A high resolution diffraction camera was developed. The camera has essentially the same construction as Guinier-camera combined with a focusing monochromator. It is possible to use a single crystal specimen in the system, which can attain higher resolution. The small change of the lattice constants due to an exsolution was investigated in order to confirm the resolution of the system. It was concluded that the change of d-spacing of 10⁻⁴nm in order can be detected by the present system.

抄録全体を表示

Cyclic loading deformation experiments on [110]_c oriented synthetic forsterite single crystals have been performed at about 1640K and ambient pressure, in order to confirm cyclic loading effects on deformation. Loading pattern was set as a systematic alternation of lower loading steps and higher loading steps. According to the present mechanical data, it seems that the response of strain rate to an additional stress has a hysteresis in the early period during which dislocation multiplication controls the deformation. With increasing the number of cyclic loading, dislocation glide comes to dominate the deformation, and then the hysteresis disappears.

抄録全体を表示

The crystal structure of LiNbO₃ with congruent composition was refined at room temperature by means of the single-crystal X-ray diffraction method under consideration of anharmonic thermal vibration. The space group is R3c with the hexagonal cell dimensions of a=5.15020(6) and c=13.8653(4) Å and Z=6. Large residual electron densities were observed after the ordinary refinement around the Nb⁵⁺ ion, which were supposed to be caused by anharmonic thermal vibration of the ion. Coincidence of the observed structure factors with the calculated ones was largely improved with the least-squares refinement containing anharmonic thermal parameters in the variables to be refined. It was revealed that the positional parameters shift significantly with this refinement from those obtained with the harmonic thermal vibration model. The Nb²⁺ ion in the present crystal has large anharmonicity in the thermal motion at room temperature. However, the magnitude is smaller than that of Ta⁵⁺ in LiTaO₃ owing to the higher ferroelectric phase transition temperature of this crystal than that of LiTaO₃. The coordination octahedra LiO₆ and NbO₆ show large distributions due to face-sharing as in the corundum-type and other related structures.

抄録全体を表示