Hengbin Zhang

Synthesis of monocrystalline composite oxides La1−xSrxFe1−yCoyO3 with the perovskite structure using polyethylene glycol-gel method

Precursors to La1−xSrxFe1−yCoyO3 have been prepared glycol as a protecting agent of colloidal particle via the sol-gel process. After the solid phase reaction at 500–600°C for 2 h, nanocrystalline composite oxides La1−xSrxFe1−yCoyO3 (x = 0.0, 0.1, 0.2, 0.4; y = 0.1, 0.2, 0.5, 0.6, 1.0) were obtained. The effects of various conditions of the synthesis processes on the products containing the various components and the preparation processes of nanocrystalline composite oxides by the direct heat decomposition method are reported. The results indicate that the solid phase reaction can be completed at a lower temperature and with a shorter reaction time and that it has a direct relationship to the distribution of the various components in the precursors.

EPR spectra of nanocrystalline composite oxides La1−xSrxFeO3 with a perovskite structure

Abstract Nanocrystals La1−xSrxFeO3 (x = 0.0, 0.1, 0.2, 0.4 and 0.6), containing crystal grains of mean diameter 12.4 nm (x = 0.0) and 4–7 nm (x = 0.1–0.6), were compacted into nanocrystalline solid materials under static pressures of 0.5, 1.0 and 1.5 GPa in the axial direction at ambient temperature. The results showed that the peak intensities of the electron paramagnetic resonance (EPR) spectra for the nanocrystalline solid materials were about 103–104 times stronger than those of conventional crystals. The EPR spectra changed with grain size and compacting pressure. The characteristics of the EPR spectra of these nanocrystalline solid materials are discussed.

XPS study on O(1s) and Fe(2p) for nanocrystalline composite oxide LaFeO3 with the perovskite structure

Abstract The changes of the chemisorbed oxygen on the interface and surface of grains and the lattice oxygen in the bulk phase have been examined by the comparison of O(1s) spectra of several uncompacted and compacted materials LaFeO 3 under the static pressures of 0.5, 1.0 and 1.5 GPa at ambient temperature. The results indicate that the amount of the chemisorbed oxygen increases with the reduction in grain sizes, and it also changes with compacting pressures. When the diameters of grains reduce to be less than 15 nm, the ratio of the chemisorbed oxygen to lattice oxygen increases dramatically. It was found that the compacting pressures also make Fe(2p) spectra change, and there are pseudozero valent iron atoms in nanocrystalline LaFeO 3 . These results reflect the differences between nanocrystalline and conventional-crystal materials.

IR transmission spectra of nanocrystalline powder materials of the composite oxides La1 − xSrxFe1 − yCoyO3 with the perovskite structure

Abstract Nanocrystalline powders of the composite oxides La 1 − x Sr x Fe 1 − y Co y O 3 ( x = 0, 0.2; y = 0.5, 1.0) with the perovskite structure are different from conventional materials with respect to their IR transmission spectra. When the mean diameters of the grains decrease to a certain extent, the band peaks are widened and the continuous vibration bands are split. The vibration modes on the grain surface depend mainly on the vibrations of incomplete molecules.

Materials chemistry communications. Preparation of nanocrystalline LaFeO3 using a stearic acid–sol method

Nanocrystalline and uniformly single phase LaFeO3 has been prepared using a stearic acid-sol method; the grain size distribution was narrow, and the mean diameter was ca. 5 nm. The morphology and properties of the material were characterized by X-ray powder diffraction, differential thermal analysis, transmission electron microscopy and electron paramagnetic resonance.

Preparation of nanocrystalline LaFeO3 using reverse drop coprecipitation with polyvinyl alcohol as protecting agent

Abstract The precursor of the nanocrystalline material LaFeO3 has been prepared using a reverse drop coprecipitation method with polyvinyl alcohol as a protecting agent. After the precursor was calcined by wet and dry methods, the nanocrystalline material obtained was characterized by DTA, XRD, TEM, etc. The results show that the solid state reaction and crystal size of the nanocrystalline material relate not only to the precursor preparation method, but also to the distribution of different components in the precursor. This paper also introduces a synthesis method using sodium dodecyl benzenesulfonate as a protecting agent.

Preparation of nanocrystalline solid material LaFe0.5Co0.5O3 with the citric acid method and its XPS study on the absorption of oxygen

Abstract The precursor of nanocrystalline material LaFe0.5Co0.5O3 was prepared using the citric acid method. After calcining the precursor at 500 °C for 2 h, the mean diameter of the crystalline grain of LaFe0.5Co0.5O3 obtained was 12.9 nm. The nanocrystalline solid material was obtained at compacting pressures of 0.5, 1.0 and 1.5 GPa. The results indicated that the distribution of various components in the precursor had a direct influence on the calcining effect. XPS measurements showed that the intensity of the absorbed oxygen (OA) was larger than that of the lattice oxygen (OL) in the nanocrystals LaFe0.5Co0.5O3 and the ratio of the absorbed oxygen to lattice oxygen changed with the compacting pressure.

IR reflectance spectra on high-pressure compacted nanocrystalline La-Sr-Fe-Co oxides

Abstract The nanocrystalline powders of composite oxides La 1 − x Sr x Fe 1 − y Co y O 3 ( x = 0, 0.1, 0.2; y = 0.5, 0.6, 0.8, 1.0) were compacted into pellets under pressures of 0.5, 1.0 and 1.5 GPa. In IR reflectance spectra, band splitting and red shift indicate the existence of various incomplete molecules with unsaturated coordinations on the surface and interface, whereas band blue shift indicates the existence of the ‘pressured bonds’ lying between the van der Waals force and covalent bond formed among the hanging-bond atoms due to the intergranular contact under different compacting pressures.

Sulfate-ion-selective electrode with nanocrystalline composite oxides La1-χSrχFe1-γCoγO3 as solid membranes

Abstract The response characteristics of the sulfate-ion-selective electrode with nanocrystalline composite oxides La 1-χ Sr χ Fe 1-γ Co γ O 3 as solid membranes are related to the membrane compositions. The experiments show that the membranes containing Sr have very low sensitivity or no response to sulfate ions; when the membranes do not contain Sr, i.e. for nanocrystalline LaFe 1-γ Co γ O 3 , the response sensitivities to sulfate ions increase with increase in γ; some of them possess the over-Nernst effect. This paper reports the effect of preparation conditions on the response characteristics as well as selectivity and pH application range of the ion-selective electrode.

Synthetic study of nanocrystalline complex oxides LaFe1–yCoyO3

A precursor to LaFe1–yCoyO3 has been prepared using the polyethylene glycol-gel method. After calcination of the precursor at 450–550 °C for 1–2 h, nanocrystalline complex oxides LaFe1–yCoyO3(y= 0.5, 0.6, 0.8) with the perovskite structure and grain diameter < ca. 10 nm were obtained; the materials were single phase and of good crystallinity. The citric acid and self-propagating synthesis methods also gave nanocrystalline materials. The results indicate that the distribution of the various components in the precursor has an important effect on the subsequent solid-state reaction.