detail byusing X-ray diffraction （XRD）, scanning electron microscopy （SEM） and parallel plate testsystem.0.7CaTiO₃-0.3(La_xNd_1-x)AlO₃solid solution was prepared by using La³⁺ to substitutethe Nd2+of the CaTiO₃-LaAlO₃ceramics. It is found that εrand τfincrease as the increase ofthe x value. The0.7CaTiO₃-0.3(La_xNd_1-x)AlO₃ceramics get the ma_x Q×f value, when x=_0.5,which may be caused by the ion ordering of the ceramics. As the increase of the sinteringtemperature, εrand Q×f value increase firstly and then have the trend of decrease. Theoptimal sintering temperature is1550℃.To adjust the microwave dielectric properties of the0.7CaTiO₃-0.3(La_0.5 Nd_0.5)AlO₃ceramics, moderate amount of SrTiO₃was added into the samples. By adding small amountof SrTiO₃, the Q×f value increases as the increase of the density. As the content of SrTiO₃increases, the Q×f value has the trend of decrease and the optimal addition content ofSrTiO₃is0.01at.%. Because of small low volume fraction of SrTiO₃, it has little effect onεrof samples. The change of the τfvalue is complicated, which needs future investigate. Asthe increase of the sintering temperature, εrand Q×f value increase firstly and then have thetrend of decrease, and the optimal sintering temperature is1550℃.To explore the effect of Ga2O₃which was added to the samples,0.7CaTiO₃-0.3(La_0.5 Nd_0.5)(Al_0.5 Ga_0.5)O₃was prepared by using50at.%Ga³⁺to replaceAl³⁺.The results shows that the Ga³⁺amount to50at.%which was substituted by Al³⁺overcomes the difficulty of getting compact ceramics. In the case of Q×f value to maintainthe same, the dielectric constant of samples gets substantial growth. Microwave dielectric properties of the0.7CaTiO₃-0.3(La_0.5 Nd_0.5)AlO₃ceramics whichwere sintering under different cooling rate were discussed. The results show that slowercooling rate is more favorable to improve the quality factor and dielectric constant of thesamples. With discussion of different sintering time and annealing under differenttemperature, the results shows that there is no direct relationship between the quality ofsamples and grain size nor rearrangement of lattice atoms.