Fe-site substitution effect on the structural and magnetic properties in SrFeO2

We investigated the Fe-site substitution effect on the structural and magnetic properties of the infinite layer iron oxide Sr(Fe(1-x)M(x))O(2) (M = Co, Mn) using synchrotron X-ray diffraction, neutron diffraction, and (57)Fe Mo?ssbauer spectroscopy. Both systems have a similar solubility limit of x ≈ 0.3, retaining the ideal infinite layer structure with a space group of P4/mmm. For the Fe-Co system, both in-plane and out-of-plane axes decrease linearly and only slightly with x, reflecting the ionic radius difference between Fe(2+) and Co(2+). For the Fe-Mn system the lattice evolution also follows Vegard's law but is anisotropic: the in-plane axis increases, while the out-of-plane decreases prominently. The magnetic properties are little influenced by Co substitution. On the contrary, Mn substitution drastically destabilizes the G-type magnetic order, featured by a significant reduction and a large distribution of the hyperfine field in the Mo?ssbauer spectra, which suggests the presence of magnetic frustration induced presumably by a ferromagnetic out-of-plane Mn-Fe interaction.     

Neutron activation analysis of Th via233Pa

A method is described for the analysis of thorium by neutron activation. The sample is brought into solution and quantitative extraction of²³³Pa is carried out in 1M HNO₃ using 0.5M HTTA in benzene. Extraction mechanisms are discussed. The use of a low-power reactor (100 kW_th) enables determination of thorium at a lower concentration limit of 50 ng for periods of irradiation, cooling and measurement of 3 hours, 24 hours and 300 seconds, respectively.     

Estimating Kinetic Parameters for the Spontaneous Polymerization of Glycidol at Elevated Temperatures

The ring‐opening polymerization of glycidol at elevated temperatures is investigated. To improve the synthesis of dendritic polyether polyols, experiments are carried out without initiator to identify the influence of thermal side reactions. This results in a step‐growth polymerization caused by the spontaneous combination of monomers. Kinetic parameters of the side reactions are estimated by fitting simulated number‐ and weight‐average molecular weights to the experimental values measured at different reaction times during the polymerization. The reactions are conducted at three different temperatures of 90, 105, and 120 °C. It is shown that thermal side reactions lead to high dispersities of the final product and are highly sensitive to the reactor operating temperature.

     

In situ observation of maghemite nanoparticle adsorption at the water/gas interface

The adsorption of (maghemite) nanoparticles at the aqueous solution/gas interface was investigated by x-ray reflectivity. Two different concentrations (0.07 g/L and 0.7 g/L) were probed. The x-ray reflectivities indicate the adsorption of nanoparticles at the liquid surface for the highly concentrated solution, while no nanoparticle adsorption could be detected at the surface of the low concentrated solution within several hours. The vertical electron density profile of the high concentration solution/gas interface indicates the formation of a low ordered monolayer of nanoparticles occupying only 6% of the interfacial region.     

Ab initio calculations of CO physisorption on ceria(1 1 1)

Applying the method of increments, we have performed MP2 and CCSD(T) calculations for the physisorption of CO on a cerium site on the ceria(1 1 1) surface. Our calculations predict an interaction energy of −0.28 eV. We have compared our calculations to previous CCSD(T) calculations for the physisorption of CO on a cerium site on the ceria(1 1 0) surface and found a difference in the interaction energy that is related to the different structure of the two surfaces. On the ceria(110) surface only 30% of the interaction energy originate from electron correlation effects, but on the ceria(111) surface almost the entire binding energy (80%) is due to electron correlation effects. Analyses of the interaction energy contributions show that most of the electron correlation part originates from the interaction of CO with the O ions in the topmost surface layer.     

Long-term structural surface modifications of mixed conducting La<Subscript>2</Subscript>NiO<Subscript>4+δ</Subscript> at high temperatures

Abstract  Long-term annealing of La₂NiO_4+δ single crystals at 1,273 K in air leads to the formation of nickel-rich Ruddlesden–Popper phases at the single-crystal surfaces. Both the composition and the morphology of these phases depend on the surface orientation; whereas only crystallites of La₄Ni₃O_10−δ were observed on (001) surfaces, both La₃Ni₂O_7−δ and La₄Ni₃O_10−δ were formed on (100) surfaces. The formation of the nickel-rich RP phases is believed to be due to surface segregation of nickel or evaporation of a volatile lanthanum species. The crystallographic (001) planes inside the La₃Ni₂O_7−δ and La₄Ni₃O_10−δ crystallites were found to be oriented in the direction of preferential crystallite growth, which indicates that the diffusion of lanthanum and nickel cations is faster along the crystallographic (001) planes than perpendicular to these planes. Graphical abstract        

NMR investigations of the silanophilic interactions of alkyl-modified silica

The ¹³C NMR spin lattice relaxation times have been measured for suspensions of chemically bonded silica particles in solutions of an organic base in deuteroacetonitrile, CD₃CN, at different base concentrations. A correlation has been observed between the relaxation rates and the ratio of the amounts of base and silica in the suspension. Thus, silanophilic interactions of chemically bonded silicas can be monitored using ¹³C NMR relaxation rates. The correlation is interpreted in terms of the rapid exchange model. The method seems to have potential for the rapid and accurate determination of equilibrium isotherms.Dedicated to Professor Dr. Dr. h.c. mult. J.F.K. Huber on the occasion of his 70th birthday