The influence of annealing at different temperatures and atmospheres on the optical rotation of Bi12SiO20 crystals

The optical activity changes in Bi12SiO20 (BSO) crystals induced by thermal annealing treatments are studied. It is found that the annealing in vacuum and hydrogen atmosphere causes decreasing of the optical rotation. Thermal treatment annealing induces reduction of Bi-ions to metallic bismuth on the surface as well as oxygen and bismuth diffusion and evaporation is supposed. Annealing in oxygen leads to partial recovery of the oxygen content in the crystals and the optical activity values tends to approach the level of un-annealed BSO crystal. (C) 2003 Elsevier B.V. All rights reserved.