Jian Sha

Thermoanalytical characteristic of nanocrystalline brookite-based titanium dioxide

Abstract Using differential-thermoanalytical (TG-DTA) measurement and X-ray diffraction (XRD) analysis, the characteristics of nanocrystalline brookite-based TiO 2 with a certain amount of anatase and rutile have been studied. There are two irreversible endothermic peaks on the DTA curve. The first peak (with weight loss on thermal-gravity TG and differential thermalgravity DTG curves) corresponds to the desorption of physical or chemical species, while the second one (without weight loss on TG and DTG curves) is related to the structural phase transition from brookite to anatase then to rutile, and the structural phase transitions are beneficial to the grain growth. In this paper, the grain size and the content of each individual phase in specimens at different temperatures are also reported.

Dielectrical behavior of nanostructured α-Fe2O3 with different annealed temperatures

The spectra of the dielectrical constant and dielectrical loss in three nanostructured α-Fin23 samples at different annealed temperatures are measured by using ac LRC method. The relaxation times of polarization and the conductance are calculated by means of the Debye mechanism and the interface effects in two kinds of polarization processes with two different relaxation times are proposed.

Size effect on structure and infrared behavior in nanocrystalline magnesium oxide

Abstract From the results of Fourier Transform Infrared (FTIR) spectra and X-ray Diffraction (XRD), we found that there exists size effect on the structure and infrared behavior in nanocrystalline MgO. When the grain size decreases, the crystal lattice dilates anisotropically, and the red shift of stretching vibrational mode coexists with the blue shift of the bending vibrational mode. We give a preliminary interpretation to the above abnormal phenomena.

Bloch wave oscillations in the mesoscopic Josephson junction

The importance of discreteness of Cooper pairs tunneling in the mesoscopic Josephson junction is addressed. The Bloch wave oscillation in the mesoscopic Josephson junction is proposed by means of the quantization for the junction in accord with the discreteness of Cooper pair.

Structural phase transition in nanostructured γ-Fe2O3

ConclusionsWe have found that there is an exothermal peak on the DTA curve of nanostructured γ-Fe2O3 sample and that this peak is not repeatable. The XRD microstructure analysis confirms for the first time that this exothermal peak corresponds to the structural phase transition from γ-Fe2O3 to α-Fe2O3. After this transition, the nanostructured Fe2O3 crystalline grains grow continuously with increasing temperature.

ANOMALOUS DIELECTRIC BEHAVIOR IN NANOCRYSTALLINE GAMMA -FE2O3

The measurements of electric capacities and dielectric loss angles for nanocrystalline γ-Fe2O3, under air and vacuum atmospheres have been conducted by using ac LRC method, and the conductivity and the polarization relaxation time have also been calculated from the frequency spectra of real and imaginary parts of the dielectric constants. The anomalous dielectric behavior implies the existence of two kinds of polarization mechanisms with different relaxation times, which are caused by the defects and the dangling bonds in the interfaces, respectively. The experimental and calculated results indicated that the polarization loss and the conductance loss are dominant in air atmosphere and vacuum, respectively.

Anomalous transport characteristics of Fe X Cu1-X granular film

The transport characteristics of FeXCu1-X granular film fabricated by rf magnetron sputtering is introduced. In a wide temperature range from 12 to 290 K the granular film exhibits an evident negative temperature dependence of resistivity. The temperature coefficient of resistance of the granular film will change its sign from negative to positive with the deposition time, the annealing condition and the atom ratio of iron to copper respectively. When the atom ratioX equals 0.64 and the deposition time is 1 min, an anomalous big negative temperature coefficient of resistance appears in our sample. XRD shows that the structure of the granular film is like amorphous, so a preliminary explanation is given according to amorphous alloy theory.

Semiconductor-Like Properties of Sputtered FexCu1-x Thin Films

Amorphous FexCu1-x thin films with x ranging from 0.21 to 0.81 have been obtained by rf-magnetron sputtering. The structure and the electric transport properties of the films can be controlled by both the composition and annealing temperature. The resistances of the films decrease with the temperature increasing from 12 to 300 K, which is the typical semiconductor characteristic. After annealing at 400° C for 5h, the amorphous FexCu1-x thin film is crystallized and exhibits electric transport property an normal metal film. The dependence of resistance-temperature characteristics of the films on the composition and deposition time is described.

Rare-earth ionic size effects on Tc in the series RBa2Cu3O7-σ

Abstract The rare-earth ionic size effects on Tc are investigated in terms of bond valence sums using the neutron diffraction data for nearly optimal doped RBa2Cu3O7-σ (R Y, La, Nd, Sm, Dy, Ho, Er, Tm, and Yd) and PrBa2Cu3O7-σ systems. The optimal hole concentration in CuO2 planes is found to decrease systematically with increasing rare-earth ionic radius except Pr-123 in the R-123 phases, which is confirmed by the two similar inverted parabolic curves of Tc vs hole concentration for Y-123 and Er-123. The anomalous property of Pr-123 is due to the depletion of hole concentration. The increase in Tc as R3+ ionic radius is interpreted as both the increase of hole distribution on the in-plane O sites relative to the in-plane Cu sites and the interplanar coupling.