Giant dielectric properties of fine-grained Na1/2Y1/2Cu3Ti4O12 ceramics prepared by mechanosynthesis and spark plasma sintering

Fine-grained ceramics of Na1/2Y1/2Cu3Ti4O12 (NYCTO) were prepared by spark plasma sintering (SPS) of mechanosynthesized nano-powder. Effect of SPS temperature from 900 up to 1000 A degrees C on the microstructure, phase structure and the dielectric and transport properties of NYCTO ceramics has been studied. The structural studies by X-ray powder diffraction indicated the formation of pure cubic phase of the NYCTO ceramics up to SPS temperature of 975 A degrees C. Decomposition of the NYCTO material was observed with increasing the SPS temperature to 1000 A degrees C. The mictrostructural studies by FE-SEM showed that the grain size increases from 245 to 520 nm when increasing the SPS temperature from 900 to 1000 A degrees C. The dielectric and transport properties of the investigated materials have been studied by impedance spectroscopy in the 120-470 K temperature range. All of the SPS NYCTO ceramics exhibit giant dielectric constant with the highest value of 3 x 10(3) observed for the sample sintered at 975 A degrees C. The observed giant dielectric response is assigned to the internal barrier layer capacitance effect, which originates from the electrical heterogeneous structure of the materials. This picture is supported by the impedance and modulus spectra of the investigated materials where semiconducting grains separated by insulating grain boundaries are observed.