Multiphonon tunneling conduction in vanadium-cobalt-tellurite glasses

Abstract

Ternary vanadium oxide glasses in the system V 2 O 5 -CoO-TeO 2 are fabricated by press quenching of glass melts, and dc conductivities ͑͒ are investigated at temperatures from 330 to 475 K for different glass compositions. From the study of the phase diagram, the glass formation region is found to be in the range of V 2 O 5 ϭ0 -85 mol %, CoOϭ0 -35 mol %, and TeO 2 ϭ25-100 mol %. These glasses contain microcrystalline clusters dispersed in the glass matrix. In the high-temperature regime above ⌰ D /2 ͑⌰ D is the Debye temperature͒, the small polaron hopping model is found to be applicable. In the low temperature ͑below ⌰ D /2͒ regime, however, both Mott's variable-range hopping and the Greaves' intermediate range hopping models are found to be not applicable. The most probable transport for the entire range of temperature and compositions is concluded to be due to multiphonon tunneling of large polarons between the microclusters, supporting the model proposed by Shimakawa. ͓S0163-1829͑99͒03029-5͔

Characterization and transport properties of V2O5–Fe2O3–TeO2 glasses

“…Because Fe 2 O 3 is not a glass network former, Fe ions are isolated in the glass network, which causes obstruction in the hopping of electrons due to the lack of oxygen bonds. A similar lowering of conductivity was also observed in V 2 O 5 -MnO-TeO 2 [11], V 2 O 5 -NiO-TeO 2 [4] and V 2 O 5 -CoO-TeO 2 [16] glasses.…”

“…This is why they have a direct influence on the isolated V@O bonds of VO 5 groups according to scheme Fe-O-V. As a result of this, they should be longer and the frequencies of vibrations should be shifted towards the lower wavenumbers. A similar manner of interaction has been discussed concerning glasses, having a V 2 O 5 -TeO 2 composition [16]. In the glass containing 62.5-65 mol% V 2 O 5 (i.e.…”

The thickness effect on the electrical conduction mechanism in titanium oxide thin films

“…Also the obtained values of VRH parameters are of the same order of magnitude as that found in a variety of metal oxide systems [12,24,25]. This indicates that the conduction in the considered temperature range is due to VRH in the investigated samples.…”

Effects of crystallization and microstructure on the dc electrical conductivity in the system xCuO–(70−x) MnO–30SiO2

“…where = θ D k/h is the optical phonon frequency (generally ν o ≈ 10 13 s -1 ) [23], h is the Planck's constant, C is the fraction of reduced transition metal ion, α is the tunneling factor (the ratio of wave function decay) and this value is taken from the literature quoted for transition metal ions doped glasses (α = 20 nm -1 ) [23], W H is the hopping energy and W D is the disorder energy defined as the difference of electronic energy between two hopping sites [24]. A typical value of W D calculated from Mott-Austin Theory is ≤ 0.1 eV [25].…”