Superconductivity and unconventional density waves in vanadium-based kagome materials AV3Sb5

Recently, the discovery of vanadium-based kagome metal AV₃Sb₅ (A= K, Rb, Cs) has attracted great interest in the field of superconductivity due to the coexistence of superconductivity, non-trivial surface state and multiple density waves. In this topical review, we present recent works of superconductivity and unconventional density waves in vanadium-based kagome materials AV₃Sb₅. We start with the unconventional charge density waves, which are thought to correlate to the time-reversal symmetry-breaking orders and the unconventional anomalous Hall effects in AV₃Sb₅. Then we discuss the superconductivity and the topological band structure. Next, we review the competition between the superconductivity and charge density waves under different conditions of pressure, chemical doping, thickness, and strains. Finally, the experimental evidence of pseudogap pair density wave is discussed.     

Calcium-based coordination polymers from a solvothermal synthesis of HKUST-1 in 3D printed autoclaves

A mixed-metal 1D coordination polymer [CaCu(HBTC)₂(H2O)₈]_n (where H₃BTC – benzene-1,3,5-tric arboxylic acid) was obtained in a solvothermal synthesis of a well-known copper-containing metal–organic framework [Cu₃(BTC)₂(H₂O)₃]_n (HKUST-1) in autoclaves 3D-printed from commercial polypropylene. This material was a source of calcium ions, apparently, leaking from a colorant (calcium carbonate) promoted by glacial acetic acid as a modulator used to produce large single crystals of HKUST-1. This finding was confirmed by elemental analysis and a model experiment that resulted in a new calcium-based 1D coordination polymer [Ca(H₂BTC)₂(H₂O)₅]_n under the same solvothermal conditions with no copper or calcium salts put into a 3D-printed autoclave.     

一种新型双吡啶悬臂Mn(Ⅱ)配合物的合成、晶体结构及DNA结合能力研究

通过3,3′-((乙烷-1,2-二基双(2-甲基吡啶杂氮二基)双(亚甲基))双(2-羟基-5-甲基苯甲醛)与2-羟基-1,3-丙二胺的缩合反应得到一种具有双吡啶悬臂的双核锰配合物。通过X射线单晶衍射确定了该配合物结构,结果显示其分子式为[Mn₂(C₃₇H₄₃N₆O₆)]·(ClO₄)₂。该配合物属于单斜晶系,P2₁/c空间群,晶胞参数为:a=1.096 50(19) nm, b=1.419 5(3) nm, c=3.109 4(5) nm, β=108.153(5)°。进一步分析表明两个二价锰离子分别与(N_amine)₂(N_imine)₂O₃和(N_imine)₂O₄体系配位,它们与配位原子形成的几何构型分别是十面体和扭曲的八面体。两个中心锰离子距离为0.331 6 nm,由酚氧原子和醋酸根共同桥联。另外,本文也利用伏安法和黏度法对该配合物与小牛胸腺DNA的结合能力进行研究,实验结果表明它们之间的结合方式为弱的插入作用。     

单层MXene纳米片Ti2N电磁特性的过渡金属(Sc、V、Zr)掺杂效应

二维材料MXene纳米片由于具有较大的比表面积和较高的电子迁移率而受到广泛的关注。本文采用基于密度泛函理论的第一性原理计算,对单层MXene纳米片Ti₂N电磁特性的过渡金属(Sc、V、Zr)掺杂效应进行了系统研究。结果表明,所有过渡金属掺杂体系结合能均为负值,结构均稳定;其中Ti₂N-Sc体系的形成能为-2.242 eV,结构更易形成,且保持稳定;掺杂后Ti₂N-Sc、Ti₂N-Zr体系磁矩增大;此外,Ti₂N-Sc体系中保留了较高的自旋极化率,达到84.9%,可预测该体系在自旋电子学中具有潜在的应用价值。     

(Sm0.5Gd0.2Nd0.3)2(Hf0.3Ce0.7)2O7复合氧化物的热物理性能

为寻求新型热障涂层用陶瓷材料,本文采用高温固相烧结法制备了(Sm_0.5Gd_0.2Nd_0.3)₂(Hf_0.3Ce_0.7)₂O₇复合氧化物。利用XRD分析了其晶体结构,SEM分析其显微组织,膨胀仪测试其热膨胀性能,激光热导仪测试其热扩散系数。结果表明,成功制备了具有单一萤石晶体结构的(Sm_0.5Gd_0.2Nd_0.3)₂(Hf_0.3Ce_0.7)₂O₇复合氧化物。其显微组织结构致密,晶界清晰无其他相存在。由于复杂的元素组成和较大的原子量,其热导率明显低于7YSZ和Sm₂Ce₂O₇。其较低的热膨胀系数则归因于B位离子较小的离子半径,但其热膨胀系数依然满足热障涂层的要求。     

CO在超临界水中的转化以及碱性钾盐的影响

构建了CO高压溶解的进气系统，在连续式反应系统中对超临界水条件下CO的转化规律进行了研究；针对生物质超临界水气化中钾盐的多样性，选择KHCO₃、K₂CO₃和KOH等三种钾盐成分，研究了它们在不同工艺条件（450-600℃、23-29 MPa、停留时间3-6 s）下对超临界水中水煤气转化过程的影响。结果表明，在无催化条件下，提高反应温度、延长停留时间均提高了CO的转化率，而压力对其影响在低压下（23-25 MPa）比较大，高压下（25-29 MPa）比较小，水煤气转化的反应动力学方程为k=10^3.75×exp（-0.66×10⁵/RT）（s^-1）。碱性钾盐均能显著提高CO转化率，其催化促进程度从大到小依次为：KHCO₃>K₂CO₃>KOH。添加碱性钾盐时，提高反应温度、延长停留时间均提高CO转化率，而压力的影响比较复杂。碱性盐对水煤气转化反应的催化是通过草酸盐（HC₂O₄^-）和甲酸盐（HCOO^-）作为中间产物进行的。