A first principles study of the in-plane strain effects on the dielectric constant of high-κ Be0.25Mg0.75O superlattice

The effects of in-plane strain on the dielectric constant of the Be0.25Mg0.75O rock salt superlattice are investigated through ab initio thermodynamics calculations. Based on a previous report that the long apical Be–O bond increased the dielectric constant, the in-plane compressive strain dielectric constant is expected to increase the dielectric constant. Unlike the zero-strain case, the apical Mg–O bonds also contribute to the increase in the dielectric constant under compressive strain. However, small Be ions tend to occupy narrow spaces in the MgO-based rock salt structure, which can lead to an increase in dielectric constant even under in-plane tensile strain, depending on the local position of Be ions and its interaction with O ions. At higher temperatures, several configurations under strain showed a significant increase in the dielectric constant due to the elongation of the apical Be–O bond. Considering temperature and strain comprehensively, this study suggests that the Be0.25MgO0.75O superlattice under −2% in-plane compressive strain could be a promising candidate structure for achieving a high-κ value of approximately 30.