Behavior, properties and structure of copper phosphate glasses

Abstract

Copper phosphate glasses with 40,50 and 60 mole% CuO are melted in air at 1000°C, 1l00°C and 1200°C using quartz or alumina crucibles, and the [Cu²⁺]/[CU(total)] ratio variations with melting time are measured. Glasses are oxidized during melting and reach equilibrium [Cu²⁺] / [CU(total)] ratios which are independent of melting temperature and identical for the 40 and 50 mole% CuO content glasses. Structural considerations rather than a conventional redox reaction seem to determine oxidation-reduction equilibrium of the glass. Thus, the [Cu²⁺] / [CU(total)] ratio in copper phosphate glass can be controlled by changing melting time. In this work, crystallization, optical absorptions, chemical durability, and structure of copper phosphate glass have been investigated depending on the [Cu²⁺] / [CU(total)] ratio in the glass as well as glass composition The crystallization of copper meta phosphate is initiated from the surface and its main crystalline phase is copper metaphosphate (Cu(P0₃)₂), independent of the [Cu²⁺]/[CU(total)] ratio in the glass. However, the crystal morphology, the relative crystallization rates and their temperature dependences are affected by the [Cu²⁺]/[CU(total)] ratio in the glass. The glass transition temperature of the glass increases as the [Cu²⁺] / [CU(total)] ratio is raised. The optical energy gap, E(opt), increases as CuO content and the [Cu²⁺]/[CU(total)] ratio in thE glass are raised. This trend is explained by speculating upon the energy band structure of copper phosphate glass. However, the Urbach energy, ΔE, is affected solely by the [Cu²⁺]/[CU(total)] ratio in the glass. The absorption band of Cu¹⁺ occurs in the vicinity of the absorption tail and is responsible for the increase of ΔE with reducing the [Cu²⁺]/[CU(total)] ratio in the glass. A broad and asymmetric absorption band centered at about 11000 cm⁻¹ is resolved into three component Gaussian absorption bands around 8500 cm⁻¹, 12000 cm⁻¹ and 13250 cm⁻¹. Each of these component absorption bands is assigned to an energy transition between the energy levels in a tetragonally distorted octahedral coordination. The position of the minimum absorption shifts to higher wavenumbers with increasing the [Cu²⁺]/[CU(total)] ratio in the glass regardless of glass composition and is responsible for color changes in the glass. The 55 mole% CuO glass dissolves more readily than either the 40 or 50 mole% CuO glass. As the [Cu²⁺]/[CU(total)] ratio in the glass decreases, the chemical durability improves. Also, the solution pH dependence of the dissolution rate in the oxidized and reduced glasses is found to differ. The structure and Cu²⁺ ion clustering of copper phosphate glass depending on the [Cu²⁺]/[CU(total)] ratio in the glass are investigated by infrared spectra, ESR, SAXS, and TEM.