Synthesis and characterisation of La0·95Sr0·05GaO3−δ, La0·95Sr0·05AlO3−δ and Y0·95Sr0·05AlO3−δ

The oxide-ion conducting phases La_0·95Sr_0·05GaO_3−δ (LSG), La_0·95Sr_0·05AlO_3−δ (LSA) and Y_0·95Sr_0·05AlO_3−δ (YSA) have been synthesised, either by solid state reaction or through a chemical route. Structural and microstructural characterisation was carried out using XRD and SEM/EDS techniques and a.c. impedance spectroscopy (250–1000°C) was employed to determine the electrical properties. Although low-temperature impedance results were strongly dependent on phase purity and microstructure, high temperature electrical conductivity data could be used to compare the electrical conductivities of LSG, LSA and YSA. Chemical modification from the well-known Sr-doped lanthanum gallate via replacement of different cations on the A and/or B site decreased the conductivity, increased the activation energies and decreased the ionic conductivities. From the results, there is no simple correlation between oxygen ion conductivity and geometric aspects related to unit cell parameters and cation radii. Instead, cation polarisability seems to play an extremely important role in designing improved oxygen ion conductors based on the perovskite structure.     

γ‐Radiation Effects on the Performance of HCCD‐PEG for Cs and Sr Extraction

Abstract

Cobalt dicarbollide and polyethylene glycol in phenyltrifluoromethyl sulfone (HCCD/PEG in FS‐13) is currently under consideration for use in the process‐scale selective extraction of fission product cesium and strontium from acidic radioactive solutions. While the Cs and Sr solvent extraction efficiency of this formulation has been previously characterized, this solvent will be exposed to high radiation doses during use, and has not been adequately investigated for radiation stability. Here, HCCD/PEG was γ‐irradiated to various absorbed doses, to a maximum of 432 kGy, using ⁶⁰Co. Irradiations were performed for the neat organic phase, and also for the organic phase in contact with 1 M‐nitric acid mixed by air sparging. Post‐irradiation solvent extraction measurements showed that Cs distribution ratios were unaffected; however, strontium distribution ratios decreased with the absorbed dose under both conditions. The decrease in the extraction efficiency for strontium was greater when in contact with the aqueous phase. The stripping performance was not affected. A mechanism, based on reaction with the products of direct diluent radiolysis, is proposed to explain the decreases in the strontium extraction efficiency.     

Preparation of La1?x Sr x CoO3 Oxide Electrode Material and its Influence on the Structure and Dielectric Performance of the Supported Ba1?x Sr x TiO3 Thin Films

Using the sol–gel method, La_1−x Sr _x CoO₃ (LSCO) electrode films were first fabricated on the Si (100) substrates, followed by the growth of Ba_1−x Sr _x TiO₃ (BST) thin films on the LSCO electrode film. The crystal structure and surface morphology of these films were characterized by XRD and SEM. The effects of Sr-doping and annealing temperature on the structure and electric resistivity of the LSCO films and the dielectric properties of the BST films were studied. Results show that the La_0.5Sr_0.5CoO₃ electrode annealed at 750 °C has the lowest electric resistivity, 1.1 × 10⁻³Ω cm. The relative permittivity of the La_0.5Sr_0.5CoO₃-supported BST films first increases and then decreases with Sr-doping. The relative permittivity of the BST film decreases while the dielectric loss increases with frequency. Among the studied BST films, Ba_0.5Sr_0.5TiO₃ has the largest relative permittivity and the smallest dielectric loss (95 and 0.1, respectively) when the frequency is 1 kHz.     

Synthesis and characterization of Ca–Sr–P coating on pure magnesium for biomedical application

There are growing evidences that Sr-containing calcium phosphate biomaterials can promote better osteo-precursor cell attachment and proliferation than pure calcium phosphate biomaterials. In this study, attempts were made to fabricate two kinds of Sr-substituted calcium phosphate (Ca–Sr–P) coatings on pure magnesium in electrolyte solutions with differing amounts of Sr(NO₃)₂ for biomedical application. The surface microstructure, composition and chemistry of the coatings were characterized by Scanning Electron Microscope (SEM), Energy-dispersive X-ray Spectroscopy (EDS), and X-ray Diffractometer (XRD), respectively. In addition, electrochemical and immersion tests were performed to evaluate the corrosion resistance of the Ca–Sr–P coated magnesium in phosphate buffered saline solution (PBS).     

NO x Storage and High Temperature Soot Oxidation on Pt–Sr/ZrO2 Catalyst

NO _x storage–release and soot oxidation have been studied using strontium promoted zirconia with different surface areas. It was found that the amount of the adsorbed NO _x increases with the increase of the support surface and Sr concentration up to 20 wt% Sr. Introduction of platinum has no effect on the amount of NO _x stored, but improve soot oxidation due to recycling of NO to NO₂. A combination of oxidation catalyst with NO _x storage materials enables to lower the temperature of 20% soot conversion up to 100 °C in comparison with un-catalyzed soot oxidation.     

Synthesis,characterization and catalytic properties of La2−x Sr x NiO4−δ

Various compositionsx in the catalyst system La_2–x Sr _x NiO_4– have been prepared by conventional techniques and characterized by X-ray powder diffraction, electron microscopy and BET surface measurements. The catalytic properties of these catalysts have been tested in the propylene oxidation reaction. The catalytic activity can be correlated with the oxygen content and with the strontium substitution.     

Structures and temperature-dependent electrical properties in Ba0.8Sr0.2TiO3–BiAlO3 electrostrictive ceramics

Lead-free piezoceramics of (1 ? x)Ba_0.8Sr_0.2TiO₃–xBiAlO₃ [(1 ? x)BST–xBA (0 ≤ x ≤ 0.12)] have been synthesized and the structures and properties have been investigated systemically. X-ray diffraction patterns indicated that the solid solution limit is close to x = 0.04, and a morphotropic phase boundary (MPB) separating tetragonal and pseudocubic phases exists near x = 0.02. The ferroelectricity weakens monotonously with increasing x, accompanied by weakened butterfly shaped bipolar strain–electric field curves. The temperature dependent properties of the composition with x = 0.02 have been typically investigated, showing that with increasing temperature, the ferroelectricity tends to be weakened. Pure electrostrictive effect has been found in the compositions with x = 0.02 and 0.03 close to room temperature temperature. Based on the results, the effects of BA on structures and electric properties were discussed.     

Synthesis and structure of a gallate of strontium with Sr–C–Ga three-center two-electron bonds

The addition reaction of strontium bis[bis(trimethylsilyl)amide] with triethylgallane yields quantitatively strontium bis[triethyl-bis(trimethylsilyl)aminogallate] (1). The strontium cation shows the unusual low coordination number of four to two nitrogen and two carbon atoms. Sr–C bond lengths with a mean value of 282 pm are observed with the Sr–C–Ga three-center two-electron bonds. Due to the mainly ionic character of this compound a fast exchange of the bridging and terminal ethyl groups is observed on the NMR time scale.     

Sol–gel synthesis of La0.6Sr0.4CoO3−x and Sm0.5Sr0.5CoO3−x cathode nanopowders for solid oxide fuel cells

Nano-powders of La_0.6Sr_0.4CoO_3?x (LSC) and Sm_0.5Sr_0.5CoO_3?x (SSC) compositions, which are being investigated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) with La(Sr)Ga(Mg)O_3?x (LSGM) as the electrolyte, were synthesized by low-temperature sol–gel method using metal nitrates and citric acid. Thermal decomposition of the citrate gels was followed by simultaneous DSC/TGA methods. Development of phases in the gels, on heat treatments at various temperatures, was monitored by X-ray diffraction. Sol–gel powders calcined at 550–1000 °C consisted of a number of phases. Single perovskite phase La_0.6Sr_0.4CoO_3?x or Sm_0.5Sr_0.5CoO_3?x powders were obtained at 1200 °C and 1300 °C, respectively. Morphological analysis of the powders calcined at various temperatures was done by scanning electron microscopy. The average crystallite size of the powders was ～15 nm after 700 °C calcinations and slowly increased to 70–100 nm after heat treatments at 1300–1400 °C.     

Coating of nano-sized ionically conductive Sr and Ca doped LaMnO3 films by sol–gel route

In this study, Sr and Ca doped LaMnO₃ thin ceramic films were coated on Al₂O₃ substrates by using a sol–gel route as the cathode material for SOFC. Nitrate precursors were used for the preparation of the thin film coating solution, and methanol and acetyl acetone were also used as the solvent and chelating agent, respectively. After the solution was prepared, an Al₂O₃ single crystal substrate was dipped into the solution. Then it was fired at 500 °C and annealed at 1025 °C for the crystallization. Coated films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), focused ion beam (FIB) and atomic force microscopy (AFM). Conductivity of the coated films was measured by the four probe Van der Pauw method. XRD, SEM, AFM and FIB characterizations of the coated film showed that the LaMnO₃ phase was formed, surface of the films was uniform and had homogenously distributed pores sized about 10 nm, mean grain size was about 60–80 nm and the film thickness was about 180 nm. The specific resistivity of the film was calculated to be 0.524 Ω m.     

柠檬酸法制备Sr—铁氧体超细粉

本文采用柠檬酸作为络合剂，制备了超细锶铁氧体超细粉，经过Ｘ射线结构分析，电子透射电子显微镜，振动样品磁强计等技术对粉末的粒径，结构和磁学性能进行了分析测试结构表明，该方法合成的锶铁氧体具有粒径小，粒度均匀，性能高，工艺简单等特点。     

Physical and magnetic properties of Mn–Zr doped La–Sr ferrite prepared by the auto-combustion route

This is the first report ever on (Mn²⁺–Zr⁴⁺) doped M-type lanthanum strontium hexaferrite with general formula, Sr_0.85La_0.15(MnZr)_xFe_12−2xO₁₉ where x=0.0, 0.25, 0.50, 0.75, and 1.0, prepared by citrate auto-combustion method. These ferrites were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), Energy dispersive X-ray spectroscopy (EDX) and Vibrating sample magnetometer (VSM). X-ray diffraction patterns show the formation of high purity hexaferrite phase without other secondary phases for all the synthesized samples. It was observed from magnetic hysteresis data that the coercive force is reduced from 5692.5 Oe to 1669.2 Oe with increase in doping contents but the net magnetization of the samples varies slightly from 60.6 to 55.2 emu/gm. High saturation magnetization (M_s), low coercivity (H_c) and remanence magnetization (M_r) values of these materials make them particularly suitable for data recording.     

Changes in ordered structure and dielectric properties with the A-site and B-site cation ratios of complex perovskites (Sr1−xBax)(Sr0·33+yTa0·67−y)O3−δ

Complex perovskites with large-sized B′-site cations, (Sr_1−xBa_x)(Sr_0·33+yTa_0·67-y)O_3−δ (0 ≦ x ≦ 1, 0 ≦ y≦ 0·17), were fabricated to examine the transformation behavior between the (1:1) and (1:2) order types and dielectric property change with A-site cation substitution. The (1:2) type order was found to appear in a limited Ba-rich composition range. Structural strain induced by size difference between the A-site and large-sized B′-site cations might be responsible for the occurrence of the (1:1) type order in perovskite compounds substituted with more than 50% Sr²⁺ on the A-site sublattice. Low ε_r and positive temperature coefficient of ε_r observed for the (1:2) ordered samples were explained by the restricted ion movement in the (1:2) type order array.     

Phase interaction and oxygen transport in La0.8Sr0.2Fe0.8Co0.2O3–(La0.9Sr0.1)0.98Ga0.8Mg0.2O3 composites

Composite ceramics made of two perovskite-type compounds, (La_0.9Sr_0.1)_0.98Ga_0.8Mg_0.2O_3−δ (LSGM) and La_0.8Sr_0.2Fe_0.8Co_0.2O_3−δ (LSFC) mixed in the ratio 60:40 wt.%, possess relatively high oxygen permeability limited by both bulk ionic conduction and surface exchange at 700−950 °C. Sintering at elevated temperatures (1320–1410 °C) necessary to obtain dense materials leads to fast interdiffusion of the components, forming almost single perovskite phase ceramics with local inhomogeneities. This phase interaction decreases the oxygen ionic transport in the composites, where the level of ionic conductivity is intermediate between those of LSGM and LSFC. The scanning electron microscopy (SEM) suggests a presence of Ga-enriched domains, probably having a high ionic conductivity. The size and concentration of these domains can be increased by decreasing sintering temperature or using preliminary coarsened LSGM powders. The maximum oxygen permeability is thus observed for the composite prepared under minimum sintering conditions sufficient to obtain gas-tight ceramics, including the use of LSGM, preliminary passivated at 1150 °C, and sintered at 1320 °C. The activation energy values for total conductivity, which is predominantly p-type electronic and slightly decreases due to component interaction, vary in the narrow range from 24.0 to 26.2 kJ/mol at 25–575 °C. The average thermal expansion coefficients (TECs) of LSGM-LSFC composites, calculated from dilatometric data in air, are (12.4–13.5)×10⁻⁶ K⁻¹ at 100–650 °C and (17.8–19.8)×10⁻⁶ K⁻¹ at 650–1000 °C.     

Crystal structure and luminescence properties of green-emitting Sr1−xAl12O19:xEu2+ phosphors

In this paper, a series of novel luminescent Sr_1−xAl₁₂O₁₉:xEu²⁺ phosphors were synthesized by a high temperature solid-state reaction. The phase structure, photoluminescence (PL) properties, as well as the decay curves were investigated. The quenching concentration of Eu²⁺ in SrAl₁₂O₁₉ was about 0.15 (mol). Upon excitation at 378 nm, the composition-optimized Sr_0.85Al₁₂O₁₉:0.15Eu²⁺ exhibited strong broad-band green emission at 530 nm with the CIE chromaticity (0.2917, 0.5736). The results indicate that Sr_1−xAl₁₂O₁₉:xEu²⁺ phosphors have potential applications as green-emitting phosphors for UV-pumped white-light LEDs.     

A novel cyano-bridged Sr(II)–Fe(III) polymer containing alternating octanuclear and tetranuclear cores

A novel cyano-bridged Sr(II)–Fe(III) polymeric complex ([Sr₃(phen)₆(H₂O)₆{Fe(CN)₆}₂]·phen·6.5H₂O)_n (1) has been synthesized and structurally characterized. The complex contains alternating octanuclear 24-membered and tetranuclear 12-membered metallocycles, which are repeated to form a polymeric chain. The Sr(II) centres are eight coordinated with distorted bicapped trigonal prismatic geometry while the Fe(III) centres have six coordinate octahedral geometry.     

Preparation and properties of (Ba0·7Sr0·3)TiO3 powders and thin films using precursor solutions formed from alkoxide-hydroxide

(Ba_0·7Sr_0·3)TiO₃ powders and thin films were prepared using alkoxide-hydroxide route. Solutions of Ba and Sr hydroxides dissolved in methanol were reacted with Ti-isopropoxide under conditions of stirring at room temperature for 15 h, and then dried under reduced pressure at ≦40°C to prepare precursors of (Ba_0·7Sr_0·3)TiO₃ powder. The amorphous precursors were hydrolyzed at 100°C by introducing nitrogen gas containing water vapor. The hydrolyzed products were crystalline nanosize powders of (Ba_0·7Sr_0·3)TiO₃. As-hydrolyzed (Ba_0·7Sr_0·3)TiO₃ powders showed a good crystallinity with cubic phase. (Ba_0·7Sr_0·3)TiO₃ thin films were also successfully prepared at 650°C on Pt/Ti/SiO₂/Si substrates from precursor solutions obtained by the reaction of alkoxide with hydroxides. The (Ba_0·7Sr_0·3)TiO₃ thin films exhibited the microstructure with fine grains as small as 20–60 nm. The dielectric constants of the thin films ranged from 600 to 800 at room temperature.     

B-cation effect on relaxor behavior and electric properties in Sr2NaNb5−xSbxO15 tungsten bronze ceramics

Sr₂NaNb_5−xSb_xO₁₅ ceramics (SNNS, x=0.0, 0.3, 0.5, 1.0) with ‘filled’ tungsten bronze structure were prepared by the conventional solid-state reaction method. Effects of introducing Sb concentration in B-sites on the microstructure, dielectric and ferroelectric properties were investigated in detail. With increasing of Sb concentration, the crystal structure of SNNS ceramics distorted slightly from the TB orthorhombic Ccm2 phase to tetragonal P4bm phase, and then to paraelectric P4/mbm phase at room temperature. The smaller ionic radius of Sb⁵⁺ (0.60 Å) compared with that of Nb⁵⁺ (0.64 Å) contributed to the shrinkage of crystal structure. It was found that accompanying with the introduction of Sb, some unique dielectric and ferroelectric behavior emerged for SNNS ceramics. Only the samples with x<0.5 showed additional dielectric anomaly in low-temperature range, which was attributed to the incommensurate superstructure ICS-associated dielectric dispersion process caused by local structural fluctuation. With increasing of Sb concentration, T_c shifted to lower temperatures, and the diffuse phase transition and relaxor behavior appeared to be exceptionally induced around T_c at higher Sb concentration. The underlying mechanisms of relaxor behavior induced by different Sb concentration in B-sites for SNNS ceramics were clarified in detail. Moreover, the ferroelectric properties deteriorated and even disappeared at higher Sb concentration, because the ceramics showed P4/mbm phase structure as a result of decreasing of T_c to lower than room temperature.