Very high-performance dielectric and non-ohmic properties of novel X8R type Ca1-1.5xHoxCu3Ti4O12/TiO2 ceramics

Very low tan delta (similar to 0.018) with stability in the frequency range of 10(2)-10(4) Hz, a giant-epsilon' of similar to 7912, temperature coefficients of the dielectric constant (Delta epsilon') of less than +/- 15% over the temperature range of -60 -165 degrees C, and alpha values of similar to 782.5 were observed in a Ca1-1.5xHoxCu3Ti4O12/TiO2 ceramic sintered at 1060 degrees C for 6 h. This ceramic is suitable for applications in X5R, X7R and X8R capacitors, and adequate for varistor applications. XRD results and backscatter FESEM-EDXS spectra, as well as elemental mapping, confirmed the presence of CaCu3Ti4O12 and TiO2 phases in all Ca1-1.5xHoxCu3Ti4O12/TiO2 ceramics. Grain sizes of the CaCu3Ti4O12 phase greatly decreased, while the TiO2 phase slightly decreased with increasing Ho3+ dopant content. Substitution of Ho3+ can cause an increase in the resistance of the insulating grain boundaries and grain resistance, leading to greatly decreased tan delta values. Very low tan delta values and nonohmic properties, as well as giant-epsilon' values, were found to depend on the microstructure of individual Ca1-1.5xHoxCu3Ti4O12/TiO2 ceramics. (C) 2018 Elsevier B.V. All rights reserved.