Brilliant effect of Ni substitution in the appearance of high dielectric constant in CaCu2.9Ni0.1Ti3.9Ni0.1O12 ceramics

Abstract

CaCu2.9Ni0.1Ti3.9Ni0.1O12 (CCNTNO) polycrystalline powder of giant dielectric constant material was successfully obtained by solid-state reaction. The sample, characterized by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM) and Raman spectroscopy, confirmed to be a pure phase CCTO associated with large grains surrounded by small ones of nearly cubic shape. The effect of Ni doping on optical properties of CaCu2.9Ni0.1Ti3.9Ni0.1O12 has been determined. Furthermore, the dielectric constants of these co-doped ceramics (CCNTNO) were higher than that of CCTO pure prepared under the same conditions of synthesis. The grain size and the dielectric constant depended absolutely on doped and sintering time. Results confirm that co-doping CCTO by Ni in both copper and titanium sintered enhanced the grain growth as the sintered time is higher than 6 h. Especially ceramic sintered at 1100 °C for 12 h shows excellent abnormal growth grain with approximately 50–100 μm sized crystallites which displayed extraordinarily high dielectric constants up to 105 at 25 °C (most exceptional behavior). Based on these results, internal barrier layer capacitance (IBLC) model was invoked to correlate the observed dielectric constant with the grain size in these samples. Loss factor and resistivity of these ceramics were equally interpreted. It must be noted also that the resistivity decreased largely if the sintering time is around 12 h as evidenced in the impedance plots.