Structural phase transitions of zintl-phase silicide BaSi2 and formation of Si clathrate Ba8Si46 at high pressures and high temperatures

Abstract

This article reviews structural phase transitions of Zintl-phase silicide BaSi2 at high pressures and high temperatures and a formation of Si clathrate Ba8Si46 from an 8:30 molar mixture of BaSi2 and Si at high pressures and high temperatures. At pressures ranging from 0 to 10 GPa and temperatures ranging from 300 to 1300 K, BaSi2 has four phases: BaSi2 phase, EuGe2 phase, SrSi2 phase, and BaSi2-IV phase. When heated at approximately 5 GPa, BaSi2 undergoes the three structural phase transitions: the BaSi2-to-EuGe2, the EuGe2-to-SrSi2, and the SrSi2-to-BaSi2-IV transitions. At 4.3 GPa, Ba8Si46 is formed by a solid state reaction of an 8:30 molar mixture of SrSi2-phase BaSi2 and Si after BaSi2 undergoes the BaSi2-to-EuGe2 and the EuGe2-to-SrSi2 transitions. The structural phase transitions of BaSi2 and formation process of Ba8Si46 are discussed comparing it with structural phase transitions of SrSi2 and of an 8:30 mixture of SrSi2-pahse SrSi2 and Si.