Finite-temperature properties of the relaxorPbMg1/3Nb2/3O3from atomistic simulations

Abstract

An atomistic numerical scheme is developed and used to study the prototype of relaxor ferroelectrics, that is PbMg 1/3 Nb 2/3 O 3 (PMN), at finite temperatures. This scheme not only reproduces known complex macroscopic properties of PMN, but also provides a deep microscopic insight into this puzzling system. In particular, relaxor properties of PMN are found to originate from the competition between (1) random electric fields arising from the alloying of Mg and Nb ions belonging to different columns of the Periodic Table within the same sublattice; (2) the simultaneous condensation of several off-center k points as a result of a specific short-range, antiferroelectriclike interaction between lead-centered dipoles; and (3) ferroelectriclike interactions. Such origins contrast with those recently proposed for the homovalent Ba(Zr,Ti)O 3 solid solution, despite the fact that these two materials have similar macroscopic properties-which therefore leads to a comprehensive understanding of relaxor ferroelectrics.

Infrared, terahertz, and microwave spectroscopy of the soft and central modes in Pb(Mg1/3Nb2/Nuzhnyy1, Petzelt2, Bovtun3 et al. 2017Phys. Rev. B21160View full textAdd to dashboardCite

“…Since the dynamics of SM is strongly temperature dependent, it seems that the former aspect could be a more natural explanation. In fact, it has been convincingly argued that the random fields are important ingredients of the relaxor behavior of PMN [42,43]. So, even though we do not have a clear understanding of the link between the random fields and the two-component SM response of PMN, which shows features of the avoided crossing with a weakly polar mode, we think that these observations constitute an important clue to disentangling the puzzle of the outstanding relaxor dynamics of the PMN crystal.…”

“…Indeed, most of the current theories (see Ref. [42] and references therein) assume that the PMN relaxor above T B should behave as a usual paraelectric material.…”

Some strategies for improving caloric responses with ferroelectrics

“…55 For instance, the existence of a scaling law for ∆T E was recently revealed in antiferroelectrics 56 using ab initio calculations. In addition, the magnitude of the negative effect is relatively smaller than its positive counterpart underlining the need to pursue more effort into the understanding of the negative electrocaloric effect.…”

Electrocaloric effects in the lead-free Ba(Zr,Ti)O3 relaxor ferroelectric from atomistic simulations

“…It is worthwhile to realize that these latter results were obtained for lead-based relaxor ferroelectrics while there are also (environmentally-friendly) lead-free relaxor ferroelectrics, such as Ba(Zr 1−x Ti x )O 3 , that are fundamentally distinct. For instance, the difference in polarizability between Ti and Zr ions in Ba(Zr 0.5 Ti 0.5 )O 3 was found to be essential to reproduce relaxor behavior via the formation of small Ti-rich PNRs embedded in a paraelectric matrix [35], while the relaxor nature of lead-based PMN was predicted to rather originate from a complex interplay between random electric fields, ferroelectric and antiferroelectric interactions -yielding much larger PNRs touching each other at low temperatures [40]. Another striking difference between Ba(Zr 0.5 Ti 0.5 )O 3 and PMN is that a recent atomistic simulation did not find any trace of a first-order paraelectric-to-ferroelectric phase transition when subjecting Ba(Zr 0.5 Ti 0.5 )O 3 to electric fields, that is, the polarization seems to always continuously evolve with the magnitude of the dc electric field in this lead-free compound [41].…”