Hidetsugu Mori

Electrical conductivity of V2O5Sb2O3TeO2 glasses

Abstract The dc conductivity of ternary V 2 O 5 Sb 2 O 3 TeO 2 glasses was studied from room temperature to 473 K. The structure of these glasses was found to become more open with increasing in TeO 2 content based upon calculation of oxygen molar volume. The glasses were found to be n-type semiconductors with conductivity of σ = 2.63 × 10 −6 to 1.46 × 10 −3 S cm −1 at 473 K for 11–62 mol% V 2 O 5 . The conduction was confirmed to be due to small polaron hopping between vanadium ions and was adiabatic for V 2 O 5 > 50 mol% and non-adiabatic for V 2 O 5 J = 0.02 to 0.11 eV which depended on the VV spacing. The carrier concentration was evaluated to be the order of 10 21 cm −3 . Estimated carrier mobility was from 10 −7 to 10 −5 cm 2 V −1 s −1 and varied significantly with V 2 O 5 content. The dominant factor determining conductivity was mobility in these glasses.

Small polaron hopping conduction in V2O5–Sb–TeO2 glasses

Abstract The dc electrical conductivity of glasses in the system V2O5–Sb–TeO2 prepared by press quenching was studied at temperatures between 303 and 473 K. The composition range of the glass formation region was found to be 10⩽TeO2⩽100 mol%, 0⩽V2O5⩽70 mol%, and 0⩽Sb⩽20 mol%, respectively. The glasses indicated n-type semiconductors from the measurement of thermoelectric power. The dc conductivities at 473 K for the present glasses were determined to be 6.38×10 −6 –7.13×10 −3 S cm −1 , indicating that the conductivity increased with increasing V2O5 concentration. Sb content also contributed to increase the conductivity and decrease activation energy for electrical conduction. A model of redox reaction during melting was proposed and quantitatively explained the reaction between V2O5 and Sb. A glass of composition 70 V 2 O 5 · 20 Sb · 10 TeO 2 (mol%) having a conductivity of 7.13×10 −3 S cm −1 at 473 K was found to be the highest conductive glass among the previous vanadium–tellurite glasses. From the conductivity-temperature relation, it was found that small polaron hopping model was applicable at the temperature above 1 2 Θ D (ΘD : the Debye temperature); the electrical conduction at T> 1 2 Θ D was due to adiabatic small polaron hopping of electrons between vanadium ions for V2O5⩾50 mol%, and non-adiabatic for 30⩽V2O5 2.90×10 −4 cm 2 V −1 s −1 at 473 K. The carrier density was obtained to be of the order of 10 20 –10 21 cm −3 , and temperature dependence of the carrier density was barely present between 423 and 473 K. The conductivity of the present glasses was primarily determined by hopping carrier mobility.

Low-temperature dc conductivity of V2O5SnOTeO2 glasses

Abstract The dc conductivity of glasses in the V2O5SnOTeO2 system was studied at temperatures between 200 and 473 K. At temperatures from room temperature (RT) to 200 K, a T − 1 4 (T is temperature) dependence of the conductivity was found, and variable-range hopping conduction was confirmed for these glasses. Mott parameters analysis gave the density of states at the Fermi level, N(EF) = 7.33 × 1019−8.45 × 1020cm−3 eV−1 at 230 K, and N(EF) increased with increasing V2O5 content (V2O5 = 40–50 mol%). At RT, variable-range hopping conduction was observed, which was attributable to large values of the disorder energy of the glasses, WD (= 0.08–0.09 eV), dominating the conduction.

Oxygen gas-sensing properties of V2O5-Sb2O3-TeO2 glass

Abstract The oxygen gas-sensing behavior, as measured by the d.c. conductivity σ, of 62.3V 2 O 5 ·4.3Sb 2 O 3 ·33.3TeO 2 glass (mol%) prepared by press-quenching was studied in Ar and O 2 gas atmospheres at temperatures between 303 and 473 K. The glass was n-type semiconducting. The conductivity was lower in O 2 and higher in Ar than that in air. The explanation for this was that V 4+ ions in the glass were oxidized by the O 2 gas which had diffused into the glass, resulting in an increase in V 5+ with time. The experimental relationship between σ and the oxygen partial pressure P O 2 agreed quantitatively with the theoretical relation σα P O 2 −1/4 . Variations in conductivity on switching the atmospheres between O 2 and Ar gases were found to be reproducible, and the O 2 gas sensitivity S at 473 K was found to be 1.2. These dynamic changes could be explained quantitatively by an oxygen diffusion model. From discussions on the gas-sensing behavior, the present glass was revealed to be potentially applicable as an O 2 gas sensor.

Oxygen gas-sensing behaviour of V2O5-SnO-TeO2 glass

The d.c. conductivity, σ, and the oxygen gas-sensing behaviour of V2O5–SnO–TeO2 glass prepared by press-quenching were studied in argon and oxygen gas atmospheres at temperatures ranging from 303–473 K. The glass of 50V2O5·20SnO·30TeO2 (mol %) was n-type semiconducting. The high-temperature conductivity was lower in oxygen and higher in argon than that in air. This was explained by the V4+ ions in the glass being oxidized by oxygen which had diffused into the glass, resulting in an increase in V5+ with time. The experimental relationship between σ and oxygen partial pressure, PO2, agreed quantitatively with the theoretical relation σ ∝ PO2-1/4. Changes in conductivity by switching the atmospheres between oxygen and argon gases were found to be reproducible. From the data of these dynamic changes, the oxygen gas sensitivity, S, at 473 K was obtained to be 1.3 in oxygen atmosphere. The dynamic changes could be quantitatively explained by an oxygen diffusion model. Throughout these discussions, the present tellurite glass was found to possess a potential applicability as an oxygen gas sensor.

Extraction of Silicon Dioxide from Waste Colored Glasses by Alkali Fusion Using Sodium Hydroxide

A process for extraction of SiO 2 from waste colored glasses by alkali fusion using NaOH was investigated. In the present study, glass waste colored bottles of green, blue, brown or black were selected as samples of waste glasses. These colored bottles were qualitatively confirmed to contain elements of Na, Mg, Al, Si, K, Ca, Ti, Mn, Fe and Cu from energy dispersive X-ray spectroscopic analysis. The condition for alkali fusion of NaOH and the waste glasses was optimized, i.e., for each bottle, the composition was NaOH: crushed glass bottle = 90:10 mass%, melting tentperature was 500°C and melting time was 2 h. For each waste colored bottle, the sodium silicate solution was prepared by using the sodium silicate obtained by alkali fusion. After mixing HCl with the obtained sodium silicate solution, Si(OH) 4 was then precipitated by boiling the solution which became to be a very strong acid. After drying the Si(OH) 4 separ ted from the solution, SiO 2 powder with purity of 99.9% was obtained. The yield of 98.3±0.9% for the SiO 2 powder extracted from the bottles was confirmed from quantitative analysis, indicating that the bottles selected in the present study contained about 60 mass% SiO 2 . From the results of yield and purity, the established process was found to have a potential applicability as a recycling process of waste glasses; various utilizations of waste glasses were expected by extracting SiO 2 which is the main component of the glasses.

Effect of annealing on d.c. conductivity of V2O5-SnO-TeO2 glasses

The d.c. conductivity (σ) of V2O5-SnO-TeO2 glasses prepared by the press-quenching method was studied at temperatures from room temperature (RT) to 473 K, and the effect of annealing on σ was investigated. The conductivity of 50V2O5·20SnO·30TeO2 glass was determined to be 3.98×10−4 Scm−1 at 473 K and was unchanged for annealing (6–48 h) at 493 K, lower than Tg = 501 K, while its density increased with annealing time. These glasses were found to be n-type semiconductors, and the conduction was confirmed to be due to adiabatic small polaron hopping for V2O5 ≧ 50 mol%, and non-adiabatic for V2O5 < 50 mol%. The activation energy for conduction, W, decreased with annealing time. Variations in oxygen molar volume of the glasses with annealing time inferred a change in glass structure, from loosely to closely packed, resulting in a decrease in vanadium ion spacing with annealing. This caused an increase in the polaron band width, producing a decrease in polaron hopping energy and W. The effect of annealing time on the density of 50V2O5·20SnO·30TeO2 glass was explained adequately by Winters formula.