Optical properties of strontium titanate monocrystals grown by Czochralski method from a cold container

The effect of annealing on absorption spectra of strontium titanate monocrystals grown by Czochralski method using direct HF-heating in a cold container is investigated. The character of crystal colouring befor annealing is determined by thermal conditions during growth as well as by presence of foreign non-controlled impurities in the initial burden. Processes of crystal surface reduction and diffusion of oxygen vacancies in the volume are shown to proceed at a noticeable rate at 770 K. Change of annealing temperature results in change of absorption spectra caused by change in electron and vacancy concentration and electron redistribution among different colouring centres. Rapid cooling of the crystal up to the temperature below 670 K after isothermal annealing partially inhibits the state attained during annealing. It permits to observe at room temperature the state corresponding to equilibria at temperatures above room temperatures