High Dielectric Constant in ACu3Ti4O12 and ACu3Ti3FeO12 Phases

Abstract High dielectric constants have been found in oxides of the type A Cu 3 Ti 4 O 12 . The most exceptional behavior is exhibited by CaCu 3 Ti 4 O 12 , 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 (CaTiO 3 ), but the TiO 6 octahedra are tilted to produce a square planar environment for Cu 2+ . The CaCu 3 Ti 4 O 12 structure down to 35 K has been examined by neutron powder diffraction. The structure remains cubic and centric. Most compositions of the type A 2/3 Cu 3 Ti 4 O 12 ( A =trivalent rare earth or Bi) show dielectric constants above 1000. The dielectric properties of isostructural compounds of the type A Cu 3 Ti 3 FeO 12 are also presented.