New helical chain structure for scandium at 240 GPa

X-ray diffraction experiments were carried out at 297 K in order to study structural-phase transitions of the trivalent rare-earth metal scandium (Sc) at pressures of up to 297 GPa. Four stages of structural transition were observed around 23, 104, 140, and 240 GPa. The crystal structure of the highest-pressure phase, Sc-V, was found to be a hexagonal lattice (S.G.: P6(1)22 or P6(5)22) consisting of 6-screw helical chains. The lattice can be derived from modulations of the interplane stacking of the (111) planes in an fcc arrangement. The occurrence of an anisotropic structure suggests the importance of interactions between 3d orbitals with their nearest-neighbor atoms.