【作者】 唐浩；

【导师】 张志英；

【作者基本信息】 武汉理工大学 ， 材料科学与工程， 2019， 硕士

【摘要】 多铁性金属有机骨架材料（Metal-Organic Frameworks,MOFs）在信息存储器、多态记忆元件、磁电传感器、可控设备等方面具有广阔的应用前景。弹性性能反映原子间的键合力,控制材料结构的稳定性,研究金属有机骨架材料的弹性性能和多铁性具有重要的理论意义和实际应用价值。本文进行了多铁性金属有€S?机骨架材料[（CH₃）₂NH₂][M（HCOO）₃]（M=Mn,Co,Ni,Mg）和[NH₄][M（HCOO）₃]（M=Mn,Co,Ni,Mg）的制备和表征,并研究了其在低频、高应力和应变条件下,低温至室温范围内的弹性性能以及与相变有关的非弹性性能和能量衰减,有利于进一步理解相变机理,促进多铁性金属有机骨架材料的发展与应用。通过水热法或扩散法制备了金属有机骨架材料[（CH₃）₂NH₂][M（HCOO）₃]（M=Mn,Co,Ni,Mg）和[NH₄][M（HCOO）₃]（M=Mn,Co,Ni,Mg）。室温下X射线衍射（X-Ray Diffraction,XRD）分析表明[（CH₃）₂NH₂][M（HCOO）₃]（M=Mn,Co,Ni,Mg）具有钙钛矿型结构,空间点阵结构为三角R c,[NH₄][M（HCOO）₃]（M=Mn,Co,Ni,Mg）具有手性结构,空间点阵结构为六方P6₃22。红外（Infra-Red,IR）和拉曼光àS?_U?谱分析表明[（CH₃）₂NH₂][M（HCOO）₃]（M=Mn,Co,Ni,Mg）官能团的主要振动包括二甲胺离子[（CH₃）₂NH₂]⁺和甲酸根离子HCOO^-的内部振动以及金属离子M²⁺的晶格振动,[NH₄][M（HCOO）₃]（M=Mn,Co,Ni,Mg）官能团的主要振动包括铵离子NH₄⁺和甲酸根离子HCOO^-的内部振动以及金属离子M²⁺的晶格振动。利用扫描电镜和透射电镜研究了样品的形貌。差示扫描量热法（Differential Scanning Calorimetry,DSC）分析表明130-300 K温度范围内[（CH₃）₂NH₂][M（HCOO）₃]（M=Mn,Co,Ni,Mg）的相变温度约为152-264 K（Mn:183-190 K,Co:152-161 K,Ni:172-180 K,Mg:261-264 K）,与铁电转变以及三角Rc至单斜Cc的结构转变有关,具有一阶相变特征,主要由二甲胺离子[（CH₃）₂NH₂]⁺的无序-有序变化引起。[NH₄][M（HCOO）₃]（M=Mn,Co,Ni,Mg）的相变温度约为172-256 K（Mn:254-255 K,Co:172-200 K,Ni:180-199 K,Mg:254-256 K）,与铁电转变以及非极性六方P6₃22至极性六方P6₃的结构相变有关,主要由铵离子的无序-有序变化引起。磁性性能测试表明[（CH₃）₂NH₂][M（HCOO）₃]（M=Mn,Co,Ni）的磁转变温度约为8.5-37.0 K（Mn:8.5K,Co:15.0 K,Ni:37.0 K）,[NH₄][M（HCOO）₃]（M=Mn,Co,Ni）的磁转变温度约为8.0-29.9 K（Mn:8.0 K,Co:10.0 K,Ni:29.9 K）,居里外斯拟合结果表明磁性转变具有反铁磁有序特征。利用动态机械分析法（Dynamic Mechanical Analysis,DMA）研究了低频（0.5-10 Hz）、高应力和应变条件下,130-300 K温度范围内弹性性能以及与铁电转变和结构转变有关的非弹性性能和能量衰减。在铁电转变温度附近,[（CH₃）₂NH₂][M（HCOO）₃]（M=Mn,Co,Ni,Mg）的储能模量E’出现谷或拐点,损耗模量E’’与损耗因子tanδ出现峰,峰高随频率的增大而减小,峰值对应的温度基本不变,显示一阶相变特征。损耗因子的峰值随频率f的变化符合幂律公式tanδ=Afⁿ,n值约为-0.382至-0.049。铁电转变温度附近明显的弹性异常和较大的能量衰减,显示较强的铁弹和铁电耦合,与局部应变和二甲胺阳离子[（CH₃）₂NH₂]⁺冻结过程的耦合作用以及外力作用下孪晶壁的运动有关。在铁电转变温度附近,[NH₄][M（HCOO）₃]（M=Mg）的储能模量出现谷或拐点,损耗模量与损耗因子出现较宽的峰,频率的影响不显著。更多还原

【Abstract】 Multiferroic Metal-Organic Frameworks（MOFs）have broad application prospects in information storage,polymorphic memory components,magnetoelectric sensors,controllable devices and so on.The elastic properties indicate the bonding forces among atoms,and control the stability of the structure.It is of great theoretical and practical importance to investigate the elastic properties and multiferroic properties of MOFs.In this paper,multiferroic MOFs[（CH₃）₂NH₂][M（HCOO）₃]（M=Mn,Co,Ni,Mg）and[NH₄][M（HCOO）₃]（M=Mn,Co,Ni,Mg）were prepared and characterized.The elastic properties under low frequency,high stress and strain conditions from low temperature to room temperature were studied,and the anelastic properties and energy dissipation related to phase transitions were investigated.It is beneficial for the further understanding of the phase transition mechanisms and the developments and applications of multiferroic MOFs.MOFs,[（CH₃）₂NH₂][M（HCOO）₃]（M=Mn,Co,Ni,Mg）and[NH₄][M（HCOO）₃]（M=Mn,Co,Ni,Mg）,were prepared by hydrothermal method or diffusion method.At room temperature,X-Ray Diffraction（XRD）analysis showed that the structure of[（CH₃）₂NH₂][M（HCOO）₃]（M=Mn,Co,Ni,Mg）was perovskite-like with space group of rohombohedral R c,and the structure of[NH₄][M（HCOO）₃]（M=Mn,Co,Ni,Mg）was chiral with space group of hexagonal P6₃22.Infrared（IR）and Raman spectroscopy analysis indicated that the main vibrational modes of the functional groups in[（CH₃）₂NH₂][M（HCOO）₃]（M=Mn,Co,Ni,Mg）included the internal vibration of dimethylamine ions[（CH₃）₂NH₂]⁺and formate ions HCOO^-,and the lattice vibration of metal ions M²⁺.The main vibrational modes of the functional groups in[NH₄][M（HCOO）₃]（M=Mn,Co,Ni,Mg）included the internal vibration of amine ions NH₄⁺and formate ions HCOO^-,and the lattice vibration of metal ions M²⁺.The morphologies of the samples were studied by Scanning Electron Microscopy（SEM）and Transmission Electron Microscopy（TEM）.Determined by Differential Scanning Calorimetry（DSC）between 130 K and300 K,the phase transitions of[（CH₃）₂NH₂][M（HCOO）₃]（M=Mn,Co,Ni,Mg）occurred around 152-264 K（Mn:183-190 K,Co:152-161 K,Ni:172-180 K,Mg:261-264 K）.They were associated with the ferroelectric transition and the structural phase transition from rohombohedral R c to monoclinic Cc.Features of the first-order phase transitions were observed.They were mainly caused by the disorder-order transitions of the[（CH₃）₂NH₂]⁺ions.The phase transitions of[NH4][M（HCOO）3]（M=Mn,Co,Ni,Mg）occurred around 172 K-256 K（Mn:254-255 K,Co:172-200 K,Ni:180-199 K,Mg:254-256 K）,and they were associated with the ferroelectric transition and the structural phase transition from non-polar hexagonal P6₃22 to polar hexagonal P6₃,which were mainly caused by the disorder-order transitions of the NH₄⁺ions.Measurements of magnetic properties showed that the magnetic transition temperatures of[（CH₃）₂NH₂][M（HCOO）₃]（M=Mn,Co,Ni）were around 8.5-37.0 K（Mn:8.5 K,Co:15.0 K,Ni:37.0 K）,and the magnetic transition temperatures of[NH₄][M（HCOO）₃]（M=Mn,Co,Ni）were around 8.0-29.9 K（Mn:8.0 K,Co:10.0 K,Ni:29.9 K）.Fitting by Curie-weiss law indicated the anti-ferromagnetic ordering feature of the magnetic transitions.Dynamic Mechanical Analysis（DMA）was used to study the elastic properties at low frequencies（0.5-10 Hz）and under high stress and high strain conditions between130 K and 300 K,and the anelastic properties and energy loss associated with the ferroelectric transitions and the structural transitions.For[（CH₃）₂NH₂][M（HCOO）₃]（M=Mn,Co,Ni,Mg）,near the ferroelectric transition temperatures,the storage modulus E’showed the valley or kinks,and the loss modulus E’’and the loss factor tanδshowed peaks.The peak height decreased at higher frequency,and the peak temperature was roughly independent of the frequency,showing the features of the first-order phase transitions.The frequency dependence of the peak height followed the power law tanδ=Afⁿ,with n value from-0.382 to-0.049.The obvious elastic anomalies and large energy loss near the ferroelectric transition temperature indicated strong coupling of ferroelasticity and ferroelectricity,and they were associated with the coupling of the local strain with the the freezing of the[（CH₃）₂NH₂]⁺ions and the mobility of the twin walls under applied stress.Near the ferroelectric transition temperature of[NH4][M（HCOO）3]（M=Mg）,the storage modulus showed the valley or kinks,and the loss modulus and the loss factor tanδshowed broad peaks,with weak frequency dependences.更多还原