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.     

Ac conductivity of BaTiO3 containing (90V2O5-10P2O5) oxide glasses dispersed with nanocrystalline particles

The frequency dependent AC conductivity (_ac) of some new multicomponent (1 – x) (90V₂O₅-10P₂O₅) + xBaTiO₃ (x = 0.1 to 0.9) type glasses containing nanocrystalline BaTiO₃ particles (observed from the transmission electron microscopic study) has been reported in the temperature range 80–400 K. The behavior of _ac is broadly similar to what has been observed previously in many other amorphous semiconductors and polymers (namely nearly linear frequency dependence and weak temperature dependence). Analysis of the experimental conductivity data shows that Long's overlapping large polaron tunneling (OLPT) mechanism is the most probable mechanism of conduction for the present BaTiO₃ doped glasses. The Quantum mechanical tunneling (QMT) model and the classical hopping of electrons over a barrier can, however, explain the AC conductivity data only below _D/2–160 K (_D is the Debye temperature). Reasonable values of the relaxation time and barrier heights related to the models have been obtained from the fits of the conductivity data.     

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.     

氧化物掺杂对钒磷铋系玻璃性能的影响

本研究制备了以V2O5、P2O5、B2O3为基体,掺杂Na2O、Li2O、CuO、Sb2O3、B2O3为辅助原料的低熔点钒磷铋系玻璃。研究了氧化物的添加对钒磷铋系玻璃的骨架网络结构、特征温度、热膨胀系数和化学稳定性的影响。实验结果表明:CuO的添加使钒磷铋系玻璃特征温度明显下降,而Na2O、Li2O、Sb2O3和B2O3的添加使钒磷铋系玻璃特征温度均有不同程度的上升。添加B2O3能够大幅度降低钒磷铋系玻璃的热膨胀系数。氧化物对钒磷铋系玻璃的耐水性影响程度为:CuO>B2O3>Sb2O3>Na2O>Li2O;耐酸性影响程度为:B2O3>CuO>Sb2O3>Na2O>Li2O;耐碱性的影响程度为:Sb2O3>Na2O>CuO>B2O3≈Li2O。配比为5%Na2O,5%Li2O,3.5%CuO,10%Sb2O3和5%B2O3制得的钒磷铋系玻璃,热膨胀系数更接近于氧化铝陶瓷基板,拥有较高的耐腐蚀性,能够用于电子浆料中。     

Aurivillius phase formation in Nb2O5 − and Bi2O3 − doped BaTiO3

The reaction sequence in the BaTiO₃–Nb₂O₅–Bi₂O₃ system leading to the core-shell microstructure that causes the temperature-stable dielectric response has been examined using X-ray diffraction. The starting oxides react to form bismuth oxide layer Aurivillius phases at low temperatures which, in turn, react with remnant oxides to form the tetragonal tungsten bronze phase, Ba₄Bi₂Ti₄Nb₆O₃₀, which acts as the source of dopants responsible for core-shell formation.     

EPR study of Cu2+ in Na2O-NaF-B2O3-Bi2O3 glasses

Electron paramagnetic resonance (EPR) studies have been performed on the glass system (30–x) NaF-xNa₂O-50B₂O₃-20Bi₂O₃ doped with CuO as a paramagnetic probe. The calculated g values indicate that Cu²⁺ is in a tetragonally elongated octahedral co-ordination, and the Jahn-Teller character gives rise to anisotropic hyperfine structure. The spin-Hamiltonian parameters and -bonding parameter, ², are calculated. Varying the fluoride ion concentration and its effect on these parameters is also discussed.     

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。     

Compositional dependence of infrared absorption spectra studies for TeO2-P2O5 and TeO2-P2O5-Bi2O3 glasses

The infrared absorption spectra of the vitreous TeO₂-P₂O₅ and Bi₂O₃-TeO₂-P₂O₅ systems are studied in the spectral region of 4000 to 200 cm^–1. Absorption bands in this range are assigned. The midband wavenumber and the absorption intensity for the attributed bands are found to be strongly and systematically dependent on glass composition. Quantitative analysis was also attempted to justify our attribution of the observed bands.     

Spectroscopic investigations of Cu2+ in Li2O-Na2O-B2O3-Bi2O3 glasses

Pure and copper doped glasses with composition,x Li ₂ O-(40-x)Na ₂ O-50B ₂ O ₃-10Bi ₂ O ₃,have been prepared over the range 0 ≤ x ≤ 40. The electron paramagnetic resonance (EPR) spectra of Cu²⁺ ions of these glasses have been recorded in the X-band at room temperature. Spin Hamiltonian parameters have been calculated. The molecular bonding coefficients, α² and β², have been calculated by recording the optical absorption spectra in the wavelength range 200–1200 nm. It has been observed that the site symmetry around Cu²⁺ ions is tetragonally distorted octahedral. The density and glass transition temperature variation with alkali content shows non-linear behaviour. The IR studies show that the glassy system contains BO₃ and BO₄ units in the disordered manner.     

Electrical conduction through MIM structures of evaporated V2O5 and V2O5/B2O3 amorphous thin films

The electrical conduction through vacuum-evaporated thin films of V₂O₅ and V₂O₅/B₂O₃ in MIM structures has been investigated. The high-field behaviour of both types of film is in accordance with the Poole-Frenkel type of mechanism. The increase in B₂O₃ content in co-evaporated V₂O₅/B₂03 films results in a decrease in the conductivity of the composite films. This is attributed to the expansion of the resultant film structure due to the network-forming effect of B₂O₃. The covaporated thin films of V₂O₅/B₂O₃ with a molar content of B₂O₃ larger than 40% are observed to be unstable because of their hygroscopic nature.     

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.     

D.c. conductivity and hopping mechanism in Bi2O3-B2O3 glasses

The physical and transport properties of semiconducting glasses are highly interesting, providing useful information regarding the structure and conduction mechanism, respectively. The physical and transport properties such as density, number of ions per unit volume, hopping distance, polaron radius, d,c. conductivity and activation energy are reported. Similarly the hopping conduction mechanism is examined. The physical property (density) is used to determine the probable structure of the glass sample. The small polaron hopping model is applied to the glass system. The methods of examining the hopping conduction mechanism are discussed in the light of the small polaron model. The methods suggested by Holstein and by Sayer and Mansingh are applied to the determination of adiabatic or non-adiabatic hopping conduction. It was observed that in this system adiabatic hopping conduction is present.     

Correlation of electrical properties and internal friction in mixed conduction glasses containing ionic and electronic conduction (1) Fe2O3-Na2O-P2O5 glasses

The electrical properties and internal friction in (40–x)Fe₂O₃·xNa₂0.60P₂O₅ glasses were measured. Two or three peak on internal friction were observed in the temperature range of –100 to 300° C at a frequency of about 1 Hz. The peak area of internal friction could be explained quantitatively by the additivity law of diffusion of Na⁺ ion and hopping of electrons which are carriers similar to those of dielectric loss. Activation energy, peak temperature of dielectric loss and internal friction showed almost the same value. Both relaxation phenomena have the same mechanism which is due to the diffusion of Na⁺ion and the hopping of electrons between Fe²⁺ Fe³⁺. The high-temperature peak is assumed to result from the interaction between protons or alkali ions and non-bridging oxygen.     

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.     

V_2O_5与Al_2O_3复合改性CaSiO_3陶瓷的烧结性能与微波介电性能

为降低CaSiO3陶瓷的烧结温度,通过在CaSiO3粉体中添加1wt%的Al2O3以及不同量的V2O5,探讨了V2O5添加量对CaSiO3陶瓷烧结性能、微观结构及微波介电性能的影响规律。结果表明:适量地添加V2O5除了能将V2O5-Al2O3/CaSiO3陶瓷的烧结温度从1 250℃降低至1 000℃外,还能抑制CaSiO3陶瓷晶粒异常长大并细化陶瓷晶粒。在烧结过程中,V2O5将熔化并以液相润湿作用促进CaSiO3陶瓷的致密化进程;同时,部分V2O5还会挥发,未挥发完全的V2O5将与基体材料反应生成第二相,第二相的出现将大幅降低陶瓷的品质因数。综合考虑陶瓷的烧结性能与微波介电性能,当V2O5添加量为6wt%时,V2O5-Al2O3/CaSiO3陶瓷在1 075℃下烧结2h后具有良好的综合性能,其介电常数为7.38,品质因数为21 218GHz。