Crystal Structure And Microwave Dielectric Properties Of CaTiO₃-LaGaO₃Ceramics System

Microwave dielectric materials with a high Q×f value, a high dielectric constant andgood stability of temperature coefficient of resonant frequency have being widelyinvestigated as the part of wireless communication technologies in the recent10years.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-LaGaO3ceramics are chosen as research system in this dissertation. Therelationships between the component formulations, process of preparation, microstructureand microwave dielectric properties of samples were discussed in detail. To decrease thehigh sintering temperature of0.64CaTiO3-0.36LaGaO3, different ratios of0.97Bi2O3-0.03Al2O3and0.76Bi2O3-0.24NiO were added in the0.64CaTiO3-0.36LaGaO3ceramics system. Unfortunately, all the samples lost good microwave properties, especiallythe Q×f value, although the sintering temperature only decreased a little. And the resultsshowed that0.97Bi2O3-0.03Al2O3and0.76Bi2O3-0.24NiO were not fit for0.64CaTiO3-0.36LaGaO3ceramics system for sintering additive.In our study, the improvement of the microwave dielectric properties can be achievedby the substitution of B-sites and the increase in ordering degree of the B-site ions. Theprice of Al2O3is cheaper than that of Ga2O3and the ionic radius and electronicconfiguration of the Al3+are similar to those of Ga3+. Therefore, if Ga3+in0.64CaTiO3–0.36LaGaO3were substituted partly by Al3+, it would be possible to develop anovel microwave dielectric material with a good microwave dielectric properties and arelatively low price. The crystal structure and microwave dielectric properties of0.64CaTiO3–0.36La[Ga(1-δ)Alδ]O3specimens have been investigated with the differentcontents of LaAlO3. The results show that the phase transformation may occur at δ=0.5,where specimens exhibited the best microwave dielectric properties with εr=45.54, Q×f=43,897GHz (@4.53GHz), τf=-1.7ppm/°C. To further investigate the influence ofsubstitution of B-sites of xCaTiO3–(1-x)La[Ga0.5Al0.5]O3, the x value was changed within 0.62≤x≤0.66. The results showed that all the samples of xCaTiO3–(1-x)La[Ga0.5Al0.5]O3(x=0.62,0.63,0.64,0.65,0.66) exhibited ρr≥96.8%, Q×f≥39,000GHz,44≤εr≤48,-8ppm/°C≤τf≤+6ppm/°C.