The structure of lithium,sodium and potassium germanate glasses,studied by Raman scattering

Polarized and depolarized Raman spectra of alkali germanate glasses are given, together with Raman powder spectra of the crystalline compounds Li₂O · 2 GeO₂; 3 Li₂O · 8 GeO₂; 2 Li₂O· 9 GeO₂; Li₂O · 7 GeO₂; 2 Na₂O · 9 GeO₂; K₂O · 2 GeO₂; K₂O · 4 GeO₂ and K₂O · 8 GeO₂.The alkali germanate glasses: xA₂O (1?x) GeO₂ are studied in the composition range 0 < x < 0.333. The vibrational modes observed in the high energy range of the Raman spectra of the crystalline compounds are interpreted in terms of symmetrical and antisymmetrical O-Ge-O and Ge-O^? stretch vibrations. The molecular structure of the germanate glasses is deduced from a comparison of the Raman spectra of the glasses with those of the crystalline compounds, together with a study of the polarization properties of the glass spectra.It is observed that 6-coordinated Ge atoms occur in a network structure which resembles the structures occurring in the crystalline compounds 2 Li₂O · 9 GeO₂ and 2 Na₂O · 9 GeO₂.In the region of 0.18 < x < 0.33 it is found that tetrahedra with one non-bridging oxygen atom are formed. These tetrahedra are probably present in a network as occurs in the crystalline digermanates Li₂O · 2 GeO₂ and K₂O · 2 GeO₂.     

Electrical and optical properties of RF-SP a-Ge:O:(H) deposited from GeO2

The electrical and optical properties of a-Ge:O:(H) prepared from sintered GeO₂ are investigated. Unlike SiO₂, GeO₂ can be reduced with H₂ gas. The properties of a-Ge:O:(H) thus prepared can be changed widely with the H₂ gas pressure, approaching those of a-Ge. It is found that, in addition to these changes, a configurational change from GeOGe to oxygen-vacancy complex occurs with increasing the H₂ gas pressure.     

Crystallization studies by thermometric methods (II). Calorimetric determination of chrystallization kinetics of sodium sulfate and sodium carbonate decahydrates

A calorimetric method was applied for the determination of crystallization kinetics of vibrationally mixed suspensions of Na₂SO₄ · 10 H₂O and Na₂CO₃ · 10 H₂O at 25°C with supersaturations up to 0.083 and 0.119 g hydrate/g free water, resp. The characteristic dimension of crystals was 0.125–0.63 mm.     

Raman spectra and structure of sodium aluminogermanate glasses

Polarized Raman spectra of x NaAlO₂·(100 ? x) GeO₂ glasses (x = 0, 5, 10, 15, 20, 25, 33, 42, and 50) are presented. Analyses of the Raman data indicate that the aluminogermanate glasses have three-dimensional network structures consisting of interconnected AlO₄ and GeO₄ tetrahedra; Na⁺ ions are present in cavities and charge balance the Al³⁺ ions. Systematic changes are observed in the frequencies, intensities and polarization characteristics of spectral bands with variations in the NaAlO₂ content of these glasses. The antisymmetric stretching mode [ν_as (TOT), where T = Al, Ge] in the high-frequency region of the spectra (800–1000 cm^?1) appears as a doublet consisting of well-defined bands in the spectra of glasses along the entire join. Both components of the high-frequency doublet shift to a lower frequency with increasing NaAlO₂ content, indicating that the ν_as (GeO₄) and ν_as(AlO₄) stretching modes are coupled. The variations in the TO force constants and TOT bond angles with change in composition most likely cause the bands to shift. The frequencies of the Raman bands of sodium aluminogermanate glasses are compared with those of the corresponding bands in isostructural sodium gallogermanate glasses. On the basis of this comparison, the origin and delocalization of the vibrational modes producing characteristic Raman bands in the spectra of these glasses are discussed. The changes observed in the Raman spectra of aluminogermanate glasses with variation in NaAlO₂ content are analogous to those observed in the spectra of glasses along the NaAlO₂SiO₂ join.     

Raman study of the structure of alkali germanosilicate glasses II. Lithium,sodium and potassium digermanosilicate glasses

Polarized and depolarized Raman spectra of lithium, sodium and potassium digermanosilicate glasses of the composition 33 A₂O 67[(1 ? y)SiO₂, y GeO₂] and powder Raman spectra of crystalline Li₂O · 2 GeO₂ and K₂O · 2 GeO₂ are given. From the Raman spectra it is concluded that the structure of the glasses mainly consists of networks of SiO₄ and GeO₄ tetrahedra with one non-bridging oxygen atom, probably mixed in a random way. The structure is comparable to that of crystalline disilicates and digermanates.     

Phase separation in GeGeO2 glasses

De Neufville prepared homogeneous glasses ranging in composition from pure GeO₂ to GeO by quenching bulk samples from the melt and by vapor deposition. For compositions in the range of 10–20 mol % excess Ge dissolved in GeO₂, he found that phase separation into amorphous Ge rich and amorphous GeO₂ phases occurred. The results reported here on a 7.5 mol % excess Ge composition using differential scanning calorimetry have shown that a two-step phase separation mechanism is operative. A homogeneous GeGeO₂ glass phase separates at 450°C into amorphous GeO₂ and amorphous GeO. The GeO phase separates at 570°C into crystalline Ge and amorphous GeO₂. The heat measured at 570°C is equal to the sum of the heats of phase separation of GeO and crystallization of Ge. The amorphous GeO₂ crystallizes at 670°C with a heat of crystallization of 4.65 kcal/mol (± 0.5). Additional support for a two-step phase separation mechanism is provided by kinetic arguments based on the viscosity dependence on composition and on the structure of the amorphous GeO phase and its stability relative to the homogeneous GeGeO₂ glass.     

Glass formation in and structural investigation of Li2S + GeS2 + GeO2 composition using Raman and IR spectroscopy

Li₂S + GeS₂ + GeO₂ ternary glasses have been prepared and a wide glass-forming range was obtained. The glass transition temperatures increase with the GeO₂ concentration in the glasses. The vibrational modes of both bridging (Ge–S–Ge) and non-bridging (Ge–S⁻) sulfurs are observed in Raman and IR spectra of binary Li₂S + GeS₂ glasses. Additions of GeO₂ to this binary glass increase the bridging oxygen band (Ge–O–Ge) at the expense of decreasing the bridging sulfur band (Ge–S–Ge), whereas the bands associated with the non-bridging sulfurs (Ge–S⁻) remain constant in intensity up to high GeO₂ concentrations. At higher concentrations of GeO₂ (⩾60%), the non-bridging oxygen band, which is not observed at low and intermediate GeO₂ concentrations, appears and grows stronger. From these observations, it is suggested that the added lithium ions favor the non-bridging sulfur sites over the oxygen sites to form non-bridging sulfurs, whereas the added oxygen prefers the higher field strength Ge⁴⁺ cation to form bridging Ge–O–Ge bonds. The structural groups in the Li₂S + GeS₂ + GeO₂ glasses that are consistent with results of Raman and IR spectra are described and are used to develop a structural model of these glasses.     

Structure of potassium germanophosphate glasses by X-ray and neutron diffraction: 3. Reverse Monte Carlo simulations

Reverse Monte Carlo (RMC) is used to investigate the origin of the first sharp diffraction peaks (FSDP) found for K₂O–GeO₂–P₂O₅ glasses at very small scattering vector Q = ～7.5 nm^?1. Structures of the ternary glass with the greatest intensity of FSDP (KGeP5 – 25/50/25 mol% K₂O/GeO₂/P₂O₅), of the binary combinations of the three oxides and of vitreous GeO₂ are modeled. Results are deduced from comparisons of the partial structure factors and inspections of model sections. The P sites are uniformly distributed in the structure of KGeP5. The K⁺ ions interact more with the PO₄ units (via O_T-corners) than with Ge-centered units. Main component of the FSDP comes from the S_GeGe(Q) factor. The FSDP is due to separations of ～1 nm between the longish Ge-rich clusters which are visible in the corresponding models. Different to our tentative structural models reported before, the PO₄ tetrahedra possess a broad distribution of numbers of O_T corners. The FSDP’s of the binary K₂O–GeO₂ and K₂O–P₂O₅ glasses (～10 nm^?1) are due to a chemical order between network former and network modifier regions. The MRO of a mixed GeO₂–P₂O₅ glass of small P₂O₅ content (FSDP at ～16 nm^?1) shows great similarity to the MRO of vitreous GeO₂.     

Writing of crystal line patterns in glass by laser irradiation

We examined the laser-induced crystallization to form the fresnoite type Ba₂TiGe₂O₈ crystal line patterns in transition metal ion doped BaO–TiO₂–GeO₂ glass. Ba₂TiGe₂O₈ crystal line was written in 0.6FeO–33.3BaO–16.7TiO₂–50GeO₂ glass by continuous wave yttrium–aluminum–garnet (YAG) laser irradiation. We obtained polarization dependence of Raman spectra in crystal line pattern. Second harmonic generation (SHG) indicated unique fringe patterns from Ba₂TiGe₂O₈ crystal lines.     

Crystal structure of Rb2[GeO2(OH)2]·2H2O

Single crystals of Rb₂[GeO₂(OH)₂] · 2H₂O are studied by X-ray diffraction. The crystals belong to the orthorhombic system, sp. gr. Pna2₁, a = 13.523(6) Å, b = 8.143(4) Å, c = 13.407(6) Å, Z = 8, R ₁ = 0.0506. In [GeO₂(OH)₂]^2? anions, the Ge-O distances (1.71–1.73(1) Å) are shorter than the Ge-OH distances (1.76–1.80(1) Å). Anions are linked to each other by pairs of hydrogen bonds to form infinite chains. The chains are linked by hydrogen bonds involving water molecules to form a 3D structure. The assignment of the bands in the IR spectrum of the compound under study is performed.     

Raman study of the structure of glasses along the join SiO2GeO2

In order to better understand the distribution of tetrahedra in multicomponent tetrahedral network structures of melts and glasses, we have investigated the Raman spectra of binary SiO₂GeO₂ glasses. We compare the Raman spectral features of the end-member glasses and discuss their vibrational origins. The mixing of GeO₂ and SiO₂ melts results in a continuous random network structure of TO₄ tetrahedra (T  Si, Ge) in the glass. Raman bands corresponding to the asymmetric stretch (v_as) of oxygen in GeOGe, SiOSi and SiOGe bonds are observed in the glasses having intermediate compositions along the SiO₂GeO₂ join. The presence of three distinct v_as (TOT) bands in the spectrum of a glass having Si/Ge one reveals that a considerable degree of SiGe disorder exists in the glass. The presence of a single symmetric oxygen stretching band in the spectra of binary SiO₂GeO₂ glasses indicates that the symmetric stretch modes (v_s) of oxygen in SiOSi, SiOGe and GeOGe bonds are strongly coupled. An observed decrease in the halfwidth of the v_s (TOT) band in the spectra of SiO₂GeO₂ glasses with increasing concentration of GeO₂ may be attributed to a decrease in the average TOT bond angle and a predominance of six-membered ring structures. Results of the present study support the assignment of the bands in the 900–1200 cm^?1 region of the alumino-silicate glasses, spectra to the v_as(AlOSi) and v_as(SiOSi) modes. In contrast to the alumino-silicate glasses, however, the SiO₂GeO₂ glasses have a much higher degree of disorder of the network-forming cations.     

Synthesis of magnesium oxysulfate whiskers in the presence of sodium dodecyl benzene sulfonate

Uniform magnesium oxysulfate (5Mg(OH)₂·MgSO₄·3H₂O) whiskers with a length of 10‐15 µm and a diameter of 0.4‐1.0 µm were synthesized in the presence of sodium dodecyl benzene sulfonate (Na‐SO₃‐C₆H₄‐C₁₂H₂₅) at 200°C for 1 h, using MgSO₄·7H₂O and NaOH as the reactants. Mg(OH)₂ precursor with poor crystallization and small crystal size was formed owing to the adsorption of sodium dodecyl benzene sulfonate on the Mg(OH)₂ surface. The quick dissolution of Mg(OH)₂ precursor in the subsequent hydrothermal reaction inhibited the occurrence of the sector‐like byproduct and promoted the formation of magnesium oxysulfate whiskers with uniform morphology. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Sub-critical crack growth in sodium germanate glasses

Sub-critical crack growth in binary sodium germanate glass was investigated over a wide range of the crack velocities, 10⁻⁷-10⁻² m s⁻¹, by using small-size specimens with double cleavage drilled compression configuration. For evaluating the intrinsic sub-critical crack growth, crack initiation and subsequent propagation of the crack were performed in heptane. With increasing Na₂O content in sodium germanate glass, sub-critical crack growth curve shifted toward higher stress intensity factors first up to 10 mol% Na₂O, but more addition of Na₂O caused the curve to shift to lower stress intensity factor regions. In other words, fracture toughness shows a maximum at the composition of 10Na₂O·90GeO₂, whose value is 1.07 MPa m^1/2. This compositional dependence of fracture toughness originates from the so-called germanate anomaly. On the other hand, the slope of sub-critical crack growth curve for the glass containing >10 mol% Na₂O was much shallower than that for soda-lime glass. These glasses are very fatigable even in inert condition. It is considered that this fatigue behavior can be caused by the microscopic structural variation, which is the presence of GeO₆ units in GeO₂ glass network, and that these units can be the fatigue crack path.     

Structure and conformation of the sodium chloride salt of N-t-Boc-Phenylalanyl-Proline (Boc-Phe-Pro·NaCl) and the dihydrate of N-t-Boc-Tyrosyl-Proline (Boc-Tyr-Pro·2H2O)

The structure and conformation of the salt of N-t-Boc-Phenylalanyl-Proline (Boc-Phe-Pro·NaCl) (C₁₉H₂₆N₂O₅NaCl) (compound 2) and the dihydrate of N-t-Boc-Tyrosyl-Proline (Boc-Tyr-Pro·2H₂O) (C₁₉H₃₀O₈N₂) (compound 1) have been investigated with X-ray crystallographic and spectroscopic methods. Boc-Phe-Pro·NaCl crystallizeds in an extended trans conformation in the space groupP2₁ with cell dimensionsa=7.961 (3),b=10.045(2), andc=13.495(4). One intermolecular hydrogen bond and one intramolecular hydrogen bond was observed for the dipeptide salt. Boc-Tyr-Pro·2H₂O crystallized in an extended trans conformation in the space group P2₁ with cell dimensionsa=7.964(1),b=10.011(1), andc=13.853(2). Six intermolecular hydrogen bonds were observed for Boc-Tyr-Pro·2H₂O. The conformation of both dipeptides reflect collagen-type of proline-compounds. The puckering mode of the pyrrolidine ring of the proline residues can be described as an approximate C₂ half-chair symmetry having an A conformation with the Cγ atom located exo and Cβ atom located endo relative to the carboxamide group, i.e., γ/β T.Cis-trans isomerism was observed in the NMR spectra of both dipeptides with a predominance for the extended side chain for the phenylalanyl and tyrosyl residues, respectively.     

Thermodynamics and kinetics of calcium oxalate crystallization in the presence of amino acids

Specific features of the crystallization of calcium oxalates (CaC₂O₄) in the presence of amino acids have been established based on thermodynamic and experimental modeling. Phase formation in the Ca²⁺–C₂O₄ ^2-–H₂O–amino acid system in a wide range of variation in the component concentrations and solution pH have been theoretically investigated. The influence of pH on the thermodynamic stability of crystallizing compounds is considered. The effect of amino acids of different structures on the formation of the CaC₂O₄ solid phase in a prototype of physiological solution is analyzed. The kinetic crystallization parameters (induction period and rate constant) and crystallite growth are determined.     

Crystal structure of chloro[1-hydroxyethane-1,1-diphosphonato(3−)]ditin(II) monohydrate Sn2(HL)Cl · H2O

The synthesis and X-ray structure analysis of Sn₂(HL)Cl · H₂O, where HL ^3? is the anion of 1-hydroxyethane-1,1-diphosphonic acid, are reported. The coordination polyhedra of two independent tin(II) atoms are the Sn(1)O₂Cl and Sn(2)O₃ trigonal pyramids, in which one of the vertices is occupied by a lone electron pair (Sn-O, 2.144–2.218 Å and Sn-Cl, 2.573 Å). The pyramids are complemented by weaker Sn?O and Sn?Cl contacts to form severely distorted (3 + 3) octahedra. The SnO₂Cl and SnO₃ pyramids are linked by the HL ^3? bridging ligands into the [Sn₂(HL)Cl]₆ cyclic molecules, which, in turn, are joined by additional Sn?O, Sn?Cl, O(H₂O)?O(L), and O(H₂O)?Cl contacts with each other and with crystallization water molecules into a three-dimensional framework.     

The elastic constant and molar volume of sodium and potassium germanate glasses and the germanate anomaly

The composition dependences of molar volume and elastic constants were investigated for sodium and potassium germanate glasses of composition xR₂O·GeO₂ (O < x < 0.65 in the sodium-glasses and O < x < 0.75 in the potassium-ones). The variation of the molar volume could be approximated by straight lines crossing at 0.18 and 0.16 in x in the sodium- and potassium-glasses, respectively. At these compositions the elastic constants showed maxima. With reference to the structures of several alkali germanate crystals, it was concluded that the fraction of GeO₆ units, N₆, reaches a maximum at 0.18 in x in the sodium-glasses (15.6) mol.% Na₂O) and at 0.16 in x in the potassium-glasses (13.8 mol.% K₂O). It was also considered that N₆ is not null at 0.5 but is null probably at 1.0 in x in the glasses. A network model of the germanate glasses was discussed.     

Phase Interaction in the Systems Sodium Selenate – Copper Selenate – Water and Sodium Selenate – Zinc Selenate – Water at 25 °C

The phase equilibrium in the systems Na₂SeO₄–CuSeO₄–H₂O and Na₂SeO₄–ZnSeO₄–H₂O were studied and it was established that new phases were obtained – double salts with a composition: Na₂Cu(SeO₄)₂ · 2 H₂O and Na₂Zn(SeO₄)₂ · 2 H₂O. The fields of phase equilibrium of the double salts in the triple systems were determined. The composition of the new phases was investigated by the Schreinemackers' method of physico-chemical analysis, and the number of the water molecules of crystallization – by thermogravimetrical analysis. An X-ray diffraction analysis of the new phases obtained was done.     

Ferrous Tartrate recognition of sodium chloride {111} and its effect on crystal growth

The surface morphology and growth pattern of some molecules could be altered by the recognition of ferrous tartrate (FeC₄H₄O₆, FeTA). We have explored this phenomenon in the aspect of growth rate and morphology alteration of sodium chloride crystals where few researches have been done. In this paper, the crystallization behavior of NaCl with added FeTA was studied by supersaturation test, conductivity, scanning electron microscopy (SEM), and X‐ray diffraction (XRD). The results showed that the supersaturation of NaCl solution could be increased to about 5.5 % in presence of FeTA prior to the onset of crystallization. Furthermore, SEM images and XRD results indicated that the addition of FeTA could change the morphology of NaCl crystal from cubic to octahedron by impeding the growth of {111} and {110} faces. Besides, the interaction between NaCl {111} face and FeTA was discussed and the possible spatial structure of FeTA was speculated through the lattice parameters of NaCl.     

The Effect of Different Inorganic Salts on the Growth Rate of NaCl Crystallized from Sea Water

A comprehensive experimental study on the effect of fourteen different inorganic salts on the growth rate of NaCl single crystals is presented. The fourteen different inorganic salts are chosen as they are present in Chinese sea water. The impurity content of each salt has been varied according to its presence in the natural sea water. The impurities are differentiated in groups related to their effect on the growth rate of NaCl. The examined impurities are: MgCl₂ · 6 H₂O, KCl, SrCl₂, NaBr, Nal, NaF, Na₂SO₄, NaBO₂ · 4 H₂O, Na₂CO₃, Na₂SiO₃ · 9 H₂O, ZnSO₄, CuSO₄ · 5 H₂O, PbCl₂, and K₄Fe(CN)₆.