According to the effective medium theory , the average microscopic electric field inside the ceramic matrix filled with conductive particles increases in the region of the PT, which results in a significant decrease in E b. Figure 4 shows the non-Ohmic properties BIRB 796 price of the CCTO/Au nanocomposites as a plot of electrical current density (J) vs. electric field strength (E). α values of the CCTO, CCTO/Au1, CCTO/Au2, CCTO/Au3, and CCTO/Au4 samples were calculated in the range of J = 1 to 10 mA/cm2 and found to be 7.38, 17.67, 11.08, 5.05, and 3.08, respectively. E b values (obtained at J = 1 mA/cm2)
were found to be 4.26 × 103, 1.25 × 104, 1.17 × 104, 2.50 × 103, and 7.84 × 102 V/cm, respectively. α and E b initially showed a strong increase with introduction of 2.5 to 5.0 vol.% of Au NPs into CCTO (inset of Figure 4). Both parameters greatly decreased with further increasing Au NPs from 10 to 20 vol.%, which is due to the percolation effect . In the region of the PT, electrical conduction in composites increased dramatically, resulting in a large decrease in selleck chemicals llc E b. This observation is consistent with the effective medium theory . Therefore, it is reasonable to suggest that the increases in ϵ′ and tanδ observed in the CCTO/Au4 sample were
mainly attributed to the percolation effect; while, the effect of grain size effect is slight. selleck inhibitor Figure 4 J – E curves of CCTO/Au nanocomposites. The inset shows values of E b and α as a function of Au concentration. The CCTO/Au1 sample exhibited the best non-Ohmic properties among all samples. These values are comparable to those observed in CaCu3Ti3.8Sn0.2O12 ceramic . There are many factors that are potentially responsible for strong improvement of non-Ohmic properties. It was found that the non-Ohmic properties of CCTO ceramics could effectively be improved by fabricating composite systems of CCTO/CTO [28, 29]. As shown in Figure 1, the observed CTO phase in Pregnenolone all of the CCTO/Au
composites tended to increase with increasing Au content. However, the non-Ohmic properties of CCTO/Au strongly degraded as the Au filler concentration increased. Thus, the excellent non-Ohmic properties of the CCTO/Au1 sample are not mainly caused by a CTO phase. For CCTO polycrystalline ceramics, the non-Ohmic behavior is due to the existence of Schottky barriers at the GBs . Thus, the existence of metallic Au NPs at the GBs of CCTO ceramics may contribute the formation of Schottky barriers at GBs. However, the mechanism by which Au NPs contribute to enhancement of non-Ohmic properties is still unclear. It is worth noting that improved nonlinear properties of the CCTO/Au1 sample may also be related to modification of microstructure. Although the introduction of metallic particles in a ceramic matrix with concentration near the PT can dramatically enhance the dielectric response, a large increase in the conduction of charge carriers was observed simultaneously, leading to decreases in E b and energy density.