Seiki Watanabe

Amorphous copper formation and related phenomena at ultrahigh pressure

Oxygen free high conductivity (OFHC) copper was slowly sheared at ultrahigh pressure at room temperature. Its transmission electron diffraction pattern (TEM diffraction pattern) showed three diffuse halo rings. Transmission electron micrographs (TEM) corresponding to this pattern showed neither dislocation nor grain boundary. These results indicate the formation of an amorphous state. This state remains at atmospheric pressure. Another TEM diffraction pattern that indicates an intermediate structure between the above amorphous state and crystalline copper was also observed.

Transformation of SiO2 to the amorphous state by shearing at high pressure

Abstract A natural α-quartz disc with flat surfaces perpendicular to (100) was sheared at 5 GPa in order to confirm that the sheared state at high pressure is not always the same as that obtained at high hydrostatic pressure. A transmission X-ray diffraction pattern taken from the sample that was sheared at high pressure revealed five broad halo rings; the pattern was taken about three months after the highpressure experiment. The ratios of the interplanar spacing corresponding to the densest radius of the smallest ring to those of the other ones are 0.610, 0.514, 0.459, and 0.399, respectively. This set of rings does not appear from α-quartz. These are approximately equal to those obtained from solids with space group Fd3m. A Raman spectroscopic study also showed the structural change due to shearing at high pressure. The spectrum appears neither from α-quartz nor from coesite. These facts indicate, therefore, that the crystalline α-quartz sample transformed to the amorphous state based on a structure consistent with Fd3m space group.

Transmission electron diffraction pattern indicating partly ordered, partly disordered solid structure

Transmission electron diffraction pattern taken at room temperature from repeatedly severely rubbed titanium showed three halo rings and three spotted rings. All the rings correspond to those of β-Ti that is usually stable above 1153 K, although the pattern was taken at room temperature at least one month after the repeated rubbing at room temperature. The possible explanation of this pattern is the formation of partly ordered, partly disordered structure.