Dimorphic LaPdSn and ErAgSn – A first principles study

The stannides LaPdSn (orthorhombic TiNiSi type, Pnma) and ErAgSn (hexagonal NdPtSb type, P63mc  ) both transform to ZrNiAl type (P–6¯2m) high-pressure phases with different transition metal-tin ordering. The electronic structure and the chemical bonding of all four modifications have been studied by quantum theoretical DFT methodologies. Geometry optimizations are in good agreement with the experimentally determined structures. Strongest bonding interactions were observed for Pd–Sn (LaPdSn) and Er–Sn (ErAgSn). These findings result from different site occupancies and the chemical natures and electronegativities of the interacting species forming the prevailing chemical bonds in the NP/HP varieties of the two compounds.

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► Structural change by HP transformation of normal-pressure NP ErAgSn and LaPdSn.
► Relative stabilities NP/HP examined from ab initio with E(V) equations of state.
► E(HP) < E(NP) for LaPdSn and E(HP) > E(NP) for ErAgSn.
► Interpreting the results based on chemical bonding analysis of pair interactions.