Hui Eun Kim

Improved dielectric properties of BaTiO3-added CaCu3Ti4O12 polycrystalline ceramics

The effects of the BaTiO3 (BTO) additive on the electrical properties of CaCu3Ti4O12 (CCTO) polycrystalline ceramics were systematically investigated. Various amounts of BTO powder up to 15 mol. % were added to CCTO powder. Each batch was ball-milled, pressed into pellets, and finally sintered at 1060°C for 12 h in air. Compared with pure CCTO sample (ɛr ∼ 52,000 and tan δ ∼ 0.38 at 100 kHz), BTO-added CCTO samples commonly showed significantly reduced dielectric losses although their dielectric constants were decreased approximately by one order of magnitude (for instance, ɛr ∼ 4,075 and tan δ ∼ 0.02 at 100 kHz for 5 mol. % BTO-added CCTO sample). In addition, the breakdown voltages of BTO-added CCTO samples were much higher than that of pure CCTO sample, and thus the leakage currents were greatly reduced at the applied voltage above ∼ 10 V. A large reduction in the dielectric losses and leakage currents is attributed to the secondary phases segregated at the CCTO grain boundary which are composed of CaTiO3, Ba4Ti12O27, and unreacted BTO.

Improved dielectric properties of CaCu3Ti4O12 films with a CaTiO3 interlayer on Pt/TiO2/SiO2/Si substrates prepared by pulsed laser deposition

We report the greatly improved dielectric properties of CaCu3Ti4O12 (CCTO) films with a 60 nm-thick CaTiO3 (CTO) interlayer on Pt/TiO2/SiO2/Si substrates. Both CCTO films and CTO interlayers were prepared by pulsed laser deposition (PLD). With increasing the thickness of CCTO from 200 nm to 1.3 μm, the dielectric constants (εr) at 10 kHz in both CCTO single-layered and CCTO/CTO double-layered films increased from ∼260 to ∼6000 and from ∼630 to ∼3700, respectively. Compared with CCTO single-layered films, CCTO/CTO double-layered films irrespective of CCTO film thickness exhibited a remarkable decrease in their dielectric losses (tanδ) (<0.1 at the frequency region of 1 - 100 kHz) and highly reduced leakage current density at room temperature. The reduced leakage currents in CCTO/CTO double-layered films are attributable to relatively higher trap ionization energies in the Poole-Frenkel conduction model.