Optimization of Synthesis Parameters for the Preparation of Dysprosium, Holmium and Erbium Silicate Systems by Solid-State Reaction

Rare earth silicate materials received growing attention in recent years, driven by their potential for use in thermal/environmental barrier coatings and for scintillation applications for gamma-ray and X-ray detectors. R2SiO5, R2Si2O7 and R4.67(SiO4)3O (where R = Dy, Ho and Er) have been prepared by the conventional solid-state synthesis method. Through a systematic study, we have optimized the synthesis conditions, from the choice of the precursor to the optimal temperature profile for the chemical reaction. We demonstrate that, despite an overlap of the thermal stability ranges of different rare earth silicate compounds and their polymorphs in the phase diagrams of the R-Si-O systems, it is feasible to prepare polycrystalline materials with a high yield of the target phase. Moreover, we offer our perspectives into the kinetics of the different chemical phases within the rare earth silicate systems. We show that the chemical reactions are faster when employing the α-cristobalite polymorph of SiO2 as a precursor, and we establish a reliable and reproducible solid-state synthesis protocol for Dy2SiO5, Ho2SiO5, Er2SiO5, Ho2Si2O7, Er2Si2O7, Dy4.67(SiO4)3O and Ho4.67(SiO4)3O. We reveal the results of our efforts to optimize the synthesis conditions for the preparation of all Dy-, Ho-, and Er-based silicate phases, which can be extended to other members of the rare earth silicate families, enabling the synthesis of bulk materials with improved phase purity.