六方氮化钨的高温高压合成与表征

HIGH PRESSURE-TEMPERATURE SYNTHESIS AND CHARACTERIZATION OF HEXAGONAL TUNGSTEN NITRIDE

周雪峰

11649147

硕士

材料工程

王善民

2018-05-30

2018-07-04

哈尔滨工业大学

深圳

过渡族金属氮化物（TMNx）表现出优异的理化性质，如：极高的硬度、优良的耐磨性与耐腐蚀性、超导、超高的熔点及丰富的磁学性能等,其中六方氮化钨（δ-WN）则具有成为硬超导材料的潜质。但由于常压下TMNx 的热力学稳定性较差，通常合成出的样品为脱氮相，且很难得到单晶样品，从而在一定程度上影响了对δ-WN 的物性研究。因此寻求一种有效的方法合成δ-WN 单晶样品，并基于单晶样品对其物性进行研究具有及其重要的意义。本文利用高温高压离子置换法制备δ-WN 样品。利用光学显微镜与扫描电子显微镜测得其尺寸在70 μm 左右。利用单晶X 射线衍射仪及透射电子显微镜确定了其单晶特征及P-6m2 空间群结构，并进一步对单晶衍射数据进行结构解析，得到了其晶格参数a 为2.927 Å，c 为2.862 Å，最终得到了其解析后的结构图。同时基于单晶的δ-WN 样品，对其硬度与杨氏模量进行了测量：其中利用维氏硬度计测得其维氏硬度为17.5 GPa，远高于之前报道的多晶样品13.8 GPa 与10.5 GPa 的硬度值；利用纳米压痕仪测得的其维氏硬度值为26.7 GPa，杨氏模量值为162.8 GPa。同时利用MPMS 测量了在2-60 K 的温度范围内-WN 的磁化率随温度的变化曲线，根据迈斯纳效应初步得到-WN 的临界超导温度为20.16 K，但其超导性能需要进一步证实。通过第一性原理计算，得到-WN 的五个独立的弹性常数C11、C33、C12、C13 和C44 分别为610 GPa、743 GPa、220 GPa、332 GPa 和112 GPa，剪切模量与弹性模量为129 GPa 与401 GPa。通过泊松比0.35 及剪切模量与弹性模量之比0.32判断出其化学键类型为离子性。此外对-WN 的能带结构与态密度进行了计算，根据费米面上态密度为有限值得到其具有金属特性。

Transition-metal nitrides (TMNs) exhibit excellent physicochemical properties such as extremely high hardness, excellent wear resistance and corrosion resistance, superconductivity, ultra-high melting point, and abundant magnetic properties. Among them, hexagonal tungsten nitride ( δ-WN) has the potential to become hard superconducting material. However, due to the poor thermodynamic stability of TMNs under atmospheric pressure, the commonly samples are nonstoichiometric, and it is difficult to obtain single crystal samples. Therefore, it is of great significance to seek an effective method for the synthesis of δ-WN single crystal samples, and to study their physical properties based on single crystal samples.In this paper, we synthesized δ-WN by ion exchange method under high temperature and pressure. Using optical microscope and scanning electron microscope, we got that the size of δ-WN was about 70 μm. We used single crystal X-ray diffractometer and transmission electron microscopy to confirm that the run sample was single crystal with P-6m2 space group. We analyzed the single crystal diffraction data to obtain lattice parameters. At the same time, based on the single-crystal δ-WN sample, the hardness and Young's modulus were tested. The Vickers hardness measured by the Vickers hardness tester was 17.5 GPa, which was much higher than the previously reported hardness (13.8 GPa and 10.5 GPa) of polycrystalline samples. The Vickers hardness value measured by nano-indenter was 26.7 GPa, and the Young's modulus value was 162.8 GPa. We used MPMS with the temperature range of 2 to 60 K to measure the susceptibility of δ-WN. According to Meissner effect, -WN had a superconducting transition temperature of 20.16 K. By first-principles calculation, five independent elastic constants C11, C33, C12, C13, and C44 of -WN were 610 GPa, 743 GPa, 220 GPa, 332 GPa, and 112 GPa respectively. The shear modulus and elastic modulus were 129 GPa, 401 GPa respectively. The Poisson's ratio of 0.35 and the ratio of the shear modulus to elastic modulus of 0.32 determined that the chemical bond type of δ-WN was ionic. In addition, the energy band structure and density of states of -WN were calculated. According to the finite density of the surface state of Fermi level, we found the metal property of -WN.

高温高压 δ-WN 单晶 维氏硬度 超导 第一性原理计算

high pressure and temperature δ-WN single crystal vickers hardness superconductivity first-principles calculation

中文

联合培养

哈尔滨工业大学

周雪峰. 六方氮化钨的高温高压合成与表征[D]. 深圳. 哈尔滨工业大学,2018.