Ionic conduction in glasses in the MnNbOF5-BaF2-BiF3 system

The electrical conductivity of oxyfluoride glasses in the MnNbOF₅-BaF₂-BiF₃ system in the temperature range 299–550 K was studied by impedance spectroscopy. It was shown that the conductivity is mainly caused by fluoride ions forming fluorobismuth polyhedra in the glass structure, being as high as 7.46 × 10^?3 S/cm (533 K) in the 20MnNbOF₅-30BaF₂-50BiF₃ system reaches, which is at the level of the best values for fluoride glasses.     

Structural integration of tellurium oxide into mixed-network-former glasses: connectivity distribution in the system NaPO(3)-TeO(2).

Sodium phosphate tellurite glasses in the system (NaPO(3))(x)(TeO(2))(1-) (x) were prepared and structurally characterized by thermal analysis, vibrational spectroscopy, X-ray photoelectron spectroscopy (XPS) and a variety of complementary solid-state nuclear magnetic resonance (NMR) techniques. Unlike the situation in other mixed-network-former glasses, the interaction between the two network formers tellurium oxide and phosphorus oxide produces no new structural units, and no sharing of the network modifier Na(2)O takes place. The glass structure can be regarded as a network of interlinked metaphosphate-type P(2) tetrahedral and TeO(4/2) antiprismatic units. The combined interpretation of the O 1s XPS data and the (31)P solid-state NMR spectra presents clear quantitative evidence for a nonstatistical connectivity distribution. Rather, the formation of homoatomic P--O--P and Te--O--Te linkages is favored over mixed P--O--Te connectivities. As a consequence of this chemical segregation effect, the spatial sodium distribution is not random, as also indicated by a detailed analysis of (31)P/(23)Na rotational echo double-resonance (REDOR) experiments.     

IR-spectral investigation of the structure of glasses in the Fe2O3-V2O5 system

The structure of glasses in the Fe₂O₃-V₂O₅ system in the 0–50 mol% Fe₂O₃ range is studied by IR-spectroscopy. It is found that the introduction of Fe₂O₃ favours the transformation of the VO₅-groups into VO₄ ones. This effect may be shown with the aid of IR-spectra, owing to the fact that these glasses are characterized by two high-frequency bands at 1020 and 930 cm^–1. The first is determined by the vibrations of the short V=O nonbridging bonds in the VO₅-groups, while the second is assigned to the vibrations of the V—O-bonds in deformed VO₄-tetrahedra.

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IR-spektroskopische Strukturuntersuchung von Gläsern des Systems Fe₂O₃-V₂O₅

Zusammenfassung Die Struktur von Gläsern des Systems Fe₂O₃-V₂O₅ in dem Bereich von 0–50 Molprozent Fe₂O₃ wurde mit Hilfe der IR-Spektroskopie untersucht. Zusatz von Fe₂O₃ begünstigt die Umwandlung der VO₅- in VO₄-Gruppen. Das kann in den IR-Spektren durch zwei Banden bei 1020 und 930 cm^–1 festgestellt werden. Die erste wird durch Schwingungen der kurzen V=O-Nichtbrücken-bindungen in den VO₅-Gruppen verursacht, die zweite wird auf Schwingungen der V—O-Bindungen in dem deformierten VO₄-Tetraeder zurückgeführt.

     

Role of Tin Difluoride and Gallium Trifluoride in Glass Formation in SnF2–GaF3–BaF2

The structure of glasses in SnF₂–GaF₃ and SnF₂–GaF₃–BaF₂ systems was investigated by IR spectroscopy. It is shown that the glass structure in systems of this type is formed by two glass-forming agents: gallium trifluoride and tin difluoride. The introduction of 5 mole % barium difluoride shifts the edge of the absorption band to the low-frequency region.     

Crystallization kinetics of bioactive glasses in the ZnO-Na2O-CaO-SiO2 system

The crystallization kinetics of Na(2)O.CaO.2SiO(2) (x = 0) and 0.68ZnO.Na(2)O.CaO.2SiO(2) (x = 0.68, where x is the ZnO stoichiometric coefficient in the glass formula) bioactive glasses have been studied using both nonisothermal and isothermal methods. The results obtained from isothermal XRPD analyses have showed that the first glass crystallizes into the isochemical Na(2)CaSi(2)O(6) phase, whereas the Na(2)ZnSiO(4) crystalline phase is obtained from the Zn-rich glass, in addition to Na(2)CaSi(2)O(6). The activation energy (Ea) for the crystallization of the Na(2)O.CaO.2SiO(2) glass is 193 +/- 10 and 203 +/- 5 kJ/mol from the isothermal in situ XRPD and nonisothermal DSC experiments, respectively. The Avrami exponent n determined from the isothermal method is 1 at low temperature (530 degrees C), and its value increases linearly with temperature increase up to 2 at 607 degrees C. For the crystallization of Na(2)CaSi(2)O(6) from the Zn-containing glass, higher values of both the crystallization temperature (667 and 661 degrees C) and Ea (223 +/- 10 and 211 +/- 5 kJ/mol) have been found from the isothermal and nonisothermal methods, respectively. The Na(2)ZnSiO(4) crystalline phase crystallizes at lower temperature with respect to Na(2)CaSi(2)O(6), and the Ea value is 266 +/- 20 and 245 +/- 15 kJ/mol from the isothermal and nonisothermal methods, respectively. The results of this work show that the addition of Zn favors the crystallization from the glass at lower temperature with respect to the Zn-free glass. In fact, it causes an increase of Ea for the Na diffusion process, determined using MD simulations, and consequently an overall increase of Ea for the crystallization process of Na(2)CaSi(2)O(6). Our results show good agreement between the Ea and n values obtained with the two different methods and confirm the reliability of the nonisothermal method applied to kinetic crystallization of glassy systems. This study allows the determination of the temperature stability field of the crystalline phases with the view of creating a different glass ceramic useful in the field of bioactive materials.     

Devitrification of Nd3+-doped glasses in the akermanite-gehlenite system

The devitrification of glasses in the akermanite-gehlenite system [(C₂Al_2?2yMg_ySi_1+yO₇ (0≤y≤1)] doped with Nd³⁺ (2% mol) has been studied. DTA was used to determine the kinetics of the process. The Avrami law α=1-exp(?kt ⁿ) withn=1 was found to hold for doped gehlenite. For pure gehlenite, parametern was determined to be 1.5. The activation energy of the devitrification process is independent of the presence of neodymium, and it is of the same order of magnitude as that for the viscous flow in molten silicates (ca. 650–750 kJ·mol^?1).     

Temperature-concentration dependence of the electrical conductivity of glasses in the Zn(PO3)2-NaF system

Temperature-concentration dependence of the electrical conductivity in glasses of the Zn(PO₃)₂-NaF system was studied and compared with similar dependences for glasses of other systems. The extremal dependences log σ = f([Na⁺]) and {ie937-1} are interpreted from the standpoint of a macroscopically inhomogeneous structure of the glasses under study.     

Structural features of diastereomeric oxazolidin-2-ones

Model diastereomeric oxazolidinones containing various substituents at positions 3 and 5 were synthesized. Several individual diastereomers bearing methyl groups at positions 4 and 5 in cis-and trans orientations were isolated. The TLC and ¹H NMR spectroscopic data suggest that diastereomers, particularly those containing the aryl substituent at position 5, are substantially different in the physical and spectral properties. The configurations of some diastereomers were established by X-ray diffraction and NOESY spectroscopy. For these compounds, the reliable assignment of the characteristic ¹H NMR signals of individual groups was made, which provided evidence for the cis or trans orientation of the methyl groups at positions 4 and 5. The scope of the method as applied to the determination of the cis and trans isomers from their ¹H NMR spectra is discussed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 133–139, January, 2007.     

Structural recovery of polymer glasses

The structural recovery of polystyrene glasses subjected to thermal cycles in the glass transition region is studied by differential scanning calorimetry and by dilatometry. Three different types of behaviour are observed in respect of the peak in the specific heat capacity or thermal expansion coefficient on heating, and are found to be in full agreement with the predictions of the KAHR model. First, for well-stabilized glasses, the dependence of the (main) peak temperature on heating rate and annealing time yields consistent values for the structure parameter x by means of the peak-shift method. Second, for poorly-stabilized glasses, the (upper) peak temperatures shift quite differently, but again consistently with theory. Third, for glasses intermediate between poorly-and well-stabilized conditions, both main and upper peaks can be observed simultaneously in the same endotherm.     

Structural features of ZrO2-Y2O3 and ZrO2-Gd2O3 nanoparticles formed under hydrothermal conditions

We synthesized nanoparticles of variable composition based on zirconium dioxide in the ZrO₂-Y₂O₃ (or Gd₂O₃)-H₂O systems under hydrothermal conditions. By X-ray diffraction and small-angle X-ray scattering studies revealed that the nanoparticles consist of crystalline core and amorphous shell. Increase of Y₂O₃ (or Gd₂O₃) content yields increases of shell size and decreases of core size. The effect is due to suppressed ZrO₂ crystallites growth caused by development of the shell preventing zirconium ions transport.     

Effect of bismuth trifluoride on the characteristics of fluoroindate glasses: The InF3-BiF3-BaF2 system

Glass formation in the InF₃-BiF₃-BaF₂ system is studied. Partial substitutions of BiF₃ for InF₃ in the InF₃-BaF₂ system reduce the glass-transition and glass-crystallization temperatures and increase the thermal stability range and refractive index. The glass structure is studied using IR and Raman spectroscopy. InF₆ and BiF_n polyhedra are identified in the system. Doping the glass with bismuth trifluoride changes the degree and linkage character of the InF₆ polyhedra in the glass network. The medium-range order length is not affected by the bismuth trifluoride concentration in the glass. The modifier cation (Ba²⁺) substantially determines the correlation length in the glasses.     

Study on the Stability of GaF3-based Glasses by Differential Scanning Calorimetry

The glass formation and devitrification of GaF₃-based glasses were studied by differential scanning calorimetry. A comparison of various simple quantitative methods to assess the level of stability of multicomponent fluoride glass systems is presented. Most of these methods are based on critical temperatures. In this paper a new parameter k _b(T) is added to the stability criteria. The stability of several GaF₃-based glasses were experimentally evaluated and correlated with the activation energies of crystallization via this new kinetic criterion and compared with those evaluated by other criteria. This revised version was published online in August 2006 with corrections to the Cover Date.     

Structural features of photochromic 2,3-epoxy-2-(p-nitrophenyl)-3-phenylindan-2-one

Conclusions On the basis of the results from an x-ray crystallographic investigation of the photochromic 2,3-epoxy-2-(p-nitrophenyl)-3-phenylindan-2-one it was shown that the C-C bond cleaved during photoexcitation is the weakest bond in the molecule even in the ground state, as occurred in the previously investigated photochromic spiropyrans.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2037–2040, September, 1988.The authors express their gratitude to A. S. Kholmanskii for providing the crystals for the investigation.     

Physical and chemical characterization and ionic conductivity of rapidly quenched glasses in the Sb2S3Ag2SAgI system

The glass-forming regions in the Sb₂S₃Ag₂SAgI ternary system have been determined after rapid roller quenching. Some physical chemical properties including density, thermal behavior, transport number, ionic conductivity, electrochemical stability, and IR absorption spectra have been investigated. The best conductivity obtained is 0.06 (Ω-cm)⁻¹ for a molar composition: 0.03Sb₂S₃0.57Ag₂S0.40AgI with an activation energy of 0.15 eV. The transport number measurements show that the glasses are essentially ionic conductors (0.991–0.998 as determined by an emf method). Using the triangular voltammetry method the redox stability domain has been determined; it is about 2 V for a current density of 0.1 mA/cm². A glass model structure has been proposed on the basis of the infrared spectra.     

Thermodynamic properties of silicate glasses and melts: IX. Bi2O3-SiO2 system

Differential high-temperature mass spectrometry was used to determine the activities of Bi₂O₃ in Bi₂O₃-SiO₂ glasses at 1000 K. The activities of SiO₂ and integral Gibbs energies in Bi₂O₃-SiO₂ glasses were determined. Negative deviations from the ideal behavior were revealed in the studied system at 1000 K.     

Structural, optical, physical and electrical properties of V2O5.SrO.B2O3 glasses

The present work aims to study the structure and variation of optical band gap, density and dc electrical conductivity in vanadium strontium borate glasses. The glass systems xV2O5.(40-x)SrO.60B2O3 and xV2O5.(60-x)B2O3.40SrO with x varying from 0 to 20 mol% were prepared by normal melt quench technique. Structural studies were made by recording IR transmission spectra. The fundamental absorption edge for all the glasses was analyzed in terms of the theory proposed by Davis and Mott. The position of absorption edge and hence the value of the optical band gap was found to depend on the semiconducting glass composition. The absorption in these glasses is believed to be associated with indirect transitions. The origin of Urbach energy is associated with the phonon-assisted indirect transitions. The change in both density and molar volume was discussed in terms of the structural modifications that take place in the glass matrix on addition of V2O5. dc conductivity of the glass systems is also reported. The change of conductivity and activation energy with composition indicates that the conduction process varies from ionic to polaronic one.     

Structural and spectroscopic investigations on Eu3+-doped alkali fluoroborate glasses

Eu³⁺-doped alkali fluoroborate glasses B₂O₃–XCO₃–NaF–Eu₂O₃ (where X = Li₂, Na₂, K₂, and Ca, Mg) have been prepared using the conventional melting technique and their structural and optical properties have been evaluated. The XRD pattern of the glasses confirmed the amorphous nature and the FTIR spectra reveal the presence of BO₃ and BO₄ units as their local structures along with the strong OH^? groups. From the absorption spectra the bonding parameters have been calculated and confirmed that the Eu–O bonds in the studied glasses are of covalent nature. Judd–Ofelt (JO) analysis has been carried out from the emission spectra. The JO parameters have been used to calculate transition probabilities (A), lifetime (τ_R) and branching ratios (β_R) and peak stimulated emission cross-section (σ_P^E) for the ⁵D₀ → ⁷F_J (J = 1, 2, 3 and 4) transitions of the Eu³⁺ ions. The decay from the ⁵D₀ level of Eu³⁺ ions in the title glasses has been measured and analysed. The lifetime of the ⁵D₀ level is found to be shorter than the reported glasses which may be due to the presence of OH^? groups.     

Structural models for yttrium aluminium borate laser glasses: NMR and EPR studies of the system (Y2O3)(0.2)-(Al2O3)x-(B2O3)(0.8-x)

The structure of laser glasses in the system (Y(2)O(3))(0.2){(Al(2)O(3))(x))(B(2)O(3))(0.8-x)} (0.15 ≤ x ≤ 0.40) has been investigated by means of (11)B, (27)Al, and (89)Y solid state NMR as well as electron spin echo envelope modulation (ESEEM) of Yb-doped samples. The latter technique has been applied for the first time to an aluminoborate glass system. (11)B magic-angle spinning (MAS)-NMR spectra reveal that, while the majority of the boron atoms are three-coordinated over the entire composition region, the fraction of three-coordinated boron atoms increases significantly with increasing x. Charge balance considerations as well as (11)B NMR lineshape analyses suggest that the dominant borate species are predominantly singly charged metaborate (BO(2/2)O(-)), doubly charged pyroborate (BO(1/2)(O(-))(2)), and (at x = 0.40) triply charged orthoborate groups. As x increases along this series, the average anionic charge per trigonal borate group increases from 1.38 to 2.91. (27)Al MAS-NMR spectra show that the alumina species are present in the coordination states four, five and six, and the fraction of four-coordinated Al increases markedly with increasing x. All of the Al coordination states are in intimate contact with both the three- and the four-coordinate boron species and vice versa, as indicated by (11)B/(27)Al rotational echo double resonance (REDOR) data. These results are consistent with the formation of a homogeneous, non-segregated glass structure. (89)Y solid state NMR spectra show a significant chemical shift trend, reflecting that the second coordination sphere becomes increasingly "aluminate-like" with increasing x. This conclusion is supported by electron spin echo envelope modulation (ESEEM) data of Yb-doped glasses, which indicate that both borate and aluminate species participate in the medium range structure of the rare-earth ions, consistent with a random spatial distribution of the glass components.