Cr3+∶MgAl2O4晶体的基态能级分裂及Jahn-Teller效应*

构造了3d3/3d7离子在三角对称晶场中考虑自旋-轨道相互作用,自旋-自旋相互作用和自旋-其它轨道相互作用的120阶微扰哈密顿矩阵.利用完全对角化该矩阵的方法计算了Cr3+∶MgAl2O4晶体的基态能级、零场分裂参量,理论计算值与实验值相符合.定量研究了自旋二重态对基态能级的贡献,证明该贡献是不可忽略的.定量研究了自旋-轨道相互作用、自旋-自旋相互作用和自旋-其它轨道相互作用对Cr3+∶MgAl2O4晶体的光谱精细结构和零场分裂参量的影响,发现自旋-轨道和自旋-自旋相互作用对基态能级和零场分裂参量的影响的程度和方式是不同的,自旋-其它轨道相互作用的影响也是不可忽略的.通过理论计算值和实验值的比较,证实了在Cr3+∶MgAl2O4晶体中Jahn-Teller效应的存在,解释了该晶体的光谱精细结构的成因.     

Structural Insights into Hysteretic Spin-Crossover in a Set of Iron(II)-2,6-bis(1H-Pyrazol-1-yl)Pyridine) Complexes

Bistable spin-crossover (SCO) complexes that undergo abrupt and hysteretic (ΔT_1/2) spin-state switching are desirable for molecule-based switching and memory applications. In this study, we report on structural facets governing hysteretic SCO in a set of iron(II)-2,6-bis(1H-pyrazol-1-yl)pyridine) (bpp) complexes – [Fe(bpp−COOEt)₂](X)₂ ⋅ CH₃NO₂ (X=ClO₄, 1 ; X=BF₄, 2 ). Stable spin-state switching – T_1/2=288 K; ΔT_1/2=62 K – is observed for 1 , whereas 2 undergoes above-room-temperature lattice-solvent content-dependent SCO – T_1/2=331 K; ΔT_1/2=43 K. Variable-temperature single-crystal X-ray diffraction studies of the complexes revealed pronounced molecular reorganizations – from the Jahn-Teller-distorted HS state to the less distorted LS state – and conformation switching of the ethyl group of the COOEt substituent upon SCO. Consequently, we propose that the large structural reorganizations rendered SCO hysteretic in 1 and 2 . Such insights shedding light on the molecular origin of thermal hysteresis might enable the design of technologically relevant molecule-based switching and memory elements.     

Tuning charge and orbital ordering in DyNiO3 by biaxial strain

The first-principles calculations were used to explore the tunable electronic structure in DyNiO₃ (DNO) under the effects of the biaxial compressive and tensile strains. We explored how the biaxial strain tunes the orbital hybridization and influences the charge and orbital ordering states. We found that breathing mode and Jahn-Teller distortion play a primary role in charge ordering state and orbital ordering state, respectively. Additionally, the calculated results revealed that the biaxial strain has the ability to manipulate the phase competition between the two states. A phase transition point has been found under tensile train. If the biaxial train is larger than the point, the system favors orbital ordering state. If the strain is smaller than the point, the system is in charge ordering state favorably.     

C78n离子的Jahn-Teller畸变和电子光谱

用INDO系列方法对C78n(D3、D3h、D?h)进行系统研究,表明C78(D3)比C78(D3h、D?h)稳定,与理论计算及实验结果一致;且随n绝对值增大,C78n总能量升高;C78n(D3、D3h、D?h)异构体的部分离子发生了Jahn-Teller畸变.以优化构型为基础,用INDO/SCI方法首次计算了C78n的电子光谱,对电子跃迁进行理论指认,讨论C78n光谱的特征吸收与C78相比发生红移的原因.     

二元低价铟溴化合物结构不稳定的从头算研究

应用较大基组的从头算法,以八配位立方构型多面体为例,研究了二元低价铟溴化合物不稳定性的微观结构原因,分析了构型的势能曲线状况和分子轨道性质．结果表明, 高对称的八配位立方构型多面体势能曲线异常平缓且分布各向异性,中心力场很弱,导致构型极易在外界因素的影响下发生变化．二元低价铟溴化合物具有无机固态化合物中少见的二阶Ｊａｈｎ－ Ｔｅｌｌｅｒ 效应     

Variation of 2 D Hydrogen Bond Topology in Diaqua-tetrafluoromanganates(III): 2-picoH[MnF4(H2O)2], TMEDAH2[MnF4(H2O)2]2, and TMBDAH2[MnF4(H2O)2]2

The crystal structures of three new diaqua-tetrafluoro-manganate(III) compounds with different organic N-cations have been determined: 2-picoH[MnF₄(H₂O)₂] 1 (2-pico = 2-methyl-pyridine), space group P2₁/c, a = 9.439, b = 13.662, c = 7.641 Å, β = 91.31°; R = 0.059; TMEDAH₂[MnF₄(H₂O)₂]₂ 2 (TMEDA = N,N,N′,N′-tetramethyl ethane diamine), space group P2₁/c, a = 5.421, b = 15.970, c = 9.677 Å, β = 96.37°, R = 0.031, and TMBDAH₂[MnF₄(H₂O)₂]₂ 3 (TMBDA = N,N,N′,N′-tetramethyl-1,4-butane-diamine), space group P2₁/n, a = 12.631, b = 5.577, c = 12.976 Å, β = 98.10°, R = 0.040. All three compounds show 2 D H-bonding networks of [MnF₄(H₂O)₂]^– anions separated by the organic cations. However, the topology of the anionic H-bonding nets is different for each compound. The anions are strongly elongated by the Jahn-Teller effect and are arranged in a ferrodistortive way in compounds 1 and 2 , whereas in compound 3 the arrangement is described as in a herringbone-like antiferrodistortive variant.     

亚微米去顶角八面体LiNi0.08Mn1.92O4正极材料制备及高温电化学性能

采用低温固相燃烧法快速制备了一种具有{111}、{110}和{100}晶面的去顶角八面体LiNi_0.08Mn_1.92O₄ (LNMO)正极材料, 其高暴露{111}晶面可以减少充放电过程中Mn的溶解, 面积相对较小的{110}和{100}晶面可增加Li⁺快速扩散的通道. 测试结果表明, 所合成的LNMO具有LiMn₂O₄特有的立方晶系结构, 其颗粒尺寸为亚微米级. LNMO的高温电化学性能优异, 在55 ℃, 1和5 C的首次放电比容量分别为109.9和98.0 mAh/g, 分别循环300次后容量保持率为75.8%和80.5%; 即使在55 ℃, 10和15 C下分别循环1000次后仍具有48.4%和49.4%的容量保持率, 而未掺杂的LiMn₂O₄于15 C循环1000次后容量损失高达98%. LNMO在55 ℃有较高的Li⁺扩散系数(D=3.86×10^-15 cm²/s)和较小的电荷转移阻抗(循环前、后R_ct=158.0和279.8 Ω)以及较低的表观活化能(E_a=17.63 kJ/mol), 说明Ni掺杂能够提高Li⁺在尖晶石型LiMn₂O₄内的扩散速率及减小锂离子在脱嵌过程中的能垒, 从而提高锂离子的扩散速率和倍率性能. 对LNMO于55 ℃循环1000次后的极片进行X射线衍射(XRD)分析, 发现LNMO电极材料的晶体结构基本保持不变, 表明Ni掺杂提高了锰酸锂材料在55 ℃长循环过程中的晶体结构稳定性, 有效抑制了Jahn-Teller效应及Mn的溶解, 显著提升了其高温电化学性能. 本工作为尖晶石LiMn₂O₄电极材料在高温方面的应用提供了借鉴.     

Nuclear spin conversion in CH F induced by an alternating electric field

The nuclear spin conversion in CH₃F molecules subjected to an alternating electric field was investigated experimentally. The conversion rate was found to be almost unaffected by low electric fields ( V/cm) but sharply increased tenfold when the electric field amplitude exceeds the values ( V/cm) sufficiently high to produce crossings of the ortho and para states of the molecule. A theoretical model for the molecular conversion in alternating electric field was developed. The results of the experiment were found to be in a good agreement with the theory. Received 23 July 1999 and Received in final form 7 September 1999     

Energy Spectrum and Its Pressure-Induced Shift and J-T Effect of ZnTe:Mn2+

By using strong-field scheme, the complete d⁵ energy matrix with symmetry has been constructed. Then, by diagonalization of this matrix at normal and various pressures,the whole energy spectrum [including the ground-state zero-field splitting (GSZFS)] and its pressure-induced shift (PS) of Znlb:Mn²⁺ have uniformly been calculated. The results are in very good agreement with experimental data. According to the eigenfimctions and PS, the assignments of four absorption bands have been given. By taking into account the dect of different deformations of t₂ and e radial wavefunctions on t₂³(⁴A₂)e²(³A₂)⁴ A₁ and t₂³(²E)e²(³A₂)⁴E, the position of the third absorption band at normal pressure has been estimated.The tetragonal field is important for GSZFS of ZnTe:Mn²⁺ and its PS, which supports the existence of tetragonal Jahn-Teller distortion in ZnTe:Mn²⁺ The physical essentials of typical levels, GSZFS and their PS have been revealed.     

Pd☎ Ions In NaCl Single Crystal: EPR and Optical Studies

EPR and optical absorption of Pd centres in as grown NaCl single crystal arc reported. The EPR spectra show that palladium forms the Pd^? centre with d_x2-y2 wave function in the ground state. This centre formation and the accompanying distortion give rise to a superhyperfine interaction of the Pd^? ion with the nuclei of the four Cl^? ligands in the plane perpendicular to the C₄ symmetry axis. The results of the fitting of axial spin Hamiltonian parameters to the experimentally observed spectra give the following values at 12K: g∥ =2.85, g ⊥ ? 2.15, A ∥29.8 × 10^?4cm^?1, A ⊥ = 5.9 7imes; 10^?4cm^?1. When the temperature increases, lines are getting broader, their amplitude decreases and a single line with g-value of g= 2.38 at g = 1/3(g∥ ?2g⊥) appears, which demonstrates the known Jahn-Teller behaviour of d⁹ ions EPR spectra.