【作者】 王伟；

【导师】 刘先松； 杜海峰；

【作者基本信息】 安徽大学 ， 材料科学与工程， 2021， 博士

【摘要】 三元金属氮化物ANM3作为金属间充型化合物,具有丰富的物理性质和潜在的功能应用属性,从上个世纪开始就逐渐进入人们的视野并成为了材料领域研究的新热点。本论文选取反钙钛矿结构铁基三元氮化物(Cu,In,Zn)NFe3为研究对象,对这个体系化合物的实验室制备过程、表面形貌、结构类型和磁性能之间的关联以及发生在磁相变温度附近磁性行为的内在物理机制进行了较为系统的研究。通过利用不同化学元素取代母体材料γ’-Fe4N中磁性铁原子的方式,调节样品晶胞中元素的种类和含量以试图改变其晶体结构和实现功能优化。本论文中所包含的铁基三元氮化物(Cu,In,Zn)NFe3的实验研究阶段性成果,为探索和利用此类氮化物新材料提供了一定的参考依据,获得的主要成果可以总结为以下几个方面:1.通过固-气反应法成功制备了 CuxNFe4-x(0.1≤x≤0.5)系列样品,XRD测试结果表明所有样品的物相检测结果均表现为反钙钛矿立方晶体结构相。随着系列样品中Cu原子掺杂量的改变,衍射峰的位置也会发生一定程度的偏移,说明Cu原子已经成功取代Fe原子进入到晶格内并使得材料的晶格常数变小,晶胞发生收缩。Cu原子能够成功掺杂母体材料γ’-Fe4N并部分进入其晶格内,取代位于晶胞顶点位置的磁性Fe原子,并且CuxNFe4-x的掺杂极限为x≤ 0.5。通过对高掺样品Cu0.5NFe3.5的低温磁性测量,其结果表明使用Cu原子进行掺杂能够降低母体材料γ’-Fe4N的居里温度,Cu0.5NFe3.5样品的磁相变温度向室温附近移动。在外加磁场恒定为100 Oe时测量获得Cu0.5NFe3.5样品的ZFC曲线,显示样品在350 K温度附近发生了磁相变而且系统仍然处于铁磁基态。CuxNFe4-x系列样品的饱和磁化强度值会对掺杂量表现出一定的敏感性,掺杂量x的值越大,其值反而越小,样品矫顽力值也表现出同样规律。CuxNFe4-x系列样品的磁导率会随掺杂量x的增加逐渐增大,并且Cu0.5NFe3.5样品在100 kHz的测试频率下的磁导率实部可以达到μ’=11.8。与此同时,总的磁损耗Pcv却随掺杂量x的增加呈逐渐减小趋势。随着Cu原子掺杂量x的逐渐增加,CuxNFe4-x材料在直流偏置场中磁导率的稳定性可以得到优化。2.通过使用非磁性In原子取代母体材料γ’-Fe4N中的磁性Fe原子成功制备了InxNFe4-x系列样品,其掺杂极限为x=0.8。当In原子进入晶格并取代位于晶胞顶点位置的Fe原子后,样品仍保持着面心立方晶体结构类型,具有的空间群为Pm3m。XRD测试结果显示所有的衍射峰会随着In原子掺杂量x的增加而逐渐较小幅度的向低角度偏移,这也说明In原子已经进入到晶格内并使得材料的晶格常数发生了变化。在该体系中,晶格常数a的值会受掺杂量的不同影响而发生波动,并在掺杂量x达到0.8后基本保持不变,这也间接表明了 In原子掺杂母体材料γ’-Fe4N的溶解度。通过对InxNFe4-x系列样品低温磁性能的测量,结果表明其磁相变温度和掺杂量之间有着强关联性,并且高掺杂量样品In0.8NFe3.2的居里温度要低于室温。InxNFe4-x系列样品的饱和磁化强度值也会与其铁原子含量表现出正相关,样品在低温区会出现逐渐加强的自旋冻结行为,并且系统逐渐呈现自旋玻璃态。通过对高掺样品In0.6NFe3.4的磁性测量与实验结果分析,验证了该系统中存在的自旋玻璃态行为,并获得相关参数(T0=73 K,zv=5.51和τ0=4.26×10-11 s)。系统中出现的自旋玻璃态行为可能是由于In原子掺杂占据顶点位置引起混合原子无序导致,或者是系统中铁磁和反铁磁作用之间的相互竞争而引起的。3.对于通过固-气反应法成功制备的ZnNFe3样品,非磁性Zn原子与Cu和In原子一样取代γ’-Fe4N晶胞顶点位置的磁性Fe原子,形成具有空间群为Pm3m(编号:221)的立方晶体结构相。ZnNFe3样品在5 um和10 um标度下的微观显微扫描电镜表明样品颗粒分布均匀,排布较为紧密,颗粒的尺寸均分布在0.5～1 um。分别在5 K、300 K和350 K下加外磁场对ZnNFe3样品进行等温磁性测量,获得的磁滞回线表明其饱和磁化强度值(Ms)在5 K时约为108.3 emu/g。在300 K(室温)时测量获得的磁滞回线没有表现出完全的线性,表明此时的磁系统中仍然具有一定的弱铁磁性。当测试温度达到350 K时,直线型的磁滞回线表明样品此时已经完全进入顺磁性状态。母体材料γ’-Fe4N在室温下会具有很高的饱和磁化强度值(Ms～210 emu/g),但是这种材料在室温下的矫顽力值却较低(Hc～20 Oe)。ZnNFe3样品的磁性却表现出明显的不同,表现出由掺杂原子Zn原子引起的磁性贡献度的改变。ZnNFe3样品相比于母体材料γ’-Fe4N,具有更低的磁相变温度、饱和磁化强度值和矫顽力值。通过对样品磁性临界行为和电子自旋共振谱的研究,结果揭示了 ZnNFe3样品中的铁磁性阻挫来源于晶格上的空位导致的磁无序和不同化学键间的短程铁磁相互作用。通过分析ZnNFe3样品的实验研究结果,发现二级相变过程会发生在该系统中。并且当外加磁场的变化范围达到ΔH=50kOe时,系统的磁熵变值(-ΔSM)可达到2.2984 J/kg K,甚至相对制冷能力(RCP)值可达247.0671 J/kg,接近传统磁制冷材料(Gd)的47%。更多还原

【Abstract】 Ternary metal nitride ANM3,as an intermetallic compound,has rich physical properties and potential functional application properties.Since the last century,it has gradually entered people’s field of vision and become the matters of general interest in the field of materials.In this thesis,the iron-based ternary nitride(Cu,In,Zn)NFe3 with anti-perovskite structure is selected as the object of study.Beside,the laboratory preparation process,surface morphology,the relationship between structure types and magnetic properties,and the internal physical mechanism of magnetic behaviors near the magnetic phase transition temperature are systematically studied.By using different chemical elements to substitute the magnetic iron atoms in the parent material γ’-Fe4N,the types and contents of elements in the sample cell were adjusted in an attempt to change its crystal structure and achieve functional optimization.The experimental results of iron-based ternary nitride(Cu,In,Zn)NFe3 included in this thesis provide a certain extent reference for exploring and utilizing this kind of new nitride material.The main achievements can be summarized as follows:1.Series of CuxNFe4_x(0.1≤x≤0.5)samples were successfully prepared by solid-gas reaction method.XRD results showed that all samples showed anti-perovskite cubic crystal structure.With the change of the doping amount of Cu atoms in the samples,the position of diffraction peaks will shift to a certain extent,which indicates that Cu atoms have successfully served as the substitute for Fe atoms in the lattice and makes the lattice constant of materials smaller when unit cells shrink.Cu atoms can successfully dope the parent material γ’-Fe4N and partially enter the crystal lattice as the substitute for the magnetic Fe atoms located at the corner of the cell.Menwhile,the limit of doping is x≤0.5 in CuxNFe4-x.The low-temperature magnetic measurement of the highly doped sample Cu0.5NFe3.5 shows that the Curie temperature of γ’-Fe4N can be reduced by doping with Cu atoms,and the magnetic phase transition temperature of Cu0.5NFe3.5 sample moves to room temperature.The ZFC curve of Cu0.5NFe3.5 sample was obtained when the applied magnetic field was constant at 100 Oe,which showed that the magnetic phase transition occurred near 350 K and the system was still in ferromagnetic ground state.Saturation magnetization value of CuxNFe4_x samples will show certain sensitivity to doping amount.The larger the doping amount x is,the smaller its value is,and the value of the coercive force of samples also shows the same rule.The magnetic permeability of CuxNFe4_x samples will gradually increase with the increase of doping amount x,and the real part of the magnetic permeability of Cu0.5NFe3.5 samples can reach μ’=11.8 at the test frequency of 100 kHz.Meanwhile,the total magnetic loss Pcv decreases gradually when the doping amount x increases.As the increase of Cu doping amount x,the stability of permeability of CuxNFe4_x material in DC bias field can be optimized.2.Series of InxNFe4-x samples were successfully prepared by using nonmagnetic indium(In)atoms instead of magnetic Fe atoms in γ’-Fe4N,and the doping limit was x=0.8.When indium atoms enter the lattice and substitute Fe atoms located at the corner of unit cells,the samples still maintain the face-centered cubic crystal structure type,with a space group of Pm3m.XRD test results show that all diffraction peaks gradually shift to a low angle with the increase of doping amount x of indium atoms,which also indicates that indium atoms have entered the lattice and changed the lattice constant of the material.In this system,the value of lattice constant a fluctuates under the influence of doping amount,and then remains basically unchanged when the doping amount x reaches 0.8.This indirectly indicates the solubility of the parent material γ’-Fe4N doped with in atoms.The low temperature magnetic properties of InxNFe4_x samples were measured,and the results showed that there is a strong correlation between the magnetic phase transition temperature and doping amount,and the Curie temperature of In0.8NFe3.2 with high doping amount is lower than room temperature.The saturation magnetization value of InxNFe4_x samples also shows a positive correlation with its iron atom content.The strengthen spin freezing behavior will happen in the samples at low temperature,and the system will gradually show a spin-glass state.The magnetic measurement and experimental results of In0.6NFe3.4,a highly doped sample,verify the existence of spin-glass behavior in the system and obtain the relevant parameters(T0=73 K,zv=5.51 and τ0=4.26×10-11 s).The spin-glass behavior in this system may be due to the disorder of mixed atoms caused by the doped indium atoms occupying the corner position,or the competition between ferromagnetic and antiferromagnetic interactions.3.For the ZnNFe3 samples successfully prepared by the solid-gas reaction method,the nonmagnetic Zn atoms inside,which like Cu and In atoms,substitute magnetic Fe atoms at the corner position of γ’-Fe4N cells,forming cubic crystal structure phase with space group Pm3m(No.:221).Scanning electron microscope(SEM)pictures of ZnNFe3 samples were taken at 5 um and 10 um scales show that the particles of the samples are evenly distributed and closely arranged,beside,the particle sizes are all distributed in 0.5～1 um.Isothermal magnetic measurements were carried out on ZnNFe3 samples with external magnetic fields at 5 K,300 K and 350 K,respectively.The hysteresis loops obtained show that the saturation magnetization value(Ms)near 108.3 emu/g at 5 K.The hysteresis loop measured at 300 K(room temperature)does not show complete linearity,which indicates that the magnetic system still has weak ferromagnetism.When the test temperature reaches 350 K,the linear hysteresis loop indicates that the sample has completely entered paramagnetic state.The parent material γ’-Fe4N has high saturation magnetization value(Ms～210 emu/g)at room temperature,but its coercive force value is low(Hc～20 Oe)at room temperature.The magnetic properties of ZnNFe3 samples are obviously different,showing the change of magnetic contribution caused by doping atom(Zn).Compared with the parent materialγ’-Fe4N,the ZnNFe3 sample has lower magnetic phase transition temperature,the value of saturation magnetization and coercive force.The magnetic critical behavior and electron spin resonance spectrum of the samples reveal that the ferromagnetic frustration in ZnNFe3 samples comes from the magnetic disorder caused by vacancies on the lattice and the short-range ferromagnetic interaction between different chemical bonds.By analyzing the experimental results of ZnNFe3 samples,it is found that the second-order phase transition process will occur in this system.And when the change range of the applied magnetic field reaches ΔH=50 kOe,the magnetic entropy change value(-ΔSM)of the system can reach 2.2984 J/kg K,furthermore,the relative cooling power(RCP)can reach 247.0671 J/kg,which is close to 47%of the traditional magnetic refrigeration material(Gd).更多还原