What is the exact structure of the AlB2-like polymorph of the CaSi2 compound?

The 3R polymorph of CaSi2

“…The E-V relations also reveal the pressure induced transition of the 6R polymorph to superconducting EuGe 2 -type CaSi 2 (at around 7 GPa), and the EuG 2 -AlB 2 transition at even higher pressures. Those transitions have already been the subject of several investigations [35][36][37]. Figure 7 shows the electronic density of states (DOS) of the 6R and 3R structures at their computed equilibrium volumes.…”

New high pressure polymorph of theCaSi2compound with Laves structure

“…1,21,22 The transition pressure giving the tetragonal tI12 (I4 1 /amd) was calculated to be 2.5 GPa. 5 Experimentally, this structure requires high temperature of about 1300 K to be obtained at 2.5 GPa according to the P -T phase diagram. 21 However, one should not necessarily consider this as a disagreement between calculations and experiment.…”

“…This is also supported by the fact that the other experimental properties were accurately reproduced theoretically. 5 At room temperature, one should wait until 7.0 GPa (Ref. 5) to obtain the EuGe 2 (P3m1) structure.…”

“…5 At room temperature, one should wait until 7.0 GPa (Ref. 5) to obtain the EuGe 2 (P3m1) structure. This pressure is correctly predicted by calculations at 6.7 GPa.…”

“…Taking into account the fact that the atomic radius of silicon is very close to the aluminum atomic radius, even if they are very different chemically, it would be very interesting to investigate the effect of changing aluminum atoms with silicon. The third argument is based on the recent result 5 showing that the true structure of the AlB 2 -like high pressure polymorph should likely be the KHg 2 derivative of the AlB 2 structure. Indeed, let us consider the α-CaCd 2 compound which is known to have the MgZn 2 Laves structure (C14) at room temperature.…”