XPS Study of Changes in the Chemical Composition of Langasite Crystal Thin Surface Layers during Vacuum Annealing

La3Ga5SiO14 langasite (LGS) crystals have been studied before and after 1000–1050 °C, 650 °C vacuum annealing. XPS studies have shown that the relative intensity of the gallium bands in the survey spectra of the as-annealed LGS crystals at elevated temperatures is one order of magnitude lower compared to the source specimen. To quantify the changes in the chemical composition of the crystal thin surface layers, we have measured depth profiles with Ar+ sputtering. It was shown that crystal surface is depleted of gallium during annealing at elevated temperatures. We suggest a model in which we attribute the changes in the chemical composition of the LGS crystal thin surface layers during vacuum annealing to the formation of the volatile Ga2O oxide. Vacuum annealing of the LGS crystals at 650 °C did not cause any significant changes in the surface chemical composition of the crystals.