Depolymerization of GeO2 and GeO2 · Sb2O3 glasses by Bi2O3

Glasses that contain at least 60 mol% GeO₂ were prepared in the Bi₂O₃ · GeO₂ and Bi₂O₃ · Sb₂O₃ · GeO₂ systems. Their densities, refractive indices, and infra-red spectra were recorded. Negative molar volume deviations and positive refraction deviations occur for all of the binary glasses. These create deviations for the 60 to 80 mol % GeO₂ ternary glasses that indicate non-ideal mixing when Sb³⁺ substitutes for Bi³⁺. Also, the main Ge-O stretching vibration shifts to as low as 695 cm^?1 for the Bi₂O₃-rich binary and ternary glasses. All of these findings show that Bi₂O₃ more effectively depolymerizes GeO₂ than does Sb₂O₃. The probable structural reasons for this behaviour are discussed.     

From eulytine to the ambidextrous crystal via the amorphous route: Lead & calcium bismuth germanate glasses

Lead and calcium bismuth germanate glasses containing at least 40 mole% GeO₂ were prepared. Physical properties and infrared spectra suggest that for glasses close to the PbO · Bi₂O₃ · 2GeO₂ composition: (a) packing efficiency is directly dependent upon cation size, (b) refraction is dependent upon cation type, (c) calcium can substitute for lead in nearly ideal fashion, (d) the open eulytine arrangement of a 2Bi₂O₃ · 3GeO₂ glass has collapsed, and (e) Ge₂O₇ dimers and small chains of GeO₄ tetrahedra (characteristic of Pb₅Ge₃O₁₁ and PbGeO₃ respectively) may persist. These findings offer a rationale for the limited yields of Ca₃Al₂Ge₃O₁₂ garnets obtained from such melts at high temperatures. A noncubic crystalline phase that may be Pb₃Bi₂Ge₃O₁₂ is also reported.     

Infra-red detection of depolymerization in Tl2O-GeO2-SiO2 glasses

Three series of glasses containing 15, 26, and 35 mol % Tl₂O were prepared in the Tl₂O-GeO₂-SiO₂ system and their infra-red spectra, densities, and refractive indices determined. Refraction decreases as SiO₂ substitutes for GeO₂ and is additive with respect to the two binary series, except for slight positive deviations with the low SiO₂content 35 mol % Tl₂O glasses. All glass series exhibit small negative molar volume deviations from additivity at low SiO₂ contents and small positive deviations from additivity at higher SiO₂ contents. The strong compositional dependence of the main infra-red stretching frequency values (1100 cm^–1 for SiO₂ and 875 cm^–1for GeO₂) are shown to be relatively sensitive indicators of changes in the polymeric makeup of these ternary oxide glasses. Loosening and/or depolymerization of either pure or damaged MO₄ networks is accompanied byv _Si-O and/orv _Ge-O shifts to smaller frequencies. The frequency changes that accompany the progressive replacement of GeO₂ by SiO₂ suggest that (a) SiO₄ tetrahedra initially replace GeO₄ tetrahedra, (b) GeO₆ octahedra subsequently transform to GeO₄ tetrahedra, and (c) GeO₄ tetrahedra finally take part in repair of damaged SiO₄ networks. Use of a previously developed infra-red isofrequency contour technique revealed similar ternary trends for the two vibrational modes of interest. This emphasizes the ability of such contour trends to reflect the overall degree of network crosslinking present in ternary oxide glasses.     

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.     

Dynamics of energy absorption versus crystallization in Bi4Ge3O12 (BGO) amorphous materials

Theoretical and experimental determinations show that the intrinsic luminescence of BGO materials is strongly influenced by GeO₄⁻ tetrahedra around Bi³⁺ ions. Besides Bi³⁺ transitions, the excitonic spectra mask the BGO bandgap. Theoretical computations give the bandgap at 5.19 eV compared with the experimental one at 5.17 eV in BGO crystals and a significant decrease at 3.26 eV in the amorphous materials. This is due to the high disordering of the GeO₄⁻ tetrahedral which also reduces the refractive index of the amorphous materials. Formation of excitonic states and their overlap with the Bi³⁺ transitions suggests that the energy absorption takes place via the p-electrons of the O₂⁻ ions and is then transferred to the Bi³⁺p-electrons (excited states) close to the conduction band. Light emission appears after de-excitation to the ground state.     

Coordination of Ti4+ and Ge4+ ions in Na2O-TiO2-GeO2 glasses—an approach based on crystallization behaviour,X-ray absorption and IR spectroscopy

The coordination state of Ti⁴⁺ and Ge⁴⁺ ions in Na₂O-TiO₂-GeO₂ glasses has been investigated. Upon crystallization of the glasses, the thermodynamically metastable hexagonal GeO₂ crystals containing 4-fold coordinated Ti⁴⁺ ions together with stable Na₄Ge₉O₂₀ crystals containing 6-fold coordinated Ti⁴⁺ ions were precipitated. The distribution of Ti⁴⁺ ions between these two crystalline phases is a reflection of the coordination state of Ti⁴⁺ ions in the starting glass. The majority of Ti⁴⁺ ions are in 6-fold coordination at a small TiO₂/Na₂O ratio and they are contained in Na₂Ge₉O₂₀, while the majority of Ti⁴⁺ ions are in 4-fold coordination at a large TiO₂/Na₂O ratio and they are contained in GeO₂ crystals. Concentrations of 4- and 6-fold coordinated Ti⁴⁺ ions have been confirmed to be similar to that in Na₂O-TiO₂-SiO₂ glasses as measured by the X-ray absorption spectrometry of Ti⁴⁺ ions. The coordination state of Ge⁴⁺ ions in the glasses have been examined by infrared (IR) spectrometry. It is found that in Na₂O-TiO₂-GeO₂ glasses Ge⁴⁺ ions have 6-fold coordination preferentially, while Ti⁴⁺ ions have 4-fold coordination except at small contents of TiO₂, indicating that the addition of TiO₂ to Na₂O-GeO₂ glasses leads to the replacement of 4-fold coordinated Ge⁴⁺ ions by 4-fold coordinated Ti⁴⁺ ions.     

Synthesis of a bismuth germanium oxide source material for Bi4Ge3O12 crystal growth

A technique has been developed for the preparation of a modified source material for the crystal growth of bismuth orthogermanate, Bi₄Ge₃O₁₂ (BGO). It includes dispersion of molten bismuth through mixing with germanium oxide (GeO₂) powder in a rotating reactor, followed by oxidation with oxygen. The source material thus prepared contains, in addition to bismuth and germanium oxides, considerable proportions of germanates (Bi₂GeO₅, Bi₄Ge₃O₁₂, and Bi₁₂GeO₂₀), which improve the reactivity of the components of the source material during homogenization before the crystal growth process. After sintering at 880°C, the density of the modified source material (3.9 g/cm³) is a factor of 1.5 higher than that of a source material prepared from Bi₂O₃ and GeO₂ powders. BGO crystals grown using the synthesized source material possess good scintillation characteristics.     

Synthesis,structural, thermal and optical properties of TeO2–Bi2O3–GeO2–Li2O glasses

In this study, synthesis and characterization of novel quaternary tellurite glass system TeO₂–Bi₂O₃–GeO₂–Li₂O is presented. The compositions include TeO₂ and GeO₂ as glass formers while different proportion of Bi₂O₃ and Li₂O act as network modifiers. Differential thermal analysis, X-ray diffraction, scanning electron microscopy energy dispersive X-ray spectroscopy, laser ablation inductively coupled plasma mass spectrometry, UV–Vis and Raman spectroscopy are applied to study the structural, thermal and optical properties of the studied glasses. Obtained glasses possess a relatively low glass transition temperature (around 300 °C) if compared to other tellurite glasses, show good thermal transparency in the visible and near infra-red (from 2.4 to 0.4 μm) and can double the frequency of laser light from its original wavelength of 1064 nm to its second-harmonic at 532 nm (i.e. second harmonic generation).     

Luminescent properties of Eu, Tb or Bi activated yttrium germanates

Preliminary studies were conducted on Eu³⁺, Tb³⁺ or Bi³⁺ doped Y₂Ge₂O₇, Y₂GeO₅ and Y₄GeO₈ phosphors. Both photoluminescence and cathodoluminescent properties of the materials were measured. Among these materials, the luminescent intensities of Y₂Ge₂O₇:Eu, Y₂GeO₅:Tb and Y₂Ge₂O₇:Bi are relatively high and the luminescent colors of them are red, green and blue, respectively. In order to improve the luminescent properties for field emission display applications, further optimization is necessary. In addition, X-ray powder diffraction results indicate that Y₄GeO₈ phase forms in an orthorhombic unit cell, the parameters of which are: a=1.4976(5) nm, b=0.9357(6) nm, c=0.5885(3) nm, V_cell=0.82467(2) nm³.     

Luminescence of 60B2O3-32CaF2-8Bi2O3 glasses codoped with chromium and neodymium

60B₂O₃-32CaF₂-8Bi₂O₃ glasses codoped with chromium and neodymium have been prepared for the first time, and their luminescence properties have been studied. The glasses have been shown to contain chromium in two oxidation states. We have obtained luminescence spectra of Cr³⁺ in octahedral coordination and Cr⁴⁺ in tetrahedral coordination. Energy transfer from Bi³⁺ to Nd³⁺ and Cr³⁺ has been demonstrated.     

Synthesis and structure of Bi2CaV2O9

A new compound in the Bi/Ca/V/O system has been found, and its structure determined from single crystal X-ray diffraction data. The new compound, Bi₂CaV₂O₉, is monoclinic with a=7.096(2), b=12.400(2), c=9.397(1) Å, β=107.19(2)°, and Z=4. The two crystallographically distinct VO₄ tetrahedra do not share corners. Thus, there is one oxygen which is not part of a VO₄ tetrahedron, and the structural formula may be written as Bi₂Ca(VO₄)₂O. Mixing of Bi³⁺ and Ca²⁺ occurs on three sites where coordination to oxygen is seven or eight.     

Flux growth of single magnetic sublattice antiferromagnetic garnets Ca3 Fe2 Ge3 O12 and Ca3 Mn2 Ge3 O12

Magnetic single crystals garnets Ca₃ X₂ Ge₃ O₁₂ with X = Mn³⁺ or Fe³⁺ containing Ca²⁺ and Ge⁴⁺ are of great interest due to the rise of an antifer-romagnetic order in one definite octahedral site. The optimal conditions for obtaining single magnetic-sublattice garnets of large size (1 cm in diameter) have been analyzed. Two groups of solvents have been tested: Bi₂ O₃ or PbO based flux. The best results were obtained with PbO flux and starting composition : % Moles 44 PbO 1b 35 GeO₂ 1b 15 CaO 1b 6 X₂ O₃.     

Phase Relations in the LiOH–ZrO2–GeO2–H2O System at 500°C and 0.1 GPa

The phases crystallizing in the LiOH–ZrO₂–GeO₂–H₂O system at 500°C and 0.1 GPa are Zr^[8]Ge^[4]O₄, Li₂Ge^[6]Ge₂ ^[4]O₆(OH)₂, Li₃HGe₄ ^[6]Ge₃ ^[4]O₁₆ · 4H₂O, and Li₂Ge^[4]O₃. These phases differ in the oxygen coordination of Ge. At a ZrO₂ : GeO₂ molar ratio of 1 : 1, increasing the LiOH concentration leads to the crystallization of a ZrO₂ + Li₂GeO₃ mixture, instead of ZrGeO₄. At ZrO₂ : GeO₂ ratios in the range 1 : 2 to 1 : 6, Li₂Ge^[6]Ge₂ ^[4]O₆(OH)₂ crystallizes together with ZrGeO₄. The formation of the structures of ZrGeO₄ and Li₂Ge^[6]Ge₂ ^[4]O₆(OH)₂ is discussed in terms of the matrix assembly of crystal structures from cyclic subpolyhedral structural units.     

Infra-red study of polymerisation in silver,thallium, and thallium aluminogermanate glasses

The infra-red spectra of silver germanate, thallium germanate, and thallium aluminogermanate glasses are presented for the 1100 cm^–1 to 400 cm^–1 region. The pseudo rare gas type Tl⁺ and Ag⁺ ions produce spectral shifts in binary germanate glasses that are similar to those reported for alkali ions. Differences for Tl⁺ may be due to its high atomic weight and polarising power. The infra-red spectral shifts observed for thallium aluminogermanate glasses are those expected if GeO₆ octahedra disappear while AlO₄ tetrahedra engage in network repair. A structurally sensitive technique for displaying ternary oxide glass infra-red spectra is outlined. This technique is capable of discerning different modes of network depolymerisation and polymerisation in ternary germanate and silicate glasses.     

The crystallization behaviour of bismuth germanate glasses

Glassy samples containing Bi₂O₃ and GeO₂ in different ratios were prepared and absorption measurements were performed on the samples in the ultraviolet region in order to determine the optical behaviour. Thermal analysis performed on the vitreous samples gave the glass transition temperature and the crystallization temperature. The main crystalline phases separated during the heat treatment were Bi₄Ge₃O₁₂ (BGO) and Bi₂GeO₅. The activation energy of the crystallization process of the sample BGO (1∶3) was measured using the isothermal method, and the value obtained was 47.1 kcal mol⁻¹; the reaction order was equal to 1.1.     

Fast Li+ ion conduction in Li2O–(Al2O3 Ga22O3)–TiO2–P2O5 glass–ceramics

Fast lithium ionic conducting glass-ceramics have been obtained by heat-treatment of glasses in the systems Li₂O–M₂O₃–TiO₂–P₂O₅ (M = Al and Ga). The glass–ceramics were mainly composed of LiTi₂(PO₄)₃ in which Ti⁴⁺ ions were partially replaced by M³⁺ ions. Considerable enhancement of the conductivity with the substitution of M³⁺ ions for Ti⁴⁺ ions was observed. The maximum conductivity obtained at room temperature was 1.3 × 10^–3 S cm^–1 for the aluminium system and 9 × 10^–4 S cm^–1 for the gallium system.     

Effect of some VA group modifiers on R2O3 (R = Sb,Bi)–ZnF2–GeO2 glasses doped with CuO by means of spectroscopic and dielectric investigations

Transparent glasses 40Sb₂O₃–20ZnF₂–(40 − x)GeO₂:xCuO, and 40Bi₂O₃–20ZnF₂–(40 − y)GeO₂:yCuO with x = 0, 0.6 and 0 ≤ y ≤ 1 wt% were prepared by melt quenching technique and were characterized by XRD and differential thermal analysis. Spectroscopic studies like optical absorption, FTIR, Raman, EPR and dielectric parameters (such as ?′, loss(tan δ), and σ_ac) were carried out to examine the modifier and dopant effect on zinc germanate glass network. Optical absorption and EPR data have revealed that the environment of Cu²⁺ ions is more ionic in bismuth series rather than antimony glasses. Reduced bismuth ions have been found in pure and at lower concentration of dopant in Bi₂O₃ mixed glasses, which are useful for IR amplifications. FTIR and Raman spectra have indicated the conversion of GeO₄ to GeO₆ structural units by forming cross linking bonds like Bi–O–Ge, Ge–O–Cu, etc., and open the glass network with integration of Bi₂O₃ and CuO doping. It is also confirmed by decreasing T_g and E_g values. The temperature dependence of dielectric parameters at different frequencies was interpreted in terms of structural changes in the glass network.     

Phase relations and crystallization of glass in the system PbO-GeO2

Thermal properties and chemical compositions of glasses suitable for crystallization of ferro-electric Pb₅Ge₃O₁₁ are described. The crystallization of lead germanate glass was investigated by DTA and X-ray diffraction. In the range from 62 to 62.5 of PbO in mole per cent, Pb₅Ge₃O₁₁ was obtained as a single phase after a heat treatment. In the chemical composition around 5PbO·3GeO₂ in the binary system of PbO-GeO₂, Pb₅Ge₃O₁₁ and two new phases of Pb₃Ge₂O₇ and Pb₃GeO₅ were found to exist. The crystal structure of Pb₃Ge₂O₇ had a hexagonal symmetry witha=10.16 Å andc=19.37 Å, and Pb₃GeO₅ was classified into orthorhombic system witha=4.85 Å,b=15.52 Å and c=11.77 Å.