Structural Evolution of the Binary System Ba-Si under High-pressure and High-temperature Conditions

Abstract

A new silicon-rich binary compound BaSi6 has been prepared by the treatment of the Ba8Si46 clathrate compound under a pressure of 15 GPa at 1000 °C, or from a stoichiometric mixture of BaSi2 and Si by treatment under similar high-pressure and high-temperature conditions. The Rietveld refinements revealed that BaSi6 is isomorphous with EuGa2Ge4, and crystallizes with space group Cmcm and the lattice parameters a = 4.485(1), b = 10.375(2), and c = 11.969(3) Å . Each Ba atom is surrounded by 18 Si atoms in an irregularly shaped polyhedron @Si18. The polyhedra are connected by sharing faces to form Ba containing tunnels along the a axis. All of the Si-rich compounds so far with atomic ratios Si/Ba > 2 in the binary system have been prepared only under high-pressure and high-temperature conditions. There is a general tendency that the Si/Ba ratio of the compounds increases with an increase of the pressure in the preparation.