Sol–gel synthesis, structure characterization and Raman spectroscopy of Gd2−2xBi2xTi2O7 solid solutions

In the present work a comparative study of the sol–gel process of different protocols: centrifugation (CEN) and dryness (DRY), leading to pyrochlore oxides with different compositions in a solid solution, Gd2−2xBi2xTi2O7 was carried out. The thermal decomposition/oxidation of the precalcined gels are investigated by differential thermal analysis (DTA) and thermogravimetric analysis (TG). Chemical changes in the powder mixtures were followed by using X-ray diffraction at high temperature showing that the substituted pyrochlore phases are stables in the domain of temperature 600–1000 °C. Raman experiments revealed the presence of two bands at 71 and 73 cm−1 in spectrum recorded for CEN and DRY samples, respectively, are assigned to the Bi–O bonds in the A site. However, refinement results show that the two powders calcined at 1000 °C present different compositions Gd1.27Bi0.73Ti2O7 and Gd1.28Bi0.72Ti2O7. The substitution of Bi3+ onto the Gd3+ sites in the pyrochlore oxide Gd2−2xBi2xTi2O7 results in a decrease of Ti–O bond.