Structures, stabilities, aromaticity, and electronic properties of C66 fullerene isomers, anions (C662?, C664?, C666?), and metallofullerenes (Sc2@C66)

Among all the 4478 classical isomers of C₆₆, C₆₆(C _s :0060) with the lowest number of pentagon–pentagon fusions was predicted to be the most stable isomer, followed by isomers C₆₆(C _2v :0011) and C₆₆(C ₂:0083). The infrared spectra and aromaticity of the most stable isomers were predicted. The relative stabilities of C₆₆ isomers change with charges or doping of metals. The structures and relative stabilities of the most stable metallofullerenes were delineated and compared with experiment. Sc₂@C₆₆(C ₂:0083) was predicted to be the most stable metallofullerene, although Sc₂@C₆₆(C _2v :0011) was observed. Charge-transfer from Sc₂ to the fused pentagons and the bonding between these two moieties significantly decrease the strain energies caused by the pair of fused pentagons thereby stabilizing the fullerene cage.     

Morphotropic phase boundary, weak ferromagnetism, and strong piezoelectric effect in Bi1 ? xCaxFeO3 ? x/2 compounds

The crystal structure and magnetic and piezoelectric properties of the Bi_{1 − x} Ca _x FeO_{3 − x/2} system (x ≤ 0.2) are studied. The crystal-structure transformations occur in the following sequence: rhombohedral (R3c) polar phase (x ≤ 0.06) → modulated polar phase (0.07 ≤ x ≤ 0.1) → modulated antipolar phase (0.11 ≤ x ≤ 0.14). The modulated polar and antipolar phases are weakly ferromagnetic with a spontaneous magnetization of 0.25 G cm³/g (x = 0.09). In the polar weak ferromagnet with x = 0.09, a uniform piezoelec- tric response 2.5 times stronger than in the initial BiFeO₃ compound is detected by the piezoelectric force microscopy.     

Effect of oxygen deficiency on the magnetic, electrical, magnetoelectric, and magnetoelastic properties of La1 ? x Sr x MnO3 ? δ manganites

This paper reports on a study of the effect of oxygen deficiency on the magnetic and electrical properties of the La_{1 − x} Sr _x MnO_{3 − δ} manganites (x = 0, 0.2, 0.4; δ = 0, 0.13, 0.2). In compositions with x = 0 and δ = 0.13 and 0.2, the temperature dependence of the magnetization M (T) can be approximated by the Langevin function with the moment of superparamagnetic clusters μ = 77μ_B (δ = 0.13) and 86μ_B (δ = 0.2) at temperatures of 25 K ≤ T ≤ 250 K, with the exception of a small temperature range near 132 K in which a maximum characteristic of the LaMnO₃ antiferromagnet is seen. These compositions, as well as Sr-doped compositions with δ ≠ 0, reveal a difference between the magnetizations of the sample cooled in a weak magnetic field and in zero field. At T = 6 K in a magnetic field of 16 kOe, the compositions with x = 0.2 and 0.4, δ = 0.13 possess a magnetic moment per formula unit lower than that with δ = 0, as well as reveal an anomalous relation between the Curie temperature T _C and the Curie paramagnetic point gJ, namely, T _C > gJ. The magnetization of compositions with x = 0.2 and 0.4, δ = 0.2 follows the Langevin function with μ = 40μ_B and 130μ_B, respectively. The electrical resistivity of samples with x = 0.4 and δ = 0.13 and 0.2 is one to two orders of magnitude larger than that of the composition with x = 0.4, δ = 0, which evidences partial or complete compensation of acceptor defects (Sr²⁺ ions) by donor defects (doubly charged O²⁻ vacancies). The above properties of oxygen-deficient compositions suggest that they contain an insulating ferro-antiferromagnetic magnetically double-phase state. The magnetoresistance and volume magnetostriction in samples with x = 0.4 and δ = 0, 0.13, and 0.2 are small; indeed, in a magnetic field of 8 kOe, they do not exceed 1.4% and 6 × 10⁻⁶, respectively. On this basis, it is concluded that the unbalanced doubly charged donors (O vacancies) are in the state with antiparallel spins and, thus, do not initiate the formation of ferron-type ferromagnetic clusters. The significance of both compensated and unbalanced doubly charged donors consists in that they give rise to the formation of fractured Mn-O-Mn bonds, which bring about lowering of the magnetic moment per formula unit in compositions with x = 0.2 and 0.4 and δ = 0.13 and the transition to superparamagnetism in compositions with x = 0.2 and 0.4, δ = 0.2. Original Russian Text ? L.I. Koroleva, D.M. Zashchirinskiĭ, T.M. Khapaeva, L.I. Gurskiĭ, N.A. Kalanda, V.M. Trukhan, R. Szymczak, B. Krzumanska, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 12, pp. 2201–2205.     

Sulfide compounds Me x Mn1 ? x S ( Me = Cr, Fe, V, Co): Technology, transport properties, and magnetic ordering

Electronic transitions of the metal-insulator type and magnetic transitions of the antiferromagnetic semiconductor-ferromagnetic metal type are established in cation-substituted manganese sulfides Me _x Mn_{1 − x} S (Me = Cr, Fe, V, Co), synthesized on the basis of MnS. The effect of negative colossal magnetoresistance is found and the regularities of change in the conductivity type and magnetic order are analyzed. Original Russian Text ? L.I. Ryabinkina, O.B. Romanova, S.S. Aplesnin, 2008, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2008, Vol. 72, No. 8, pp. 1115–1117.     

Power corrections in e+e?→π+π?,K+K? and B→Kπ,ππ

CLEO-c measurements of the timelike form factors F _π , F _K at ?s=3.671\sqrt{s}=3.671 GeV provide a direct probe of power corrections (PC’s) at energies near m _B . PC’s in F _π,K and B→Kπ,ππ are separated into perturbative and soft parts. In F _π,K the latter are ≥O(10) larger. A PC fit to the B→Kπ,ππ data also yields a ≥O(10) soft-to-perturbative hierarchy for the QCD penguin PC’s. Hence, both can be attributed to dominance of the soft-overlap between energetic (approximately) back-to-back collinear partons, and consistency of the B→Kπ,ππ fit with the Standard Model appears to be naturally realized. The CP asymmetries S_{Ks p⁰}S_{K_{s} \pi^{0}}, C_{Ks p⁰}C_{K_{s} \pi^{0}} are well determined, providing a clean test for new physics.     

Electrical conductivity and magnetic properties of La1 ? xCaxMn1 ? yFeyO3 ceramic samples (x = 0.67, y = 0, 0.05)

The temperature dependences of the magnetic susceptibility χ(T) and the electrical resistivity ρ(T) of ceramic samples of La_{1 − x} Ca _x MnO₃ with x = 0.67 (LCMO) and La_{1 − x} Ca _x Mn_{1 − y} Fe _y O₃ with x = 0.67 and y = 0.05 (LCMFO) are investigated in magnetic fields B = 50–10⁵ G and the temperature range T = 4.2–400 K. Both samples undergo a transition from the paramagnetic state to a state with charge (orbital) ordering (CO) at temperatures T _CO ≈ 272 K for LCMO and T _CO ≈ 222 K for LCMFO. The behavior of the paramagnetic phase in the temperature range 320–400 K for LCMO and 260–400 K for LCMFO is described by the Curie-Weiss law with effective Bohr magneton numbers p _eff = 4.83 μ_B (LCMO) and 4.77 μ_B (LCMFO), respectively. The disagreement between the observed positive Weiss temperatures (θ ≈ 175 K (LCMO) and θ ≈ 134 K (LCMFO)) and negative Weiss temperatures required for the antiferromagnetic ground state can be explained by the phase separation and transition to the charge-ordered state. The magnetic irreversibility for T < T _CO is accounted for by the existence of a mixture of the ferromagnetic and antiferromagnetic phases, as well as the cluster glass phase. At low temperatures, doping with iron enhances the frustration of the system, which manifests itself in a more regular behavior of the decay rate of the remanent magnetization with time. The temperature dependence of the electrical resistivity in the range of the charge-ordered phase conforms to the variable-range hopping model. The behavior of the electrical resistivity is governed by the complex structure of the density of localized states near the Fermi level, which includes a soft Coulomb gap Δ = 0.464 eV for LCMO and 0.446 eV for LCMFO. It is established that the ratio between the localization radii of charge carriers a for LCMFO and a _und for LCMO is a/a _und = 0.88. Original Russian Text ? V.S. Zakhvalinskiĭ, R. Laiho, T.S. Orlova, A.V. Khokhulin, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 1, pp. 61–68.     

Structure, phase transitions, 55Mn NMR, and magnetoresistive properties of La0.6Sr0.2Mn1.2 ? yCryO3 ± δ

The structure and properties of lanthanum strontium manganite perovskites La_0.6Sr_0.2Mn_{1.2 − y} Cr _y O_{3 ± δ} (y = 0–0.3) sintered at 1430°C have been studied by X-ray, resistive, and magnetic (χ_ac and ⁵⁵Mn NMR) methods. The parameter of the rhombohedrally distorted (R $ \bar 3 $ \bar 3 c) perovskite structure decreases with increasing y. The real perovskite structure contains point (anion and cation vacancies) and cluster-type nanostructure defects. The analysis of asymmetrically broadened ⁵⁵Mn NMR spectra has confirmed the high-frequency electron-hole exchange Mn³⁺ ↔ Mn⁴⁺ and local inhomogeneity of their surrounding by other ions and point and cluster-type defects. An increase in the Cr content leads to an increase in the resistivity and the magnetoresistive effect and a decrease in the metal-semiconductor and ferromagnetic-paramagnetic phase transition temperatures (T _ms and T _c ) due to the distortion of the exchange interactions Mn³⁺ ↔ Mn⁴⁺ by chromium ions, vacancies, and clusters. Introduction of Cr decreases the ferromagnetic component and increases the activation energy. The magnetoresistive effect near T _ms and T _c is caused by scattering of charge carriers from intercrystallite nanostructure inhomogeneities of the lattice, and the low-temperature effect is associated with the tunneling on mesostructural intercrystallite boundaries.     

Magnetic, magetostrictive properties, spin reorientation and M?ssbauer effect of Tb0.3Dy0.7?xPrx(Fe0.9Al0.1)1.95 alloys

The effect of Pr substitution for Dy on the magnetic and magnetostrictive properties, anisotropy, spin reorientation and M?ssbauer effect of a series of Tb_0.3Dy_0.7−x Pr _x (Fe_0.9Al_0.1)_1.95 (x=0, 0.1, 0.20, 0.25, 0.30, 0.35) alloys at room temperature have been investigated. It was found that a small amount of Pr substitution is beneficial to a decrease in the magnetocrystalline anisotropy for the Tb_0.3Dy_0.7−x Pr _x (Fe_0.9Al_0.1)_1.95 alloys. The magnetostriction decreases drastically with increasing x and the magnetostrictive effect disappears for x>0.2. However, the magnetostriction exhibits a slightly bigger value at x=0.1 than the free alloys and is saturated more easily with the magnetic field H. The saturation magnetization and Curie temperature decrease monotonously, but the spontaneous magnetostriction increases linearly with increasing x, whereas the spin reorientation temperature increases first, then decreases rapidly and reaches the maximum at x=0.1. The analysis of M?ssbauer spectra indicated that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry with the Pr concentration x, namely spin reorientation. Compared with Al substitution for Fe, the effect of Pr substitution for Dy on spin reorientation is relatively small. The hyperfine field increases with Pr concentration increasing, and the isomer shifts and the quadrupole splitting (QS) show weak concentration dependence. Supported by the National Natural Science Foundation of China (Grant No. 10574059), the Natural Science Foundation of Gansu Province (Grant No. 0710RJZA074), the Second Scientific Research Project of Bureau of Gansu Education and ‘Qing Lan’ Talent Engineering Funds of Lanzhou Jiaotong University     

Lithium ion transport in PVC/PEG 2000 blend polymer electrolytes complexed with LiX (X=ClO 4? , BF 4? , and CF3SO 3? )

This paper describes preparation and characterization of polyvinyl chloride and polyethylene glycol 2000 blend polymer electrolytes with LiX (X=ClO₄⁻, BF₄⁻, and CF₃SO₃⁻) salt by solution casting technique. Ethylene carbonate and propylene carbonate mixture was used as the plasticizers. LiClO₄-based electrolytes exhibited better ionic conduction behavior than other salts. The thermal profiles ascertain the stability of the membranes up to 120°C by differential scanning calorimetry. Complexation and crystallinity were studied through X-ray diffraction measurements. Phase morphological study reveals the porous nature of the polymer electrolyte membranes.     

Structure and M?ssbauer studies of manganese monosulfide solid solutions MxMn1 ? xS (M = Cr, Fe)

This paper reports on the results of the synthesis and study of the diffraction patterns and M?ssbauer spectra of single crystals of homogeneous M xMn_{1 − x} S solid solutions with a cubic NaCl structure prepared by the cation substitution of 3d elements for divalent manganese ions in manganese monosulfide. It has been shown that, similarly to the hydrostatic pressure, the substitution of 3d ions with a smaller ionic radius is accompanied by the contraction of the MnS cubic cell. The calculated lattice parameters agree with the experimental data. The homogeneous region of the formation of homogeneous solid solutions is limited in composition x, which depends on the choice of a substitutional cation.     

Study of B c → J / ψ π , η c π decays with?perturbative?QCD?approach

The B _c →J/ψ π, η _c π decays are studied with the perturbative QCD approach. It is found that the form factors and for the B _c →J/ψ, η _c transitions and the branching ratios are sensitive to the parameters ω, v, f _J/ψ and , where ω and v are the parameters of the charmonium wave functions for a Coulomb potential and the harmonic-oscillator potential, respectively, and f _J/ψ and are the decay constants of the J/ψ and η _c mesons, respectively. The large branching ratios and the clear signals of the final states make the B _c →J/ψ π, η _c π decays the prospective channels for measurements at the hadron colliders.     

57Fe and 119Sn probe M?ssbauer spectroscopy investigation of perovskite-type double manganite family CaCuxMn7?xO12 (x = 0, 0.15, 3)

CaCu _x Mn_7−x O₁₂ (x = 0, 0.15, 3) manganites were studied by ⁵⁷Fe and ¹¹⁹Sn probe M?ssbauer spectroscopy. It was established that the ⁵⁷Fe and ¹¹⁹Sn probe cations are stabilized in the octahedral positions of the manganite structures by substituting the manganese cations. The magnetic and structure phase transition temperatures of CaMn₇O₁₂ and CaCu_0.15Mn_6.85O₁₂ manganites fell upon the introduction of ⁵⁷Fe probe cations into their structures. It was concluded that intrasublattice Mn⁴⁺-O-Mn⁴⁺ exchange interactions play a noticeable role in the formation of the magnetic structure of CaCu₃Mn₄O₁₂ manganite.     

Structure, ferroelectric and piezoelectric properties of?(Bi0.98?xLa0.02Na1?x)0.5BaxTiO3 lead-free ceramics

Lead-free (Bi_0.98−x La_0.02Na_1−x )_0.5Ba _x TiO₃ ceramics have been prepared by an ordinary sintering technique and their structure, ferroelectric and piezoelectric properties have been studied. The results of X-ray diffraction show that La²⁺ and Ba²⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a new solid solution with a pure perovskite structure, and a morphotropic phase boundary (MPB) exists at 0.04<x<0.10. Compared with pure Bi_0.5Na_0.5TiO₃ ceramics, the (Bi_0.98−x La_0.02Na_1−x )_0.5Ba _x TiO₃ ceramics possess much smaller coercive field E _c and larger remanent polarization P _r. Because of the low E _c (3.38 kV/mm), large P _r (46.2 μC/cm²) and the formation of the MPB of rhombohedral and tetragonal phases, the piezoelectric properties of the ceramics are significantly enhanced at x=0.06: d ₃₃=181 pC/N and k _p=36.3%. The depolarization temperature T _d reaches a minimum value near the MPB. The ceramics exhibit relaxor characteristic, which is probably a result from the cation disordering in the 12-fold coordination sites. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics may contain both polar and non-polar regions at the temperatures above T _d.     

Synthesis of Eu x Si6? z Al z O z N8? z green phosphor and?its?luminescent properties

Rare-earth-doped oxynitride or nitride compounds have been reported to be photoluminescent and may then serve as new phosphors because of their good thermal and chemical stabilities. In this work, Eu²⁺-doped β-SiAlON phosphor with a composition of Eu _x Si_6−z Al _z O _z N_8−z (x=0.018, z=0.23) was prepared by gas-pressured solid state reaction. The crystallinity and particle morphology of the prepared phosphor were characterized. The Stokes shift and zero-phonon line were calculated mathematically and estimated from the spectral data. The temperature dependence of photoluminescence was measured from 25 to 250°C. The prepared Eu²⁺-doped β-SiAlON green phosphor showed superior thermal quenching property compared to silicate (SrBaSiO₄:Eu²⁺) green phosphor. The white light-emitting diode (LED) back-lighting unit (BLU) using the prepared β-SiAlON:Eu²⁺ green phosphor exhibited higher color gamut than a commercial silicate phosphor.     

New nonlinear optical crystals of the M1 ? xSc3 ? yYx + y(BO3)4 (M = Ce, Pr, or Nd) family

New Y_0.57M_0.72Sc_2.71(BO₃)₄ (M = Pr or Nd) nonlinear optical crystals of the huntite structural type with sp. gr. R32 were grown by the high-temperature solution-melt method. The analogous phase with cerium was prepared by solid-state synthesis. Lattice parameters were established by X-ray diffraction patterns of the powder.     

Manifestation of anomalous properties of HgTe lattice vibrations in Hg1 ? xZxTe (Z = Cd, Mn, Zn) alloys

Alloys (solid solutions) Hg_{1 − x} Z _x Te (Z = Cd, Mn, Zn) with a variation in their composition are characterized by the double-mode type of rearrangement of the vibrational spectrum of the crystal lattice, and these alloys retain the properties of lattice vibrations of the binary alloy components. The HgTe-enriched alloys under consideration also retain the anomalous properties of HgTe lattice vibrations with their additional low-frequency 105 cm⁻¹ mode, which is forbidden according to the symmetry selection rules. An analysis has been made of the specific features of the manifestation of the 105 cm⁻¹ mode in the alloys as compared to HgTe, in particular, its splitting into several modes ω _n (n = 0, 1, 2) due to the presence of two cations Hg and Z (Cd, Mn, Zn) in the cation sublattice. The thermal activation of the low-frequency 105 cm⁻¹ mode in the HgMnTe and HgZnTe alloys almost coincides with that observed in HgTe, but the activation energy of the mode for HgCdTe differs substantially from that for HgTe. Moreover, the conditions providing the activation of the 105 cm⁻¹ mode in the n-HgCdTe and p-HgCdTe alloys are different.     

Quantum-chemical features of Ln—O interatomic interactions in LnNbxOy (Ln=La, Ce, Pr, Nd, Pm, Sm, Eu) systems

Properties of the lanthanide—oxygen bonds in lanthanide niobates LnNb₇O₁₂(Ln=La, Ce, Pr, Nd, Pm, Sm, Eu) have been studied using the ab initio cluster X _α discrete variational method with two different basis sets of molecular orbitals. It has been found that the structural instability of lanthanides LnNb₇O₁₂ (Ln=Nd, Sm) observed in experiments is due to the combined effect of decrease in the stability of [LnO₈] cluster and increase in quantum-mechanical Ln—O repulsion when the minimum near neodymium (in the first model of the basis set of molecular orbitals) or praseodymium (in the second model of the basis set of molecular orbitals) atoms is passed.     

Study of high-temperature oxygen permeability in Sr1 ? xLaxCo0.8 ? yNbyFe0.2O3 ? z perovskites

The oxygen permeability of ceramic SrCo_{0.8 − y} Fe_0.2Nb _y O_{3 − z} (0 ≤ y ≤ 0.2) and La_0.3Sr_0.7Co_0.6Fe_0.2Nb_0.2O_{3 − z} disc membranes as a function of temperature and oxygen partial pressure was studied. Kinetic analysis was performed based on the experimental data on oxygen permeability as a function of oxygen partial pressure.     

碱金属Li,Na,K,Rb,Cs,Fr的ns2S1/2,np2P1/2,3/2, nd2D3/2,5/2 和nf2F5/2,7/2 里德伯能级理论研究

本文在多通道量子数亏损理论(MQDT)框架下,利用相对论多通道理论(RMCT),分别在冻结实近似、 考虑Δl=-1的偶极极化效应、Δl=+1的偶极极化效应、Δl=± 1的偶极极化效应、伸缩模效应以及同时考虑偶极极化效应和伸缩模效应等不同层次近似下,系统地计算了碱金属Li, Na, K, Rb, Cs和Fr七个里德伯系列的能级,即ns²S_1/2, np²P_1/2, np²P_3/2, nd²D_3/2, nd²D_5/2, nf²F_5/2 和nf²F_7/2.计算结果表明,电子关联效应对碱金属原子的里德伯能级的影响很大.总的来说,偶极极化效应比伸缩模效应重要,而在偶极极化效应中, Δl = + 1的偶极极化效应比Δl = - 1的偶极极化效应重要.但对于Na的ns²S_1/2,(nd²D_3/2,nd²D_5/2)里德伯系列的能级,和Li的(np²P_1/2,np²P_3/2)里德伯系列的能级,是伸缩模效应比较重要.