Reorientable dipolar CuCa antisite and anomalous screening in CaCu3Ti4O12

Based on first-principles calculations, we show that the abundant CuCa antisite defect contributes sizably to dielectric screening in single-crystal CaCu3Ti4O12. CuCa 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 CuCa-induced response is consistent with experiment.