Synthesis of disordered pyrochlores, A2Ti2O7 (A=Y, Gd and Dy), by mechanical milling of constituent oxides

This paper reports the mechanochemical synthesis and the structural and microstructural characterization of three titanates, A2Ti2O7 (A=Y, Gd and Dy), with a pyrochlore-like structure.Starting from stoichiometric mixtures of elemental oxides TiO2 and A2O3, single-phase samples of highly disordered pyrochlores were obtained after milling. Differential thermal analysis of the as prepared powders showed in every case the presence of a single exothermic event at temperatures close to 800 °C. The evolution of the structure and microstructure of these highly-disordered pyrochlores with temperature was studied by combining XRD and IR and Raman spectroscopies. On heating, both the cation and anion arrays in Y2Ti2O7 and Dy2Ti2O7, order by two independent processes. The exothermic events observed in DTA have their origin in the ordering of the anion sublattice, whereas cation ordering progress smoothly with temperature. Gadolinium titanate, Gd2Ti2O7, behaves differently to the other two compounds studied concerning the cation sublattice: no evidence of cation disorder is observed, even in the just-milled sample.