Glass formation and structure of glasses in the ZnO―Bi2O3―WO3―MoO3 system

The glass formation region in the ternary ZnO―Bi₂O₃―WO₃ system is determined by melt quenching technique (cooling rates 10¹-10² K/s). New original glasses are obtained in a narrow concentration range with high WO₃ content (60-75 mol%). Homogeneous glasses of the composition (100 − x)[0.2ZnO·0.3Bi₂O₃·0.5WO₃]xMoO₃, were obtained between 20 and 60 mol% MoO₃. Characterization of the amorphous samples was made by x-ray diffraction (XRD), differential thermal analysis (DTA) and infrared spectroscopy (IR). The thermal stability of glasses decreases with the increasing of MoO₃ content. The glass transition temperature, T_g, varies between 340-480 °C, while the crystallization temperature, T_x, varies between 388-531 °C. The tungstate glasses possess higher crystallization temperature (T_x over 500 °C) in comparison with the other vanadate and molybdate non-traditional glasses. The glass network is realized by transformation of three-dimensional structure of WO₃ into a layered one, consisting mainly of WO₆ units. We supposed that the network of quaternary glasses is built up by MoO₄, MoO₆ and WO₆. At low concentration ZnO and Bi₂O₃ facilitate the disorder in the supercooled melts, while at high concentration stimulate crystallization processes. These oxides belong to the intermediate ones.     

Glass formation and structure of Na2SSiO2 and Na2SB2O3 glasses

Glass-forming regions of the systems Na₂SSiO₂ and Na₂SB₂O₃ have been investigated in order to clarify whether Na₂S could be substituted for Na₂O in sodium silicate or borate glasses, and the results were interpreted in terms of the structures of silicate and borate glasses. No difference was found in the glass-forming range of SiO₂ content between the Na₂SSiO₂ and Na₂OSiO₂ systems, and the red color of Na₂SSiO₂ glasses suggests that the formation of polysulfides in the glass structure is probably due to the entrance of sulfur ions in the non-bridging sites of the glass network. On the other hand, not all of the sulfur added to the glass batches could be retained in the Na₂SB₂O₃ glasses and the amount remaining in the glass products changed depending upon the amount of sodium ions in the glasses. Only a trace of sulfur was observed in the glasses containing less than 13 mol% of Na₂S in the batches, but the sulfur content in the glasses increased steeply with sodium content up to 35 mol%, reached the maximum and then decreased slowly with sodium content. The insolubility of sulfur in the glasses with low sodium content was interpreted based on the compositional dependence of basicity of alkali-borate glasses, and the change in solubility of sulfur with sodium concentration was explained based on the well-known boron anomaly caused by the change in the coordination state of boron and on the formation of non-bridging oxygens or sulfurs in the glass structure.     

Infrared spectra and structure of superionic conducting glasses in the system AgIAg2OMoO3

Thin blown films of glasses with the mole ratio Ag₂O/MoO₃ = 1 in the system AgIAg₂OMoO₃ (or the pseudobinary system AgIAg₂MoO₄) show three absorption bands in the range 4000-200 cm^?1; 875 cm^?1 (w), 780 cm^?1 (s), and 320 cm^?1 (m, b), which are characteristic of tetrahedral MoO₄^2? ions. The glasses with the ratio Ag₂O/MoO₃ < 1 have two additional bands at 600 cm^?1 (w) and 450 cm^?1 (vw), which are characteristic of condensed ions of MoO₄ tetrahedra, probably Mo₂ O₇^2? ions. These glasses are thus composed of Ag⁺, I^?, MoO₄^2?, and probably Mo₂O₇^2? ions, and classified as “ionic” glasses containing one type of cations. The presence of partial covalency in the Ag⁺… ^?OMo link and the influence of ion exchange of Ag⁺ with K⁺ on IR spectra are discussed. The molar volume of the glasses with the ratio Ag₂O/MoO₃ = 1 is primarily determined by a fairly dense packing of the constituent anions, I^? and MoO₄^2?.     

Brillouin scattering measurements of attenuation and velocity of hypersounds in SiO2B2O3 glasses

Measurements of hypersound wave velocity and attenuation (20–30 GHz) were made at room temperature by Brillouin scattering in SiO₂O₂O₃ glasses. The attenuation shows a maximum with composition. An explanation of this maximum is given in relation to the glass structure. It is thought that this maximum may be due to a coupling effect of hypersounds with structural relaxational process involving SiSi and SiOB bonds.     

Surface kinetics of nitrogen dissolution and its correlation to the slag structure in the CaO―SiO2, CaO―Al2O3, and CaO―SiO2―Al2O3 slag system

The kinetics of nitrogen dissolution into molten slag at 1873 K was investigated by an isotope exchange technique. Rate constants were correlated with the molten slag structure obtained from FT-IR spectra. The rate constant in the CaO―SiO₂ binary system showed a maximum value at a specific slag composition followed by a decrease in the rate due to excess O²⁻ blocking the surface sites for nitrogen adsorption. The rate constant in the CaO―Al₂O₃ binary system was comparatively constant within the experimental range of 45 mass% to 60 mass%. The rate constant in the CaO―SiO₂―Al₂O₃ ternary slag system was measured within the boundary of the liquidus line and showed a close correlation with the slag structure. Furthermore, the rate constant in the CaO―SiO₂―Al₂O₃ ternary system was found to be significantly higher compared to the binary system due to the correlated effect of lower binding energies of the Al―O bonds and the increased number of reaction sites available when smaller Si―O tetrahedral were simultaneously present with Al―O bonds.     

Nuclear magnetic resonance studies of the glasses in the system Na2OB2O3SiO2

The ¹¹B NMR spectra have been used to study the structure of glasses in the system Na₂OB₂O₃SiO₂. The fraction of BO₄ units, and the fraction of BO₃ units with one or two nonbridging oxygens, are measured and analyzed according to a structural model. The results indicate that: (1) for a sodium oxide to boron oxide ratio of 0.5 or less, the Na⁺¹ ions are attracted primarily by the borate network; therefore, the ternary glasses can be viewed as binary sodium borate glasses diluted by SiO₂; (2) when the sodium oxide to boron oxide ratio exceeds 0.5, the additional Na₂O results in the formation of [BSi₄O₁₀]^?1 units at the expense of diborate and SiO₄ units. In this process, Na⁺¹ ions are still taken up only by the borate network. After all the available SiO₄ units are consumed to form [BSi₄O₁₀]^?1 units, additional Na⁺¹ ions are proportionally shared between the borate and silicate networks.     

Mössbauer study in the glass system PbO · 2B2O3 · Fe2O3

The Mössbauer technique has been employed to study the structure and crystallite formation in the glass system PbO · 2B₂O₃ containing upto 30 wt% Fe₂O₃. Like alkali borate glasses, this glass system also exhibits a broadened quadrupole doublet and iron ions are present in Fe³⁺ state. Above about 20 wt%, the crystallites of magnetically ordered states have been identified. Susceptibility variation with concentration suggests the formation of a superparamagnetic state.     

11B and 27Al NMR studies of glasses in the system Na2OB2O3Al2O3 (“NABAL”)

¹¹B and ²⁷Al nuclear magnetic resonances (NMR) in glasses of the NABAL system Na₂OB₂O₃Al₂O₃ have been studied as a function of composition. From the boron data, the fraction of four-coordinated BO₄ units has been determined via computer analysis of the NMR spectra; the method is similar to that employed previously for binary and other ternary borate glasses. The ²⁷Al NMR indicates no abrupt change in the average aluminum environment. Certain linear relationships have been found which yield detailed information on the competing processes of BO₃, BO₄ and AlO₄ formation, and the formation of triclusters consisting of three tetrahedra having one oxygen in common. Furthermore, it is concluded that the oxygen available for the formation of various aluminum-containing species is a function of the soda concentration only and that the conversion to AlO₄ is favored as compared with BO₄.     

Photoconductivity of oxychalcogenide glasses in the system As2Se3CdO

The photoconductivity of oxychalcogenide glasses in the system As₂Se₃CdO was investigated. When 2–3 mol % CdO was added, the photoresponse peak of the parent glass As₂Se₃ in the vicinity of 740 nm became broader and a little weaker. The addition of more than about 4 mol % CdO brought about a sharp and strong peak at 720 nm and a broad peak at 860 nm. X-ray diffraction and electron microscopic observations revealed the presence of crystalline CdSe in the glass matrix, indicating that the reaction As₂Se₃ + 3CdO → As₂O₃ + 3CdSe took place in the melting process of these glasses. Tempeature and light intensity dependences of the photocurrent lead to the conclusion that the above spectral photoresponse is greatly affected by the presence of the dispersed crystalline CdSe.     

Electronic structure and properties of oxide glasses (II) Basicity measured by copper(II) ion probe in Na2OP2O5, K2OB2O3 and K2SO4ZnSO4 glasses

The correlation between the basicity of oxygens measured by the Cu(II) ion probe and the non-bonding electron density on oxygens in alkali borate glasses was considered. The basicity was measured for K₂OB₂O₃, Na₂OP₂O₅ and K₂SO₄ZnSO₄ glasses and categorized into two types, δ and π, according to the symmetry property of the bonding between a Cu(II) ion and oxygen. The π basicity for borate and phosphate glasses showed an abrupt increase in the vicinity of 17 and 50 mol% alkali oxide, respectively. The values of π-type basicity varied with the composition of glass, being larger in the order: sulfate < phosphate ? borate, whereas δ basicity was constant irrespective of the glass composition. Such a change of the basicity with the composition of glass was interpreted in terms of behavior of non-bonding levels of the ligand oxygens in a glass network.     

The effect of different alkali ions on the optical and magnetic properties of R2O−B2O3 + MnO2 glasses

Spectrophotometric, magnetic studies and chemical analyses of a number of binary alkali borate glasses containing manganese were carried out in order to throw some light on the structure of these glasses and on the forms in which manganese exists in borate glasses.The results obtained could be explained on the basis that manganese exists in glasses in two different states; divalent manganese coordinated with tetrahedral arrangements with oxygen and shows four bands at about 400, 460, 490 and 530 nm with very low molecular extinction coefficients, and trivalent manganese assuming octahedral symmetry having a broad band at 470–500 nm which under some conditions shows splittings to two or three peaks with high values of molecular extinction coefficients.The paramagnetic character of the glasses containing manganese is usually attributed to the presence of five and four unpaired electrons in the divalent and trivalent states of manganese, respectively. The ratio of trivalent to divalent manganese ions depends on several factors, including the polarisability of the oxygen ligands surrounding the manganese ions, the presence of bridging and non-bridging oxygen and the type of alkali ion present.     

Small polaron conduction in V2O5P2O5 glasses

Dc conductivity measurements have been made between 90 and 520 K on three bulk samples of V₂O₅P₂O₅ glass. Heat treatment is found to result in a reduction of the activation energy at a given temperature and this is most noticeable at low temperatures. The behaviour at low temperatures can be described using Mott's variable range hopping arguments, and at high temperatures by non-adiabatic small polaron hopping between nearest neighbours. At intermediate temperatures a simple model is used in which excitations by optical and acoustic phonons are considered to make independent contributions to the jump frequency. Mott's theory is extended to the polaron case for $\text{T>}\text{1}\text{4}\text{?}$ and is shown to be in good agreement with results. Values for $\text{r}{}_{\mathrm{<mtext>p</mtext>}}\text{(～2.8}\text{A}\text{?}\text{)}$ the polaron radius and $\text{α(～3.5}\text{A}\text{?}{}^{\mathrm{?1}}\text{)}$ the electron decay constant are shown to be consistent with the model for small polarons. A method is suggested for obtaining α and N(E_F) from the ac conductivity and the slope of 1nσ versus $\text{1}\text{T}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$ at low temperatures. Values of N(E) are obtained which correlate with those obtained by the previous analysis. This implies that the disorder energy separating adjacent sites Δ₀ is large (～0.4 eV) in these materials.     

Glass formation in the systems (K or Cs)2O(Nb or Ta)2O5Al2O3

The glass-forming ability of melts in the systems K₂O(Nb and/or Ta)₂O₅Al₂O₃ as well as those in which K₂O was replaced with Li₂O, Na₂O, Cs₂O, BaO or PbO was investigated. Some melts in the systems (K or Cs)₂O(Nb and/or Ta)₂O₅Al₂O₃ could be made into glasses by cooling, yielding practically useful amounts. The structures of these glasses were discussed on the basis of their infrared spectroscopic and X-ray emission spectroscopic analyses.     

EPR study of crystalline and vitreous forms of the Li2OAl2O3SiO2 system

The epr spectra of V⁴⁺ and radiation centres have been studied in β-eucryptite (LiAlSiO₄), β-, γ-spodumene (LiAlSi₂O₆) and in glasses prepared by the fusion of the single crystals. It is shown that the electronic structures of the vitreous state in the Li₂OAl₂O₃SiO₂ system and that of the crystalline forms differ considerably. The change of the electronic structure on crystallization is not direct, but is realized through the intermediate state whose electronic structure differs from that of glasses and crystals.     

A new modification of Ba[B5O8(OH)] · H2O, the refined structure of Ba2[B5O9]Cl · 0.5H2O, and the role of the pentaborate structural units in the formation of the quadratic optical nonlinearity

The structure of a new modification of the barium pentaborate β-Ba[B₅O₈(OH)] · H₂O synthesized under hydrothermal conditions is investigated. This structure differs from the previously studied structure of the α-Ba[B₅O₈(OH)] · H₂O compound by a shorter interlayer spacing and a higher degree of filling of the intersheet space with water molecules and barium atoms (the space group P is retained). The structure of the Ba₂[B₅O₉] Cl · 0.5H₂O pentaborate from the family of orthorhombic hilgardites (space group Pnn2) is refined, and the property of this crystal to generate the second optical harmonic is revealed. It is found that the previously studied pentaborate Ba₅[B₂₀O₃₃(OH)₄]H₂O exhibits a nonlinear optical activity. The relationship between the structure and properties of hydrous and anhydrous pentaborates is discussed. Original Russian Text ? E.L. Belokoneva, S.Yu. Stefanovich, M.A. Erilov, O.V. Dimitrova, N.N. Mochenova, 2008, published in Kristallografiya, 2008, Vol. 53, No. 2, pp. 255–263.     

Electrical conductivity and photoconductivity of As2S3PbS glasses

Measurements of dc electrical conductivity and photoconductivity of various glassy compositions (x = 0.1?0.625) in (As₂S₃)_1?x(PbS)_x have been made. Experimental results of the temperature dependence of dc conductivity from room temperature to 200°C (which includes the glass transition temperature) are reported. All the compositions exhibit intrinsic conduction in the measured temperature range. Thermal activation energy, glass transition temperature and σ₀ for the compositions studied, were determined from the experimental data. The low value of $\text{σ}{}_0\text{(10?10}{}^{\mathrm{?2}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$) in these semiconducting glasses is attributed to the greater participation of localized states in the conduction process.In the measurements of photoconductivity, the variation of photocurrent with temperature, photon energy, light intensity and electric field is observed. The recombination model has been involved to explain the results of photoconductivity. Both electrical and photoconductivity data support the presence of higher density of localized states in the x = 0.1 composition than in others.     

0.2wt% Bi2O3、CuO、B2O3对5Ca0.6La0.267TiO3-5Ca(Mg1/3Nb2/3)O3微波介质陶瓷的性能影响

采用传统的固相反应法,研究了三种烧结助剂Bi2O3、CuO、B2O3对5Ca0.6La0.267TiO3-5Ca(Mg1/3Nb2/3)O3微波介质陶瓷的烧结性能和介电性能的影响。实验结果表明,掺入0.2wt%的Bi2O3、CuO、B2O3产生了液相,有效地降低了体系的烧结温度。Bi2O3和CuO的加入没有改变烧结体的微观形貌,它们介电常数和品质因数随烧结温度的变化趋势和体积密度趋于一致,均在体积密度最大时最高。当温度大于1300℃时,加入0.2wt%B2O3试样有柱状晶体生成,并随着烧结温度的升高而增多,柱状晶体的存在可能促使Q×f值较大的提高,当烧结温度过高时(1350℃),由于柱状晶体过多使得烧结体不均匀导致Q×f值下降。Bi2O3、CuO、B2O3的加入没有改变烧结体的晶相组成,因此所有烧结体均有近零的温度系数。结果表明,加入0.2wt%B2O3的5Ca0.6La0.267TiO3-5Ca(Mg1/3Nb2/3)O3在1325℃烧结温度具有最佳的介电性能:εr=54.87,Q×f=55 726 GHz,τf=-0.6 ppm/℃。     

Infrared transmission of (R2O OR R’O)–(TiO2, Nb2O5 OR Ta2O5)-Al2O3 glasses

The new families of aluminate glasses obtained by the present authors from their melts in the systems K₂O–Ta₂O₅–Al₂O₃, Na₂O–K₂O–Ta₂O₅–Al₂O₃, K₂O –Cs₂O– Ta₂O₅–Al₂O₃, K₂O–Nb₂O₅–Al₂O₃, Na₂Oz.sbnd;K₂O–TiO₂–Al₂O₃, BaO–TiO₂–Al₂O₃, BaO–ZrO₂–TiO₂–Al₂O₃ and Na₂O–K₂O–BaO–ZrO₂–Ta₂O₅–TiO₂ –Al₂O₃ showed high transmissions of visible and infrared (IR) radiation ranging from 0.4 to about 6 μm, as well as high refractive indices up to 2.0. Their physical and chemical properties such as glass-forming ability, softening temperature, hardness and hygroscopicity were comparable to conventional silicate glasses. These properties are useful for IR applications. The cause of the high IR transmission of the aluminate glasses was interpreted in terms of the masses of the constituent cations and the single bond strengths of the cations with oxygen ions.     

B2O3对YCaZrVIG铁氧体微结构及性能的影响

采用传统固相法制备添加B2O3的YCaZrVIG铁氧体,研究了B2O3添加量对其烧结温度、微结构和磁性能的影响。结果表明,添加的B2O3对材料的物相没有影响,所有样品均为单相石榴石结构。添加B2O3显著降低了YCaZrVIG铁氧体的烧结温度,且使颗粒尺寸逐渐减小。添加1.8wt%B2O3的样品,烧结温度约为1200℃,且体积密度最大。进一步提高B2O3添加量至3.0wt%,烧结温度又略有提高,且晶粒尺寸变得不均匀。随着B2O3添加量的增加,4πMs和Br先显著增大后减小,而Hc则减小后急剧增大。适当提高烧结温度,有利于Hc的减小。B2O3添加量为1.8wt%、1290℃烧结保温4 h制得的YCaZrVIG铁氧体综合性能较佳:Db=4.80 g.cm-3,4πMs=1670 Gs,Br=682 Gs,Hc=0.86 Oe。