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

Abstract

Numerical simulations have been performed to study hydrogen interstitial diffusion and ferroelectric degradation in lead titanate films. The computational method consists of two parts: hydrogen diffusion property calculations using density functional theory (DFT) and ferroelectric property calculations using molecular dynamics (MD) simulations. The hydrogen interstitial diffusion path and the activation energy have been obtained using DFT calculations. With the obtained diffusion properties, the distributions of hydrogen impurities have been calculated using Fick’s second law and used as input to MD simulations, with various diffusion times and hydrogen surface concentrations. It has been found that magnitudes of remnant polarization and coercive electric fields decrease with increasing the diffusion time and the hydrogen surface concentration. The distribution of hydrogen impurities is another critical factor to ferroelectric responses. Compared to a uniform distribution of hydrogen impurities, the nonuniform distribution diminishes the ferroelectric properties more severely. A heavily defective region due to the nonuniform hydrogen distribution reduces the effective film thickness and induces the in-plane ferroelectric domain formations.