Structural,optical and morphological properties of La,Cu co-doped SnO2 nanocrystals by co-precipitation method

Sn_0.96−xLa_0.04Cu_xO₂ (0 ⩽ x ⩽ 0.03) nanocrystals have been successfully synthesized by employing a simple co-precipitation method. The crystal structure of the synthesized nanocrystals was found to be tetragonal rutile of tin oxide by using X-ray diffraction technique and was not affected by doping. The change in lattice parameters was discussed based on the secondary phase formation and presence of Cu²⁺/Cu³⁺ in LaSnO₂ lattice. The variation in size and shape of the nanocrystals by Cu-doping was discussed using scanning electron microscope. The chemical stoichiometry of Sn, Cu, La and O was confirmed by energy dispersive X-ray spectra. The best optical transparency and lower absorption observed at Sn_0.97La_0.02Cu_0.01O₂ nanocrystals seems to be optimal for industrial applications especially as transparent electrode. The initial blue shift of energy gap from 3.65 eV (Cu = 0%) to 3.78 eV (Cu = 1%) (ΔE_g ≈ 0.13 eV) is due to the distortion in the crystal structure of the host compound and generation of defects. The red shift of energy gap after Cu = 1% is due to the charge-transfer transitions between the metal ions d-electrons and the SnO₂ conduction or valence band. Lattice mode of SnO₂ at 686 cm⁻¹ in Sn_0.98La_0.02O₂ nanocrystals and anti-symmetric SnOSn stretching mode of the surface bridging oxide around 634–642 cm⁻¹ in Cu doped Sn_0.98La_0.02O₂ nanocrystals was confirmed by Fourier transform infrared spectra.     

Synthesis of green-emitting (Gd,La, Tb)2O(WO4)2 phosphors

Green-emitting (Gd_1−x−yLa_xTb_y)₂O(WO₄)₂ (0 ⩽ x ⩽ 0.05, 0.05 ⩽ y ⩽ 0.15) phosphors were synthesized in a single phase form by the conventional solid-state reaction method, and their photoluminescent properties were characterized. The (Gd_1−x−yLa_xTb_y)₂O(WO₄)₂ phosphors showed strong and broad excitation bands from 230 to 350 nm, corresponding to the energy transition from the 4f⁸ to 4f⁷5d configuration of Tb³⁺ and the charge-transfer (CT) transition of O²⁻−W⁶⁺. The oxytungstate phosphors exhibited typical emission peaks assigned to the transition from ⁵D₄ to ⁷F_J (J = 6, 5, 4, and 3) of Tb³⁺, and the luminescence emission intensity was effectively enhanced by the La³⁺ doping into the host Gd₂O(WO₄)₂ lattice. The highest green emission intensity was obtained for (Gd_0.87La_0.03Tb_0.10)₂O(WO₄)₂, where the relative emission intensity was 63% that of a commercial green-emitting (La_0.52Ce_0.31Tb_0.17)PO₄ phosphor.     

Investigation of the localized oxide ion interstitials of PbWO4-based oxide ion conductors by means of impedance spectroscopy

Impedance spectra were measured for two types of lanthanum-substituted PbWO₄ systems (Pb_1 − xLa_2x/3WO₄ and Pb_1 − xLa_xWO_4 + x/2), from which the relaxation phenomena associated with oxide ion conduction were investigated. Profiles of the imaginary part of the electric modulus normalized at the peak position were not essentially varied with temperature or composition for Pb_1 − xLa_2x/3WO₄ system, whereas broadening of the modulus peak was observed for Pb_1 − xLa_xWO_4 + x/2 system. We attributed this broadening to the localization of oxide ion interstitials since it appeared only for the latter system and the peak broadening grew larger with decreasing temperature.     

Preparation,structure and electrical conductivity of pyrochlore-type samarium–lanthanum zirconate ceramics

A series of zirconate compounds with the general formula Sm_2–xLa_xZr₂O₇ (0 ? x ? 1.0) were prepared by pressureless-sintering method at 1973 K for 10 h in air. The relative density, structure and electrical conductivity of Sm_2–xLa_xZr₂O₇ ceramics were investigated by the Archimedes method, X-ray diffraction and impedance spectroscopy measurements. Sm_2–xLa_xZr₂O₇ (0 ? x ? 1.0) ceramics exhibit a pyrochlore-type structure. The measured electrical conductivity of Sm_2–xLa_xZr₂O₇ ceramics obeys the Arrhenius relation and gradually increases with increasing temperature from 673 to 1173 K. Sm_2–xLa_xZr₂O₇ ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10^?4 to 1.0 atm at all test temperature levels. The electrical conductivity of Sm_2–xLa_xZr₂O₇ ceramics decreases with increasing lanthanum content at identical temperature levels.     

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.     

Phase relations and high temperature-XRD studies of Gd2−xNdxTi2O7 solid solutions

A series of compositions with the general formula Gd_2−xNd_xTi₂O₇ (0.0 ≤ x ≤ 2.0) was prepared by ceramic sintering and characterized by powder XRD. Nd³⁺ has been used as a surrogate for Am³⁺, an actinide found in spent nuclear fuel. One end member, Gd₂Ti₂O₇, had the pyrochlore structure and formed solid solutions with Nd₂Ti₂O₇ up to the nominal composition Gd_1.2Nd_0.8Ti₂O₇. An increase in lattice parameter was observed as a function of x in the series Gd_2−xNd_xTi₂O₇ in the composition range 0.0 ≤ x ≤ 0.8. Compositions Gd_2−xNd_xTi₂O₇ in the range 0.8 ≤ x ≤ 1.4 were biphasic. From x ≥ 1.6, the solid solutions are monoclinic, isotypic with Nd₂Ti₂O_7. These results were explained based on the radius (r_A/r_B) ratio of the cations. High temperature-XRD studies on cubic pyrochlores showing thermal expansion are reported.     

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.     

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.     

Cation distribution in the Bi4 − xRExTi3O12 (RE = La,Nd) solid solution and Curie temperature dependence

Bi_4 ? xRE_xTi₃O₁₂ (RE = La, Nd) ferroelectric powders were prepared by a co-precipitation route. Raman spectroscopy and X-ray diffraction were employed to determine the crystal site of La³⁺ and Nd³⁺ as well as the effect of their addition on the crystal structure. It was found that La atoms were not only placed preferentially in pseudo-perovskite A sites for concentrations x ≤ 1.2 but also substituted for Bi³⁺ in (Bi₂O₂)^2 + layers for greater concentrations. A similar behavior was observed with the limit value x = 0.8 in case of Nd³⁺. In solid solution La or Nd³⁺ ions diminish the distortions in the octahedron formed by oxygen atoms, so there is a tendency to undergo a transition in crystal symmetry from orthorhombic to tetragonal. Finally differential scanning calorimetry (DSC) shows a linear dependence of the Curie temperature (T_c) when the amount of La³⁺ or Nd³⁺ was increased.     

Effects of interstitial Li+ ions on the properties of novel Li4.08Zn0.04Si0.96O4 ceramic electrolyte

The aim of this work was to investigate the effects of interstitial ions in the novel Li_4 + 2xZn_xSi_1 − xO₄ (x = 0.04) compound prepared via sol gel method. The compound was indexed to the monoclinic unit cell in the space group P2_1/m and the chemical composition of the compound was very close to the designed composition. The introduction of two interstitial Li⁺ ions increased charge carrier concentration in the doped system resulting in an enhancement of conductivity by an order of magnitude as compared to that of the parent compound, Li₄SiO₄. The compound of Li_4.08Zn_0.04Si_0.96O₄ exhibited total conductivity values of 2.51 × 10^− 5 S cm^− 1 at ambient temperature and 3.01 × 10^− 3 S cm^− 1 at 500 °C. Ionic transference number corresponding to Li⁺ ion transport was also found to be higher than the value obtained for the parent compound. This proved that interstitial Li⁺ ions contributed to the total conductivity in the sample. Linear sweep voltammetry result showed that the Li_4.08Zn_0.04Si_0.96O₄ ceramic electrolyte was electrochemically stable up to 5.80 V versus a Li/Li⁺ reference electrode.     

Electrical conductivity of LaxSr2−xFe1−yRuyO4±δ

Materials of the K₂NiF₄ structure type have been prepared and the electrical conductivity in air determined for a number of compositions in the La_xSr_2−xFe_1−yRu_yO_4±δ solid solution series including three with Ru substituted for Fe on the B site: La_0.2Sr_1.8Fe_0.6Ru_0.4O_4±δ, La_0.4Sr_1.6Fe_0.7Ru_0.3O_4±δ, and La_0.6Sr_1.4Fe_0.8Ru_0.2O_4±δ. Overall the total conductivity values measured were lower than expected for the Ru-doped materials, with a peak conductivity of ≈2 S cm⁻¹ at 700 °C. In the undoped La_xSr_2−xFeO_4±δ materials, a significant jump in conductivity was observed between the x = 0.7 and 0.8 compositions and was related to the bonding in the materials and the Fe³⁺/Fe⁴⁺ redox behaviour. In all materials, the conduction behaviour was found to follow a semi-conducting trend.     

La and Co substituted M-type barium ferrites processed by sol–gel combustion synthesis

The flake-like Ba_1−xLa_xCo_xFe_12−xO₁₉ (x = 0.0–0.4) were synthesized using sol–gel combustion synthesis process followed by the thermal insulation process and heating treatment. The synthesis process was investigated and the structure details, morphology, and magnetic properties were evaluated. TG/DTA was used to investigate the formation mechanism and to identify the thermal insulation temperature at 400 °C followed by the heat treatment temperature at 1200 °C. XRD patterns demonstrated that the unit cell volume and particle size decreased with the increase of the substitution content. The typical particles size was in the range of 1–2 μm in the planar dimension whilst the thickness was in the range of 200–500 nm. It was found from the VSM graphs that the saturation magnetizations M_s reached a maximum of 68.15 emu g⁻¹ at x = 0.3 and then decreases to 64.72 emu g⁻¹ at x = 0.3 whilst the coercivity H_c sustained decreases from 2190.70 to 1181.07 Oe g⁻¹ with substitution content increased from 0 to 0.4.     

Hydrothermal synthesis of Sr–Ce–Sn–Mn–O mixed oxidic/stannate pyrochlore and its catalytic performance for NO reduction

Mixed oxides and pyrochlore-type materials based on the Sr, Ce, Sn, and Mn elements have been prepared by hydrothermal method using a mixture of nitrate salts at 200 °C for 40 h under N₂ atmosphere. Two groups of solids were synthesized: (i) (Sr_xCe_1?x)₂Sn₂O_7±δ (0.345 ≤ x ≤ 0.365) and (ii) (Sr_xCe_1?x)₂(Sn_yMn_1?y)₂O_7±δ (0.345 ≤ x ≤ 0.365, 0.385 ≤ y ≤ 0.395). The structure of the solids were studied by X-ray diffraction and the main crystal phases determined were SnO₂, (SrCe)₂Sn₂O₇ and a trace amount of CeO₂ in group (i) and only SnO₂ and CeO₂ were detected in group (ii). The mixed oxides/stannate pyrochlore have been tested as catalyst for NO reduction with hydrocarbons (CH₄, C₂H₄, and C₃H₆) in the presence of O₂. The CeO₂ containing stannate Sr_2xCe_2?2xSn₂O_7±δ pyrochlore coexist with SnO₂ (group (i)) was found to be the best for NO + C₃H₆ reaction giving very high N₂ production at 350 °C in the presence of O₂ and water vapor. SnO₂ as well as CeO₂ alone were also synthesized by the hydrothermal method and their NO reduction properties have been compared with those of the groups (i) and (ii).     

Formation and thermal properties of fluorite-pyrochlore composite structure in La2(ZrxCe1 − x)2O7 oxide system

Rare-earth oxides of La₂(Zr_xCe_1 ? x)₂O₇ for thermal barrier coatings (TBCs) are fabricated via a solid-state reaction at 1600 °C. As the phase formation, microstructure, and thermal properties of these oxides are examined, a fluorite–pyrochlore composite structure is found in the La₂(Zr_xCe_1 ? x)₂O₇ system. This composite structure is composed of coarse Ce-rich fluorite and fine Zr-rich pyrochlore grains. From XRD and microstructural analysis, the lattice parameter and volume fraction of each phase are evaluated in order to obtain the intrinsic thermal conductivity value of composite-structured oxide with porosity calibration. The thermal conductivity of the composite structure is similar to that of pyrochlore La₂Zr₂O₇, which is attributed to phonon scattering by phase boundaries.     

Fabrication and electrical properties of Si-based La10−xBix(SiO4)6O3 apatite ionic conductor

In this paper we report an investigation about the relationship between Bi content and conductivity for the La_10?xBi_x(SiO₄)₆O₃ (x = 0.5–2) specimens. Increasing Bi content in apatite-type La_10?xBi_x(SiO₄)₆O₃ specimen leads to increasing the average grain size and sinterability because some Bi ion deposited at grain boundaries which promotes grain growth. The relative sintered density of the La₈Bi₂(SiO₄)₆O₃ specimen is 98%. There is a small shift in diffraction angle of XRD peaks, complicated lattice distortion was observed in the X-ray pattern with increasing content of Bi. Electrical conductivity of La_10?xBi_x(SiO₄)₆O₃ specimen increased with increasing Bi contents and the value of the La₈Bi₂(SiO₄)₆O₃ specimen is 2.4 × 10^?4 S cm^?1 at 700 °C.     

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).     

Microwave dielectric properties of Ba3La2Ti2Nb2−xTaxO15 ceramics

High dielectric constant and low loss ceramics in the system Ba₃La₂Ti₂Nb_2−xTa_xO₁₅ (x = 0–2) have been prepared by conventional solid-state ceramic route. Ba₃La₂Ti₂Nb_2−xTa_xO₁₅ solid solutions adopted A₅B₄O₁₅ cation-deficient hexagonal perovskite structure for all compositions. The materials were characterized at microwave frequencies. They show a linear variation of dielectric properties with the value of x. Their dielectric constant varies from 49.8 to 45.1, quality factor Q_u × f from 22,000 to 31,040 GHz and temperature variation of resonant frequency from + 6.9 to − 13.4 ppm/°C as the value of x increases. These low loss ceramics might be used for dielectric resonator (DR) applications.     

Synthesis of lanthanum zirconium oxide nanomaterials through composite-hydroxide-mediated approach

A novel thermal barrier coating material, lanthanum zirconium oxide (La₂Zr₂O₇) has been synthesized through the composite-hydroxide-mediated method at low temperature. The phase structures, morphology, thermal stability and thermal conductivity of the as-synthesized La₂Zr₂O₇ were investigated systematically. The X-ray diffraction (XRD) patterns revealed a single phase with cubic pyrochlore structure for La₂Zr₂O₇ after treated at 1300 °C for 100 h. The transmission electron microscope (TEM) and scanning electron microscope (SEM) analyses showed that the sample was made up of sphere-like nanoparticles with the size between 50 and 100 nm. Furthermore, the thermal analysis result demonstrated the La₂Zr₂O₇ sample had high thermal stability even at 1300 °C. As the temperature increased to 1200 °C, the thermal conductivity value could be as low as 1.75 W m^?1 K^?1. Due to the high-temperature stability and lower thermal conductivity, the La₂Zr₂O₇ material is expected to be a promising candidate for the use of thermal barrier coatings.     

Microwave dielectric properties of Ba(Mg1/3Ta(2−2x)/3Wx/3Tix/3)O3 ceramics

The microwave dielectric properties of ceramics based on Ba(Mg_1/3Ta_(2−2x)/3W_x/3Ti_x/3)O₃ is investigated as a function of x. The densification as well as dielectric properties deteriorate with increase in the substitution levels of (Ti_1/3W_1/3)^3.33+ at (Ta_2/3)^3.33+ site in Ba(Mg_1/3Ta_2/3)O₃. The τ_f is approaching zero between x = 0.1 and 0.15 in Ba(Mg_1/3Ta_(2−2x)/3W_x/3Ti_x/3)O₃ where quality factor is reasonably good (Q_u × f = 80,000–90,000 GHz). The Ba(Mg_1/3Ta_(2−2x)/3W_x/3Ti_x/3)O₃ with x = 1.0 has ɛ_r = 15.4, τ_f = −25.1 ppm/°C, Q_u × f = 35,400 GHz.     

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%.