Understanding doped perovskite ferroelectrics with defective dipole model

While doping is widely used for tuning physical properties of perovskites in experiments, it remains a challenge to exactly know how doping achieves the desired effects. Here, we propose an empirical and computationally tractable model to understand the effects of doping with Fe-doped BaTiO3 as an example. This model assumes that the lattice sites occupied by a Fe ion and its nearest six neighbors lose their ability to polarize, giving rise to a small cluster of defective dipoles. Employing this model in Monte Carlo simulations, many important features such as reduced polarization and the convergence of phase transition temperatures, which have been observed experimentally in acceptor doped systems, are successfully obtained. Based on microscopic information of dipole configurations, we provide insights into the driving forces behind doping effects and propose that active dipoles, which exist in proximity to the defective dipoles, can account for experimentally observed phenomena. Close attention to these dipoles is necessary to understand and predict doping effects.Peer reviewe

Thermal evolution of polar nanoregions identified by the relaxation time of electric modulus in the Bi 1/2

The correspondence between the temperature dependence of phase structures and the experimental physical properties was made clear for the first time in the Bi1/2Na1/2TiO3 system according to in situ XRD, in situ Raman and impedance spectroscopy. XRD profiles show pseudo-cubic symmetry independent of temperature, while one of the Raman models disappears near 620 K, indicating that the local symmetry increases. The temperature dependence of the main relaxation time of the electric modulus spectra can be divided into four regions, characterizing the thermal evolution of polar nanoregions (PNRs) with different symmetries and a phase transition between rhombohedral and tetragonal symmetry. Therefore, the relaxation times of the electric modulus provide a way to estimate the local phase transition and the thermal evolution of R3c and P4bm PNRs