Nanoscale disorder in CaCu3Ti4O12: A new route to the enhanced dielectric response

Significant nanoscale disorder of Cu and Ca atomic substitution is observed in CaCu3Ti4O12, based on our integrated study using quantitative electron diffraction and extended x-ray absorption fine structure. Unambiguous identification of this previously omitted disorder is made possible by the unique sensitivity of these probes to valence-electron distribution and short-range order. Furthermore, first-principles-based theoretical analysis indicates that the Ca-site Cu atoms possess partially filled degenerate eg states, suggesting significant boost of dielectric response from additional low-energy electronic contributions. Our study points to a new route of enhancing dielectric response in transitional metal oxides by exploiting the strong electronic correlation beyond classical static pictures.