Photochromism of a BaMgSiO₄ Phase Prepared with a Nonstoichiometric Nominal Composition

抄録

Barium magnesium silicate, BaMgSiO₄, sintered together with H₃BO₃ in a reducing atmosphere is known to show photochromism, with the generation of a pink color following UV irradiation. It is thought that this photochromism originates from oxygen vacancies in the silicate. In this work, we investigated the nominal Ba-deficient composition Ba_1-xMgSiO_4-x (0 ≤ x ≤ 0.05) in an attempt to effectively generate oxygen vacancies in the silicate. BaMgSiO₄ phases were obtained from a combination of BaCO₃, MgO and SiO₂, without the addition of H₃BO₃, by sintering in a reducing atmosphere. All samples were pink-colored after UV irradiation and this photochromism was confirmed to be an intrinsic property of BaMgSiO₄. The color densities of our samples were inferior to that of a previously reported sample sintered with the addition of H₃BO₃, and the addition of H₃BO₃ is believed to improve the photochromism color density. A tendency for the color density to decrease with increasing Ba-deficiency was found among our samples. The observed degradation of the photochromism is discussed based on nonstoichiometry in the BaMgSiO₄ phase.