Oxygen Migration in Dense Spark Plasma Sintered Aluminum‐Doped Neodymium Silicate Apatite Electrolytes

Neodymium silicate apatites are promising intermediate temperature (500°C–700°C) electrolytes for solid oxide fuel cells. The introduction of Al promotes isotropic percolation of O^2?, and at low levels (0.83–2.0 wt% Al) enhances bulk conductivity. To better understand the effect of Al‐doping on intrinsic conductivity, and the impact of grain boundaries on the transport, dense Nd_9.33+x/3Al_xSi_6?xO₂₆ (0 ≤ x ≤ 2) pellets were prepared by spark plasma sintering. Phase purity of the products was established by powder X‐ray diffraction and the microstructure examined by scanning electron microscopy. The ionic conductivity measured by AC impedance spectroscopy for the spark plasma sintered ceramics were compared with transport in single crystals of similar composition. Intermediate Al‐doping (0.5 ≤ x ≤ 1.5) delivered superior overall conductivity for both the polycrystalline and single crystal specimens.     

Analysis of the conduction mechanisms of the Ni doped apatite-type lanthanum silicate electrolyte ceramics synthesized by the combustion method

In this study, the nickel doped apatite-type lanthanum silicate La_9.33Si_6-xNi_xO_26-x (x = 0, .5, 1.0, 1.5, 2.0) (LSNO) electrolyte powders were successfully generated by using the urea nitrate combustion method at 600°C and 6–8 min. The optimal sintering temperature was determined to be 1500°C on the basis of the linear shrinkage, relative density as a function of temperature, and microcosmic analysis. It was observed that Ni²⁺ successfully replaced Si⁴⁺ in [SiO₄] to form the [Si(Ni)O₄] tetrahedra. LSNO had a typical p6₃/m apatite structure of high purity. A significant change in the cell volume of the doped samples was observed, and the cell volume increased with the doped nickel content. The conductivity reached the peak value at x = 1.0 (1.21 × 10⁻³ S·cm⁻¹, 700°C). Nickel doping introduced the oxygen vacancies and expanded the channels for interstitial oxygen conduction. Further, it also directly reduced the amount of interstitial oxygen in the LSO structure. This led to an enhancement in the conductivity of La_9.33Si_6-xNi_xO_26-x, followed by a decrease on increasing the doped nickel content. The conductivity enhancement in the Ni-doped LSO resulted from the combination of two mechanisms, namely, the oxygen vacancy defect and lattice volume enhancement mechanism.     

Fe doping effect on EuTiO3: The magnetic properties and giant magnetocaloric effect

The magnetic properties and magnetocaloric effect for EuTi_1-xFe_xO₃ (x = 0.05, 0.1) compounds are investigated. When a part of Ti⁴⁺ions were substituted by Fe ions, the AFM ordering can be significantly changed to be FM. The EuTi_1-xFe_xO₃ (x = 0.05, 0.1) compounds exhibit a PM to FM transition with decreasing temperature and the Curie temperature is 6 K. Under the field changes of 1 T, and RC are valued to be 10.1 J/kg K and 50.2 J/kg for EuTi_0.95Fe_0.05O₃; 9.6 J/kg K and 47.7 J/kg for EuTi_0.9Fe_0.1O₃, without magnetic and thermal hysteresis. RC is almost twice as much as EuTiO₃ (27 J/kg) as substitution of Fe³⁺ ions for Ti⁴⁺ions, which may be attributed to the magnetic transition (AFM to FM). Therefore, the giant and large RC suggest the EuTi_1-xFe_xO₃ compounds are good materials for magnetic refrigerant.     

The relationship between crystal structure and modified microwave dielectric properties of Ca3SnSi2-xGexO9 ceramics

Ca₃SnSi_2-xGe_xO₉ (0 ≤ x ≤ 0.8) and (1–y) Ca₃SnSi_1.6Ge_0.4O₉ – y CaSnSiO₅ – 2 wt% LiF (y = 0.4 and 0.5) microwave dielectric ceramics were prepared by traditional solid-state reaction through sintering at 1250°C–1425°C for 5 h and at 875°C for 2 h, respectively. Ge⁴⁺ replaced Si⁴⁺, and Ca₃SnSi_2-xGe_xO₉ (0 ≤ x ≤ 0.4) solid solutions were obtained. At 0.1 ≤ x ≤ 0.4, the Ge⁴⁺ substitution for Si⁴⁺ decreased the sintering temperature of Ca₃SnSi_2-xGe_xO₉ from 1425 to 1300°C, the SnO₆ octahedral distortions, and the average CaO₇ decahedral distortions, which affected the τ_f value. The large average decahedral distortions corresponded with nearer-zero τ_f values at Ca₃SnSi_2-xGe_xO₉ (0.1 ≤ x ≤ 0.4) ceramics. The τ_f value and sintering temperature of Ca₃SnSi_2-xGe_xO₉ (x = 0.4) ceramic were adjusted to near-zero by CaSnSiO₅ and decreased to 875°C upon the addition of 2 wt% LiF. The (1 – y) Ca₃SnSi_1.6Ge_0.4O₉ – y CaSnSiO₅ – 2 wt% LiF (y = 0.5) ceramic sintered at 875°C for 2 h exhibited good microwave dielectric properties: ε_r = 10.3, Q × f = 14 300 GHz (at 12.2 GHz), and τ_f = ‒5.8 ppm/°C.     

Scaling Effects in Sodium Zirconium Silicate Phosphate (Na1+xZr2SixP3−xO12) Ion‐Conducting Thin Films

Preparation of sodium zirconium silicate phosphate (NaSICon), Na_1+xZr₂Si_xP_3?xO₁₂ (0.25 ≤ x ≤ 1.0), thin films has been investigated via a chemical solution approach on platinized silicon substrates. Increasing the silicon content resulted in a reduction in the crystallite size and a reduction in the measured ionic conductivity. Processing temperature was also found to affect microstructure and ionic conductivity with higher processing temperatures resulting in larger crystallite sizes and higher ionic conductivities. The highest room temperature sodium ion conductivity was measured for an x = 0.25 composition at 2.3 × 10^?5 S/cm. The decreasing ionic conductivity trends with increasing silicon content and decreasing processing temperature are consistent with grain boundary and defect scattering of conducting ions.     

Ca-doped PrBa1-xCaxCoCuO5+δ (x = 0–0.2) as cathode materials for solid oxide fuel cells

Ca-doped perovskite oxides PrBa_1-xCa_xCoCuO_5+δ (PBCCCO, x = 0–0.2) were prepared and investigated as SOFC cathode materials. PBCCCO samples are single perovskite structure with P4/mmm space group. Pr, Cu and Co ions in PBCCCO samples exist in the form of Pr³⁺/Pr⁴⁺, Cu²⁺/Cu⁺ and Co³⁺/Co⁴⁺ multi-valence states. The average TECs of PBCCCO samples were reduced from 17.4 × 10^?6 K^?1 (x = 0) to 16.7 × 10^?6 (x = 0.1) and 16.1 × 10^?6 K^?1 (x = 0.2) whin RT-900°С. The electrical conductivity and electrochemical catalytic activity of PBCCCO perovskites was enhanced obviously by Ca doping. The ASR values decreased by 60.1% (@650 °C), 68.9% (@700 °C), 71.0% (@750 °C) and 72.8% (@800 °C) respectively when Ca doping content increased from x = 0 to 0.2. These results suggest PBCCCO sample with Ca doing content x = 0.2 can be a promising cathode for IT-SOFC.     

Enhanced Thermoelectric Performance of CdO Ceramics Via Ba2+ Doping

Polycrystalline Cd_1?xBa_xO (0 ≤ x ≤ 0.08) ceramics were synthesized via conventional solid‐state reaction method, and the effect of Ba²⁺ doping on the microstructure as well as the thermoelectric transport properties of the samples were investigated. It was found that doping of Ba²⁺ can inhibit the grain growth of CdO, resulting in a considerable reduction in grain size. Moreover, with the increase in Ba²⁺ doping content, both the electrical conductivity and the thermal conductivity of Cd_1?xBa_xO decreased, whereas the Seebeck coefficient increased. A high ZT value of 0.47 was achieved for Cd_0.99Ba_0.01O at 1000 K, 38% higher than the undoped CdO, mostly due to reduction of the thermal conductivity.     

Effect of Ce-doping on microstructure and electrical properties of LaAlO3 ceramics

A series of novel negative temperature coefficient (NTC) thermistor materials based on La_1-xCe_xAlO₃ (0 ≤ x ≤ 0.2) ceramics were synthesized via the solid-state route. X-ray diffraction results confirmed the successful doping of Ce in the La_1-xCe_xAlO₃ crystal and the formation of a good solid solution. Scanning electron microscopy results indicated that Ce doping is beneficial for grain growth and reduces the porosity of the samples. With the increase in the Ce doping amount, the average grain size increased from 2.1793 to 10.7344 μm, and densities of the ceramics increased from 93.15% to 99.26%. The temperature vs resistance curve indicated that Ce doping reduces the resistivity of LaAlO₃ materials, while reducing the B_200/1400 value of the LaAlO₃ ceramic. For a doping amount of 0.2, the B_200/1400 value of the LaAlO₃ ceramic decreased from 18175.1 to 4897.7K, and the resistivity at 1000 °C decreased from 68971.87 to 1105.15 Ω cm. In addition, the La_1-xCe_xAlO₃ (0 ≤ x ≤ 0.2) series materials exhibited good linear NTC characteristics. X-ray photoelectron spectroscopy results revealed that the resistivity of the LaAlO₃ materials decreased after Ce doping owing to the transformation between the Ce⁴⁺ and Ce³⁺ valence states，and the concentration of Ce³⁺ increased with the increase in the Ce doping amount. Ce³⁺ increases the concentration of oxygen vacancies, decreasing the resistance. Impedance analysis findings suggested that the resistance of the La_1-xCe_xAlO₃ (0 ＜ x ≤ 0.2) material mainly originates from the grain. These results indicate that Ce doping is an effective method to reduce the resistivity of LaAlO₃. Consequently, La_1-xCe_xAlO₃ (0 ≤ x ≤ 0.2) is a promising material for NTC applications.     

Effect of TiO2 Doping on the Structure and Microwave Dielectric Properties of Cordierite Ceramics

The (1?x)Mg₂Al₄Si₅O₁₈–xTiO₂ |(1?x)MAS‐xT| (0 ≤ x ≤ 0.35) cordierite ceramics are fabricated by solid‐state reaction method for obtaining near‐zero temperature coefficient of resonant frequency (τ_f). The XRD and SEM results show that (1?x)MAS‐xT (0 ≤ x ≤ 0.10) ceramics exhibit single cordierite solid solution, whereas as 0.15 ≤ x ≤ 0.35, present composite phases of Mg₂Al₄Si₅O₁₈ solution and TiO₂. Rietveld refinements of XRD data suggest that the [(Si₄Al₂)O₁₈] hexagonal shape in cordierite structure happens to alternate change from nonsymmetrical hexagonal rings to almost centrosymmetrical equilateral rings as x increases to 0.10 comparing to that of x = 0. As Ti⁴⁺ ions squeeze into the [(Si₄Al₂)O₁₈] rings structure, the orientation and shapes of the rings begin to rotate and expand from initial state of [1–20] (x = 0) to near [210] direction (x = 0.10), and then continue to expand toward close to [110] direction (x = 0.25). Due to centrosymmetry adjustment of [(Si₄Al₂)O₁₈] hexagonal rings and of other microstructure factors improvement, the (1?x)MAS‐xT (x = 0.10) cordierite solution achieves optimum quality factor Q_f: ε_r = 6.3, Q_f = 55 400 GHz (17.6 GHz), τ_f = ?21 ppm/°C. The (1?x)MAS‐xT (x = 0.25) composites obtain a near‐zero temperature coefficient of resonance frequency: ε_r = 6.8, Q_f = 37 800 GHz (18.4 GHz), τ_f = ?0.2 ppm/°C.     

The improving thick film properties of Er2O3 doping fcc-ZrO2 type solid electrolyte for SOFC applications

In this study, the binary system of (ZrO₂)_1-x(Er₂O₃)_x was investigated in the doping range of x; 0.02 ≤ x ≤ 0.12 by the Pechini method. According to X-ray diffraction (XRD) measurement results, Er₂O₃ doping face-centered cubic (fcc) ZrO₂-based solid solution was stabilized in the doping range of 0.08 ≤ x ≤ 0.12 at 1200°C for 12 hours. Thick films of fcc-ZrO₂ type powders were produced using ethyl cellulose organic binder mixture and spin-coating method. The crystallographic, microstructural, and electrical conductivity properties of the thick films were characterized via XRD, SEM, and a.c. impedance measurements, respectively. 8-ESZ ((ZrO₂)_1-x(Er₂O₃)_x, x = 0.08) thick film electrolyte showed the highest electrical conduction level which is 2.51 × 10⁻² ohm⁻¹ cm⁻¹ at 850°C under 150 mL min⁻¹ O₂ volumetric flow rate. All thick film properties of fcc-ESZ materials were optimized and improved experimentally for using as a solid electrolyte component in solid oxide fuel cell (SOFC) systems. A pre-treatment of 8-ESZ and the cathode-supported type electrochemical cell were primarily fabricated. The power density measurements of 40-LNF (LaNi_1-xFe_xO₃, x = 0.4) Cathode|Cathode Active (50:50 wt % 40-LNF:8-ESZ)| 8-ESZ Electrolyte|Anode Active (60:40 wt % NiO:8-ESZ)|NiO Anode Electrode cell stack suggest that the produced electrolytes had the usefully properties for SOFC applications.     

Structure Stability and Microwave Dielectric Properties of (1 − x) Ba(Mg1/2W1/2) O3 + xBa(Y2/3W1/3)O3 Ceramics

The structure stabilities of double perovskite ceramics‐ (1 ? x) Ba(Mg_1/2W_1/2)O₃ + xBa(Y_2/3W_1/3)O₃ (0.01 ≤ x ≤ 0.4) have been studied by X‐ray powder diffraction (XRD), scanning electron microscopy (SEM), and Raman spectrometry in this study. The microwave dielectric properties of the ceramics were studied with a network analyzer at the frequency of about 8–11 GHz. The results showed that all the compounds exhibited face‐centered cubic perovskite structure. Part of Y³⁺ and W⁶⁺ cations occupied 4a‐site and the remaining Y³⁺ and Mg²⁺ distributed over 4b‐site, respectively, and kept the B‐site ratio 1:1 ordered. Local ordering of Y³⁺/Mg²⁺ on 4b‐site and Y³⁺/W⁶⁺ cations on 4a‐site within the short‐range scale could be observed with increasing Y‐doping content. The decomposition of the double perovskite compound at high temperature was successfully suppressed by doping with Y on B‐site. However, Ba₂Y_0.667WO₆ impurity phase appeared when x > 0.1. The optimized dielectric permittivity increased with the increase in Y doping. The optimized Q × f value was remarkably improved with small amount of Y doping (x ≤ 0.02) and reached a maximum value of about 160 000 GHz at x = 0.02 composition. Further increasing in Y doping led to the decrease in Q × f value. All compositions exhibited negative τ_f values. The absolute value of τ_f decreased with increasing Y‐doping content. Excellent combined microwave dielectric properties with ε_r = 20, Q × f = 160 000 GHz, and τ_f = ?21 ppm/°C could be obtained for x = 0.02 composition.     

Effect of Si4+ substitution on mechanical and thermal expansion properties of Ca0.5Sr0.5Zr4P6O24 ceramics

The Ca_(1+x)/2Sr_(1+x)/2Zr₄P_6-2xSi_2xO₂₄ (CSZP_6-2xS_2x, 0 ≤ x ≤ 0.3) ceramics were prepared using powders synthesized by co-precipitation method, and the effects of Si⁴⁺ substitution on the structure, mechanical, and thermal expansion properties were investigated. The optimum sintering time was 4 hours, which greatly shortened the sintering process. By controlling the appropriate composition and sintering temperature, a single phase with the typical NaZr₂P₃O₁₂ structure was obtained. As a function of x increasing, the parameter a increased and then decreased, while the parameter c and unit cell volume both increased. The mechanical property of CSZP_6-2xS_2x ceramics was affected with increasing amount of Si⁴⁺ content. The Si⁴⁺ substitution could increase the thermal expansion anisotropy and lead to the generation of microcracks, which are responsible for the increase in the amount of hysteresis between heating and cooling curves. The thermal expansion decreased progressively from 1.8 to 0.8 × 10⁻⁶/°C. The investigations indicate that the CSZP_6-2xS_2x ceramics are potential materials in high temperature applications     

Tunable size and shape of conductive poly(N‐methylaniline) based on surfactant template and doping

Poly(N‐methylaniline) (PNMA) is one of the polyaniline derivatives with N‐substituted position. Polyaniline derivatives have attracted attention due to their higher solubility in common solvents than pristine polyaniline, but they still possess lower electrical conductivity. In this work, PNMA was synthesized via chemical oxidative polymerization in an ethanol–water system. The effect of surfactant type, namely anionic sodium dodecylbenzenesulfonate (SDBS), cationic cetyltrimethylammonium bromide and non‐ionic Tween20, on the electrical conductivity, doping level and morphology was investigated. PNMA prepared with the SDBS system possessed the highest electrical conductivity among the obtained PNMAs with and without surfactants. The effect of $N_{{\mathrm{\text{HClO}}}_4}$/N_NMA dopant mole ratios on the re‐doping, crystallinity, morphology and particle size was also examined. Using an $N_{{\mathrm{\text{HClO}}}_4}$/N_NMA mole ratio of 10:1 in the re‐doping process provided the highest electrical conductivity of 15.53 ± 2.5 S cm^?1, a doping level of 55.59%, along with hollow spherical particles with the thinnest membrane. Electron microscopy images revealed that the morphology of PNMA particles depended mainly on the surfactant type but not the $N_{{\mathrm{\text{HClO}}}_4}$/N_NMA mole ratio. © 2019 Society of Chemical Industry     

Crystal structure,far-infrared spectra,and microwave dielectric properties of bazirite-type BaZr(Si1-xGex)3O9 ceramics

Novel BaZr(Si_1-xGe_x)₃O₉ (0 ≤ x ≤ 1.0) microwave dielectric ceramics were prepared by solid-state reaction sintering at 1200–1450 °C for 5 h Ge⁴⁺ ions occupied the Si⁴⁺ positions, and BaZr(Si_1-xGe_x)₃O₉ solid solutions were obtained. The BaZr(Si_1-xGe_x)₃O₉ (0 ≤ x ≤ 1.0) ceramics exhibited hexagonal structures with P-6c2 space groups and octahedral layers and [Si/Ge₃O₉]^6- rings. Owing to these structural characteristics, the ceramics exhibited low permittivity. With an increase in x, the relative permittivity (ε_r) values of the BaZr(Si_1-xGe_x)₃O₉ (0 ≤ x ≤ 1.0) ceramics increased from 7.68 (x = 0) to 9.45 (x = 1.0), while their quality factor (Q × f) values first increased and then decreased. The Q × f value (10,300 GHz at 13.43 GHz) of the BaZrSi₃O₉ (x = 0) ceramic improved with the substitution of Si⁴⁺ by Ge⁴⁺. A high Q × f value (36,100 GHz at 13.81 GHz) was obtained for the BaZr(Si_1-xGe_x)₃O₉ (x = 0.2) ceramic, and the Q × f values of the BaZr(Si_1-xGe_x)₃O₉ ceramics could be controlled by varying the Si/Ge-site bond valence. The temperature coefficient of resonance frequency (τ_f) values of the BaZr(Si_1-xGe_x)₃O₉ ceramics were mainly affected by the O2-site bond valence, and the optimum τ_f value (?22.8 ppm/°C) was achieved for the BaZrSi₃O₉ ceramic. The BaZr(Si_1-xGe_x)₃O₉ (x = 0.2) ceramic showed the optimum microwave dielectric properties (ε_r = 8.36, Q × f = 36,100 GHz at 13.81 GHz, and τ_f = ?34.5 ppm/°C).     

Crystal structure,phonon modes,and bond characteristics of AgPb2B2V3O12 (B = Mg,Zn) microwave ceramics

AgPb₂B₂V₃O₁₂ (B = Mg, Zn) ceramics with low sintering temperature were synthesized via the conventional solid-state reaction route. Rietveld refinements of the X-ray diffraction patterns confirm cubic symmetry with space group . The number of observed vibrational modes and those predicted by group theoretical calculations also confirm the space group. At the optimum sintering temperature of 750°C/4 hours, AgPb₂Mg₂V₃O₁₂ has a relative permittivity of 23.3 ± 0.2, unloaded quality factor () of 26 900 ± 500 GHz (), and temperature coefficient of resonant frequency of 19.3 ± 1 ppm/°C, while AgPb₂Zn₂V₃O₁₂ has the corresponding values of 26.4 ± 0.2, 28 400 ± 500 GHz () and –18.4 ± 1 ppm/°C at 590°C/4 hours. Microwave dielectric properties of a few reported garnets and Pb₂AgB₂V₃O₁₂ (B = Mg, Zn) ceramics were correlated with their intrinsic characteristics such as the Raman shifts as well as width of A_1g Raman bands. Higher quality factor was obtained for lower full width at half-maxima (FWHMs) values of A_1g modes. The increase in B-site bond valence contributes to high and low |τ_f| with the substitution of Zn²⁺ by Mg²⁺. Furthermore, the high ionic polarizability and unit cell volume with Zn²⁺substitution contribute to increased relative permittivity.     

Electrical conduction behavior in nonstoichiometric BaBixNb5O15±δ tungsten bronze ceramics

The BaBi_xNb₅O_15±δ (BB_xN, 0.98 ≤ x ≤ 1.02) ceramics were synthesized via solid-state reaction to investigate the effect of Bi³⁺ nonstoichiometry on their microstructure and electrical conduction behavior. The study of the relationship between structure and conductive behavior revealed two main conclusions: (1) as the concentration of Bi³⁺ content increased, from deficiency to excess, the oxygen vacancies decreased, and the lattice unit volume V gradually increased; (2) there was a low-frequency Warburg electrode response besides the medium-frequency grain boundary response and high-frequency grain response, and the Bi³⁺ introduction could reduce conductivity. In addition, the dielectric anomalies indicated by the T₁ peak and the T₂ peak at 300 °C and 500 °C are related to the Warburg electrode response and to the Bi vacancy and oxygen vacancy defects, respectively.     

Voltage‐Dependent Bulk Resistivity of SrTiO3:Mg Ceramics

Single phase ceramics of composition Sr(Ti_1–xMg_x)O_3–x: 0 ≤ x ≤ 0.01 were prepared by sol–gel synthesis and characterized by X‐ray diffraction, scanning electron microscopy, impedance spectroscopy, and current–voltage measurements. The bulk and grain‐boundary conductivities increase on application of a small dc bias voltage in the range 3–200 V/cm and at temperatures in the range 150°C–800°C. A qualitatively similar increase in conductivity occurs on increasing in the surrounding atmosphere, which shows that conduction is p type. The conductivity increase is reversible on removal of the dc bias or on reducing and is not observed in undoped SrTiO₃. It is an intrinsic property of the bulk material, differs from the voltage‐dependent effects observed with varistors and is attributed to changes in redox equilibria between oxygen species at the surface which cause changes in carrier concentration in the interior. A capacitive model of this low‐field dc bias effect is presented and compared with a memristive model of high field resistance degradation.     

Microwave dielectric properties and thermally stimulated depolarization of Al-doped Ba4(Sm,Nd)9.33Ti18O54 ceramics

Ba₄(Sm_0.15Nd_0.85)_9.33Ti_18-zAl_3z/4O₅₄ (BSNT-zAl, 0.0 ≤ z ≤ 2.5) ceramics were prepared via a solid-state reaction, and the effects of Al doping on the microwave dielectric properties and defect behavior of the title compound were studied. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) photographs suggested that Al ions successfully entered the lattice to form tungsten-bronze-like solid solutions. With a small amount of Al substitution, the relative dielectric constant (ε_r), and the temperature coefficient of resonant frequency (τ_f) values decreased, whereas the quality factor (Q × f) substantially increased by approximately 50%. The defect-related extrinsic dielectric loss was clarified via the thermally stimulated depolarization current (TSDC) technique. With Al doping, the TSDC relaxation of across-grain-boundary oxygen vacancies () vanished, whereas that of defect dipoles () appeared at relatively low temperatures. Therefore, in the BSNT-zAl ceramics, oxygen vacancies were more inclined to interconnect with to form defect dipoles. This could reduce the activity of and account for the notable improvement in the Q × f values. In particular, the excellent characteristics of ε_r = 67.33, Q × f = 16 530 GHz, and τ_f = +0.87 ppm/°C were achieved in the specimens with z = 1.5 sintered at 1350°C for 4 hours.     

Oxygen permeation characteristics of sol‐gel derived barium‐substituted strontium ferrite membranes

The pervoskite‐type oxides have received attention due to their potential applications in catalysis, solid oxide fuel cells, gas sensors, and gas separable membranes. In view of their importance in oxygen separation from air, Ba_xSr_1?xFeO_3?δ (0≤x≤1.0) samples have been synthesized by sol‐gel process and investigated with regard to phase(s), oxygen permeation, and electrical conductivity. These compounds possess at room temperature, a perovskite‐type cubic, mixture of rhombohedral and hexagonal, and hexagonal phase(s) depending upon the composition 0≤x≤0.94, x=0.96‐0.98, and x=1.0, respectively. The barium incorporation causes initially enhancement but decrease in electrical conductivity above x=0.94. Above 800°C, all the compositions exhibit a stable cubic phase. The compacts made in the form of discs serve as stable oxygen permeable membranes displaying flux density () of ~2.45‐3.58 mL/cm².min at 1000°C. A good correlation has been demonstrated between the oxygen permeation and the electrical conductivity data. The maximum values of and conductivity correspond to Ba_xSr_1?xFeO_3?δ (x=0.94) with a perovskite‐type cubic structure. Hence, this membrane is quite suitable for oxygen separation technology.