Ultrasonic Study on Jahn-Teller Distortions in La1=3Sr2=3CoO3

The longitudinal ultrasonic velocity (Vl), attenuation (ffl), magnetization and resistivity of single phase polycrystalline La1=3Sr2=3CoO3 were measured as a function of temperature from 20 K to 300 K. The resistivity shows metallic behavior in the whole temperature range and a kink at 235 K was observed, which coincides with the ferromagnetic transition temperature (Tc). As the temperature cools down from Tc, the Vl softens conspicuously at beginning and reaches a minimum at 120 K. After that the Vl dramatically stiffens below 120 K accompanied by a wide attenuation peak. The analysis of the results suggests that these ultrasonic anomalies may correspond to local lattice distortions via the Jahn-Teller effect of intermediate spin Co3+.     

Single-Metal-Encapsulated Double-Cage [Pt@Sn17]4−: An Exception from Group 14 Endohedral Clusters

Group 14 endohedral clusters containing a metal center inside usually possess a single cage topological structure, but here an unexpected single-metal-filled double-cage cluster, [Pt@Sn₁₇]⁴⁻ ( 1 a ) is reported. It can be seen as a combination of the more extended Pt-filled [Pt@Sn₉] cage and hollow [Sn₉] cage sharing a central Sn atom, which is offset from the central position. This double-cage species represents the largest group 14 intermetalloid cluster encapsulating a single transition metal atom. DFT calculations show that the capsule-like architecture of [Sn₁₇]⁴⁻, similar to that found in [Pt₂@Sn₁₇]⁴⁻, is unstable if filled with a single Pt atom and collapses to the title cluster 1 a upon geometry optimization. Deviation of the central Sn atom occurs due to the vibronic coupling as a consequence of pseudo-Jahn-Teller distortion leading to the bent C_s-symmetrical structure, in contrast to the more symmetrical D_2d cage previously reported in [Ni₂@Sn₁₇]⁴⁻.     

Co2+:ZnAl2O4晶体电子光谱及其2E态双重谱线结构的Jahn-Teller效应研究

在中间场耦合图象中,利用Racak不可约张量算符法和Wigner－Eckart定理,建立了3d⁷(C_3v)电子组态的完全能量矩阵;利用该矩阵研究了Co²⁺:ZnAl₂O₄晶体的电子光谱,理论与观测十分吻合．首次定量地解释了2E态的双重谱线结构,并从理论上预言了⁴A₂基态2.93cm^-1的零场分裂(ZFS)．研究结果定量地表明,Jahn－Teller效应所致Co²⁺:ZnAl₂O₄晶体Co²⁺中心局域结构的畸变假设是合理的．     

Synthesis, structure, magnetic properties and structural distortion under high pressure of a new osmate, Sr2CuOsO6

A new osmate Sr₂CuOsO₆ was synthesized and its structure refined using powder synchrotron X-ray diffraction. The results of the Reitveld refinements indicate complete B-cation order in a double perovskite crystal structure. Furthermore, the analysis of the B-cation bond lengths indicates a symmetric coordination around Os, as opposed to a significant distortion of Cu-O bond lengths. The octahedral distortion around Cu(II) is characteristic of a Jahn-Teller distortion. Within the crystal structure of Sr₂CuOsO₆, the long Cu-O bonds are aligned in the same direction along the c-axis in the tetragonal unit cell. This parallel arrangement of long Cu-O bonds produces a lattice parameter ratio, c/(2^1/2a), that is greater than unity. The magnetic susceptibility of Sr₂CuOsO₆ was measured using a SQUID magnetometer and was observed to be consistent with an assignment of Cu(II)-Os(VI) formal oxidation states, thus confirming the bond valences calculated on the basis of the crystal structure. In perovskites, octahedral tilting and bond shortening are two competing compression mechanisms. Compression mechanisms of this double perovskite were characterized using high-pressure synchrotron X-ray diffraction. Application of hydrostatic pressure up to 6 GPa significantly decreased the lattice parameter ratio, demonstrating the primary compression mechanism is a shortening of the long Cu-O bond.     

Compression mechanisms of symmetric and Jahn-Teller distorted octahedra in double perovskites: A2CuWO6 (A=Sr, Ba), Sr2CoMoO6, and La2LiRuO6

Synchrotron X-ray powder diffraction was used to study the high pressure dependence of the lattice parameter and structural evolution of the monoclinic La₂LiRuO₆ and tetragonal Sr₂CoMoO₆, Sr₂CuWO₆, and Ba₂CuWO₆ double perovskite phases. The c lattice parameters of Sr₂CuWO₆ and Ba₂CuWO₆ decreased more rapidly than the a lattice parameters and Ba₂CuWO₆ exhibited a more anisotropic compression compared to Sr₂CuWO₆. Based on lower pressure refinements of Ba₂CuWO₆, the anisotropic compression is proposed to be due to the preferential compression of the Cu-O bonds containing cooperative Jahn-Teller distortions aligned parallel to the c-axis, which is in contrast to Sr₂CoMoO₆, where the change in the octahedral tilting and symmetric bond compression is the prevailing compression mechanism. The bulk moduli were obtained from a fit of the volume-pressure data using the second-order Murnaghan equation of state.     

Synthesis and electrochemical properties of nonstoichiometric LiAlxMn2−xO4−δ as cathode materials for rechargeable lithium ion battery

Nonstoichiometric spinel oxides, LiAl_xMn_2−xO_4−δ (x=0.1,0.2), were synthesized under controlled partial pressure of oxygen, and their elecrochemical performances were investigated. As an Al content increases, solubility limit of the oxygen nonstoichiometry, δ, increased, while partial molar enthalpy of the formation of oxygen nonstoichiometry decreased.Cycle performance of LiAl_xMn_2−xO₄ showed significant improvement comparing with that of LiMn₂O₄ cathode. However, the decrease of theoretical capacity was accompanied with Al doping. Nonstoichiometric LiAl_xMn_2−xO_4−δ showed the increase in capacity with keeping good cycle performances as well as stoichiometric LiAl_xMn_2−xO₄. Although the introduction of oxygen nonstoichiometry leads to the increase of Mn³⁺ which is known as Jahn-Teller ion, DSC curves for LiAl_xMn_2−xO_4−δ showed no exothermic peak due to phase transition arising from Jahn-Teller distortion around room temperature.     

A charge-stabilized Jahn-Teller Distortion of the Mixed Valence System NaBa2Cu3O6

The crystal structure of NaBa₂M₃O₆ contains an unusual hexagonal prism composed of linked MO₄ squares. This unit is distorted in the M = Cu compound but undistorted in the M = Ni material. Electronic structure calculations show an orbital degeneracy and electronic stabilization on distortion of the hexagonal prism at the electron count appropriate for the Cu compound. The preferred distortion is determined by considering how the nature of both the occupied and unoccupied metal d orbitals are consistent with the metal oxidation states set by the stoichiometry. The results provide added insights into the nature of mixed valence compounds. The synthesis of Na₂BaM₃O₆ is encouraged.     

Dynamical Jahn-Teller effect in the first excited

Jahn-Teller effect of C₆₀ monoanion in the first electronically excited states was theoretically investigated. The orbital vibronic coupling parameters for t_1g next lowest unoccupied molecular orbitals were derived from the Kohn-Sham orbital levels calculated using a frozen phonon approach with both hybrid B3LYP and CAM-B3LYP functionals, which take long-range interaction correction into consideration. With these coupling parameters, the vibronic states of first excited were derived by exactly diagonalizing dynamical Jahn-Teller Hamiltonian. The results showed that dynamical Jahn-Teller effects are more significant in the first excited than those in the ground electronic states. This work also clarified that CAM-B3LYP gives results closer to experimental data than B3LYP.     

Ein Fluoridphosphat von Mangan(III) mit ungewöhnlicher Schichtstruktur: Na7[Mn5F13(PO4)3(H2O)3]

A Fluoride Phosphate of Manganese(III) with Unusual Layer Structure: Na₇[Mn₅F₁₃(PO₄)₃(H₂O)₃] The title compound was crystallized from a solution of MnF₃ · 3 H₂O in aqueous HF by addition of NaH₂PO₄ · H₂O in 2 M phosphoric acid. The crystal structure has been determined at 295 and 150 K on a trigonal crystal twinned by merohedry: Space group P3c1, Z = 4, a = 1055,0(1), c = 2314,0(1) pm (a = 1052,5(1), c = 2304,2(1) pm at 150 K), wR₂ = 0.0651 (0.0651). The structure contains anionic layers formed by triangular moieties of three [MnF₃O₂(H₂O)] octahedra sharing one common μ₃-F atom and bridged by three phosphate groups. Three of those groups, respectively, are interconnected by two [MnF₃O₃] octahedra over six phosphate O-atoms to form a trigonal layer in the a,b plane. Stacking of these layers gives channels along the c axis in which most of the Na⁺ ions are located. The [MnF₃O₂(H₂O)] octahedra show strong elongation along the μ₃-F–Mn–OH₂ axis mainly due to the Jahn-Teller effect whereas in the [MnF₃O₃] octahedra with C₃ symmetry weak signs only of a dynamical Jahn-Teller-effect can be observed. The magnetic properties (μ_eff = 4.61 μ_B, 3-D ordering point T_N = 3.3 K) were determined on powders and possible magnetic exchange pathways are discussed.