La and Ca co-doped ceria-based electrolyte materials for IT-SOFCs

Co-doped ceria-based electrolytes of Ce_1−xLa_x−yCa_yO_2−δ, wherein x = 0.15 and 0.20, 0 ≤ y ≤ x, were sintered from powders obtained by solid state reaction method. The phase identification, thermal expansion and ionic conductivities of samples were studied by X-ray diffraction (XRD), dilatometry and AC impedance spectroscopy (IS). Results showed that the samples of co-doping with La and Ca can significantly increase the ionic conductivity and lower activation energies compared with those of the singly doped ones in the temperature range of 500-800 °C. The ionic conductivities of co-doping samples decrease with Ca content. Although both systems reached the optimum ionic conductivity at y = 0.05, Ce_0.85La_0.15−yCa_yO_2−δ exhibits better electrical performance. The results also showed that all the synthesized samples were fluorite-type ceria-based solid solutions. The thermal expansion was linear for all the samples.     

Structural characterization of 0.5PbMg1/3Nb2/3O3-0.5BaxPb(1−x)TiO3 powders

The present work reports the effects caused by barium on phase formation, morphology and sintering of lead magnesium niobate-lead titanate (PMN-50PT). Ab initio study of 0.5Pb(Mg_1/3Nb_2/3)O₃-0.5(Ba_xPb_(1−x)TiO₃) ceramic powders, with x = 0, 0.20, and 0.40 was proposed, considering that the partial substitution of lead by barium can reestablish the equilibrium of monoclinic-tetragonal phases in the system. It was verified that even for 40 mol% of barium, it was possible to obtain pyrochlore-free PMN-PT powders. The increase of the lattice parameters of PMN-PT doped-powders confirmed dopant incorporation into the perovskite phase. The presence of barium improved the reactivity of the powders, with an average particle size of 120 nm for 40 mol% of barium against 167 nm for the pure sample. Although high barium content (40 mol%) was deleterious for a dense ceramic, contents up to 20 mol% allowed 95% density when sintered at 1100 °C for 4 h.     

Preparation of Ca-doped LaFeO3 nanopowders in a reverse microemulsion and their visible light photocatalytic activity

Nanoparticles of lanthanum ferrite (LaFeO₃) and calcium-doped LaFeO₃ (La_1−xCa_xFeO₃, x = 0.05-0.20) with perovskite-type structure have been prepared in a reverse microemulsion. Perovskite powder could be obtained at 500 °C for 3 h. The prepared powders were characterized by thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD) and UV-Vis absorption spectroscopy. The visible-light photocatalytic activity of the photocatalysts was tested with methylene blue as an objective decomposition substance using fluorescence light as a visible light resource. The results showed that partial substitution of La³⁺ in LaFeO₃ with Ca²⁺ could decrease the crystalline size, enhance visible light absorption and improve visible light photocatalytic activity.     

Properties of the PLZTN x/54/46 (0.4 ≤ x ≤ 1.4) ceramic system

Even though the PZT ceramic system has been thoroughly studied and modified with different additives, no numerous reports have been published focusing on the PZT double ‘soft’ modification with La³⁺ and Nb⁵⁺ (PLZTN). In this paper, we explore the structural, morphological, dielectric, ferroelectric and piezoelectric properties of the PLZTN system for different doping levels (x_La3+ = x_Nb5+ = 0.4, 0.6, 0.8, 1.0 and 1.4 at.%) synthesized by conventional powders reaction. The temperature dependence of the piezoelectric response of poled ceramic disks is also analyzed and, according to its overall features, an optimum modification is proposed in order to develop PZT-based sensors for several applications.     

Structural and electrical properties of La2−xBaxMo2O9−x/2 (x = 0-0.18)

La_2−xBa_xMo₂O_9−x/2 (x ≤ 0.18) have been prepared by solid state reaction method. The lattice parameter of La_2−xBa_xMo₂O_9−x/2 (x ≤ 0.18) determined by XRD data refinement shows a linear dependence on the dopant Ba content x. For the specimen with a La/Ba molar ratio of 0.18-0.2, additional reflection of secondary phase exists in the XRD pattern, so the value of solubility limit for Ba in La₂Mo₂O₉ is defined in range of 0.18 < x < 0.2. As the replacement degree of La³⁺ by Ba²⁺ increases, the bulk conductivity of La_2−xBa_xMo₂O_9−x/2 (x ≤ 0.18) decreases initially and then increases, a minimum value at La_1.9Ba_0.1Mo₂O_8.95 exists. Hebb-Wagner studies in argon atmosphere, which use an oxide-ion blocking electrode, show that La_2−xBa_xMo₂O_9−x/2 (x ≤ 0.18) are predominantly oxide-ion conducting in the temperature ranging from 773 to 1173 K. The average thermal expansion coefficient of La_1.84Ba_0.16Mo₂O_8.92 determined by high-temperature XRD was deduced as great as 17.5 × 10⁻⁶ K⁻¹ between 298 and 1173 K.     

Sol–gel synthesis of Cr substituted Li0.5Fe2.5O4: Cation distribution,structural and magnetic properties

Li_0.5Cr_xFe_2.5−xO₄ powders with fine sized particles were successfully synthesized by sol–gel auto combustion, using lithium nitrate, ferric nitrate, chromium nitrate, and citric acid as the starting materials. The process takes only a few minutes to obtain as-prepared Cr-substituted lithium ferrite powders. The resultant powders were annealed at 600 °C for 4 h and investigated by thermogravimeter/differential thermal analyzer (TG/DTA), X-ray diffractometer (XRD) and vibrating sample magnetometer (VSM). Lattice parameter, bulk density and particle size are found to decrease with increasing Cr concentration, whereas X-ray density and porosity showed an increasing trend with the Cr content. Cation distribution indicates that the chromium ion occupy octahedral B-site. The magnetic moments calculated from Neel's molecular field model are in agreement in the experiment result, which indicates that the saturation magnetization decreases linearly from 37.36 to 4.27 emu/g with increasing Cr³⁺ content. However, coercivity, it increases with the Cr³⁺ substitution.     

Nanometric Pb1−xLaxTiO3 (x = 0, 0.13 and 0.27) powders obtained by the polymeric precursor method

PLT (Pb_1−xLa_xTiO₃, in which x = 0, 0.13 and 0.27) powders were successfully synthesized using the polymeric precursor method, based on the Pechini method. The polymeric precursors were calcined at temperatures ranging from 350 to 500 °C for 4 h. X-ray diffraction (XRD) showed the evolution of the crystalline phase starting from the amorphous precursor. Thermogravimetric analyses (TG) and differential thermal analyses (DTA) of the powder precursors showed the influence of the pH on the elimination of organic material. PLT powders have a tendency to form agglomerates, what can be verified by comparing the values of the average particle sizes obtained by Brunauer-Emmett-Teller method, BET (D_BET) with the values of the average crystallite sizes obtained by XRD (D_XRD).     

Preparation and characterization of La-doped Ba(1 − x)SrxTiO3 powders and thin films

Ba_(1 − x)Sr_xTiO₃ powders with different Ba/Sr ratios (x = 0.10, 0.25, 0.40, 0.55, 0.70) and La-doped Ba_0.9Sr_0.1TiO₃·yLa powders (y = 0.002, 0.004, 0.006, 0.008, 0.010) have been prepared by sol-gel technology using dehydrated barium-acetate, strontium-carbonate, lanthanum-nitrate, and titanium-isopropoxide as raw materials. The experimental results show that the dielectric properties of Ba_(1 − x)Sr_xTiO₃ powders depend on the Ba/Sr ratios. When the Sr fraction is 0.10, the dielectric constant is relatively higher and the dielectric loss is relatively lower, which are more than 2000 and less than 2.0 × 10^− 2 at 1000 Hz, respectively, the most important is that this kind of powder has better frequency stability. La-doping can increase the dielectric constant distinctly, but the dielectric loss can also be increased. Their dielectric properties at 1.0 × 10³ Hz are better than those at 1.0 × 10⁵ Hz. At 1.0 × 10³ Hz the dielectric constant is much higher, while the dielectric loss is much lower. The dielectric constant of different La-doping contents is nearly 3.5 × 10⁴ and the dielectric loss is less than 0.20 when La fraction is 0.008. The La-doped BST sample also has better frequency stability, especially at high frequency. La-doped BST thin films are successfully deposited on mild steel substrates by using plasma spray system with suspension precursors of Ba_0.90Sr_0.10TiO₃·0.8La powders. The XRD patterns of Ba_0.90Sr_0.10TiO₃ and Ba_0.90Sr_0.10TiO₃·0.8La powders are almost the same. No new peaks appear after La-doping, but the peaks move slightly to a larger degree, which indicates that the element La has entered the lattice of the Ba_0.90Sr_0.10TiO₃ and has made the constant of the crystal cell reduce. The XRD pattern of the thin films is just like that of the Ba_0.90Sr_0.10TiO₃·0.8La powders except a peak corresponding to Fe substrate. The SEM results show that the thin films have a uniform and smooth surface. The morphology of cross-section shows a columnar grain structure indicating smooth surface and uniform thickness of the film. The thickness of the film is about 15 um. The thin films obtained are expected to be prospective material for applications in tunable microwave devices.     

Preparation and characterisation of La10−xGe5.5Al0.5O26±δ apatites by freeze-drying precursor method

Nanocrystalline powders of La_10−xGe_5.5Al_0.5O_26±δ (x = 0-0.5) with an average crystallite size of 50 nm were prepared by a freeze-drying precursor method. These powders were used to obtain dense ceramic materials at rather low temperature as 1100-1200 °C for 1 h and to study the transport properties by impedance spectroscopy. The composition with the highest La-content (x = 0) exhibits a second-order phase transition from triclinic () to hexagonal (P6₃/m) space groups around 750 °C, whereas for x ≥ 0.2 the materials presents hexagonal structure in the whole temperature range studied. The thermal properties of these materials were investigated by high temperature X-ray diffraction (XRD), thermal analysis (TG/DTA) and impedance spectroscopy. These results confirmed the incorporation of water in the germanate-apatite structure. However, the conductivity resulted to be independent on the gas atmosphere used, which seems to indicate that the proton contribution to the overall conductivity is negligible in these materials.     

Effects of La substitution for Nd in (Nd2−xLax)BaZnO5 solid solutions on microwave dielectric properties and crystal structure

The synthesis and microwave dielectric characterization of (Nd_2−xLa_x)BaZnO₅ solid solutions were studied. The samples obtained were single phase over the whole composition range and the lattice parameters of solid solutions were linearly increased with increasing the composition. Moreover, the expansion of the volume in the RO₈ (R=Nd and La) and BaO₁₀ polyhedra and ZnO₄ tetrahedron were recognized when Nd ions were substituted by La. These variations in the lattice parameters and volumes of the polyhedra are basically attributed to the differences in ionic radii between Nd³⁺ and La³⁺ ions. From the evaluation of microwave dielectric properties, it was shown that the appropriate τ_f values ranging from 4.6 to −5.0 ppm/°C are obtained by La substitution for Nd ion, and the highest Q · f value was 17,832 GHz at x=2.     

Phase stabilization and microstructural studies of lead lanthanum titanate thin films

Thin ferroelectric films of PLTx (Pb_1−xLa_xTi_1−x/4O₃) have been prepared by a sol-gel spin coating process. As deposited films were thermally treated for crystallization and formation of perovskite structure. Characterization of these films by X-ray diffraction (XRD) have been carried out for various concentrations of La (x = 0.04, 0.08 and 0.12) on ITO coated corning glass substrates. For a better understanding of the crystallization mechanism, the investigations were carried out on films annealed at temperatures (350, 450, 550 and 650 °C). Characterization of these films by X-ray diffraction shows that the films annealed at 650 °C exhibit tetragonal phase with perovskite structure. Atomic force microscope (AFM) images are characterized by slight surface roughness with a uniform crack free, densely packed structure. Fourier transform infrared spectra (FTIR) studies of PLTx thin films (x = 0.08) deposited on Si substrates have been carried out to get more information about the phase stabilization.     

Synthesis of perovskite-type (La1−xCax)FeO3 (0 ≤ x ≤ 0.2) at low temperature

Gel formation was realized by adding citric acid to a solution of La(NO₃)₃·5H₂O, Ca(NO₃)₂·4H₂O, and Fe(NO₃)₂·9H₂O. Perovskite-type (La_1−xCa_x)FeO₃ (0 ≤ x ≤ 0.2) was synthesized by firing the gel at 500 °C in air for 1 h. The crystallite size (D_1 2 1) decreased with increasing x, while the specific surface area was 6.8-9.4 m²/g and independent of x. The XPS measurement of the (La_1−xCa_x)FeO₃ surface indicated that the Ca²⁺ ion content increased with increasing x, while the Fe ion content was independent of x. Catalytic activity for CO oxidation increased with increasing x.     

Synthesis of spherical nanostructured LiMxMn2−xO4 (M = Ni, Co, and Ti; 0 ≤ x ≤ 0.2) via a single-step ultrasonic spray pyrolysis method and their high rate charge-discharge performances

LiM_xMn_2−xO₄ (M = Ni²⁺, Co³⁺, and Ti⁴⁺; 0 ≤ x ≤ 0.2) spinels were prepared via a single-step ultrasonic spray pyrolysis method. Comparative studies on powder properties and high rate charge-discharge electrochemical performances (from 1 to 15 C) were performed. XRD identified that pure spinel phase was obtained and M was successfully substituted for Mn in spinel lattice. SEM and TEM studies confirmed that powders had a feature of ‘spherical nanostructural’, that is, powders consisted of spherical secondary particles with the size of about 1 μm, which were developed from close-packed primary particles with several tens of nanometers. Substitutions enhanced density of second particles to different extents, depending on M and its content. Charge-discharge tests showed that as-prepared LiMn₂O₄ could deliver excellent rate performance (around 100 mAh/g at 10 C). Ni substitution contributed to improving electrochemical performances. In the voltage range of 4.95-3.5 V, the materials showed much better electrochemical performances than LiMn₂O₄ in terms of capacity, cycleability and rate capability.     

The Fe K-edge X-ray absorption characteristics of La1−xSrxFeO3−δ prepared by solid state reaction

Perovskites of the composition La_1−xSr_xFeO_3−δ (x = 0.0, 0.1, 0.5, 0.9, 1.0) were prepared by the conventional solid state reaction route. The single phase behaviour was assessed by XRD analysis, the electronic properties were investigated by Fe K-edge X-ray absorption spectroscopy. The work is focused on the valence state of iron and the oxygen vacancies of the perovskites investigated. The XRD measurements revealed that the solid state reaction yields cubic perovskites for x = 1, 0.9, rhombohedral perovskites for x = 0.5, and orthorhombic perovskites for x = 0, 0.1. The X-ray absorption data are discussed in detail with respect to Fe K-edge shift, white-line intensity, pre-edge features, and the EXAFS data. The first peak in the Fourier transform of the Chi × k³ and Chi × k² functions was simulated for a detailed analysis of scattering contributions from the first oxygen shell to evaluate the Fe-O bond length. The substitution of lanthanum by strontium leads to a corresponding increase of the iron valence state and thus to the formation of the Jahn-Teller Fe⁴⁺ ion. This is causing disorder in the first coordination shell and thus an increase of the Debye-Waller factor with increasing x. The Fe-O bond length obtained from XRD and especially from X-ray absorption data are consistent with δ-values close to zero.     

Electrochemical properties of (La1−xTix)0.67Mg0.33Ni2.75Co0.25 (x = 0-0.20, at%) hydrogen storage alloys

(La_1−xTi_x)_0.67Mg_0.33Ni_2.75Co_0.25 (x = 0, 0.05, 0.10, 0.15 and 0.20, at%) alloys are synthesized by arc-melting and subsequent heat solid-liquid diffusing techniques, and the crystalline structures and electrochemical properties of the alloys are investigated systematically. The structural analysis results show that all the alloys mainly consist of (La, Mg)Ni₃ phase with the rhombohedral PuNi₃-type structure and LaNi₅ phase with the hexagonal CaCu₅-type structure. However, when the Ti content is higher than 0.10, a little amount of TiNi₃ phase start to form. Electrochemical measurements show that the alloy electrodes could be activated to their maximum discharge capacity within four cycles, the maximum discharge capacity is around 321.9-384.6 mAh g⁻¹, both the cyclic stability and the high-rate discharge ability first increased and then decrease with increasing x. All the results show that a little amount of Ti substitution for La in AB₃-type hydrogen storage alloys is effective to the improvement of the overall electrochemical properties.     

Synthesis of (1 − x)Ca2/5Sm2/5TiO3-xLi1/2Nd1/2TiO3 ceramic powder via ethylenediaminetetraacetic acid precursor

(1 − x)Ca_2/5Sm_2/5TiO₃-xLi_1/2Nd_1/2TiO₃ (CSLNT) ceramic powder was prepared by a liquid mixing method using ethylenediaminetetraacetic acid (EDTA) as the chelating agent. TG, DTA, XRD and TEM characterized the precursors and derived oxide powders. When x = 0.3, perovskite CSLNT was synthesized at 1000 °C for 3 h in air. The CSLNT (x = 0.3) ceramics sintered at 1200 °C for 3 h show excellent microwave dielectric properties of ?_r = 99, Q_f = 6200 GHz and τ_f = 9 × 10⁻⁶ °C⁻¹.     

Synthesis and characterization of pyrochlore-type solid solutions Y2−xLaxRu2O7

New pyrochlore-type solid solutions Y_2−xLa_xRu₂O₇ have been synthesized for x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 as single-phase materials. The lattice parameters for these solid solutions are linear with x and range from 1.0140 nm (x=0.0) to 1.0257 nm (x=0.6). All the samples show semiconducting behavior with an activation energy of about 0.1 eV. They show the spin-glass-like magnetic transition at low temperatures. Its transition temperature T_G decreases from 77 K for Y₂Ru₂O₇ with increasing the La³⁺ content.     

Novel multiferroic La0.95Sb0.05FeO3 orthoferrite

A series of La_1−xSb_xFeO₃ was prepared using the conventional solid state method. XRD revealed the formation of the orthorhombic structure with space group Pbnm. The data showed that, the molar magnetic susceptibility and coercive field H_C were increased from 9.16 × 10⁻³ to 26.9 × 10⁻³ emu g⁻¹ mol and 1196 to 5465 Oe from for LaFeO₃ to La_0.95Sb_0.05FeO₃, respectively. The coercive field (H_C) of the sample with x = 0.05 increased 6 times than that of the parent LaFeO₃ and the saturation magnetization (M_s) was increased from 0.1614 emu g⁻¹ for the parent LaFeO₃ to 0.2654 emu g⁻¹ for the doped sample_. The dielectric constant (?′) was increased with increasing the Sb³⁺ content. The ac conductivity (σ) increases from 2.36 × 10⁻³ Ω⁻¹ m⁻¹ for the LaFeO₃ to 30 × 10⁻³ Ω⁻¹ m⁻¹ for the sample La_0.95Sb_0.05FeO₃ at T = 553 K and frequency 1 MHz. The sample La_0.95Sb_0.05FeO₃ is concluded to be a novel single phase multiferroic material.     

Preparation, characterization and electrical conductivity studies of nanocrystalline La doped BaMoO4

Different compositions of scheelite type nanocrystalline La doped BaMoO₄ [Ba_1−xLa_xMoO_4+x/2, where x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5] samples were prepared by acrylamide assisted sol-gel combustion process. Dried gels prepared at 60 °C were heated at different temperatures and characterized using TG/DTA, XRD, FTIR and SEM-EDX techniques. From XRD patterns, crystalline phases for La doped BaMoO₄ samples were confirmed and their average crystallite sizes were calculated using Scherrer's formula and it was found to be less than 80 nm. Structure and thermal behavior of scheelite type nanocrystalline La doped BaMoO₄ samples were identified respectively using FTIR and TG/DTA measurements. Microstructure and existence of O, La, Ba and Mo elements in the La doped BaMoO₄ samples were obtained from SEM-EDX and HRTEMtechniques. The ‘d’ spacing values were obtained for different (h k l) planes and were well matched with the standard BaMoO₄. (h k l) values for different directions of planes were assigned for the observed HRTEM images and were matched with standard BaMoO₄. Grain and grain boundary conductivities were evaluated by analyzing the impedance data, using the Winfit software, measured at different temperatures.     

Infrared to visible upconversion emissions of La1-0.02-xEr0.02YbxOF nanorods

In this work, well-crystallized La_1-0.02-xEr_0.02Yb_xOF (x = 0, 0.08, 0.06, 0.04, 0.02) nanorods were prepared by annealing the hydrothermally synthesized La_1-0.02-xEr_0.02Yb_xF₃ nanocrystals at ambient condition. The structural properties of these samples were characterized by XRD and TEM (HRTEM), the results show that the nanorods have a pure tetragonal structure and a preferential growth along the (1 0 1) direction, the average length and cross-section radius are 340 nm and 65 nm. Excited by 984 nm continuous wave laser, strong red (643-677 nm), strong green (515-557 nm) and weak violet (382-417 nm) upconversion emissions have been observed in these nanorods. The influence of Yb³⁺ concentration on the upconversion emission intensity has been discussed. The possible upconversion mechanisms were proposed through research on pump power dependence of upconversion integrated intensity. Especially, both two-photon process and three-photon process were contributed to the green upconversion in lower Yb³⁺ concentration doped nanorods.