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.

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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.