Phase diagram of SrSi2 to 40 kbar and 1200°C

The pressure-temperature phase diagram of dimorphic SrSi₂ was investigated in the pressure range 10–40 kbar and temperature range 600–1200°C in a belt-type apparatus. The phase boundary between cubic SrSi₂I (SrSi₂-type) and tetragonal SrSi₂II (-ThSi₂-type) was studied by X-ray techniques in quenched samples. The curvature of the equilibrium line was not resolved. Molar volumes of both polymorphs have been measured in the temperature range 20–400°C at ambient pressure. From the slope of the equilibrium line in the pressure-temperature diagram and the change in molar volume, approximate values of the entropy and heat of transition SrSi₂(I–II) have been calculated.

In the silicon sublattice of both polymorphs of SrSi₂ the topologically simplest three-dimensional three-connected nets are found to be slightly distorted from their ideal configurations. The ideal SrSi₂-type net represents the three-connected analogy to the four-connected diamond net.