Zero thermal expansion in metal-organic framework with imidazole dicarboxylate ligands

Exploring new abnormal thermal expansion materials is important to understand the nature of thermal expansion.Metal-organic framework(MOF)with unique structure flexibility is an ideal material to study the thermal expansion.This work adopts the high-resolution variable-temperature powder x-ray diffraction to investigate the structure and intrinsic thermal expansion in Sr-MOF([Sr(DMPhH_(2)IDC)_(2)]_n).It has the unique honeycomb structure with one-dimensional(1 D)channels along the c-axis direction,the a-b plane displays layer structure.The thermal expansion behavior has strong relationship with the structure,ZTE appears in the a-b plane and large PTE along the c-axis direction.The possible mechanism is that the a/b layers have enough space for the transverse thermal vibration of polydentate ligands,while along the c-axis direction is not.This work not only reports one interesting zero thermal expansion material,but also provides new understanding for thermal expansion mechanism from the perspective of the structural model.

Strong Coupling of Magnetism and Lattice Induces Near-Zero Thermal Expansion over Broad Temperature Windows in ErFe10V2−xMox Compounds

Alloys with low thermal expansion could overcome thermal stress issues under temperature-fluctuated conditions and possess important application prospects,while they are restricted to finite chemical components and temperature windows.In this study,we report a novel class of near-zero thermal expansion(near ZTE)alloys,ErFe_(10)V_(2−x)Mo_(x),over a wide temperature range(120–440 K).Neutron diffraction and magnetic measurements demonstrated that the ErFe_(10)V_(2−x)Mo_(x)compounds exhibited complex ferrimagnetic(FIM)structures below Curie temperature(TC).The near-ZTE behaviors were closely related to the itinerant Fe 3d moments in the collinear FIM states,as well as the geometric[−Fe−Fe−]linkages.Further,X-ray absorption near-edge structure(XANES)spectra revealed that the nonmagnetic substitution changed the electronic valence states of Fe atoms,which,in turn,changed Fe 3d moments and TC,hence,regulating the thermal expansion behaviors.Our work provides an insight into chemical modifications of thermal expansion in magnetic intermetallic compounds.

Zero and controllable thermal expansion in HfMgMo(3-x)WxO(12)

HfMgMo（3-x）WxO（12） with x = 0.5, 1.0, 1.5, 2.0, and 2.5 are developed with a simple solid state method. With increasing the content of W, solid solutions of Hf Mg Mo3-xWx O12 crystallize in an orthorhombic structure for x≤2.0 and a monoclinic structure for x2.0. A near-zero thermal expansion（ZTE） is realized for HfMgMo（2.5）W（0.5）O（12） and negative coefficients of thermal expansion（NCTE） are achieved for other compositions with different values. The ZTE and variation of NCTE are attributed to the difference in electronegativity between W and Mo and incorporation of a different amount of W, which cause variable distortion of the octahedra and softening of the MoO4 tetrahedra, and hence an enhanced NCTE in the a- and c-axis and reduced CTE in the b-axis as revealed by Raman spectroscopy and x-ray diffraction.

Zero thermal expansion in Cs_(2)W_(3)O_(10)

Zero thermal expansion materials are important for the practical applications due to their shape stability as changing temperature.The reported concept of average atomic volume is an available method to hunt new zero thermal expansion materials.Here,according to this concept,a tetragonal tungstate Cs_(2)W_(3)O_(10)with zero expansion has been found.There is no structure phase transition as increasing temperature from 150 K to 573 K.The coefficient of thermal expansion of axes and volume areαa=0.0074×10^(-6)K^(-1),αc=1.63×10^(-6)K^(-1),andαV=1.60×10^(-6)K^(-1),respectively,in the temperature range of 150~573 K.The temperature-and pressure-dependent Raman spectra reveal that the vibrations of WO6octahedra libration modes with positive total anharmonicity and W-O-W bending mode with negative Grüneisen parameter are possibly the origin of zero thermal expansion in Cs_(2)W_(3)O_(10).

Crystallization Behavior and Kinetics of Lithium Aluminosilicate Glasses with Various Li_(2)O Contents

The crystallization behavior of Li_(2)O-Al_(2)O_(3)-SiO_(2) glasses with various concentration of Li2O were investigated by DSC,XRD,and FE-SEM.The h/l-quartz s.s.is the main crystalline phase for all of the glass with the heat treatment of 720℃/3 h+800℃/1.5 h while the crystallinity and crystal size increase with the increase of Li2O contents.Due to the negative thermal expansion coefficient of h/l-quartz s.s.,the thermal expansion coefficient of glass-ceramics decreases with the increasing of Li2O contents.When the Li2O content is 9mol%,the near-zero CTE20-700℃=-0.09×10^(-6)℃^(-1) is obtained upon the heat treatment of 720℃/3 h+800℃/1.5 h.The crystallization activation energy of the glass with 9mol%Li2O is about 351 kJ/mol,and the crystallization mechanism is volume crystallization.

织构与磁体积效应协同作用诱导Mn_(x)Fe_(5-x)Si_(3)合金产生二维零热膨胀

零热膨胀合金在精密控制工程中具有独特的应用.然而,实现零热膨胀的苛刻条件,即自旋、晶格和电荷之间存在的适当耦合,使得零热膨胀合金的种类稀少.在这项工作中,我们报告了一种在体积表现为正热膨胀合金中,通过调节晶体学取向和磁体积效应来实现二维零热膨胀行为的途径.基于此,我们在MnFe4Si3中获得了宽温度区间(10-310 K)的具有热膨胀系数α_(1)=0.45×10^(-7)K^(-1)的二维零热膨胀合金.同步加速器X射线衍射、中子衍射、电镜和磁性测试的结果表明,这种零热膨胀行为由6g位置上的Fe在a-b面内的磁矩以及块体织构共同决定.此外,Mn_(1.5)Fe_(3.5)Si_(3)和Mn_(2)Fe_(3)Si_(3)化合物表现出混磁性和负热膨胀行为,这起源于Fe_(4d)-Fe_(6g)(J_(FM))铁磁性和Mn_(4d)-Mn_(6g)(J_(AFM))反铁磁性相互作用之间的竞争.这种方法能够扩展到其他磁性或铁电材料中,以设计新的低膨胀或负膨胀块体材料.