Electrical responses and dielectric relaxations in giant permittivity NaCu_3Ti_3TaO_(12) ceramics

摘要

Dielectric relaxations and electrical responses in NaCu_3Ti_3TaO_(12) ceramics were investigated as a function of temperature. NaCu_3Ti_3TaO_(12) ceramics exhibit giant dielectric constants with values of ε' ~ 1.45-2.08 × 10~4. Two sets of thermally activated dielectric relaxations were observed in low and high temperature ranges. Sintering conditions have an insignificant influence on the microstructure of NaCu_3Ti_3TaO_(12) ceramics, and have a slight impact on their ε' values. Thermally activated electrical responses of grains and grain boundaries have been studied at different temperatures by using complex admittance and impedance spectroscopy analyses, respectively. The low temperature relaxation mechanism is found to correlate closely with electrical response of semiconducting grains; whereas the apparent high s' values are attributed to electrical response of insulating grain boundaries. These results support the internal barrier layer capacitor model to explain the giant dielectric properties of NaCu_3Ti_3TaO_(12) ceramics. Additionally, high temperature relaxation may be attributed to the sample-electrode effect and/or defect ordering.