Physical properties of lead iron phosphate glasses containing Cr2O3

The influence of Cr₂O₃ on glass forming characteristics and physical properties of PbO-Fe₂O₃-P₂O₅ glasses has been investigated by Raman and Mössbauer spectroscopies, X-ray diffraction analysis (XRD), Differential Thermal Analysis (DTA), Scanning Electron Microscopy (SEM) and impedance spectroscopy. Glasses of the general composition xCr₂O₃-(28.3-x)PbO-28.7Fe₂O₃-43.0P₂O₅, 0 ≤ × ≤ 10, (mol%) were prepared by conventional melt-quenching technique. The compositions containing up to 4 mol% Cr₂O₃ formed fully amorphous samples and their Raman spectra show systematic increase in the fraction of orthophosphate Q⁰ units with increasing Cr₂O₃ content and O/P ratio.On the other hand, compositions containing 8 and 10 mol% Cr₂O₃ partially crystallized during cooling and annealing to Fe₇(PO₄)₆, Fe₂Pb₃(PO₄)₄ and Cr₂Pb₃(PO₄)₄. A high tendency for crystallization of these melts is related to the high O/P (> 4) and Fe²⁺/Fe_tot (≈ 0.60) ratios.Electrical conductivity of xCr₂O₃-(28.3-x)PbO-28.7Fe₂O₃-43.0P₂O₅, 0 ≤ × ≤ 10, (mol%) compositions is independent of Cr₂O₃ and controlled entirely by the polaron transfer between Fe²⁺ and Fe³⁺ ions.     

Characterization of iron phosphate glasses prepared by microwave heating

Phosphate glasses have been prepared by melting batch materials in electric furnaces, induction furnaces, and in microwave ovens. In the present work mixtures of (NH₄)₂HPO₄ and Fe₃O₄ or Fe₂O₃ were exposed to microwave energy, heated to 1200 °C, and cast to produce iron phosphate glasses. Glasses were also produced in electric furnaces for comparison. The material was analyzed by X-ray diffraction, Mössbauer spectroscopy, and differential thermal analysis. For magnetite-based glasses produced in an electric furnace, the Fe²⁺/(Fe²⁺ + Fe³⁺) ratio is compatible with the value in the batch material. The Fe²⁺/(Fe²⁺ + Fe³⁺) ratio is higher for glasses produced in a microwave oven. Glasses with nominal composition 55Fe₃O₄–45P₂O₅ (mol%) produced in an electric furnace present an arranged magnetic phase with hyperfine field that could be associated to hematite (estimated to be 21%). All the glasses submitted to heat treatments for crystallization present the following crystalline phases: FePO₄, Fe₃(PO₄)₂, Fe(PO₃)₃, Fe(PO₃)₂ and Fe₇(PO₄)₆. The amount of these phases depends on the glass composition, and glass preparation procedure. Microwave heating allows to reach melting temperatures at high heating rates, making the procedure easy and economical, but care should be taken concerning the final Fe²⁺/(Fe²⁺ + Fe³⁺) ratio.     

X-ray photoelectron spectroscopy (XPS) and magnetic susceptibility studies of vanadium phosphate glasses

Vanadium phosphate glasses with the nominal chemical composition [(V₂O₅)_x(P₂O₅)_1?x], where x = 0.30, 0.40, 0.50, and 0.60, have been prepared and investigated by X-ray photoelectron spectroscopy (XPS) and magnetization measurements. Asymmetries found in the O 1s, P 2p, and V 2p core level spectra indicate the presence of primarily P–O–P, P–O–V, and V–O–V structural bonds, a spin–orbit splitting of the P 2p core level, and more than one valence state of V ions being present. The magnetic susceptibility data for these glasses follow a Curie–Weiss behavior which also indicates the presence of some V ions existing in a magnetic state, i.e., a valence state other than that of the non-magnetic V⁵⁺. From qualitative comparisons of the abundance of the bridging oxygen or P–O–P sites as determined from the areas under the various O 1s peaks with the abundances of differing phosphate structural groups associated with the presence of different valence states of the vanadium ions, a glass structure model consisting of a mixture of vanadate phosphate phases is proposed for these glass samples. These include V₂O₅, VOPO₄, (VO)₂P₂O₇, VO(PO₃), and V(PO₃)₃ with the abundance of orthophosphate (PO₄)^3? units increasing with increasing vanadium content.     

Crystal structure of Rb<Subscript>2</Subscript>[Ti(VO<Subscript>2</Subscript>)<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>]

The crystal structure of the new compound Rb₂[Ti(VO₂)₃(PO₄)₃] obtained by hydrothermal synthesis in the RbCl-TiPO₄-V₂O₅-B₂O₃-H₂O system (a = 13.604(2) Å, c = 9.386(2) Å, sp. gr. P6cc, Z = 4, ρ_calcd = 3.32 g/cm³) has been studied by X-ray diffraction (Xcalibur-S-CCD diffractometer, R = 0.038). It is shown that the isotypism of Rb₂[Ti(VO₂)₃(PO₄)₃] and Cs₂[Ti(VO₂)₃(PO₄)₃] is caused by the flexibility of a mixed anionic framework composed of phosphorus tetrahedra, vanadium five-vertex polyhedra, and titanium octahedra (bases of the crystal structures of these compounds). The topological correlations between the structures of titanium-vanadyl phosphates and benitoite and beryl silicates are analyzed.     

Effects in B–doped KDP crystals irradiated with neutrons of large spectra energy

The results obtained for the r₆₃ electro‐optic coefficient of B‐doped and undoped KDP (KH₂PO₄) crystals irradiated with neutrons (including thermalized neutrons) produced by scattering of 30 Mev cyclotron protons on a target of Ta²⁰¹, are presented and compared to those obtained for non‐irradiated doped and undoped crystals. The B‐doped (H₃BO₃, Na₂B₄O₇ and Li₂B₄O₇) crystals were obtained by the conventional growth method by temperature decrease with 1 wt % dopant concentration in solution. The thermal neutron flux was around ϕ = 1. 10¹⁰ n/cm² s. Pulses of ∼15 μs long, in damped oscillatory mode (V= 8 kV, τ=1.95 μs) were used for the electro‐optic measurements. A Pockels cell, a photomultiplier, a He‐Ne laser (λ=632.8 nm, 5 mW, linearly polarized) and a Tk 720 A oscilloscope complete the experimental setup. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal structure of <Emphasis Type="Italic">L</Emphasis>-serine phosphate

The crystal structure of L-serine phosphate (C₃O₃NH₇ · H₃PO₄) is determined by single-crystal X-ray diffraction. The unit cell parameters are as follows: a = 9.134(5) Å, b = 9.489(5) Å, c = 4.615(5) Å, γ = 99.54(5)°, space group P2₁, and Z = 2. The amino group of serine is protonated by a hydrogen atom of the phosphoric acid. The H₂PO ₄ ^1? ions are linked by hydrogen bonds into infinite ribbons aligned along the twofold screw axes. The ribbons form layers alternating with layers of serine molecules, which are directly linked by hydrogen bonds.     

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?.     

Electrical properties of phosphate glasses

The electrical properties of glasses in the Na₂OP₂O₅, Ag₂OP₂O₅ and (1?x)Na₂OxAg₂OP₂O₅ systems have been measured over a range of temperature and composition.The properties of the Na₂OP₂O₅ and Ag₂OP₂O₅ glasses have been compared within the phosphate system as well as with silicate glasses. The silver-containing glasses show higher conductivity and lower temperature coefficients when compared with the sodium-containing glasses. A maximum in the room temperature resistivity of the (1?x)Na₂O?xAg₂O?P₂O₅ system was found around the mole ratio of 0.16:0.84 Ag₂O:Na₂O, indicating a mixed-alkali effect. A similar effect was seen in the tan δ, but not in the T_g-against-composition plots. A linear relationship was noted for the tan δ-versus-log₁₀ (resistivity) plot, as has been seen in other glass-forming systems.     

Crystal structures of two modifications of sodium pentahydrogendiphosphate NaH5(PO4)2

Two crystalline modifications of NaH₅(PO₄)₂ are obtained by the reaction of Na₂CO₃ with an excess of orthophosphoric acid. The crystal structures of α-and β-NaH₅(PO₄)₂ are determined by X-ray diffraction analysis. The crystal data are a = 8.484(4) Å, b = 7.842(3) Å, c = 10.353(4) Å, β = 90.50(3)°, V = 689.3(3) ų, space group P2₁/c, Z = 4, and R ₁ = 0.0250 for the α modification and a = 7.127(2) Å, b = 13.346(4) Å, c = 7.177(2) Å, β = 95.5(2)°, V = 679.5(3) ų, space group P2₁/c, Z = 4, and R ₁ = 0.0232 for the β modification. Based of the hydrogen-bond system, the formulas of the α and β modifications can be represented as Na(H₂PO₄)(H₃PO₄) and Na[H(H₂PO₄)₂], respectively. They correspond to the stable and metastable forms of the compound.     

Density-structure correlations in Na2O-CaO-P2O5-SiO2 bioactive glasses

Relations for Na₂O-CaO-SiO₂ glasses have been developed to calculate the density of Na₂O-CaO-P₂O₅-SiO₂ bioactive glasses. The calculation makes use of NMR results of O’Donnell et al. indicating that P₂O₅ forms a separate phase, containing Na₃PO₄ and Ca₃(PO₄)₂, in the investigated glasses. The volume of the silicate units is the same as that found in Na₂O-CaO-SiO₂, Na₂O-SiO₂, and CaO-SiO₂ glasses. Similarly, the volume of PO₄ units is equivalent to that in Na₃PO₄ and Ca₃(PO₄)₂. Calculated densities are consistent with the experimental data.     

Identification of a new family of diphosphate compounds, AI2BII3(P2O7)2: Structures of Ag2Co3(P2O7)2, Ag2Mn3(P2O7)2, and Na2Cd3(P2O7)2

Syntheses and single-crystal X-ray structural results are reported for three new mixed diphosphates of the family A^I ₂B^II ₃(P₂O₇)₂; Ag₂Co₃(P₂O₇)₂ (I), Ag₂Mn₃(P₂O₇)₂ (II), and Na₂Cd₃(P₂O₇)₂ (III). All crystallize in the triclinic system, space group P1 bar: (I) a = 5.351(4), b = 6.375(4), c = 16.532(4) Å, = 80.83(6) = 81.45(4), = 72.87(5)°, V = 528.9(6) ų, Z = 2, D _calc = 4.649 mg/m³, R/Rw = 0.0428/0.0548 for 3949 obs. reflns; (II) a = 5.432(7), b = 6.619(6), c = 16.51(3) Å, = 80.78(8) = 82.43(9), = 72.82(7)°, V = 557.7(13) ų, Z = 2, D _calc = 4.338 mg/m³, R/Rw = 0.0679/0.1303 for 2100 obs. reflns and (III) a = 5.67(3), b = 7.08(4), c = 7.90(4) Å, = 77.0(2), = 82.5(2), = 67.8(2)°, V = 286(3) ų, Z = 2, D _calc = 4.249 mg/m³, R/Rw = 0.0307/0.0342 for 1945 obs. reflns. (I) and (II) are isostructural but (III) is of a different type. All three structures are characterized by layers of P₂O₇ groups alternating with layers of mixed metal atoms. Differences are seen in the conglomerate bonding patterns of B atoms and in the irregular geometry of Ag in (I) and (II) compared to the octahedral bonding seen for Na in (III). The differences in structure may be understood in terms of the ratios of the ionic radii of A and B atoms.     

IR fundamental spectra and structure of pyrophosphate glasses along the 2ZnO·P2O5–2Me2O·P2O5 join (Me being Na and Li)

The IR reflection spectra of mixed zinc alkali pyrophosphate glasses in the broad frequency ranges are reported and the quantitative treatment of these with a version of the dispersion analysis method was conducted based on the specific analytical model of the complex dielectric constant of glasses. Numerical data on the optical constants, band frequencies, and band intensities are calculated. Results obtained are interpreted in terms of vibrations of the (PO₃)²⁻ and (PO₂)⁻ terminal groups, (PO₄)³⁻ anion, and P–O–P bridge. The presence of all these groups in the structures of glasses under study is confirmed and the formation of the (P₃O₉)³⁻ ring metaphosphate anion rather than the chain polymeric phosphate anions is suggested. The gradual decrease in the width of the anion distribution toward the pyrophoshate anion with the Me₂O for ZnO substitution is also confirmed. It is shown that this decrease determines the IR spectrum variations observed in the 0 to about 27 mol% Na₂O composition range. The amounts of the (PO₄)³⁻ and (P₃O₉)³⁻ anions are shown to become negligible in the structures of glasses with Na₂O content greater than 30 mol%, and the IR spectrum variations observed in the 27–45 mol% Na₂O composition range are shown to be mostly due to the intensity redistribution from the low-frequency component of the asymmetric stretch of the (PO₃)²⁻ terminal group to the high-frequency component of the same stretch.     

Doping of a high calcium oxide metaphosphate glass with titanium dioxide

This study investigates the effect of doping a high calcium oxide containing metaphosphate glass series (CaO)₄₀(Na₂O)₁₀(P₂O₅)₅₀ with TiO₂ (1, 3, and 5 mol%). TiO₂ incorporation increased the density and glass transition temperature while reduced the degradation rate (5 mol% in particular) by twofold compared with (CaO)₃₀ system reported previously. This has been confirmed by ion release and the minimal pH changes. TiP₂O₇, NaCa(PO₃)₃ and CaP₂O₆ phases were detected for all TiO₂-containing ceramics. XPS showed that the surface is composed of Ca, P, and Ti. Ti was recognized mainly as TiO₂, but its total amount was lower than theoretical values. ³¹P magic angle spinning (MAS) NMR showed a downfield shift of the ³¹P lineshape with increasing TiO₂, interpreted as an effect of the titanium cation rather than an increase in the phosphate network connectivity. FTIR showed that incorporation of TiO₂ increased the strength of the phosphate chains, and the O/P ratio while introducing more Q¹ units into the structure at the expense of the Q² units. There were no differences, however, in surface topography roughness and free energies between these glasses. These results suggested that TiO₂ and CaO were acting synergistically in producing glasses with controllable bulk and structural properties.     

Interaction in the molten system Rb2O‐P2O5‐TiO2‐NiO. Crystal structure of the langbeinite‐related Rb2Ni0.5Ti1.5(PO4)3

The interaction in the molten system Rb₂O‐P₂O₅‐TiO₂‐NiO was investigated at different molar ratios Rb/P = 0.5‐1.3, fixed Ti/P = 0.15, Ti/Ni = 1.0 at temperature range 1073–953 K. The conditions of formation of complex phosphates RbTi₂(PO₄)₃, Rb₂Ni_0.5Ti_1.5(PO₄)₃ and RbNiPO₄ have been determined. The new phosphate Rb₂Ni_0.5Ti_1.5(PO₄)₃ (space group P2₁3, a = 9.9386(2) Å) has been obtained and investigated by the single crystal X‐ray diffraction and FTIR‐spectroscopy. It has langbeinite‐like structure, that is built up from mixed (Ni/Ti)O₆‐octahedra and РО₄‐tetrahedra. Rubidium atoms are located in closed cavities of 3D‐framework.     

Polymorphism of the borophosphate anion in K(Fe,Al)[BP<Subscript>2</Subscript>O<Subscript>8</Subscript>(OH)] and Rb(Al,Fe)[BP<Subscript>2</Subscript>O<Subscript>8</Subscript>(OH)] crystal structures

The crystal structure of two borophosphates, Rb(Al,Fe)[BP₂O₈(OH)] (a = 9.381(6), b = 8.398(5), c = 9.579(6) Å, β = 102.605(10)°, sp. gr. P2₁/c) and K(Fe,Al)[BP₂O₈(OH)] (a = 5.139(2), b = 8.065(4), c = 8.290(4)Å, α = 86.841(8)°, β = 80.346(8)°, γ = 86.622(8)°, sp. gr. P \(\bar 1\)), obtained by hydrothermal synthesis in the AlCl₃: FeCl₃: K₃PO₄(Rb₃PO₄): B₂O₃: H₂O system has been established using X-ray diffraction (Bruker Smart diffractometer, T = 100 K). Hydrogen atoms are located and their coordinates and thermal parameters are refined. It is shown that the polymorphism of the [BP₂O₈(OH)]^4? borophosphate anion has a morphotropic nature and is related to the substitutions both in the cationic part of the structure and in the octahedral position of the anionic mixed framework. The synthesis of new isotypic triclinic compounds under hydrothermal conditions is predicted.     

The double phosphates MIMIIPO4 (MI – Na,K; MII – Mg,Mn, Co,Ni, Zn) – synthesis from chloride melts and characterization

The particularities of the chemical interaction in systems M^IPO₃‐M^IIO(or Mn₂O₃)‐M^ICl (M^I – Na, K; M^II – Mg, Co, Ni, Zn) have been investigated at the temperature 1073 K and molar ratios P/M^x = 1 or 2 and M^ICl/(M^IPO₃ + M^IIO(or Mn₂O₃)) = 30. The conditions of formation of complex phosphates M^ІM^IIPO₄ and Na₄Ni₃(PO₄)₂P₂O₇ have been found. Influences of the nature of alkali and bivalent metals on the products composition were discussed. The advantages of chloride melts using (synthesis time reduction and temperature reducing) for preparing of complex phosphates were shown. The synthesized compounds have been characterized using the powder X‐ray diffraction, Fourier transform infrared and diffuse reflectance spectroscopies.     

Crystal structure of <Emphasis Type="Italic">L</Emphasis>-alanine phosphate

The crystal structure of L-alanine phosphate (C₃O₂NH₇ · H₃PO₄) is determined by the single-crystal diffraction technique; a = 11.918(1) Å, b = 9.117(1) Å, c = 7.285(1) Å, γ = 104.7(1)°, space group P2₁, and Z = 4. The amino group of the alanine is protonated by the hydrogen atom of the phosphoric acid. Pairs of H₂PO ₄ ^? hydrogen-bonded ions are packed into layers alternating with layers of alanine molecules in the crystal. No hydrogen bonds are formed immediately between the alanine molecules.     

Structural study of PbO-MoO3-P2O5 glasses by Raman and NMR spectroscopy

Glasses in the ternary system PbO-MoO₃-P₂O₅ were prepared in three compositional series (100 − x)[0.5PbO-0.5P₂O₅]-xMoO₃ (A), 50PbO-yMoO₃-(50 − y)P₂O₅ (B) and (50 − z)PbO-xMoO₃-50P₂O₅ (C) and their structure was studied by Raman and ³¹P NMR spectroscopies. In the compositional series (100 − x)[0.5PbO-0.5P₂O₅]-xMoO₃ homogeneous glasses were prepared in the concentration region of 0-70 mol% MoO₃. Their glass transition temperature increases with increasing MoO₃ content having a maximum at x = 50 mol% MoO₃. ³¹P MAS NMR spectra reveal that in the glass series (A) the incorporation of MoO₃ results in the shortening of phosphate chains and gradual transformation Q² units into Q² and Q⁰ units, prevailing in glasses with a high MoO₃ content. Octahedral structural units MoO₆ dominate in most glass compositions and they are present also in the structure of Pb(MoO₂)₂(PO₄)₂ compound corresponding to the glass composition 50Pb(PO₃)₂-50MoO₃. The analysis of Raman spectra of glasses of the (B) series with a high MoO₃ content showed the transformation of octahedral MoO₆ units into tetrahedral MoO₄ units.     

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.     

Glasses and glass-ceramics in the oxyfluoride ternary system Pb(PO3)2-WO3-PbF2

Glasses were prepared by the melt-quenching method in the ternary system Pb(PO₃)₂-WO₃-PbF₂ and doped with Er³⁺ in order to prepare luminescent transparent glass-ceramics. This work focused on thermal and structural characterization of tungsten lead-phosphate glasses and crystallization study for preparing transparent glass-ceramics. Thermal properties such as thermal stability and crystallization behavior upon heating were investigated by DSC in function of PbF₂ content. For low PbF₂ concentrations, only one crystallization peak due to Pb₃(PO₄)₂ is observed whereas samples containing more than 15% of PbF₂ present another exothermic event at lower temperatures related with precipitation of PbF₂, Pb₂P₂O₇ and Pb₂OF₂. Structural investigations by Raman spectroscopy suggest that PbF₂ modifies the tungsten-phosphate network through the formation of P―F and P―O―Pb bonds but the average network connectivity remains almost constant. A crystallization study has been performed by DSC to investigate the dominant crystallization mechanisms in these glasses and it has been established that Pb₃(PO₄)₂ is nucleated on the surface whereas PbF₂, Pb₂P₂O₇ and Pb₂OF₂ crystallize dominantly from the glassy bulk. Transparent glass-ceramics containing nanosized PbF₂ crystallites were also prepared by suitable heat-treatment on the glass sample containing 20% of PbF₂ and Raman microscopy of these glass-ceramics supports the crystallization mechanisms determined by DSC.