高压下Ni_3Al热力学性质的第一性原理研究北大核心CSCD

运用第一性原理方法结合准谐Debye-Grüneisen模型研究了高压下Ni3Al的热力学性质,拟合了Ni3Al的状态方程,计算了不同压强下Ni3Al的弹性模量及吉布斯自由能等热力学性质随温度的变化关系.计算结果表明:采用七阶Birch-Murnaghan方程拟合的晶格常数与实验测量结果吻合较好;零压下弹性模量、吉布斯自由能、焓、熵、热容和体膨胀系数随温度的变化与实验值符合较好;在特定压强下,Ni3Al的弹性模量和吉布斯自由能随温度升高而减小,焓、熵随温度升高而增加;预测的德拜温度约为500K,与实验值符合较好.     

高压下Ni3Al热力学性质的第一性原理研究

运用第一性原理方法结合准谐Debye-Grüneisen模型研究了高压下Ni3Al的热力学性质,拟合了Ni3Al的状态方程,计算了不同压强下Ni3Al的弹性模量及吉布斯自由能等热力学性质随温度的变化关系. 计算结果表明：采用七阶Birch-Murnaghan方程拟合的晶格常数与实验测量结果吻合较好;零压下弹性模量、吉布斯自由能、焓、熵、热容和体膨胀系数随温度的变化与实验值符合较好;在特定压强下,Ni3Al的弹性模量和吉布斯自由能随温度升高而减小,焓、熵随温度升高而增加;预测的德拜温度约为500K,与实验值符合较好.     

Quantitative determination of anti-structured defects applied to alloys of a wide chemical range

Anti-structured defects bridge atom migration among heterogeneous sublattices facilitating diffusion but could also result in the collapse of ordered structure.Component distribution Ni_(75)Al_xV_(25-x) alloys are investigated using a microscopic phase field model to illuminate relations between anti-structured defects and composition,precipitate order,precipitate type,and phase stability.The Ni_(75)Al_xV_(25-x) alloys undergo single Ni_3V(stage Ⅰ),dual Ni_3Al and Ni_3V(stage Ⅱ with Ni_3V prior;and stage Ⅲ with Ni_3Al prior),and single Ni_3Al(stage Ⅳ) with enhanced aluminum level.For Ni_3V phase,anti-structured defects(V_(Ni1),Niy,except V_(Ni2)) and substitution defects(Al_(Ni1),Al_(Ni2),Al_v) exhibit a positive correlation to aluminum in stage I,the positive trend becomes to negative correlation or smooth during stage Ⅱ.For Ni_3 Al phase,anti-structured defects(Al_(Ni),Ni_(Al)) and substitution defects(V_(Ni),V_(Al)) have a positive correlation to aluminum in stage Ⅱ,but Ni_(Al) goes down since stage Ⅲ and lasts to stage Ⅳ.V_(Ni) and V_(Al) fluctuate when Ni_3Al precipitates prior,but go down drastically in stageⅣ.Precipitate type conversion of single Ni_3V/dual(Ni_3V+Ni_3Al) affects Ni_3V defects,while dual(Ni_3V+Ni_3Al)/single Ni_3 Al has little effect on Ni_3Al defects.Precipitate order swap occurred in the dual phase region affects on Ni_3Al defects but not on Ni_3V.     

Ni_(60)Al_(20)V_(20)中熵合金沉淀过程微扩散相场法模拟

纳米级L1_2结构的γ′有序相形态、析出过程和原子排布等对镍基中熵合金强化具有重要作用.本文采用微扩散相场动力学模型探究Ni_(60)Al_(20)V_(20)中熵合金沉淀过程微观机理,以原子占据晶格位置的几率为场变量描述微结构变化,结合反演算法,通过分析γ′相和θ相原子图像演化,序参数变化,体积分数变化等,探讨了γ′(Ni3Al)和θ(DO_(22))有序相的沉淀机制.研究结果表明:Ni_(60)Al_(20)V_(20)中熵合金无序相有序化动力学过程中,L1_0相和DO_(22)相同时析出, L1_0相逐渐转变为L1_2-γ′相,而传统Ni_(75)Al_(7.5)V_(17.5)合金沉淀序列是先析出L1_0相,L1_0转变为L1_2相后, DO_(22)相在L1_2相的反相畴界处析出. L1_0向L1_2转变时,面心立方晶格a位被Ni原子占据, b位被Al原子和V共同占据.原子等成分有序化形成DO_(22)结构q单相有序畴,随后失稳分解; L1_0结构非经典形核,逐渐转化为L1_2-γ′相并失稳分解. Ni-Al第一近邻原子间相互作用势随温度线性升高,随长程序参数增加逐渐增加; Ni_(60)Al_(20)V_(20)中熵合金孕育期随温度升高而时间变长.本文研究适用于Ni-Al-V中熵合金设计.     

Al~(3+)/Mo~(6+)双离子取代ZrV_2O_7中Zr~(4+)/V~(5+)实现近零膨胀

采用固相烧结法制备了Zri_(1-x)Al_(2-x)V_(2-x)Mo_xO_7(0≤x≤0.9),并通过调整Al~(3+)/Mo~(6+)对ZrV_2O_7中的Zr~(4+)/V~(5+)离子替代量来实现近零膨胀,对于较小的x值(x≤0.3),材料保持了与ZrV_2O_7相同的立方相结构.随着Al~(3+)/Mo~(6+)替代量的增加,(Al/Zr)~-和(Mo/V)~+之间的库仑相互作用逐渐加强,这种库仑相互作用导致材料中未发生畸变的立方相晶体结构逐渐减少.当x≥0.7时,材料中立方相晶体结构完全消失.在425-750 K温度区间内,Zr_(0.5)Al_(0.5)M_(0.6)O_7展示出近零膨胀性质(-0.39×l0~(-6)K~(-1)).Zr_(0.5)Al_(1.5)V_(1.5)Mo_(0.5)O_7的低热膨胀性能可能与Al~(3+)/Mo~(6+)对ZrV_2O_7中Zr~(4+)/V~(5+)部分替代引起部分晶体结构发生的畸变及其对未替代部分的晶格结构的影响有关.     

环面黑洞的热力学函数

本文把宇宙学常数看成与压强相当的动力学变量,研究了环面黑洞的热力学函数.计算得到环面黑洞的状态方程,环面黑洞的Smarr关系.然后通过计算其欧氏作用量得到了吉布斯函数,并进一步求得环面黑洞的自由能、内能和热力学焓,以及环面黑洞的定压热容和定容热容.结果表明:环面黑洞没有范德瓦耳斯型的相变.环面黑洞的定压热容大于零,定容热容等于零,故是一个稳定的热力学系统.     

Ni_3(Ti_x,V_(1-x))合金系中的长周期结构

本文利用电子衍射及高分辨点阵象实验方法证实了Ni_3(Ti_x,V_(1-x))合金系在铸态下存在有9R,10H,16H,20H,21H,44H等长周期结构以及2H结构。它们与体心四方基体相(结构与Ni_3V相同)及六角基体相(结构与Ni_3Ti相同)有固定取向关系:{001}_(长周期)∥{001}_(Ni_3Ti)∥{112}_(Ni_3V);〈100〉_(长周期)∥〈100〉_(Ni_3Ti)∥〈110〉_(Ni_3V_-)。样品经长期高温退火处理后其它长周期结构均向9R结构转变。     

大块金属玻璃Al_(7.5)Cu_(17.8)Ni_(10.7)Zr_(64)的耐Ar~(2+)离子辐照性能研究

利用能量为3 Me V的Ar~(12+)离子辐照金属玻璃Al_(7.5)Cu_(17.8)Ni_(10.7)Zr_(64)和金属W,研究了金属玻璃的Ar离子辐照损伤,辐照剂量分别为1×1014,1×1015和1×1016ions/cm~2。XRD分析发现在不同剂量辐照下Al_(7.5)Cu_(17.8)Ni_(10.7)Zr_(64)均保持非晶为主要结构。不同剂量辐照后的金属玻璃样品表面没有明显的辐照损伤,而金属W在剂量为1×016ions/cm2时表面出现大面积不规则的裂纹和孔洞。AFM分析显示Al_(7.5)Cu_(17.8)Ni_(10.7)Zr_(64)的表面均方根粗糙度随辐照剂量的增大而增大;辐照后金属玻璃的表面硬度略有降低,而金属W的硬度有所升高。在低于金属玻璃的玻璃化转变温度时,金属玻璃Al_(7.5)Cu_(17.8)Ni_(10.7)Zr_(64)的耐Ar~(12+)溅射能力好于金属W。     

高温高压下合金碳化物Fe3Mo3C热力学性质的第一性原理计算

基于平面波赝势密度泛函理论的第一性原理与准谐德拜模型结合的方法研究了高温高压下合金碳化物Fe₃Mo₃C的热力学性质.在压强范围为0～40 GPa和温度范围为0～1200 K的条件下,Fe₃Mo₃C的体积比V/V₀、体弹性模量B和德拜温度θ受压强的影响比温度更大.温度一定时,体弹性模量和德拜温度随压强的增大而迅速增大. Fe₃Mo₃C的热容C_v、熵S以及热膨胀系数α受温度的影响较压强更大.压强一定时,材料的热容、熵以及热膨胀系数均随温度升高单调增大,其中,热容和热膨胀系数随温度先快速上升后趋于平缓,最后热容接近于Dulong-Petit极限.     

理想气体热容的声学测试技术研究

根据热力学基本定律导出的一些热力学关系式,确定了各种热力学参数之间的普遍关联.只要知道了流体在理想气体状态下热容随温度的函数关系以及流体的状态方程,就能确定出该流体的内能、焓、熵、自由能、自由焓、(火用)以及逸度系数等热力学参数.此外,理想气体状态下的热容数据,还可用以反推分子结构与分子间相互作用的微观特性.因此,用实验方法确定工质在理想气体状态下的热容,对于流体工质热物性的研究具有十分重要的意义和作用.     

常压下固态KNO2热力学性质的密度泛函理论研究

采用密度泛函理论结合准谐德拜模型研究常压下300~725 K间KNO₂立方结构的热力学性质,重点分析常压下定压热容、定容热容、熵、德拜温度、体膨胀系数、平衡体积和体弹模量随温度的变化.结果显示,常压下计算的定压热容随温度的变化与实验数据符合较好,而计算的熵与实验数据相差较大.计算得到KNO₂的平均体膨胀系数约为1.837 8×10^-5K^-1,常温下(300 K)KNO₂的德拜温度约为667.13K.     

Thermodynamics and elastic properties of Ta from first-principles calculations

<正>Within the framework of the quasiharmonic approximation,the thermodynamics and elastic properties of Ta, including phonon density of states(DOS),equation of state,linear thermal expansion coefficient,entropy,enthalpy, heat capacity,elastic constants,bulk modulus,shear modulus,Young’s modulus,microhardness,and sound velocity, are studied using the first-principles projector-augmented wave method.The vibrational contribution to Helmholtz free energy is evaluated from the first-principles phonon DOS and the Debye model.The thermal electronic contribution to Helmholtz free energy is estimated from the integration over the electronic DOS.By comparing the experimental results with the calculation results from the first-principles and the Debye model,it is found that the thermodynamic properties of Ta are depicted well by the first-principles.The elastic properties of Ta from the first-principles are consistent with the available experimental data.     

Anharmonic Properties of Aluminum from Direct Free Energy Interpolation Method

We compare the direct free energy interpolation(DFEI) method and the quasi-harmonic approximation(QHA) in calculating of the equation of states and thermodynamic properties of prototype Al. The Gibbs free energy of Al is calculated using the DFEI method based on the high-temperature phonon density of states reduced from classical molecular dynamics simulations. Then, we reproduce the thermal expansion coefficients, the specific heat, the isothermal bulk modulus of Al accurately. By comparing the results from the DFEI method and the QHA, we find that the DFEI method is indeed more accurate in calculating anharmonic properties than the QHA.     

CaS电子结构和热力学性质的第一性原理计算

根据密度泛函理论,采用平面波赝势和广义梯度方法,计算了Ca S的晶体结构和电子结构.通过准谐徳拜模型预测了硫化钙的体积变化率、体弹模量、热膨胀系数分别与温度和压强的变化关系,以及热容和温度的变化关系.     

氧化苦参碱在0.9%NaCl溶液中溶解的热动力学性质

采用Calvet RD496-2000型微量量热计在常压及309.65 K条件下,测得了氧化苦参碱在0.9%NaCl溶液中的溶解焓,确定了其微分溶解热和积分溶解热,阐明了其溶解过程的动力学方程,并且获得其溶解过程的半衰期.     

高压下硫化钙的弹性和热力学性质的第一性原理计算

利用基于密度泛函理论的第一性原理平面波赝势方法结合准谐德拜模型研究NaCl结构的CaS在高压下的弹性和热力学性质.计算得到的零温零压下的晶格常数、体弹模量与实验值符合得很好.弹性常数和弹性模量随着压强的增大而增大.压强对体弹模量和热膨胀系数的影响大于温度的影响.热容随压强的升高而降低,在高温下热容接近于Dulong-Petit极限.通过求解Gibbs自由能计算得到B1结构和B2结构CaS的相变压为36.61 GPa.     

Five-parameter equation of solids considering thermal effect which correctly incorporates cohesive energy

A five-parameter equation of state (EOS) is proposed, which correctly incorporates the cohesive energy data without physically incorrect oscillations in both extreme high pressure and expansion regions. Based on a modified Einstein model, the thermal effect is included in the proposed EOS complying with the zero-pressure condition. With this thermal EOS applied to five solids (Ar, Al, Au, Cu and Li), some important thermodynamic properties as isotherm, isochore, thermal expansion coefficient, volume modulus, heat capacity and Hugoniot are calculated for each selected solid with good agreement with experimental data, which confirms the validity of the present work     

Pseudo-potential investigations of structural, elastic and thermal properties of tungsten disilicide

The plane-wave pseudopotential method using the generalized gradient approximation within the density functional theory is used to investigate the structure and bulk modulus of WSi₂. The quasi-harmonic Debye model, using a set of total energy versus cell volume obtained with the plane-wave pseudopotential method, is applied to the study of the elastic properties and vibrational effects. We have analysed the bulk modulus of WSi₂ up to 1600~K. The major trend shows that the WSi₂ crystal becomes more compressible when the temperature rises and the increase of compressibility leads to the decrease of Debye temperature. The predicted temperature and pressure effects on the thermal expansion, heat capacity and Debye temperatures are determined from the non-equilibrium Gibbs functions and compared with the data available.     

First-Principles Calculations of Elastic and Thermal Properties of Lanthanum Hexaboride

The plane-wave pseudopotentiai method using the generaiized gradient approximation within the framework of density functional theory is applied to anaylse the bulk modulus, thermal expansion coefficient and heat capacity of LaB6. The quasi-harmonic Debye model, using a set of total energy versus volume obtained with the plane-wave pseudopotential method, is applied to the study of the thermal properties and vibrationai effects. We analyse the bulk modulus of LaB6 up to 1500 K. The elastic properties calculations show that our system is mechanically stable. For the heat capacity and the thermal expansion, significant differences in properties are observed above 300K. The calculated zero pressure bulk modulus is in good agreement with the experimental data. Moreover, the Debye temperatures are determined from the non-equilibrium Gibbs functions and compared to available data.