Abstract
The structure of copper tellurite and borotellurite glasses is studied by x-ray and neutron diffraction, reverse Monte Carlo (RMC) simulations, FTIR, Raman and 11B MAS-NMR spectroscopy. Copper tellurite sample with 15 mol% CuO forms precipitates of tetragonal TeO2 within the glass matrix on melt quenching. The glass forming ability of the xCuO–(100−x)TeO2 system enhances with increase in CuO concentration from 15 to 20 mol% and also with the addition of B2O3. RMC simulations on the neutron diffraction data found that the Cu–O and Te–O bond lengths are approximately at equal distances in the range: 1·96 to 1·98±0·02 Å, while the nearest O–O distance is at 2·71±0·02 Å. Neutron and Raman results on the Te–O speciation are in agreement and confirmed that the Te–O coordination decreases with an increase in CuO and B2O3 molar concentrations in the tellurite and borotellurite glasses, respectively. RMC studies found that Cu2+ has tetrahedral coordination with oxygen, as predicted by Jahn–Teller distortion and that Cu–O and Te–O structural units have very similar size and geometry. The copper tellurite glass-ceramic sample with 15 mol% CuO was heat treated and it formed crystalline precipitates of TeO2 and CuTe2O5 upon devitrification; the average Te–O coordination was significantly smaller in the glass as compared to that in the crystalline sample.
Highlights
The decrease in density is due to the replacement of heavier TeO2 (159·6 amu) by the lighter B2O3 (69·62 amu) (Table 1) while the molar volume decreases due to the replacement of larger Te4+ (0·66 Å) by the smaller B3+ (0·11 Å).(56) Both density and molar volume decrease with increase in B2O3 mol% in copper borotellurite glasses and similar effects are reported in other glass systems such as silver borotellurites and tungsten tellurites.[57,58]
The band in the range: 820 to 1130 cm−1 is due to the B–O bond vibrations in BO4 units while the band from 1130 to 1550 cm−1 is due to BO3 structural units.[37]. The addition of B2O3 up to 30 mol% in copper borotellurite glasses decreases the intensity of the absorption band in the range: 450 to 1130 cm−1 which confirms the decrease in the concentration of Te–O–Te linkages and BO4 units
The short range structure of copper tellurite and borotellurite glasses was studied by multiple techniques
Summary
Tellurite glasses have several attractive properties such as high refractive indices, low melting points, low phonon energies, high dielectric constants and high transmittance from visible to the near-infrared range of the electromagnetic spectrum; and have applications in nonlinear optical devices for second and third harmonic generation and in optical waveguides for light communication.[1,2,3,4] Tellurite glasses and glass ceramics that contain transition metal oxides such as CuO and V2O5 are semiconducting and show significant electronic conduction and have potential electrochemical applications as cathode materials in secondary batteries.[5,6,7]. TeO4 and TeO3 are the basic structural units of the tellurite glass network and both these structural units contain a lone pair of electrons at the equatorial sites.[8,9] The addition of transition metal oxides in tellurite glasses modifies the structure by forming new ionic bonds and creates nonbridging oxygens that affect the electrical conductivity, thermal stability and optical properties of glasses.[10,11,12,13] The addition of. Physics and Chemistry of Glasses: European Journal of Glass Science and Technology Part B Volume 61 Number 1 February 2020
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