High Dielectric Constant in ACu3Ti4O12 and ACu3Ti3FeO12 Phases

High dielectric constants have been found in oxides of the type ACu3Ti4O12. The most exceptional behavior is exhibited by CaCu3Ti4O12, which shows a dielectric constant at 1 kHz of about 12,000 that is nearly constant from room temperature to 300°C. The cubic structure of these materials is related to that of perovskite (CaTiO3), but the TiO6 octahedra are tilted to produce a square planar environment for Cu2+. The CaCu3Ti4O12 structure down to 35 K has been examined by neutron powder diffraction. The structure remains cubic and centric. Most compositions of the type A2/3Cu3Ti4O12 (A=trivalent rare earth or Bi) show dielectric constants above 1000. The dielectric properties of isostructural compounds of the type ACu3Ti3FeO12 are also presented.