Effect of composition on Bi2O3–SiO2–GeO2 glass properties

Abstract

Glasses with composition Bi4(SixGe 1– x )3O12, where x = 0.33, 0.5 and 0.06, were obtained by melting for 30 min and two-step melting. Their characteristic temperatures, densities, refractive indices and microhardness were determined and the composition dependences studied. Glasses in the system Bi 2 O 3 –GeO 2 –SiO 2 are used in optics, electronics, and the telecommunications industry as laser materials when doped with rare-earth elements and as cryogenic charged-particle detectors when reduced in a hydrogen atmosphere. The possibility using these glasses as a basis to obtain glass ceramic materials with scintillation properties is of greatest interest, since many sensitive scintillation elements currently used have a number of substantial drawbacks. For example, NaI and LiI crystals are hygroscopic, which causes instruments to malfunction; CsI is nonhygroscopic but it is unstable under high irradiation doses, which sharply curtails its applicability. ZnS single crystals cannot be used to detect -radiation because of the lose transmission in the visible range. The range of application of single-crystal KI is limited by the presence of 40 K in it. In addition, each material mentioned above requires activating additives, which are required in order for it to scintillate. In this light there is promise in using single crystals with the structure of eulytin (Bi4X3O12, where X = Si, Ge) as the active element, since the centers of emission are bismuth ions, making activators unnecessary. For equal volumes BGO and BSO crystals show higher photon detection efficiency than other scintillation crystals. The undoubted advantages of eulytins are their mechanical properties and nonhygroscopicity. In view of the difficulties arising in growing eulytin crystals, which greatly increase production costs, a step forward is the use of glass ceramic materials based on glasses with equivalent composition. Matrix glasses are produced using well-perfected classic technologies, and glass ceramic materials can be obtained from them by easily accessible methods — heat treatment or laser irradiation. Transparent glass ceramic materials based on glass with the compositions 2Bi 2 O 3 ;3SiO 2 and 2Bi 2 O 3 ;3GeO 2 , containing up to 70% eulytin crystallites and possessing scintillation properties close to those single crystals, have now been obtained. As in the case of single crystals these properties of bismuth-germanate glass ceramics are higher while the radiation resistance is lower than for bismuth-silicate. In turn, bismuth-silicate glass ceramic is characterized by the opposite properties (the scintillation properties are lower but the radiation resistance is higher) [1]. Therefore, combining the useful properties of both materials in a single material is a topical problem. Most works are devoted to studying phase equilibria in the binary systems Bi2O3–GeO2 and Bi2O3–SiO2. The ternary system Bi 2 O 3 –GeO 2 –SiO 2 has been less studied. Glass formation in the indicated system was studied in [2]: the characteristic temperatures were determined, nontransparent glass ceramic materials based on these glasses were obtained, and the composition of the crystallizing phases and the lattice parameters of the crystals formed were determined.