Phase transitions ofBaSi2at high pressures and high temperatures

In situ x-ray diffraction measurements reveal that ${\mathrm{BaSi}}_2$ 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 ${\mathrm{AB}}_2$-type compounds such as dioxides of 4A group elements.