Phase Transitions of Alkaline-Earth-Metal Disilicides MAESi2 (MAE = Ca, Sr, and Ba) at High Pressures and High Temperatures

The structural phase transitions of alkaline-earth-metal disilicides MAESi2 (MAE = Ca, Sr, and Ba) at high pressures and high temperatures were investigated by the in situ X-ray diffraction technique. At pressures ranging from 0 to 15.5 GPa and temperatures ranging from 300 to 1300 K, CaSi2 has three high-pressure phases: EuGe2 phase, α-ThSi2 phase, and AlB2-like phase. At pressures ranging from 0 to 7.8 GPa and temperatures ranging from 300 to 1300 K, SrSi2 has a high-pressure phase, the α-ThSi2 one. BaSi2 was confirmed to have three high-pressure phases, the SrSi2, the EuGe2, and BaSi2-IV, in the pressure−temperature region ranging from 0 to 9.5 GPa and from 300 to 1300 K. In MAESi2, the structures that appear at high pressures are the same as those of alkaline-earth disilicides or rare-earth disilicides with a smaller volume per chemical formula unit under ambient conditions. The observed structural sequence is different from that already known in other AX2-type compounds. This is due to the fact that the same structure is observed at the same volume region in MAESi2.