Successive phase transition of a Cd-Yb 1/1 crystalline approximant under high pressure

Watanuki, Tetsu; Machida, Akihiko; Kawana, Daichi; Aoki, Katsutoshi; Tsai, A. P.*

The phase study of a Cd-Yb 1/1 approximant crystal over a wide pressure and temperature range is crucial for the comparison study between periodic and quasi-periodic crystals. Our previous X-ray diffraction study revealed that the Cd4 tetrahedra, the most inner part of the atomic clusters, exhibit various structural ordering in the orientation sensitive to pressure and temperature. Five ordered phases appear in a P-T span up to 5.2 GPa and down to 10K. In this study we surveyed higher pressure region up to 30 GPa at room temperature. Single crystal diffraction experiments at SPring-8 (BL22XU) using a helium pressure medium in a diamond anvil cell elucidated that the crystal undergoes successive structural phase transition with an alternation of the period. The bcc phase at ambient pressure transformed to a 3-fold ordered phase at about 12 GPa, and to 4-fold one at about 20 GPa. These phases are different from those found at the previous study.