Electrical properties and thermal expansion of cobalt doped apatite-type lanthanum silicates based electrolytes for IT-SOFC

The thermal expansion and conductivities have been investigated for Co³⁺ doped lanthanum silicates. The apatite-type lanthanum silicates with formula La₁₀Si_6?xCo_xO_27?x/2 (x = 0.2, 0.4, 0.6, 0.8, 1.0, 1.5) were synthesized by sol–gel process. The thermal expansion coefficient (TEC) of La₁₀Si_6?xCo_xO_27?x/2 was improved with increasing cobalt content because of the lower valence and larger radius of Co³⁺ ion compared to Si⁴⁺. Analysis of AC impedance spectroscopy showed that conductivity increased first and then decreased with increasing cobalt content. There is an optimum doping amount of cobalt and La₁₀Si_5.2Co_0.8O_26.6 exhibits the highest conductivity of 3.33 × 10^?2 S/cm at 800 °C. When x ≤ 0.8, the local distortion caused by doping with Co³⁺ can significantly affect the oxygen channels and assist the migration of the interstitial oxide ions, resulting in the improvement of ionic conductivity. However, excess Co³⁺ dopant (0.8 < x ≤ 1.5) reduced the number of interstitial oxide ions and decreased the conductivity.     

Lithium solubility limit in ZnGa2O4:Bi0.0013+,Li+ phosphor

The lithium solubility limit, photoluminescence (PL) and photoluminescence excitation (PLE) properties of lithium ion co-activated ZnGa₂O₄:Bi³⁺,Li⁺ phosphor have been investigated. A LiGaO₂ second phase began to appear from 3 mol% Li⁺ ion co-activated ZnGa₂O₄:Bi³⁺,Li⁺ phosphor. The enhanced brightness of blue (λ_ex = 254 nm) and white (λ_ex = 315 nm) colors of bismuth ions doped ZnGa₂O₄:Bi³⁺,Li⁺ phosphor was assigned to the formation of LiGaO₂. Bi³⁺ activated lithium zinc gallate phosphor showed a more enhanced PLE peak around 315 nm than that of lithium zinc gallate phosphor when λ_em = 520 nm. Thus, we observed that the PL intensity of ZnGa₂O₄:Bi³⁺,Li⁺ phosphor with λ_em = 520 nm was much greater than that of ZnGa₂O₄:Li⁺ phosphor. Also, ZnGa₂O₄:Bi³⁺,Li⁺ phosphor exhibited a shorter decay time than that of ZnGa₂O₄:Li⁺ phosphor by about a factor of about 2.     

Structural and electrochemical characterization of layered 0.3Li2MnO3·0.7LiMn0.35−x/3Ni0.5−x/3Co0.15−x/3CrxO2 cathode synthesized by spray drying

Cr doped 0.3Li₂MnO₃·0.7LiMn_0.35−x/3Ni_0.5−x/3Co_0.15−x/3Cr_xO₂ (x = 0, 0.02, 0.04, 0.06) as a cathode material for Li-ion battery has been successfully synthesized by spray drying and subsequent calcination. The effects of Cr dopant on the structural and electrochemical properties of this material have been investigated by XRD, SEM, EDS, charge–discharge measurements, Ac impedance spectroscopy as well as cyclic voltammetry. These results demonstrated that the element Cr distributed uniformly in these materials. With the Cr content increasing, lattice parameters a and c decrease and less Li ion locates in transition metal site. Among the synthesized Cr-doped materials, when x = 0.04, this material shows the best electrochemical properties. Between 2.5 and 4.8 V (vs. Li/Li⁺), the initial discharge capacities of the materials increased from 143 to 168 mA h g⁻¹ at a constant current density of 250 mA g⁻¹. After 50 cycles, the capacity retention of the materials raised from 83% to 93%.     

Investigation of La3 + Doped Yb2Sn2O7 as new thermal barrier materials

Low thermal conductivity is one of the key requirements for thermal barrier coating materials. From the consideration of crystal structure and ion radius, La^3 + Doped Yb₂Sn₂O₇ ceramics with pyrochlore crystal structures were synthesized by sol–gel method as candidates of thermal barrier materials in aero-engines. As La^3 + and Yb^3 + ions have the largest radius difference in lanthanoid group, La^3 + ions were expected to produce significant disorders by replacing Yb^3 + ions in cation layers of Yb₂Sn₂O₇. Both experimental and computational phase analyses were carried out, and good agreement had been obtained. The lattice constants of solid solution (La_xYb_1 − x)₂Sn₂O₇ (x = 0.3, 0.5, 0.7) increased linearly when the content of La^3 + was increased. The thermal properties (thermal conductivity and coefficients of thermal expansion) of the synthesized materials had been compared with traditional 8 wt.% yttria stabilized zirconia (8YSZ) and La₂Zr₂O₇ (LZ). It was found that La^3 + Doped Yb₂Sn₂O₇ exhibited lower thermal conductivities than un-doped stannates. Amongst all compositions studied, (La_0.5Yb_0.5)₂Sn₂O₇ exhibited the lowest thermal conductivity (0.851 W·m^− 1·K^− 1 at room temperature), which was much lower than that of 8YSZ (1.353 W·m^− 1·K^− 1), and possessed a high coefficient of thermal expansion (CTE), 13.530 × 10^− 6 K^− 1 at 950 °C.     

Experimental study of the crystal structure of the Mg15 − xZnxSr3 ternary solid solution in the Mg–Zn–Sr system at 300 °C

A new ternary compound, Mg_15 − xZn_xSr₃ with extensive solid solubility in the Mg–Zn–Sr system was observed and studied using electron probe microanalysis (EPMA), scanning electron microscopy SEM, and X-ray techniques. The solid solubility limits of this compound were found to be Mg_15 − xZn_xSr₃ (0.24 ≤ x ≤ 10.58, at.%) at 300 °C using a diffusion couple and several equilibrated alloys. Analysis of the X-ray diffraction (XRD) patterns was carried out by Rietveld method. XRD data has shown that this solid solution crystallizes in the hexagonal P6₃/mmc (194) space group with the Ni₁₁Si₄Sc₃ prototype. The lattice parameters decrease linearly with decreasing Mg content indicating substitutional solid solubility. The fractional atomic occupancy of the 6h, 6g, 4f, 2b and 12k sites of this compound are function of Mg content.     

Thermoelectric and magnetic properties of Ca3Co4–xCuxO9 + δ with x = 0.00, 0.05, 0.07, 0.10 and 0.15

Ca₃Co_4–xCu_xO_9 + δ (x = 0.00, 0.05, 0.07, 0.10 and 0.15) samples were prepared by conventional solid-state synthesis and their thermoelectric properties were systematically investigated. The thermopower of all the samples was positive, indicating that the predominant carriers are holes over the entire temperature range. Ca₃Co_3.85Cu_0.15O_9 + δ had the highest power factor of 2.17 μW cm⁻¹ K⁻² at 141 K, representing an improvement of about 64.4% compared to undoped Ca₃Co₄O_9 + δ. Magnetization measurements indicated that all the samples exhibit a low-spin state of cobalt ions. The observed effective magnetic moments decreased with increasing copper content.     

The magnetocaloric effect in (Gd0.74Tb0.26)5(SixGe1−x)4 alloys

The magnetic phase transition and magnetocaloric effect of the alloys of Gd_0.74Tb_0.26 and (Gd_0.74Tb_0.26)₅(Si_xGe_1−x)₄ (x = 0.43, 0.50, 0.505) have been investigated by magnetization measurement. Experimental results show that partial substitution of the Gd by Tb in Gd₅(Si_xGe_1−x)₄ system keeps the first order magnetic transition. Although the values of transition temperature decrease, the as-cast (Gd_0.74Tb_0.26)₅(Si_0.43Ge_0.57)₄ and annealed (Gd_0.74Tb_0.26)₅(Si_0.50Ge_0.50)₄ alloys display large magnetic entropy change up to 18.89 J kg^− 1 K^− 1 and 13.79 J kg^− 1 K^− 1 near their transition temperatures in the low magnetic field change of 0–2.0 T, respectively.     

Preparation and characterization of Ruthenium doped Li4Ti5O12 anode material for the enhancement of rate capability and cyclic stability

Li₄Ti₅O₁₂ and Ru-doped Li₄Ti₅O₁₂ with the formulation of Li₄Ti_4.99Ru_0.01O₁₂ were prepared by a modified solid-state method. The structure and electrochemical properties of the as-prepared powders were systematically investigated. Li₄Ti_4.99Ru_0.01O₁₂ exhibited an excellent rate capability with a discharge capacity of 146 mAhg^? 1 at 1 C, 126 mAhg^? 1 at 5 C, 119 mAhg^? 1 at 10 C and even 107 mAhg^? 1 at 20 C. Electrochemical impedance spectra (EIS) reveal that the Li₄Ti_4.99Ru_0.01O₁₂ exhibited the improved electronic conductivity and higher lithium-ion diffusivity than that of Li₄Ti₅O₁₂. The novel Li₄Ti_4.99Ru_0.01O₁₂ material stands as a promising potentially high rate anode material for the lithium ion batteries.     

Spectroscopic investigations on Eu3+ ions in Li–K–Zn fluorotellurite glasses

Eu³⁺ ions incorporated Li–K–Zn fluorotellurite glasses, (70 − x)TeO₂ + 10Li₂O + 10K₂O + 10ZnF₂ + xEu₂O₃, (0 ⩽ x ⩽ 2 mol%) were prepared via melt quenching technique. Optical absorption from ⁷F₀ and ⁷F₁ levels of the Eu³⁺-doped glass has been studied to examine the covalent bonding characteristics, energy band gap and Judd–Ofelt intensity parameters. The emission spectra (⁵D₀ → ⁷F_0,1,2,3,4) of the glasses were used to estimate the luminescence enhancement, asymmetric environment in the vicinity of Eu³⁺ ions, stimulated emission cross section and branching ratios. The phonon side band mechanism of ⁵D₂ level of the Eu³⁺ ions in the prepared glass was examined by considering the excitation and Raman spectra. The radiative lifetime calculated using Judd–Ofelt parameters was compared with the experimental lifetime to estimate the quantum efficiency of ⁵D₀ level of Eu³⁺ ions in Li–K–Zn fluorotellurite glass.     

Synthesis and crystal structure of tetramethylammonium fluoride octadecasil

Octadecasil, a clathrate-type inclusion compound, has been synthesized hydrothermally at 453 K with a gel having the composition 1.0SiO₂:0.53tetramethylammonium (TMA⁺):0.54fluoride:86H₂O. The crystal structure has been determined based on powder X-ray diffraction data taken at 298 K, and has been refined using Rietveld method. The result confirms the AST-type, all-silica framework model developed by Caullet et al. [P. Caullet, J.L. Guth, J. Hazm, J.M. Lamblin, H. Gies, Eur. J. Solid State Inorg. Chem. 28 (1991) 345]. Furthermore, by using a rigid body model the position and orientation of the occluded TMA⁺ cation in the rhombododecahedral [4⁶6¹²] cage can be determined; F⁻ anion has been located in the hexahedral [4⁶] cage. The unit cell parameters, in the tetragonal space group I4/m, have been refined as: a = b = 9.07 Å, c = 13.44 Å, cell volume = 1104.97 Å³. The refined unit cell composition is |[N(CH₃)₄⁺]_2.0F⁻_1.9|[Si₂₀O₄₀], i.e., both TMA⁺ and F⁻ ions possess near full occupancies, and compensate each other's electronic charges. The crystallization of the AST framework structure is the result of a cooperative structure-directing effect of both ions.     

Synthesis,spectral character,electrochemical performance and in situ structure studies of Li1+xV3O8 cathode material prepared by tartaric acid assisted sol–gel process

Lithium-ion battery cathode material Li_1+xV₃O₈ was synthesized by a tartaric acid assisted sol–gel method and thermally treated at 350 °C, 450 °C and 550 °C for 3 h for the formation of Li_1+xV₃O₈ phase. The synthesized samples were fully characterized by FTIR, TG/DTA, XRD and charge–discharge tests. Li_1+xV₃O₈ material synthesized by tartaric acid assisted route, followed by heat treatment at 450 °C for 3 h shows best electro-chemical performance. It shows a high initial capacity of 249 mAh g^?1 and still reserves a discharge capacity of 260 mAh g^?1 after 50 cycles. Moreover, for all tartaric assisted products, no capacity decadence is observed in 50 cycles. The in situ X-ray measurements reveal a two-phase transition mechanism in the lithium intercalation/deintercalation process. During lithium extraction, the structure of the delithiated compound changes from Li₄V₃O₈ (x > 3.1) to the original LiV₃O₈ phase (x < 1.4) via the coexistence state of these two phases (1.4 < x < 3.2). An obvious contraction, especially at Li(3)–Li(4) transition, along a axis and a slight expansion along b axis are also observed.     

Microwave-induced combustion synthesis of Li0.5Fe2.5−xCrxO4 powder and their characterization

Li_0.5Fe_2.5−xCr_xO₄ (0 ≦ x ≦ 1.0) powders with small and uniformly sized particles were successfully synthesized by microwave-induced combustion, using lithium nitrate, iron nitrate, chromium nitrate, and carbohydrazide as the starting materials. The process takes only a few minutes to obtain as-received Cr-substituted lithium ferrite powders. The resultant powders annealed at 650 °C for 2 h and were investigated by thermogravimeter/differential thermal analyzer (TG/DTA), X-ray diffractometer (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and thermomagnetic analysis (TMA). The results revealed that the lattice constant decreases linearly with increasing of Cr content in Li_0.5Fe_2.5−xCr_xO₄ specimens. Moreover, the magnetic properties of Cr-substituted lithium ferrite were also strongly affected by Cr content. The saturation magnetization, remanent magnetization, and coercive force decrease monotonously with increasing of Cr content.     

From Bi4V2O11 to Li28Bi4V2O11 by electrochemical lithium insertion:: versatile applications in lithium batteries

The compound Bi₄V₂O₁₁ has been tested as a positive electrode in room temperature electrochemical lithium cells. When the cells are discharged down to 0.5 V the reaction of Bi₄V₂O₁₁ with 28 lithium ions develops a theoretical specific capacity of 700 A h kg⁻¹. Hence, this compound could be used as cathode in primary lithium batteries. Besides, we consider the fact that in the low voltage region (1.3–0.5 V) Li₂₈Bi₄V₂O₁₁ develops about 360 A h kg⁻¹ at 0.7 V, and, therefore, this material is proposed as a negative electrode in lithium ion batteries. The mechanism of the reaction of Bi₄V₂O₁₁ with 28 lithium ions is not yet fully understood, although some guidelines can be given.     

Synthesis and properties of Ce1−xGdxO2−x/2 solid solution prepared by flame spray pyrolysis

Flame spray pyrolysis, which produces ultrafine particles, was applied to the synthesis of Ce_1−xGd_xO_2−x/2 solid solutions by substituting Gd from a mole fraction of 0–0.40. The solubility limit of Gd in the Ce_1−xGd_xO_2−x/2 solid solution produced by flame spray pyrolysis was between 0.25 and 0.30, which is consistent with the reported value. The as-prepared Ce_1−xGd_xO_2−x/2 particles had a square morphology and a nanometer range in the equivalent diameter. The small particle size made it possible to reduce the sintering temperature of the Ce_1−xGd_xO_2−x/2 solid solution from 1650 °C to 1400 °C for the ceria-based solid electrolytes produced by the solid state preparation. The maximum ionic conductivity was achieved when the mole fraction of Gd was 0.25. The mole fraction for the highest ionic conductivity was the same as the particles produced by hydrothermal synthesis. However, the ionic conductivity of the Ce_1−xGd_xO_2−x/2 prepared by the flame spray pyrolysis (1.01 × 10⁻² S/cm at 600 °C) was higher than that prepared by the hydrothermal synthesis (7.53 × 10⁻³ S/cm at 600 °C).     

Influence of Ga3+ ions on spectroscopic and dielectric features of multi component lithium lead boro bismuth silicate glasses doped with manganese ions

Multi-component glasses of the chemical composition 19.5Li₂O–20PbO–20B₂O₃–30SiO–(10 − x)Bi₂O₃–0.5MnO:xGa₂O₃ with 0 ≤ x ≤ 5.0 have been synthesized. Spectroscopic (optical absorption, IR, Raman and ESR) and dielectric properties were investigated. Optical absorption and ESR spectral studies have indicated that managanese ions do exist in Mn³⁺ state in addition to Mn²⁺ state in the samples containing low concentration of Ga₂O₃. The IR and Raman studies indicated increasing degree of disorder in the glass network with the concentration of Ga₂O₃ up to 3.0 mol%. The dielectric constant, loss and ac conductivity are observed to increase with the concentration of Ga₂O₃ up to 3.0 mol%. The quantitative analysis of the results of dielectric properties has indicated an increase in the insulating strength of the glasses as the concentration of Ga₂O₃ is raised beyond 3.0 mol%. This has been attributed to adaption of gallium ions from octahedral to tetrahedral coordination.     

Li4Ti5O12/Li3SbO4/C composite anode for high rate lithium-ion batteries

Nanocrystalline Li₄Ti₅O₁₂/Li₃SbO₄/C composite-prepared by mechanical ball-milling of Li₄Ti₅O₁₂ (synthesized by aqueous combustion), Li₃SbO₄ (synthesized by solid state method) and activated carbon, has been investigated as anode in lithium-ion coin cells and compared to pristine Li₄Ti₅O₁₂. Galvanostatic charge–discharge measurements in the potential window of 0.05–2.0 V show three plateau regions corresponding to Li insertion/extraction in the composite: a large flat plateau at ~ 1.52/1.59 V, followed by a second plateau at ~ 0.75/1.1 V and a sloppy tail at ~ 0.4/0.6 V. While the plateaus at ~ 0.4/0.6 V and ~ 1.52/1.59 V correspond to Li₄Ti₅O₁₂, the other one at ~ 0.75/1.1 V corresponds to Li₃SbO₄. At a high rate of ~ 15 C, the capacity for Li₄Ti₅O₁₂/Li₃SbO₄/C composite is found to be 105 mAhg^?1 retaining ~ 78% of its initial capacity compared to only 58 mAhg^?1 (~ 27% of the initial capacity) at 14 C for pristine Li₄Ti₅O₁₂ up to 100 cycles. Thus, such composite material might find application in lithium-ion batteries requiring high rate of charge and discharge.     

Physical and optical properties of Co2+, Ni2+ doped 20ZnO + xLi2O + (30 − x)K2O + 50B2O3 (5 ≤ x ≤ 25) glasses: Observation of mixed alkali effect

Co²⁺ and Ni²⁺ ions doped 20ZnO + xLi₂O + (30 ? x) K₂O + 50B₂O₃ (5 ≤ x ≤ 25) mol% glasses are prepared using melt quenching technique. Structural changes of the prepared glasses by addition of transition metal oxides, CoO and NiO are investigated by UV–vis–NIR, FT-IR spectroscopy and XRD. The XRD pattern indicates the amorphous nature of prepared glasses. FT-IR measurements of the all glasses revealed that the network structure of the glasses are mainly based on BO₃ and BO₄ units placed in different structural groups in which the BO₃ units being dominant. The optical absorption spectra suggest the site symmetry of Co²⁺ and Ni²⁺ ions in the glasses are near octahedral. Crystal field and inter-electronic repulsion parameters are also evaluated. The optical band gap and Urbach energies exhibited the mixed alkali effect. Various physical parameters such as density, refractive index, optical dielectric constant, polaron radius, electronic polarizability and inter-ionic distance are also determined.     

Effects of SrTiO3 on dielectric and piezoelectric properties of K0.48Na0.48Li0.04Nb0.96Ta0.04O3-based piezoceramics

In this study, (100 ? x) K_0.48Na_0.48Li_0.04Nb_0.96Ta_0.04O₃ ? xSrTiO₃ (0 ≤ x ≤ 10) ceramics were fabricated via normal sintering of synthesized powder by using solid state reaction. All ceramics revealed pure perovskite structure, indicating formation of solid solution between KNNLT and ST up to 10%. With increasing x, the crystal structure of ceramics changed from orthorhombic to tetragonal and finally pseudocubic symmetry when x = 10. Ceramic containing 1% ST had orthorhombic and tetragonal symmetries, simultaneously. Investigation of the variation of dielectric constant of ceramics versus temperature revealed that for ceramic with x = 1, polymorphic phase transition (PPT) temperature between orthorhombic and tetragonal is less than room temperature. Thus coexistence of two different structures in this ceramic is due to vicinity of its composition to morphotropic phase boundary (MPB). As a result, the maximum piezoelectric constant was measured for this ceramic. Ceramics containing 5 and 7.5% ST tend to appear relaxor ferroelectric behavior which is because of chemical inhomogeneities in both A- and B-sites of the ABO₃ perovskite structure.     

Structure and microwave dielectric characteristics of lithium-excess Ca0.6Nd0.8/3TiO3/(Li0.5Nd0.5)TiO3 ceramics

Compositions based on (1−x)Ca_0.6Nd_8/3TiO₃−x(Li_1/2Nd_1/2)TiO₃ + yLi (CNLNTx + yLi, x = 0.30–0.60, y = 0–0.05), suitable for microwave applications have been developed by systematically adding excess lithium in order to tune the microwave dielectric properties and lower sintering temperature. Addition of 0.03 excess-Li simultaneously reduced the sintering temperature and improved the relative density of sintered CNLNTx ceramics. The excess Li addition can compensate the evaporation of Li during sintering process and decrease the secondary phase content. The CNLNTx (x = 0.45) ceramics with 0.03 Li excess sintered at 1190 °C have single phase orthorhombic perovskite structure, together with the optimum combination of microwave dielectric properties of ɛ_r = 129, Q × f = 3600 GHz, τ_f = 38 ppm/°C. Obviously, excess-Li addition can efficiently decrease the sintering temperature and improve the microwave dielectric properties. The high permittivity and relatively low sintering temperatures of lithium-excess Ca_0.6Nd_0.8/3TiO₃/(Li_0.5Nd_0.5)TiO₃ ceramics are ideal for the development of low cost ultra-small dielectric loaded antenna.     

Perovskite phase stabilization and dielectric properties of Pb(Zn1/3Ta2/3)O3–BaTiO3 ceramics

The phase structure and dielectric properties of (1 − x)Pb(Zn_1/3Ta_2/3)O₃–xBaTiO₃ (x = 0.00–0.40) ceramics were investigated. Pure perovskite is obtained when x ≥ 0.24. With increasing BT content, the diffuse phase transition and frequency dissipation of the dielectric constant increase and the dielectric maxima temperature decreases. It is related to the existing of Ba(Zn_1/3Ta_2/3)O₃ paraelectric microregions and the incomplete solid solution reaction between Pb(Zn_1/3Ta_2/3)O₃ and BaTiO₃.