Increasing the conductivity of V2O5-TeO2 glass by crystallization: structure and charge transfer studies

Abstract

In the present paper, V2O5-TeO2 glass was prepared by the melt-quenching technique. Crystallization of glass with a vanadium content higher than 35%mol results in an increase in electrical conductivity by a few orders of magnitude and a decrease in activation energy from ~0.40 to ~0.12 eV. In this work, a critical review of existing charge transfer models was presented on the example of V2O5-TeO2 glass and glass–ceramics. Schnakenberg’s and Friedman-Triberis’ charge transfer models were found to be applicable to both glass and glass–ceramics. Optical phonon frequencies obtained from Schnakenberg’s model are in agreement with FTIR studies. Values of activation energies obtained from the Schnakenberg model decrease after crystallization. Friedman-Triberis’ model shows an increase in the density of states near the Fermi level from 1019 eV−1 cm−3 in glass, to 1021 eV−1 cm−3 in glass ceramics. Structural studies show that the main crystallizing phase is Te2V2O9 which occurs with the V2O5 shell in glasses with compositions 50–50%mol and 45–55%mol. It is concluded that crystallization results in the reduction of vanadium ions in the remaining glass matrix which leads to an increase in the V4+/V5+ ratio and therefore, an increase in electrical conductivity.

Enhancing electrical properties by in-situ controlled nanocrystallization of V2O5 -TeO2 glass

“…On the contrary, changes in the activation temperature (Fig. 7 (b)) are much less significant than observed previously in glasses [5,30,31] may be involved in the charge transfer in VTGC. The V6O13 compound displayed comparable activation energies of the conduction process [32,33], which can be attributed to its V 4+/ V 5+ ratio (a crucial factor for SPH) being similar to that of the V3O7 compound.…”

“…2 (e)), which crystallizes in the monoclinic structure with C2/c symmetry. In earlier work [5], the The glass and glass-ceramics FTIR spectra (Fig. 3) revealed characteristic absorption bands corresponding to various bond types.…”

“…The decline in 𝑊 with decreasing temperature in the 250C sample is a distinguishing feature of SPH. Mott [26] showed that for SPH activation energy (𝑊) should decrease with decreasing temperature at temperatures below 𝜃 𝑂𝑃 /4 (where, 𝜃 𝑂𝑃 = ℎ𝑣 0𝑃 , and 𝑣 0𝑃 is the optical frequency correlated with SPH process [5]), remain stable between 𝜃 𝑂𝑃 /2 < 𝑇 < 𝜃 𝑂𝑃 /4, but increase with increasing temperature above 𝜃 𝑂𝑃 /2 [25]. This observation, in agreement with previous studies [5], shows that higher annealing temperature leads to a more significant decrease of 𝑣 0𝑃 .…”

“…Our previous study of direct current (DC) conductivity of V2O5-TeO2 glass-ceramics (VTGC) also showed the applicability of the small polaron hopping (SPH) model, employing the Schnakenberg polaron hopping model and Triberis-Friedman percolative SPH [5]. However, such low activation energies as ~0.1 eV present in VTGC are not usual in SPH charge transfer, and none of the vanadium oxide allotropes has yet been addressed as directly responsible for such high conductivity in the VOGC.…”

“…Small polaron creation and hopping between ions with different valence states, such as V 4+ and V 5+ , play a crucial role in the electrical conductivity of TMO glass and have been previously considered as possible charge transfer mechanism in VOGC [5]. Research conducted by Garbarczyk et al significantly contributed to understanding the electrical conductivity process in glass-ceramics [6][7][8][9][10].…”