Grain size effect on the giant dielectric constant of CaCu_3Ti_4O_(12) nanoceramics prepared by mechanosynthesis and spark plasma sintering

摘要

In the present work, CaCu_3Ti_4O_(12) (CCTO) nanoceramics with different grain sizes were prepared by spark plasma sintering (SPS) at different temperatures (SPS-800, SPS-900, SPS-975, and SPS-1050) of the mechanosynthesized nano-powder. Structural and microstructural properties were studied by XRD and field-emission scanning electron microscope measurements. The grain size of CCTO nanoceramics increases from 80 nm to ～200 nm for the ceramics sintered at 800 ℃ and 975 ℃, respectively. Further increase of SPS temperature to 1050 ℃ leads to micro-sized ceramics of 2-3 μm. The electrical and dielectric properties of the investigated ceramics were studied by impedance spectroscopy. Giant dielectric constant was observed in CCTO nanoceramics. The dielectric constant increases with increasing the grain size of the nanoceramics with values of 8.3 × 10~3, 2.4 × 10~4, and 3.2 × 10~4 for SPS-800, SPS-900, and SPS-975, respectively. For the micro-sized SPS-1050 ceramics, the dielectric constant dropped to 2.14 × 10~4. The dielectric behavior is interpreted within the internal barrier layer capacitance picture due to the electrical inhomogeneity of the ceramics. Besides the resistive grain boundaries that are usually observed in CCTO ceramics, domain boundaries appear as a second source of internal layers in the current nanoceramics.