钙钛矿NaFeF_3结构物性的理论研究及应力和掺杂调控
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摘要
利用第一性原理计算研究了氟化物钙钛矿NaFeF_3的基态电子态和磁构型,并模拟分析了衬底应力和阴离子置换对材料基本物性的影响.计算结果表明, NaFeF_3块材的G-AFM磁基态十分稳定,不会受到衬底应力调控以及F位氧掺杂的影响.当低浓度掺杂(～8.3%)时,氧离子倾向于替换FeF2面内的F,形成非对称的Fe-O-Fe链,导致产生局域极化.此外,不对等的Fe—O键还会在氧离子两侧的Fe上形成电荷序,进而产生非零净磁矩.值得注意的是,该局域极化和亚铁磁性均源于不等位氧掺杂,因此有可能通过外电场调控实现极化翻转并同时改变净磁矩的方向实现电控磁.更高浓度的氧掺杂会使得Fe的化合价整体升高, Fe离子上的局部电荷序和净磁矩随之消失.该研究结果有望促进氟化物的理论和实验研究,并为多铁性材料的设计研发提供新的材料.
On the basis of first-principles calculations, the systematic researches of the structural, electronic and magnetic properties of NaFeF_3 are carried out in the present work. The influences of anion substitution and strain effect are taken into consideration in the reaearch.First, the basic properties of the NaFeF_3 bulk are determined. The fully relaxed structure exhibits a distinct GdFeO_3-type distortion and a relatively weak Jahn-Teller distortion. The band gap is estimated at 3 eV from our DFT calculations with Hubbard U correction. Moreover, the magnetic structure is of G-type antiferromagnetism(G-AFM). This intrinsic G-AFM magnetic state is robust, and cannot be easily destroyed by small perturbations, includinganion doping and epitaxial strain.Secondly, we study the oxygen doping effect on the properties of material with considering the fact that the radius of oxygen anion is very close to that of fluoride anion, and the oxygen substitution can be accommodated by the further oxidation of iron cation from divalent to trivalent state. According to our energy comparison calculations, when one of the twelve F sites in the NaFeF_3 unit cell is taken up by an oxygen anion, whose corresponding doping concentration is approximately 8.3%, the O ion is more likely to occupy the in-plane site of the FeF_6 octahedron. This low concentration doping may induce unequal Fe—O bonds, which lead to diverse valence states of surrounding Fe cations, and therefore result in local polarization and non-zero net magnetic moment. The local dipole and magnetic moment are inherently correlated with each other due to the common origin, i.e., the incoordinate Fe— O bonds. Therefore, the net magnetic moment together with the local polarization may be reversed simultaneously by an external electric field. However, when the doping concentration is further increased to 33%, the overall iron valence will rise to a higher state where the local charge order and the net moment disappear.In addition, the electronic properties of NaFeF_3 also show obvious change due to the influence of biaxial strain. Specifically, the energy gap decreases monotonically as the in-plane stress gradually changes from compression to extension. However, the band structure does not change significantly. The top of the valence band and the bottom of the conduction band are both located at the Gamma point, thus making it a direct bandgap semiconductor material with an adjustable energy gap.These findings may promote further theoretical and experimental research on fluoride family and introduce a new candidate to the multiferroic field.
On the basis of first-principles calculations, the systematic researches of the structural, electronic and magnetic properties of NaFeF_3 are carried out in the present work. The influences of anion substitution and strain effect are taken into consideration in the reaearch.First, the basic properties of the NaFeF_3 bulk are determined. The fully relaxed structure exhibits a distinct GdFeO_3-type distortion and a relatively weak Jahn-Teller distortion. The band gap is estimated at 3 eV from our DFT calculations with Hubbard U correction. Moreover, the magnetic structure is of G-type antiferromagnetism(G-AFM). This intrinsic G-AFM magnetic state is robust, and cannot be easily destroyed by small perturbations, includinganion doping and epitaxial strain.Secondly, we study the oxygen doping effect on the properties of material with considering the fact that the radius of oxygen anion is very close to that of fluoride anion, and the oxygen substitution can be accommodated by the further oxidation of iron cation from divalent to trivalent state. According to our energy comparison calculations, when one of the twelve F sites in the NaFeF_3 unit cell is taken up by an oxygen anion, whose corresponding doping concentration is approximately 8.3%, the O ion is more likely to occupy the in-plane site of the FeF_6 octahedron. This low concentration doping may induce unequal Fe—O bonds, which lead to diverse valence states of surrounding Fe cations, and therefore result in local polarization and non-zero net magnetic moment. The local dipole and magnetic moment are inherently correlated with each other due to the common origin, i.e., the incoordinate Fe— O bonds. Therefore, the net magnetic moment together with the local polarization may be reversed simultaneously by an external electric field. However, when the doping concentration is further increased to 33%, the overall iron valence will rise to a higher state where the local charge order and the net moment disappear.In addition, the electronic properties of NaFeF_3 also show obvious change due to the influence of biaxial strain. Specifically, the energy gap decreases monotonically as the in-plane stress gradually changes from compression to extension. However, the band structure does not change significantly. The top of the valence band and the bottom of the conduction band are both located at the Gamma point, thus making it a direct bandgap semiconductor material with an adjustable energy gap.These findings may promote further theoretical and experimental research on fluoride family and introduce a new candidate to the multiferroic field.
引文
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[24]Zheng X X,Wang D,Tang L M,Chen K Q 2015 Mod.Phys.Lett. B 29 1550137
[25]Yan S L,Tang L M,Zhao Y Q 2016 Acta Phys.Sin.65077301(in Chinese)[颜送灵,唐黎明,赵宇清2016物理学报65 077301]
[26]Li X X,Yang J L 2016 Natl.Sci.Rev.3 365
[2]Ohtomo A,Hwang H Y 2004 Nature 427 423
[3]Chen H,Kolpak A M,Isamail-Beigi S 2010 Adv.Mater.222881
[4]Garcia-Castro A C,Romero A H,Bousquest E 2016 Phys.Rev.Lett.116 117202
[5]Margadonna S,Karotsis G 2006 J.Am.Chem.Soc.12816436
[6]Binggeli N,Altarelli M 2004 Phys.Rev.B 70 085117
[7]Yamauchi K,Picozzi S 2010 Phys.Rev.Lett.105 10720
[8]Karamyan A A 1973 Phys.Stat.Sol. A 16 419
[9]Brown-Acquaye H A,Lane A P,Inorg J 1981 Nuc. Chem.433143
[10]Ni S,Ma J,Lv X,Yang X,Zhang L 2014 Mater.Lett.124264
[11]Hao L,Liu K,Cheng S,Wang Y,Xu Y,Qian H 2017 Mater.Lett.196 145
[12]Wang R T,Tai E G,Chen J Y,Xu G,LaPierre R,Goktas N I,Hu N 2019 Ceram.Inter.45 64
[13]Dhanapala B D,Munasinghe H N,Suescun L,Rabuffetti F A2017 Inorg.Chem.56 13311
[14]Bernal F L,Yusenko K V,Sottmann J,Drathen C,Guignard J,Lovvik C M,Crichton W A,Margadonna S 2014 Inorg.Mater.53 12205
[15]Kresse G,Hafner J 1993 Phys.Rev.B 47 558
[16]Kresse G,Furthmuller J 1996 Phys.Rev.B 54 11169
[17]Perdew J P,Burke K,Ernzerhof M 1996 Phys.Rev.Lett.773865
[18]Perdew J P,Ruzsinszky A,Csonka G I,Vydrov O A,Scuseria G E,Constantin L A,Zhou X,Burke K 2008 Phys.Rev.Lett.100 136406
[19]Monkhorst H J,Pack J D 1976 Phys.Rev.B 13 5188
[20]Alaria J,Borisov P,Dyer M S,Manning T D,Lepadatu S,Cain M G,Mishina E D,Sherstyuk N E,Ilyin N A,Hadermann J,Lederman D,Claridge J B,Rosseinsky M J2014 Chem.Sci.5 1599
[21]Garcia-Castro A C,Romero A H,Bousquet E 2014 Phys.Rev.B 90 064113
[22]Friedman Z,Melamud M,Makovsky J,Shaked H 1970 Phys.Rev.B 2 179
[23]Shane J R,Lyons D H,Kestigian M 1967 J.Appl. Phys.381280
[24]Zheng X X,Wang D,Tang L M,Chen K Q 2015 Mod.Phys.Lett. B 29 1550137
[25]Yan S L,Tang L M,Zhao Y Q 2016 Acta Phys.Sin.65077301(in Chinese)[颜送灵,唐黎明,赵宇清2016物理学报65 077301]
[26]Li X X,Yang J L 2016 Natl.Sci.Rev.3 365
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