Broadband dielectric spectroscopy on single-crystalline and ceramic   CaCu3Ti4O12
  We present dielectric measurements of the colossal dielectric constant material CaCu3Ti4O12 extending up to 1.3 GHz also covering so far only rarely investigated single crystalline samples. Special emphasis is put on the second relaxation reported in several works on polycrystals, which we detect also in single crystals. For polycrystalline samples we provide a recipe to achieve values of the dielectric constant as high as in single crystals. 
S. Krohns, P. Lunkenheimer, S.G. Ebbinghaus, and A. Loidl