Pressure-Induced Phase Transitions in the Cd-Yb Periodic Approximant to a Quasicrystal

Abstract

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 quasiperiodic crystals. The Cd(4) tetrahedra, the most inner part of the atomic clusters, exhibited various structural ordering in the orientation sensitive to pressure and temperature. Five ordered phases appeared in a P-T span up to 5.2 GPa and down to 10 K. The propagation direction of ordering alternated from [110] to <111> to at about 1.0 GPa and again to [110] at 3.5-4.3 GPa. The primarily ordered phases that appeared by cooling to 210-250 K between 1.0-5.2 GPa further transformed to finely ordered ones at 120-155 K. Besides the original short-range type interaction, a long-range type interaction was likely developed under pressure to lead to the primary ordering of Cd(4) tetrahedra. Coexistence of these interactions is responsible for the complicated phase behavior.

In-situ high-pressure X-ray diffraction on the Zn6Sc 1/1 periodic cubic approximant to a quasicrystal

“…a very large unit cell with a lattice parameter of about 5.5 nm. The resulting pressure-temperature phase diagram is different from that of Cd 6 Yb, which was reported by Watanuki et al (2006). …”

“…A similar dynamical flexibility was observed in the quasicrystal [17] , although in that case the freezing of the tetrahedra occurs progressively, as in a glassy system. Watanuki et al (2006) have investigated the phase diagram of Cd 6 Yb at simultaneous LT and high-pressures and observed five new superstructure schemes, labeled from I to V, as a function of the applied pressure up to 5.2 GPa [18]. They found that the ordering scheme is sensitive to the temperature and pressure: at ambient pressure the LT superstructure (phase I) has a propagation vector along [110] direction of the HT phase, breaking the cubic symmetry.…”

Effect of atom substitution on the low-temperature phase transitions in Cd- and Zn-based 1/1 cubic approximants

“…Watanuki et al have reported that T c increases under high pressure for Cd 6 Yb, indicating that the reduction of the space inside the 2nd dodecahedron shell promotes ordering of the tetrahedra [17]. One interesting fact concerning this point is that T c does not increase with the reduction of the lattice constant, i.e., the reduction of the space inside the 2nd dodecahedron shell, as seen in Figs.…”

Development of Symmetry Concepts for Aperiodic Crystals

“…A comparable phase transition is that in the decagonal quasicrystal, AlCoNi [37]. Another example of a phase transition related to quasicrystals is one in an approximant of the quasicrystal, CdYb [38]. For phase transitions from a quasicrystal to a modulated quasicrystal, one may use the same technique as for the transition from a lattice periodic structure to an incommensurate modulated phase [39,40].…”