High pressure induced distortion in face centered cubic phase of thallium
Significance The III A metals (i.e. Al, Ga, and In) have displayed complexity of structural phase transitions under high pressure. The contribution of d electrons to valence states has been investigated previously and has been suggested to be responsible for that behavior. Here, another III A metal, Tl, is predicted to be an unusual distorted f.c.c. structure (b.c.t. at high pressure and then is confirmed by using the angle dispersive X ray diffraction method. The enhancement of sp d mixing states at valence bands with the increasing pressure is suspected to be the cause of distortion in Tl. The transformation pathway of Tl is intended to be h.c.p f.c.c b.c.t. under compression. Tl is an important element in high temperature superconducting compounds; thus the present study has great implications in the area of superconductivity. The complex and unusual high pressure phase transition of III A (i.e. Al, Ga, and In) metals have been investigated in the last several decades because of their interesting periodic table position between the elements having metallic and covalent bonding. Our present first principles based electronic structure calculations and experimental investigation have revealed the unusual distortion in face centered cubic (f.c.c. phase of the heavy element thallium (Tl) induced by the high pressure. We have predicted body centered tetragonal (b.c.t) phase at 83 GPa using an evolutionary algorithm coupled with ab initio calculations, and this prediction has been confirmed with a slightly distorted parameter (2 x a c)/c lowered by 1% using an angle dispersive X ray diffraction technique. The density functional theory (DFT) based calculations suggest that s p mixing states and the valence core overlapping of 6s and 5d states play the most important roles for the phase transitions along the pathway h.c.p f.c.c. b.c.t.
Proceedings of the National Academy of Sciences