Raman and photoluminescence spectroscopic studies on structural disorder in oxygen deficient Gd2Ti2O7-d single crystals

TL;DR

This study uses Raman and photoluminescence spectroscopy to analyze how thermal annealing reduces oxygen vacancies and improves structural order in Gd2Ti2O7-d single crystals, demonstrating a non-destructive way to assess crystal quality.

Contribution

It provides new insights into the correlation between thermal treatment and structural disorder in Gd2Ti2O7-d crystals using spectroscopic techniques.

Findings

Oxygen vacancies decrease with annealing

Raman intensity of specific modes increases with annealing

Photoluminescence indicates reduction of structural defects

Abstract

We report on Raman and photoluminescence spectroscopic studies on oxygen vacancy induced structural disorder in Gd2Ti2O7-d single crystals grown by optical floating zone technique under argon atmosphere. The oxygen vacancies in Gd2Ti2O7-d wafers decrease with thermal annealing in an 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-d. 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-d crystals.