Doped Strontium Cerate Research Articles

Growth of proton conducting strontium cerate composites

The increased population and modern way of life have greatly depleted the effectiveness of traditional energy production methods. There is a strong demand for environmentally friendly and renewable alternatives to replace the old systems. Sustainable energy production systems have emerged as a vital replacement for the conventional use of fossil fuels. Among these, solid oxide fuel cells (SOFCs) play a significant role. Recently, researchers have developed electrolyte components for SOFCs using proton-conducting perovskites with excellent conductivity. This critical assessment presents a yearly overview of innovative strategies for utilizing doped strontium cerate perovskites in energy production systems, a novel approach. The importance of identifying dopants that can enhance conductivity and stability in strontium cerate composites is emphasized, creating a crucial element for high-performance energy systems. Through a comparative study, it's been found that rare earth elements with smaller ionic radii, such as thulium-doped strontium cerium zirconate in an additional composite form, can outperform the traditionally used ytterbium-doped strontium cerate composites in proton-conducting applications.

Study on structural and photoluminescence property of SrCeO3 and SrCe0.98Sm0.02O3 perovskites

Perovskites with improved structural and photoluminescence properties can be furnished by doping with rare earth elements. Strontium cerate perovskite host matrix plays a prime role in energy devices due to improved functional property, namely electrical conductivity. Electrochemical cells, hydrogen extractors, sensors have been greatly manufactured by innovators in past decade using doped strontium cerate perovskites. But only minimal innovation in the area of luminescence of this particular perovskite was found. In the present study, SrCeO3 and SrCe0.98Sm0.02O3 perovskites are synthesized for investigating the photoluminescence spectra. The perovskites are prepared by gel combustion technique. X-ray diffraction studies were carried out to investigate the evolution of the crystalline phase of the ceramic powder. Absorption bands in the UV region occur due to charge transfer transitions between the 4f orbital of Ce4+ and 2p orbital of oxygen ion in SrCeO3. Under UV excitations, the prepared perovskite nano phosphors show blue emission and orange-red emission respectively and was confirmed using CIE 1931 chromaticity diagram. The vibrational modes were further analysed using Raman spectra. So, these perovskites can be promising candidate as blue phosphor and red phosphor in light-emitting devices and applications.

Assessing the improved luminescence of SrCe1-xSmxO3 perovskite by concentration controlled extra oxidizer substitution

Strontium cerate perovskite nano phosphors when doped with rare earth elements show improved functional properties such as electrical conductivity and photoluminescence. Electrical conductivity investigations on doped strontium cerates have been studied widely over decades for application in electrochemical cells, hydrogen sensors, hydrogen extractors, etc. But only minimal research has been developed in the amelioration of photoluminescence in rare earth-doped strontium cerates. In the present study, samarium-doped strontium cerate perovskite nanophosphors were considered for utilization in optoelectronic applications. The perovskites SrCe1-xSmxO3 (x = 0.01,0.02,0.03) were prepared via a low-temperature gel combustion approach with citric acid as chelating agent and ammonia solution as an extra oxidizer. The influence of concentration variation on the evolution behaviour of the crystalline phase as well as the luminescence characteristics of ceramic powders are investigated using X-ray diffraction and Photoluminescence characterization techniques. Experimental results indicate that the calcinating temperature of 1223 K in gel combustion synthesis, much lower than the conventional solid-state reaction is only needed for the single-phase perovskite formation. Also, a comparison study of the luminescence behaviour by replacing internal constituent extra oxidizer ammonia solution with ammonium nitrate is observed in this study, and conditions for maximum luminescence intensity are hence discussed. The observed results on photoluminescence studies indicate that an enhancement in the luminescence intensity of SrCe0.98Sm0.02O3 occurred when we replaced extra oxidizer ammonia solution with ammonium nitrate. Thus, a bright orange-scarlet red emitting perovskite nano phosphor SrCe0.98Sm0.02O3 by the later technique can be synthesized and can act as an inevitable red phosphor coating the chip in LEDs, which can be a great revolution in energy savings applications.

Understanding the effect of Ce and Zr on chemical expansion in yttrium doped strontium cerate and zirconate by high temperature X-ray analysis and density functional theory

Aliovalent cation-doped perovskite-type oxides (ABO3) exhibit proton conductivity originating from the hydration of oxide ion vacancies, which is accompanied by structural deformation, i.e. chemical expansion. The chemical expansion may lead to failure in electrochemical devices, and thus it is necessary to understand the causes of this process at the atomic scale. In this study, the chemical expansion behaviors of Y-doped strontium cerate and zirconate were comparatively investigated. High-temperature X-ray diffraction (HT-XRD) and thermogravimetric analysis (TGA) revealed that the cerate exhibits larger chemical expansion. Density Functional Theory (DFT) calculations revealed that this tendency can be accounted for by the different atomic distribution of the Y dopant between the cerate and zirconate, which results in differences in the size of the oxide ion vacancies to be hydrated as well as different elastic character.

Thermoluminescence study of beta irradiated Sr2CeO4:Eu3+ phosphor synthesized using solution-combustion process

Eu3+ doped strontium cerate (Sr2CeO4:Eu3+) phosphor was synthesized by solution - combustion technique using urea as a reducer at initiating temperature of 600 °C. The morphological, structural and thermoluminescence (TL) properties of Sr2CeO4:Eu3+ were investigated. X-ray diffraction patterns revealed the polycrystalline nature of Sr2CeO4:Eu3+ with single phase. The scanning electron microscopy photographs shows that the particle size distributions of all phosphor powders are rather broad with particle diameters in the range from ~ 50 nm to ~ 2 µm. The TL glow curve was found which composed of two well defined peaks at around 323 and 372 K. The electron-trapping properties in terms of TL glow curves are discussed in detail. The TL intensity was recorded for different beta doses and it is seen to increase with increasing doses. A linear behaviour of the TL intensity and peak temperature versus irradiation dose was found for dose up to 185 Gy. The effect of different heating rates was also studied and is seen to cause slight peak temperature shifts. Repeated measurements on the same sample seem not to have any effect on peak temperature positions and TL intensity indicating the sample was stable. Different kinetic parameters like activation energy (E), frequency factor (s) and geometrical factor (μg) were calculated for different TL glow curves. Trap depths were also calculated by different methods including initial rise, variable heating rate and peak shape methods.

Gadolinium Doped Strontium Cerate Prepared by Citric-Nitrate Auto-Combustion Process and Intermediate Temperature Electrical Properties of Its Composite Electrolyte

Gadolinium Doped Strontium Cerate Prepared by Citric-Nitrate Auto-Combustion Process and Intermediate Temperature Electrical Properties of Its Composite Electrolyte

Ultraviolet to near-infrared conversion in Nd3+ doped strontium cerate nanophosphors

Novel NIR luminescent nanomaterial, Sr2CeO4:Nd3+ was successfully prepared with Pechini method. The Sr2CeO4:Nd3+ nanophosphors had an orthorhombic crystal structure, and showed plate-like morphology with length of about 260nm and width of about 130nm. Upon UV light excitation, the Sr2CeO4:Nd3+ nanophosphors exhibited strong NIR emission for the first time. The possible mechanisms of energy transfer for Nd3+ doped Sr2CeO4 were briefly analyzed. The Sr2CeO4:Nd3+ nanophosphors may be poised to be exploited in near-infrared light amplified applications or used as a high efficiency laser material based on their peculiar optical properties.

Conductivity and chemical stability of SrCe0.92Nb0.03Tm0.05O3− membrane prepared by modified sol–gel method

Abstract SrCe 0.92 Nb 0.03 Tm 0.05 O 3− δ powders were synthesized by a modified sol–gel method using citrate as a chelating agent. X-ray diffraction (XRD) analysis verified SrCe 0.92 Nb 0.03 Tm 0.05 O 3− δ powders and membranes consisting of a single perovskite phase. The morphologies of the sintered membranes were investigated by using scanning electron microscopy (SEM) technique. Stability tests demonstrated that the Nb introduction into doped strontium cerate greatly enhanced the chemical stability. Electrical conductivities of SrCe 0.92 Nb 0.03 Tm 0.05 O 3− δ and SrCe 0.95 Tm 0.05 O 3− δ were measured by the four-point DC method under 10% H 2 /He atmosphere and temperatures (700–900 °C). With a maximum conductivity of 0.0067 S cm −1 at 900 °C, the total electrical conductivity of SrCe 0.92 Nb 0.03 Tm 0.05 O 3− δ increases with increasing temperature. The H 2 permeation flux of SrCe 0.92 Nb 0.03 Tm 0.05 O 3− δ is 0.035 mL cm −2 min −1 when 40% H 2 /He and Ar were used respectively as the feed and sweeping gases at 900 °C.

Experimental and theoretical studies of hydrogen permeation for doped strontium cerates

Non-galvanic hydrogen permeation properties of SrCe 0.95Yb 0.05O 3 − α (SCYb-5) and SrCe 0.95Tm 0.05O 3 − α (SCTm-5) dense membranes were investigated in a ‘wet’ hydrogen atmosphere where water vapour partial pressures were well defined and monitored for the entire duration of the experiments. The theoretical modelling of hydrogen permeation flux for SCYb-5 and SCTm-5 was also undertaken, and compared with experimental results. The parameter tuning was also performed by fitting the model to the experimental data obtained in this study. The experimental hydrogen permeation flux for SCYb-5 and SCTm-5 dense membranes was 6.8e − 9 mol/cm 2/s and 7.1e − 9 mol/cm 2/s, respectively, under the upstream hydrogen partial pressure of 0.25 atm (25%H 2/Ar) at 900 °C. As expected, the hydrogen permeation flux increases with the increase in the upstream hydrogen partial pressures, reaching the maximum flux of 1.4e − 8 mol/cm 2/s and 1.6e − 8 mol/cm 2/s, for SCYb-5 and SCTm-5 respectively, under the upstream hydrogen partial pressure of 1 atm (100%H 2) at 900 °C. Previous modelling used hydrogen permeation data collected by others in a permeation test conducted in a ‘dry’ hydrogen atmosphere (with unknown water vapour pressures). The modelled hydrogen permeation flux agreed well with the experimental data attained in this study, for both SCYb-5 and SCTm-5 samples. The parameter tuning further improved the model predictions for those samples. It was apparent that the modelled hydrogen flux agreed better with the experimental data obtained in this study (i.e. in a wet hydrogen atmosphere with known water vapour pressures).

Effects of hydrogen on phase stability of ytterbium doped strontium cerates

The effect of hydrogen on the phase stability of both SrCe 0.95Yb 0.05O 3 − α , (SCYb-5) powder and disk samples in both dry and wet hydrogen atmospheres was investigated. It was found that decomposition of the perovskite phase was especially evident in the disk samples treated in a dry hydrogen atmosphere , probably due to reduction of the tetravalent cerium ions to trivalent cerium ions in the sample. It was interesting to find that the extent of the decomposition of the perovskite phase was most influenced by the status (i.e. either disk or powder form) of the SCYb-5 samples, rather than the temperature or the extent of the reducing atmospheres. The findings of this study indicate that relaxation kinetics may play an important role in the phase stability of perovskite materials.

Hydrogen permeation through terbium doped strontium cerate membranes enabled by presence of reducing gas in the downstream

Hydrogen permeation through SrCe 1− x Tb x O 3− δ ( x = 0.025, 0.05 and 0.10) membranes using various gas streams as the sweep was investigated. Hydrogen impermeable SrCe 1− x Tb x O 3− δ membranes with air or inert gas in the downstream become hydrogen permeable when there is a reducing gas, such carbon monoxide or hydrogen, existing in the downstream. The membrane remains hydrogen permeable after the downstream sweep gas is changed from the reducing gas to the inert gas. This phenomenon is explained by the electronic conductivity of the materials. These results further confirm that SrCe 1− x Tb x O 3− δ (0.025 < x < 0.1) is a mixed proton–electron conducting material in a hydrogen containing atmosphere. The activation energy of hydrogen permeation is close to the activation energy of electronic conduction of the materials, confirming that the hydrogen permeation is determined by the electronic conductivity of the material. For SrCe 0.95Tb 0.05O 3− δ , increasing the downstream CO partial pressure from 0.001 to 0.1 atm leads to a small increase in hydrogen flux from 1.4 × 10 −2 to 1.6 × 10 −2 ml/cm 2 min. The hydrogen flux of SrCe 1− x Tb x O 3− δ increases with upstream hydrogen partial pressure.

Numerical study of hydrogen permeation flux in ytterbium doped strontium cerate and thulium doped strontium cerate (II)

This study analyses the hydrogen permeation flux model with (1) modifications in the defect concentration calculations where the concentration of substitutional cation on cerium site is utilised as the independent variable for the calculation, instead of the previous step-wise calculation with the concentration of oxygen vacancy as the independent variable and (2) the additional terms to include the oxygen partial pressure gradients for calculation of hydrogen permeation flux. The modification in the defect concentration method allows a short model simulation run time, which consequently allows incorporation of the concentration constraints in the parametric sensitivity analysis, but still produces the same set of defect concentrations as calculated in the previous methods. It is also found in this study that the discrepancy between the model and experimental results (in terms of the effect of changes in hydrogen partial pressure gradients on the hydrogen permeation flux) is not due to the influence of oxygen partial pressure gradients. Parametric sensitivity analysis shows that there is no significant difference in the sensitivity of the model by comparing Case A and B. The result of parameter tuning to predict the hydrogen permeation flux for 5% thulium doped strontium cerate in Case B shows a similar trend to the previous study (Case A). These results suggest negligible oxygen ion conductivities in these types of membrane, as reported in the literature.

Protonic and electronic conductivities of terbium doped strontium cerates

Electronic and protonic conductivities of Tb doped SrCeO 3 were measured in a hydrogen containing and hydrogen-free atmosphere of the same oxygen partial pressure in 500–900 °C. In a H 2 containing atmosphere, the material exhibits mixed electronic and proton-conductivity and, for SrCe 0.95Tb 0.05O 3-δ, the proton transfer number increases with decreasing temperature, from about 0.4 at 900 °C to about 0.8 at 500 °C. The total conductivity for SrCe 0.95Tb 0.05O 3-δ decreases from about 3 × 10 − 3 S/cm in the reducing atmosphere to 4 × 10 − 5 S/cm in air at 900 °C with an activation energy respectively of 39 kJ/mol and 76 kJ/mol for protonic and n-type electronic conduction. Results of XRD analysis show a decrease in the lattice volume of the SrCe 1- x Tb x O 3-δ with increasing Tb concentration. SrCe 1- x Tb x O 3-δ exhibits negligible proton-conductivity with x smaller than 0.005. At 800 °C under a reducing atmosphere, SrCe 1-xTb xO 3-δ, with x > 0.005, are mixed electronic and proton conductors with a maximum proton-conductivity of about 3 × 10 − 3 S/cm at x = 0.025 and proton transfer number of about 0.7 for x in the range of 0.005–0.125.

Mixed pronton–electron conducting properties of Yb doped strontium cerate

The electrical conductivity and hydrogen permeation properties of \({\hbox{Sr}\hbox{Ce}_{0.8}\hbox{Yb}_{0.2}\hbox{O}_{3-d}}\) membranes were studied as a function of temperature and \({P_{{\rm H}_{2}}}\) gradient. The bulk conductivity of \({\hbox{Sr}\hbox{Ce}_{0.8}\hbox{Yb}_{0.2}\hbox{O}_{3-d}}\) was an order of magnitude higher than the grain boundary conductivity over the temperature range 100–250 °C in feed gas of 4% H2/balance He (pH2O = 0.03 atm). The significantly lower grain boundary conductivity indicates that larger-grained materials might be more suitable for proton transport. The hydrogen flux through the membranes is proportional to thickness down to 0.7 mm. The hydrogen permeation flux increases with an increase in \({{P_{{\rm H}_{2}}}}\) gradient where the increase in hydrogen flux was explained by an increase in electron conduction as a function of temperature. The ambipolar conductivity calculated from hydrogen permeation fluxes shows the same \({{P_{{\rm H}_{2}}}}\) and \({{P_{{\rm O}_{2}}}}\) dependence as electron concentrations. The hydrogen and oxygen potential dependence of the ambipolar conductivity (\({\log \sigma_{\rm amb} =\log P_{\rm H_2}^{1/2} }\), \({\log \sigma_{\rm amb} =\log P_{{\rm O}_{2}}^{1/4} }\)) was understood from the defect structure. From this, it was confirmed that hydrogen permeation might be limited by electron transport at wet reducing atmosphere. From the temperature dependence of the electronic conductivity, the activation energy calculated at wet reducing conditions is 0.63 eV.

Monitoring of water dissolution into high temperature protonic conductors

Water dissolution into a doped strontium cerate ceramics was monitored with Raman spectroscopy. Since a Raman band at 630 cm − 1 is observed when the ceramics possess oxygen vacancies, and a relative intensity of the band to that of the main band at 345 cm − 1 ( I 630/ I 345) is proportional to its oxygen vacancy concentration, the parameter I 630/ I 345 was examined for the understanding of water dissolution behavior into the lattice. The parameter for quenched samples after annealing decreased gradually with an increase in water vapor partial pressure, P(H 2O) during annealing due to water dissolution, resulting in disappearance of some oxygen vacancies. An in situ monitoring of water dissolution into this ceramics was also performed employing an atmosphere-controlled system.

Microstructural analysis of doped-strontium cerate thin film membranes fabricated via polymer precursor technique

Nanocrystalline thin film membranes of terbium (Tb)-doped strontium cerate (SrCeO 3), which is of interest in the hydrogen (H 2) separation and solid oxide fuel cells (SOFCs), was synthesized via polymer precursor technique. Continuous and dense thin film membranes of composition SrCe 0.95Tb 0.05O 3 − δ were prepared using spin-coating technique by utilizing ethylene glycol (EG)-based polymeric precursor. The polymeric precursor was deposited on silicon-based substrates, and converted to dense polycrystalline thin film ceramic membranes by sintering at relatively low temperatures. The number of spin-coating cycles and sintering temperatures were systematically varied to study their effect on the film morphology, thickness, and crystallite size within the membranes. Fourier transform infrared (FTIR) spectroscopy was utilized to study the changes in the polymer chemistry during the membrane processing. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to examine thermal decomposition and thermodynamics of the synthesized precursor, respectively. The scanning electron microscopy (SEM) analysis was used to study the surface morphology and estimate average particle size as a function of number of spin-coating cycles and sintering temperatures. Atomic force microscope (AFM) was utilized to determine the roughness and quality of the spin-coated films. The membrane thickness, crystal structure, and nanocrystallite size were determined using focused ion-beam (FIB) milling and X-ray diffraction (XRD) techniques. Furthermore, the surface chemistry of the thin film membranes was studied by means of X-ray photoelectron spectroscopy (XPS). This study demonstrated that by using the EG-based polymeric precursor, dense and continuous Tb-doped SrCeO 3 thin film membranes, having thicknesses in the range of 0.2–2 μm and average nanocrystallite size of 8–70 nm, can be effectively synthesized by controlling the number of spin-coating cycles and sintering temperature.

Thick film miniaturized HCl gas sensor

Planar miniaturized HCl sensors were fabricated using thick films of the proton conducting solid electrolyte of strontium cerate doped with 10 mol% Nd 2O 3 interfaced with chloride ion conducting SrCl 2. The proton conducting film was fabricated by screen-printing using an ink of the doped strontium cerate on an alumina substrate which was then fired at 1773 K. SEM and EDAX analysis showed that the film is dense and bonds closely to the substrate, although some reactions were observed at the interface between the strontium cerate film and the alumina substrate. Results from impedance spectroscopy showed that conductivity of the thick film is similar to that of bulk strontium cerate. SrCl 2 was applied on the cerate film as a slurry from an aqueous solution which was then subsequently heated to 1153 K. Sensors based on forming an electrochemical chain with the two electrolytes showed fairly good HCl sensing properties in the 830–973 K temperature range. The emf values obtained were linear with respect to the logarithm of HCl concentration over a wide range (from several to 1000 ppm). The tubular sensors were also tested under similar conditions. The results given by film sensors are qualitatively comparable to the bulk tubular sensors, although not in complete quantitative agreement.

Thermodesorption study of barium and strontium cerates

The method of thermodesorption spectroscopy has been used for study of kinetic of hydrogen, oxygen and water molecule release from doped and undoped barium and strontium cerates. It was found that oxygen and water molecules are released from doped barium cerate samples whereas only water molecule desorption took place from doped strontium cerate samples. Shapes of thermodesorption spectra for pure barium cerate indicate that phase transformations take place in low and high temperature regions. It was shown that oxygen molecule desorption from doped barium cerates can be described by a second-order kinetic equation and an activation energies of reaction were determined.

Electrochemical Characterization of Mixed Conducting Ba(Ce0.8−yPryGd0.2)O2.9 Cathodes

The high proton conductivities of doped barium and strontium cerates has led to their consideration as electrolytes in fuel cells operating at intermediate temperatures (600-800°C). The electrochemical properties of Pr-doped barium gadolinium cerate have been investigated as part of our assessment of new mixed-conducting electrodes in fuel cells with barium cerate electrolytes. Substitution of Pr for Ce increases the total and electronic conductivities, and the total conductivity of exceeds ∼0.75 S/cm at 800°C in dry air. Electromotive force measurements indicate that the Pr-substituted samples also retain high proton and oxygen-ion conductivities despite their decreased ionic transport numbers. Cathodes prepared using these mixed-conducting Pr-doped barium-gadolinium cerates exhibit low cathodic overpotentials in electrolyte fuel cells. For example, the cathodic overpotential resistance of a cathode is at 800°C at current densities This is the lowest cathodic overpotential resistance reported for a perovskite electrode on a proton-conducting electrolyte fuel cell at this temperature. © 2000 The Electrochemical Society. All rights reserved.

Preparation and characterization of proton conducting terbium doped strontium cerate membranes

SrCe 0.95Tb 0.05O 3− δ (SCT) membranes with perovskite-type structure were prepared by the citrate method. Both gas-permeable and hermetic membranes can be obtained through the control of sintering steps. Membranes made from powders treated by an intermediate sintering step tend to be porous and gas-permeable, while hermetic membranes can be formed at lower final sintering temperatures by eliminating the intermediate sintering step. The membranes can be gas-tight even at a relative density of 71%. The density of the membrane increases with the increase of final sintering temperature. The oxalic acid method does not produce SCT with desired perovskite structure due to deficiency of strontium in the solid precipitates. The SCT membranes show appreciable proton conduction in a hydrogen-containing atmosphere.