Spark Plasma Sintering Of BaTiO₃ Based Composite Ceramics

In recent years, materials showing colossal dielectric constant have drawn considerable attention not only for academic reasons but also for the miniaturization of capacitive electronic elements. In the present thesis, the microstructure, dielectric characteristics of BaTiO3-based composite ceramics prepared by spark plasma sintering were systematically investigated. New systems of giant dielectric constant composite were prepared by using spark plasma sintering.Dense (1-x)BaZr0.2Ti0.8O3/xCaCu3Ti4O12 ((1-x)BZT/xCCTO) composite ceramics were prepared by spark plasma sinterin. The results of XRD and SEM showed that the (1-x)BZT/xCCTO composite mainly consisted of BaZro.2Ti0.8O3 and CaCu3Ti4012 phases. For x=0.9, a wide dielectric constant platform as high as 4,000 was gained in the temperature range from 150 to 550 K, which was caused by the competition of low temperature ferroelectric peaks of BaZr0.2Ti0.8O3 and high temperature dielectric relaxation of CaCu3Ti4O12. The dielectric relaxtion of (1-x)BZT/xCCTO at low temperatures can be well fitted with Debye equation. It seems that the dielectric response of (1-x)BZT/xCCTO composite doesn't obey the Maxwell-Garnet equation and Bruggeman equation.Dense Ba0.4Sr0.6TiO3/CaCu3Ti4O12 ((1-x)BST/xCCTO) composite ceramics were fabricated by spark plasma sintering. No tertiary phase was found by XRD and SEM-EDS. A wide dielectric constant platform as high as 2,000 was gained in 200-400K, which may be cause by the competition of low temperature ferroelectric peaks of Ba0.4Sr0.6TiO3 and high temperature dielectric relaxation of CaCu3Ti4O12. The dielectric response of (1-x)BST/xCCTO composite ceramics can be well explained with the Maxwell-Garnet equation.Ba(Zr0.2Ti0.8)O3/carbon nanotube (BZT/xCNT) composites were prepared by spark plasma sintering and characterized by SEM. The composites exhibited colossal dielectric constant up to several 105 with relatively low dielectric loss over a wide temperature range from 250 K to 400 K. For composite with 0.025 wt% CNT, the dielectric constant and dielectric loss at 50℃and 1 kHz were 6.1x105 and 0.074, respectively. The high dielectric constant can be explained by the Maxwell-Wagner polarization originating from the CNT and Ba(Zr0.2Ti0.8)O3 interfaces, percolation and microcapacitance microstructure.