Local structure and thermal durability of semiconducting
xBaO·(90??
x)V
2O
5 · 10Fe
2O
3 glasses (
x = 20, 30 and 40),
NTA glass TM, before and after isothermal annealing were investigated by
57Fe-Mössbauer spectroscopy and differential thermal analysis (DTA). An identical isomer shift (
$\mathit{\delta}$ ) of 0.39 ± 0.01 mm s
???1 and a systematic increase in the quadrupole splitting (
Δ) were observed from 0.70 ± 0.02 to 0.80 ± 0.02 mm s
???1 with an increasing BaO content, showing an increase in the local distortion of Fe
IIIO
4 tetrahedra. From the slope of the straight line in the
T g–
Δ plot of
NTA glass TM, it proved that Fe
III plays a role of network former. Large Debye temperature (
Θ D) values of 1000 and 486 K were respectively obtained for 20BaO · 70V
2O
5 · 10Fe
2O
3 glass before and after isothermal annealing at 400°C for 60 min, respectively. This result also suggests that Fe
III atoms constitute the glass network composed of tetrahedral FeO
4, tetrahedral VO
4 and pyramidal VO
5 units. The electric conductivity of 20BaO · 70V
2O
5 · 10Fe
2O
3 glass increased from 1.6 × 10
???5 to 5.8 × 10
???2 S cm
???1 after isothermal annealing at 450°C for 2,000 min. These results suggest that the drastic increase in the electric conductivity caused by heat treatment is closely related to the structural relaxation of the glass network structure.
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