Molecular dynamics simulations of ferroelectric domain formation by oxygen vacancy

Abstract

An oxygen vacancy, known to be detrimental to ferroelectric properties, has been investigated numerically for the potential uses to control ferroelectric domains in films using molecular dynamics simulations based on the first-principles effective Hamiltonian. As an electron donor, an oxygen vacancy generates inhomogeneous electrostatic and displacement fields which impose preferred polarization directions near the oxygen vacancy. When the oxygen vacancies are placed at the top and bottom interfaces, the out-of-plane polarizations are locally developed near the interfaces in the directions away from the interfaces. These polarizations from the interfaces are in opposite directions so that the overall out-of-plane polarization becomes significantly reduced. In the middle of the films, the in-plane domains are formed with containing 90° a 1 /a 2 domain walls and the films are polarized along the [1 1 0] direction even when no electric field is applied. With oxygen vacancies placed at the top interface only, the films exhibit asymmetric hysteresis loops, confirming that the oxygen vacancies are one of the possible sources of ferroelectric imprint. It has been qualitatively demonstrated that the domain structures in the imprint films can be turned on and off by controlling an external field along the thickness direction. This study shows qualitatively that the oxygen vacancies can be utilized for tuning ferroelectric domain structures in films.

Controllable Distribution and Reversible Migration of Charges in BiFeO3-Based Films on Si Substrates

“…thought that the biased coercive field of Si-doped HfO 2 on the p-Si substrate was caused by the depolarization field, counteracted by the charge trapping at the interface . Fan et al believed that the decrease in the compensation charge at the interface was the main reason for the polarization relaxation of BiFeO 3 (BFO) on the ZnO substrate, while through molecular dynamics simulation, Zhu et al showed that the aggregation of oxygen vacancies at the interface could significantly reduce the ferroelectric polarization . Some other works focus on the electrical transport in the ferroelectric/semiconductor heterostructures.…”

“…17 Fan et al believed that the decrease in the compensation charge at the interface was the main reason for the polarization relaxation of BiFeO 3 (BFO) on the ZnO substrate, 18 while through molecular dynamics simulation, Zhu et al showed that the aggregation of oxygen vacancies at the interface could significantly reduce the ferroelectric polarization. 19 Some other works focus on the electrical transport in the ferroelectric/semiconductor heterostructures. For instance, Hao et al detected the electron injection from the n-Si substrate to the n-BaTiO 3 film, 20 transfer and distribution, need to be further confirmed and understood.…”

Numerical simulations of hydrogen interstitial diffusion and ferroelectricity degradation in lead titanate films

“…MD simulations [29,45,46] with the first-principles effective Hamiltonian were performed in the domains of N x × 16 × 16 unit cell (u.c.) with the film thickness N x = 64 u.c.…”

Electrical Characteristics of Nanoelectromechanical Relay with Multi-Domain HfO2-Based Ferroelectric Materials

“…However, the formation of multi-domains in HfO 2 -based ferroelectric materials is inevitable, owing to the non-uniform polarization originating from the presence of various grain sizes [20] and various crystallite orientations in polycrystalline ferroelectric structures [21]. Recently, several studies have been suggested to control domain formations in ferroelectric such as utilizing oxygen vacancies [22]. To predict the electrical characteristics of an NC + NEM relay in detail, it is essential to study the effects of a multi-domain ferroelectric material on the NEM relay.…”