Influence of Fe3+ on perovskite oxides: La2/3Ca1/3Mn1-x Fe x O3

The structure and magnetoresistance properties in sintered samples of La_2/3Ca_1/3Mn_1-x Fe _x O₃(0≤x≤0.84) are studied by using Mössbauer spectroscopy, XRD and magnetic measurement. There are antiferromagnetic interactions between Fe and its nearest neighbors (Fe, Mn) when 0 <x ≤0.67, which are important factors influencing the double-exchange between Mn³⁺ and Mn⁴⁺, Curie temperature, magnetic moment and GMR. It is suggested that the Mn³⁺ (Fe³⁺) /Mn⁴⁺ system also consists of magnetic clusters with different sizes.     

Relativistic RPA and Giant Resonances in β Stable and Unstable Nuclei

The nuclear isoscalar and isovector giant resonances in stable and unstable nuclei are studied in the framework of the relativistic random phase approximation. The classical meson propagators with nonlinear self-interactions are constructed in momentum space from the second variation of the action. The relativistic models with the parameter sets, TMI and NLSH, which provide good account of static ground state properties, can also well describe the collective states of nuclei, such as giant resonances. The isovector giant dipole resonances in the unstable Ar isotope chain are investigated.     

钛酸锶(SrTiO3)低温时的自发极化

对自由能取极小可得到一系列方程,原则上可以确定任意系统相变时的行为.在105K SrTiO3发生立方一四方的反铁畸变,考虑量子效应,从吉布斯自由能形式出发,计算了介电常数,并讨论低温时的居里一外斯行为.     

A new approach to the giant component problem

We study the largest component of a random (multi)graph on n vertices with a given degree sequence. We let n → ∞. Then, under some regularity conditions on the degree sequences, we give conditions on the asymptotic shape of the degree sequence that imply that with high probability all the components are small, and other conditions that imply that with high probability there is a giant component and the sizes of its vertex and edge sets satisfy a law of large numbers; under suitable assumptions these are the only two possibilities. In particular, we recover the results by Molloy and Reed on the size of the largest component in a random graph with a given degree sequence. We further obtain a new sharp result for the giant component just above the threshold, generalizing the case of G(n,p) with np = 1 + ω(n)n^?1/3, where ω(n) → ∞ arbitrarily slowly. Our method is based on the properties of empirical distributions of independent random variables, and leads to simple proofs. © 2008 Wiley Periodicals, Inc. Random Struct. Alg., 2009     

X-ray and dielectric characterization of Co doped tetragonal BaTiO3 ceramics

ABSTRACT

The crystal structure modifications of BaTiO₃ induced by cobalt doping were studied. The polycrystalline (1 ? x)BaTiO₃ + xCo₂O₃ samples, with x ≤ 10 wt.%, were prepared by high temperature sintering conventional method. According to X-ray phase and structural characterization, performed by full-profile Rietveld refinement technique, all synthesized samples showed tetragonal symmetry perovskite structure with minor amount of parasitic phases. Pure single-phase composition has been detected only in the low level of doping BaTiO₃. It was indicated that substitution of Co for the Ti sites in the (1 ? x)BaTiO₃ + xCo₂O₃ series led to decrease of tetragonality (c/a) of the BaTiO₃ perovskite structure. This effect almost vanished in the (1 ? x)BaTiO₃ + xCo₂O₃ samples with nominal Co content higher than ～1 wt.%, in which precipitation of parasitic Co-containing phases CoO and Co₂TiO₄ has been observed. Based on the results, the solubility limit of Co in Ti sub-lattice in the (1 ? x)BaTiO₃ + xCo₂O₃ series is estimated as x = 0.75 wt.%.     

Characterization and coordination of intercalation - Non-intercalation phase transition in a new hybrid halide perovskite (n-C16H33NH3)2 ZnCl4

The ac conductivity σ(ω,T) and the complex dielectric permittivity ε^•(ω,T) as function of temperature 100 K < T < 400 K and frequency in the range 1 kHz ≤ f ≤ 100 kHz, as well as some thermal characterizations, namely the differential scanning calorimetry (DSC) and the differential thermal analysis (DTA) thermograms, were, measured and presented for polycrystalline virgin samples of the titled compound. It is one member of the long-chain of Zn hybrids of the series (n-C_nH_2n+1NH₃)₂ZnCl₄ (n = 8–18) and hence it belongs to the class of thermal energy storage materials.Our data evidenced that the hybrid undergoes a first order solid-solid structural phase transition from an intercalation to a non-intercalation at ≈373 K which is associated with an increase in the interlayer spacing “d” by 19.3%. In the room temperature phase, the hybrid is intercalated and tends to crystallize in an isolated square tetrahedra of zero-dimensional (0D) but arranged in the crystal system in two-dimensional (2D) via the assisted charge hydrogen bonds NH…Cl. It is therefore highly packed and hence have a highly transition temperature, highly thermal energy storage compared with other hybrids of the same n but of different M. These novelties characteristics suggested that the hybrid is more suitable for solar energy research. The even-odd effect, which is only common for Zn and Co in the room temperature phase and absent for other compounds, as well as the mechanism of the phase change have been discussed. The role of the coordination of the divalent metal ion and the dimensionality of the isolated unit (MCl₄)⁻² (M = Zn and/or Co) are considered. Comparison of the current phase transition with that of Zn compounds (n = 8, 10, 12, and 14) has been given.     

Asymmetric shock heating and the terrestrial magma ocean origin of the Moon

One of the difficulties of the current giant impact model for the origin of the Moon is to explain the marked similarity in the isotopic compositions and the substantial differences in the major element chemistry. Physics of shock heating is analyzed to show that the degree of heating is asymmetric between the impactor and the target, if the target (the proto-Earth) had a magma-ocean but the impactor did not. The magma ocean is heated much more than the solid impactor and the vapor-rich jets come mainly from the magma-ocean from which the Moon might have been formed. In this scenario, the similarity and differences in the composition between the Moon and Earth would be explained as a natural consequence of a collision in the later stage of planetary formation. Including the asymmetry in shock heating is the first step toward explaining the chemical composition of the Moon.     

Excess permittivity and excess conductivity of binary fluid mixture isobutyric acid – water along the coexistence curve

Excess permittivity and excess conductivity of the binary fluid mixture isobutyric acid–water (I–W) have been computed at three temperatures and along the coexistence curve, on the basis of refractive index and electrical conductivity data of the mixture. The other related properties, molar volume, molar refraction and polarisablities have also been reported. The temperature dependence of the molar refraction was also examined. The results have been interpreted in terms of the nature of specific intermolecular interactions between the components.     

Giant Vortex States in a Long Superconducting Cylinder with a Hole in Center

We have theoretically studied the nucleation of superconductivity in doubly connected superconductors in the form of long superconducting cylinders. The giant vortex states are investigated with the nonlinear Ginzburg-Landau theory. The solutions of Ginzburg-Landau equations are solved numerically with relaxation method. The quantum size effect is clearly shown through the calculation of free energy.     

Dependence of the Amplification of Giant Raman Scattering and Fluorescence on the Distance between an Adsorbed Molecule and a Metal Surface

We have studied the effect of the long-range amplification of secondary radiation of the molecules of oxazine 1 adsorbed on the surface of thin silver film covered by 1–7 Langmuir monolayers of stearic acid. We show that the intensity of the giant Raman scattering (GRS) changes proportionally to r ^–1 with removal of a molecule from the surface of a metal, which is in good agreement with the theory. The distances over which the strength of the electric field enhanced by the surface makes a substantial contribution to the processes mentioned are of the order of 10 nm.