金屬碳化物力學(xué)和熱力學(xué)性質(zhì)第一性原理研究
發(fā)布時(shí)間：2018-12-17 16:30
【摘要】：二元金屬碳化物有著豐富的晶格結(jié)構(gòu)形式和優(yōu)異的物理化學(xué)性能,因而在物理學(xué)、化學(xué)、材料科學(xué)及地球科學(xué)中有著巨大的應(yīng)用價(jià)值。利用基于密度泛函理論(Density functional theory)的第一性原理計(jì)算方法,本論文研究了稀土金屬碳化物Yb-C系統(tǒng)和堿土金屬碳化物Ca-C系統(tǒng)的力學(xué)和熱力學(xué)性質(zhì)。論文主要研究了兩方面的問題:一是研究了Habburd U值對(duì)計(jì)算Yb-C系統(tǒng)(其中包括Fm-3m相的YbC、I-43d相的Yb_2C_3、I4/mmm相的YbC_2和P63/mmc相的YbC_6)力學(xué)和熱力學(xué)性質(zhì)的影響;二是研究了壓強(qiáng)對(duì)堿土金屬碳化物Ca-C系統(tǒng)(其中包括C2/m相的Ca_2C_3、C2/m相和Pnma相的Ca_2C)力學(xué)性質(zhì)的影響。4f電子的關(guān)聯(lián)效應(yīng)對(duì)于稀土金屬碳化物的電子結(jié)構(gòu)和熱力學(xué)性質(zhì)有重要的作用。本論文中,我們運(yùn)用了GGA+U的方法,計(jì)算了4f電子在不同Hubbard U值修正下,YbC、Yb_2C_3、YbC_2和YbC_6的力學(xué)和熱力學(xué)性質(zhì)。結(jié)果表明,四種鐿碳化物的晶格常數(shù)明顯地伴隨著U值的增大而增大,相反的,它們的彈性常數(shù)多數(shù)隨著Hubbard U值的增大而減小。采用VRH近似(Voigt-Reuss-Hill approximation),我們計(jì)算了四種鐿碳化物的體彈模量B、楊氏模量E和剪切模量G,并發(fā)現(xiàn)它們的值與Hubbard U值也表現(xiàn)出明顯的相關(guān)性。YbC_6的B、E和G的值在四種碳化物中最大而呈現(xiàn)出質(zhì)地硬和脆的力學(xué)特性,而YbC_2則呈現(xiàn)出質(zhì)地軟和易延展的力學(xué)特性。利用各向異性指數(shù)和因子,我們分析了四種鐿碳化物的力學(xué)各向異性。聲子譜計(jì)算發(fā)現(xiàn),只有YbC_2和YbC_6是動(dòng)力學(xué)穩(wěn)定相,這與實(shí)驗(yàn)的結(jié)論是一致的。壓強(qiáng)能改變材料中原子之間的成鍵特性從而帶來材料物理性能的改變。本論文中,我們研究了不同壓強(qiáng)下C2/m相的Ca_2C_3(C2/m-Ca_2C_3)、C2/m相的Ca_2C(C2/m-Ca_2C)和Pnma相的Ca_2C(Pnma-Ca_2C)的力學(xué)性質(zhì)。它們的彈性常數(shù)C11、C22和C_33的數(shù)值伴隨著壓強(qiáng)呈現(xiàn)出增長(zhǎng)趨勢(shì),且0到30 GPa下的C2/m-Ca_2C_3、0到7.5 GPa下的C/2m-Ca_2C和7.5到30 GPa下的Pnma-Ca_2C都符合Born-Huang晶格動(dòng)力學(xué)穩(wěn)定標(biāo)準(zhǔn)。它們的體彈模量B、楊氏模量E和剪切模量G都隨著壓強(qiáng)的升高而升高。各向異性百分比分析表明三種鈣碳結(jié)構(gòu)的各向異性隨著壓強(qiáng)的升高而增大。此外,C2/m-Ca_2C的彈性模量B和E以及各向異性百分比AB在5至7 GPa壓強(qiáng)范圍內(nèi)增長(zhǎng)趨勢(shì)幾乎消失,這預(yù)示著相變的產(chǎn)生。我們的研究表明,4f電子的強(qiáng)關(guān)聯(lián)效應(yīng)對(duì)鐿碳稀土金屬化合物的力學(xué)和熱力學(xué)性質(zhì)有著顯著的影響;我們關(guān)于鈣碳?jí)A土金屬碳化物壓強(qiáng)下力學(xué)性質(zhì)的研究,完善了對(duì)于新近發(fā)現(xiàn)的鈣碳相的力學(xué)性質(zhì)的認(rèn)知。
[Abstract]:Binary metal carbides have great application value in physics, chemistry, material science and earth science because of their rich lattice structure and excellent physical and chemical properties. Based on density functional theory (Density functional theory), the mechanical and thermodynamic properties of rare earth metal carbide Yb-C system and alkali earth metal carbide Ca-C system are studied in this paper. This paper mainly studies two problems: first, we study the Habburd U-value pair calculation of Yb-C system (including the Yb_2C_3, of YbC,I-43d phase of Fm-3m phase). The influence of YbC_2 of I4/mmm phase and YbC_6 of P63/mmc phase on mechanical and thermodynamic properties; The second is to study the pressure pair alkali earth metal carbides Ca-C system (including C 2 / m phase Ca_2C_3,). The correlation effect of 4f electrons plays an important role in the electronic structure and thermodynamic properties of rare earth metal carbides. In this paper, we use the GGA U method to calculate the mechanical and thermodynamic properties of YbC,Yb_2C_3,YbC_2 and YbC_6 for 4f electrons modified by different Hubbard U values. The results show that the lattice constants of the four ytterbium carbides increase obviously with the increase of U value. On the contrary, the elastic constants of the four ytterbium carbides decrease with the increase of Hubbard U value. The VRH approximation (Voigt-Reuss-Hill approximation),) is used to calculate the bulk elastic modulus (B), Young's modulus (E) and shear modulus (G) of four ytterbium carbides, and it is found that their values are also significantly correlated with the Hubbard U value. The values of E and G are the largest among the four carbides, showing the mechanical properties of hardness and brittleness, while the mechanical properties of YbC_2 are soft and extensible. Using anisotropy exponents and factors, we analyze the mechanical anisotropy of four ytterbium carbides. The calculation of phonon spectra shows that only YbC_2 and YbC_6 are kinetic stable phase, which is consistent with the experimental results. The pressure energy changes the bonding properties between atoms in the material, which leads to the change of the material physical properties. In this paper, we study the mechanical properties of Ca_2C_3 (C2/m-Ca_2C_3), Ca_2C (C2/m-Ca_2C) of C _ 2 / m phase and Ca_2C (Pnma-Ca_2C) of Pnma phase at different pressures. Their elastic constants C _ 11 C _ 22 and C _ S _ 33 show an increasing trend along with the pressure. Moreover, the C/2m-Ca_2C of C _ 2 / m -Ca _ 2C _ (2) C _ (2) C _ ( Their bulk elastic modulus B, Young's modulus E and shear modulus G all increase with the increase of pressure. The anisotropy percentage analysis shows that the anisotropy of the three calcium carbon structures increases with the increase of pressure. In addition, the elastic modulus B and E of C2/m-Ca_2C and the anisotropic percentage AB almost disappear in the range of 5 to 7 GPa pressure, which indicates the generation of phase transition. Our results show that the strong correlation effect of 4f electrons has a significant effect on the mechanical and thermodynamic properties of ytterbium carbon-rare earth metal compounds. Our study on the mechanical properties of calcium carbon alkali earth carbide under pressure has improved the understanding of the mechanical properties of the recently discovered calcium carbon phase.
【學(xué)位授予單位】：煙臺(tái)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2016
【分類號(hào)】：O611.3;O641.1
，
本文編號(hào)：2384449
[Abstract]:Binary metal carbides have great application value in physics, chemistry, material science and earth science because of their rich lattice structure and excellent physical and chemical properties. Based on density functional theory (Density functional theory), the mechanical and thermodynamic properties of rare earth metal carbide Yb-C system and alkali earth metal carbide Ca-C system are studied in this paper. This paper mainly studies two problems: first, we study the Habburd U-value pair calculation of Yb-C system (including the Yb_2C_3, of YbC,I-43d phase of Fm-3m phase). The influence of YbC_2 of I4/mmm phase and YbC_6 of P63/mmc phase on mechanical and thermodynamic properties; The second is to study the pressure pair alkali earth metal carbides Ca-C system (including C 2 / m phase Ca_2C_3,). The correlation effect of 4f electrons plays an important role in the electronic structure and thermodynamic properties of rare earth metal carbides. In this paper, we use the GGA U method to calculate the mechanical and thermodynamic properties of YbC,Yb_2C_3,YbC_2 and YbC_6 for 4f electrons modified by different Hubbard U values. The results show that the lattice constants of the four ytterbium carbides increase obviously with the increase of U value. On the contrary, the elastic constants of the four ytterbium carbides decrease with the increase of Hubbard U value. The VRH approximation (Voigt-Reuss-Hill approximation),) is used to calculate the bulk elastic modulus (B), Young's modulus (E) and shear modulus (G) of four ytterbium carbides, and it is found that their values are also significantly correlated with the Hubbard U value. The values of E and G are the largest among the four carbides, showing the mechanical properties of hardness and brittleness, while the mechanical properties of YbC_2 are soft and extensible. Using anisotropy exponents and factors, we analyze the mechanical anisotropy of four ytterbium carbides. The calculation of phonon spectra shows that only YbC_2 and YbC_6 are kinetic stable phase, which is consistent with the experimental results. The pressure energy changes the bonding properties between atoms in the material, which leads to the change of the material physical properties. In this paper, we study the mechanical properties of Ca_2C_3 (C2/m-Ca_2C_3), Ca_2C (C2/m-Ca_2C) of C _ 2 / m phase and Ca_2C (Pnma-Ca_2C) of Pnma phase at different pressures. Their elastic constants C _ 11 C _ 22 and C _ S _ 33 show an increasing trend along with the pressure. Moreover, the C/2m-Ca_2C of C _ 2 / m -Ca _ 2C _ (2) C _ (2) C _ ( Their bulk elastic modulus B, Young's modulus E and shear modulus G all increase with the increase of pressure. The anisotropy percentage analysis shows that the anisotropy of the three calcium carbon structures increases with the increase of pressure. In addition, the elastic modulus B and E of C2/m-Ca_2C and the anisotropic percentage AB almost disappear in the range of 5 to 7 GPa pressure, which indicates the generation of phase transition. Our results show that the strong correlation effect of 4f electrons has a significant effect on the mechanical and thermodynamic properties of ytterbium carbon-rare earth metal compounds. Our study on the mechanical properties of calcium carbon alkali earth carbide under pressure has improved the understanding of the mechanical properties of the recently discovered calcium carbon phase.
【學(xué)位授予單位】：煙臺(tái)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2016
【分類號(hào)】：O611.3;O641.1
，
本文編號(hào)：2384449
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