Polymeric citrate precursor route to the synthesis of the high dielectric constant oxide, CaCu₃Ti₄O₁₂

Abstract

Using citric acid and ethylene glycol, a polymeric precursor of the above compound was obtained at low temperatures (135 °C) which on subsequent heat treatments led to pure CaCu₃Ti₄O₁₂ at 1000 °C. On sintering further at 1000 °C (20 h), the disks show high density (98%) and the dielectric constant was of the order of 3000 at 1 kHz. The dielectric loss varies between 0.3 and 0.35 (till 100 kHz) beyond that it increases sharply from 0.35 to 0.7 in the frequency range of 100-500 kHz. Our studies on dielectric properties of the above oxide, synthesized by the ceramic method and sintered under the same conditions, led to a dielectric constant of around 2200 at 1 kHz. The dielectric constant decreases with frequency in the oxides obtained by either of the above methods. Scanning electron micrographs (SEM) show much larger grains (nearly spherical) of 2-4 μm in the solid obtained by the ceramic route while the grains were much smaller (0.5-1.0 μm) in the oxide prepared by the polymeric citrate precursor route.