Strontium Substitution Research Articles

Structural Characterization of Microwave-Assisted Solution-Synthesized Strontium-Substituted Hydroxyapatite

Hydroxyapatite and strontium-substituted hydroxyapatite nanoparticles (n-HA and Sr-HA) were prepared by microwave-assisted solution synthesis with aqueous solutions of various Sr/(Sr[Formula: see text]Ca) molar ratios ranging from 0% to 15%. The structural properties of the hydroxyapatite powders were investigated by X-ray powder diffraction, Fourier transform infrared spectroscopy and Raman spectra, field emission scanning electron microscopy coupled with energy dispersive X-ray spectrometry and transmission electron microscopy. The results confirmed that strontium ions had been incorporated into the hydroxyapatite lattice. The synthetic n-HA and Sr-HA nanocrystalline consisted of hydroxyapatite crystalline phase with hexagonal structure, and the particle size was 30–40 × 60–70[Formula: see text]nm and 40–50 × 70–80[Formula: see text]nm, respectively. The calcined HA particle size ranged from about 120[Formula: see text]nm to 150[Formula: see text]nm, the calcined Sr-HA products were composed of spherical aggregates with a size of about 70–100[Formula: see text]nm. The incorporation of Sr ions lead to the formation of vacancies in the crystal structure of the HA. The results indicated that the strontium substitution did not change the crystal structures. More Sr resulted in less calcined crystallites and formed agglomerates owing to the size effect.

Crystal structure, oxygen nonstoichiometry, thermal expansion and conductivity of (Nd,Sr)(Fe,Co)O3 − δ oxides

A series of samples with overall composition Nd1−xSrxFe1−yCoyO3−δ (x=0.7, 0.0≤y≤1.0) and (y=0.3, 0.0≤x≤1.0) were prepared by glycerol nitrate technique and characterized by X-ray diffraction, thermogravimetric analysis, iodometric titration and dilatometry. Nd1−xSrxFe0.7Co0.3O3−δ with 0.0≤x≤0.5 possesses orthorhombic structure (sp. gr. Pbnm) and reveals O-type→O/-type→O-type structural transition around x=0.3. The orthorhombic distortion decreases with the increasing strontium substitution and solid solutions Nd1−xSrxFe0.7Co0.3O3−δ with 0.7≤x≤1.0 and Nd0.3Sr0.7Fe1−yCoyO3−δ with 0.0≤y≤1.0 exhibit the cubic structure (sp. gr. Pm3m). The structural parameters were refined using Rietveld full-profile analysis. The changes of oxygen content in Nd1−xSrxFe1−yCoyO3−δ versus temperature were determined by the thermogravimetric analysis. The gradual substitution of neodymium by strontium or of iron by cobalt leads to the decrease of oxygen content. The thermal expansion measurements of Nd1−xSrxFe0.7Co0.3O3−δ (x=0.3; 0.4; 0.5 and 0.7) were performed and chemical expansion constituents have been separated. The electrical conductivity significantly increased with strontium content in low temperature range. The influence of Sr content diminished in high temperature range.

On the sol-gel synthesis and characterization of (BaSr)(CeZr)O3-based fuel cell electrolytes

Proton-conducting ceramics have been very useful due to their potential applications in fuel cells, electrolysers, and hydrogen membranes. The proton-conducting fuel cell electrolytes (Ba1−xSrx)(Ce0.75Zr0.10Y0.15)O3−δ (x = 0–1.0) have been synthesized through sol-gel method and characterized with regard to phase, structural stability, and electrical conductivity. The structural behavior has been investigated by X-ray diffraction and theRaman spectroscopy. The XRD analysis shows perovskite-type cubic structure and values of lattice parameter lie in the range of ~4.29 to ~4.40 A. Strontium substitution leads to lattice contraction, strengthening of the metal-oxygen bond, and increase of oxygen content (3−δ). The Raman spectra show different types of stretching/vibrations corresponding to octahedral, M-O stretching, and oxygen vacancies. The electrical conduction was found to be protonic in nature and decreases with increase of strontium insertion. The composition x = 0.4 shows relatively better structural stability against humid air/boiling water condition while inferior in carbon dioxide atmosphere.

Effect of Strontium Doping on the Structural, Morphological, and Dielectric Properties of PZT Ceramics

Strontium-modified lead zirconate titanate ceramics was prepared by the polymeric precursor method. The effect of Pb (II) substitution by Sr (II) in A site of the perovskite structure at molar percentages of 0.0, 0.2, 0.4 and 0.6 mol% was investigated through XRD and Rietveld method. The increasing of strontium amount displaces the morphotropic phase boundary toward to tetragonal phase and that results can be associated to the tetragonal lattice expansion besides the rhombohedral opposite phenomenon. The effect of strontium substitution on the dielectric properties for sintered ceramics is also investigated and showed the strontium substitution leads to reduction of weight loss and increasing of density for sintered ceramic. The Kc and Tc oscillates as function of ceramic morphology and is not possible to verify the existence of conductive intergrains defects by loss tangent curves. An intrinsic event can be occurring because considerable lattice distortion was verified in tetragonal and rhombohedral structures for powder samples.

A- and B-site doping effect on physicochemical properties of Sr2−xBaxMMoO6 (M = Mg, Mn, Fe) double perovskites — candidate anode materials for SOFCs

In this work, we evaluate the physicochemical properties of Sr[Formula: see text]BaxMMoO6 (M [Formula: see text] Mg, Mn, Fe) double perovskites as alternative anode materials for solid oxide fuel cells, for which the effect of substitution of strontium by barium in a full range of compositions is studied. The crystal structure, microstructure, characterization of transport properties (electrical conductivity, Seebeck coefficient) and oxygen content as a function of temperature, as well as chemical stability in oxidizing and reducing conditions are discussed. Fe- and Mo-containing Sr[Formula: see text]BaxFeMoO6 oxides show very high total conductivities with values of 100–1000 S[Formula: see text][Formula: see text]cm[Formula: see text], while Sr[Formula: see text]BaxMgMoO6 present good redox stability.

Effects of strontium substitution on the phase transformation and crystal structure of calcium phosphate derived by chemical precipitation

This study focused on the effects of strontium substitution on the phase transformation and crystal structure of calcium phosphate. Chemical precipitation was used to prepare Sr-doped hydroxyapatite (HA) precursor powders. The phase transformation of the as-prepared samples during sintering was analyzed. The powders were characterized by X-ray diffraction, X-ray fluorescence spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Quantitative analysis of the phase content and fine structure was performed by Rietveld refinement. Sr doping was found to facilitate the phase transformation from HA to beta-tricalcium phosphate (β-TCP) at 1000°C. The β-TCP content increased with increasing Sr content, causing a decline in the ratio of HA to β-TCP. With Sr contents of ≤5mol%, HA remained the major phase in the biphasic mixtures; in contrast, with Sr contents of ≥15mol%, the mass fraction of β-TCP exceeded 50%. The incorporation of Sr2+ into HA and β-TCP caused the lattice parameters of both phases to increase. Additionally, Sr incorporation slightly enhanced the binding energy of Ca. The study confirmed that Sr doping could be used to modulate the phase fractions of HA and β-TCP. The effective partial substitution of Sr in both HA and β-TCP makes these materials promising for bone repair.

Strontium substitution in apatitic CaP cements effectively attenuates osteoclastic resorption but does not inhibit osteoclastogenesis

Strontium ions were discovered to exert a dual effect on bone turnover, namely an inhibition of cell-driven bone resorption and a simultaneous stimulation of new bone tissue formation. A variety of strontium containing calcium phosphate bone cements (SrCPC) have been developed to benefit from both effects to locally support the healing of osteoporotic bone defects. While the stimulating effect of strontium modification on bone forming cells has been demonstrated in a number of studies, this study focuses on the inhibition and/or reduction of osteoclastogenesis and osteoclastic resorption by a strontium substituted calcium phosphate bone cement (SrCPC). Human peripheral blood mononuclear cells (PBMC) were differentiated into osteoclasts in the presence of different Sr2+-concentrations as well as on the surface of SrCPC disks. Osteoclastogenesis of PBMC was shown to be merely unaffected by medium Sr2+-concentrations comparable to those released from SrCPC in vitro (0.05–0.15mM). However, an altering effect of 0.1mM strontium on the cytoskeleton of osteoclast-like cells was shown. In direct contact to SrCPC disks, these cells exhibited typical morphological features and osteoclast markers on both RNA and protein level were formed. However, calcium phosphate resorption was significantly decreased on strontium-containing cements in comparison to a strontium-free control. This was accompanied by an intracellular accumulation of strontium that increased with substrate strontium content as demonstrated by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). This study illustrates that SrCPC do not inhibit osteoclastogenesis but significantly attenuate osteoclastic substrate resorption in vitro. Statement of SignificanceStrontium ions have been shown to promote bone formation and inhibit bone resorption. Therefore strontium is successfully used in the treatment of osteoporosis and also inspired the development of strontium-containing strontium/calcium phosphate bone cements (SrCPC). Studies have shown the positive effects of SrCPC on bone formation, however, the inhibiting effect of strontium on bone resorption in the context of such cements has not been shown so far. We found that the formation of bone-resorbing osteoclasts is not inhibited, but that their resorption activity is decreased in contact to SrCPC. The former is important since those cells play an important role in the bone cell signaling. The latter is a key requirement in osteoporosis therapy, which addresses excess bone resorption.

Development of novel strontium containing bioactive glass based calcium phosphate cement

ObjectiveThe aim of this study was to investigate the effect on properties of increasing strontium substitution for calcium in bioactive glasses used as precursors for novel calcium phosphate cements. MethodsGlasses were produced by progressively substituting strontium for calcium. Cements were prepared by mixing the glass powder with Ca(H2PO4)2 powder with a 2.5% solution of Na2HPO4. Setting times and compressive strength were measured after 1h, 1 day, 7 days and 28 days immersion in Tris buffer solution. X-ray diffraction (XRD), Fourier transform infrared spectroscopy and radiopacity were measured and crystal morphology was assessed using scanning electron microscopy. ResultsA correlation between the phases formed, morphology of the crystallites, setting time and compressive strength were analyzed. Setting time increased proportionally with strontium substitution in the glass up to 25%, whereas for higher substitutions it decreased. Compressive strength showed a maximum value of 12.5MPa and was strongly influenced by the interlocking of the crystals and their morphology. XRD showed that the presence of strontium influenced the crystal phases formed. Octacalcium phosphate (Ca8H2(PO4)6·5H2O, OCP) was the main phase present after 1h and 1 day whereas after 28 days OCP was completely transformed to strontium-containing hydroxyapatite (SrxCa(10−x)(PO4)6(OH)2, SrHA). Radiopacity increased proportionally to strontium substitution in the glass. SignificanceA novel method to develop a bone substitute forming in vitro SrHA as a final product by using a bioactive glass as a precursor was shown. These novel injectable bioactive glass cements are promising materials for dental and orthopedic applications. Further in vivo characterizations are being conducted.

Structure and activity of strontium substituted LaCoO3 perovskite catalysts for syngas conversion

Study of the catalytic activity of LaCoO3 perovskite catalysts with varying degrees of strontium substitution (La1-xSrxCoO3) in the Fischer–Tropsch synthesis is presented for the first time in this paper. It was found that Sr substitution improves the catalyst’s reducibility and increasing strontium substitution beyond a threshold of 10mol% Sr has an inverse effect on the catalytic performance in the syngas conversion. For x≤0.1, the catalysts exhibited a stable rhombohedral structure, which leads to well dispersion of active centre Co0 during the reduction process and displayed a high catalytic activity. For x≥0.2 the catalyst structure was gradually changed, from a rhombohedral to a less stable cubic structure, and leads to Co0 sintering. The turnover frequency of Co atom in the Fischer–Tropsch reaction decreased significantly with increasing strontium substitution levels due to the loss of active catalyst surface. The La0.9Sr0.1CoO3 catalyst showed the highest catalytic activity in the Fischer–Tropsch synthesis.

Highly controlled coating of strontium-doped hydroxyapatite on electrospun poly(ɛ-caprolactone) fibers.

Electrospun fibers show great potential as scaffolds for bone tissue engineering due to their architectural biomimicry to the extracellular matrix (ECM). Cation substitution of strontium for calcium in hydroxyapatite (HAp) positively influences the mechanism of bone remodeling including enhancing bone regeneration and reducing bone resorption. The objective of this study was to attach strontium-doped HAp (SrHAp) to electrospun poly(ɛ-caprolactone) (PCL) fibers for creation of novel composite scaffolds that can not only mimic the architecture and composition of ECM but also affect bone remodeling favorably. We demonstrated for the first time the highly controlled SrHAp coatings on electrospun PCL fibers. We showed the reproducible manufacturing of composite fiber scaffolds with controllable thickness, composition, and morphology of SrHAp coatings. We further showed that the released strontium and calcium cations from coatings could reach effective concentrations within 1 day and endure more than 28 days. Additionally, the Young's modulus of the SrHAp-coated PCL fibers was up to around six times higher than that of raw fibers dependent on the coating thickness and composition. Together, this novel class of composite fiber scaffolds may hold great promise for bone regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 753-763, 2017.

Synthesis of Strontium Substituted Hydroxyapatite through Different Precipitation Routes

The aim of this work was to evaluate the effect of precursor materials used in the synthesis on the Sr incorporation levels into the hydroxyapatite (HAp) lattice and to characterize the synthesis products. HAp powders containing various amounts of Sr were synthesized through three different precipitation routes. In all cases, the as-synthesized products were found to be pure HAp. However, atomic absorption spectrometry analysis showed that by reacting orthophosphoric acid with calcium hydroxide and strontium hydroxide, as well as by reacting diammonium hydrogen phosphate with calcium nitrate tetrahydrate and strontium nitrate a significant proportion of the Sr added, did not substitute into the HAp lattice. X-ray diffraction analysis revealed that the effect of substituting relatively high amounts (up to 3.69 ± 0.37 wt.%) of Sr into the HAp lattice was to decrease the cristallinity. Brunauer-Emmett-Teller (nitrogen absorption) analysis showed that the incorporation of Sr reduced particle sizes of the precipitated HAp products. Contrary, scanning electron microscopy revealed that the incorporation of Sr increased length of the precipitated needle-like particles.

Gel-derived SiO2–CaO–P2O5 bioactive glasses and glass-ceramics modified by SrO addition

The effect of SrO substitution for CaO in two sol–gel glasses with different chemical compositions (mol%) A2Sr: (54−x)CaO–xSrO–6P2O5–40SiO2 and S2Sr: (16−x)CaO–xSrO–4P2O5–80SiO2 (x=0, 1, 3 and 5) stabilized at 700°C on their structure (XRD, FTIR) and bioactive properties (SBF test) was investigated. Preliminary in vitro tests using human articular chondrocytes of selected A2Sr glass were also conducted. Moreover, the subject of this study was to detect the changes on material properties after heat treatment at 1300°C. The results show that the effect of strontium substitution on structure, bioactivity and crystallization after treatment at both the above temperatures strongly depends on CaO/SiO2 molar ratio. The presence of 3–5mol% of strontium ions creates more expanded glass structure but does not markedly affect crystallization ability after low temperature treatment. Sintering at 1300°C of A2 type glasses results in crystallization of pseudowollastonite, hydroxyapatite and also Sr-substituted hydroxyapatite for 3–5mol% of SrO substitution. The increase of strontium concentration in silica-rich materials after sintering leads to appearance of calcium strontium phosphate instead of calcium phosphate. Bioactivity evaluation indicates that substitution of Sr for Ca delays calcium phosphate formation on the materials surface only in the case of silica-rich glasses treated at 700°C. Calcium-rich glasses, after both temperature treatments, reveals high bioactivity, while crystal size of hydroxyapatite decreases with increasing Sr content. High temperature treatment of high-silica glasses inhibits their bioactivity. Preliminary in vitro tests shows Sr addition to have a positive effects on human articular chondrocytes proliferation and to inhibit cell matrix biomineralization.

Strontium substituted bioactive glasses for tissue engineered scaffolds: the importance of octacalcium phosphate.

Porous bioactive glasses are attractive for use as bone scaffolds. There is increasing interest in strontium containing bone grafts, since strontium ions are known to up-regulate osteoblasts and down regulate osteoclasts. This paper investigates the influence of partial to full substitution of strontium for calcium on the dissolution and phase formation of a multicomponent high phosphate content bioactive glass. The glasses were synthesised by a high temperature melt quench route and ground to a powder of <38 microns. The dissolution of this powder and its ability to form apatite like phases after immersion in Tris buffer (pH 7.4) and simulated body fluid (SBF) was followed by inductively coupled plasma optical emission spectroscopy (ICP), Fourier transform infra red spectroscopy (FTIR), X-ray powder diffraction (XRD) and 31P solid state nuclear magnetic resonance spectroscopy up to 42 days of immersion. ICP indicated that all three glasses dissolved at approximately the same rate. The all calcium (SP-0Sr-35Ca) glass showed evidence of apatite like phase formation in both Tris buffer and SBF, as demonstrated after 3 days by FTIR and XRD analysis of the precipitate that formed during the acellular dissolution bioactivity studies. The strontium substituted SP-17Sr-17Ca glass showed no clear evidence of apatite like phase formation in Tris, but evidence of an apatite like phase was observed after 7 days incubation in SBF. The SP-35Sr-0Ca glass formed a new crystalline phase termed “X Phase” in Tris buffer which FTIR indicated was a form of crystalline orthophosphate. The SP-35Sr-0Ca glass appeared to support apatite like phase formation in SBF by 28 days incubation. The results indicate that strontium substitution for calcium in high phosphate content bioactive glasses can retard apatite like phase formation. It is proposed that apatite formation with high phosphate bioactive glasses occurs via an octacalcium phosphate (OCP) precursor phase that subsequently transforms to apatite. The equivalent octa-strontium phosphate does not exist and consequently in the absence of calcium, apatite formation does not occur. The amount of strontium that can be substituted for calcium in OCP probably determines the amount of strontium in the final apatite phase and the speed with which it forms.

Developing an in situ forming polyphosphate coacervate as a new liquid embolic agent: From experimental design to pilot animal study

A radiopaque temporary liquid embolic agent was synthesized from polyphosphate (PP) coacervates and optimized using a design of experiments approach. Variables studied were: strontium substitution (0–15mol%), barium substitution (0–15mol%), PP concentration and degree of polymerization of the polyphosphate (Dp). The viscosity, radiopacity and cell viability of the resulting coacervates were measured for 60 formulations and response surface modeling was used to determine the optimum coacervate that maximized radiopacity and cell viability. The optimum coacervate made from PP with a large Dp (9.5g NaPP/100mL, 2.2mol% Sr, 9mol% Ba and 3.8mol% Ca) was taken forward to a pilot animal trial. In this rabbit model, PP embolic agent successfully occluded the central auricular artery with promising biocompatibility. Further study is required to optimize the cohesiveness and clinical effectiveness of PP as an in situ setting temporary embolic agent. Statement of significanceThis article describes the development of a new radiopaque temporary liquid embolic agent from the optimization using design of experiments to a pilot animal study. Embolization is a minimally invasive interventional radiology procedure used to block blood flow in a targeted blood vessel. This procedure is used to treat many conditions including: tumors, aneurysms and arteriovenous malformations. Currently, no inherent radiopaque embolic agents are available in the clinic, which would allow for direct imaging of the material during the procedure and follow up treatment.

Therapeutic Ion-Releasing Bioactive Glass Ionomer Cements with Improved Mechanical Strength and Radiopacity

Bioactive glasses (BG) are used to regenerate bone, as they degrade and release therapeutic ions. Glass ionomer cements (GIC) are used in dentistry, can be delivered by injection and set in situ by a reaction between an acid-degradable glass and a polymeric acid. Our aim was to combine the advantages of BG and GIC, and we investigated the use of alkali-free BG (SiO2-CaO-CaF2-MgO) with 0 to 50% of calcium replaced by strontium, as the beneficial effects of strontium on bone formation are well documented. When mixing BG and poly(vinyl phosphonic-co-acrylic acid), ions were released fast (up to 90% within 15 minutes at pH 1), which resulted in GIC setting, as followed by infrared spectroscopy. GIC mixed well and set to hard cements (compressive strength up to 35 MPa), staying hard when in contact with aqueous solution. This is in contrast to GIC prepared with poly(acrylic acid), which were shown previously to become soft in contact with water. Strontium release from GIC increased linearly with strontium for calcium substitution, allowing for tailoring of strontium release depending on clinical requirements. Furthermore, strontium substitution increased GIC radiopacity. GIC passed ISO10993 cytotoxicity test, making them promising candidates for use as injectable bone cements.

Synthesis and Characterization of Calcium Phosphate Compounds with Strontium and Magnesium Ionic Substitutions

Los bioceramicos ofrecen ventajas en la reparacion y regeneracion de tejidos duros utilizandose como relleno en cavidades oseas y como relleno particulado en cementos oseos de aplicaciones quirurgicas. Regeneracion y estimulacion de la osteosintesis a traves de la liberacion de iones esenciales, como el estroncio (Sr) y magnesio (Mg) es un campo relativamente nuevo. Por lo tanto, existe un gran interes en la investigacion de diversas sustituciones ionicos sobre la estructura cristalografica y las caracteristicas para su uso en la prevencion de osteoporosis y aumento de la formacion osea con disminuir la resorcion osea. En este estudio, se sintetizo muestras de fosfato de calcio con sustituciones ionicos Sr y Mg. Las muestras se caracterizaron usando difraccion de rayos X, espectroscopia infrarroja por transformada de Fourier, y la espectroscopia de masas con plasma acoplado inductivamente. Se observo hidroxiapatita, fosfato tricalcico beta, y las fases amorfas. Dependiendo de la sustitucion ionica, el tamano del cristal y cristalinidad variaron de 22 nm a 130 nm y de 84% a 99,6%, respectivamente. La relacion Ca/P vario desde 0,72 hasta 1,82. Los resultados demostraron el efecto de las inclusiones de Sr y Mg en fosfato de calcio en parametros importantes que se utilizan en varias aplicaciones de bioceramicos.

The osteogenic response of mesenchymal stromal cells to strontium-substituted bioactive glasses.

Bioactive glasses are known to stimulate bone healing, and the incorporation of strontium has the potential to increase their potency. In this study, calcium oxide in the 45S5 bioactive glass composition was partially (50%, Sr50) or fully (100%, Sr100) substituted with strontium oxide on a molar basis. The effects of the substitution on bioactive glass properties were studied, including density, solubility, and in vitro cytotoxicity. Stimulation of osteogenic differentiation was investigated using mesenchymal stromal cells obtained from rat bone marrow. Strontium substitution resulted in altered physical properties including increased solubility. Statistically significant reductions in cell viability were observed with the addition of bioactive glass powders to culture medium. Specifically, addition of ≥ 13.3 mg/ml of 45S5 bioactive glass or Sr50, or ≥ 6.7 mg/ml of Sr100, resulted in significant inhibition. Real‐time PCR analyses detected the upregulation of genes associated with osteoblastic differentiation in the presence of all bioactive glass compositions. Some genes, including Alpl and Bglap, were further stimulated in the presence of Sr50 and Sr100. It was concluded that strontium‐substituted bioactive glasses promoted osteogenesis in a differentiating bone cell culture model and, therefore, have considerable potential for use as improved bioactive glasses for bone tissue regeneration. © 2015 The Authors. Journal of Tissue Engineering and Regenerative Medicine Published by John Wiley & Sons Ltd.

Strontium-Containing Apatite/Poly Lactide Composites Favoring Osteogenic Differentiation and in Vivo Bone Formation

Strontium was shown to enhance bone growth; however, its oral administration may lead to severe side effects. The application of strontium in orthopedic biomaterials may therefore be an alternative to achieve targeted and sustained strontium treatment to the surgery site in aid of bone growth locally. In this study, strontium-containing composites were prepared by introducing various levels of strontium into amorphous apatite and extruding the obtained apatite powders into polylactide in a weight ratio of 1:1. Strontium substitution increased apatite dissolution and enhanced the degradation behavior of the resulting composites. Sustained and dose-dependent strontium release from the composites was observed for up to 24 weeks in simulated physiological solution, indicating that strontium release can be tuned by its substitution level in the embedded apatite. Strontium-containing composites enhanced the osteogenic differentiation of murine mesenchymal stromal cells in vitro in a dose-dependent fashion. After heterotopic implantation with the combination of rhBMP-2, bone formation on strontium-containing composites was enhanced. These results suggest that strontium-releasing composites provide a local ion-rich (i.e., Sr2+ as well as Ca2+ and PO43–) environment that favors osteogenic differentiation and in vivo bone formation

Effects of strontium doping on the structure, oxygen nonstoichiometry and electrochemical performance of Pr2−xSrxNi0.6Cu0.4O4+δ (0.1 ≤ x ≤ 0.5) cathode materials

Pr2−xSrxNi0.6Cu0.4O4+δ (PSNCO, x = 0.1, 0.3, 0.5) oxides with K2NiF4-type structure are synthesized by a glycine–nitrate process as potential cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). The influence of strontium substitution on the structure, oxygen nonstoichiometry, electrical property and electrochemical performance is investigated. Iodometric titration method is employed to study the oxygen nonstoichiometry and the formal valence of nickel. The maximum electrical conductivity reaches 109 S cm−1 at 450 °C in air for Pr1.7Sr0.3Ni0.6Cu0.4O4+δ material. Area specific resistance (ASR) values of all compositions are below 0.11 Ω cm2 at 800 °C, and the Pr1.7Sr0.3Ni0.6Cu0.4O4+δ composition has the lowest ASR value of 0.063 Ω cm2 at 800 °C. Open circuit voltage (OCV) and maximum power density of the single cell (NiO–SDC/SDC/PSNCO) are 0.767 V and 353 mW cm−2 at 800 °C, respectively. The preliminary results indicate that Pr2−xSrxNi0.6Cu0.4O4+δ materials could be good candidates for IT-SOFCs cathode materials.

Studies on luminescence from a cerium-doped strontium stannate phosphor.

The crystal structure and morphology of Ce(3+) -doped SrSnO3 materials prepared using the solid-state reaction method were extensively characterized using experimental techniques. X-Ray diffraction results show that the cerium substitution of strontium does not change the structure of the strontium stannate. Raman spectroscopy was used to investigate the microstructures and lattice vibrations. Environmental scanning electron microscopy images showed that phosphors aggregate and their particles form irregular shapes. SrSnO3 exhibits an intense green emission with a broad band originating from the 5d(1) → 4f(1) transition of cerium. It was observed that, after exposure to beta-irradiation, the glow curve of this material has two broad thermoluminescence peaks, one centered at ~ 127°C and the other at ~ 245°C for a heating rate of 5 K/s. The kinetic parameters, which include the frequency factor and the activation energy of the material, were calculated using Chen's method, after beta-irradiation. The fading and reusability of the phosphor were also studied and it was found that the phosphor is suitable for radiation dosimetry.