Compositional changes in Ca3TaGa3Si2O14 single crystals upon high-temperature reducing treatment

Abstract The impact of the long-term reducing annealing (168 h at 1000 °C in a 99.5% Ar + 0.5% H 2 gas mixture) on the structural and optical properties of piezoelectric Ca 3 TaGa 3 Si 2 O 14 (CTGS) single crystals is investigated. The study employs various complementary analytical techniques, including X-ray diffraction (XRD), Raman spectroscopy, optical microscopy, electron probe microanalysis (EPMA), and UV–Vis spectroscopy to investigate the effects of this treatment. The annealing process led to the formation of a complex, anisotropic diffusion layer on the CTGS surface, consisting of an opaque surface-adjacent layer approximately 80–90 μm thick, followed by an intermediate region extending 200–300 μm into the crystal. XRD analysis revealed the formation of new phases on the sample surface, including tantalum and calcium oxides, which is further supported by EPMA, indicating evaporation of gallium suboxide from the surface. Graphical Abstract