Electrical conductivity and local structure of lithium iron tungsten vanadate glass

Abstract

A relationship between physical properties and local structure of 20Li2O·10Fe2O3·xWO3·(70–x)V2O5 glass, abbreviated as xLFWV glass (x = 0 − 25 in mol%), was investigated by 57Fe-Mossbauer spectroscopy, Fourier transform infrared spectroscopy (FT-IR), differential thermal analysis (DTA), leaching test using 20 vol% HCl and DC two- or four-probe method. 57Fe-Mossbauer spectra of xLFWV glass showed an increase of quadrupole splitting (Δ) from 0.67 to 0.73±0.02 mm s − 1 and a constant isomer shift (δ) of 0.39±0.01 mm s − 1 with an increase of ‘x’ from 0 to 25. This suggests that FeIIIO4 tetrahedra gradually increase their local distortion along with a substitution of WO3 for V2O5. DTA of xLFWV glass showed an increase in glass transition temperature (Tg) from 252 to 298\(_{\pm 5}^{\circ}\)C with an increase of ‘x’. Composition dependency of Tg and Δ indicates that FeIII atoms occupy substitutional sites of WO6 octahedra as network former (NWF), since a large slope of 680 K (mm s − 1) − 1 was obtained in Tg − Δ plot. Comparable electrical conductivities (σ) of 2.5 × 10 − 6, 1.9 × 10 − 6, 8.4 × 10 − 7 and 2.9 × 10 − 6 S cm − 1 obtained for xLFWV glasses with ‘x’ of 0, 10, 20 and 25, respectively increased to 2.4 × 10 − 2, 2.4 × 10 − 3, 3.5 × 10 − 4 and 8.8 × 10 − 5 S cm − 1 after annealing at 400 °C for 100 min. Smaller Δ values of 0.58 and 0.67±0.02 mm s − 1 obtained in annealed xLFWV glasses with ‘x’ of 0 and 10, respectively indicate that structural relaxation occurs in VO4 units of vanadate glass units, as had been observed in other vanadate glasses.