O KVV Auger emission versus resonant photoemission at the O K edge of high-Tc superconductors

Photoelectron spectroscopy results on single crystals of the superconductors Bi₂Sr₂CaCu₂O₈,Bi₂Sr₂CuO₆, Ba_0.6K_0.4BiO₃ and the semiconductor Ba_0.9K_0.1BiO₃ are reported for the photon energy region around the O K absorption threshold. The development of the O-KVV Auger structure has been carefully monitored as a function of photon energy. A non-monotonic behavior displaying a feature at a constant binding energy of about 14 eV was found for Bi₂Sr₂CaCu₂O₈ and Bi₂Sr₂CuO₆ in a narrow photon energy region of 1 eV at the main edge of the O K absorption spectrum around 530 eV. The corresponding enhancement, connected with the autoionization of O 2p states, is absent in Ba_1−xK_xBiO ₃ in contrast to Bi₂Sr₂CaCu₂O₈ and Bi₂Sr₂CuO₆. The resonant enhancement is more pronounced for Bi₂Sr₂CuO₆ as compared to Bi₂Sr₂CaCu₂O₈, which can be explained by a lower charge carrier concentration in the former case, leading to a more localized nature of intermediate O 2p states. The model parameters Cu d–d and O p–p Coulomb interactions and the charge transfer energy Δ are estimated from the experiments.     

氢化氧化铝的同位素效应研究

在B3LYP/6-311++G(d,p)水平上预测了Al2O3H3分子的较低能量构型.其基态构型具有C s对称性,电子态为1A′.通过研究Al2O3M3和M2(M=H,D,T)的能量E、定容热容C V和熵S,用电子振动近似讨论了Al2O3+3/2M2→Al2O3M3反应的氢同位素效应,得到了Al2O3氢化的热力学函数?H0,?S0,?G0,及平衡压力与温度的关系.研究表明,氧化物Al2O3吸附氢(氘,氚)反应的同位素排代效应顺序为氚排代氘,氘排代氢,与钛等金属的同位素排代顺序相反.但排代效应都非常弱,且随着温度的增加趋于消失.     

非晶锂离子导体B2O3-Li2O-LiCl一Al2O3中VO2+的电子自旋共振

两种非晶锂离子导体B₂O₃-0.7Li₂O-0.7LiCl-xAl₂O₃-0.1V₂O₅(x=0.05和0.15)的电子自旋共振谱研究表明:(i)ESR线型是高斯型,证实V₂O₅添加量适当;(ii)超精细结构来源于VO²⁺络离子,具有四角对称性,属C_4v群。越精细耦合张量的平行分量平均值A_//=0.0175cm^-1,垂直分量A_⊥=0.0063cm^-1。由g_//(g_⊥)求出其基态²B_2g与第一激发态²E_g的能级间距△₁=2.46×10⁴ cm^-1,基态与第二激发态²B_1g的能级间距△₂=3.03×10⁴ cm^-1;(iii)变温实验证实:Al₂O₃组分较少(x=0.05)的非晶ESR强度比x=0.15的非晶高3倍至2倍,而Al₂O₃组分越多则ESR强度随温升下降越小。     

Interprétation de la susceptibilité magnétique de l'oxysulfure de samarium par un modèle de champ cristallin

The paramagnetic susceptibility of polycrystalline samarium oxysulfide has been measured between 3° and 300°K. The data are interpreted with an approximation to the crystal potential of the form

V_c = _JV₂⁰O₂⁰ + β_JV₄⁰O₄⁰ + β_JV₄³O₄³

and correction taking into account exchange is made. The energy levels and crystal fields parameters have been calculated. Fluorescence studies of Gd₂O₂S: Sm³⁺ and Y₂O₂S: Sm³⁺ have confirmed these results.     

A study on the nonstoichiometry of tin oxides by coulometric titration

In this investigation, nonstoichiometries and defect structures of tin oxides were studied between 694 and 990 K by coulometric titration using solid state electrolyte (YSZ) cells. The relationship between nonstoichiometry of the oxide (x) and equilibrium oxygen partial pressure (P_o2) was expressed by the proportionality: xP_O2^−1/6. An intermediate oxide phase, Sn₃O₄ between Sn and SnO₂ was observed in the temperature range of 696–732 K. The standard Gibbs energy of formation of Sn₃O₄ via the reaction; was found to be ΔG^o_Sn3O4 = −1163960+417.36 T (J/mol). The standard Gibbs energy change for the defect formation reaction in SnO_2−x was calculated to be ΔG^o_SnO2−x = 3.05×10⁵−38.97 T (J/mol)).     

A new family of magnetoelectric materials: A2M4O9(A = Ta, Nb; M = Mn, Co)

The existence of the magnetoelectric (ME) effect in the transition metal niobates and tantalates A₂M₄O₉(A = Ta, Nb; M = Mn, Co) has been confirmed by the observation of the electrically induced magnetic moment in these materials. Both parallel and prependicular ME susceptibilities were measured as a function of temperature in powder specimens. The transition temperatures were found to be 110 ±1 (Nb₂Mn₄O₉), 103 ±1 (Ta₂Mn₄O₉), 27.0 ±0.5 (Nb₂Co₄O₉), and 20.6 ±0.5°K (Ta₂Co₄O₉) from the ME measurements.     

Role of the interfacial state: a comparison of Co/Al2O3/NiFe and La0.7Ca0.3MnO3/Al2O3/La0.7Ca0.3MnO3 tunnel junctions

Two junctions of Co/Al₂O₃/NiFe (J₁) and La_0.7Ca_0.3MnO₃/Al₂O₃/La_0.7Ca_0.3MnO₃ (J₂) were prepared to compare their tunneling magnetoresistance (TMR) in consideration of interfacial state effects. The structural and transport properties of the layered samples were characterized by X-ray and magnetic measurements, showing indeed an interfacial state dependence. The influences such as from a CoO sublayer in J₁ and from interfacial coherence in J₂ were discussed. The largest TMR observed amounts to 16% (290 K) for J₁ and 65% (40 K) for J₂.     

NMR study of local hole distribution, spin fluctuation and superconductivity in Tl2Ba2Ca2Cu3O10

⁶³Cu, ¹⁷O and ²⁰⁵Tl NMR have been performed in the high-T_c superconductor Tl₂Ba₂Ca₂Cu₃O₁₀ whose T_c(max) is 127 K. The hole densities at Cu and oxygen sites in the CuO₂ plane have been extracted from the nuclear quadrupole frequency ν_Q. The striking feature is that the Cu holes are significantly transferred to oxygen site due to strong hybridization between Cu and oxygen. From an analysis of T₁ and T_2G, it has been found that the spectral weight of the spin fluctuation is transferred to higher energy compared to YBa₂Cu₃O₇, while the magnetic correlation length ξ does not differ much. Thus, it is suggested that the higher T_c is due to higher characteristic energy of spin fluctuations, i.e. the superconductivity is spin fluctuation mediated. The superconducting properties are consistently explained by a d-wave superconductivity model with a finite density of states (DOS) at the Fermi level. We show that the disorder of the Ca/TlO layer caused by the partial inter-substitution of Tl and Ca is responsible for the potential scattering to produce such a DOS. It is found that if such a potential scattering were absent, T_c would go up to 132 K which is quite close to the record T_c realized in the Hg based compound.     

Absorption cross sections for antiprotons on carbon, aluminum and copper at 485 and 597 MeV/c

Absorption cross sections for antiprotons on C, Al and Cu have been measured by a transmission method at 485 and 597 MeV/c. Nuclei are shown to be black to antiprotons at these momenta. Using the available data up to 280 GeV/c, the momentum dependence of the absorption cross sections is investigated. Empirically, a simple expression σ_abs = γ(p/p₀)^−β, with β and γ constants and p₀ = 1 GeV/c, gives a good account of the data in a remarkably wide momentum range, 0.5–280 GeV/c.     

Pressure-induced phase transition of B-type Y_2O_3

The synthesized monoclinic(B-type) phase of Y_2O_3 has been investigated by in situ angle-dispersive x-ray diffraction in a diamond anvil cell up to 44 GPa at room temperature. A phase transition occurs from monoclinic(B-type) to hexagonal(A-type) phase at 23.5 GPa and these two phases coexist even at the highest pressure. Parameters of isothermal equation of state are V_0= 69.0(1) ~3, K_0= 159(3) GPa, K_0= 4(fixed) for the B-type phase and V_0= 67.8(2) ~3, K_0= 156(3) GPa,K'_0= 4(fixed) for the A-type phase. The structural anisotropy increases with increasing pressure for both phases.     

Electrical properties of ZrO2-In2O3-Y2O3 and its application to a membrane for gas separation

Electrical properties of In₂O₃-doped yttria-stabilized zirconia (In-YSZ) were investigated. The solubility limit of In₂O₃ in YSZ (10 mol% Y₂O₃) is 17.5 mol%. The total conductivity depended on the concentration of In₂O₃. The activation energy of In-YSZ was higher than that of YSZ. From the oxygen partial pressure (P_o2) dependence of the total conductivity of In-YSZ, the electronic conductivity increased with increasing In₂O₃ concentration at low oxygen partial pressures and at high temperature. From the results, we discussed the applicability of In-YSZ to a membrane for hydrogen production from direct water splitting at high temperature.     

Influence of alkali metal superoxides on structure,electronic,and optical properties of Be_(12)O_(12) nanocage:Density functional theory study

The effect of alkali metal superoxides M_3O(M = Li,Na,K) on the electronic and optical properties of a Be_(12)O_(12) nanocage was studied by density functional theory(DFT) and time-dependent density functional theory(TD-DFT).The energy gaps(Eg) of all configurations were calculated.Generally,the adsorption of alkali metal superoxides on the Be_(12)O_(12) nanocage causes a decrease of Eg.Electric dipole moment μ,polarizability α,and static first hyperpolarizability β were calculated and it was shown that the adsorption of alkali metal superoxides on Be_(12)O_(12) increases its polarizability.It was found that the absorption of M_3 O on Be_(12)O_(12) nanocluster improves its nonlinear optical properties.The highest first hyperpolarizability(β≈ 214000 a.u.) is obtained in the K_3O–Be_(12)O_(12)nanocluster.The TD-DFT calculations were performed to investigate the origin of the first hyperpolarizabilities and it was shown that a higher first hyperpolarizability belongs to the structure that has a lower transition energy.     

Pseudo-billiards

A new class of Hamiltonian dynamical systems with two degrees of freedom and kinetic energy of the form T = c₁|p₁| + c₂|p₂| (called “pseudo-billiards”) is studied. For any kind of interaction, the canonical equations can always be integrated on sequential time intervals; i.e. in principle all the trajectories can be found explicitly.

Depending on the potential, a dynamical system of this class can either be completely integrable or behave just as a usual non-integrable Hamiltonian system with two degrees of freedom: in its phase space there exist invariant tori, stochastic layers, domains of global chaos, etc. Pseudo-billiard models of both the types are considered.

If a potential of a pseudo-billiard system has critical points (equilibria), then trajectories close to these points (“loops”) can exist; they can be treated as images of self-localized objects with finite duration. Such a model (with quartic potential) is also studied.     

Synthesis and electrophysical properties of novel lithium ion conducting oxides

Novel lithium ion conducting oxides with perovskite structure have been synthesized and studied. It has been found that the La_2/3−xLi_3xTiO₃ and La_2/3−xLi_3xNb₂O₆ compounds have a perovskite structure at 1/24 < x < 1/6 and 0 < x < 3/10, respectively. The results of investigating the electrical properties of both groups of perovskites indicate a high lithium ion conductivity.     

On the thermodynamics of LiBr·xH2O(x=0, 1/2, 1) and electrical conductivity of LiBr·xH2O(Al2O3) composites

The thermodynamics of the LiBr·xH₂O system have been studied using TGA and DSC. Therefrom evidence for the existence of the hemihydrate phase LiBr·1/2H₂O was obtained. Enthalpies of formation of the hemihydrate and monohydrate have been determined to be about -6213 cal/mol and -11303 cal/mol respectively. The electrical conductivity of anhydrous LiBr-γAl₂O₃ composites has shown that the presence of γ-Al₂O₃ particles results in enhanced electrical conduction over the temperature range from 298 to 833 K. Extension of the DSC studies to the LiI-Al₂O₃ composites containing moisture suggests the presence of the hemihydrate phase also; TGA results are however inconclusive for the LiI hemihydrate. The anomalous conductivity enhancements below 416 K, and the behavior in low moisture ambients are explained in terms of a metastable hemihydrate phase layer, at the LiX-Al₂O₃ interfaces.     

Nuclear magnetic resonance relaxometry of the normal heart: Relationship between collagen content and relaxation times of the four chambers

The use of nuclear magnetic resonance (NMR) relaxation time measurements for characterization of abnormal cardiac tissue depends upon knowledge of variations of relaxation times of normal myocardium and determinants of these variations. We calculated in vitro NMR T₁ and T₂ relaxation times of canine myocardium from the four cardiac chambers, and determined hydroxyproline concentration (as a measure of collagen) and percent water content of the samples. We found both water content and T₁ relaxation time of the right ventricle to be significantly greater than the left atrium (p < 0.05). T₂ relaxation time of the left ventricle was found to be shorter than each of the other three chambers (p < 0.05). There were significant correlations between the spin-lattice relaxation time and both percent water content (r = 0.58) and hydroxyproline concentration (r = 0.45). A significant correlation was also found between T₂ relaxation time and hydroxyproline concentration (r = 0.49). When T₁ and T₂ were adjusted for water and hydroxyproline content, there was no longer any evidence for significant interchamber differences for either T₁ or T₂. These data suggest that differences in NMR relaxation times exist among the four chambers of the normal canine heart. Furthermore, a major determinant of myocardial spin-lattice relaxation time is tissue water content while both collagen content and percent water content significantly contribute to variability in cardiac chamber T₂ relaxation times.     

Fixed charge and interface traps at heterovalent interfaces between Si(1 0 0) and non-crystalline Al2O3–Ta2O5 alloys

Characterization by Auger electron spectroscopy (AES) and Fourier transformation infrared spectroscopy (FTIR) confirms (Ta₂O₅)_x(Al₂O₃)_1−x alloys are homogeneous pseudo-binary alloys with increased thermal stability with respect to end member oxides, Ta₂O₅ and Al₂O₃. Capacitance–voltage (C–V) and current density–voltage (J–V) data as a function of temperate show that the Ta d-states of the alloys act as localized electron traps, and are at an energy approximately equal to the conduction band offset of Ta₂O₅ with respect to Si.     

Auger parameters for sulfur-containing compounds using a mixed aluminum-silver excitation source

A mixed X-ray source (Al K-Ag L) has been used to obtain the precise Auger parameters (S2p_3/2-S KL₂₃L₂₃) for about sixty sulfur-containing compounds. A two-dimensional chemical state plot for the identification of the valence state of sulfur in a compound and of the specific sulfur-containing compound is presented.     

Structural modulation and physical properties of cobalt-doped layered La_2M_5As_3O_2(M=Cu,Ni) compounds

We investigate the structural variation and physical properties of layered La_2M_5As_3O_2(M=Cu,Ni) compound upon Co doping. It is found that the substitution of Co ion just induces the monotonous change of lattice constants without observing the anomalous kink in superconducting La_2(Cu~(1-x)Nix)_5 As_3O_2 solid-solutions. Meanwhile, this doping barely changes As–As bond length in [M_5As_3]~(2-) subunit(±2%), being significantly smaller than 7% shrinkage of that in La_2(Cu~(1-x)Nix)_5 As_3 O_2. Therefore, the doping dependence of crystal structure exhibits similar trend with Ba~(1-x)K_xFe_2 As_2 without the interference of As1–As 2 bonding, implying that the Co substitution for Cu/Ni is hole-doped. In terms of physical property, La2(Cu1-xCox)~5As_3O_2 turns into itinerant ferromagnetic metal, while La2(Ni1-x Cox)5 As3 O2 shows paramagnetism and suppressed structural phase transition upon Co-doping. The distinct structural variation and absence of superconductivity provide important clues to understand the effect of As–As bond in [M_5 As_3]~(2-) subunit.     

Phase equilibria at low oxygen partial pressure in the Y---Ba---Cu---O system

The phase equilibria around YBa₂Cu₃O_7−x (123) and YBa₂Cu₄O₈ (124) phases at low oxygen partial pressure (1 atm) were investigated by X-ray diffraction and thermal analysis. The coexistence of 123 and 124 phase was confirmed under 1 atm oxygen pressure. By using the high temperature X-ray diffraction method, the univariant reaction YBa₂Cu₃O_7−x+Cu₂OY₂BaCu₂O₂+O₂ was identified. The oxygen partial pressure dependence of several univariant reactions has been investigated and the existence of two invariant reactions of L+O₂YBa₂Cu₃O_7−x+ BaCuO₂+CuO+Cu₂O and L+Y₂BaCuO₅+O₂YBa₂Cu₃O_7−x+CuO+Cu₂O was deduced to occur at 1103 K under 0.0032 atm O₂ and at 1143 K under 0.0085 atm O₂, respectively.