Nonstoichiometry of the New Laser Host LiCaAlF6

LiCAF (LiCaAlF₆) and LiSAF (LiSrAlF₆) single crystals were grown by the Czochralski technique. DTA measurements of the grown crystals and of different mixtures within the ternary systems LiF—Me^IIF₂—AlF₃ (Me^II = Ca, Sr) lead to the conclusion, that LiCAF melts incongruently with a deficiency of CaF₂. For LiSAF congruent melting and no deviation from the ideal stoichiometry could be observed. From DTA results the enthalpies of fusion were determined: ΔH_LiCAF ≈? 110 kJ/mol, ΔH_LiSAF ≈? 80 kJ/mol. The circumstance, that LiSAF crystals are usually reported to have much better optical properties in comparison to LiCAF is attributed to these differences in the thermodynamic behaviour.