Aligned α-Fe2O3 nanowires over large areas were successfully synthesized by oxidation of pure iron. Most of the assynthesized α-Fe2O3 nanowire arrays, grown vertically from the surface of the substrate, are perfect and single crystals with diameters of 20-40nm and lengths of 2-5lm. The high surface density of the nanowires (108-109cm-2) is considered to be responsible for the aligned growth. The size of the α-Fe2O3 nanowires may be tailored to required dimension by adjusting the flowing rate of the gases as well as the time and temperature of reaction. The aligned arrays of α-Fe2O3 nanowires reported here offered opportunities for both fundamental research and technological applications.

The combinative energy between two structural blocks in La2-xMxCuO4 (M=Ba, Sr), with different M concentration, has been calculated with holes in different positions in the CuO2 planes on the basis of a block model. The relationship between the combinative energy and superconductivity has been investigated. The results indicate that there is an interesting correlation among the combinative energy, the Tc value, and the positions of the doped holes, which are originated from the substitution of Ba2+ or Sr2+ for La3+. Although there are some similarities in correlation between La2-xBaxCuO4 (0.03<x<0.25) and La2-xSrxCuO4 (0.075<x<0.3), there are also some notable differences which may be originated from different properties of the substituted elements: barium and strontium. The results not only suggest that the interaction between perovskite-type and rocksalt-type blocks plays an essential role in high-Tc superconductivity, but also give us some clues of the influence of the position of the holes within the CuO2 plane.

We have structurally studied the elaborated single crystal of YBa2Cu3O7-δ using high-resolution x-ray diffraction, including ϕ-scan, rocking curve, reflectivity and small angle scattering. The results show that the single crystal is natively inhomogeneous. The rocking curve of 00l reflection indicates that the c-axis lattice constant of the crystal varies in a narrow range, clearly showing a multilayer characteristic. The reflectivity measurement supports this result; it also shows an obvious multilayer characteristic. The small angle scattering indicates that, although the c-axis lattice constant is little different in the crystal, it shows a long period of about 700Å. The local work function measurement using a scanning tunnelling microscope demonstrates that the crystal is inhomogeneous, supporting the results of x-ray analyses. These facts tell us that so far we have not completely understood the structure of high-Tc superconductors.

Abstract. Low-temperature thermal expansion and its correlation with oxygen nonstoichiometry have been studied for Bi1.7Pb0.3Sr2Ca2Cu3O10+y samples. An anomalously big jump of the thermal expansion in the c direction of Bi1: 7Pb0:3Sr2Ca2Cu3O10+y has been observed at a temperature slightly above the superconductivity transition temperature. The corresponding temperature and the magnitude of the jump are found to be correlated with the oxygen nonstoichiometry, carrier concentration and superconductivity. The results reveal that the anomalously big jump of the thermal expansion is an electron-assisted lattice softening transition. Its correlation with the superconductivity suggests that phonon-electron interaction still plays a certain role in the superconductivity in high-Tc cuprates.

Based on a block model, separating the unit cell of YBa2Cu3O7-δ into perovskite and rock salt blocks, the combinative energy between the two blocks in the YBa2Cu3O7-δwith the differentδvalue, from 0.07 to 0.62, was calculated. A close relationship between the superconducting transition temperature and the combinative energy in YBa2Cu3O7-δis established, and the change of the combinative energy is closely related to the transformation from orthorhombic Ⅰ to Ⅱ. The results also give a clue to reconsider the role of the orthorhombic Ⅰ and Ⅱ in YBa2Cu3O7-δ. The calculation of the holes in different planes supplies abundant information about the charge distribution in YBa2Cu3O7-δ, which may possibly connect the electronic phase diagram and the fluctuations of the stripe phase. The results show that the interaction between the two blocks is of great importance for high Tc superconductivity.