Understanding ultrahigh dielectric response in tricritical ferroelectrics

Ferroelectric material exhibits large dielectric response owing to its peculiar polarization states, which has been found a variety of applications on electrical power equipment and high-tech products. Very recent investigations reported that ultrahigh dielectric permittivity occurs at the tricritical triple point (TTP for short) of ferroelectrics. However, the reason is unclear and there is still lack of theoretical explanation. Here, Landau model is employed to investigate the mechanism of enhanced dielectric response regarding thermodynamically tricritical phenomenon. The six-order Landau-Devonshire polynomial is used to calculate the intrinsic dielectric permittivity which is mainly caused by lattice deformation. Then the Landau-Ginzburg expression is applied to study the width and energy of ferroelectric domain walls around the TTP, which determines the extrinsic dielectric response induced by the movement of domain walls. As a result, the intrinsic and extrinsic dielectric responses are both enhanced approaching to TTP, which leads to the ultrahigh dielectric permittivity for tricritical ferroelectrics.