Thermodynamic properties of nonstoichiometric oxygen in manganite Ca<Subscript>0.9</Subscript>Pr<Subscript>0.1</Subscript>MnO<Subscript>3–δ</Subscript>

The chemical potential of oxygen Δμ_O relative to its standard state in the gas phase was calculated from the experimental dependences of the oxygen content in various polymorphic modifications of Ca_0.9Pr_0.1MnO_3–δ on the partial pressure and temperature. The partial molar enthalpy \(\Delta {\overline H _O}\) and entropy \(\Delta {\overline S _O}\) of oxygen were obtained from the linear temperature dependences of Δμ_O. Based on the ideal solution approximation, \(\Delta {\overline H _O}\) and \(\Delta {\overline S _O}\) were correlated with the enthalpies and entropies of the defect formation reactions, the concentrations of manganese cations, and the oxygen nonstoichiometry. The thermal excitation of Mn⁴⁺ cations was shown to substantially affect the thermodynamic functions of oxygen.     

Electronic and magnetic structures and conductivity of strontium ferrite: An ab initio LSDA + U approach

Using the first-principle nonempirical linear muffin-tin orbital method in the tight-binding approximation (TB-LMTO) to the LSDA + U approximation, the electronic and magnetic structures and defect formation in strontium ferrite Sr₃Fe₂O₆ are studied. It is found that Sr₃Fe₂O₆ is a G type antiferromagnetic with the semiconductor electronic structure. The calculated band gap of 1.82 eV agrees well with experimental value (～2 eV). The ferrite spectrum corresponds to that of a semiconductor with a band gap of charge transfer. Iron ions in Sr₃Fe₂O₆ are in a high-spin state and have configuration t _2g ^↑3 e _g ^↑2 e _g ^↓1 . The calculated local magnetic moment on the iron ions is 3.9 μ_B. The presence of iron ions with a magnetic moment approaching 4 μ_B in Sr₃Fe₂O₆ is explained by strong hybridization of 3d orbitals of iron and 2p orbitals of oxygen. The high-spin state of iron ions is described by d ⁵ + d ⁶ L states with predominant contribution d ⁶L, where L is a hole on oxygen. Based on ab initio LSDA + U calculations, various types and configurations of defects in the oxygen sublattice (oxygen vacancies, anti-Frenkel defects) are studied and a model for ionic transport in Sr₃Fe₂O₆ is proposed.     

Oxidation of primary alcohols to aldehydes with oxygen catalysed by tetra-n-propylammonium perruthenate

The liquid-phase oxidation of a series of saturated and unsaturated non-allylic alcohols to aldehydes with oxygen or air catalysed by tetra-n-propylammonium perruthenate (TPAP, represented as [(n-Pr)₄N]RuO₄) at 80–110 °C is shown to proceed with selectivities of 72–91% at 55–80% alcohol conversion. The unsaturated alcohols, such as 9-decenol, 9-octadecenol and β-citronellol, give the corresponding unsaturated aldehydes without competing double bond attack. The time course of oxidation indicates a complex reaction mechanism. The results on oxidation of a test alcohol, t-Bu(Ph)CHOH, suggest that one-electron processes do not play an important role in the TPAP-catalysed aerobic oxidation of alcohols.     

5-Acylmethyl-3-(2-pyridyl)-1,2,4-triazines: Synthesis and Complexes with Cu(II)

5-Acylmethyl-3-(2-pyridyl)-1,2,4-triazines are easily prepared from accessible 3-(2-pyridyl)-1,2,4-triazine 4-oxides by reaction of the latter with acetophenone or trifluoroacetone in the presence of NaH. The compounds obtained behaved as efficient ligands in reaction with CuCl₂ furnishing dimeric neutral complexes with Cu(II) whose structure was investigated by means of X-ray diffraction analysis.     

Alkylation of p-substituted phenols by heteropoly acids

Liquid-phase alkylation of p-tert-butylphenol (TBP) and p-cresol by olefins and benzyl chloride in the presence of solid heteropoly acids (HPA) H₃PW₁₂O₄₀ and 25% H₃PW₁₂O₄₀/SiO₂ at 100–150°C provides high yields of mono- and disubstituted products. HPAs are more active than H₂SO₄, easily separated from the reaction mixture and can be used repeatedly. -- () - () H₃PW₁₂O₄₀ 25% H₃PW₁₂O₄₀/SiO₂ 100–150°C - - . , H₂SO₄, - - .     

Search for Θ+(1540) in exclusive proton-induced reaction p + C(N) \to \Theta ^ + \bar \kappa ^0 + C(N) at the energy of 70 GeV

A search for narrow Θ⁺(1540), a candidate for a pentaquark baryon with positive strangeness, has been performed in an exclusive proton-induced reaction $p + C(N) \to \Theta ^ + \bar \kappa ^0 + C(N)$ on carbon nuclei or quasifree nucleons at $E_{beam} = 70GeV(\sqrt s = 11.5GeV)$ studying nK ⁺, pK _S ⁰ , and pK _L ⁰ decay channels of Θ⁺(1540) in four different final states of the $\Theta ^ + \bar K^0 $ system. In order to assess the quality of the identification of the final states with neutron or K _L ⁰ , we reconstructed Λ(1520) → nK _S ⁰ and ? → K _L ⁰ K _S ⁰ decays in the calibration reactions p + C(N) → Λ (1520)K ⁺+C(N) and p+C(N) → p?+C(N). We found no evidence for a narrow pentaquark peak in any of the studied final states and decay channels. Assuming that the production characteristics of the $\Theta ^ + \bar K^0 $ system are not drastically different from those of the Λ(1520)K ⁺ and p? systems, we established upper limits on the cross-section ratios $\sigma (\Theta ^ + \bar K^0 )/\sigma (\Lambda (1520)K^ + ) < 0.02$ and $\sigma (\Theta ^ + \bar K^0 )/\sigma (p\phi ) < 0.15$ at 90% C.L. and a preliminary upper limit for the forward-hemisphere cross section $\sigma (\Theta ^ + \bar K^0 )$ nb/nucleon.     

Resonances and off-specular scattering in neutron waveguides

Off-specular neutron scattering from layered resonant systems has been studied. As an example, tri-layer neutron waveguides have been investigated experimentally by neutron reflectometry. In such systems, the neutron wave function is strongly localized in the guiding layer. The resonant states in the total reflection region lead to enhanced off-specular scattering from the interface roughness. The relation between the resonant states and off-specular scattering is discussed.     

Ab initio studies on the interplay between spin-orbit interaction and Coulomb correlation in Sr2IrO4 and Ba2IrO4

Ab initio analyses of A(2)IrO(4) (A=Sr,Ba) are presented. Effective Hubbard-type models for Ir 5d t(2g) manifolds downfolded from the global band structure are solved based on the dynamical mean-field theory. The results for A=Sr and Ba correctly reproduce paramagnetic metals undergoing continuous transitions to insulators below the Néel temperature T(N). These compounds are classified not into Mott insulators but into Slater insulators. However, the insulating gap opens by a synergy of the Néel order and significant band renormalization, which is also manifested by a 2D bad metallic behavior in the paramagnetic phase near the quantum criticality.     

An anomalous -ω interference in the reaction ee → 3π

It is shown that in the π⁺π⁻ meson mass-spectrum in the reaction e⁺e⁻ → π⁺π⁻π⁰ at 2E > 1 GeV one should expect the anomalously large effect of the -ω interference. It can be used as a tool for the elucidation of the details of the e⁺e⁻ → Vπ reaction dynamics and as the additional possibility for the determination of the electromagnetic -ω mixing parameters.