Symmetry determination by CBED has been carried out for LiZnTa3O9 and LiGaTa3O9 crystals, which were first grown in our laboratory, LiZnTa3O9 is rhombohedral with lattice parameters, a=0.557 nm, a=56.12°,The point group is 3m and the space group is R3c. LiCaTa3O9 is tetragonal with lattice parameters a=0.778 nm, c=0.783nm. The point group is 4/mmm.
Using electron microscopy and electron diffration methods, we have investigated the microstructures, shortrange order and their changes with increasing temperature in amorphous Tb31Fe69 and Tb27Fe73 films prepared by vapour deposition in a vacuum of 10-5 torr. The process of crystallization have also been observed and analysed. The microstructures of samples with different oxygen contamination and different annealing temperatures were found to be different. However, the phase separation of both samples seemed to occure by a mechanism similar to spinodal decomposition, by which an initial amorphous phase first decomposed into two or more compsitionally discrete amorphous phase, each of which then crystallized independently with rising temperature. Thus, the whole process of crystallization consisted of several stages. Finally a poly-crystalline mixture would be formed.
The crystal structure of high-Tc superconductors in the Ba-Y-Cu-O system has been investigated by means of X-ray powder diffraction and electron microscopy. The results indicate that the superstructure based on the distorted cubic perovskite subcell is responsible for the high-Tc superconducting transition at about 90 K. The high-Tc superconducting phase is pseudo-tetragonal with triple periods (3ap) along the (001) direction. The different diamagnetic and resistance behaviour is connected with different proportions of this phase in the samples.
Dynamic extinction lines which occur in CBED patterns have been used to determine the presence of twofold screw axis and glide plane in Li2O·3Nb2O5. The space group is found to be P21/a.
BaTiO3 crystals are very useful as an excellent photorefractive materials. But the growth of BaTiO3 crystals is very difficult due to some special chemical and physical properties of them. The BaTiO3 crystals in good optical quality have been grown successfully by Top Seed Solution Growth (TSSG) technique but the crystal defects happened easyly due to the unsuitable in the crystal growth conditions even just a little. The temperature distribution near the crystal growth front, the suitable seeding temperature, stabilyty of the growth interface and so on are very important to keep the crystal growth well and in good optical quality. All of these main conditions for growing of crystals were researched detailly in our experiments and discussed detailly in this paper.
Structurai analysis of Li2O·14Nb2O5 has been carried out by combined convergent-beam electron diffraction (CBED) and high resolution electron microscopy (HREM) in an analytical electron microscope with a point resolution of 0.4 nm. The space group C2/m is confirmed by CBED. HREM structure image shows that Li2O·14Nb2O5 is made up of 4×4 blocks of oxygen octahedrons The 3×3 channels within the 4×4 blocks and the metal atoms at the centres of the octahedrons which are 0.38 nm apart are clearly resolved. Combined CBED and HREM for structural analysis is an important development in electron crystallography.
Defects in photorefractive BaTiO3 crystal, obtained by the top seed solution growth method, have been studied by analytical electron microscopy. Thin foils containing inclusions for transmission electron micrsocopy (TEM) were prepared by ion milling the mechanically polished thin sections. Combining diffraction and electron energy loss spectroscopy in a TEM, the inclusions were identified as amorphous Ba-Ti-O and Ba6Ti17O40. Other microdefects which are only visible in the TEM have been identified as crystalline precipitates.
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