Coexistence of ferromagnetism and ferroelasticity in a single material is an intriguing phenomenon,but has been rarely found.Here we studied both the ferromagnetism and ferroelasticity in a group of LaCoO3 films with ...Coexistence of ferromagnetism and ferroelasticity in a single material is an intriguing phenomenon,but has been rarely found.Here we studied both the ferromagnetism and ferroelasticity in a group of LaCoO3 films with systematically tuned atomic structures.We found that all films exhibit ferroelastic domains with four-fold symmetry and the larger domain size(higher elasticity)is always accompanied by stronger ferromagnetism.We performed synchrotron x-ray diffraction studies to investigate the backbone structure of the CoO6 octahedra,and found that both the ferromagnetism and the elasticity are simultaneously enhanced when the in-plane Co–O–Co bond angles are straightened.Therefore the study demonstrates the inextricable correlation between the ferromagnetism and ferroelasticity mediated through the octahedral backbone structure,which may open up new possibilities to develop multifunctional materials.展开更多
Hafnium zirconium oxides(HZO),which exhibit ferroelectric properties,are promising materials for nanoscale device fabrication due to their high complementary metal-oxide-semiconductor(CMOS) compatibility.In addition t...Hafnium zirconium oxides(HZO),which exhibit ferroelectric properties,are promising materials for nanoscale device fabrication due to their high complementary metal-oxide-semiconductor(CMOS) compatibility.In addition to piezoelectricity,ferroelectricity,and flexoelectricity,this study reports the observation of ferroelasticity using piezoelectric force microscopy(PFM) and scanning transmission electron microscopy(STEM).The dynamics of 90° ferroelastic domains in HZO thin films are investigated under the influence of an electric field.Switching of the retentive domains is observed through repeated wake-up measurements.This study presents a possibility of enhancing polarization in HZO thin films during wake-up processes.展开更多
The fascinating properties arising from the interaction between different ferroic states of two-dimensional(2D) materials have inspired tremendous research interest in the past few years.Under the first-principles cal...The fascinating properties arising from the interaction between different ferroic states of two-dimensional(2D) materials have inspired tremendous research interest in the past few years.Under the first-principles calculations,we predict the coexistence of antiferromagnetic and ferroelastic states in VOX(X=Cl,Br,I) monolayers.The results illustrate that the VOX monolayers exhibit indirect bandgap characteristics,i.e.,their gaps decrease with the halide elements changing from Cl to I.The ground states of all these VOX monolayers are antiferromagnetic(AFM) with the magnetic moments contributed by the V 3d electrons.Furthermore,the magnetic ground state changing from AFM to ferromagnetism(FM) can be realized by doping carriers.In addition,the moderate ferroelastic transition barrier and reversible switching signal ensure their high performances of nonvolatile memory devices.Our findings not only offer an ideal platform for investigating the multiferroic properties,but also provide candidate materials for potential applications in spintronics.展开更多
Raman scattering measurements of K_2 Sr（MoO_4）2 were performed in the temperature range of 25–750？C. The Raman spectrum of the low-temperature phase α-K_2 Sr（MoO_4）2 that was obtained by first-principle calcula...Raman scattering measurements of K_2 Sr（MoO_4）2 were performed in the temperature range of 25–750？C. The Raman spectrum of the low-temperature phase α-K_2 Sr（MoO_4）2 that was obtained by first-principle calculations indicated that the Raman bands in the wavenumber region of 250–500 cm-1 are related to Mo–O bending vibrations in MoO4 tetrahedra,while the Raman bands in the wavenumber region of 650–950 cm-1 are attributed to stretching vibrations of Mo–O bonds.The temperature-dependent Raman spectra reveal that K_2 Sr（MoO_4）2 exhibits two sets of modifications in the Raman spectra at ～ 150？C and ～ 475？C, attributed to structural phase transitions. The large change of the Raman spectra in the temperature range of 150？C to 475？C suggests structural instability of the medium-temperature phase β-K_2 Sr（MoO_4）2.展开更多
Ferroelastic hybrid perovskite materials have been revealed the significance in the applications of switches,sensors,actuators,etc.However,it remains a challenge to design high-temperature ferroelastic to meet the req...Ferroelastic hybrid perovskite materials have been revealed the significance in the applications of switches,sensors,actuators,etc.However,it remains a challenge to design high-temperature ferroelastic to meet the requirements for the practical applications.Herein,we reported an one-dimensional organicinorganic hybrid perovskites(OIHP)(3-methylpyrazolium)CdCl_(3)(3-MBCC),which possesses a mmmF2/m ferroelastic phase transition at 263 K.Moreover,utilizing crystal engineering,we replace-CH_(3) with-NH_(2) and-H,which increases the intermolecular force between organic cations and inorganic frameworks.The phase transition temperature of(3-aminopyrazolium)CdCl_(3)(3-ABCC),and(pyrazolium)CdCl_(3)(BCC)increased by 73 K and 10 K,respectively.Particularly,BCC undergoes an unconventional inverse temperature symmetry breaking(ISTB)ferroelastic phase transition around 273 K.Differently,it transforms from a high symmetry low-temperature paraelastic phase(point group 2/m)to a low symmetry high-temperature ferroelastic phase(point group ī)originating from the rare mechanism of displacement of organic cations phase transition.It means that crystal BCC retains in ferroelastic phase above 273 K until melting point(446 K).Furthermore,characteristic ferroelastic domain patterns on crystal BCC are confirmed with polarized optical microscopy.Our study enriches the molecular mechanism of ferroelastics in the family of organic-inorganic hybrids and opens up a new avenue for exploring high-temperature ferroic materials.展开更多
Molecular-based ferroelastics with dielectric switching properties are highly desirable for their applications on microelectronic dielectric switches,sensors,data storage,and so on.However,the current reports mostly f...Molecular-based ferroelastics with dielectric switching properties are highly desirable for their applications on microelectronic dielectric switches,sensors,data storage,and so on.However,the current reports mostly focus on organic-inorganic hybrids containing toxic heavy metal atoms,and the relatively low phase transition temperature limits their application.In this paper,low-toxic organic salt ferroelastic enantiomers(R/S)-4-fluoro-1-azabicyclo[3.2.1]octonium chloride[(R/S)-F-321]were designed and synthesized under the introducing chirality strategy.They undergo a 432F422-type ferroelastic phase transition with a high Curie temperature(Tc)of 470 K,simultaneously exhibiting excellent dielectric switching characteristics.In addition to the ordered-disordered movement of cations,the significant displacement of anions is also responsible for such high Tc and large dielectric switching ratios,which is very rare in molecular-based switching materials.This work enriches the development of molecular ferroelastic switching materials and gives inspiration for the exploration of environmentally friendly high Tc organic salt ferroelastics with prominent switching performances.展开更多
Molecular ferroelastics with the natural features of mechanical flexibility and switchable spontaneous strain have attracted widespread attention in the scientific community due to their potential applications in tuna...Molecular ferroelastics with the natural features of mechanical flexibility and switchable spontaneous strain have attracted widespread attention in the scientific community due to their potential applications in tunable gratings,flexible memorizers,strain sensors,and intelligent actuators.However,most designs of molecular ferroelastics remain in the stage of blind exploration,posing a challenge to achieve a functional ferroelastic more effectively.Herein,we have successfully obtained a molecular ferroelastic,[Me_(2)NH(CH_(2))_(2)NH_(3)](ReO_(4))_(2)(Me_(2)NH(CH_(2))_(2)NH_(3)=N,N-dimethylethylenediammonium),under the guidance of the mono-/double-protonation strategy.The_double-protonated[Me_(2)NH(CH_(2))_(2)NH_(3)](ReO_(4))_(2) undergoes a paraelastic-ferroelastic phase transition with the Aizu notation of 2/mFi at 322 K.Meanwhile,the theoretical calculation and experimental measurement simultaneously show that[Me_(2)NH(CH_(2))_(2)NH_(3)](ReO_(4))_(2) possesses good mechanical flexibility,because its elastic modulus(E)of 8.26 GPa and hardness(H)of 0.45 GPa are smaller than the average values of organic crystals(E of 12.05 GPa and H of 0.5 GPa),which makes it promising to apply in wearable pressure sensors,implantable medical sensors,high-precision tuners,etc.This work further enriches the molecular ferroelastic family and demonstrates that mono-/double-protonation is one of the effective molecular modification strategies for designing ferroelastics.展开更多
The 6–8 wt%yttria-stabilized zirconia with a tetragonal structure(t’-YSZ)is extensively employed in thermal barrier coatings.The exceptional fracture toughness of t’-YSZ can be attributed to its distinctive ferroel...The 6–8 wt%yttria-stabilized zirconia with a tetragonal structure(t’-YSZ)is extensively employed in thermal barrier coatings.The exceptional fracture toughness of t’-YSZ can be attributed to its distinctive ferroelastic toughening mechanism.Microstructure and interface tension play a critical role in ferroelastic variant switching at the micro-and nano-scale.This paper presents an original thermodynamically consistent phase field(PF)theory for analyzing ferroelastic variant switching at the micro-and nano-scale of t’-YSZ.The theory incorporates strain gradient elasticity using higher-order elastic energy and interface tension tensor via geometric nonlinearity to represent biaxial tension resulting from interface energy.Subsequently,a mixed-type formulation is employed to implement the higher-order theory through the finite element method.For an interface in equilibrium,the effects of strain gradient elasticity result in a more uniform distribution of stresses,whereas the presence of interface tension tensor significantly amplifies the stress magnitude at the interface.The introduction of an interface tension tensor increases the maximum value of stress at the interface by a factor of 4 to 10.The nucleation and evolution of variants at a pre-existing crack tip in a mono-phase t’-YSZ have also been studied.The strain gradient elasticity is capable of capturing the size effect of ferroelastic variant switching associated with microstructures in experiments.Specifically,when the grain size approaches that of the specimen,the critical load required for variant switching at the crack tip increases,resulting in greater dissipation of elastic energy during ferroelastic variant switching.Moreover,the interface tension accelerates the evolution of variants.The presented framework exhibits significant potential in modeling ferroelastic variant switching at the micro-and nano-scale.展开更多
Hybrid ferroelastic crystals have garnered considerable interest due to their promising potential as mechanical switches and sensors.The anomalous ferroelastic phase transitions,in which ferroelasticity occurs in the ...Hybrid ferroelastic crystals have garnered considerable interest due to their promising potential as mechanical switches and sensors.The anomalous ferroelastic phase transitions,in which ferroelasticity occurs in the hightemperature phase rather than the low-temperature phase,are of particular interest,but they are sporadically-documented and none of them is involved in breaking of the chemical bonds.Herein,a hydroxyl-containing cation,i.e.,Me_(3)NOH^(+),is employed to construct a three-dimensional hybrid crystal(Me_(3)NOH)_(2)KBiCl_(6)(1).This crystal undergoes distinct twostep structural phase transitions with space-group changes of Pna21–P112_(1)–P63mc,belonging to an anomalous temperaturereversed mm2F2 ferroelastic transition and a normal 6mmF2 ferroelastic transition,respectively.The anomalous ferroelastic transition is entirely driven by switchable K–O coordination bonds involving breaking and reformation.Notably,the dynamic behavior of Me_(3)NOH^(+)cations along with the distortion of inorganic framework enables the manifestation of unusual“high-low-medium”second-harmonic generation-switching behaviors.This study presents the enormous benefits of switchable coordination bonds for inducing anomalous ferroelastic phase transitions,offering valuable insight for the exploration of new multifunctional ferroelastic materials.展开更多
The primary purpose of this work is to optimize the thermophysical properties of rare-earth tan-talate ceramics using the high-entropy effect.Here,the high-entropy rare-earth tantalate ceramic(Y_(0.1)Nd_(0.1)Sm_(0.1)G...The primary purpose of this work is to optimize the thermophysical properties of rare-earth tan-talate ceramics using the high-entropy effect.Here,the high-entropy rare-earth tantalate ceramic(Y_(0.1)Nd_(0.1)Sm_(0.1)Gd_(0.1)Dy_(0.1)Ho_(0.1)Er_(0.1)Tm_(0.1)Yb_(0.1)Lu_(0.1))TaO_(4)((10RE_(0.1))TaO_(4))is synthesized successfully.The lat-tice distortion and oxygen vacancy concentration are characterized firstly in the rare-earth tantalates.Notably,compared with single rare-earth tantalates,the thermal conductivity of(10RE_(0.1))TaO_(4) is reduced by 16%-45%at 100℃ and 22%-45%at 800℃,and it also presents lower phonon thermal conductivity in the entire temperature range from 100 to 1200℃.The phonon thermal conductivity(1.0-2.2 W m^(-1) K^(-1),100-1200℃)of(10RE_(0.1))TaO_(4) is lower than that of the currently reported high-entropy four-,five-and six-component rare-earth tantalates.This is the result of scattering by the ferroelastic domain,lattice distortion associated with size and mass disorder,and point defects,which target low-,mid-and high-frequency phonons.Furthermore,(10RE_(0.1))TaO_(4),as an improved candidate for thermal barrier coatings materials(TBCs),has a higher thermal expansion coefficient(10.5×10^(-6)K^(-1) at 1400℃),lower Young’s modulus(123 GPa)and better high-temperature phase stability than that of single rare-earth tantalates.展开更多
Two-dimensional organic-inorganic hybrid ferroelastics with high-temperature reversible phase transitions are very rare and have become one of the research hotspots in the field of ferroelastic materials.Herein,we rep...Two-dimensional organic-inorganic hybrid ferroelastics with high-temperature reversible phase transitions are very rare and have become one of the research hotspots in the field of ferroelastic materials.Herein,we report three new layered organic-inorganic hybrid perovskites based on halogen-substituted phenethylaminium,(3-XC_(6)H_(5)CH_(2)CH_(2)NH_(3))_(2)[CdCl_(4)](X=F(1),CI(2)and Br(3)).They undergo structural phase transitions at 376/371 K,436/430 K,and 421/411 K,respectively,between the isomorphic hightemperature phases(space group I4/mmm,Z=2)and different room-temperature phases with the reduced structural symmetries,i.e.,P21/a(Z=2)in 1,Pi(Z=4)in 2,and P21/a(Z=4)in 3,respectively.These ferroelastic transitions arise from the order-disorder transition of organic cations together with the synchronous displacement of inorganic layers,accompanying with feroelastic spontaneous strains of 0.16,0.13 and 0.12 for 1-3,respectively.By enriching layered perovskite ferroelastics based on halogensubstituted cations,this work provides important clues for exploring new ferroic materials based on hybrid crystals.展开更多
Lead-based organic-inorganic hybrids occupy a niche in the field of optoelectronics due to exceptional semiconducting properties and potential ferroelasticity.Nevertheless,the possible toxicity of lead restricts their...Lead-based organic-inorganic hybrids occupy a niche in the field of optoelectronics due to exceptional semiconducting properties and potential ferroelasticity.Nevertheless,the possible toxicity of lead restricts their widespread application to a certain extent.Herein,two new lead-free ferroelastic semiconductors are reported:[DMMClEA]_(3)Bi_(2)Br_(9)(compound 1)and[DMMClEA]_(3)Sb_(2)Br_(9)(compound 2)(DMMClEA=N-(chloromethyl)-N,N-dimethylethylammonium),in which the inorganic framework neatly arranges with[Bi_(2)Br_(9)]^(3−)/[Sb_(2)Br_(9)]^(3−)polyhedrons shared by face,forming an A_(3)B_(2)X_(9)-type structure.Both compounds 1 and 2 possess two-step phase transitions,including a3mF2/m-type ferroelastic phase transition,based on the Aizu rule.In addition,dual dielectric switches endow the application toward sensor devices.This finding enriches A_(3)B_(2)X_(9)-type zero-dimensional hybrid ferroelastics and provides an approach to designing high-performance,lead-free perovskite semiconductors with dielectric functionality.展开更多
Multifunctional switchable materials are attracting tremendous interest because of their great application potential in signal processing,information encryption,and smart devices.Here,we reported an organic-inorganic ...Multifunctional switchable materials are attracting tremendous interest because of their great application potential in signal processing,information encryption,and smart devices.Here,we reported an organic-inorganic hybrid thermochromic ferroelastic crystal,[TMIm][CuCl_(4)](TMIm=1,1,3,3-tetramethylimidazolidinium),which undergoes two reversible phase transitions at 333 K and 419 K,respectively.Intriguingly,these three phases experience a remarkable ferroelastic-paraelastic-ferroelastic(2/m-mmm-2/m)transition,which remains relatively unexplored in ferroelastics.Moreover,the ferroelastic domains can be simultaneously switched under temperature and stress stimuli.Meanwhile,[TMIm][CuCl_(4)]exhibits thermochromic phenomenon,endowing it with extra spectral encryption possibilities during information processing.Combined with dielectric switching behavior,[TMIm][Cu Cl_(4)]are promising for practical applications in memory devices,next-generation sensors,and encryption technology.展开更多
Ferroelastic materials with switchable spontaneous strain possess widely potential applications in the field of energy and information conversion.Recently,organic-inorganic hybrid halide double perovskites (OIHHDPs) h...Ferroelastic materials with switchable spontaneous strain possess widely potential applications in the field of energy and information conversion.Recently,organic-inorganic hybrid halide double perovskites (OIHHDPs) have become a charming new platform for developing various functional materials,such as ferroelectrics,fluorescence and X–ray detection.Nevertheless,OIHHDP ferroelastic materials,especially high-temperature ones,are rare.Herein,we initially synthesized an OIHHDP ferroelastic,(2,2-difluoroethanamine)_(2)[(NH_(4))InCl_6](1),which possesses a ferroelastic phase transition at 407 K.Moreover,thanks to the flexible B-site for OIHHDPs,we replaced the NH_(4)^(+) ions within[(NH_(4))InCl_6]_n^(2n–)formworks with K^(+)ions,which endows with coordination bonds between 2,2-difluoroethanamine organic cations and[KInCl_6]_n^(2n–)formworks.Due to the existence of coordination bonds,the phase transition temperature of (2,2-difluoroethanamine)_(2)[KInCl_6](2) can reach 458 K.As far as we know,this value is the highest reported in OIHHDP ferroelastics.This work offers inspiration for the design of high-temperature OIHHDP phase transition materials including ferroelectrics and ferroelastics.展开更多
The broad operating temperature range is sought for molecular ferroic materials who are expected to be applied to flexible and electronic materials.Hydrogen bonds,an effective force between molecules,are important to ...The broad operating temperature range is sought for molecular ferroic materials who are expected to be applied to flexible and electronic materials.Hydrogen bonds,an effective force between molecules,are important to regulate the molecule structure and their condition,helping a higher temperature range for ferroic materials.Here,we report a molecular perovskite ferroelastic(Me-Hdabco)Rb[BF_(4)]_(3)(Me-Hdabco=N-methyldabconium)which shows high temperature(T_(1)=322.5 K and T_(2)=381K)ferroelastic phase transitions.The ferroelastic phase transition temperature range of(Me-Hdabco)Rb[BF_(4)]_(3) is significantly increased by 71 K compared with[Meda-bco-F]Rb[BF_(4)]_(3)(Medabco-F=1-fluoro-4-methyl-1,4-diazoniabicyclo[2.2.2]octane).Structural analysis and thermal analysis demonstrate the ferroelastic phase transition is mainly attributed to dynamic cations order and disorder transformation.Therefore,new hydrogen bonds generated between cations and the Rb_(8)[BF_(4)]_(12) frame increase their intermolecular force,which is beneficial to improving the phase transition temperature.This finding has an important impact on the utilization of weak interactionforces to design and optimize functional materials.展开更多
The hysteresis phenomena of ferroelectric/ferroelastic material in polarization procedure are investigated. Some assumptions are presented based on the published experimental data. The electrical yielding criterion, m...The hysteresis phenomena of ferroelectric/ferroelastic material in polarization procedure are investigated. Some assumptions are presented based on the published experimental data. The electrical yielding criterion, mechanical yielding criterion and isotropic hardening model are established. The flow theory in incremental forms in polarization procedure is presented. The nonlinear constitutive law for electrical-mechanical coupling is proposed phenomenologically. Finally, the nonlinear constitutive law expressed in a form of matrices and vectors, which is immediately associated with finite element analysis, is formulated. In the example problem of a rectangular specimen subjected to a uniaxial electric field, the procedure from virgin state to fully polarized state is simulated. Afterward, a uniaxial compressive loading is applied to depolarizing the specimen. Results are in agreement with the experimental data.展开更多
Yttrium tantalate(YTaO_(4))is the next generation of higher service temperature thermal barrier coatings(TBCs)materials due to its smaller volume effect in phase change,lower thermal conductivity and unique ferroelast...Yttrium tantalate(YTaO_(4))is the next generation of higher service temperature thermal barrier coatings(TBCs)materials due to its smaller volume effect in phase change,lower thermal conductivity and unique ferroelastic domain structure.However,the low fracture toughness limits its application.We first characterized the diffraction patterns of variants,and two variants(M_(1)and M_(2))observed in transmission electron microscopy(TEM)results were determined from four possible variants by mechanical derivation.The role of Zr^(4+)doping in ferroelastic toughening was explained in detail.With the increase of Zr^(4+)doping concentration,the monoclinic angle β and the domain rotation angleαdecrease,respectively.The spontaneous strain component and the principal strain in the main space also have a similar decreasing trend.The decrease of the ferroelastic domain inversion energy barrier is beneficial to the improvement of fracture toughness.Combining the results of Vickers indentation,we found that Zr^(4+)could be enriched at the domain boundary to inhibit the generation of cracks.An appropriate amount of Zr^(4+)is conducive to the improvement of fracture toughness,and the excessive Zr^(4+)will reduce the fracture toughness due to the generation of by-product t-ZrO_(2).So,the optimal composition is Y_(0.44)Ta_(0.44)Zr_(0.12)O_(2) and the best fracture toughness(2.9–3.8MPa m^(1/2))is equivalent to the commercial 8YSZ.This result will promote the application of a new generation of TBCs.展开更多
A new bromethyl-substituted molecular rotor, [Cu（dabcoCH2Br）（H2O）Br3] （dabcoCH2Br＋=1-（2-bromethyl）-1,4-diazoniabi- cyclo[2.2.2]octane cation）, which belongs to a family of balomethyl-substituted molecular rot...A new bromethyl-substituted molecular rotor, [Cu（dabcoCH2Br）（H2O）Br3] （dabcoCH2Br＋=1-（2-bromethyl）-1,4-diazoniabi- cyclo[2.2.2]octane cation）, which belongs to a family of balomethyl-substituted molecular rotors, was synthesized and struc- turally characterized. The reversible phase transition at ca. 250 K was well established for this molecular rotor by thermal analyses, variable-temperature X-ray diffraction, and variable temperature dielectric measurements. The order-disorder trans- formation of the rotator part （dabco moiety） causes ferroelastic phase transition with an Aizu notation of mmmF2/m from high- temperature orthorhombic phase （Pbnm） to low-temperature monoclinic phase （P21/n）. More important, in reference to the density functional theory calculations and structural analyses, the key factors to tune the phase transition behaviors were dis- cussed in detail for this family of halomethyl-substituted molecular rotors.展开更多
We propose a possible ferroelastic switching pathway of two-dimensional(2 D)honeycomb lattice(including graphene,BN,stanene,etc.)that may swap its armchair and zigzag direction,reversing an unprecedented strain of 73....We propose a possible ferroelastic switching pathway of two-dimensional(2 D)honeycomb lattice(including graphene,BN,stanene,etc.)that may swap its armchair and zigzag direction,reversing an unprecedented strain of 73.2%.Our ab initio calculations reveal that such pathway cannot work in covalent systems like graphene and BN;for monolayer with metallic bonds like stanene,stanane and In Bi that have all been synthesized,however,such pathway can be feasible with a low switching barrier(<0.15 eV)and stress(<graphene upon 1%tensile strain),also with the highest energy/stress point in the elastic region.Their distinct behaviors are attributed to the different feature of covalent bonds and metallic bonds:the former is rigid with directionality,while the latter is malleable with ductility.A general trend of linear decrease in switching barrier with uprising metallicity for the same group compounds is revealed.Similar behaviors can be extended to bulk zinc-blended or wurtzite structure that can be deemed as multilayer stacking of buckled monolayer.Binary compounds like In Bi monolayer are even multiferroics with both in-plane and vertical ferroelectricity as well as nontrivial topological properties.展开更多
Two-dimensional(2D)ferromagnetic and ferroelectric materials attract unprecedented attention due to the spontaneous-symmetry-breaking induced novel properties and multifarious potential applications.Here we systematic...Two-dimensional(2D)ferromagnetic and ferroelectric materials attract unprecedented attention due to the spontaneous-symmetry-breaking induced novel properties and multifarious potential applications.Here we systematically investigate a large family(148)of 2D MGeX3(M=metal elements,X=O/S/Se/Te)by means of the high-throughput first-principles calculations,and focus on their possible ferroic properties including ferromagnetism,ferroelectricity,and ferroelasticity.We discover eight stable 2D ferromagnets including five semiconductors and three half-metals,212D antiferromagnets,and 11 stable 2D ferroelectric semiconductors including two multiferroic materials.Particularly,MnGeSe3 and MnGeTe3 are predicted to be room-temperature 2D ferromagnetic half metals with Tc of 490 and 308 K,respectively.It is probably for the first time that ferroelectricity is uncovered in 2D MGeX3 family,which derives from the spontaneous symmetry breaking induced by unexpected displacements of Ge-Ge atomic pairs,and we also reveal that the electric polarizations are in proportion to the ratio of electronegativity of X and M atoms,and IVB group metal elements are highly favored for 2D ferroelectricity.Magnetic tunnel junction and water-splitting photocatalyst based on 2D ferroic MGeX3 are proposed as examples of wide potential applications.The atlas of ferroicity in 2D MGeX3 materials will spur great interest in experimental studies and would lead to diverse applications.展开更多
基金the National Natural Science Foun-dation of China(Grant Nos.52072244 and 12104305)the Science and Technology Commission of Shanghai Municipal-ity(Grant No.21JC1405000)the ShanghaiTech Startup Fund.This research used resources of the Advanced Photon Source,a U.S.Department of Energy(DOE)Office of Sci-ence User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No.DE-AC02-06CH11357.
文摘Coexistence of ferromagnetism and ferroelasticity in a single material is an intriguing phenomenon,but has been rarely found.Here we studied both the ferromagnetism and ferroelasticity in a group of LaCoO3 films with systematically tuned atomic structures.We found that all films exhibit ferroelastic domains with four-fold symmetry and the larger domain size(higher elasticity)is always accompanied by stronger ferromagnetism.We performed synchrotron x-ray diffraction studies to investigate the backbone structure of the CoO6 octahedra,and found that both the ferromagnetism and the elasticity are simultaneously enhanced when the in-plane Co–O–Co bond angles are straightened.Therefore the study demonstrates the inextricable correlation between the ferromagnetism and ferroelasticity mediated through the octahedral backbone structure,which may open up new possibilities to develop multifunctional materials.
基金Project supported by the the National Key Research and Development Program of China (Grant No. 2022YFA1402902)the National Natural Science Foundation of China (Grant Nos. 12074119, 12204171, 12134003, and 12374145)+1 种基金the Chenguang Program Foundation of Shanghai Education Development Foundation and Shanghai Municipal Education Commission, ECNU (East China Normal University) Multifunctional Platform for Innovation (006)the Fundamental Research Funds for the Central Universities。
文摘Hafnium zirconium oxides(HZO),which exhibit ferroelectric properties,are promising materials for nanoscale device fabrication due to their high complementary metal-oxide-semiconductor(CMOS) compatibility.In addition to piezoelectricity,ferroelectricity,and flexoelectricity,this study reports the observation of ferroelasticity using piezoelectric force microscopy(PFM) and scanning transmission electron microscopy(STEM).The dynamics of 90° ferroelastic domains in HZO thin films are investigated under the influence of an electric field.Switching of the retentive domains is observed through repeated wake-up measurements.This study presents a possibility of enhancing polarization in HZO thin films during wake-up processes.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12104344 and 61674003)the Shandong Provincial Natural Science Foundation,China(Grant No.ZR2021QA096)+1 种基金the Science and Technology Development Program of Weifang High-tech Industrial Development Zone,China(Grant No.2020KJHM03)the Doctoral Research Start-up Foundation of Weifang University,China(Grant No.2021BS05)。
文摘The fascinating properties arising from the interaction between different ferroic states of two-dimensional(2D) materials have inspired tremendous research interest in the past few years.Under the first-principles calculations,we predict the coexistence of antiferromagnetic and ferroelastic states in VOX(X=Cl,Br,I) monolayers.The results illustrate that the VOX monolayers exhibit indirect bandgap characteristics,i.e.,their gaps decrease with the halide elements changing from Cl to I.The ground states of all these VOX monolayers are antiferromagnetic(AFM) with the magnetic moments contributed by the V 3d electrons.Furthermore,the magnetic ground state changing from AFM to ferromagnetism(FM) can be realized by doping carriers.In addition,the moderate ferroelastic transition barrier and reversible switching signal ensure their high performances of nonvolatile memory devices.Our findings not only offer an ideal platform for investigating the multiferroic properties,but also provide candidate materials for potential applications in spintronics.
基金Project supported by the Natural Science Foundation of Anhui Province,China(Grant Nos.KJ2018A0588 and KJ2017A625)
文摘Raman scattering measurements of K_2 Sr（MoO_4）2 were performed in the temperature range of 25–750？C. The Raman spectrum of the low-temperature phase α-K_2 Sr（MoO_4）2 that was obtained by first-principle calculations indicated that the Raman bands in the wavenumber region of 250–500 cm-1 are related to Mo–O bending vibrations in MoO4 tetrahedra,while the Raman bands in the wavenumber region of 650–950 cm-1 are attributed to stretching vibrations of Mo–O bonds.The temperature-dependent Raman spectra reveal that K_2 Sr（MoO_4）2 exhibits two sets of modifications in the Raman spectra at ～ 150？C and ～ 475？C, attributed to structural phase transitions. The large change of the Raman spectra in the temperature range of 150？C to 475？C suggests structural instability of the medium-temperature phase β-K_2 Sr（MoO_4）2.
基金support from the National Natural Science Foundation of China(No.22175079)support from the National Natural Science Foundation of China(No.22205087)+2 种基金the Open Project Program of Jiangxi Provincial Key Laboratory of Functional Molecular Materials Chemistry,Jiangxi University of Science and Technology(No.20212BCD42018)National Natural Science Foundation of China(No.22275075)Natural Science Foundation of Jiangxi Province(Nos.20204BCJ22015 and 20202ACBL203001).
文摘Ferroelastic hybrid perovskite materials have been revealed the significance in the applications of switches,sensors,actuators,etc.However,it remains a challenge to design high-temperature ferroelastic to meet the requirements for the practical applications.Herein,we reported an one-dimensional organicinorganic hybrid perovskites(OIHP)(3-methylpyrazolium)CdCl_(3)(3-MBCC),which possesses a mmmF2/m ferroelastic phase transition at 263 K.Moreover,utilizing crystal engineering,we replace-CH_(3) with-NH_(2) and-H,which increases the intermolecular force between organic cations and inorganic frameworks.The phase transition temperature of(3-aminopyrazolium)CdCl_(3)(3-ABCC),and(pyrazolium)CdCl_(3)(BCC)increased by 73 K and 10 K,respectively.Particularly,BCC undergoes an unconventional inverse temperature symmetry breaking(ISTB)ferroelastic phase transition around 273 K.Differently,it transforms from a high symmetry low-temperature paraelastic phase(point group 2/m)to a low symmetry high-temperature ferroelastic phase(point group ī)originating from the rare mechanism of displacement of organic cations phase transition.It means that crystal BCC retains in ferroelastic phase above 273 K until melting point(446 K).Furthermore,characteristic ferroelastic domain patterns on crystal BCC are confirmed with polarized optical microscopy.Our study enriches the molecular mechanism of ferroelastics in the family of organic-inorganic hybrids and opens up a new avenue for exploring high-temperature ferroic materials.
基金supported by the National Natural Science Foundation of China(No.22201120)。
文摘Molecular-based ferroelastics with dielectric switching properties are highly desirable for their applications on microelectronic dielectric switches,sensors,data storage,and so on.However,the current reports mostly focus on organic-inorganic hybrids containing toxic heavy metal atoms,and the relatively low phase transition temperature limits their application.In this paper,low-toxic organic salt ferroelastic enantiomers(R/S)-4-fluoro-1-azabicyclo[3.2.1]octonium chloride[(R/S)-F-321]were designed and synthesized under the introducing chirality strategy.They undergo a 432F422-type ferroelastic phase transition with a high Curie temperature(Tc)of 470 K,simultaneously exhibiting excellent dielectric switching characteristics.In addition to the ordered-disordered movement of cations,the significant displacement of anions is also responsible for such high Tc and large dielectric switching ratios,which is very rare in molecular-based switching materials.This work enriches the development of molecular ferroelastic switching materials and gives inspiration for the exploration of environmentally friendly high Tc organic salt ferroelastics with prominent switching performances.
基金financially supported by Southeast University and the National Natural Science Foundation of China(Grant Nos.21991141 and 22371258).
文摘Molecular ferroelastics with the natural features of mechanical flexibility and switchable spontaneous strain have attracted widespread attention in the scientific community due to their potential applications in tunable gratings,flexible memorizers,strain sensors,and intelligent actuators.However,most designs of molecular ferroelastics remain in the stage of blind exploration,posing a challenge to achieve a functional ferroelastic more effectively.Herein,we have successfully obtained a molecular ferroelastic,[Me_(2)NH(CH_(2))_(2)NH_(3)](ReO_(4))_(2)(Me_(2)NH(CH_(2))_(2)NH_(3)=N,N-dimethylethylenediammonium),under the guidance of the mono-/double-protonation strategy.The_double-protonated[Me_(2)NH(CH_(2))_(2)NH_(3)](ReO_(4))_(2) undergoes a paraelastic-ferroelastic phase transition with the Aizu notation of 2/mFi at 322 K.Meanwhile,the theoretical calculation and experimental measurement simultaneously show that[Me_(2)NH(CH_(2))_(2)NH_(3)](ReO_(4))_(2) possesses good mechanical flexibility,because its elastic modulus(E)of 8.26 GPa and hardness(H)of 0.45 GPa are smaller than the average values of organic crystals(E of 12.05 GPa and H of 0.5 GPa),which makes it promising to apply in wearable pressure sensors,implantable medical sensors,high-precision tuners,etc.This work further enriches the molecular ferroelastic family and demonstrates that mono-/double-protonation is one of the effective molecular modification strategies for designing ferroelastics.
基金supported by the National Natural Science Foundation of China(Grant Nos.11890684,12032001&51590891)the Technology Innovation Leading Program of Shaanxi(Grant No.2022TD-28)Hunan Provincial Natural Science Innovation Research Group Fund(Grant No.2020JJ1005)。
文摘The 6–8 wt%yttria-stabilized zirconia with a tetragonal structure(t’-YSZ)is extensively employed in thermal barrier coatings.The exceptional fracture toughness of t’-YSZ can be attributed to its distinctive ferroelastic toughening mechanism.Microstructure and interface tension play a critical role in ferroelastic variant switching at the micro-and nano-scale.This paper presents an original thermodynamically consistent phase field(PF)theory for analyzing ferroelastic variant switching at the micro-and nano-scale of t’-YSZ.The theory incorporates strain gradient elasticity using higher-order elastic energy and interface tension tensor via geometric nonlinearity to represent biaxial tension resulting from interface energy.Subsequently,a mixed-type formulation is employed to implement the higher-order theory through the finite element method.For an interface in equilibrium,the effects of strain gradient elasticity result in a more uniform distribution of stresses,whereas the presence of interface tension tensor significantly amplifies the stress magnitude at the interface.The introduction of an interface tension tensor increases the maximum value of stress at the interface by a factor of 4 to 10.The nucleation and evolution of variants at a pre-existing crack tip in a mono-phase t’-YSZ have also been studied.The strain gradient elasticity is capable of capturing the size effect of ferroelastic variant switching associated with microstructures in experiments.Specifically,when the grain size approaches that of the specimen,the critical load required for variant switching at the crack tip increases,resulting in greater dissipation of elastic energy during ferroelastic variant switching.Moreover,the interface tension accelerates the evolution of variants.The presented framework exhibits significant potential in modeling ferroelastic variant switching at the micro-and nano-scale.
基金supported by the National Natural Science Foundation Of China(22071273 and 21821003)the Fundamental Research Funds for the Central Universities,Sun Yat-Sen University(23lgzy001).
文摘Hybrid ferroelastic crystals have garnered considerable interest due to their promising potential as mechanical switches and sensors.The anomalous ferroelastic phase transitions,in which ferroelasticity occurs in the hightemperature phase rather than the low-temperature phase,are of particular interest,but they are sporadically-documented and none of them is involved in breaking of the chemical bonds.Herein,a hydroxyl-containing cation,i.e.,Me_(3)NOH^(+),is employed to construct a three-dimensional hybrid crystal(Me_(3)NOH)_(2)KBiCl_(6)(1).This crystal undergoes distinct twostep structural phase transitions with space-group changes of Pna21–P112_(1)–P63mc,belonging to an anomalous temperaturereversed mm2F2 ferroelastic transition and a normal 6mmF2 ferroelastic transition,respectively.The anomalous ferroelastic transition is entirely driven by switchable K–O coordination bonds involving breaking and reformation.Notably,the dynamic behavior of Me_(3)NOH^(+)cations along with the distortion of inorganic framework enables the manifestation of unusual“high-low-medium”second-harmonic generation-switching behaviors.This study presents the enormous benefits of switchable coordination bonds for inducing anomalous ferroelastic phase transitions,offering valuable insight for the exploration of new multifunctional ferroelastic materials.
基金financially supported by the Rare and Precious Metals Material Genetic Engineering Project of Yunnan Province(Nos.202102AB080019-1 and 202002AB080001-1)the Yun-nan Fundamental Research Projects(Nos.202101AW070011 and 202101BE070001-015).
文摘The primary purpose of this work is to optimize the thermophysical properties of rare-earth tan-talate ceramics using the high-entropy effect.Here,the high-entropy rare-earth tantalate ceramic(Y_(0.1)Nd_(0.1)Sm_(0.1)Gd_(0.1)Dy_(0.1)Ho_(0.1)Er_(0.1)Tm_(0.1)Yb_(0.1)Lu_(0.1))TaO_(4)((10RE_(0.1))TaO_(4))is synthesized successfully.The lat-tice distortion and oxygen vacancy concentration are characterized firstly in the rare-earth tantalates.Notably,compared with single rare-earth tantalates,the thermal conductivity of(10RE_(0.1))TaO_(4) is reduced by 16%-45%at 100℃ and 22%-45%at 800℃,and it also presents lower phonon thermal conductivity in the entire temperature range from 100 to 1200℃.The phonon thermal conductivity(1.0-2.2 W m^(-1) K^(-1),100-1200℃)of(10RE_(0.1))TaO_(4) is lower than that of the currently reported high-entropy four-,five-and six-component rare-earth tantalates.This is the result of scattering by the ferroelastic domain,lattice distortion associated with size and mass disorder,and point defects,which target low-,mid-and high-frequency phonons.Furthermore,(10RE_(0.1))TaO_(4),as an improved candidate for thermal barrier coatings materials(TBCs),has a higher thermal expansion coefficient(10.5×10^(-6)K^(-1) at 1400℃),lower Young’s modulus(123 GPa)and better high-temperature phase stability than that of single rare-earth tantalates.
基金supported by National Natural Science Foundation of China(NSFC,Nos.22071273 and 21821003)Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program(No.2017BT01C161).
文摘Two-dimensional organic-inorganic hybrid ferroelastics with high-temperature reversible phase transitions are very rare and have become one of the research hotspots in the field of ferroelastic materials.Herein,we report three new layered organic-inorganic hybrid perovskites based on halogen-substituted phenethylaminium,(3-XC_(6)H_(5)CH_(2)CH_(2)NH_(3))_(2)[CdCl_(4)](X=F(1),CI(2)and Br(3)).They undergo structural phase transitions at 376/371 K,436/430 K,and 421/411 K,respectively,between the isomorphic hightemperature phases(space group I4/mmm,Z=2)and different room-temperature phases with the reduced structural symmetries,i.e.,P21/a(Z=2)in 1,Pi(Z=4)in 2,and P21/a(Z=4)in 3,respectively.These ferroelastic transitions arise from the order-disorder transition of organic cations together with the synchronous displacement of inorganic layers,accompanying with feroelastic spontaneous strains of 0.16,0.13 and 0.12 for 1-3,respectively.By enriching layered perovskite ferroelastics based on halogensubstituted cations,this work provides important clues for exploring new ferroic materials based on hybrid crystals.
基金financially supported by the National Natural Science Foundation of China(grant no.21991141).
文摘Lead-based organic-inorganic hybrids occupy a niche in the field of optoelectronics due to exceptional semiconducting properties and potential ferroelasticity.Nevertheless,the possible toxicity of lead restricts their widespread application to a certain extent.Herein,two new lead-free ferroelastic semiconductors are reported:[DMMClEA]_(3)Bi_(2)Br_(9)(compound 1)and[DMMClEA]_(3)Sb_(2)Br_(9)(compound 2)(DMMClEA=N-(chloromethyl)-N,N-dimethylethylammonium),in which the inorganic framework neatly arranges with[Bi_(2)Br_(9)]^(3−)/[Sb_(2)Br_(9)]^(3−)polyhedrons shared by face,forming an A_(3)B_(2)X_(9)-type structure.Both compounds 1 and 2 possess two-step phase transitions,including a3mF2/m-type ferroelastic phase transition,based on the Aizu rule.In addition,dual dielectric switches endow the application toward sensor devices.This finding enriches A_(3)B_(2)X_(9)-type zero-dimensional hybrid ferroelastics and provides an approach to designing high-performance,lead-free perovskite semiconductors with dielectric functionality.
基金supported by the National Natural Science Foundation of China(Nos.21975114,11904151 and 22105094)。
文摘Multifunctional switchable materials are attracting tremendous interest because of their great application potential in signal processing,information encryption,and smart devices.Here,we reported an organic-inorganic hybrid thermochromic ferroelastic crystal,[TMIm][CuCl_(4)](TMIm=1,1,3,3-tetramethylimidazolidinium),which undergoes two reversible phase transitions at 333 K and 419 K,respectively.Intriguingly,these three phases experience a remarkable ferroelastic-paraelastic-ferroelastic(2/m-mmm-2/m)transition,which remains relatively unexplored in ferroelastics.Moreover,the ferroelastic domains can be simultaneously switched under temperature and stress stimuli.Meanwhile,[TMIm][CuCl_(4)]exhibits thermochromic phenomenon,endowing it with extra spectral encryption possibilities during information processing.Combined with dielectric switching behavior,[TMIm][Cu Cl_(4)]are promising for practical applications in memory devices,next-generation sensors,and encryption technology.
基金supported financially by the National Key Research and Development Program of China (No. 2017YFA0204800)National Natural Science Foundation of China (Nos. 22175079 and 21875093)+1 种基金Natural Science Foundation of Jiangxi Province (Nos. 20204BCJ22015 and 20202ACBL203001)Jiangxi Provincial Department of Education Science and Technology Research Project (No. GJJ210812)。
文摘Ferroelastic materials with switchable spontaneous strain possess widely potential applications in the field of energy and information conversion.Recently,organic-inorganic hybrid halide double perovskites (OIHHDPs) have become a charming new platform for developing various functional materials,such as ferroelectrics,fluorescence and X–ray detection.Nevertheless,OIHHDP ferroelastic materials,especially high-temperature ones,are rare.Herein,we initially synthesized an OIHHDP ferroelastic,(2,2-difluoroethanamine)_(2)[(NH_(4))InCl_6](1),which possesses a ferroelastic phase transition at 407 K.Moreover,thanks to the flexible B-site for OIHHDPs,we replaced the NH_(4)^(+) ions within[(NH_(4))InCl_6]_n^(2n–)formworks with K^(+)ions,which endows with coordination bonds between 2,2-difluoroethanamine organic cations and[KInCl_6]_n^(2n–)formworks.Due to the existence of coordination bonds,the phase transition temperature of (2,2-difluoroethanamine)_(2)[KInCl_6](2) can reach 458 K.As far as we know,this value is the highest reported in OIHHDP ferroelastics.This work offers inspiration for the design of high-temperature OIHHDP phase transition materials including ferroelectrics and ferroelastics.
基金This work was supported by the National Key Research and Development Program of China(Grant No.2017YFA0204800)and Southeast University。
文摘The broad operating temperature range is sought for molecular ferroic materials who are expected to be applied to flexible and electronic materials.Hydrogen bonds,an effective force between molecules,are important to regulate the molecule structure and their condition,helping a higher temperature range for ferroic materials.Here,we report a molecular perovskite ferroelastic(Me-Hdabco)Rb[BF_(4)]_(3)(Me-Hdabco=N-methyldabconium)which shows high temperature(T_(1)=322.5 K and T_(2)=381K)ferroelastic phase transitions.The ferroelastic phase transition temperature range of(Me-Hdabco)Rb[BF_(4)]_(3) is significantly increased by 71 K compared with[Meda-bco-F]Rb[BF_(4)]_(3)(Medabco-F=1-fluoro-4-methyl-1,4-diazoniabicyclo[2.2.2]octane).Structural analysis and thermal analysis demonstrate the ferroelastic phase transition is mainly attributed to dynamic cations order and disorder transformation.Therefore,new hydrogen bonds generated between cations and the Rb_(8)[BF_(4)]_(12) frame increase their intermolecular force,which is beneficial to improving the phase transition temperature.This finding has an important impact on the utilization of weak interactionforces to design and optimize functional materials.
基金Supported by the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 2005247004)
文摘The hysteresis phenomena of ferroelectric/ferroelastic material in polarization procedure are investigated. Some assumptions are presented based on the published experimental data. The electrical yielding criterion, mechanical yielding criterion and isotropic hardening model are established. The flow theory in incremental forms in polarization procedure is presented. The nonlinear constitutive law for electrical-mechanical coupling is proposed phenomenologically. Finally, the nonlinear constitutive law expressed in a form of matrices and vectors, which is immediately associated with finite element analysis, is formulated. In the example problem of a rectangular specimen subjected to a uniaxial electric field, the procedure from virgin state to fully polarized state is simulated. Afterward, a uniaxial compressive loading is applied to depolarizing the specimen. Results are in agreement with the experimental data.
基金the National Natural Science Foundation of China(Nos.11890684 and 52102142)the Foundation for Innovative Research Groups of Hunan Province(No.2020JJ1005)。
文摘Yttrium tantalate(YTaO_(4))is the next generation of higher service temperature thermal barrier coatings(TBCs)materials due to its smaller volume effect in phase change,lower thermal conductivity and unique ferroelastic domain structure.However,the low fracture toughness limits its application.We first characterized the diffraction patterns of variants,and two variants(M_(1)and M_(2))observed in transmission electron microscopy(TEM)results were determined from four possible variants by mechanical derivation.The role of Zr^(4+)doping in ferroelastic toughening was explained in detail.With the increase of Zr^(4+)doping concentration,the monoclinic angle β and the domain rotation angleαdecrease,respectively.The spontaneous strain component and the principal strain in the main space also have a similar decreasing trend.The decrease of the ferroelastic domain inversion energy barrier is beneficial to the improvement of fracture toughness.Combining the results of Vickers indentation,we found that Zr^(4+)could be enriched at the domain boundary to inhibit the generation of cracks.An appropriate amount of Zr^(4+)is conducive to the improvement of fracture toughness,and the excessive Zr^(4+)will reduce the fracture toughness due to the generation of by-product t-ZrO_(2).So,the optimal composition is Y_(0.44)Ta_(0.44)Zr_(0.12)O_(2) and the best fracture toughness(2.9–3.8MPa m^(1/2))is equivalent to the commercial 8YSZ.This result will promote the application of a new generation of TBCs.
基金supported by the National Natural Science Foundation of China(21290173,21301198)the National Basic Research Program of China(2012CB821706)the Natural Science Foundation of Guangdong(S2012030006240)
文摘A new bromethyl-substituted molecular rotor, [Cu（dabcoCH2Br）（H2O）Br3] （dabcoCH2Br＋=1-（2-bromethyl）-1,4-diazoniabi- cyclo[2.2.2]octane cation）, which belongs to a family of balomethyl-substituted molecular rotors, was synthesized and struc- turally characterized. The reversible phase transition at ca. 250 K was well established for this molecular rotor by thermal analyses, variable-temperature X-ray diffraction, and variable temperature dielectric measurements. The order-disorder trans- formation of the rotator part （dabco moiety） causes ferroelastic phase transition with an Aizu notation of mmmF2/m from high- temperature orthorhombic phase （Pbnm） to low-temperature monoclinic phase （P21/n）. More important, in reference to the density functional theory calculations and structural analyses, the key factors to tune the phase transition behaviors were dis- cussed in detail for this family of halomethyl-substituted molecular rotors.
基金supported by the National Natural Science Foundation of China(21573084).
文摘We propose a possible ferroelastic switching pathway of two-dimensional(2 D)honeycomb lattice(including graphene,BN,stanene,etc.)that may swap its armchair and zigzag direction,reversing an unprecedented strain of 73.2%.Our ab initio calculations reveal that such pathway cannot work in covalent systems like graphene and BN;for monolayer with metallic bonds like stanene,stanane and In Bi that have all been synthesized,however,such pathway can be feasible with a low switching barrier(<0.15 eV)and stress(<graphene upon 1%tensile strain),also with the highest energy/stress point in the elastic region.Their distinct behaviors are attributed to the different feature of covalent bonds and metallic bonds:the former is rigid with directionality,while the latter is malleable with ductility.A general trend of linear decrease in switching barrier with uprising metallicity for the same group compounds is revealed.Similar behaviors can be extended to bulk zinc-blended or wurtzite structure that can be deemed as multilayer stacking of buckled monolayer.Binary compounds like In Bi monolayer are even multiferroics with both in-plane and vertical ferroelectricity as well as nontrivial topological properties.
基金This work is supported in part by the National Key R&D Program of China(No.2018YFA0305800)the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB28000000)+2 种基金the National Natural Science Foundation of China(No.11834014)the Beijing Municipal Science and Technology Commission(No.Z118100004218001)the fundamental research funds for the central universities,and University of Chinese Academy of Sciences.
文摘Two-dimensional(2D)ferromagnetic and ferroelectric materials attract unprecedented attention due to the spontaneous-symmetry-breaking induced novel properties and multifarious potential applications.Here we systematically investigate a large family(148)of 2D MGeX3(M=metal elements,X=O/S/Se/Te)by means of the high-throughput first-principles calculations,and focus on their possible ferroic properties including ferromagnetism,ferroelectricity,and ferroelasticity.We discover eight stable 2D ferromagnets including five semiconductors and three half-metals,212D antiferromagnets,and 11 stable 2D ferroelectric semiconductors including two multiferroic materials.Particularly,MnGeSe3 and MnGeTe3 are predicted to be room-temperature 2D ferromagnetic half metals with Tc of 490 and 308 K,respectively.It is probably for the first time that ferroelectricity is uncovered in 2D MGeX3 family,which derives from the spontaneous symmetry breaking induced by unexpected displacements of Ge-Ge atomic pairs,and we also reveal that the electric polarizations are in proportion to the ratio of electronegativity of X and M atoms,and IVB group metal elements are highly favored for 2D ferroelectricity.Magnetic tunnel junction and water-splitting photocatalyst based on 2D ferroic MGeX3 are proposed as examples of wide potential applications.The atlas of ferroicity in 2D MGeX3 materials will spur great interest in experimental studies and would lead to diverse applications.
