Synthesis and Characterization of Titanosilicate with the Structure of Umbite

A zeolitic titanosilicate with the composition of K_2TiSi_3O_9·H_2O, a structural analogue of natural mineral umbite K_2ZrSi_3O_9·H_2O, was hydrothermally synthesized in the SiO_2-TiO_2-K_2O-H_2O system and characterized by means of powder X-ray diffraction, SEM, IR and thermal analysis. The effects of TiO_2/SiO_2 and OH -/SiO_2 ratios on the crystallization of the umbite were discussed. The influence of the organic additives on the morphology of the crystal was also investigated and the crystals with different shapes were obtained.

Effect of Microgravity on Interface Structural Features in Space Crystal Growth

The distribution of Ca^(2+)at boundary layer ofα-LiIO3 crystal grown both in space and on earth was studied by the synchrotron x-ray fluorescence microanalysis.It was found that:(1)the Ca^(2+)concentration in the space-crystal is higher than that in the earth-crystal,(2)a sharp discontinuity of Ca^(2+)concentration is found at boundary layers of space-crystals alone.This finding provides an evidence of microgravity effect on interface structural features in space crystal growth.

Synchrotron X-Ray Study on Structures of Ni_(80)Fe_(20)/Cu Superlattices

We showed that,in contrast to the results in literature,the Bragg peak intensity of Ni_(80)Fe_(20)/Cu superlattices is enhanced at the incident x-ray energy slightly higher than the absorption edge of the heavier element(Cu).The atomic density at Ni_(80)Fe_(20)/Cu interface was analysed by the diffraction anomalous fine structure technology with the incident angle of x-ray fixed at the first Bragg peak.Our results demonstrate the epitaxy growth of Ni_(80)Fe_(20)/Cu superlattices.Upon annealing,the epitaxity of Ni_(80)Fe_(20)/Cu multilayers becomes poor but the local crystallinity in each layer is improved.

Asymmetrical Spin-Polarized Tunneling in a Composed-Barrier Magnetic Tunnel Junctions Under the Forward and Reverse Biases

Based on the two-band model and nearly-free-electron approximation, the tunnel current, conductance and mag-netoresistance of the composed-barrier magnetic tunnel junctions ( MTJ ) under the forward and reverse biases are discussed, respectively, and the numerical results are compared with the experimental results of the single-barrier MTJ . We find that there exists an asymmetrical spin-polarized tunneling in this structure under the forward and reverse biases. It suggests that this type of MTJ will provide novel functions to the potential applications of traditional types of MTJ.

Inner Modulation in Quasicrystals and Approximants

Through a detailed analysis,it is found out that a quasilattice can be considered as one consisting of several mutually incommensurate interpenetrating sublattices,each sublattice being a modulated crystalline lattice.The modulation periods in one sublattice are given by the basic periodicities of the other sublattices.Also analyzed is the approximant quasilattice whose sublattices being mutually commensurate.In the density wave picture,the combination of crystal structures into one quasicrystal(or approximant)phase can be done in a natural procedure.

Effect of the Transition Sublayers at the Interfaces on Giant Magnetoresistance

A thin transition sublayer between the ferromagnetic and the nonmagnetic sublayers is introduced for describing the interface roughness and/or the interface alloying.Based on the Kubo formalism in the real spaces,the giant magnetoresistance effects for both the cases of the structures with and without the transition sublayers at the interfaces are discussed.The numerical results show that the transition sublayers induce a phase shift on the curves of magnetoresistance(MR)vs the thicknesses of the ferromagnetic and the nonmagnetic sublayers,and there exists a critical thickness dc of the ferromagnetic sublayer,the ratio of the MR values for the structures with and without the transition sublayers at the interfaces changes at the critical thickness.

IN SITU OBSERVATION OF THE H-INDUCED DEFECTS IN SILICON SINGLE CRYSTALS

The hydrogen-induced defeats in FZ silicon grown in hydrogen atmosphere hare been investigated by both the conventional and the in situ white beam synchrotron radiation topography.The formation process of the defects is discussed.

Characterization of CoCrFeO_(4) Nanocrystals Prepared by a Sol-Gel Method

CoCrFeO_(4) nanocrystals have been synthesized using a sol-gel method.The specimen has an average grain size of 8.1 nm.The zero-field-cooled and field-cooled curves show a superparamagnetic transition occurring at a blocking temperature of TB≈249 K.The increase in coercivity of CoCrFeO_(4) nanocrystals with the decreasing temperature has been detected below the blocking temperature and could be explained by the Stoner-Wohlfarth theory.The temperature dependence of saturation magnetization shows that Bloch's law holds but with the Bloch exponent lower than the bulk value.