| The main driving force for the microelectronics technology is integration, miniaturization and fast pace of electronic components. Materials with high dielectric constant are the core materials of electronic components, such as Dynamic Random Access Memory (DRAM) and Multilayer Ceramic Capacitor (MLCC). The hot topic of high dielectric constant materials is focused on the miniaturization and high-performance of electronic components.M. A. Subramanian et al. reported that CaCu3Ti4O12 (CCTO) exhibited enormously large dielectric constant about 12000 at low frequency, and the dielectric constant was temperature independent from room temperature to 300℃. Then CCTO has attracted considerable attention because of its high dielectric properties for potential applications. Although CCTO ceramics has large dielectric constant, the dielectric loss of is also relatively too high for practical application. To find a new material with high dielectric constant, low dielectric loss and good temperature stability is an urgent and significant practical subject for the research of giant dielectric material.Na0.5Bi0.5Cu3Ti4O12 (NBCTO) is isostructural with CaCu3Ti4O12 (CCTO). In this paper, the phase structure, microstructure and dielectric properties of Na0.5Bi0.5Cu3Ti4O12 ceramics prepared under different conditions were studied. The A-site substitution of Na0.5Bi0.5Cu3Ti4O12 ceramics was also studied to accommodate the high dielectric constant and lower dielectric loss.Through systematically study the effect of different conditions on dielectric properties of Na0.5Bi0.5Cu3Ti4O12 ceramics, it was found when the samples were precalcined at 800℃and sintered at 1000℃for 7.5 h, the Na0.5Bi0.5Cu3Ti4O12 ceramics had a pure perovskite structure, clearer grain boundary, higher density, and huger dielectric constant. The dielectric constant was about 13495, and the dielectric loss was 0.031. In addition, the dielectric properties of NBCTO had good temperature stability (-4.19%～-0.44%) from-60℃to 150℃. Complex impedance results revealed that the grain was semiconducting and the grain boundaries was insulating. The grain resistance Rg was 12.10 Q-cm and the grain boundary resistance Rgb was 2.009×105Ω·cm, the higher permittivity can be explain by the internal barrier layer capacitance (IBLC) model.Then the effect of K+ and Li+substitution for Na+ on the phase structure, microstructure and dielectric properties of Na0.5Bi0.5Cu3Ti4O12 ceramics was discussed, respectively. When the substitution content is fewer, Na0.5-xKxBi0.5Cu3Ti4O12 (NKBCTO) and Na0.5-xLixBi0.5Cu3Ti4O12 (NLBCTO) all showed a pure perovskite the structure. But CuO or Cu2O phase could be detected when the substitution content is 0.15. With increasing the K+ and Li+, the dielectric properties became worse. When K+ and Li+ content is 0.05, the obtained ceramics had lower dielectric constant (8616 and 7062) and higher dielectric loss (0.0417and 0.0585) compared with those of NBCTO. But the ceramics showed good temperature stability of -4.17%～+0.31% and -4.57%～+0.60%, respectively. The results showed that K+ and Li+ substitution for Na+ of Na0.5Bi0.5Cu3Ti4O12 ceramic could not improve the dielectric properties.Lastly, the effect of La3+ content on the phase structure, microstructure and dielectric properties of NBCTO ceramics were discussed. The results showed that La3+ substitution could decrease the sintering temperature. When x=0.10, the sintering temperature decreased from 1000℃to 970℃, and the obtained NBLCTO ceramics also exhibited good dielectric properties as follows:higher permittivity (1.02x 104), lower dielectric loss (0.022), and good temperature stability (-1.87%～+3.27%). In a word, the NBLCTO ceramics was the potential giant dielectric material for application of electronic components such as DRAM and MLCC etc. |
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