Crystallization and microstructure of glasses in the system Na2O/MnO/SiO2/Fe2O3

Glasses with the compositions (100 − x)(0.16Na₂O/0.10MnO/0.74SiO₂)/xFe₂O₃, (x = 5-30) and 16Na₂O/10MnO/(74 − y)SiO₂/yFe₂O₃ (y = 5-30) were studied using X-ray diffraction and scanning electron microscopy. The effect of the chemical composition and the thermal history on the phase formation and the resulting microstructure was investigated. During cooling, the precipitation of ferrimagnetic solid solutions Fe₃O₄/Mn₃O₄ was observed. These crystals show dendritic or platelet shape, whereby the platelets are ferromagnetic and the dendrites - mainly paramagnetic. The tendency towards crystallization can be suppressed by increasing the Na₂O-concentration. In contrast to glasses without manganese oxide, the precipitation of hematite is not observed. Therefore, the addition of reducing agents is not required, in order to crystallize large volume concentrations of the ferrimagnetic phase.     

Crystal growth of tetragonal GeO2 and Na4Ge9O20 and a comparison of their optical properties with glasses

Tetragonal GeO₂ has been prepared by the top-seed solution technique with different orientations of the seed. Large single crystals of Na₄Ge₉O₂₀ have been grown by the Czochralski method from a stoichiometric melt. Refractive indices of both crystals and of vitreous samples have been measured between 2 and 4.5 eV. Both crystals display an unusual dispersion of birefringence which is compared to stress induced birefringence of vitreous samples.     

Synthesis of (Na2O,PbO)-Nb2O5, (Na2O,BaO)-Nb2O5, and (K2O,SrO)-Nb2O5 thin films using sol-gel method

Homogeneous pore-free Ba₂NaNb₅O₁₅, KSr₂Nb₅O₁₅, and 2·Na₂O-PbO-6·Nb₂O₅ thin films were fabricated on sapphire substrates using the sol-gel technique. By controlling the gelation and coating process, thickness of thin films fabricated was controllable from ~ 40 nm to ~ 10 μm. Synthesized thin films possessed highly preferred orientated microstructure. Another advantage of this method is the subsequent heat treatment temperature dramatically decreased compared with other methods. This increases stoichiometry control and makes the large scale fabrication more feasible and efficient.     

Oligoselenidogermanate (III): Zur kenntnis von Na6Ge2Se6 und Na8Ge4Se10

The following new oligomeric selenidogermanates (III) have been prepared and structurally characterized: Na₆Ge₂Se₆: monoclinic, space group $\text{P}\text{2}{}_1\text{c}$ (No. 14) a = 836.7(5) pm, b = 1192.4(8) pm, c = 815.8(5) pmβ = 118.63(15)°.The compound is isotypic to K₆Sn₂Te₆, essential structure elements are [Ge₂Se₆]^6? anions.Na₈Ge₄Se₁₀: triclinic, space group P1? (No. 2) a = 707.4(5) pm, b = 809.8(5) pm, c = 1065.7(6) pmα = 73.44(15)°, β = 70.84(15)°, ?= 81.73(15)°Two Ge₂Se₆ octahedra are connected by a common edge forming a six-membered cyclic [(GeSe₂)₄Se₂]^8? anion.     

Role of bismuth and titanium in Na2O-Bi2O3-TiO2-P2O5 glasses and a model of structural units

0.60Na₂O-0.40P₂O₅ and (0.55−z)Na₂O-0.05Bi₂O₃-zTiO₂-0.40P₂O₅ glasses (0≤z≤0.15) were prepared by melting at 1000°C mixtures of Na₂CO₃, Bi₂O₃, TiO₂ and (NH₄)₂HPO₄. Differential Scanning Calorimetry (DSC) measurements give the variation of glass transition temperature (T_g) from 269°C (for 0.60Na₂O-0.40P₂O₅) to 440°C (for z=0.15). The density measurements increases from 2.25 to 3.01 g/cm³. FTIR spectroscopy shows the evolution of the phosphate skeleton: (PO₃)_∞ chains for 0.60Na₂O-0.40P₂O₅ to P₂O₇⁴⁻ groups in the glasses containing Bi₂O₃ or both Bi₂O₃ and TiO₂. When bismuth oxide and titania are added to sodium phosphate glass, phosphate chains are depolymerized by the incorporation of distorted Bi(6) and Ti(6) units through POBi and POTi bonds. Bi₂O₃ and TiO₂ are assumed to be present as six co-ordinated octahedral [BiO_6/2]³⁻and [TiO_6/2]²⁻ units again with shared corners. This is accompanied by the simultaneous conversion of [POO_3/2] into [PO_4/2]⁺ units which achieves charge neutrality in the glasses.     

Glass-recrystallization of ferroelectric Pb5Ge3O11

Thin plate-like crystals of ferroelectric Pb₅Ge_3?xSi_xO₁₁ (0 ≤ x ≤ 1.5) were prepared by a glass-recrystallization technique during which the glass was heat-treated at 600 to 720°C. The crystals show preferred orientation with the polar c-axis perpendicular to the sample surface, an ideal geometry for pyroelectric infrared detectors.     

Nanocrystallization of SrBi2Nb2O9 from glasses in the system Li2B4O7---SrO---Bi2O3---Nb2O5

Transparent glasses in the system (100−x)Li₂B₄O₇–x(SrO---Bi₂O₃---Nb₂O₅) (10≤x≤60) (in molar ratio) were fabricated by a conventional melt-quenching technique. Amorphous and glassy characteristics of the as-quenched samples were established via X-ray powder diffraction (XRD) and differential thermal analyses (DTA) respectively. Glass–ceramics embedded with strontium bismuth niobate, SrBi₂Nb₂O₉ (SBN) nanocrystals were produced by heat-treating the as-quenched glasses at temperatures higher than 500 °C. Perovskite SBN phase formation through an intermediate fluorite phase in the glass matrix was confirmed by XRD and transmission electron microscopy (TEM). Infrared and Raman spectroscopic studies corroborate the observation of fluorite phase formation. The dielectric constant (_r) and the loss factor (D) for the lithium borate, Li₂B₄O₇ (LBO) glass comprising randomly oriented SBN nanocrystals were determined and compared with those predicted based on the various dielectric mixture rule formalism. The dielectric constant was found to increase with increasing SBN content in LBO glass matrix.     

Electrical properties of glasses in the Na2O–MoO3–P2O5 system

A range of coloured electronic or mixed ionic–electronic glasses has been evidenced in the Na₂O–MoO₃–P₂O₅ system. The properties of these glasses have been studied along different composition lines corresponding either to a fixed Na₂O content or a constant Mo/P ratio. An EPR spectroscopy investigation of these glasses has allowed to determine the Mo⁵⁺ ion percentages in these materials. The electrical properties of these glasses have been studied by impedance spectroscopy, and the electronic and ionic contributions have been evaluated. The properties of these sodium glasses have been compared with those of lithium glasses with the same compositions.     

Ionic conductivity in Na5GdSi4O12

Na₅GdSi₄O₁₂ has been prepared by solid state reaction. Na⁺ ion conductivity is 3 × 10^?1 (ohm-cm)^?1 at 300° with an activation energy for conduction of 6.5 kcal/mole. The structure of isotypic Na₅YSi₄O₁₂ is characterized by Si₁₂O₃₆ rings stacked to form columns held apart by MO₆ octahedra. Immobile Na atoms are situated within the rings. The high conductivity arises from the presence of mobile Na atoms between the columns.     

Structural study of (50 − x)Na2O-xCuO-10Bi2O3-40P2O5 glasses

(50−x)Na₂O-xCuO-10Bi₂O₃-40P₂O₅ glasses (0≤x≤25) were prepared by melting at 900-1100°C mixtures of Na₂CO₃, Bi₂O₃, CuO and (NH₄)₂HPO₄. DSC measurements give the variation of glass transition temperature T_g from 318 (x=0) to 378°C (x=25). FTIR spectroscopy shows the evolution of the phosphate skeleton: (PO₃)_∞ chains for 60Na₂O-40P₂O₅ to P₂O₇ groups in the glass containing Bi₂O₃ or both Bi₂O₃ and CuO. When bismuth and copper oxides replace Na₂O, phosphate chains are depolymerized by the incorporation of Bi₂O₃ and CuO through POBi and POCu bonds. P₂O₇ groups are predominant structural units in the richest CuO glass. The variation of T_g also supports these results.     

Synthesis and Li ion conductivity of Li2O-Nb2O5-P2O5 glasses and glass-ceramics

Glasses with the compositions of xLi₂O-(70 − x)Nb₂O₅-30P₂O₅, x = 30-60, and their glass-ceramics are synthesized using a conventional melt-quenching method and heat treatments in an electric furnace, and Li⁺ ion conductivities of glasses and glass-ceramics are examined to clarify whether the glasses and glass-ceramics prepared have a potential as Li⁺ conductive electrolytes or not. The electrical conductivity (σ) of the glasses increases monotonously with increasing Li₂O content, and the glass of 60Li₂O-10Nb₂O₅-30P₂O₅ shows the value of σ = 2.35 × 10⁻⁶ S/cm at room temperature and the activation energy (E_a) of 0.48 eV for Li⁺ ion mobility in the temperature range of 25-200 °C. It is found that two kinds of the crystalline phases of Li₃PO₄ and NbPO₅ are formed in the crystallization of the glasses and the crystallization results in the decrease in Li⁺ ion conductivity in all samples, indicating that any high Li⁺ ion conducting crystalline phases have not been formed in the present glasses. 60Li₂O-10Nb₂O₅-30P₂O₅ glass shows a bulk nanocrystallization (Li₃PO₄ nanocrystals with a diameter of ∼70 nm) and the glass-ceramic obtained by a heat treatment at 544 °C for 3 h in air exhibits the values of σ = 1.23 × 10⁻⁷ S/cm at room temperature and E_a = 0.49 eV.     

Preparation, dielectric and ferroelectric properties of Pb5Ge3O11 and Pb5Ge2.85Si0.15O11 thin films fabricated by sol-gel process

Lead germanate-silicate (Pb₅Ge_2.85Si_0.15O₁₁) ferroelectric thin films were successfully fabricated on Pt/Ti/SiO₂/(100)Si substrates by the sol-gel process. The thin films were fabricated by multi-coating at preheating temperatures of 350 and 450 °C. After annealing the thin films at 600 °C, the films exhibited c-axis preferred orientation. The degree of c-axis preferred orientation of the thin films preheated at 350 °C was higher than that of films preheated at 450 °C. Grain growth was influenced by the annealing time. The thin films exhibited a well-saturated ferroelectric P-E hysteresis loop when preheated at 350 °C and annealed at 600 °C for 1.5 h. The values of the remanent polarization (Pr) and the coercive field (Ec) were approximately 2.1 μC/cm² and 100 kV/cm, respectively.     

Sol-gel preparation and properties of TiO2-P2O5 bulk glasses

Monolithic transparent and colorless, or Ti³⁺-free TiO₂-P₂O₅ glasses containing very large amounts of TiO₂ (up to 93 mol%) were successfully prepared by heat-treating the xerogels, which were made from titanium tetraisopropoxide and triethyl phosphate, through the sol-gel reaction. The density and refractive index n_632.8 nm of the sol-gel-derived glasses were higher than the melt-derived glasses of the corresponding compositions. The glasses of TiO₂ content of larger than 80 mol% seemed somewhat porous, but n_632.8 nm of these glasses was very high as 2.2-2.3. Higher density and higher n_632.8 nm than the melt-derived glasses were considered to be due to more abundance of six-fold coordinated Ti⁴⁺ ions.     

Effect of Al2O3 concentration on zirconolite (Ca(Zr,Hf)Ti2O7) crystallization in (TiO2,ZrO2,HfO2)-rich SiO2–Al2O3–CaO–Na2O glasses

Glass-ceramic matrices containing zirconolite (nominally Ca(Zr,Hf)Ti₂O₇) crystals in their bulk that would incorporate high proportions of minor actinides (Np, Am, Cm) or plutonium could be envisaged for their immobilization. Zirconolite-based glass-ceramics can be prepared by controlled crystallization of zirconolite in glasses belonging to SiO₂–Al₂O₃–CaO–Na₂O–TiO₂–ZrO₂–HfO₂ system. In this study, neodymium was used as trivalent actinides surrogate. Increasing Al₂O₃ concentration in glass composition had a strong effect on the nucleation rate I _z of zirconolite crystals in the bulk, on the amount of neodymium incorporated in zirconolite phase and on the crystal growth rate of silicate phases (titanite + anorthite) from glass surface. These results could be explained by the existence of competition—in favor of aluminum—between Al³⁺ and (Ti⁴⁺, Zr⁴⁺, Hf⁴⁺) ions for their association with charge compensators cations to facilitate their incorporation in the glassy network. Differential thermal analysis (DTA) was used to study exothermal effects associated with bulk and surface crystallization. ²⁷Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra showed that aluminum enters glasses network predominantly in 4-fold coordination. Neodymium optical absorption and fluorescence spectroscopies showed that the Al₂O₃ concentration changes performed in this study had not significant effect on Nd³⁺ ions environment in glasses.     

Piezoelectric properties of Pb5Ge3O11 bonded PZT composites

Pb₅Ge₃O₁₁ was used to form dense piezoelectric composites with PZT at temperatures below 1000°C. The composite material demonstrated that the ferroelectric component may be stabilized against depoling by an insulating grain boundary phase. Composites prepared using 30% Pb₅Ge₃O₁₁ almost fully stabilized the polarization against reverse field of 40 kv/cm, with d₃₃ = 65 × 10^?12 m/v and k = 470.     

X-ray diffraction studies of glasses in the TeO2V2O5 system

The short-range order in glasses of the TeO₂V₂O₅ system is studied with the aid of X-ray diffraction. It is found that the main structural units in most of the glasses are VO₅- and TeO₃-groups. The assumption is made that their structures gradually change; sheet complexes are formed close to V₂O₅; chains - around 2TeO₂V₂O₅, and a tridimensional aperiodic network in glasses from TeO₂.     

Preparation and characterization of dense sodium superionic conducting Na5YSi4O12 (NYS)

Na₅YSi₄O₁₂ has been prepared from spray-frozen/freeze-dried precursor powders calcined at 620°C for three hours. Sintering at 1140°C for 30 minutes gave a ceramic of 97.7% theoretical density. The material was single phase NYS with a 300°C resistivity of 6.5 Ωcm, an activation energy for Na⁺ ion conduction of 20.1 kJ/mol, a flexural strength of 75 MPa, a duplex fine grain structure of (0.1–3μm) and a constant linear thermal expansion coefficient (25–470°C) of 13.1 × 10^?6/°C ±5%. The properties of the NYS ceramics are especially sensitive to small soda deficiencies.     

Sol-gel synthesis and structural characterisation of binary TiO2-P2O5 glasses

An improved method for the sol-gel synthesis of binary (TiO₂)_0.5(P₂O₅)_0.5 glasses has been developed. Elemental analysis of the products showed that the loss of phosphorous upon drying and heat treatment is low. The structure of the heat-treated glasses was studied using neutron diffraction and high-energy X-ray diffraction, analysis of which revealed a structure consisting of PO₄ tetrahedra and TiO₆ octahedra sharing corners in a three-dimensional amorphous network. The Reverse Monte Carlo method was used to produce a structural model which illustrated that the structure of the glass is, at the near-neighbour level, closely analogous to the superstructure of crystalline TiP₂O₇. No significant atomic-scale structural differences were observed between glasses prepared by acid- or base-catalysed sol-gel reactions.     

MBi2Ge2O8 molten glasses: A new host environment for the growth of garnets,spinels, and related phases

The molar volumes of MO/Bi₂O₃/2 GeO₂ glasses ($\text{M= Zn, Cd, Ca, Sr, Pb, \& Ba}$) vary directly with cation volume and inversely with cation field strength. Small needles of ZnBi₂Ge₂O₈ (up to 0.75 mm) & SrBi₂Ge₂O₈ (up to 0.20 mm) can form during slow cooling of the parent melts. Al₂O₃ (or Ga₂O₃) additions expand these glasses by introducing AlO₄ Tetrahedra. Precipitation of spinel-like arrays from such molten polyhedral jumbles requires more Al₂O₃ (or Ga₂O₃) with larger cations for solubility reasons. This is confirmed by the nuclei concentrations.     

Synthese et conductivite des verres du systeme B2O3Na2ONa2SO4

New glasses with sodium ion carriers have been obtained in the B₂O₃Na₂ONa₂SO₄ system. Their conductivities have been measured vs temperature and composition. Raman spectroscopy brings information about the behavior of sodium sulfate in the vitreous matrix.