The field of solid solutions in ternary system of synthetic apatite-type alkaline earth element-yttrium-silicate oxybritholite phases of the composition: AEEδY10−δ[SiO4]6O3−0.5δ, where AEE=Ca, Sr and Ba

This contribution deals with the synthesis, properties and investigation of the field of solid solutions formed between the three end-members of apatite-type alkaline earth element-yttrium-silicate oxybritholites with the hexagonal structure (P63/m). The stoichiometric composition of these compounds corresponds to the formula AEEδY10−δ(SiO4)6O3−0.5δ, where AEE=Ca, Sr and Ba and parameter δ→2. These compounds and their solid solutions crystallize from non-equilibrium high temperature flux as the main product of sinter-crystallization process. Increasing ionic radius of AEE cations has significant effect to the lattice parameters, properties and miscibility of apatite phases. While there is non-limited miscibility of solid solutions formed between Ca2Y8[SiO4]6O2 and Sr2Y8[SiO4]6O2, the highest content of barium in the binary solution with these species is limited to 28% and 38%, respectively. The connecting line of these points marks out the borderline for the field of solid solutions in the ternary system. All attempts for the preparation of pure Ba2Y8[SiO4]6O2 end-member via the ceramic method were not successful.