Improved dielectric properties of the CaCu3Ti4O12 composites using BaTiO3-coated powder as precursor

A high dielectric loss and a large leakage current of CaCu3Ti4O12 (CCTO) ceramics could be greatly suppressed by using BaTiO3 (BTO)-coated CCTO powder as precursor. BTO-coated CCTO precursors with 5, 10, and 15 mol% BTO relative to CCTO were prepared by a sol-gel process and a subsequent calcination at 850 °C for 3 h in pure oxygen gas atmosphere. All samples were sintered at 1060 °C for 12 h in air. Compared with pure CCTO sample of εr ∼ 52,000 and tan δ ∼ 0.38 at 100 kHz, all CCTO composite samples exhibited significantly reduced dielectric losses and leakage currents. Among all CCTO composite samples, the sample using 5 mol% BTO-coated CCTO powder exhibited the most improved properties of the dielectric loss (tan δ ∼ 0.04 up to 100 kHz) and the leakage current (less than 1% up to DC field of ∼1 kV/cm) although a large suppression in its dielectric constant (εr ∼ 6000 up to 100 kHz) was unavoidable. This improvement is mainly attributed to a relatively uniform distribution of the second phases such as Ba4Ti12O27 and CaTiO3 at the CCTO grain boundary, which were formed by the chemical reaction between CCTO and BTO during the sintering process.