The development of multivalent ion conductors and their application for chemical sensors

New types of multivalent ion conducting solid electrolytes have been extensively developed and their applications for chemical sensors were investigated. Among the trivalent ion conductors, the highest ion conductivity was realized with the (Al_xZr_1−x)_4/(4−x)Nb(PO₄)₃ solid electrolyte and the value reaches the region between yttria stabilized zirconia (YSZ) and calcia stabilized zirconia (CSZ) of the representative oxide anion conductors. The above described Al³⁺ ion conducting (Al_xZr_1−x)_4/(4−x)Nb(PO₄)₃ solid electrolyte was combined with YSZ, with accompanying the Y₂O₃-KNO₂ solid solution as an auxiliary electrode for nitrogen monoxide (NO) gas sensing. The sensor response was rapid and a reproducible output was continuously observed obeying the Nernst theoretical relationship in a typical NO gas content region in exhaust gases. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15 – 21, 2002.     

Electrical and magnetic properties of [(CoFeZr)x(Al2O3)1 ? x/(α-SiH)]n multilayer structures

The concentration dependences of the electrical resistivity and complex permeability of [“(Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} ”/“α-Si: H”] _n multilayer structures and (Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} composites have been studied. It has been established that introduction of a semiconductor interlayer into the (Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} composites substantially decreases the electrical resistivity of [“(Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} ”/“α-Si: H”] _n multilayer structures. The concentration dependences of the real and imaginary parts of the complex permeability of the [“(Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} ”/“α-Si: H”] _n nanomultilayer structures substantially differ from those of the (Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} composites. The real part of the complex permeability of the [“(Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} ”/“α-Si: H”] _n nanomultilayer structures follows the curve with a minimum near the percolation threshold of the composite, and the imaginary part smoothly decreases as the ferromagnetic phase concentration increases. The results obtained are explained by the increase in the bifurcation temperature due to the conduction electrons of the semiconductor interlayer, which favor magnetic ordering of ferromagnetic grains.     

Sodium superionic conductor sputter-deposited coatings

Thin sodium superionic conductor (Nasicon) coatings are deposited on rotating substrates by co-sputtering in the reactive mode of a Zr-Si and a Na₃PO₄ target. The influence of the discharge current and of the target-to-substrate distance is investigated owing to the targeted Na₃Zr₂Si₂PO₁₂ stoichiometry. A thermo-structural analysis shows that the amorphous as-deposited coating of convenient composition crystallises around 700 °C in the monoclinic structure. Electrical measurements performed at room temperature after various annealing treatments indicate a ionic conductivity of about 2·10⁻³ S·cm⁻¹, consistent with that of bulk Nasicon. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Effect of V5+ in the complex Li3xLa2/3−xTiO3-LaPO4 system

Lithium fast ion conductors of the composition Li_0.3La_2/3Ti_0.7P_0.3−xV_xO_3.3 (LTV) based on mixtures of Li_3xLa_2/3−xTiO₃ and LaPO₄ were prepared by solid state reaction at high temperature (≈ 1300 °C). AC impedance measurements indicate total conductivities of about 1 × 10⁻⁴ Scm⁻¹ for compositions of x=0∼0.3 at room temperature with an activation energy of ≈18 kJ·mol⁻¹ in the temperature range from 30 to 400 °C. X-ray powder diffraction patterns showed that the LTV system is composed of Li_3xLa_2/3−xTiO₃ perovskite solid solution and LaP_1−xV_xO₄ solid solution.     

The effect of LaPO4 in the LixLa2/3Ti1−xPxO3+x system

Lithium ion conductors of the overall composition Li_xLa_2/3Ti_1−xP_xO_3+x (hereafter referred to as LTP) based on La_2/3TiO₃ were prepared by solid state reaction at high temperature (1300 °C). AC impedance measurements indicate that the total conductivities are of the order of 10⁻⁴ S·cm⁻¹ when x=0.28 − 0.35 at room temperature and have an activation energy of 18 kJ·mol⁻¹ in the temperature range from room temperature to 400 °C. X-ray powder diffraction patterns showed that the LTP system has a complex composition, which contains the solid solution perovskite Li_3xLa_2/3−xTiO₃ and LaPO₄.     

New bismuth ion conducting solid electrolyte

A new trivalent bismuth ion conducting solid electrolyte, (Bi_xGe_1 − x)_{4/(4 − x)}Ta(PO₄)₃, was successfully developed by selecting the NASICON-type GeTa(PO₄)₃ as the mother solid. Although bismuth has two kinds of valence states of + 3 and + 5, it was clear that pure trivalent Bi³⁺ ion conduction, without any electronic conduction by a valence change of bismuth in the oxygen pressure range over 10^− 3 Pa, was realized by selecting the crystal structure and constituents of the solid.     

Ionic conductivity in the system Li9−4xZrx〈PO4〉3

Lithium ion conductors of composition Li_9−4xZr_x〈PO₄〉₃ (0.0 < x < 2.0) have been prepared by the conventional solid state reaction and also by a wet chemical method. X-ray diffraction patterns reveal identical crystallographic morphology for the compounds prepared by the two methods. However, they can be prepared and sintered at much lower temperatures by the wet chemical method. Their conductivities are also higher. Compared to pure Li₃PO₄, one of the end member of the series, the conductivity increases sharply with substitution of lithium by zirconium. The highest conductivity has been obtained in the composition Li_1.8Zr_1.8〈PO₄〉₃ (x = 1.8), prepared by the wet chemical method. The conductivity value of 10⁻³ ω⁻¹ cm⁻¹ is obtained at around 225°C with an activation energy of about 0.5 eV.     

The NASICON solid solution Li1−x La x /3Zr2(PO4)3: optimization of the sintering process and ionic conductivity measurements

The Li_1−x La _{x /3}Zr₂(PO₄)₃ NASICON-type compounds (0 ≤ x ≤ 1) have been synthesized in powder form by a sol-gel method and sintered for ionic conductivity measurements. In order to improve the compactness of the ceramic without decomposition of the compound, several sintering processes have been tested for one member of the solid solution (x = 0.6): the use of sintering aids (ZnO, B₂O₃, TiO₂ and LiNO₃), a ball-milling of the synthesized powder, a flash heating, high isostatic pressure, and spark plasma sintering. Finally, a satisfactory compactness of 85% is obtained compared to the referenced value (63%) obtained by uniaxial and isostatic pressing. The ionic conductivity study was performed by impedance spectroscopy. It shows that, despite the formation of vacancies, the substitution Li⁺→ 1/3 La³⁺ + 2/3 □ has unfortunately no influence on the conduction for 0 ≤ x ≤ 0.7 since the ionic conductivity remains identical to the LiZr₂(PO₄)₃ one. For higher x values, the ionic conductivity strongly decreases.     

Solvothermal synthesis of LiCo<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>PO<Subscript>4</Subscript>/C cathode materials for lithium-ion batteries

LiCo_1−x Mn _x PO₄/C cathode materials are selectively synthesized by a solvothermal method in ethylene glycol solvent using glucose, LiCl, H₃PO₄, MnCl₂·4H₂O, and Co(NO₃)₂·6H₂O as precursors. The obtained samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) and the electrochemical performances are also evaluated using a LAND CT2001A battery test system at room temperature. XRD result demonstrates the formation of LiCo_1−x Mn _x PO₄ solid solution and the enlarged channels are benefit for Li⁺ migration. SEM graph indicates that the particle size of LiCo_0.5Mn_0.5PO₄/C is about several hundred nanometers and aggregates to large particles located in the range of 2–3 μm. TEM image illustrates that the core/shell-structured LiCo_0.5Mn_0.5PO₄/C solid solution is indeed obtained by this method. The high specific surface area (35 m²/g) of LiCo_0.5Mn_0.5PO₄/C could make this solid solution contact with the electrolyte more sufficiently and benefit for Li⁺ transportation. The capacity, flat voltage, and cyclical stability of LiCo_1−x Mn _x PO₄/C are improved compared to LiMnPO₄ and LiCoPO₄ due to the improved electronic conductivity and lithium-ion conductivity which resulted from carbon coating and foreign element incorporation.     

The study of lithium fast ion conductors of Li3xLa0.67−xScyTi1−2yNbyO3 system

Perovskite-type lithium fast ion conductors of Li_3xLa_0.67−xSc_yTi_1−2yNb_yO₃ system were prepared by solid state reaction. X-Ray powder diffraction shows that perovskite solid solution form in the ranges of x=0.10, y≤0.10. AC impedance measurements indicate that the bulk conductivities and the total conductivities are of the order of 10⁻⁴ S·cm⁻¹ and 10⁻⁵ S·cm⁻¹ at 25 °C respectively. The compositions have low bulk activation energies of about 17 kJ/mol in the temperature ranges of 298 – 523 K and total activation energies of about 37 kJ/mol in the temperature ranges of 298 – 523 K.     

Ferroelectric phase stabilization, phase transformations and?thermal properties in (1? x )PbZrO3– x Pb(Co1/3Nb2/3)O3 solid solution

The solid solution between the antiferroelectric PbZrO₃ (PZ) and relaxor ferroelectric Pb(Co_1/3Nb_2/3)O₃ (PCoN) was synthesized by the columbite method. The phase structure and thermal properties of (1−x)PZ–xPCoN, where x=0.0–0.3, were investigated. With these data, the ferroelectric phase diagram between PZ and PCoN has been established. The crystal structure data obtained from XRD indicates that the solid solution PZ–PCoN, where x=0.0–0.3, successively transforms from orthorhombic to rhombohedral symmetry with an increase in PCoN concentration. The AFE→FE phase transition was found in the compositions of 0.0≤x≤0.10. The AFE→FE phase transition shift to lower temperatures with higher compositions of x. The width of the temperature range of FE phase was increased with increasing amount of PCoN. It is apparent that the replacement of the Zr⁴⁺ ion by (Co_1/3Nb_2/3)⁴⁺ ions would decrease the driving force for antiparallel shift of Pb²⁺ ions, because they interrupt the translational symmetry. This interruption caused the appearance of a rhombohedral ferroelectric phase when the amount of PCoN was more than 10 mol%.     

A method for determining a solid solution of the Pb(Hf1−yZry)1−xTixO3 type used for electromechanical energy conversion

The mechanical stress-forced Ferroelectric F→Antiferroelectric AF transition energy conversion is reviewed. The temperature-composition phase diagram of PbHf_1−xTi_xO₃+1%La₂O₃ is established. The composition of a suitable material such as a ternary solid solution of the Pb(Hf_1−yZr_y)_1−xTi_xO₃+1%La₂O₃ type, characterized by a low transition pressure, is theoretically determined by a graphic construction using the Goldschmidt factor. Experimental results on the prepared material are given.     

Effect of sintering conditions on the properties of sol-gel-derived Li<Subscript>1.3</Subscript>Al<Subscript>0.3</Subscript>Ti<Subscript>1.7</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Solid electrolyte Li_1.3Al_0.3Ti_1.7(PO₄)₃ was prepared by sol-gel method under different sintering conditions. The structural identification, surface morphology, electrochemical window, ionic conductivity, and activation energy of the Li_1.3Al_0.3Ti_1.7(PO₄)₃ sintered pellets were investigated by X-ray diffraction, scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. It is found that the sintering temperature and time have considerable effect on the properties of the Li_1.3Al_0.3Ti_1.7(PO₄)₃ sintered pellets. The Li_1.3Al_0.3Ti_1.7(PO₄)₃ pellet sintered at 900 °C for 2 h is denser than the pellets sintered at other conditions. Different sintering conditions result in the sintered pellet with different porosity. However, the sintering conditions have little effect on the electrochemical window of Li_1.3Al_0.3Ti_1.7(PO₄)₃. Among the Li_1.3Al_0.3Ti_1.7(PO₄)₃ pellets sintered at various conditions, the pellet sintered at 900 °C for 2 h shows the highest ionic conductivity of 3.46 × 10⁻⁴ S cm⁻¹ and the lowest activation energy of 0.2821 eV.     

Optical characterization in Pb(Zr1?xTix)1?yNbyO3 ferroelectric ceramic system

In this work, visible photoluminescence was observed at room temperature in a sintered Pb(Zr_1-xTi_x)_1-y Nb_yO₃\mathrm{Pb}(\mathrm{Zr}_{1-x}\mathrm{Ti}_{x})_{1-y} \mathrm{Nb}_{y}\mathrm{O}_{3} perovskite-type structure system, doped with Nb using the next excitation bands 325, 373 and 457 nm. The intensity and energy of such emissions have been studied by changing the Nb concentration (0<y<0.01) and the Ti content (x), with x=0.20,0.40,0.53,0.60 and 0.80, on both sides of the morphotropic phase boundary (MPB) zone. The principal bands become visible at energies of 1.73, 2.56 and 3.35 eV. The results reveal the role of the Nb⁵⁺ ion substitutions by Zr⁴⁺ or Ti⁴⁺ ions and the symmetry presented in the rhombohedral or tetragonal side of the MPB. Raman spectra which are similar for compositions: 20/80, 40/60 and 53/47 (tetragonal phases) show nine bands, centered around 137, 194, 269, 331, 434, 550, 612, 712 and 750 cm⁻¹. The spectra for samples 60/40 and 80/20, rhombohedral phase, show significant differences, only six bands appear, centered around 124, 209, 234, 330, 549 and 682 cm⁻¹. In addition, optical absorption spectroscopy, structural and micro-structural measurements were carried out by using Uv-vis spectroscopy, X-ray diffraction and scanning electron microscopy techniques, respectively. The experimental results of band gap energy, e.g., in our samples are in accordance with the findings by J. Baedi et al. in the calculations of band structure, energy gap and density of states for different phases of Pb(Zr_1−x Ti _x )O₃ using density functional theory (DFT).     

The effect of the sputtering process ambient on the magnetic state and phase composition of the film nanocomposites (Fe0.45Co0.45Zr0.10) x (Al2O3)1−x

The effect of oxygen-containing ambient arising at sputtering of granular nanocomposites (Fe_0.45Co_0.45Zr_0.10) _x (Al₂O₃)_1−x (30 at.%≤x≤65 at.%) on their magnetic state and phase composition has been investigated. It was shown that the presence of oxygen resulted in the formation of oxide shells preventing the ferromagnetic interaction between Co_0.45Fe_0.45Zr_0.10 nanoparticles and also the formation of metallic percolative net beyond the percolation threshold (as opposed to the films prepared in pure argon atmosphere).     

Progress in the lithium insertion mechanism in Cu3P

Copper phosphide, Cu₃P has been synthesized using a ceramic route, and its electrochemical behaviour versus lithium has been studied studied galvanostatic and potentiodynamic measurements and in situ X-ray diffraction analysis. The insertion/extraction mechanism proceeds with the formation of at least three different Li_xCu_3−xP (x=1, 2, 3) phases. The electrochemical behaviour of Cu₃P samples obtained from ceramic and solvothermal syntheses are compared to further understanding of the complex redox mechanism occurring during insertion/extraction. First-principle electronic structure calculations show that discharge probably begins with the formation of a solid solution Li_xCu_3−yP (x<0.5). Paper presented at the Patras Conference on Solid State Ionics-Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

The nature of conduction pathways in mixed alkali phosphate glasses

In this paper we discuss the nature of the ion conduction pathways in Li_xRb_1−xPO₃ glasses. Our investigations are based on a bond valence analysis of reverse Monte Carlo (RMC) produced structural models in quantitative agreement with neutron and X-ray diffraction data. In a previous letter [11] we have shown that this approach enables us to reproduce and understand the mixed alkali effect (MAE) directly from the structural models. The results have shown that the drastic drop of the conductivity for an intermediate composition (x ≈ 0.5) is mainly caused due to the blocking by immobile unlike cations, which is highly effective since the two types of alkali ions are randomly mixed and have distinctly different conduction pathways of low dimensionality. Here, we explore the local dimensionality of the pathways and discuss its implications for the network of pathways and the related ionic conductivity. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Effects of niobium on thermal stability and corrosion behavior of glassy Cu-Zr-Al-Nb alloys

The corrosion behavior of Cu_95−xZr_xAl₅ (x=40, 42.5 and 45 at.%) in 1 N HCl, 3 mass% NaCl and 1 N H₂SO₄ solutions was studied. As Zr content increases, the corrosion resistance is slightly enhanced. In order to improve the corrosion resistance of the Cu-Zr-Al glassy alloy, Nb was selected to substitute Cu. Although the supercooled liquid region ΔT_x of the Cu-Zr-Al glassy alloys decreases with increasing Nb content, the alloys still retain high glass-forming ability and bulk glassy samples with 1.5 mm diameter can be obtained when up to 5 at.% Nb was added. It is found that the addition of Nb results in improvement of the corrosion resistance of the glassy Cu-Zr-Al alloys.     

Features of the behavior of longitudinal static and dynamic dielectric, piezoelectric, and elastic characteristics of KH2PO4 and NH4H2PO4 crystals

Along with their electromechanical coupling coefficients, the longitudinal dielectric, piezoelectric and elastic characteristics in ferroelectric KH₂PO₄ and antiferroelectric NH₄H₂PO₄ crystals are calculated using a modified proton ordering model that considers piezoelectric coupling and the four-particle cluster approximation. The possibility of detecting piezoactivity in solid solutions of K_{1 − x} (NH₄)xH₂PO₄ is substantiated.