By suitably pressurizing iron substrates under different conditions, the resulting α-Fe2O3 nanostructures, formed by its direct thermal oxidation, can gradually change in succession from nanowires to nanoleaves and to micropillars as the pressure is increased. The inter-relation between the pressure conditions and the resulting nanostructure is studied by density functional calculations using ultrasoft pseudopotentials with a plane-wave basis method and with the generalized gradient approximation (GGA). It is shown that the shape of the formed nanostructures is primarily determined by the anisotropic activation energy and, as the latter is lowered, there is a shape change from wire to pillar. A simulation model of diffusion using the Monte Carlo method is applied in the 3-D (dimensional) case to show how the anisotropic activation energy influences the growth process of the α-Fe2O3 nanostructure. The present study provides a way to control the shape of the nanostructures grown by the thermal-oxidation method.

The growing mechanism of α-Fe2O3 nanowires synthesized by thermal oxidation of iron is studied by the Monte Carlo method. Using a model of diffusion, the effects of synthesizing temperature, oxygen density and annealing on the morphology of the nanowires have been simulated. The results show that nanowires with a large head can only be obtained under the correct temperature and a sufficiently high density of oxygen. Under a low temperature or a low density of oxygen, particles can be obtained. And under a high temperature or after annealing, the nanowires will become thicker. The results are consistent with our experiments. This fact indicates that the growth of α-Fe2O3 nanowires should be a diffusion process and provides an approach for improving the quality of the nanowires.

By carefully controlling the reacting conditions, including atmosphere, temperature, and time, α-Fe2O3 nanoleaves have been synthesized by oxygenating pure iron. X-ray diffraction and transmission electronic microscope analyses demonstrate that the nanoleaves are single crystalline. The X-ray photoelectron spectrum, Raman spectrum, optical absorption spectrum, and photoluminescence spectrum are also carried out to characterize the nanoleaves. Magnetic measurement shows that the blocking temperature of the nanoleaves is about 120 K and the coercivity decreases as temperature increases. The more interesting is that a small exchange bias is found in 2 T field cooling hysteresis loops. This small exchange bias may possibly originate from a different magnetic order on the surface of the nanoleaves or the coexistence of a tiny amount of Fe3O4.

The nanowires of hematite (α-Fe2O3) have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy. It is discovered that there are three main shapes of α-Fe2O3 nanowires, needle-tip, large-tip, and bamboo-like. A diffusion equation is used to simulate the process of the growth of hematite nanowires. It is found that growing mechanism is quite different from normal vapor–liquid–solid and vapor–solid ways, but roughly a diffusion mechanism.The bamboo-like nanowire of hematite is occasionally observed. In the nod and branch, The Fe content is much more higher than that in the culm. The Fe/O ratio in the culm is identical. The growing mechanism may be a simple diffusion process.

•The superconductivity has close relationship with the structure of Y1−xSrxBa2−xLaxCu3Oy.•The decrease of Tc has close relationship with the increase of the combinative energy.•The structural factor should be taken into account when considering the mechanism of high Tc superconductivity.The compensated systems of Y1−xSrxBa2−xLaxCu3Oy were synthesized and characterized by DC magnetization measurements and X-ray diffraction. The structures of the samples were refined by Rietveld method. Although the carrier concentration in the samples is constant at different doping levels, the superconductivity evidently changes. The combinative energy in the system was calculated and it was discovered that the decrease of Tc has close relationship with the increase of the combinative energy. It is suggested that the structural factor should be taken into account when considering the mechanism of high Tc superconductivity.

•It is found that the fixed-triangle in YxPr1−xBa2Cu3O7 has something to do with superconductivity.•A low frequency mode in Raman spectrum may be caused by the fixed-triangle.•The coupling between electron and phonon is of importance in this system.In order to explore how important the electron–phonon coupling is in high Tc superconductors, we calculate the phonon frequencies at Gamma-point of the YxPr1−xBa2Cu3O7 system by considering a special local structure in the YxPr1−xBa2Cu3O7, which is so called “fixed triangle”. It is found that a low frequency mode is possibly caused by the “fixed triangle” and roughly matches the experiment of Raman spectrum, which suggests that the coupling between electron and phonon is of importance in this system.