Phase transitions of BaSi2 at high pressures and high temperatures

In situ x-ray diffraction measurements reveal that BaSi2 has three high-pressure, high-temperature phases: a trigonal, a cubic, and an additional phase, at pressures up to 7 GPa and temperatures up to 1300 K. The trigonal phase exists at lower temperatures than previously reported, and the additional phase appears in the pressure-temperature region reported as the trigonal region previously. The structures that appear at high pressures are the same as those at ambient conditions of the other alkaline-earth-metal disilicides with a smaller atomic number metal. This is different from structural sequence for pure elements or for AB(2)-type compounds such as dioxides of 4A group elements. [S0163-1829(98)07841-2].