First-principles study on structural, electronic, and ferroelectric properties of high-temperature RMn2O5 (R = Sm, Gd, Dy)

Abstract

As a class of type-II multiferroics, RMn2O5 compounds show intriguing magnetoelectric coupling behaviors. However, the crystallographic characteristics of the high-temperature paramagnetic phase remain controversial. In present work, by employing PBEsol and SCAN exchange-correlation functionals, we have performed first-principles calculations to study the structural, electronic, and ferroelectric properties of the high-temperature RMn2O5 (R = Sm, Gd, Dy) compounds. According to our calculations, it is revealed that the high-temperature phase of RMn2O5 should be viewed as a super-paraelectric state due to the degeneracy of total energy for the centrosymmetric Pbam and polar Pm/P2 structures. Due to its unique structural and electronic properties, under certain external stimuli, the high-temperature RMn2O5 can develops the so-called electronic ferroelectricity through charge transition/transfer between Mn4+ and Mn3+ sites. In addition, the predicted ferroelectric polarization in the monoclinic Pm/P2 structures is no more than 1 μC/cm2. Our results may offer an alternative understanding for the complicated magnetoelectric behaviors occurred in the RMn2O5 family.