Elastic properties of Li<Subscript>2</Subscript>Zn<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> single crystals

The complete elastic modulus matrix of Li₂Zn₂(MoO₄)₃ single crystals has been measured for the first time. The sound velocity has been measured in different directions of the crystals by a pulse-phase method. The measurement results have been used to calculate elastic moduli. The sound velocity has been calculated in the three main crystallographic planes of the crystals.     

Electrical conduction and relaxation mechanism in Li<Subscript>2</Subscript>AlZr[PO<Subscript>4</Subscript>]<Subscript>3</Subscript>

Li-ion electrolyte NASICON type Li₂AlZr[PO₄]₃ has been prepared by Solid State Reaction method. Formation of the sample has been confirmed by XRD and TGA–DTA analysis. Electrical conductivity studies have been performed in the frequency range 42 Hz–5 MHz within the temperature range 523–623 K using aluminium as blocking electrodes. The conductivity has been found to be 1 × 10⁻⁵ S cm⁻¹ at 623 K. Dielectric spectra show the decrease in dielectric constant with increase in frequency. Dielectric loss spectra reveal that dc conduction contribution predominates in the sample. Spectroscopic plots of complex modulus suggest the Non-Debye behaviour of the electrical relaxation within the temperature range studied.     

Luminescence properties of terbium-doped Li<Subscript>3</Subscript>PO<Subscript>4</Subscript> phosphor for radiation dosimetry

A polycrystalline sample of Li₃PO₄:Tb³⁺ phosphor was successfully synthesized using solid-state diffusion method. This synthesis method is of low cost, low temperature and does not require any other atmospheres for the synthesis. The powder X-ray diffraction (PXRD), photoluminescence (PL) emission and excitation spectra, thermoluminescence (TL) and optically stimulated luminescence (OSL) were measured. The particle size was calculated using the Debye Scherrer formula and found to be 79.42 nm. PL emission spectra of Li₃PO₄:Tb³⁺ phosphor show the strong prominent peak at 544 nm corresponding to ⁵D₄ to ⁷F₅ transitions of Tb³⁺. The OSL sensitivity of prepared Li₃PO₄:Tb³⁺ phosphor was 50% of that of α-Al₂O₃:C. Its decay curve consists of three components with photoionization cross-sections 0.44 × 10^?17, 3.09 × 10^?17 and 23×10^?17 cm². The TL glow curve of the prepared sample consists of two characteristic peaks, which were deconvoluted using the peak fit software, and kinetic parameters were determined using the peak shape method. TL intensity was compared with that of the commercially available TLD-500 phosphor. OSL dose response was linear in the measured range and the minimum detectable dose (MDD) was found to be 67.42 μGy, while fading of the OSL signal was found to be about 27% in 4200 min after which the OSL signal stabilizes.     

Mn-doped Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> nanocrystal with enhanced electrochemical properties based on aerosol synthesis method

Mn-doped Li₃V_2?x Mn _x (PO₄)₃ nanocrystals with enhanced electrochemical properties for lithium-ion batteries were synthesized by aerosol process successfully. The nanocrystals synthesized from aerosol-assisted spray process have an average particle size smaller than 500 nm, with some initial particle size of about 100 nm. The Mn-doped Li₃V₂(PO₄)₃ cathode materials show higher capacity and coulombic efficiency than pure Li₃V₂(PO₄)₃ materials. Especially, the Mn-doped Li₃V_1.94Mn_0.06(PO₄)₃ shows a capacity of 130 mAh/g in the voltage range of 3.0–4.4 V and a coulombic efficiency of 99.5 % at 1C. The results from XRD, SEM, HRTEM, and EIS suggested that lattice changes of Li₃V₂(PO₄)₃ due to Mn doping and the fine particles enabled by aerosol-assisted spray process can significantly reduce the charge-transfer resistance and improve the apparent Li⁺ diffusion coefficient of insertion/desertion in the electrodes, which were the critical reason of better electrochemical performance of Mn-doped Li₃V₂(PO₄)₃ cathode materials.     

Na<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-CaMoO<Subscript>4</Subscript>-Ce<Subscript>2/3</Subscript>MoO<Subscript>4</Subscript> scheelite-like solid solutions

We have studied tetragonal scheelite-like solid solutions in the ternary system Na₂MoO₄-CaMoO₄-Ce_2/3MoO₄: Na _0.7Ca_y Ce_{1.1 ? 2y/3} (MoO₄)₂ (0 ≤ y ≤ 0.6) and Na_0.3 Ca_zCe_{1.23? 2z/3} (MoO₄)₂ (0 ≤ z ≤ 1.4). The solid solutions melt congruently at temperatures from 1100 to 1200°C. Their lattice parameters have been determined. Using reflection spectra, we evaluated the color parameters of all the samples studied.     

Thermal Analysis of the Ternary System Li<Subscript>2</Subscript>WO<Subscript>4</Subscript>-WO<Subscript>3</Subscript>-Li<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript>

Thermal analysis results indicate that the liquidus surface of the Li₂WO₄-WO₃-Li₂B₄O₇ system consists of the primary phase fields of Li₂WO₄, Li₂B₄O₇, WO₃, Li₂WO₄ · WO₃ (congruent melting), 3Li₂WO₄ · 2Li₂B₄O₇ (congruent melting), and Li₂WO₄ · 3WO₃ (incongruent melting). Low-melting-point compositions are selected that are potentially attractive for the low-temperature synthesis of lithium tungsten bronze powders.     

New,thermally stable Gd<Subscript>11</Subscript>(GeO<Subscript>4</Subscript>)(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>O<Subscript>10</Subscript>-based upconversion phosphors

A series of Gd_11–x–y Yb _x Er _y GeP₃O₂₆ germanate phosphates differing in the ratio of the Yb³⁺ and Er³⁺ active ions have been synthesized, and their luminescence spectra have been measured. According to X-ray diffraction characterization results, all of the synthesized germanate phosphates are single-phase and have a triclinic structure (sp. gr. P1). We have measured upconversion luminescence spectra due to the Er^{3+ 2}H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 radiative transitions in the synthesized gadolinium ytterbium erbium germanate phosphates and determined the luminescence upconversion energy yield (B _en) in Gd_11–x–y Yb _x Er _y GeP₃O₂₆. The effects of the concentrations and ratio of the dopants in the Gd₁₁(GeO₄)(PO₄)₃O₁₀ germanate phosphate host on B _en and the ratio of the luminescence intensities in the red and green spectral regions (R/G) have been assessed.     

Erbium zirconium phosphate Er<Subscript>0.33</Subscript>Zr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> of the NaZr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> family. Structure contraction on heating

Erbium zirconium phosphate Er_0.33Zr₂(PO₄)₃, a member of the family of structural analogs of NaZr₂(PO₄)₃ (NZP), was prepared by the sol-gel process and studied by X-ray phase analysis, IR spectroscopy, and differential scanning calorimetry. The behavior of erbium zirconium phosphate on heating in the temperature interval from 25 to 625°C was studied by high-temperature X-ray diffraction. Expansion and contraction along different crystallographic directions and contraction of the structure as a whole were found. The overall contraction is due to higher contribution of the negative axial thermal expansion coefficients α _a and α _b to α_av and hence to the volume expansion of the phosphate. On heating to 900°C, the NZP structure is preserved.     

High-temperature crystal chemistry of Na<Subscript>6</Subscript>(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>O(MoO<Subscript>4</Subscript>)<Subscript>4</Subscript>

Thermal deformations of Na₆(UO₂)₂O(MoO₄)₄ were studied by high-temperature powder X-ray diffraction. The compound crystallizes in the triclinic system, space group Р\(\bar 1\), a = 7.636(7), b = 8.163(6), c = 8.746(4) Å, α = 72.32(9)°, β = 79.36(4)°, γ = 65.79(5)°, V = 472.74(4) ų. It is stable in the temperature interval 20–700°С. The thermal expansion coefficients (TECs) are α₁₁ = 25.5 × 10^–6, α₂₂ = 7.8 × 10^–6, and α₃₃ = 1.1 × 10^–6 (°C)^–1. The orientation of the TEC pattern relative to the crystallographic axes is a₃₃^Z = 45°, a₃₃^X = 122°, a₂₂^Z = 59°, and a₂₂^X = 66°. The anisotropy of the thermal expansion is due to specific features of the crystal structure of the compound.     

Phase transitions of the NASICON-type mixed phosphates LiM<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> (M = Ti,Zr) and LiInNb(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

The structural phase transitions of LiTi₂(PO₄)₃, LiInNb(PO₄)₃, and LiZr₂(PO₄)₃ have been studied by X-ray diffraction, impedance spectroscopy, ⁷Li NMR spectroscopy, and calorimetry. The results indicate that, as the temperature is raised, the lithium ions in the structure of LiTi₂(PO₄)₃ and LiInNb(PO₄)₃ redistribute between the M1 and M2 sites. The thermal expansion coefficients along the crystallographic axes of LiTi₂(PO₄)₃ and LiInNb(PO₄)₃ are estimated.     

Synthesis and conductivity studies of Li<Subscript>1.5</Subscript>Al<Subscript>0.5</Subscript>Ge<Subscript>1.5</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> solid electrolyte

This paper describes the preparation of a lithium ion conducting solid electrolyte with the composition Li_1.5Al_0.5Ge_1.5(PO₄)₃ by a new liquid-phase method with the use of the water-soluble salts Al(NO₃)₃ · 9H₂O, LiNO₃ · 3H₂O, and (NH₄)₂HPO₄ and the germano-oxalic acid H₂[Ge(C₂O₄)₃]. The synthesized materials have been characterized by X-ray diffraction, differential scanning calorimetry, thermogravimetry, and impedance spectroscopy. The results demonstrate that sintering of the synthesized amorphous powders at a temperature of 650°C leads to the formation of phase-pure Li_1.5Al_0.5Ge_1.5(PO₄)₃. The ionic conductivity of the electrolyte measured at frequencies from 10 Hz to 2 MHz using pellets with an 86% relative density was 4.2 × 10^–4 S/cm.     

Superprotonic CsH<Subscript>2</Subscript>PO<Subscript>4</Subscript>-CsHSO<Subscript>4</Subscript> solid solutions

We have performed partial HSO₄⁻ substitution in CsH₂PO₄ and studied the associated structural changes and the proton conductivity of the resultant (CsH₂PO₄)_{1 − x} (CsHSO₄) _x solid solutions in the range x = 0.01–0.3. The results indicate that, at room temperature, the solid solutions are disordered. In the range x = 0.01–0.1, they are isostructural with the low-temperature phase of CsH₂PO₄ (sp. gr. P2₁/m), and their unit-cell parameters increase with x, whereas in the range x = 0.15–0.3 the solid solutions are isostructural with the high-temperature, cubic phase of CsH₂PO₄ (Pm3m), and their unit-cell parameter decreases. The conductivity of the (CsH₂PO₄)_{1 − x} (CsHSO₄) _x solid solutions with x ≤ 0.3 depends significantly on their composition and increases at low temperatures by up to four orders of magnitude, approaching that of the superionic phase of CsH₂PO₄ in the range x = 0.15–0.3 because of the hydrogen bond weakening and increased proton mobility. The conductivity of the superionic phase decreases with increasing x by no more than a factor of 1.5–2, and the superionic phase transition, which occurs at 231°C in CsH₂PO₄, shifts to lower temperatures and disappears for x ≥ 0.15. The activation energy for low-temperature conduction decreases with increasing x: from 0.9 eV in CsH₂PO₄ to 0.48 eV at x = 0.1.     

Synthesis and luminescence properties of a Li<Subscript>3</Subscript>BaCaY<Subscript>3</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>8</Subscript>:Er<Superscript>3+</Superscript> phosphor with a layered scheelite-like structure

A Li₃BaCaY₃(MoO₄)₈:Er³⁺ phosphor with a scheelite-like structure (sp. gr. C2/c) has been synthesized and its luminescence properties have been studied. The phosphor has been characterized by X-ray diffraction, differential thermal analysis, and IR spectroscopy.     

Phase transitions and high-temperature crystal chemistry of polymorphous modifications of Cs<Subscript>2</Subscript>(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)

Phase transitions and thermal deformations of - and -Cs₂(UO₂)₂(MoO₄)₃ were studied by high-temperature X-ray diffraction analysis. In heating of -Cs₂(UO₂)₂(MoO₄)₃ to 625 ± 25°C, the reconstructive phase transition proceeds. -Cs₂(UO₂)₂(MoO₄)₃ is stable up to 700 ±25°C. The thermal expansion of both phases is sharply anisotropic: ₁₁ = 10 × 10^–6, ₂₂ = 33 × 10^–6, ₃₃ = 10 × 10^–6, _V = 53 × 10^–6 deg^–1 for -Cs(UO₂)₂(MoO₄)₃ and ₁₁ = 13 × 10^–6, ₃₃ = 3 × 10^–6, _V = 31 × 10^–6 deg^–1 for -Cs₂ (UO₂)₂ (MoO₄)₃. The anisotropy of thermal expansion is explained by features of the crystal structure of the compounds.Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 405–407.Original Russian Text Copyright © 2004 by Nazarchuk, Krivovichev, Filatov.     

Lithium ion conductivity of LiLaO<Subscript>2</Subscript>-Li<Subscript>2</Subscript>ZrO<Subscript>3</Subscript> solid solutions

The limits of the LiLaO₂-and Li₂ZrO₃-based solid solutions in the LiLaO₂-Li₂ZrO₃ system have been determined: 0–10 mol % Li₂ZrO₃ and 0–5 mol % LiLaO₂, respectively. We have studied the transport properties (electronic conductivity, temperature and composition dependences of conductivity and activation energy) of lithium lanthanate and the solid solutions in the LiLaO₂-Li₂ZrO₃ system. Conduction in LiLaO₂ is likely due to lithium ion transport through a polyhedral network.     

Chlorine impurity content of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> and GeO<Subscript>2</Subscript>

Bismuth(III) and germanium(IV) oxides are used as precursors for the crystal growth of bismuth orthogermanate. The chlorine content of the starting oxides is critical to the engineering performance of this material. We propose a simple, high-speed technique for determining the chlorine content of bismuth(III) and germanium(IV) oxides, down to 5 × 10^?4 wt %, using capillary electrophoresis.     

Polycrystalline materials in MoO<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript>–V<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Melt quenching technique was applied to study tendency for phase formation and amorphization in the MoO₃–ZrO₂–V₂O₅ system. By X-ray diffraction were detected the main crystalline phases separated during the quenching: Zr(MoO₄)₂, V₂MoO₈, (Mo_0.3V_0.7)₂O₅, V_0.95Mo_0.97O₅ but in a wide concentration range the dominant crystalline phase was monoclinic ZrO₂. The average particle sizes of the obtained crystal phases were in the range 30–50 nm. A narrow glass formation area was situated, near MoO₃–V₂O₅ side. The glass-crystalline samples were obtained in the MoO₃- and V₂O₅-rich compositions. The phase formation was proven by IR analysis also. IR data showed that the main structural units built up the glass network are corner shared VO₅ and MoO₆ groups while in the corresponding crystal V₂MoO₈ phase MeO₆ (Me = V, Mo) octahedra are corner and edge shared (band at 580 cm⁻¹).     

Low-temperature pyroelectric properties of Li<Subscript>2</Subscript>SO<Subscript>4</Subscript>

The pyroelectric properties of lithium sulfate have been studied theoretically on the hypothesis of a pseudosymmetry of the structure of its polar phase. Analytical expressions are proposed for the temperature dependences of its pyroelectric polarization and pyroelectric coefficient at low temperatures and near the polymorphic transformation. The pyroelectric and piezoelectric coefficients of a polar crystal are shown to be in direct proportion.     

Improved photocatalytic degradation of organic dye using Ag<Subscript>3</Subscript>PO<Subscript>4</Subscript>/MoS<Subscript>2</Subscript> nanocomposite

Highly efficient Ag₃PO₄/MoS₂ nanocomposite photocatalyst was synthesized using a wet chemical route with a low weight percentage of highly exfoliated MoS₂ (0.1 wt.%) and monodispersed Ag₃PO₄ nanoparticles (~5.4 nm). The structural and optical properties of the nanocomposite were studied using various characterization techniques, such as XRD, TEM, Raman and absorption spectroscopy. The composite exhibits markedly enhanced photocatalytic activity with a low lamp power (60 W). Using this composite, a high kinetic rate constant (k) value of 0.244 min^-1 was found. It was observed that ~97.6% of dye degrade over the surface of nanocomposite catalyst within 15 min of illumination. The improved photocatalytic activity of Ag₃PO₄/MoS₂ nanocomposite is attributed to the efficient interfacial charge separation, which was supported by the PL results. Large surface area of MoS₂ nanosheets incorporated with well dispersed Ag₃PO₄ nanoparticles further increases charge separation, contributing to enhanced degradation efficiency. A possible mechanism for charge separation is also discussed.     

Electrical Conductivity and Electrochemical Characteristics of Na<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>-Based NASICON-Type Materials

NASICON-type materials with the compositions Na₃V_2–xAl_x(PO₄)₃, Na₃V_{2 - x}Fe_x(PO₄)₃, Na_{3 + x}V_2–xNi_x(PO₄)₃, and Na₃V_{2 - x}Cr_x(PO₄)₃ (x = 0, 0.03, 0.05, and 0.1) have been prepared and characterized by X-ray diffraction analysis, electron microscopy, and impedance spectroscopy. The results demonstrate that the highest electrical conductivity among the samples studied is offered by the material doped with 5% Fe: Na₃V_1.9Fe_0.1(PO₄)₃. The activation energy for low-temperature conduction in the doped materials decreases from 84 ± 2 to 54 ± 1 kJ/mol and that for high-temperature conduction is ~33 kJ/mol. The discharge capacity of Na₃V_1.9Fe_0.1(PO₄)₃/C under typical working conditions of cathodes of sodium ion batteries has been shown to exceed that of Na₃V₂(PO₄)₃/C. The capacity of the more porous material prepared by the Pechini process (Na₃V_1.9Fe_0.1(PO₄)₃/C-{II}) approaches the theoretical one at a low charge–discharge rate and retains its high level as the charge rate is raised (its discharge capacity was 117.6, 108.8, and 82.6 mAh/g at a discharge rate of 0.1C, 2C, and 8C, respectively).