First-principle calculations of the structural, elastic and bonding properties of Cs2NaLnCl6 (Ln=La-Lu) cubic elpasolites

For the first time the structural, elastic and bonding properties of 15 elpasolite crystals Cs2NaLnCl6 (Ln denotes all lanthanides from La to Lu) were calculated systematically using the CRYSTAL09 program. Several trends in the variation of these properties in relation to the atomic number Z of the Ln ions were found; in particular, the lattice parameter of these compounds decreases with Z (which can lead to the increased crystal field splittings of the 5d states for the heavier Ln ions), whereas the elastic constants and Debye temperature increase. The degree of covalency of the Ln-Cl chemical bonds is increased toward the end of the lanthanide series.