X-ray diffraction and Raman spectroscopy on Gd2(Ti2−yTey)O7 prepared at high pressure and high temperature

A series of Te-substituted pyrochlores of stoichiometry Gd2(Ti2−yTey)O7 (y ≤ 0.2) were prepared under high-pressure and high-temperature conditions and characterized by X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. X-ray diffraction and X-ray photoelectron spectroscopy studies revealed that the Te4+ and Te6+ ions occupy the Ti4+sites; the percentage of the contribution of Te6+ increases as tellurium content. These substitutions induce an increase of the volume of the TiO6 octahedron due to the increase in the Ti–O(2) bond length, which preserves the oxygen positional parameter (x48f) and the Gd–O(1) bond length. Results of Raman spectroscopy showed a significant shift to higher frequencies of the Eg mode associated to the O(2) sublattice, as well an increase in the full-width-at-half-maximum intensity (FWHM) of the F2g mode (O–Gd–O bending) as the level of Te substitution for Ti increases. These results are discussed and compared with those reported in the literature.