Physical, Optical, and Spectroscopic Studies on MgO-BaO-B2O3 Glasses

The mixed alkaline effect in double alkaline borate glasses MgO-BaO-B2O3 containing small proportions of copper oxide (CuO) has been studied. The glass samples are characterized by optical absorption, electron paramagnetic resonance (EPR), and Fourier transform infrared spectroscopy (FTIR). A red shift in optical absorption peaks with increasing MgO (decreasing BaO) concentration has been observed. The values of “ ” tensor and hyperfine “ ” tensor have shown inflections with glass composition. The number of spins and paramagnetic susceptibility ( ) also exhibited mixed alkaline effect. The broadening of glass network with increase in MgO concentration is found from the FTIR spectra. Interestingly both density and molar volume have shown decreasing trend with glass composition. The optical band gaps exhibited a nonlinear compositional dependence. As expected, the glass samples possessed higher values of optical basicity (Λ), molar electronic polarizability ( ), and Urbach energy ( ). 1. Introduction Binary alkali and alkaline borate glasses R2O-B2O3 (R = Li, Na, K, Cs, Ca, Mg, Ba, etc.) have been studied extensively by several authors [1, 2]. It is known that boric acid forms stable glasses with alkaline earth oxides (R = MgO, CaO, SrO, BaO) and at the same time alkaline earth oxides improve glass forming ability. These oxides act as glass network formers (GNF) at low concentrations and behave as glass network modifiers (GNM) at higher concentrations [3]. Several researches reported mixed alkali effect (MAE) in borate glasses containing alkali oxides in varying proportions using several experimental techniques such as EPR, Optical absorption, and impedance measurements [4]. The studies on mixed alkali effect (MAE) suggested [5] that alkali ions tend to preserve their local structural environment in the glass system. Liu et al. [6] suggested that alkaline earth ions can also show similar effect, namely, mixed alkaline effect. Miyoshi et al. [7] observed similar behavior of CaO as that of Na2O in their glass systems. The mixed alkaline earth effect is exhibited when one alkaline earth ion is substituted progressively with another one in the glass network. It is of great importance to look into the mixed alkaline effect in glasses as it changes the properties (such as electrical conductivity, , microhardness, refractive index, and density) in a nonpredictive manner [8]. Many researchers focused mainly on mixed alkali borate glasses, but little efforts have been put in to study mixed alkaline effect. In this paper, we have made an attempt to study this