金属钒,铌,钽的电子结构和物理性质

依据纯金属单原子理论(OA)确定了体心立方结构(bcc)V，Nb，Ta的电子结构依次为[Ar](3dn)^1.68(3dc)^2.94(4Sc)^0.18(4sf)^0.20，[Kr](4dn)^0.25(4dc)^4．15(5Sc)^0.21(5Sf)^0.39，[Xe](5dn)^0(5de)^3.92(6Se)^0.59(6Sf)^0.50；并对V，Nb，Ta的面心立方结构(fcc)和密排六方结构(hcp)初态特征晶体的电子结构进行了研究。在此基础上定性地解释了V，Nb，Ta的电子结构和晶体结构之间的关系；定性解释了bcc结构V，Nb，Ta之间力学性质和输运性质的差异与电子结构的关系；定量计算了其晶格常数、结合能、势能曲线、弹性和热膨胀系数随温度的变化。     

面心立方和亚稳液相Au的原子状态及物理性质与温度变化关系的Debye-Grüneisen模型研究

结合纯金属单原子(OA)理论和Debye-Grüneisen模型研究了SGTE纯单质数据库中面心立方和亚稳液相Au的原子状态、原子势能、原子动能、原子体积、体弹性模量和热膨胀系数等物理性质随温度的变化关系,结果表明:电子结构计算结果与第一原理方法一致;原子的单键半径随温度升高而增大;原子动能随温度升高明显增大,并且其速率是原子势能的4倍多;体弹性模量随温度升高而缓慢下降;线热膨胀系数随温度的变化规律与实验值吻合较好。固体向液相转变时,共价d电子减少27.4%,共价s电子增加152%,自由s电子减小88.5%,非键电子数目增加近23%,使得原子的配位方向性减弱,自由度增大;电子结构的转变是导致原子单键半径增大和体积增加及其他物理性质发生改变的根本原因。     

金属中氦缺陷的第一性原理研究

采用第一性原理方法研究了面心立方fcc、体心立方bcc和六方密堆hcp结构金属中氦缺陷,计算分析了三种晶体结构金属中四面体间隙位置、八面体间隙位置和替代位置氦原子的形成能.并比较了fcc、bcc和hcp结构中不同位置氦点缺陷的稳定性.     

双层钙钛矿锰氧化物Nd_(1.15)Tb_(0.05)Sr_(1.8)Mn_2O_7的磁性和电性研究

采用传统固相反应法制备双层锰氧化物Nd1.15Tb0.05Sr1.8Mn2O7多晶样品,通过测量样品的X射线衍射谱、磁化强度随温度变化曲线(M-T曲线)以及电阻率随温度变化曲线(ρ-T曲线),对其磁性和电输运性质进行了研究。结果表明,样品随温度的升高先后经历了四个磁转变点:奈尔温度点(TN≈50 K)、电荷有序温度点(TCO≈67 K)、居里温度点(TC≈107 K)和类Griffiths温度点(TG≈275 K)。在低温部分样品处于反铁磁-铁磁共存态,表现出了团簇自旋玻璃行为;在TC到TG温度范围内,样品处于铁磁-顺磁共存态,即存在类Griffiths相;在TG温度以上,样品处于纯顺磁态。其电输运性质表明,随温度的升高,样品的磁电阻率降低,没有发生金属-绝缘转变。通过对115 K~300 K温度范围内的ρ-T曲线拟合发现,样品在高温部分基本遵循三维变程跳跃的导电方式。     

钯-氢体系的物理化学性质

对钯-氢体系的物理化学性质进行了综合评述。钯是一种面心立方（fcc)结构的吸氢金属，氢原子溶解在晶格中，占据八面体间隙位（O），形成fcc的子晶格，吸氢时晶格发生等方性膨胀；氢在钯中的扩散路径为0-T-O跃迁，存在反同位素效应；钯氢化物的氢同位素分离因子较大，并受到温度、氢浓度等因数的影响；钯-氢体系的p-c等温线表现出良好的坪台性，Pd-H和Pd-D均存在在临界点，尚未确定Pd-T有无临界点；单晶钯-氢反应动力学与不同的晶面有关；钯-氚老化效应。     

ZrB2电子结构和光学声学性质的第一性原理计算

利用第一性原理计算了ZrB2的电子结构、光学和晶格动力学性质.对ZrB2的能带和电子态密度(DOS)的计算表明,ZrB2具有金属特征,导带主要由B2p轨道反键态和Zr4d电子构成.B原子的σ键由2s和2p杂化轨道形成,Pz轨道单独形成一个连续的π键,这些态之间的跃迁在吸收光谱中会体现出来.布居分析表明,ZrB2中原子间的电荷转移类似于MgB2,Zr4d的电子向B2pz转移.zrB2声子态密度表明,B原子对高频部分贡献最大.温度为0 K时,ZrB2的德拜温度为59.14.     

高压高温条件下铍弹性性能数值模拟

基于密度泛函理论(DFT)的平面波赝势方法对密排六方结构(hcp)铍(α-Be)的弹性性能进行了第一性原理计算研究。利用Material Studio软件的CASTEP模块并采用广义梯度近似(GGA)完成计算。分别得到了铍单晶体的弹性常数,铍多晶体的体积模量、剪切模量、杨氏模量、泊松比等参数对外加静水压变化(0~100 GPa)和对环境温度(0~1300 K)变化的变化规律。还利用第一性原理数值模拟方法对体心立方结构(bcc)的铍(β-Be)的弹性性能进行了计算。计算结果与文献实验数据符合度高。结果显示:各弹性参数值随压力的增长而单调增加,升温过程的影响作用则相反;描述铍晶体变形耦合性的C_(12)和C_(13)对压力或温度变化比其他弹性参数更为敏感;加压过程使铍晶格结构参数c/a值增加并趋向理想密排值,而在温升过程中这个值则持续降低;加压过程是一个原子密堆度提高的过程,据此对铍高压hcp-fcc(面心立方结构)相变的可能性和实现形式进行了讨论。     

铂铑合金系基本力学性能的第一性原理研究

采用密度泛函理论和虚晶近似方法对铂铑合金系的结构和力学性能进行计算。给出了常用低Rh含量和鲜有相关研究报道的高Rh含量合金的晶格常数、弹性系数和体积模量(B)等。通过晶格常数计算了不同合金的密度,与实测结果基本一致。通过弹性系数和力学稳定性判据发现该合金系结构是稳定的。计算的合金杨氏模量(E),剪切模量(G)与实验结果接近。随Rh含量的增加,G,E均增加,但B,G/B和泊松比均减小。通过分析确定随Rh含量的增加,合金的拉伸曲线变陡,延伸率变小,塑性变形难度增加。基于位错应变能的计算结果,发现随着Rh含量的增加位错应变能也增加,但Rh含量低于40%(质量分数)时增速较快,高于40%后变缓,该关系与实测的Rh含量与硬度、抗拉强度的关系一致。通过判定材料塑脆转变的G/B比值与Rh含量的关系,发现以Rh含量为40%为界,小于该值时Rh含量增加比值下降迅速,说明合金脆性增加较快,高于40%后比值减小变缓,表明合金脆性增加变缓。综合分析后认为随Rh含量增加铂铑合金的变形抗力增加、延伸率下降,脆性增加,导致合金塑性加工难度增大,但该变化速度为先快后慢,大致以Rh含量等于40%为界。对于低Rh含量的铂铑合金可以进行大变形量冷加工,而高Rh含量的铂铑合金只有通过提高温度,从而降低材料的G和E值才能进行一定的塑性加工。     

碳原子在钴粘结相中的扩散系数

对硬质合金渗碳时碳原子在粘结相钴中的扩散系数进行了研究,假定C与O、N等非金属扩散原子在液态金属中的扩散具有相似之处,导出了一个求算碳原子在液态金属钴中的扩散系数方程式(DAB=Do(dB/dA)exp[-0.17Tm(16 Ko)/T]).式中:Do为液态金属自扩散ARRHENIUS方程的频率因子,dB和dA分别为溶剂金属原子和扩散原子的直径,Tm为金属的熔点温度,K0为溶剂金属原子的价态,T为扩散温度.)该方程适用于碳及其它非金属扩散原子在液态金属中的扩散系数计算,经与实测结果对比,证明其计算结果与实测结果具有较好的一致性.     

微合金化对双相中熵合金组织与力学性能影响研究

采用水冷铜坩埚磁悬浮熔炼和铜模负压吸铸法制备了(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_100-xCu_x,(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_100-xAg_x以及(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_100-2xCu_xAg_x (x=0,0.5,1,1.5和2;原子分数)3种中熵合金体系,探究了通过添加正的混合焓元素Cu,Ag合金化于面心立方(fcc)结构的中熵合金基体,调控组织制备了双相fcc的新型中熵合金,并采用Olson-Cohen热力学模型计算fcc中熵合金的层错能...     

RECrO3电子结构与导电性能的关系

利用量子化学的SCF-Xα-SW电子结构计算方法,计算得到了RE₄Cr₂O₉(RE=La,Pr, Nd,Sm,Gd,Dy,Ho,Er)等体系的电子态密度分布、费米能和能隙宽度等电子结构参数,并结合 RECrO₃导电陶瓷的导电特征,分析了导电性能和电子结构参数之间的关系.研究表明:随着RE原子序数的增加,其费米能附近的态密度依次增大,主要为f电子,非f电子数量逐渐减少,因此,参与导电的电子应与f电子无关.这是RECrO₃导电陶瓷电导率随RE原子序数增大而下降的主要原因.     

Local atomic structure evolution of liquid gadolinium and yttrium during solidification:An ab initio study

Local atomic structure evolution of pure gadolinium(Gd) and yttrium(Y) during solidification was investigated by using ab initio molecular dynamics(AIMD) simulation.The calculated results indicate that the local short-range order(SRO) in liquid Gd and Y is similar to some transitional metals with an asymmetric shape of the second peak in static structure factors.Moreover,the formation of icosahedral local motifs as a function of temperature decreases the diffusivity,which explains the connection...     

Electronic structure of the SrAl2O4：Eu^2＋ persistent luminescence material

The electronic structure of the strontium aluminate (SrAl₂O₄:Eu²⁺) materials was studied with a combined experimental and theoretical approach. The UV-VUV synchrotron radiation was applied in the experimental study while the electronic structure of the non-optimized and optimized crystal structure were investigated theoretically by using the density functional theory. The structure of the valence and conduction bands as well as the band gap energy of the material together with the position of the Eu²⁺ 4f^{7 8}S_7/2 ground state were calculated. The calculated band gap energy (6.4 eV) agreed well with the experimental value of 6.6 eV. The valence band consisted mainly of oxygen states whereas the bottom of the conduction band of strontium states. In agreement with the experimental results, the calculated 4f^{7 8}S_7/2 ground state of Eu²⁺ lies in the energy gap of the host. The position of the 4f⁷ ground state depended on the Coulomb repulsion strength. The position of the 4f⁷ ground state with respect to the valence and conduction bands was discussed using theoretical and experimental evidence available.     

Structure and Magnetic Properties of HoFe_(12-x) Mn_x Compounds

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Magnetic Properties of Ga Doped Nd-Fe-B Sintered Magnets

The magnetic properties of Nd_(16)Fe_(77)B_7 and Nd_(16)Fe_((61-x))Co_(16)Ga_xB_7(x=0,1,2,4,7)have been measured.Itis found that the remanent magnetization(Br),maximum energy product(BH)_(max)and the Curie temperature(T_c)decrease with the increase of Ga content.The coercive force(He)increases with the increase of Ga contentwhen x is less than 2,but decreases when x>2.At x=2,the coercive force reaches its maximum value.It is alsofound in all the samples investigated that there is a linear relationship between H_c~(1/2)and T~(2/3),which can not beexplained by Gaunt's wall barrier model.The temperature dependence of the calculated values of H_v and(4bf)has been discussed.     

Temperature sensing behavior of Tm~(3+):~1G_4(a),~1G_4(b) in oxyfluoride glass ceramics containing BaYb_xY_(1-x)F_5 nanocrystals

Tm~(3+)-doped transparent oxyfluoride glass ceramics containing BaYb_xY((1-x))F_5 nanocrystals were prepared via high temperature solid phase melting method,of which up-conversion emission is achieved by the Yb~(3+)-mediated energy transfer process.The required photon number of Tm~(3+)ions emissions in BaYb_xY_((1-x))F_5 nanocrystals was calculated through the luminescence spectra,revealing the strong dependence of energy transfer mechanism on Yb~(3+)ions concentration.Meanwhile,based on the fluore scence intensity ratio technology,the effect of different energy transfer mechanism on the temperature sensitivity was investigated by the temperature-dependent luminescence intensity of thermally coupled energy levels of Tm~(3+):~1G_4(a),~1G_4(b).The obtained sensitivity decreases with the increase of Yb~(3+)ions content,which is mainly attributed to the changes in photon absorption process of Tm~(3+):~1G_4(b).     

Effect of Rolling Process on Microstructure and Properties of 95CrMo Drill Steel

In order to improve the strength and toughness of 95CrMo steel and explore a short flow process,a direct rolling process was employed,and the effect of finishing rolling process on microstructure and mechanical properties was investigated.The results show that,with the decrease of finishing rolling temperature,inter-lamellar spacing in-creases,the strength as well as hardness has a general increase,and secondary cementite is distributed uniformly but represents a remarkable decrease in size.Based on Hall-Petch type equation,an effective relationship of yield strength and pearlite structure parameters was established.The correlation coefficients between the measured and calculated strength were more than 0.9 5 ,which indicated a high reliability of the relationship.By analyzing the indi-vidual strength contributions of pearlite structures,yield strength was found to have a more great dependence on pearlite inter-lamellar spacing than colony size.     

含钡二元合金熔体热力学性质的计算

根据Miedema二元合金生成热模型，结合相关热力学数据，对Si-Ca二元合金熔体在1623K时的组元活度进行了计算，计算结果与实测结果吻合较好。并进一步对Ba-Si、Ba-Al和Ba-Ca3种二元含钡合金熔体的生成热△H及1873K时的过剩熵S^E、过剩自由能G^E以及不同温度下各组元的活度等热力学性质进行了计算。结果表明：3种合金的△H、S^E和G^E均为负值，且S^E绝对值的最大值为4．424J／mol，可以近似认为3种合金熔体的S^E为零；Ba-Si和Ba-Al合金熔体的活度相对于理想溶液存在较大负偏差，而Ba-Ca合金熔体的活度与理想溶液偏差较小。     

Thermochemical Properties of Ternary Complexes of RE Perchlorate withGlycine and Imidazole

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