Optical, electrical, and X-ray-structural studies on Verneuil-grown SrTiO 3 single crystal: Annealing study

Abstract

In order to clarify crystal defect effects on the physical phenomena observed for a SrTiO 3 single crystal grown by Verneuil method, the optical density and photoluminescence spectra, complex impedance spectra, and crystal structure were fully studied for the as-grown crystal boule. The as-grown crystal boule consists of a shell (which is colorless transparent and electrically good insulator) and a core (which is dark blue and has a high electrical conductivity (>10 –3 Ω –1cm –1), and a colossal static dielectric constant (>10 6) at room temperature). The as-grown single crystal was then annealed at 973 K in an Ar–H 2 gas stream. With the progressing of annealing, the as-grown single crystal becomes colorless-transparent insulator and the static dielectric constant decreases down to approximately 300 at room temperature. The X-ray crystallographic studies indicate that the crystallinity is almost independent of the annealing, while the dielectric property is considerably affected by the annealing. A model on the basis of a (Ti 3+–oxygen vacancy) complex defect is proposed for explaining the observed properties of SrTiO 3.