Non-adiabatic polaron hopping conduction in semiconducting V2O5-Bi2O3 oxide glasses doped with BaTiO3

BaTiO₃-doped (5–40 wt %) 90V₂O₅-10Bi₂O₃ (VB) glasses have been prepared by a quick quenching technique. The d.c. electrical conductivities, _d.c., of these glasses have been reported in the temperature range 80–450 K. The electrical conductivity of these glasses, which arises due to the presence of V⁴⁺ and V⁵⁺ ions, has been analysed in the light of the small-polaron hopping conduction mechanism. The adiabatic hopping conduction valid for the undoped VB glasses (with 80–95 mol % V₂O₅), in the high-temperature region, is changed to a non-adiabatic hopping mechanism in the BaTiO₃-doped VB glasses. At lower temperatures, however, a variable range hopping (VRH) mechanism dominates the conduction mechanism in both the glass systems. Such a change-over from adiabatic to non-adiabatic conduction mechanism is a new feature in transition metal oxide glasses. Various parameters, such as density of states at the Fermi level N(E_F), electron wave-function decay constant, , polaron radius, r _p, and its effective mass, m _p ^* , etc., have been obtained for all the glass samples from a critical analysis of the electrical conductivity data satisfying the theory of polaron hopping conduction.     

Electrical conductivity of molybdenum phosphate (MoO3 : P2O5) glasses

The dc conductivity of molybdenum phosphate glasses with the batch composition [(MoO₃)_z(P₂O₅)_z-1 where z = 0.55, 0.60, 0.65, 0.70, and 0.75 has been studied. The non-linearity of the Arrhenius plot (ln() versus T^-1>) may be due to processes involving several similar activation energies, conduction by small polarons, or variable range hopping of carriers. The electrical conductivity results for these glasses have been discussed by applying the two models suggested by Meunier et al. and it has been found that the use of the small polaron model yields physically plausible values for W_H and W_D within experimental error.     

Spectroscopic,electrical and EPR studies of binary semiconducting oxide glasses containing 50 mol% V2O5

Recent measurements on the V₂O₅-GeO₂ glass system consisting of an equimolar mixture of V₂O₅ and GeO₂ revealed that increase in electrical conductivity of these glasses upon annealing could be attributed to the increase in V⁴⁺ and V³⁺ content which accompanied the microstructure formation. In the present work we report a similar study on V₂O₅-TeO₂ and V₂O₅-P₂O₅ glass systems. It was found that in tellurite glass V³⁺ content increased upon annealing and V⁴⁺ content remained unchanged. In phosphate glass some increase in V⁴⁺ and no significant change in V³⁺ contents were observed. V³⁺ and V⁴⁺ contents in glasses could be best estimated from optical and electron paramagnetic resonance spectra, respectively.     

Preparation and characterization of binary V2O5-Bi2O3 glasses

Characterization of the binary V₂O₅-Bi₂O₃ glasses prepared by rapidly quenching the melt has been made from the studies of X-ray diffraction, scanning electron microscopy, infrared absorption, differential thermal analysis, electron paramagnetic resonance, chemical analysis, density and electrical properties. Stable glasses are obtained for 95 to 75 mol % V₂O₅ by quenching on a stainless steel substrate, while quenching on a copper substrate extends the glass formation range from 95 to 70 mol % V₂O₅. The V-O bond vibration in the glasses occurs at 1020 cm^–1 and the V^5% ion exists in six-fold coordination as in crystalline V₂O₅. All the glasses appear to be in single phase. The spin concentration in the glasses is found to be independent of temperature. A second heat-treatment at 255° C develops crystalline phase in the glasses. Unlike infrared absorption, electron paramagnetic resonance, density and chemical compositions, the electrical and thermal (DTA) properties are found to be slightly sensitive to the thermal history of preparation of the glasses. The high-temperature (300 to 500 K) conduction in the glasses seems to be due to adiabatic hopping of polarons. The thermopower is observed to be independent of temperature and provides evidence for small polaron formation in the glasses.     

Seebeck coefficient of V2O5-R2O3-TeO2 (R = Sb or Bi) glasses

The thermoelectric power of glasses in the systems V₂O₅-Sb₂O₃-TeO₂ and V₂O₅-Bi₂O₃-TeO₂ was measured at temperatures in the range 373–473 K. The glasses in both systems were found to be n-type semiconductors. The Seebeck coefficient, Q, at 473 K was determined as –192 to –151 VK^–1 for V₂O₅-Sb₂O₃-TeO₂ glasses, and –391 to –202 VK^–1 for V₂O₅-Bi₂O₃-TeO₂ glasses. For these glasses in both systems, Heikes' formula was satisfied adequately for the relationship between Q and In [C _v/(1-C_v)] (C _v = V⁴⁺/V_total, C _v is the ratio of the concentration of reduced vanadium ions), and discussions confirmed small polaron hopping conduction of the glasses in both systems. Mackenzie's formula relating to Q and V⁵⁺/V⁴⁺ was also applicable to the glasses in both systems, and it was concluded that the dominant factor determining Q was C _v.     

Electron spin resonance study in P2O5-MoO3 and P2O5-MoO3-CaO glasses

ESR spectra of the glass systems P₂O₅-MoO₃ and P₂O₅-MoO₃-CaO are presented. The electron spin resonance results showed a strongly exchange-narrowed interaction with the [Mo⁵⁺]/[Mo⁶⁺] ratio and line shapes independent of temperature over the range 77 to 300 K. This result supports the concept of temperature-dependent mobility of the carriers and an unchanged paramagnetic site over this temperature range. The more important difference between the spectra of the binary and ternary glasses is that in the former with an increase in MoO₃ content the concentration of Mo⁵⁺ ions decreases but in ternary glasses it is reversed, i.e. the ion concentration of Mo⁵⁺ increases with increase in MoO₃ content.     

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 T_g = 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 Winter's formula.     

掺Sm2O3的P2O5-BaO-Al2O3玻璃的形成及部分光学性能

随着信息技术、激光技术和军事技术的快速发展,各种功能玻璃材料的研究受到了科研工作者的极大关注。采用两步熔融法观察了空白试样和掺加Sm2O3 的玻璃形成区,结果表明随着稀土含量的增加,形成区缩小,Sm2O3 的含量不能>15%mol;通过红外光谱仪和分光光度计研究了玻璃的结构和吸收谱线,结果显示:随 Al2O3 含量增加,[PO3-4 ]基团的振动特征吸收峰逐渐缩小直至消失,同时随稀土含量的增加出现尖锐的P—O—Sm键振动吸收峰;吸收光谱中吸收峰强度随稀土含量增加逐步增强,透过率下降。     

Preparation, characterization and conductivity studies of AgI-Ag2O-(TeO2 + P2O5) fast ionic conducting glasses

Silverphosphotellurate (SPT) quaternary fast ionic conducting (FIC) glasses of compositions AgI-Ag₂O-[(1 – x)P₂O₅ + xTeO₂], x = 0.0 to 1.0 in steps of 0.1, were prepared by melt quenching. All SPT compounds were characterized by X-ray diffraction and the amorphous nature of the samples was confirmed. The structure of all compositions was examined by Fourier Transform Infrared Spectroscopy. The glass transition temperature (T _g) was determined for all SPT samples, using differential scanning calorimetry. Complex impedance measurements were made on all glasses in the frequency range 40 Hz to 100 kHz. Impedance data were analyzed using Boukamp equivalent circuit software and the bulk conductivity was obtained. The highest conductivity ( = 1.59*10^–2 S/cm) was shown by the composition 60%AgI – 26.67%Ag₂O – 13.33% (0.3P₂O₅ + 0.7TeO₂).     

Electrical properties of V2O5-PbO-GeO2 glasses

Glasses in the V₂O₅-PbO-GeO₂ system containing 55 mol% V₂O₅ were found to undergo a droplet-type phase separation. The dispersed phase is rich in GeO₂. The volume percent of this phase increases with increasing GeO₂/PbO ratio in the glass. When the volume percent of dispersed phase is small, the direct current conductivity depends mainly on the continuous phase. When the dispersed phase reaches about 42 vol%, a second kind of phase separation appears in the continuous phase and thus alters the conductivity dramatically. Providing that the heterogeneity is taken into consideration, all the conductivities of phase-separated glasses can be explained by the theory proposed by Mott.     

Niobium(V) oxide (Nb2O5): application to phosphoproteomics

Proteomics-based analysis of signaling cascades relies on a growing suite of affinity resins and methods aimed at efficient enrichment of phosphorylated peptides from complex biological mixtures. Given the heterogeneity of phosphopeptides and the overlap in chemical properties between phospho- and unmodified peptides, it is likely that the use of multiple resins will provide the best combination of specificity, yield, and coverage for large-scale proteomics studies. Recently titanium and zirconium dioxides have been used successfully for enrichment of phosphopeptides. Here we report the first demonstration that niobium pentoxide (Nb 2O 5) provides for efficient enrichment and recovery ( approximately 50-100%) of phosphopeptides from simple mixtures and facilitates identification of several hundred putative sites of phosphorylation from cell lysate. Comparison of phosphorylated peptides identified from Nb 2O 5 and TiO 2 with sequences in the PhosphoELM database suggests a useful degree of divergence in the selectivity of these metal oxide resins. Collectively our data indicate that Nb 2O 5 provides efficient enrichment for phosphopeptides and offers a complementary approach for large-scale phosphoproteomics studies.     

Electrical properties of Sb2O3–CaO–V2O5 glasses and glass-ceramics

The d.c. conductivity (σ) of (a) glasses prepared by the press-quenching method and (b) glass-ceramics (crystallized glass) produced by post-heat treatment was investigated in the system Sb₂O₃–CaO–V₂O₅ and their conduction mechanism was studied. The glasses were n-type semiconductors with σ = 2.6 × 10^-6 ∼ 2.8 × 10^-5 S cm^-1 at 333 K for varying glass compositions. The conduction was attributed to small polaron hopping in the adiabatic regime. The estimated carrier density was 1.7 ∼ 3.8 × 10²¹ cm^-3 for V₂O₅ = 70 ∼ 80 mol% and the mobility was 3.5 × 10^-9 to 6.9 × 10^-8 cm² V^-1 s^-1. Crystallization raised the conductivity by a factor of 10³. The crystalline product in the glass-ceramics was Ca_0.17V₂O₅. The glass-ceramics were n-type semiconductors, and the conduction was interpreted by a superposition of the small polaron hopping in the crystalline and glassy phases. This revised version was published online in November 2006 with corrections to the Cover Date.