Structure,chemical stability and electrical conductivity of perovskite La0.6Sr0.4M0.3Fe0.7O3−δ (M = Co,Ti) oxides

The perovskite La_0.6Sr_0.4M_0.3Fe_0.7O_3?δ (M = Co, Ti) powders have been synthesized by the citrate gel method. The structural and chemical stability of the La_0.6Sr_0.4M_0.3Fe_0.7O_3?δ (M = Co, Ti) oxides were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) techniques. The electrical conductivities of the sintered La_0.6Sr_0.4M_0.3Fe_0.7O_3?δ (M = Co, Ti) ceramics were measured. The results demonstrate the chemical stability in H₂/helium (He) atmosphere of the La_0.6Sr_0.4Ti_0.3Fe_0.7O_3?δ oxide is improved significantly compared to that of the La_0.6Sr_0.4Co_0.3Fe_0.7O_3?δ oxide. The incorporation of Ti^3+/4+ ions in the perovskite structure can significantly stabilize the neighboring oxygen octahedral due to the stronger bonding strength, leading to the enhanced structural and chemical stability of the La_0.6Sr_0.4Ti_0.3Fe_0.7O_3?δ. In addition, the perovskite La_0.6Sr_0.4M_0.3Fe_0.7O_3?δ (M = Co, Ti) oxides possess much higher chemical stability in CO₂/He atmosphere than that of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ oxide, in which the perovskite structure is destroyed completely in a flowing CO₂-containing atmosphere.     

Magnetic,Magnetocaloric Properties and Phenomenological Model of Perovskite Type: Sr3Fe2+xMo1−xO9−3x/2 (x = 0.45, 0.60, and 1.00)

Journal of Superconductivity and Novel Magnetism - We investigate in detail the magnetic, magnetocaloric properties and phenomenological model of perovskite type:...     

Synthesis and electrical conductivity of La0.6Sr0.4Ru1−xMgxO3−δ (x = 0–0.6) perovskite solid solution

Sr and Mg were doped at La- and Ru-sites of perovskite oxide LaRuO₃, respectively, to enhance electrical conductivity and catalytic property as a cathode material for a low temperature solid oxide fuel cell. Crystal structure and particle morphology of La_0.6Sr_0.4Ru_1?xMg_xO_3?δ powders (shorten as LSRM) and electrical conductivity of sintered LSRM were studied. LSRM powders (x = 0–0.6) were prepared by co-precipitation method using metal nitrate solutions and ammonium carbonate solution. The freeze-dried powders were heated at 1273 K in air to form LSRM solid solution of orthorhombic structure. The true densities and particle sizes of LSRM solid solution, where valence of Ru was estimated to be 3+, decreased with increasing Mg content. The electrical conductivity of LSRM at x = 0–0.3 was almost independent of temperature and was in a range of 19–360 S cm^?1 at 1073 K. Hole conduction contributed to the high electrical conductivities. LSRM at x = 0.4 and 0.5 was a mixed conductor of oxide ions and holes, and showed a conductivity of 11 S cm^?1 at 1073 K in air. This conductivity decreased at a lower oxygen pressure and reached a constant value below 10 Pa of oxygen pressure.     

Structure,nonstoichiometry, sintering and oxygen permeability of perovskite SrCo1−2x(Fe,Nb)xO3−δ (x = 0.05, 0.10) oxides

The novel Fe/Nb co-substituted SrCo_1?2x(Fe,Nb)_xO_3?δ (x = 0.05, 0.10) oxides have been synthesized and characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetry (TG), and scanning electron microscopy (SEM). The XRD and DSC results demonstrate that the structural stability of the Fe/Nb co-substituted samples x = 0.05, 0.10 is improved greatly compared to the sample x = 0.00. The Fe/Nb co-doping in the SrCoO_3?δ oxide results in the improved structural stability of the SrCo_1?2x(Fe,Nb)_xO_3?δ (x = 0.05, 0.10) oxides. The nonstoichiometric and sintering properties were investigated by TG and SEM, and the oxygen permeation fluxes were measured at 800–950 °C for the sample x = 0.10. The improved oxygen permeability of the ceramic SrCo_1?2x(Fe,Nb)_xO_3?δ (x = 0.10) membrane compared to the (Ba_0.5Sr_0.5)(Co_0.8Fe_0.2)O_3?δ and SrCo_0.8Fe_0.2O_3–δ membranes, was observed under an air/He oxygen partial pressure gradient at 800–950 °C.     

AC and DC Conductivity Studies on Lead-Free Ceramics: Sr1–xCaxBi4Ti4O15(x = 0, 0.2, 0.4, 0.6, 0.8)

Sr_1–xCa_xBi₄Ti₄O₁₅ [x = 0, 0.2, 0.4, 0.6, 0.8] ceramics are synthesized by solid-state reactive technique. Structural analyses are done by x-ray diffraction data. Morphological studies were carried out by scanning electron microscope, and the data showed plate-like structures. To understand the conductivity mechanism, frequency and temperature dependency of AC and DC conductivity studies are carried out. The conductivity measurements are done using an impedance analyzer (Wayn–Kerr) in the temperature range 100–600°C. The frequency-dependent AC conductivity at different temperatures indicates that the conduction process follows the universal power law, and the hopping frequency shifts toward higher frequency side with increase in temperature, below which the conductivity is frequency independent. The variation of DC conductivity confirms that the ceramics exhibit negative temperature coefficient of resistance behavior at high temperature. DC conductivity values do not show any linearity with doping concentration; for a particular composition SCBT06, the DC conductivity was low.     

Structural and Electrical Properties of Monovalent Doped Manganites Pr0.6Sr0.4−x K x MnO3 (x=0, 0.05 and 0.1)

Structural and electrical properties of the mixed-valence monovalent doped manganites Pr_0.6Sr_0.4?x K _x MnO₃ (x=0, 0.05 and 0.1), prepared using the conventional solid-state synthesis method, have been investigated. Rietveld refinement of the X-ray diffraction patterns at room temperature shows a slight increase in unit cell volume with K content and confirms that all powder samples are single phase and crystallize in the orthorhombic structure with Pnma space group. Electrical resistivity measurements under and without magnetic field show a transition from the metallic to insulating behavior. The electrical conductivity is improved with increasing K content. The resistivity data in metallic region were fitted according to the electron–electron scattering process while in insulating region they were fitted using the small polaron hopping SPH model and Mott’s variable range hopping VRH model.     

Electrical Resistivity Behavior and VRH Transport Mechanism in Semiconducting La0.6Sr0.4Mn1−2x Fe x Cr x O3 (0.10≤x≤0.25) Manganites

The transport properties and conduction mechanism in La_0.6Sr_0.4Mn_1?2x Fe _x Cr _x O₃ (0≤x≤0.3) have been investigated. The undoped samples show metal–semiconductor transition with a peak of resistivity at a temperature T _P , whereas for all doped compounds the semiconducting behavior persists in the whole temperature range. The insertion of Cr³⁺ and Fe³⁺ ions leads to the increase of resistivity because the simultaneous substitution of Fe³⁺ and Cr³⁺ for Mn³⁺ reduces the number of available hopping sites for the Mn e _g↑ electron and suppresses the double-exchange mechanism. It was found that the transport mechanism for substituted samples is dominated by the variable range hopping of small polarons between localized states in a model where the various parameters estimated from Mott’s relation obey the variable range hopping (VRH) mechanism.     

La0.6Sr0.4Co0.2Fe0.79M0.01O3−δ (M = Ni,Pd) perovskites synthesized by Citrate-EDTA method: Oxygen vacancies effect on electrochemical properties

La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ (LSCF08), La_0.6Sr_0.4Co_0.2Fe_0.79Ni_0.01O_3?δ (LSCF08-Ni) and La_0.6Sr_0.4Co_0.2Fe_0.79Pd_0.01O_3?δ (LSCF08-Pd) perovskites were synthesized by Citrate-EDTA method, by using NiCl₂ or PdCl₂ as metal precursors, and their physicochemical properties were characterized by XRD, TGA, TPD and TPR. XRD data evidenced an expansion of the lattice parameters of LSCF08-Pd, while a contraction of the lattice occurred for LSCF08-Ni, with respect to the undoped LSCF, suggesting different oxygen vacancies content in the perovskite (confirmed by TGA) likely due to a different oxidation state of Ni and Pd species stabilized in the structure.TEM analyses performed over LSCF08-Pd revealed the presence of metallic Pd nanoparticles well dispersed in the matrix that accounts for the increased reducibility of the Co and Fe species with respect to LSCF08-Ni and undoped perovskite. AC impedance measurements that were carried out on symmetric cells consisting of LSCF-based materials deposited onto Ce_0.8Gd_0.2O_2?δ (GDC) electrolyte proved the enhanced electrochemical performances of Ni/Pd doped LSCF.The electrochemical characterization of LSCF08, LSCF08-Ni and LSCF08-Pd electrodes was completed by performing cyclic voltammetry experiments in the range of temperature 600–800?°C, varying the potential (U) between 0.3?V and ?1?V, at scan rates in the range 1–50?mV?s^?1 and working under flow of 0.7?vol% O₂ in He (30?ml/min).     

Mössbauer spectra and magnetic properties of Tm0.65Sr0.35Fe x Mn1 − x O3 (x = 0.3, 0.35, 0.4)

We report Mössbauer spectroscopy results for Tm_0.65Sr_0.35Fe _x Mn_{1 ? x} O₃ (x = 0.3?0.4) at 300 and 80 K. Like in the case of lighter lanthanide ferromanganites, we observe phase separation of the magnetic sub- system: a magnetic phase shows up in the spectra in the form of a Zeeman sextet and “paramagnetic” dou- blets.     

Structural and Magnetic Properties of Pr0.6Sr0.4Mn1−x Fe x O3 (0≤x≤0.3) Manganites Oxide Prepared by the Ball Milling Method

We present the structural and magnetic properties of Pr_0.6Sr_0.4Mn_1?x Fe _x O₃ (x=0, 0.1, 0.2, and 0.3) compounds. Samples have been prepared by the ball milling method. Rietveld refinements of the X-ray powder diffraction data show that all our synthesized samples are single phase and crystallize in the orthorhombic symmetry with the Pnma space group. The unit cell volume increases with increasing the Fe content. The infrared spectrum shows two active bands, which can be ascribed to the internal stretching and bending modes. The magnetization measurements versus temperature showed that Fe doping leads to a weakening of the ferromagnetic ordering at low temperature, the Curie temperature T _C decreases from 300 K for x=0.0 to 88 K for x=0.2. The magnetization versus applied magnetic measurements at low temperature lead to conclude that the substitution of Mn³⁺ ions by Fe³⁺ ions triggers antiferromagnetic interactions between the Fe³⁺ and Mn⁴⁺ spins, and also the magnetization versus applied magnetic measurements at room temperature shows a small hysteresis loop and a low coercive field, which indicates that the samples are superparamagnetic.     

The investigation of the effect of K doping on the structural,magnetic, and magnetocaloric properties of La1.4−xKxCa1.6Mn2O7 (0.0 ≤ x ≤ 0.4) double perovskite manganite

Journal of Materials Science: Materials in Electronics - In this study, the effect of potassium doping on the morphological, crystallographic, magnetic and magnetocaloric properties of...     

Effect of configurational entropy on dielectric properties of high-entropy perovskite oxides (Ce0.5,K0.5)x[(Bi0.5,Na0.5)0.25Ba0.25Sr0.25Ca0.25]1−xTiO3

Journal of Materials Science: Materials in Electronics - A new kind of high-entropy perovskite oxides (Ce,K)x[(Bi,Na)BaSrCa]1?xTiO3 (x-CKBNBSCTO) were synthesized by using a traditional...     

Novel SrCo1 − 2x(Fe,Nb)xO3 − δ (x = 0.05, 0.10) oxides targeting CO2 capture and O2 enrichment: Structural stability and oxygen sorption properties

The novel Fe/Nb co-doped SrCo_1 ? 2x(Fe,Nb)_xO_3 ? δ (x = 0.05, 0.10) perovskite oxides were synthesized by the solid-state method. Structural and chemical stability of the SrCo_1 ? 2x(Fe,Nb)_xO_3 ? δ (x = 0.05, 0.10) oxides were studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and X-ray diffraction (XRD). The results demonstrated that the structural and chemical stability of the Fe/Nb co-doped SrCo_1 ? 2x(Fe,Nb)_xO_3 ? δ (x = 0.05, 0.10) is improved significantly. The oxygen sorption properties of the SrCo_1 ? 2x(Fe,Nb)_xO_3 ? δ (x = 0.05, 0.10) oxides were investigated between 300–900 °C in air, and the high oxygen sorption capacity of 11.5 and 10.3 mL O₂ (STP)/g oxide, respectively, are obtained.     

Ba<Subscript>1−x</Subscript>La<Subscript>x</Subscript>Fe<Subscript>12</Subscript>O<Subscript>19</Subscript> (x = 0.0, 0.2, 0.4, 0.6) hollow microspheres: material parameters,magnetic and microwave absorbing properties

Ba_1?xLa_xFe₁₂O₁₉ (x = 0.0, 0.2, 0.4, 0.6) hollow ceramic microspheres (HCMs) have been prepared by combining self-reactive quenching method with heat treatment. Their material parameters, magnetic and microwave absorbing properties were investigated. It was observed that after doping of lanthanum, the material parameters showed a little change except hexagonal crystal disappearing. And the magnetic properties of HCMs were decided by lanthanum content and material parameters. With the lathanum increases from 0.0 to 0.6, the saturation magnetization (Ms) values initially increased, and then decreased sharply to a minimum value, and increased again, moreover, the coercive force (Hc) values were reduced first, and then increased, and decrease to a minimum value. Absorbing properties tests indicate that after La³⁺-doped, at 2 mm thickness, the effective absorbing band (<?10 dB) was reduced to 4.7, 5 and 4.4 GHz, respectively, the minimum reflectance would decrease in low substituted level (x ≤ 0.4) and increase in high level (x = 0.6), and the frequency shifts to low frequency with the increasing of doping content. In 1.5–3 mm range, with the increasing of thickness, the absorption peak of Ba_1?xLa_xFe₁₂O₁₉ (x = 0.2, 0.4, 0.6) HCMs shifts to low frequency and the absorption intensity increases, the effective absorbing band can up to 10, 8.1 and 8 GHz, respectively.