Influence of MeF2 (Me = Mg, Ca, Sr, and Ba) on the electrical properties of glasses in the MeF2-Na2B4O7 system

Glasses in the MeF₂-Na₂B₄O₇ (Me = Mg, Ca, Sr, and Ba) system have been synthesized. It is shown that the glass formation is observed at a MeF₂ content of up to 40 mol %. The influence of the MeF₂ content on the electrical conductivity and the fluorine concentration in the glass bulk is examined. From the analysis of the concentration dependence of the electrical conductivity with due regard for the fluorine content, it is concluded that the glass structure is predominantly built up of the polar groupings Na⁺[BO_4/2]^-, Na⁺[F-BO_3/2], Me _1/2 ²⁺ [BO_4/2]⁻, Me _1/2 ²⁺ [F⁻BO_3/2], [MeF_4/2], and [MeF_6/3] and the BO_3/2 nonpolar structural-chemical units. The electricity transport is governed by the migration of sodium ions formed upon dissociation of the Na+[BO_4/2]^-and Na+[F^-BO_3/2] groupings. An increase in the MeF₂ content leads to a decrease in the total concentration of sodium ions, a decrease in the Na⁺[BO_4/2]^- concentration, and an increase in the Na⁺[F^-BO_3/2] concentration. Upon introduction of MeF₂ up to ∼20 mol %, the fluorine losses during the synthesis are caused by the dehydration of glass melt. An addition of 20–25 mol % MeF₂ brings about the saturation of the glass by the [F^-BO_3/2]-type structural units, so that the fluorine concentration reaches a saturation in the structures of calcium-, strontium-, and barium-containing glasses and increases in magnesium-containing glasses, owing to the formation of the [MgF+_6/3] groupings.     

Electrical Properties and the Structure of Glasses in the xNa2O–(1 – x)2PbO · B2O3 System

The temperature–concentration dependences of the electrical conductivity and the activation energy for electrical conduction of glasses in the Na₂O–B₂O₃ and Na₂O–2PbO · B₂O₃ systems are studied. The investigation into the nature of the electrical conduction in these glasses reveals that the contribution from the electronic component (10^–3%) of the conductivity is within the sensitivity of the Liang–Wagner technique. A considerable alkali conductivity is observed upon introduction of more than 12 mol % Na₂O. The true transport number of sodium _Na is as large as unity at [Na₂O] 15 mol %. It is shown that the observed temperature–concentration dependences of the electrical and transport properties are governed by the ratio between the concentrations of polar and nonpolar structural–chemical units of the Na⁺[BO_4/2]^–, Na⁺[O^–BO_2/2] Na⁺[O^–BO_2/2], Pb²⁺ _1/2[BO_4/2]^–, Pb²⁺ _1/2[O^–BO_2/2], and [BO_3/2] types.     

Effect of Fluorine Ion on the Electrical Properties of Glasses in the Na2O–P2O5 System

The temperature–concentration dependence of the electrical conductivity of glasses in the NaPO₃–NaF system has been investigated. The regularities revealed are interpreted from the standpoint of the structural microinhomogeneity of glasses, which is due to the formation of polar structural units of the Na⁺[O^–POO_2/2], Na₂ ⁺[O^– ₂POO_1/2], Na⁺[F^–POO_2/2], and Na⁺F^– types. It is shown that the concentration dependence of the electrical conductivity is governed by the ratio between the concentrations of these structural units.     

The evolution of the mold flux melt structure during the process of fluorine replacement by B2O3

This study presented the melt structure evolution of mold flux during the substitution of fluorine by B₂O₃, and a computational model for the degree of polymerization (DOP) for borosilicate structure was developed. The results showed that the reduction of fluorine content would promote the replacement of F in [SiF₆]-octahedral unit by the dissociative free oxygen ions (O²⁻), and release F⁻ ions into the melt to compensate the reduction of F⁻ ions. With the 2 mass% addition of B₂O₃, the original Si–O–Si bond would be disrupted, and connect with [BO₃]-trihedral to form boroxol ring structure containing [BO₂O⁻]-trihedral and [BO₃]-trihedral structural units. Then, the Si–O–B bond that [BO₃]-trihedral links [SiO₄]-tetrahedral in boroxol ring was destroyed with the further addition of B₂O₃, and then the [BO₃]-trihedral could link with the dissociative Q¹(Si) and Q⁰(Si) structural units to transform into [BO₄]-tetrahedral and form a borosilicate long chain. Finally, with 6 mass% addition of B₂O₃, the borosilicate chain would combine with simple borate and borosilicate structures, and a complex borosilicate structure containing boroxol ring with certain symmetry was formed ultimately. Besides, the calculated result of DOP suggested that the DOP of the melt structure improved during the process of fluorine replacement by B₂O₃.     

Factors influencing the structure of electrochemically prepared α-MnO2 and γ-MnO2 phases

The α- and γ-phases of MnO₂ prepared by electrolysis of MnSO₄ and M_xSO₄ (where M = Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ or Mg²⁺) in aqueous solutions at various pH and voltage E_v values under ambient conditions have been systematically studied. The structures of powdery MnO₂ produced are found to depend on the radius of the M^z+ counter cation in addition to the pH and E_v conditions. In order to achieve the α-phase for MnO₂ formation under neutral pH condition, the radius of counter cation must be equal to or greater than 1.41 Å, the size of the K⁺ cation. The relative concentration ratio of [MnO₄⁻]_transient/[Mn²⁺], which is related to the pH-E_v conditions, also affects the structure of MnO₂ produced with counter ions smaller than K⁺. For samples prepared in acidified solution with the counter ions of Li⁺, Na⁺ or Mg²⁺ at 2.2 V, the electrolysis products display the γ-MnO₂ phase while those prepared at 2.8 V electrolysis produce a mixture of γ-MnO₂ and α-MnO₂ phases. Single phase of α-MnO₂ is identified in the 5 V electrolysis products. Furthermore, the valence state of manganese was found to decrease as the applied voltage was reduced from 5.0 to 2.2 V. This implies that the lower [MnO₄⁻]_transient/[Mn²⁺] ratio or the less oxidative condition is responsible for the non-stoichiometric MnO₂ structure with oxygen deficiency.     

Electrical conductivity and the nature of charge carriers in glasses of the Tl<Subscript>2</Subscript>O-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The concentration dependence of the electrical conductivity of glasses in the Tl₂O-B₂O₃ system is studied. The nature of charge carriers in this system is experimentally investigated for the first time. It is demonstrated using the Hittorf, Tubandt, and Hebb-Liang-Wagner techniques and the Faraday law that neither Tl⁺ ions nor electrons are involved in the electricity transport. The verification of the Faraday law does not reveal the presence of thallium in the amalgam of the cathode or a change in the sample weight after electrolysis, to within the experimental error. This allows one to make the inference that protons can be charge carriers in glasses of the Tl₂O-B₂O₃ system. It is shown using extended X-ray absorption fine structure (EXAFS) spectroscopy that Tl³⁺ ions and thallium Tl⁰ reduced to the metallic state are absent in the structure of the glasses under investigation. This means that thallium in glasses of the Tl₂O-B₂O₃ system occurs only in the form of Tl⁺ ions. The analysis of the IR spectroscopic data leads to only a qualitative conclusion that the water content in the glasses insignificantly increases with an increase in the thallium oxide content. An increase in the electrical conductivity of glasses in the Tl₂O-B₂O₃ system with an increase in the thallium oxide content is explained by the increase in the number of protons formed upon dissociation of H⁺[BO_4/2]^? structural-chemical units, because their concentration increases with increasing Tl₂O content. In the structure of boron oxide, impurity hydrogen enters predominantly into the composition of H⁺[O_2/2BO^?] structural-chemical units, for which the dissociation energy is higher than that for the H⁺[BO_4/2]^? structural-chemical units. The increase in the concentration of H⁺[BO_4/2]^? structural-chemical units is accompanied by the increase in the number of dissociated protons, which are charge carriers in glasses of the Tl₂O-B₂O₃ system.     

Effect of Na2O on the High‐Temperature Thermal Conductivity and Structure of Na2O–B2O3 Melts

The effect of Na₂O and temperature on the thermal conductivity of the Na₂O–B₂O₃ binary system has been measured using the hot‐wire method to examine the relationship between the thermal conductivity and structure in high‐temperature melts. The thermal conductivity of the binary melt is measured from 1173 to 1473 K in the fully liquid state. The thermal conductivity slightly increases with Na₂O content up to 20 wt%. Above 20 wt% Na₂O, the thermal conductivity decreases with increasing Na₂O. The network structure of molten glass was analyzed using Fourier transform infrared (FTIR), Raman spectroscopy, and XPS. The FTIR analysis shows that 3‐D complex borate structures, such as tri‐, tetra‐, and pentaborate are made by [BO₄] tetrahedral units interconnected with 2‐D structure boroxol rings in the low Na₂O region. Above 20 wt% Na₂O content, nonbridged oxygen in [BO₂O^?] units and diborate groups increase with increase in Na₂O. The same tendency is shown by the Raman spectroscopy and XPS analyses. The Raman analysis shows that boroxol rings disappeared with large [BO₄] groups, such as tri‐, tetra‐, and pentaborate structures, which increase at low Na₂O content. Isolated diborate groups and nonbridged oxygen in [BO₂O^?] units increase at high Na₂O content. It can be inferred that single structure units, such as isolated diborate groups, interfere with conduction. The XPS analysis results show that free oxygen produced by the interconnection of Na₂O in the borate structure does not cause significant changes to O^2? in the low Na₂O region, but increases the O^o and decreases the O^?. Above 20 wt% Na₂O, O^? slightly increases and O^o shows a decreasing trend.     

Ab initio calculations of the interaction between thiophene and ionic liquids

The fundamental natures of the interaction between thiophene and ionic liquids of 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]⁺[PF₆]⁻) and 1-n-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]⁺[BF₄]⁻) were investigated using ab initio calculations and correlated with previous experimental results. The optimized structures show that the anions of the ionic liquids are situated outside the ring plane of the thiophene, with the fluorine atoms interacting with the hydrogen atoms of the thiophene, and the cation of the ionic liquids approaches the thiophene with its positively charged atoms approaching the negatively charged atoms of TS. It is concluded that thiophene molecules interact with the ionic liquids mainly via Coulombian attraction. Further analysis explained the results obtained from an absorption experiment that the molar ratios of the absorbed thiophene to the ionic liquids were approximately 3.5/1 and 2.4/1 for [BMIM]⁺[PF₆]⁻ and [BMIM]⁺[BF₄]⁻, respectively. The strong electron donation of the phosphorus atom to the fluorine atoms in the PF₆⁻ cluster is believed to be the major factor resulting in the higher molar ratio of thiophene/[BMIM]⁺[PF₆]⁻. The other factor is the difference of the compactness between the cation and the anion in the two ionic liquids.     

Synthesis optimization of Li1 + x[Mn0.45Co0.40Ni0.15]O2 with different spherical sizes via co-precipitation

Li_1 + x[Mn_0.45Co_0.40Ni_0.15]O₂ spherical cathode materials with different sizes (about 2 and 5 μm) were fabricated by calcining uniform spherical metal carbonate, [Mn_0.45Co_0.40Ni_0.15]CO₃ with lithium hydroxide at high temperature. The precursor of spherical metal carbonate, [Mn_0.45Co_0.40Ni_0.15]CO₃, was obtained via co-precipitation method at room temperature, which was significantly dependent on synthetic conditions, such as the reaction temperature, the concentration of NH₄HCO₃, and stirring speed, etc. The optimized condition resulted in [Mn_0.45Co_0.40Ni_0.15]CO₃, of which the particle size distribution was uniform and the particle shape was spherical. The final products, Li_1 + x[Mn_0.45Co_0.40Ni_0.15]O₂, had a well-ordered layered structure and uniform homogeneity. Raman spectroscopy analysis showed the Raman-active species E_g and A_1g modes were observed at 488, 473 cm^− 1 and 597, 590 cm^− 1, respectively, for the obtained spherical cathode materials.     

Color-tunable properties based on complex anion substitution in Eu2+ doped Ca8Sc2(PO4)6-y(SiO4)1+y phosphor

We synthesized and investigated the effect of Eu²⁺ ions doping in a novel phosphor-silicate Ca₈Sc₂(PO₄)₆(SiO₄) phosphor. The structure and photoluminescence properties were determined by X-ray powder diffraction Rietveld refinement, diffuse reflection spectra, emission-excitation spectra, decay curves and temperature dependence spectra. The phosphors showed an asymmetric broad-band blue emission (Eu²⁺) with peak at 470?nm. Furthermore, we presented the Ca_7.96Sc₂(PO₄)_6-y(SiO₄)_1+y:0.04Eu²⁺ phosphors by co-substituting [Eu²⁺-Si⁴⁺] for [Ca²⁺-P⁵⁺], and different behaviors of luminescence evolution in response to structural variation were verified among the series of phosphors. The results were attributed to the presence of multi Ca²⁺ sites, resulting in the mixing of blue and green emissions for Eu²⁺ ions. The complex anion substitution of [PO₄]^3- by [SiO₄]^4- induced an increased crystal field splitting of the Eu²⁺ ions, which caused a decrease in emission energy from the 5d excited state to the 4f ground state and a resultant red-shift from 470?nm to 520?nm. All the properties indicated that the Ca₈Sc₂(PO₄)₆(SiO₄):Eu²⁺ phosphors have potential application for color-tunable WLEDs.     

A novel disubstituted Lindqvist-type polyoxomolybdate [Te2Mo4O19] supporting two organic vanadyl moieties: Synthesis, characterization, and crystal structure of {[V(2,2-bipy)2]2(4,4-bipy)[Te2Mo4O19]}

The first example of disubstituted Lindqvist-type polyoxomolybdate {[V(2,2-bipy)₂]₂(4,4-bipy)[Te₂Mo₄O₁₉]} has been synthesized hydrothermally and characterized by elemental analyses, XPS, IR, TG-DTA and X-ray single crystal diffraction. The structural analysis shows that the neutral molecular unit [V(2,2-bipy)₂]₂[Te₂Mo₄O₁₉] consists of a novel Lindqvist-type polyanion [Te₂Mo₄O₁₉]⁶⁻ supporting two vanadyl moieties [V(2,2-bipy)₂]³⁺, and such neutral molecules are joined together by π − π stacking interactions between the pyridine groups to form a two-dimensional grid-like network with non-coordinating “guest” 4,4-bipys encapsulated.     

Luminescent properties of Sr2B2O5: Tm,Na blue phosphor

A novel blue phosphor, Sr₂B₂O₅: Tm³⁺, Na⁺ for white light-emitting diodes (W-LEDs) was prepared by solid-state synthesis and its structure and luminescence properties were investigated. This phosphor can be effectively excited within the broad near ultraviolet (NUV) wavelength region, from 340 nm to 370 nm, and exhibits a satisfactory blue performance. The emission peaks are observed at 457 nm (blue) and 475 nm (blue), due to the respective transitions of ¹D₂→³F₄ and ¹G₄→H₆. Seven mole percent of doping concentration of Tm³⁺ was shown to be optimal. Concentration quenching occurs when Tm³⁺ concentration is beyond 7 mol%, its mechanism being explained by dipole–dipole interaction of Tm³⁺ and being confirmed by decay property measurements. We have made a deep analysis on the effect of charge compensation reagent on luminescence intensity. Good blue emissions with the CIE chromaticity coordinates (0.173, 0.165) could be achieved. Our results suggest that the Sr₂B₂O₅: Tm³⁺, Na⁺ phosphor is a potential blue-emitting material.     

Structural and electrochemical behaviors of metastable Li2/3[Ni1/3Mn2/3]O2 modified by metal element substitution

Layered metastable lithium manganese oxides, Li_2/3[Ni_1/3−xMn_2/3−yM_x+y]O₂ (x = y = 1/36 for M = Al, Co, and Fe and x = 2/36, y = 0 for M = Mg) were prepared by the ion exchange of Li for Na in P2-Na_2/3[Ni_1/3−xMn_2/3−yM_x+y]O₂ precursors. The Al and Co doping produced the T^#2 structure with the space group Cmca. On the other hand, the Fe and Mg doped samples had the O6 structure with space group R-3m. Electron diffraction revealed the 1:2 type ordering within the Ni_1/3−xMn_2/3−yM_x+yO₂ slab. It was found that the stacking sequence and electrochemical performance of the Li cells containing T^#2-Li_2/3[Ni_1/3Mn_2/3]O₂ were affected by the doping with small amounts of Al, Co, Fe, and Mg. The discharge capacity of the Al doped sample was around 200 mAh g⁻¹ in the voltage range between 2.0 and 4.7 V at the current density of 14.4 mA g⁻¹ along with a good capacity retention. Moreover, for the Al and Co doped and undoped oxides, the irreversible phase transition of the T^#2 into the O2 structure was observed during the initial lithium deintercalation.     

Competitive nanocrystallization of Na3ScF6 and NaYbF4 in aluminosilicate glass and optical spectroscopy of Ln3+ dopants

The precipitation of monoclinic Na₃ScF₆ nanocrystals from aluminosilicate glass with specially designed compositions of SiO₂-Al₂O₃-Na₂O-NaF-ScF₃-YbF₃ was achieved for the first time. Impressively, competitive nanocrystallization of cubic NaYbF₄ and monoclinic Na₃ScF₆ has been evidenced to be dependent on Na⁺ content and F/Na ratio in glass. Adopting Er³⁺ and Eu³⁺ dopants as structural probes, optical spectroscopic analyses verified that these emissive centers preferred to partition into NaYbF₄ nanocrystals rather than Na₃ScF₆ ones.     

Solution and solid phase electrochemical behaviour of [Os(bpy)3]3[P2W18O62]

[Os(bpy)₃]₃[P₂W₁₈O₆₂] has been synthesised and characterised by elemental analysis, spectroscopic (UV-vis, IR spectroscopy) and electrochemical techniques. In 0.1 M Bu₄NPF₆ DMSO the complex shows a series of redox couples associated with the Os^3+/2+ and bipyridine ligands of the cationic [Os(bpy)₃]²⁺ moiety and the tungsten-oxo framework of the associated Dawson parent heteropolyanion, [P₂W₁₈O₆₂]⁶⁻. At this electrolyte concentration, the Os³⁺ redox form of the complex was seen to adsorb onto the electrode surface. When the electrolyte concentration is lowered to 0.01 M Bu₄NPF₆ in addition to the Os^3+/2+ redox couple, the redox process associated with the [P₂W₁₈O₆₂]^8−/7− couple also exhibited properties indicating surface based processes were present. Electroactive films of the complex were formed on carbon macroelectrodes by the redox switching of the transition metal within the complex. Voltammetric investigations into the film's behaviour in a range of buffer solutions (pH 2.0, 4.5 and 7.0) were performed. The films were found to possess better stability in acidic pH and the same pH dependence for the tungsten-oxo framework of the heteropolyanions as in solution. Solid state electrochemical measurements on mechanically attached microparticles of the complex were performed, with the effect of both the nature and concentration of the aqueous electrolyte on this behaviour being investigated. Upon redox switching between the Os^2+/3+ redox states, there is an associated insertion/expulsion of anions from/to the solution phase. Scanning electron micrographs of these solid state films were attained before and after redox cycling.     

Activity coefficients of Na2O in molten NaCl,Na2SO4, and Na2CO3

Measurements of the cell

have been used to determine activity coefficients of Na₂O in molten NaCl, Na₂SO₄ and Na₂CO₃. Extreme negative deviations from Raoult's law were observed (γ < 10^?3). In NaCl and Na₂SO₄, γ is independent of concentration below 1 m/o Na₂O, but in Na₂CO₃, the activity is nearly independent of concentration, probably because the oxide reacts with dissolved O₂ to form superoxide (O^?₂).     

Influence of lithium-based products proposed for counteracting ASR on the chemistry of pore solution and cement hydrates

Low- and high-alkali cement pastes were made with or without LiNO₃ or a Li-bearing glass. The [Li]/[Na+K] molar ratio was kept constant to 0.74. The specimens were stored at 23, 38, and 60 °C in sealed containers. After 3, 7, 28, and 91 days, their pore solutions were extracted and analysed, and their residual water contents were obtained by drying. The Li glass was found to react quite slowly, and the corresponding [Li⁺] in solution progressively increased with time, temperature, fineness (as-received glass vs. ground glass), and the [Na⁺+K⁺] concentration in solution. This glass increased the pH by about 0.1, and by about 0.2 after it was finely ground. In contrast, LiNO₃ decreased the pH by about 0.1, despite significantly increasing the [Na⁺+K⁺] in the pore solution. The higher the total %Na₂O_e content (including Li) in the original mixtures, the higher the total alkali content incorporated in the cement hydrates. The [Li⁺]-[Na⁺+K⁺] ratio in solution was about half of the initial ratio (0.74), while this ratio in the cement hydrates was always over 1.1. Li is the alkali most preferentially incorporated into the cement hydrates, while K is the least.     

Supramolecular π–π assembly of a neutral [Cu(salen)] complex via the templating effect of an ionic inorganic complex Na2[Cu(mnt)2] forming a framework type material having well-defined channels

A classical ionic inorganic complex Na₂[Cu(mnt)₂] (mnt²⁻ = maleonitriledithiolate = 1,2-dicyanoethylenedithiolate), that acts as a template in assembling neutral [Cu(salen)] (salen = bis(salicylidene)ethylenediamine) complexes forming a framework type arrangement, is accommodated in the channel formed in the crystal structure of a new type of host–guest compound [Cu(salen)]₄ · Na₂[Cu(mnt)₂] (1). The non-covalent supramolecular interactions among [Cu(salen)] complexes and between [Cu(salen)] and [Cu(mnt)₂]²⁻ complexes in the crystal lattice of 1 result in weak antiferromagnetic coupling.     

Synthesis and structure of the n = 4 member of the framework aluminium alkylenediphosphonate series Al2[O3PCnH2nPO3](H2O)2F2

We report here the solvothermal synthesis and crystal structure of the hybrid inorganic-organic framework material Al₂[O₃PC₄H₈PO₃](H₂O)₂F₂⋅2H₂O (monoclinic, 1P2₁/m, a = 4.961(2) ?, b = 11.930(5) ?, c = 10.727(5) ?, β = 93.972(6)^∘, Z = 2, R(F, F² > 2σ) = 0.094, R_w(F², all data) = 0.262), the third member of the Al₂[O₃PC_nH_2nPO₃](H₂O)₂F₂ framework series. The structure is formed from corrugated chains of corner-sharing AlO₄F₂ octahedra in which alternating AlO₄F₂ octahedra contain two fluorine atoms in a trans or a cis configuration. The diphosphonate groups link the chains together through Al-O-P-O-Al bridges and through the butyl groups to form a three-dimensional framework structure containing a one-dimensional channel system consisting of one type of channel only. The channels contain four extra-framework water molecules per unit cell. The formation of this member of the series shows that the form of the alkyl chain can successfully define the number of channel types and the channel length in this hybrid framework system.     

Effect of the Al2O3/SiO2 mass ratio on the crystallization behavior of CaO-SiO2-MgO-Al2O3 slags using confocal laser scanning microscopy

The crystallization behavior of a CaO-SiO₂-MgO-Al₂O₃ slag system with varying Al₂O₃/SiO₂ mass ratios from 0.03 to 1.10 has been investigated using a confocal laser scanning microscopy (CLSM). The resulting continuous cooling transformation (CCT) and time-temperature-transformation (TTT) curves showed that the initial crystallization temperature increased and the incubation time for crystallization slightly decreased with increasing Al₂O₃/SiO₂ ratio. The crystal growth rate first increased and then decreased with decreasing isothermal temperature. X-ray diffraction (XRD) analysis suggested that Ca₂MgSi₂O₇ or Ca₃MgSi₂O₈ precipitated as the primary phase at lower Al₂O₃/SiO₂ ratios, while the Ca₂Al₂SiO₇ phase was preferred at higher Al₂O₃/SiO₂ ratios. The observed crystalline phases correlated well with the expected thermodynamic predictions from FactSage. In addition, structural analysis using ²⁷Al magic angle spinning nuclear magnetic resonance (²⁷Al MAS-NMR) microscopy of the as-quenched slags indicated the presence of a higher ratio of tetrahedral [AlO₄]^5-structural units with increasing Al₂O₃/SiO₂ ratio, which enhanced the polymerization of tetrahedral [AlO₄]^5- and [SiO₄]^4- structural units to form Ca₂Al₂SiO₇.