Abstract
A physical understanding of the nature of spatially modulated phases (SMPs) in rare-earth-doped antiferrodistortive (AFD) multiferroics and how they behave close to surfaces and interfaces is lacking. Here the emergence of the antiferroelectric (AFE), ferroelectric (FE), or ferrielectric (AFE-FE) spatial modulation in the vicinity of the morphotropic phase transition in LaxBi1-xFeO3 (x∼0.2) is explored on the atomic level using high-resolution scanning transmission electron microscopy (HRSTEM). The suppression, or "melting,"of the AFE-type SMP in the vicinity of the AFD twin wall/surface junction is revealed by HRSTEM in La0.22Bi0.78FeO3 films and explained by the hybrid approach combining Landau-Ginzburg-Devonshire (LGD) phenomenology and the semimicroscopic four-sublattice model (FSM). The LGD-FSM approach reduces the problem of AFE (or AFE-FE) SMP emergence and stability to the thermodynamic analysis of the free-energy functional with AFE, FE, and AFD long-range order parameters and two master parameters: The FE-AFE coupling strength between four neighboring A sites and the nonstoichiometry factor, which are proportional to the variations of La concentration in LaxBi1-xFeO3 films. We establish that the surface-induced melting of SMPs and the associated broadening of AFE AFD domain walls minimize the film free energy under certain conditions imposed on the master parameters and gradient energy below the critical value. The observed behavior provides insight into the origin of SMPs in AFD multiferroics.
| Original language | English |
|---|---|
| Article number | 075426 |
| Journal | Physical Review B |
| Volume | 102 |
| Issue number | 7 |
| DOIs | |
| State | Published - Aug 15 2020 |
Funding
Authors are very grateful to the referees for useful comments and stimulating discussions. This material was based upon work (S.V.K and C.T.N.) supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, and performed in the Center for Nanophase Materials Sciences, supported by the Division of Scientific User Facilities. A portion of the FEM was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility (CNMS Proposal No. 257). D.C. is grateful for financial support from the National Natural Science Foundation of China (Grants No. U1832104 and No. 11704130), the Guangzhou Science and Technology Project (Grant No. 201906010016), and Guangdong Provincial Key Laboratory of Optical Information Materials and Technology (Grant No. 2017B030301007). The work of A.N.M was supported by the National Academy of Sciences of Ukraine (the Target Program of Basic Research of the National Academy of Sciences of Ukraine “Prospective basic research and innovative development of nanomaterials and nanotechnologies for 2020 - 2024”, Project No. 1/20-H, state registration No. 0120U102306) and has received funding from the European Union's Horizon 2020 research and innovation program under Marie Skłodowska-Curie Grant Agreement No. 778070. This work was partially supported by U.S. DOE. ORNL is managed by UT-Battelle, LLC, under Contract No. DE-AC0500OR22725 for the US Department of Energy.
| Funders | Funder number |
|---|---|
| Center for Nanophase Materials Sciences | |
| Guangdong Provincial Key Laboratory of Optical Information Materials and Technology | 2017B030301007 |
| U.S. Department of Energy | |
| Office of Science | |
| Basic Energy Sciences | |
| Oak Ridge National Laboratory | DE-AC0500OR22725 |
| Horizon 2020 Framework Programme | |
| National Natural Science Foundation of China | U1832104, 11704130 |
| National Academy of Sciences of Ukraine | 1/20-H, 0120U102306 |
| Horizon 2020 | 778070 |
| Guangzhou Municipal Science and Technology Project | 201906010016 |