Study of the origin of the defects in La3Ga5.5Ta0.5O14 single crystals

We performed a comprehensive study of the properties of La3Ga5.5Ta0·5O14 crystals grown in different atmospheres before and after the post-growth treatments (annealing in air and vacuum) using different methods to clarify the origin of defects. The optical properties and elemental composition of the crystals depend on the growth atmosphere and the atmosphere of annealing. The absorption spectra of the colored crystals contain two strong broad bands in the UV spectral region (λmax∼290 and λmax ∼370 nm), one broad band in the visible range (λmax ∼480 nm). The spectra of the colorless crystals show a weak band at λmax ∼290 nm. The data obtained by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy indicate that there is a difference in the ratio of the main elements in dependence on the growth atmosphere and lack of gallium is observed at any growth atmosphere. An analysis of X-ray diffuse scattering indicates that the predominant type of defects is vacancy-type. There are more vacancy-type defects in crystals grown in Ar + O2 atmosphere than in Ar. On the base of the results of our study, we propose a self-consistent model of the defect origin in LGT crystals. The main defects are the Schottky-type defects. With add of oxygen in the growth atmosphere, F-centers are formed. During annealing in air, the concentration of the F-centers increases, and annealing in a vacuum leads to the destruction of F-centers.