Understanding the effect of rare-earth doping in ABO3 ferroelectrics on capacitive energy storage

Rare-earth doping, even in trace amounts, can significantly regulate the energy storage performance of ferroelectric materials by synergistically adjusting microscopic behaviors such as crystal structure and energy bands. However, understanding the mechanisms by which different rare-earth elements influence the energy storage performance such as polarization and breakdown remains a major challenge. To address this, we use density functional theory to systematically investigate the effect of rare-earth doping on the microscopic ferroelectric behavior in three ABO₃ perovskite ferroelectrics by substituting A-site or B-site ions with 15 types of rare-earth ions. The results show that when introducing rare-earth ions, lattice structure and electronic state distribution can be rebuilt due to strong volume effect and hybridization, thereby altering the ion displacement polarization, reversal energy barrier, and energy gap. Notably, their effects highly depend on the occupancy of rare-earth ions on the A-site or B-site. For A-site doping, a decrease in the ionic radius of rare-earth ions generally leads to increases in the c/a ratio, polarization strength, reversal energy barrier, and energy gap, whereas B-site doping shows the opposite trends. This work reveals the underlying mechanisms of rare-earth doping on affecting the energy storage performance and provides important theoretical guidance for engineering rare-earth doping in perovskite ferroelectrics.