X-ray diffraction and Raman spectroscopy on Gd 2(Ti 2− yTe y)O 7 prepared at high pressure and high temperature

Abstract

A series of Te-substituted pyrochlores of stoichiometry Gd 2(Ti 2− y Te y )O 7 ( 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 Te 4+ and Te 6+ ions occupy the Ti 4+sites; the percentage of the contribution of Te 6+ increases as tellurium content. These substitutions induce an increase of the volume of the TiO 6 octahedron due to the increase in the Ti–O(2) bond length, which preserves the oxygen positional parameter ( x 48f ) and the Gd–O(1) bond length. Results of Raman spectroscopy showed a significant shift to higher frequencies of the E g mode associated to the O(2) sublattice, as well an increase in the full-width-at-half-maximum intensity (FWHM) of the F 2g 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.