Reorientable dipolar Cu-Ca antisite and anomalous screening in CaCu3Ti4O12

Based on first-principles calculations, we show that the abundant Cu-Ca antisite defect contributes sizably to dielectric screening in single-crystal CaCu3Ti4O12. Cu-Ca has a multi-minimum off-center equilibrium configuration, whereby it possesses a large and easily reorientable dipole moment. The low-temperature and frequency cut-off behavior of Cu-Ca-induced response is consistent with experiment.