立方氮化铌的高温高压合成与表征

发布时间：2018-04-19 01:23

  本文选题：高温高压合成 + 立方氮化铌　； 参考：《四川师范大学》2017年硕士论文

【摘要】：过渡金属氮化物(TMN_x)具有丰富的力学、电学、磁学、超导和催化等性能,在物理和材料等领域受到了广泛关注,硬超导材料立方氮化铌(δ-NbN)就是其代表之一。但由于TMN_x在常压下热力学稳定性通常较差,在合成过程中容易高温脱氮,使得理想化学计量比的δ-NbN合成相对困难,大多数样品通常为缺氮相的δ-NbN_x,在一定程度上影响了对δ-NbN的物性研究。例如,δ-NbN的体弹模量B_0=348GPa就是使用NbN0.90(1)样品在非静水压条件下通过高压原位同步辐射实验测得的,具有一定争议。因此,寻找有效途径合成理想化学计量比的δ-NbN并以之为样品进行物性研究具有重要意义。近年来,高温高压技术被逐步应用到了TMN_x的合成中,并成功合成了大量在常压下未能合成的高含氮量TMN_x和较难合成的理想化学计量比的TMN。相比于常压,高压条件更有利于提高TMN_x的热力学稳定性,有利于高含氮量TMN_x和理想化学计量比TMN的合成。因此,本文选用高温高压技术来合成理想化学计量比的δ-NbN,进而开展高压原位同步辐射实验和电阻率、磁化率、室温塞贝克系数测试,并结合第一性原理计算研究δ-NbN的弹性、塑性性质以及能带结构,具体结果如下:首先进行压力和温度标定实验,为合成实验提供了0-15.5GPa、0-1700℃的压力和温度条件保障,然后以KNbO3和hBN为原料在5.5GPa、1400℃条件下成功合成了接近理想化学计量比的δ-Nb N,解决了理想化学计量比δ-NbN的合成困难问题,保障了物性测量的样品需求。以所合成接近理想化学计量比的δ-NbN为样品,在静水压条件下进行高压原位同步辐射实验,得到δ-NbN体弹模量的精确结果B_0=319(2)GPa,证明了δ-NbN的强抗压缩能力,为研究抗压缩性能的物理机制提供了重要参考价值。通过电学、磁学和热电测试,得到δ-NbN的超导临界温度和室温塞贝克系数分别为T_c=15.3K和S=4.37uV/K。通过第一性原理计算,得到δ-NbN的单晶弹性常数、体弹模量、剪切模量和泊松比分别为C11=706.1GPa、C12=110.3GPa、C44=93.1GPa、BH=308.9GPa、GH=151.7GPa和v=0.29。研究了δ-NbN在剪切作用下的应力-应变曲线,其最小剪切强度为(111)1 1 2滑移系上的23.4GPa。此外,还计算了δ-NbN的能带结构和分波态密度(PDOS),给出了其表现金属性的理论解释。
[Abstract]:Transition metal nitride (TMNX), with rich mechanical, electrical, magnetic, superconducting and catalytic properties, has attracted extensive attention in physical and material fields, among which the hard superconducting material, cubic niobium nitride (未 -NbN) is one of its representatives.However, due to the poor thermodynamic stability of TMN_x under atmospheric pressure and the easy denitrification at high temperature during the synthesis process, it is relatively difficult to synthesize 未 -NbN with ideal stoichiometric ratio.Most of the samples are usually 未 -NbNx with nitrogen deficiency phase, which influences the physical properties of 未 -NbN to some extent.For example, the bulk elastic modulus (B_0=348GPa) of 未 -NbN is measured by using NbN0.901) samples under non-hydrostatic pressure through high-pressure in-situ synchrotron radiation experiments, which is controversial.Therefore, it is of great significance to find an effective way to synthesize 未 -NbN with ideal stoichiometric ratio and take it as a sample to study the physical properties of 未 -NbN.In recent years, high temperature and high pressure technology has been applied to the synthesis of TMN_x, and a large number of TMN_x with high nitrogen content and ideal stoichiometric ratio which can not be synthesized under atmospheric pressure have been successfully synthesized.Compared with the normal pressure, the high pressure condition is more favorable to improve the thermodynamic stability of TMN_x and the synthesis of TMN_x with high nitrogen content and ideal stoichiometric ratio TMN.Therefore, the 未 -NbN with ideal stoichiometric ratio is synthesized by using high temperature and high pressure technique, and the high pressure in situ synchrotron radiation experiments and the measurements of resistivity, magnetic susceptibility, room temperature Seebeck coefficient are carried out, and the elasticity of 未 -NbN is studied by means of first-principle calculation.The plastic properties and band structure are as follows: firstly, the pressure and temperature calibration experiments are carried out, which provide the pressure and temperature conditions of 0-15.5 GPa-1,700 鈩，

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