Origin of ferroelectric-like hysteresis loop of CaCu3Ti4O12 ceramic   studied by impedance and micro-Raman spectroscopy
  Ferroelectric-like hysteresis loops of CaCu3Ti4O12 (CCTO) ceramic have been observed. We found that this unusual feature does not arise from the displacement of the Ti ions in the TiO6 octahedron, but apparently comes from the charges at the grain boundaries which consist of a CuO layer. The relaxation time of 2.9 milliseconds by the charges from the grain boundary, nearly corresponding to the inverse P - V sampling frequency of 1kHz, has been found in the impedance spectrum. According to the micro-Raman mapping, the CuO layer is found in the grain boundary and is perfectly distinguished from the CCTO grain. 
Sungmin Park, Hyosang Kwon, Doyoung Park, Hyeonsik Cheong, Gwangseo   Park
cond-mat.mtrl-sci