Anisotropic phase transition of rutile under shock compression |
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Authors: | Keiji Kusaba Masae Kikuchi Kiyoto Fukuoka Yasuhiko Syono |
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Institution: | 1. Institute for Materials Research, Tohoku University, 980, Sendai, Japan
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Abstract: | Shock recovery experiments for single crystal and powdered specimens of TiO2 with the rutile structure were performed in the pressure range up to 72 GPa. Single crystal specimens were shocked parallel to 100], 110] and 001] directions. X-ray powder diffraction analysis showed that the amount of -PbO2 type TiO2 produced by shock-loading depended strongly on the shock propagation direction. The maximum yield (about 70%) was observed for shock loading to 36 GPa parallel to the 100] direction. In the 001] shock direction, the yield is much smaller than that of the 100] direction. This anisotropic yield was consistent with the observed anisotropy of the phase transition pressure in shock compression measurements. However, transformation to the -PbO2 type cannot explain the large volume change observed above about 20 GPa. On the basis of the high pressure behavior of MnF2, we assumed that the high pressure phase was either fluorite or distorted fluorite type and that the phase conversion to the -PbO2 type was induced spontaneously in the pressure reduction process.We present a displacive mechanism of phase transition under shock compression from the rutile structure to the fluorite structure, in which the rutile 100] is shown to correspond to the fluorite 001] or 110] and the rutile 001] to the fluorite 110]. Direct evidence is obtained by examining the 100] shocked specimen by high resolution electron microscopy. |
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