The effect of Ca-rich on the electric properties of Ca1+xCu3−xTi4O12 polycrystalline system

Abstract

▶ Ca 1+ x Cu 3− x Ti 4 O 12 compounds are comprised of CCTO and CTO phases when Ca atoms are excess compared with traditional CCTO. ▶ The microstructures of the CCTO-based have a reverse effect on the values of permittivity and the values of nonlinear coefficient and breakdown voltage for CCTO-based ceramics. ▶ The change of Ca/Cu ratio can effectively tune up the dielectric properties and non-ohmic behaviors of CCTO-based ceramics. Ca 1+ x Cu 3− x Ti 4 O 12 ( x = 0, 0.25, 0.5, 1) ceramics were prepared using the conventional solid-state reaction method. The XRD patterns show that Ca 1 +x Cu 3− x Ti 4 O 12 compounds are comprised of CaCu 3 Ti 4 O 12 (CCTO) and CaTiO 3 (CTO) phases compared with the traditional CCTO and the content of CTO phase increases with the increase of x . The micrographs demonstrate that the sample for x = 0 has larger grain size 8–10 μm. However, for the samples ( x = 0.25, 0.5, 1), the mean grain size decreases markedly with the increase of CTO phase. The measurement for electric properties indicates that the permittivity values decrease with the increase of Ca atoms, but the breakdown electric field E b and the nonlinear coefficient α values have a behavior reverse to it. The nonlinear coefficient α reaches 28 for x = 1, yet it is only 11.4 for x = 0 in the current range of 1–10 mA. This can be ascribed to the reduction of grain size and the changes in the electric conductivity of main grains and grain boundary with increasing Ca/Cu ratio. Imbalances between Ca and Cu atoms with Ca in excess can favor the non-ohmic properties in detriment to the dielectric property and a suitable Ca/Cu ratio can be selected to adjust the permittivity and I–V nonlinearity, according to different desired device applications.