Significantly Improved Colossal Dielectric Properties and Maxwell-Wagner Relaxation of TiO(2)-Rich Na(1/2)Y(1/2)Cu(3)Ti(4+x)O(12) Ceramics.

In this work, the colossal dielectric properties and Maxwell-Wagner relaxation of TiO(2)-rich Na(1/2)Y(1/2)Cu(3)Ti(4+x)O(12) (x = 0-0.2) ceramics prepared by a solid-state reaction method are investigated. A single phase of Na(1/2)Y(1/2)Cu(3)Ti(4)O(12) is achieved without the detection of any impurity phase. The highly dense microstructure is obtained, and the mean grain size is significantly reduced by a factor of 10 by increasing Ti molar ratio, resulting in an increased grain boundary density and hence grain boundary resistance (R(gb)). The colossal permittivities of ε' ~ 0.7-1.4 × 10(4) with slightly dependent on frequency in the frequency range of 10(2)-10(6) Hz are obtained in the TiO(2)-rich Na(1/2)Y(1/2)Cu(3)Ti(4+x)O(12) ceramics, while the dielectric loss tangent is reduced to tanδ ~ 0.016-0.020 at 1 kHz due to the increased R(gb). The semiconducting grain resistance (R(g)) of the Na(1/2)Y(1/2)Cu(3)Ti(4+x)O(12) ceramics increases with increasing x, corresponding to the decrease in Cu(+)/Cu(2+) ratio. The nonlinear electrical properties of the TiO(2)-rich Na(1/2)Y(1/2)Cu(3)Ti(4+x)O(12) ceramics can also be improved. The colossal dielectric and nonlinear electrical properties of the TiO(2)-rich Na(1/2)Y(1/2)Cu(3)Ti(4+x)O(12) ceramics are explained by the Maxwell-Wagner relaxation model based on the formation of the Schottky barrier at the grain boundary.