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 M AE Si 2 (M AE = 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, CaSi 2 has three high-pressure phases: EuGe 2 phase, α-ThSi 2 phase, and AlB 2 -like phase. At pressures ranging from 0 to 7.8 GPa and temperatures ranging from 300 to 1300 K, SrSi 2 has a high-pressure phase, the α-ThSi 2 one. BaSi 2 was confirmed to have three high-pressure phases, the SrSi 2, the EuGe 2, and BaSi 2 -IV, in the pressure−temperature region ranging from 0 to 9.5 GPa and from 300 to 1300 K. In M AE Si 2, 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 AX 2 -type compounds. This is due to the fact that the same structure is observed at the same volume region in M AE Si 2 .