Abstract
Although ZrSiO$_4$ is the most well-known compound in the zircon-structured family (space group I41/amd), the experimental conditions for preparing pure and well-crystallized phases which are doped with a tetravalent element via hydrothermal synthesis has never been clearly discussed in the literature. With the aim to answer this question, the experimental conditions of preparation of ZrSiO$_4$ and (Zr,Ce)SiO$_4$ were investigated in order to synthesize well-crystallized and pure phases. A multiparametric study has been carried out using soft hydrothermal conditions, with variables including reactant concentration, initial pH of the reactive medium, and duration of the hydrothermal treatment. Pure ZrSiO$_4$ was obtained through hydrothermal treatment for 7 days at 250°C, within a large acidity range (1.0 ≤ pH ≤ 9.0) and starting from C$_{Si}$ ≈ C$_{Zr}$ ≥ 0.2 M. As hydrothermally prepared zircon structured phases can be both hydrated and hydroxylated, its annealed form was also studied after heating to 1000°C. Based on these results, the synthesis of (Zr,Ce)SiO4 solid solutions were also investigated. The optimal hydrothermal conditions to acquire pure and crystallized phases were obtained in 7 days at 250°C with initial pH = 1 and concentration of the reactants equal to 0.2 mol·L 1. This led to Zr1-xCexSiO$_4$ solid solutions with the incorporated Ce content up to 40 mol.%. Samples were characterized by multiple methods, including lab and synchrotron PXRD, IR and Raman spectroscopies, SEM, and TGA. Moreover, it was found that these phases were thermally stable in air up to at least 1000°C.