锰硼化合物的高温高压合成及其物性研究

发布时间：2018-01-14 00:29

本文关键词：锰硼化合物的高温高压合成及其物性研究　出处：《吉林大学》2017年博士论文　论文类型：学位论文

【摘要】：过渡金属具有较高的价电子密度,具有很强的抵抗体积形变能力,但是抗剪切能力差,虽然有较高的体弹性模量,但是硬度不高;轻元素硼、碳、氮可以形成方向性极强的共价键,形成的化合物具有很强的抵抗剪切应力的能力。过渡金属轻元素化合物,在过渡金属中引入强共价键网络,使之同时具有两者的特点,可以形成了一种类似于“钢筋混凝土”的高强度晶体结构;另外,由于过渡金属丰富的价电子,可以为形成的化合物带来丰富的物理化学性质,因而该体系是一种潜在的高硬度多功能材料。磁性材料在现代机电系统、磁电子学等方面有重要应用;硬质材料可以往往具有较强的化学键、化学性质稳定、抗氧化性强等特点,同时具有耐磨、抗形变等优点;为寻找满足极端条件应用的高硬度磁性材料有着重大的物理学和材料学意义。本文针对潜在的高硬度磁性锰硼化合物进行了研究,利用高温高压的方法对锰硼体系进行了系统的合成,并利用实验与理论模拟相结合的方法对锰硼化合物的结构、力学性质、磁学性质、成键特性等进行深入的探究,得到了一些有价值的成果:一、利用高温高压这种特殊方法对锰硼体系进行了实验合成,得到了锰硼体系在高压下的相图。合成出了Mn2B(SG:I4/mcm)、Cr B结构的Mn B(SG:I41/amd)、Fe B结构的Mn B(SG:Pnma)、Ta3B4结构的Mn3B4(SG:Immm)、Al B2结构的Mn B2(SG:P6/mmm)以及Mn B4(SG:P21/c)。发现高温高压下锰硼化合物的合成有以下特点:(1)合成硼浓度高于50%的锰硼化合物均需要硼单质过量;(2)Mn B4的在高压下的合成区间变窄(3)高压条件下得到了一种Cr B结构的Mn B新结构;以上结果说明高温高压对于丰富物质的相图是一种十分有效的手段。二、在Mn B晶体当中,硼原子在锰金属晶格当中形成了一维无限长“之”字状硼链,使得锰原子之间的距离得到了一定的扩大,实现了从锰金属的反铁磁性磁序向铁磁性磁序的转变。磁学参数测试表明Mn B具有较高的居里转变温度、较低的矫顽力以及较高的磁饱和强度,表明Mn B是一种优异的高温铁磁材料。此外,由于强共价键“之”字状硼链的引入,Mn B的维氏硬度值达到了16 GPa左右,远高于传统铁磁性材料的硬度值。“之”字状硼链的引入形成了一种高硬度的铁磁性材料,使得铁磁性材料更加接近更强、更轻、更节能的目标,为铁磁性材料在极端条件下的应用打下了坚实的基础。三、当锰硼化学配比达到1:2时,硼原子形成了石墨烯状的六元环空间骨架,锰原子层与硼原子层交替排列,形成了一种BICs类型的晶体结构。由于石墨烯状硼层空的π价带,实验上始终未能合成出石墨烯状的硼烯。X射线光电子能谱与第一性原理计算结果均表明:在BICs晶体Mn B2当中,由于锰原子向硼原子层中转移了一定量的电子,六元环状的硼层空的π价带得到了填充,实现了石墨烯状硼层的在Mn B2晶体中稳定存在。由于石墨烯状硼层的填充,锰原子层之间的距离得到了扩大,锰原子之间的交换作用发生了改变,实现了反铁磁性锰金属向弱铁磁性Mn B2的转变;同时,由于石墨烯状硼层内部存在较强的共价键,六元环状硼层具有很强的力学性质,导致Mn B2在c轴方向具有极高的硬度值。这种方向性极高的硬度与铁磁性性质可能将在涂层防护、极端条件下的磁器件等领域得到一定的应用。四、随着硼元素浓度的增加,硼浓度驱动硼原子亚结构分别经历了Mn2B的孤立硼原子、Fe B结构的Mn B和Cr B结构的Mn B中的“之”字链状、Mn3B4的聚合“之”字链、Mn B2的石墨烯状硼层、Mn B4的三维空间笼状结构。随着硼原子亚结构的演变,锰硼化合物的硬度经历了先增加、后减小、再增加的过程。说明硼含量与硬度并非呈线性关系;高的电子密度、三维空间结构对硬度的提升有一定的帮助,但是一定的硼浓度将会产生层状结构硼化物,对高硬度将产生致命的影响。随着硼浓度的不断升高,锰硼化合物的磁性依次经历了顺磁性、铁磁性、反铁磁性、顺磁性的演变过程,这与硼原子亚结构进入锰金属晶格当中,不同程度地扩大了锰原子之间的距离,进而影响到了锰原子之间的交换作用有关。根据硼浓度对锰硼化合物硬度和磁性的影响可知:硬质磁性功能材料的设计需要同时兼顾材料的硬度设计理论与磁性理论,选择合适的过渡金属元素和轻元素种类与化学配比,达到晶体同时兼具较高硬度与优异磁性的目的。综上,通过高温高压的方法对Mn-B体系进行系统的合成,得到了一系列不同配比的锰硼化合物,绘制了Mn-B体系在高压下的合成相图,为锰硼化合物高温高压合成提供了精确的合成相图。合成出了一批具有较良好磁学性能且硬度较高的物质,高温铁磁性硬质多功能材料Cr B结构的Mn B和Fe B结构的Mn B、方向性高硬度的磁性材料Mn B2以及出现Peierls相变的Mn B4材料。发现通过高温高压这种特殊手段对锰硼体系的电子密度、电子结构、成键特性以及晶体结构的调节的规律,并能通过温度、压力及前驱物组份等条件控制不同种类的硼原子空间骨架。以硼浓度为变量研究了锰硼化合物的硬度、磁性的变化规律,发现了硬度与硼浓度之间并非线性关系,硼浓度通过改变锰原子之间的距离影响了锰硼化合物的磁性。该工作当中得到的硼浓度对硬度和磁性的作用规律为今后寻找铁磁性高硬度材料指明了方向。
[Abstract]:The valence electron density of transition metal has high, has a strong resistance volume deformation ability, but the anti shearing ability is poor, while the elastic modulus is higher, but the hardness is not high; the light element boron, carbon, nitrogen can form a covalent bond with strong direction, the formation of compounds with strong ability to resist shear stress. Transitionmetal compounds, the strong covalent bond network in transition metal, which has the characteristics of both, can form a high strength crystal structure similar to the "reinforced concrete"; in addition, because the transition metal valence electron rich, can bring extensive physical and chemical properties for the formation of compounds, so the system is a potential high hardness multifunctional material. Magnetic materials in the modern electrical system, have important applications in magnetic electronics etc.; hard materials can have a strong chemical bond, The characteristics of chemical stability, oxidation resistance is strong, also has the advantages of deformation resistance and wear resistance, high hardness; for meet the extreme conditions of magnetic material has a significant application of physics and materials science. Aiming at the potential of high hardness magnetic manganese boron compounds were studied, using the method of high temperature and pressure of the system synthesis of manganese boron system, magnetic properties, and method of using a combination of experimental and theoretical simulation of manganese and boron compounds, mechanical properties, bonding properties in-depth inquiry, obtained some valuable achievements: first, the special method of using high pressure and high temperature experiments were carried out on the synthesis of manganese and boron in the system. The phase diagram of manganese boron system under high pressure. The synthesis of Mn2B (SG:I4/mcm), Cr B Mn (SG:I41/amd) B structure, Fe structure of B Mn B (SG:Pnma), Ta3B4 Mn3B4 (SG: Immm) structure, Al (SG:P6/ B2 Mn B2 structure MMM) and Mn B4 (SG:P21/c) has the following characteristics. The synthesis of manganese boron compounds under high temperature and high pressure: (1) the synthesis of boron concentration is higher than 50% of the manganese boron compounds to elemental boron excess; (2) under high pressure synthesis of narrow interval Mn B4 (3) high pressure can be obtained under the conditions of new Mn B the structure of a Cr B structure; the above results showed that high temperature and high pressure is a very effective method for the phase diagram of material abundance. Two in Mn, B crystal, boron atoms to form an infinite one dimensional zigzag chain in boron manganese metal lattice, the manganese atomic distances must be to expand, to achieve the transition from antiferromagnetic magnetic order to manganese metal ferromagnetic order. Magnetic parameters test showed that the Curie temperature Mn B with high and low coercivity and high saturation magnetization, showed that the Mn B is a kind of high temperature ferromagnetic material excellent. In addition, because The introduction of a strong covalent bond of zigzag boron chain, Vivtorinox Mn B hardness value reached about 16 GPa, much higher than the traditional iron magnetic material hardness. "Introduction" shaped boron chain formed a ferromagnetic material with high hardness, the ferromagnetic material is more close to the more stronger. Light, more energy-efficient, a solid foundation for the application of ferromagnetic materials under extreme conditions. In three, when the ratio of 1:2 chemical manganese and boron, boron atoms form six membered ring space framework of graphene like manganese and boron atoms, atomic layer layer arranged alternately, forming a crystal structure type of BICs. As the valence band graphene like boron layer empty, experiment has been unable to synthesize graphene like boron by.X ray photoelectron spectroscopy results show that calculated with the first principle: in BICs crystal Mn B2, due to boron manganese atom atomic layer in a quantitative power transfer Son, the six membered ring of boron vacancies are filled valence band PI, the graphene like layer of boron in Mn B2 crystal is stable. Due to the filling of graphene like layers of boron, manganese atomic layer between the distance has been expanded, changed the exchange interaction between manganese atoms, to achieve the transformation anti ferromagnetic manganese metal to the weak ferromagnetic Mn B2; at the same time, due to the presence of strong covalent bonds of graphene like boron layer, six membered boron layer has strong mechanical properties, resulting in Mn B2 has a very high hardness value in the direction of C axis. The direction of magnetic properties of high hardness and may in the coating protection, can be widely applied in areas such as the magnetic device under extreme conditions. Four, with the increase of boron concentration, concentration of boron boron atom driven sub structure respectively through isolated boron atoms Mn2B, Fe B B and Cr B structure of the Mn structure of the Mn B " Chain polymerization, zigzag chains Mn3B4, graphene like boron layer of Mn B2, Mn B4 3D cage structure. With the evolution of the boron atom substructure, manganese and boron compounds through the hardness first increased, then decreased, and then increased. The process shows that there is a linear relationship between boron content and hardness is not; high electron density, will help enhance the three-dimensional structure of hardness, but will produce certain concentration of boron layered boride, will be fatal to high hardness. With the increasing concentration of boron, magnetic manganese boron compounds experienced a paramagnetic, ferromagnetic, antiferromagnetic, CIS the evolution of magnetic, and the boron atom substructure into manganese metal lattice, different degrees of expansion of manganese atom distance between, and thus affect the exchange interaction between manganese atoms. According to the boron concentration of manganese boron compounds and magnetic hardness The influence of design of hard magnetic functional materials need to consider the hardness of the material design theory and the theory of magnetism, choose suitable transition metal elements and light elements and chemical composition, crystal to both high hardness and excellent magnetic properties. Therefore, systematic synthesis of Mn-B system by means of high temperature and high pressure. A series of different ratio of manganese and boron compounds, synthesis of phase diagrams of Mn-B system under high pressure, provides accurate phase diagrams for the synthesis of manganese boron compounds in high temperature and high pressure. The synthesis of a number of relatively good magnetic properties and high hardness material, high temperature hard ferromagnetic multifunctional material Cr B structure Mn B and Fe B structure of Mn B, Mn B2 magnetic material direction of high hardness and Mn B4 Peierls. The phase change material of manganese boron body with high temperature and pressure of this special means Department of electron density, electron structure, bonding properties and crystal structure of the regulation of law, and by the temperature, the boron atom space framework of different kinds of control pressure and precursor componentthese conditions. Variables of Mn boron compounds with boron concentration for hardness, magnetic variation, hardness and found the non-linear relationship between the concentration of boron, boron concentration of magnetic manganese boron compounds by changing the distance between the manganese atoms. The role of boron concentration in hardness and magnetic properties is the ferromagnetic materials with high hardness and pointed out a direction.

【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ163

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