Raman and Photoluminescence Spectroscopic Studies on Structural Disorder in Oxygen Deficient Gd₂Ti₂O_7‐δ Single Crystals

Abstract

We report on Raman and photoluminescence spectroscopic studies on oxygen vacancy induced structural disorder in Gd2Ti2O7- single crystals grown by optical floating zone technique under argon atmosphere. The oxygen vacancies in Gd2Ti2O7- wafers decrease with thermal annealing in air atmosphere. The full width at half maximum of X-ray diffraction rocking curve decreases from 245 to 157 arc-second and the optical transmittance increases from 23 to 87 % (at 1000 nm) upon post growth thermal annealing. Raman spectroscopic studies reveal a monotonic increase in intensity of O-Gd-O (Eg) and Ti-O (A1g) stretching modes with thermal annealing.Since these modes are associated with modulation of oxygen x parameter which is sensitive to Ti-O octahedron distortion, the increase in Raman intensity indicates an improvement in structural ordering of oxygen sub-lattice in Gd2Ti2O7-. Moreover, the photoluminescence studies also corroborate the Raman analysis in terms of reduction of structural defects associated with oxygen vacancies as a function of thermal annealing. This study demonstrates the effectiveness of using Raman spectroscopy to probe the structural disorder in Gd2Ti2O7- crystals.

Emerging disorder in Gd2(Ti1−xZrx)2O7 pyrochlores matrices for radioactive waste disposal: symmetry lowering versus defect clustering

“…The Anti-Frenkel defect leaves the O1 site depleted, affecting the A 1g component of band M5 ultimately leading to a decrease in intensity of M5 (ref. 91, 105 and 106) (see Fig. 3c).…”

“…Both the modes related to M5 and M6 harden on Zr-substitution because of short O1–O3 distances in Zr-rich composition, being M5 particularly sensitive to O–O interactions. 91,106 Indeed, as revealed by Rietveld analysis, Zr doping in Gd 2 (Ti 1− x Zr x ) 2 O 7 brings to progressive O3 site occupation and O1–O3 distances that are much shorter than the O1–O1 (≈2.7 Å) and O1–O2 (≈2.9 Å) ones.…”

Understanding of charge relaxation dynamics of Sr doped on Gd 2 Ti 2 O 7 pyrochlore system as Electrolyte for IT-SOFCs

“…displays Raman spectra of all Sr-doped compositions of GTO. Group theory calculations suggest that pyrochlore compounds exhibit six Raman-active fundamental modes (A lg + E g + 3F 2g ) distributed among irreducible representations[33][34][35][36][37][38]. Since A and B cations occupy centrosymmetry sites and do not contribute to Raman-active modes, only O(1) and O(2) atoms participate in Raman…”