Impurity and radiation defects in LiB<Subscript>3</Subscript>O<Subscript>5</Subscript> crystals. The nature of centers in LiB<Subscript>3</Subscript>O<Subscript>5</Subscript> crystals,which are responsible for coloration during the long-term operation of optical elements

An attempt is made to explain the causes of coloration of LiB₃O₅ crystals after their long-term operation as laser elements. By EPR and optical spectroscopy the impurity and radiation centers are studied in as-grown LiB₃O₅ crystals and in the crystals whose color appeared after the long-term operation as laser elements. In a number of as-grown crystals a copper impurity is detected. EPR spectral parameters and the structural positions of Cu²⁺ ions are found. Defect formation features in electron irradiated as-grown LiB₃O₅ crystals and in the most colored regions of crystals of spent laser elements are analyzed. It is shown that in both growth crystals and crystals after long-term operation as laser elements the same set of radiation defects is observed: oxygen O^– in the interstitial position, an O^– hole center in the crystal structure, and the B²⁺ electron center due to the removal of an oxygen atom near the lithium vacancy. The only distinction is that the concentration of these radiation defects in crystals long used as laser elements is higher than that in growth ones by an order of magnitude. The results obtained enable the conclusion that the cause of coloration of LiB₃O₅ crystals is photo-induced diffusion of lithium atoms and their capture by cation vacancies in the dark part of the crystal, which provides the formation and accumulation of lithium vacancies in the region where the laser beam passes.     

Cobalt boride catalysts for hydrogen storage systems based on NH<Subscript>3</Subscript>BH<Subscript>3</Subscript> and NaBH<Subscript>4</Subscript>

The catalytic activity of cobalt borides forming in situ under conditions of NH₃BH₃ and NaBH₄ hydrolysis have been investigated. The reaction properties of the catalysts depend on the nature of the hydride. According to high-temperature X-ray diffraction, thermal analysis, high-resolution transmission electron microscopy, IR spectroscopy, and chemical analysis data, the nature of the hydride determines the particle size, chemical composition, and crystallization properties of the cobalt borides.     

Synthesis and characterization of a new hybrid TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> filler for lithium conducting gel electrolytes

This paper describes the synthesis and properties of a new type of ceramic fillers for composite polymer gel electrolytes. Hybrid TiO₂-SiO₂ ceramic powders have been obtained by co-precipitation from titanium(IV) sulfate solution using sodium silicate as the precipitating agent. The resulting submicron-size powders have been applied as fillers for composite polymer gel electrolytes for Li-ion batteries based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF/HFP) copolymeric membranes. The powders, dry membranes and gel electrolytes have been examined structurally and electrochemically, showing favorable properties in terms of electrolyte uptake and electrochemical characteristics in Li-ion cells.     

Structure and properties of H<Subscript>8</Subscript>(PW<Subscript>11</Subscript>TiO<Subscript>39</Subscript>)<Subscript>2</Subscript>O heteropoly acid

Heteropoly acid (HPA) H₈(PW₁₁TiO₃₉)₂O·xH₂O (I) is synthesized by three different ways and studied by chemical analysis, potentiometric titration, mass-spectrometry, IR, ³¹P, ¹⁸³W, and ¹⁷O NMR spectroscopy, thermogravimetry, and transmission electron microscopy. Anion I consists of two subparticles of the Keggin structure bridged by Ti-O-Ti. The dimeric anion exists in HPA aqueous solutions at [I] > 0.02 M. At pH > 0.6 it splits to a [PW₁₁TiO₄₀]⁵⁻ monomer stable up to pH ∼ 6. When heated (150–400)°C, I splits into H₃PW₁₂O₄₀ and, apparently, H₃PW₁₀Ti₂O₃₈ without phase separation. Thermolysis products are soluble and when dissolved in water turn again into I. Complete decomposition of I to oxides occurs at ∼450°C.     

Structure and lithium mobility of Li<Subscript>4</Subscript>Pt<Subscript>3</Subscript>Si

The lithium-rich silicide Li₄Pt₃Si was synthesised from the elements by high-temperature synthesis in a sealed niobium ampoule. Its structure was refined on the basis of single-crystal X-ray diffraction data: R32, a = 693.7(2), c = 1627.1(4) pm, wR2 = 0.0762, 525 F² values and 21 variables. The striking structural motifs of the Li₄Pt₃Si structure are silicon atoms with a slightly distorted trigonal prismatic platinum coordination with short Si–Pt distances (238–246 pm). Always two trigonal prisms are condensed via a common Pt₃ triangle, and these double units built up a three-dimensional network by condensation via common corners. The channels left by this prismatic network are filled by two crystallographically independent lithium sites in a 3:1 ratio. The single crystal X-ray data were fully confirmed by neutron powder diffraction and ⁷Li magic-angle spinning (MAS)–nuclear magnetic resonance (NMR) results. The two distinct lithium sites are well differentiated by their ⁷Li isotropic chemical shift and nuclear electric quadrupolar interaction parameters. MAS-NMR spectra reveal signal coalescence effects above 300 K, indicating chemical exchange between the lithium sites on the millisecond timescale. The spectra can be simulated with a simple two-site exchange model. From the resulting temperature-dependent correlation times, an activation energy of 50 kJ/mol is extracted.     

New scandium rhodium boride Sc<Subscript>4</Subscript>Rh<Subscript>17</Subscript>B<Subscript>12</Subscript> with a framework structure: synthesis,crystal structure,and properties

The new scandium rhodium boride Sc₄Rh₁₇B₁₂ was synthesized by arc-melting of the elements followed by annealing in inert atmosphere. The crystal structure of Sc₄Rh₁₇B₁₂ was solved using single crystal X-ray diffraction data. The structure can be described as a three-dimensional frame-work formed by trigonal prisms [BRh₆] and [BRh₅Sc] with isolated boron atoms inside the prisms and trigonal prisms [BRh₅B] representing the coordination polyhedra of paired boron atoms. The temperature dependences of the magnetic susceptibility and specific resistance of Sc₄Rh₁₇B₁₂ revealed that the compound is a Pauli paramagnet and shows metal-like specific resistance.     

Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/nitrogen-doped reduced graphene oxide nanocomposite with enhanced lithium storage properties

The three-dimensional porous Li₃V₂(PO₄)₃/nitrogen-doped reduced graphene oxide (LVP/N-RGO) composite was prepared by a facile one-pot hydrothermal method and evaluated as cathode material for lithium-ion batteries. It is clearly seen that the novel porous structure of the as-prepared LVP/N-RGO significantly facilitates electron transfer and lithium-ion diffusion, as well as markedly restrains the agglomeration of Li₃V₂(PO₄)₃ (LVP) nanoparticles. The introduction of N atom also has positive influence on the conductivity of RGO, which improves the kinetics of electrochemical reaction during the charge and discharge cycles. It can be found that the resultant LVP/N-RGO composite exhibits superior rate properties (92 mA h g^?1 at 30 C) and outstanding cycle performance (122 mA h g^?1 after 300 cycles at 5 C), indicating that nitrogen-doped RGO could be used to improve the electrochemical properties of LVP cathodes for high-power lithium-ion battery application.

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Graphical abstract The three-dimensional porous Li₃V₂(PO₄)₃/nitrogen-doped reduced graphene oxide composite with significantly accelerating electron transfer and lithium-ion diffusion exhibits superior rate property and outstanding cycle performance.

     

The crystal structure of Ho<Subscript>4</Subscript>Ni<Subscript>11</Subscript>In<Subscript>20</Subscript>

The polycrystalline Ho₄Ni₁₁In₂₀ was obtained by arc-melting of the elements. The subsequent high temperature procedure was used for single crystal growth. Crystal structure of the compound was investigated by X-ray single crystal method: U₄Ni₁₁Ga₂₀ type, C 2/m, a = 22.4528(17), b = 4.2947(3), c = 16.5587(13) Å, β = 124.591(5)°, R1 = 0.0276, wR2 = 0.0493 for 1989 independent reflections with [I>2σ(I)].The structure is composed of three-dimensional network from Ni and In atoms in which Ho atoms fill distorted pentagonal channels. Open image in new window     

The synthesis and selected properties of Co<Subscript>2</Subscript>InV<Subscript>3</Subscript>O<Subscript>11</Subscript>

It has been demonstrated that Co₂V₂O₇ and InVO₄ react with each other forming a new compound of the Co₂InV₃O₁₁ formula, when their molar ratio is equal to 1:1, or among CoCO₃, In₂O₃ and V₂O₅, mixed at a molar ratio of 4:1:3. This compound melts incongruently at the temperature of 960±5°C, depositing crystals of InVO₄. It crystallizes in the triclinic system and the unit cell parameters amount to: a=0.6524(6) nm, b=0.6885(5) nm, c=1.0290(4) nm, α=96.5°, β=104.1°, γ=100.9°, Z=2. The phase equilibria being established in the Co₂V₂O₇–InVO₄ system over the whole components concentration range up to the solidus line were described.     

Electrospun Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> composite nanofibers for enhanced high-rate lithium ion batteries

Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers with the mean diameter of ca. 60 nm have been synthesized via facile electrospinning. When the molar ratio of Li to Ti is 4.8:5, the Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers exhibit initial discharge capacity of 216.07 mAh g^?1 at 0.1 C, rate capability of 151 mAh g^?1 after being cycled at 20 C, and cycling stability of 122.93 mAh g^?1 after 1000 cycles at 20 C. Compared with pure Li₄Ti₅O₁₂ nanofibers and Li₂TiO₃ nanofibers, Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers show better performance when used as anode materials for lithium ion batteries. The enhanced electrochemical performances are explained by the incorporation of appropriate Li₂TiO₃ which could strengthen the structure stability of the hosted materials and has fast Li⁺-conductor characteristics, and the nanostructure of nanofibers which could offer high specific area between the active materials and electrolyte and shorten diffusion paths for ionic transport and electronic conduction. Our new findings provide an effective synthetic way to produce high-performance Li₄Ti₅O₁₂ anodes for lithium rechargeable batteries.     

Synthesis,structure, and electric properties of oxygen-deficient perovskites Ba<Subscript>3</Subscript>In<Subscript>2</Subscript>ZrO<Subscript>8</Subscript> and Ba<Subscript>4</Subscript>In<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>11</Subscript>

Perovskite phases Ba₃In₂ZrO₈ and Ba₄In₂Zr₂O₁₁ with the nominal concentration of structural oxygen vacancies 1/9 and 1/12, respectively, were synthesized by solid-phase and solution methods. X-ray diffraction showed cubic symmetry of both phases with the unit cell parameter a = 0.4193(2) and 0.4204(3) nm, respectively. The absence of superstructural lines resulted in the conclusion on statistical arrangement of oxygen vacancies. Thermogravimetry and mass spectrometry proved that both phases can reversibly absorb water from gas phase (pH₂O = 2 × 10⁻² atm) with observed correlation between the concentration of oxygen vacancies and amount of absorbed water. The total water amount was up to 0.9 mol per formula unit or, if recalculated for perovskite unit ABO₃, 0.3 and 0.23 mol H₂O, respectively. The temperature curves of coductivity in the atmosphere with various partial water vapor pressures (pH₂O = 3 × 10⁻⁵ and 2 × 10⁻² atm) showed significantly higher conductivity and lower activation energy (0.52 eV) in humid atmosphere due to proton transfer. The proton conductivity is up to 5 × 10⁻⁴ Ohm⁻¹ cm⁻¹ at 300°C for Ba₃In₂ZrO₈ specimen. IR spectrometry showed that protons in the structure exist primarily in OH-groups.     

Synthesis and characterization of a new monophosphate (C<Subscript>6</Subscript>H<Subscript>16</Subscript>N<Subscript>2</Subscript>)(H<Subscript>2</Subscript>PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Chemical preparation, crystal structure, and NMR spectroscopy of a new trans-2,5-dimethylpiperazinium monophosphate are given. This new compound crystallizes in the triclinic system, with the space group P-1 and the following parameters: a = 6.5033(3), b = 7.6942(4), c = 8.1473(5) Å, α = 114.997(3), β = 92.341(3), γ = 113.136(3), V = 329.14(3) ų, Z = 1, and D_x = 1.565 g cm^?3. The crystal structure has been determined and refined to R = 0.030 and R _w(F ²) = 0.032 using 1558 independent reflections. The structure can be described as infinite [H₂PO₄] _n ^n? chains with (C₆H₁₆N₂)²⁺ organic cations anchored between adjacent polyanions to form columns of anions and cations running along the b axis. This compound has also been investigated by IR, thermal, and solid-state, ¹³C and ³¹P MAS NMR spectroscopies and Ab initio calculations.     

Synthesis and study of (hexacaprolactam)trionium dodecamolybdophosphate (C<Subscript>6</Subscript>H<Subscript>11</Subscript>NO)<Subscript>6</Subscript>H<Subscript>3</Subscript>[PMo<Subscript>12</Subscript>O<Subscript>40</Subscript>]

(Hexacaprolactam)trionium dodecamolybdophosphate (C₆H₁₁NO)₆H₃[PMo₁₂O₄₀] has been prepared and studied by means of chemical and X-ray diffraction analysis as well as NMR and IR spectroscopy.     

Thermodynamic properties and functions of condensed Bi<Subscript>8</Subscript>O<Subscript>11</Subscript>

The values of ΔH°₂₉₈, S°₂₉₈, H°₂₉₈–H°₀, T, ΔH _fus, and C _p(T), as well as the temperature dependences of the Gibbs energy function, are calculated for Bi₈O₁₁ oxide by proven computational methods.     

Natural graphite enhanced the electrochemical performance of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> cathode material for lithium ion batteries

Natural graphite treated by mechanical activation can be directly applied to the preparation of Li₃V₂(PO₄)₃. The carbon-coated Li₃V₂(PO₄)₃ with monoclinic structure was successfully synthesized by using natural graphite as carbon source and reducing agent. The amount of activated graphite is optimized by X-ray diffraction, scanning electron microscope, transmission electron microscope, Raman spectrum, galvanostatic charge/discharge measurements, cyclic voltammetry, and electrochemical impedance spectroscopy tests. Our results show that Li₃V₂(PO₄)₃ (LVP)-10G exhibits the highest initial discharge capacity of 189 mAh g^?1 at 0.1 C and 162.9 mAh g^?1 at 1 C in the voltage range of 3.0–4.8 V. Therefore, natural graphite is a promising carbon source for LVP cathode material in lithium ion batteries.     

Crystal structure of a new ternary molybdate in the Rb<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-Eu<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript>-Hf(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript> system

A ternary salt system Rb₂MoO₄-Eu₂(MoO₄)₃-Hf(MoO₄)₂ was studied in the subsolidus area by X-ray phase analysis. A novel ternary molybdate, Rb_4.98Eu_0.86Hf_1.11(MoO₄)₆, formed in the system. The Rb_4.98Eu_0.86Hf_1.11(MoO₄)₆ rubidium-europium-hafnium molybdate crystals were grown by solution-melt crystallization under the spontaneous nucleation conditions. The structure and composition of this compound were refined by single crystal X-ray diffraction (X8 APEX automated diffractometer, MoK _α radiation, 1753 F(hkl), R = 0.0183). The crystals are trigonal, a = b = 10.7264(1) Å, c = 38.6130(8) Å, V = 3847.44(9) ų, Z = 6, space group R \(\bar 3\) c. The three-dimensional mixed framework of the structure comprises Mo tetrahedra and two types of octahedra, (Eu,Hf)O₆ and HfO₆. The large cavities of the framework include two types of the rubidium atom. The distribution of the Eu³⁺ and Hf⁴⁺ cations over two crystallographic positions was refined.     

The synthesis and properties of solid solutions based on Ba<Subscript>4</Subscript>Ca<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>11</Subscript>

(Ba_{1 ? x} Ca _x )₆Nb₂O₁₁ solid solutions were synthesized. The compositions were shown to be single-phase at 0.23 ≤ x ≤ 0.47 and have a double perovskite cubic structure with an incomplete oxygen sublattice. The interaction of solid solutions with water vapor and their electrical properties were studied. In dry atmosphere, these complex oxides were mixed oxygen-hole conductors. In humid atmosphere, they intercalated water and exhibited protonic conductivity. The influence of Ba/Ca isovalent substitution, the dynamics of the oxygen sublattice, and the concentration of intercalated water on the value and contribution of protonic and hole conductivity was analyzed.     

Synthesis and crystal structure of the new complex oxide Ca<Subscript>7</Subscript>Mn<Subscript>2.14</Subscript> Ga<Subscript>5.86</Subscript>O<Subscript>17.93</Subscript>

The complex oxide Ca₇Mn_2.14Ga_5.86O_17.93 was synthesized by the solid-state reaction in a sealed evacuated quartz tube at 1000 °C. Its crystal structure was determined by electron diffraction and X-ray powder diffraction. The structure can be represented as a tetrahedral framework, viz., the polyanion [(Mn_0.285Ga_0.715)₁₅O_29.86]^19- stabilized by the incorporated cation [Ca₁₄GaO₆]₁₉₊. The polycation consists of the GaO₆ octahedra surrounded by the Ca atoms, which are arranged to form a cube capped at all places. The tetrahedral framework is partially disordered due to the presence of tetrahedra with two possible orientations in the positions (0, 0, 0) and (x, x, x) with x ≈ 0.15 and 0.17. The relationship between the Ca₇Mn_2.14Ga_5.86O_17.93 structures and related ordered phases with the symmetry F23, as well as the influence of the oxygen content on the ordering in the tetrahedral framework, are discussed.     

Synthesis and electrochemical properties of yttrium-doped LiMn<Subscript>0.98</Subscript>Y<Subscript>0.02</Subscript>O<Subscript>2</Subscript> for lithium secondary batteries

Yttrium-doped lithium manganese oxide (LiMn_0.98Y_0.02O₂) was prepared by ion exchange of lithium for sodium in NaMn_0.98Y_0.02O₂ precursors obtained by using rheological phase reaction method. This material had small particle size, which was composed of grain size of about 100 nm. Especially, LiMn_0.98Y_0.02O₂ delivered the initial discharge capacity of about 191 mA h g⁻¹ at room temperature when cycled between 2.0 and 4.4 V vs Li/Li⁺. Moreover, it showed an excellent cycling behavior, its specific capacity remained above 173 mA h g⁻¹ after 20 cycles, and the material did not transform into spinel structure during the electrochemical cycling according to the cyclic voltammograms and X-ray powder diffraction. The electrochemical results revealed that the doping of Y³⁺ improved the performance of LiMnO₂ considerably.