發(fā)布時間：2018-04-19 01:23

  本文選題：高溫高壓合成 + 立方氮化鈮��； 參考：《四川師范大學》2017年碩士論文

【摘要】：過渡金屬氮化物(TMN_x)具有豐富的力學、電學、磁學、超導和催化等性能,在物理和材料等領域受到了廣泛關注,硬超導材料立方氮化鈮(δ-NbN)就是其代表之一。但由于TMN_x在常壓下熱力學穩(wěn)定性通常較差,在合成過程中容易高溫脫氮,使得理想化學計量比的δ-NbN合成相對困難,大多數(shù)樣品通常為缺氮相的δ-NbN_x,在一定程度上影響了對δ-NbN的物性研究。例如,δ-NbN的體彈模量B_0=348GPa就是使用NbN0.90(1)樣品在非靜水壓條件下通過高壓原位同步輻射實驗測得的,具有一定爭議。因此,尋找有效途徑合成理想化學計量比的δ-NbN并以之為樣品進行物性研究具有重要意義。近年來,高溫高壓技術被逐步應用到了TMN_x的合成中,并成功合成了大量在常壓下未能合成的高含氮量TMN_x和較難合成的理想化學計量比的TMN。相比于常壓,高壓條件更有利于提高TMN_x的熱力學穩(wěn)定性,有利于高含氮量TMN_x和理想化學計量比TMN的合成。因此,本文選用高溫高壓技術來合成理想化學計量比的δ-NbN,進而開展高壓原位同步輻射實驗和電阻率、磁化率、室溫塞貝克系數(shù)測試,并結(jié)合第一性原理計算研究δ-NbN的彈性、塑性性質(zhì)以及能帶結(jié)構(gòu),具體結(jié)果如下:首先進行壓力和溫度標定實驗,為合成實驗提供了0-15.5GPa、0-1700℃的壓力和溫度條件保障,然后以KNbO3和hBN為原料在5.5GPa、1400℃條件下成功合成了接近理想化學計量比的δ-Nb N,解決了理想化學計量比δ-NbN的合成困難問題,保障了物性測量的樣品需求。以所合成接近理想化學計量比的δ-NbN為樣品,在靜水壓條件下進行高壓原位同步輻射實驗,得到δ-NbN體彈模量的精確結(jié)果B_0=319(2)GPa,證明了δ-NbN的強抗壓縮能力,為研究抗壓縮性能的物理機制提供了重要參考價值。通過電學、磁學和熱電測試,得到δ-NbN的超導臨界溫度和室溫塞貝克系數(shù)分別為T_c=15.3K和S=4.37uV/K。通過第一性原理計算,得到δ-NbN的單晶彈性常數(shù)、體彈模量、剪切模量和泊松比分別為C11=706.1GPa、C12=110.3GPa、C44=93.1GPa、BH=308.9GPa、GH=151.7GPa和v=0.29。研究了δ-NbN在剪切作用下的應力-應變曲線,其最小剪切強度為(111)1 1 2滑移系上的23.4GPa。此外,還計算了δ-NbN的能帶結(jié)構(gòu)和分波態(tài)密度(PDOS),給出了其表現(xiàn)金屬性的理論解釋。
[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，

本文編號：1770973