Sr Co-doping Research Articles

Osteo-angiogenic activity of a micro/nano hierarchical SrSi-codoped hydroxyapatite coating on zirconium alloy

Numerous studies highlight the significance of biomimetic metallic implant surfaces for enhancing osseointegration through synergistic regulation of osteogenesis-angiogenesis. However, achieving clinical demands through singular structural or compositional biomimicry poses challenges. Therefore, the integration of both structural and compositional biomimicry, to closely emulate the host bone surface, is crucial for maximizing the biological activity of metallic implants. We synthesized a micro/nano hierarchical SrSi-codoped hydroxyapatite coating on Zr16Nb12Ti alloy through a simple microarc oxidation-hydrothermal reaction. Results revealed that Si doping enhances hydroxyapatite (HA) growth along the c-axis, forming large-sized nanorods. However, co-doping of Sr and Si inhibits grain growth by reducing crystal growth freedom, yielding a finer HA nanowire coating (MH-SrSi). MH-SrSi exhibits outstanding hydrophilicity attributed to the finer HA nanowires on the coating surface, promoting the adhesion of proteins and cells. Additionally, the released Sr and Si from MH-SrSi stimulate the secretion of osteogenesis-related proteins in osteoblasts and angiogenesis-related factors in endothelial cells, exhibiting a synergistic effect on promoting osteogenesis and angiogenesis. In vivo evaluation mirrors these results and shows that the micro/nano hierarchical structures of MH-SrSi elicited inward bone growth. Overall, MH-SrSi, combining structural biomimicry and compositional biomimicry, exhibits excellent osseointegration capability, making it a promising candidate for implant materials.

Ca and Sr co-doping induced oxygen vacancies in 3DOM La2−xSrxCe2−yCayO7−δ catalysts for boosting low-temperature oxidative coupling of methane

It is urgent to develop catalysts with application potential for oxidative coupling of methane (OCM) at relatively lower temperature. Herein, three-dimensional ordered macroporous (3DOM) La2−xSrxCe2−yCayO7−δ (A2B2O7-type) catalysts with disordered defective cubic fluorite phased structure were successfully prepared by a colloidal crystal template method. 3DOM structure promotes the accessibility of the gaseous reactants (O2 and CH4) to the active sites. The co-doping of Ca and Sr ions in La2−xSrxCe2−yCayO7−δ catalysts improved the formation of oxygen vacancies, thereby leading to increased density of surface-active oxygen species (O2−) for the activation of CH4 and the formation of C2 products (C2H6 and C2H4). 3DOM La2−xSrxCe2−yCayO7−δ catalysts exhibit high catalytic activity for OCM at low temperature. 3DOM La1.7Sr0.3Ce1.7Ca0.3O7−δ catalyst with the highest density of O2− species exhibited the highest catalytic activity for low-temperature OCM, i.e., its CH4 conversion, selectivity and yield of C2 products at 650 °C are 32.2%, 66.1% and 21.3%, respectively. The mechanism was proposed that the increase in surface oxygen vacancies induced by the co-doping of Ca and Sr ions boosts the key step of CH bond breaking and CC bond coupling in catalyzing low-temperature OCM. It is meaningful for the development of the low-temperature and high-efficient catalysts for OCM reaction in practical application.

Gelatin-mediated gallium-doped SrHA composite coatings with sequential antimicrobial and osteogenic functions for infected bone defect repair

In this study, gallium- and gelatin-modified strontium-doped hydroxyapatite (SrHA-Gel-Ga) bilayer coatings were prepared on titanium substrates by electrodeposition and spin-coating techniques. The results showed that gallium and gelatin were uniformly doped into the SrHA coatings, which exhibited good hydrophilicity and bioactivity. Furthermore, SrHA-Gel-Ga demonstrated good antimicrobial properties against E. coli and S. aureus, especially S. aureus. The co-doping of Sr and gelatin in the coatings was effective in mitigating the cytotoxicity of Ga. SrHA-Gel-Ga was better able to promote the adhesion, proliferation and early differentiation of MC3T3-E1 cells. This study provides a new strategy for the development of anti-infective bone repair coatings.

Design Sr, Mn-doped 3DOM LaCoO3 perovskite catalysts with excellent SO2 resistance for benzene catalytic combustion

Anti SO2 poisoning is a major scientific challenge in the field of VOCs catalytic combustion. To enhance sulfur resistance of 3DOM LaCoO3 perovskite catalysts, the strontium (Sr) and manganese (Mn) elements were doped to regulate and control its microstructure and electronic valence states of active metals. The macropore structure is constructed to accelerate the adsorption and diffusion of benzene and intermediate species and promote the deep oxidation in ordered macropores. Surprisingly, we observed that the co-doping of Sr and Mn components resulted in the superior catalytic performance for benzene catalytic combustion. Especially, the sulfur resistance of LaCoO3 catalyst was significantly improved due to the doping of Sr and Mn species. Through various characterizations, it is discovered that the doping of Mn component in 3DOM LaCoO3 perovskite catalyst could promote the formation of active Co3+ species due to the excellent redox properties between Mn&+ and Co&+ species (Mn4++Co2+→Mn3++Co3+), while the co-doping of Sr and Mn elements could produce and form some new active species. On one hand, Sr and Mn may act as an electron promoter to increase the concentration of Co3+ and Oads. On the other hand, Sr and Mn can act as a structure promoter to enhance the specific surface area and promote the dispersion of active Co species. The research provides valuable reference for the development of highly efficient catalysts for the industrial degradation of benzene.

Structural, Electrical, and Thermoelectric Properties of La and Sr Co-Doped CaMnO3 Compounds

Polycrystalline samples of CaMnO3 and Ca0.98-xSrxLa0.02MnO3(x = 0.00, 0.02, 0.04, 0.06) were prepared by citrate sol-gel route. X-ray diffraction technique was used to confirm the single phase of the samples. Morphology, Elemental compositions were carried out using scanning electron microscopy & energy dispersive spectroscopy respectively. Raman spectroscopy measurements reveal that the structural distortion is mainly due to the rotation of MnO6 octahedral than Jahn Teller. Electrical resistivity measurements were carried out on sintered samples using the DC four-probe method and they disclose that La and Sr Co-doping can lower the resistivity. Thermoelectric properties were evaluated in the range of 303 K and 673 K, indicating that the majority of charge carriers are electrons. Among all the prepared co-doped La/Sr samples, Ca0.94Sr0.04La0.02MnO3 possess a higher power factor.

Physicochemical, osteogenic and antimicrobial properties of graphene oxide reinforced silver/strontium-doped hydroxyapatite on titanium for potential orthopedic applications

Variety of ion-doped apatite coatings, especially strontium substituted hydroxyapatite (SrHA), have attracted eventful attention for medical metal surface modifications due to their excellent cytocompatibility and organizational affinity. However, they are still not commercially used in clinics because of their inappropriate biomechanical properties, and lack of osteoinductivity and antibacterial capabilities. Here, silver (Ag) doped SrHA (SrAgHA)/graphene oxide (GO) composite coatings were fabricated on titanium (Ti) substrate via electrodeposition (ED) and this combination has been reported for the first time. Morphological observations revealed that GO facilitated HA pricker-like crystals to grow in longitudinal directions, changing into a bone-like microneedles structure. SrAgHA/GO showed good mechanical properties to ensure mechanical strength required for the bone repair coating. The roughness of samples decreased from 120 ± 19 μm for the SrAgHA/GO coated Ti to 527 ± 66 μm for HA coated Ti. Although the introduction of GO makes the composite coating have a significant decreased roughness, it has no effect on the hydrophilicity of the composite coating, which is almost superpotropic. Ion release evaluation demonstrated that the presence of GO slowed the release rate of Sr and Ag, which was beneficial to reduce the cytotoxicity accompanying high concentration of Ag release. Simultaneously, GO increased the surface hydrophilicity and mechanical strength of the SrAgHA/GO. In addition, the corrosion rates of investigated coatings increased in the following order: SrAgHA/GO<SrHA/GO<SrAgHA<HA<Ti. SrAgHA/GO coatings demonstrated an effective antibacterial effect against common bacteria in clinical. The co-doping of Sr and GO in SrAgHA/GO coatings can effectively mitigate the cytotoxicity of Ag and promote the cytocompatibility of HA. The SrAgHA/GO coating did not exhibit any cytotoxicity, which can greatly promote adhesion, extension, proliferation and early differentiation of osteoblasts. Therefore, high cytocompatibility, excellent antimicrobial activity, and good mechanical properties of the SrAgHA/GO-coated Ti samples combined with its exceptional corrosion resistance performance displayed the beautiful prospect of the SrAgHA/GO-coated Ti for applications in hard tissue implant.

Quantifying the Improvement in Dielectric Properties of BaSrTiO3-Based Ceramics by Adding MgO.

Barium titanate (BaTiO3, BT) is the main raw material of multilayer ceramic capacitors. As thinner layers of dielectric elements require smaller BT grain diameters, BT-MgO composites have been widely studied owing to the plasticity of MgO and its inhibition of grain growth. However, further improvements of the dielectric properties of the BT-MgO system are still urgently needed. Herein, composite ceramics of Ba0.7Sr0.3Ti0.9925Tm0.01O3 (BST)-x mol% MgO (x = 1, 2, 3, 4, 5) were prepared. The dielectric constant of BST-1 mol% MgO at room temperature was approximately 3800, which was 1/3 times higher than that of BT-MgO composite ceramics. The dielectric loss was less than 0.004 and 2/3 that of BT-MgO composite ceramics. The Curie temperature of BST doped with MgO was below 0 °C. The anomalous increase in dielectric constant was caused by the co-doping of Sr and Tm with BT, while the reduced dielectric loss was due to the uniform dispersion of MgO at grain boundaries, which hinders grain growth. The Curie temperature shift was mainly due to accumulated oxygen vacancies. Thus, this work provides new solutions to further improve the dielectric properties of the BT-MgO system, including changing the doping elements and adjusting the doping ratio.

The effect of a Ta, Sr co-doping strategy on physical and electrochemical properties of Li7La3Zr2O12 electrolytes

In this study, Ta single-doped Li6.4La3Zr1.4Ta0.6O12 (Ta0.6) and a series of Ta, Sr co-doped Li6.4+xLa3-xSrxZr1.4Ta0.6O12 (Ta0.6Srx, x = 0.1, 0.2, 0.3, and 0.4) electrolytes are synthesized via a two-step process. The XRD result reveals that all samples have a pure cubic phase, which indicates that Ta5+ and Sr2+ can enter the lattice of LLZO and stabilize the cubic phase. The SEM images exhibit that all samples have a dense microstructure and tight grain boundary without obvious holes. The excellent properties are achieved when the doping amount of Sr reaches 0.2 mol. Among all designed samples, the Ta0.6Sr0.2 has the highest Li+ conductivity and relative density of 8.54 × 10−4 S cm−1 and 98.79%, respectively, as well as the lowest activation energy roughly 0.302 eV. Additionally, the symmetrical cell's galvanostatic cycling data show that it has excellent cycling performance and extremely low overpotentials even after 350 cycles, indicating that it can be successfully applied to next-generation all-solid-state lithium-ion batteries (ASSLIBs).

Band gap tuning in MgGeN2 chalcopyrite with Sr and Sn doping: An ab-initio investigation

In this paper, we have investigated the impact of mono and co-doping of Sr/Sn on the electronic, optical and structural properties of MgGeN2. The effects of Sr/Sn doping at Mg/Ge site are investigated to explore the potential of pure and doped compounds in optoelectronic applications. For the investigations of electronic and optical properties such as, energy bands, density of states, dielectric tensors, absorption coefficient, reflectivity and refractivity spectra, of MgGeN2, Mg1-xSrxGeN2, MgGe1-xSnxN2 and Mg1-xSrxGe1-xSnxN2 (x = 0.0625, 0.125) compounds, we have used the Perdew-Burke-Ernzerhof generalized gradient approximation potential and further ameliorated by Tran-Blaha modified Becke Johnson exchange co-relation potential. The stability of the doped compounds is discussed in terms of formation energy and binding energy for the mono and co-doped compounds. It is observed that the doping of Sr/Sn at Mg/Ge reduces the band gap of MgGeN2. The energy gap of MgGeN2 reduces from 2.90 eV to 2.25 eV with 12.5% co-doping of Sr and Sn. The potential of pure and doped compounds for optoelectronic applications are discussed in terms of their optical properties.

Growth, luminescence, defects and scintillation properties of Sr co-doped LiI:Eu single crystal scintillator

To improve performance characteristics of Eu doped LiI single crystal scintillators for thermal neutron detection, single crystals having different concentrations of Sr co-doping were grown. One of the major disadvantages of these scintillators is the absence of any pulse shape discrimination of neutron and gamma radiations. Some degree of discrimination in these crystals could be introduced with the help of Sr co-doping. The effects of co-doping on crystal structure, electronic properties, defects, luminescence, self-absorption, and scintillation properties have been studied in detail.

Adjusting the Covalency of Metal-Oxygen Bonds in LaCoO3 by Sr and Fe Cation Codoping to Achieve Highly Efficient Electrocatalysts for Aprotic Lithium-Oxygen Batteries.

Developing high-efficiency dual-functional catalysts to promote oxygen electrode reactions is critical for achieving high-performance aprotic lithium-oxygen (Li-O2) batteries. Herein, Sr and Fe cation-codoped LaCoO3 perovskite (La0.8Sr0.2Co0.8Fe0.2O3-σ, LSCFO) porous nanoparticles are fabricated as promising electrocatalysts for Li-O2 cells. The results demonstrate that the LSCFO-based Li-O2 batteries exhibit an extremely low overpotential of 0.32 V, ultrahigh specific capacity of 26 833 mA h g-1, and superior long-term cycling stability (200 cycles at 300 mA g-1). These prominent performances can be partially attributed to the existence of abundant coordination unsaturated sites caused by oxygen vacancies in LSCFO. Most importantly, density functional theory (DFT) calculations reveal that codoping of Sr and Fe cations in LaCoO3 results in the increased covalency of Co 3d-O 2p bonds and the transition of Co3+ from an ordinary low-spin state to an intermediate-spin state, eventually resulting in the transformation from nonconductor LCO to metallic LSCFO. In addition, based on the theoretical calculations, it is found that the inherent adsorption capability of LSCFO toward the LiO2 intermediate is reduced due to the increased covalency of Co 3d-O 2p bonds, leading to the formation of large granule-like Li2O2, which can be effectively decomposed on the LSCFO surface during the charging process. Notably, this work demonstrates a unique insight into the design of advanced perovskite oxide catalysts via adjusting the covalency of transition-metal-oxygen bonds for high-performance metal-air batteries.

The Effect of Co-Doping at the A-Site on the Structure and Oxide Ion Conductivity in (Ba0.5-xSrx)La0.5InO3-δ: A Molecular Dynamics Study.

A molecular dynamics simulation was used to investigate the structural and transport properties of a (Ba0.5−xSrx)La0.5InO3−δ (x = 0, 0.1, 0.2) oxygen ion conductor. Previous studies reported that the ionic conductivity of Ba-doped LaInO3 decreases because Ba dopant forms a narrow oxygen path in the lattice, which could hinder the diffusion of oxygen ions. In this study, we reveal the mechanism to improve ionic conductivity by Ba and Sr co-doping on an La site in LaInO3 perovskite oxide. The results show that the ionic conductivity of (Ba0.5−xSrx)La0.5InO3−δ increases with an increasing number of Sr ions because oxygen diffusion paths which contain Sr ions have a larger critical radius than those containing Ba ions. The radial distribution function (RDF) calculations show that the peak heights in compositions including Sr ions were lower and broadened, meaning that the oxygen ions moved easily into other oxygen sites.

Fabrication and biological evaluation of the coating co‐doped strontium and zinc nanoparticles on porous pure titanium surface by hydrothermal method

Background For dental implants, early infection and peri-implantitis after implant restoration are major reasons for implant failure. Plaque biofilm formation is the initiator for implant-related infection. Therefore, it is urgent to develop a new antibacterial implant materials or treatment methods. Aim/Hypothesis In this study, Sr- and Zn- incorporated micro nano-structured titanium surface with nanorods (MNT-Sr Zn) was fabricated by a two-step hydrothermal process, aiming to improve osseointegration and reduce implant failure caused by implant-related infection and broaden new ideas for the future research Material and Methods The Mod Ti surfaces were used as a control. The characterization of different surfaces was detected by a field emission scanning electron microscope (FE-SEM) equipped with energy dispersive spectra (EDS) detector, x-ray diffractometer (XRD) and inductively coupled plasma mass spectroscopy (ICP-MS). Meanwhile, Staphylococcus aureus (S. aureus) was selected to evaluate antibacterial properties through Live Dead Staining and watching the adhesive bacterial morphology under FE-SEM. What's more, rat bone marrow-derived mesenchymal stem cells (rBMSCs) were cultured on the surfaces to detect their early osteogenic properties, like the alkaline phosphatase(ALP) activity and the expressions of osteogenesis related genes. Results The results confirmed that nanorod-like particles with a diameter of about 30-50 nm of MNT-Sr Zn composed of well-crystallized ZnO and SrTiO3 phases. In the EDS spectra, the elements of Zn and Sr were evenly distributed, and approximately 1.49 ± 0.16 wt% and 21.69 ± 2.74 wt% respectively. Besides, the release of Sr2+ and Zn2+ was a controlled and long-term process. More importantly, Zn-containing nanorod-like particles and the morphology could work together, slightly decreasing adhesion of S. aureus but increasing the proportion of dead cells, thus inhibiting subsequent biofilm formation, compared with the controlled group. In addition to this, MNT-Sr Zn could enhance the osteogenic differentiation via the upregulation of the transcription of osteogenic related genes and the expression of ALP in vitro. Conclusion and Clinical Implications This research provides a new surface modification method on titanium substrate for multi-functional implant material development. Due to the co-doping of Sr and Zn in the coating, biomechanical stability, antibacterial capability and early osteogenic inductive effect are enhanced, which has the potential to be applied in dental implantation in the future.

Improved thermoelectric performance in Pr and Sr Co-doped CaMnO3 materials

The enhancement of thermoelectric performance should be a compromise of electrical as well as thermal transports with reasonably little reduction of thermopower. In this study, the effects of co-doping by rare earth Pr and alkaline earth Sr on perovskite Ca0.92-xPr0.08SrxMnO3 (x = 0, 0.01, 0.02, 0.03, 0.04) bulk materials are evaluated in terms of the phase composition, microstructure, grain combination, electrical transport as well as the thermal transport properties. The results show that perovskite type phases are reserved for the doped bulk materials. The bulk Material porosity can be decreased obviously and better grain interconnection is formed by introducing co-doping. The electrical conductivity is enhanced due to increased carrier concentration and mobility. The carriers for the intrinsic CaMnO3 and the co-doped Ca0.92-xPr0.08SrxMnO3 (x = 0, 0.01, 0.02, 0.03, 0.04) bulk materials follow the adiabatic polaron transport model; the activation energy as well as the band gap are reduced. The total thermal conductivity is further reduced by co-doping of Sr comparing with the Pr single-doped bulk materials. The co-doping is effective for further confining the thermal conduction. The ZT values of the co-doped samples are increased by 12.5%, 18.7%, 25% and 18.7% comparing with the Pr single-doped materials, respectively.

Facile single phase synthesis of Sr, Co co-doped BiFeO3 nanoparticles for boosting photocatalytic and magnetic properties

In this article, we demonstrate the synthesis of single phase Bi1-xSrxFe1-yCoyO3 (x = y = 0, x = 0.02; y = 0.01, 0.03, 0.05, 0.07) using a facile sol-gel route. The powder X-ray diffraction measurements of all the samples confirm the pure phase rhombohedral structure with a small lattice distortion. The morphological analysis demonstrated decrease in average particle size from ~ 64 to 41 nm with increasing Co doping in Bi0.98Sr0.02Fe1-yCoyO3 due to slower growth rate. Mössbauer study reveals the change in oxidation state of iron (Fe3+ → Fe2+) at higher doping concentration of Co. Further, the successful co-doping of Sr, Co into BiFeO3 lattice remarkably enhances the saturation magnetization value from 0.8 emu/g to 2.3 emu/g and remnant magnetization from 0.08 emu/g to 0.532 emu/g. The enhanced magnetic properties of Sr, Co co-doped BiFeO3 nanoparticles is ascribed to the breaking of cycloidal spin structure, more number of uncompensated spin on the surface, and oxygen vacancies. Moreover, these samples were found to be highly efficient for the degradation of Rhodamin B (RhB) dye under visible light irradiation. The best RhB degradation activity was observed with 7% Co doping Bi0.98Sr0.02Fe1-yCoyO3 (BSFCO7) due to its lower bandgap, reduced average particle size and larger specific surface area.

Synthesis of trace element Si and Sr codoping hydroxyapatite with non-cytotoxicity and enhanced cell proliferation and differentiation.

The main inorganic minerals in natural bones are non-stoichiometric hydroxyapatite (HA, Ca10[PO4]6[OH]2) doped with various trace elements, which may possess important biochemical effects. To investigate the functions of Sr and Si elements in human hard tissues, non-doped HA, trace Si doped HA, Si and Sr codoped HA with the concentration of natural bones are synthesized by hydrothermal method in this study. The samples are characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM). The biological activities are evaluated via cytotoxicity study, adhesion and proliferation of osteoblast measurement, and alkaline phosphatase (ALP) assay. All the synthesized materials are HA phase, which have hierarchical structures with oriented HA nanorods assembled into the platy particles. These materials are non-cytotoxic against L929 cells line even at 400μg/ml powder suspension. The results clearly indicate that the proliferation of L929 cells increases with trace elements doping from trace Si-HA to Si+Sr-HA. The adhesion and proliferation of osteoblast measurement illustrates that proliferation of osteoblasts advances about 1.3 times for Si-HA and about 1.8 times for Si+Sr-HA compared with undoped HA. In general, Si-HA with trace Si element shows enhanced cell differentiation, and Si+Sr-HA dual-doped with Si and Sr elements presents increased biological activity compared with Si-HA.

Improving the bioactivity and corrosion resistance properties of electrodeposited hydroxyapatite coating by dual doping of bivalent strontium and manganese ion

Abstract The key property in the preparation of a biomaterial is to facilitate the regeneration and/or replacement of injured organs and tissues. To obtain such a biomaterial, strontium and manganese co-substituted hydroxyapatite (SrMnHA) ceramic coatings on commercially pure titanium (CP-Ti) were successfully prepared by a cathodic electrodeposition method. The formation of SrMnHA coating was investigated using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and inductively coupled plasma. Co-doping of Sr 2 + and Mn 2 + ions decreased hydroxyapatite unit cell volume and grain sizes. Obtained coatings were crack-free and dense, which led to the decrease in the corrosion current densities of CP-Ti in physiological solutions. The dissolution tests performed on SrMnHA resulted in the leaching of Sr 2 + and Mn 2 + at low levels. SrMnHAs have moderately hydrophilic surfaces with a contact angle of 23.8°. Additionally, the MC3T3-E1 cells show better cell morphology, adhesion, spreading, proliferation and expression of alkaline phosphatase on SrMnHA than on HA. The excellent biocompatibility of SrMnHA is mainly attributed to a probable effect of a combination of good surface wettability and ion release (Sr 2 + and Mn 2 + ). Results suggest that SrMnHA composite-coated CP-Ti can be a potential candidate for orthopaedic applications.

Effect of La and Sr co-doping on electric and magnetic properties of multiferroic La0.1Bi0.9−xSrxFeO(3−x/2) ceramics

[Formula: see text] ceramics were synthesized by solid-state reaction method, and their magnetic properties and conductive characteristics were investigated and discussed. It is found that La-doped [Formula: see text] ceramic without [Formula: see text] doping is a rhombohedrally distorted perovskite structure, and with the increase of the [Formula: see text] concentration, the phase transits gradually from rhombohedral to pseudo cubic symmetry. Electrical and magnetic properties show strong dependence on [Formula: see text] dopant level. The measurement demonstrates that [Formula: see text] with 30% [Formula: see text] dopant exhibits the lowest values of the leakage current, dielectric constant [Formula: see text] and dielectric loss [Formula: see text]. And the highest value of saturation magnetization of about 4.5 emu/g is observed in 60% Sr-doped [Formula: see text]. An abnormal enhancement of the conductivity was observed in [Formula: see text] ceramics with [Formula: see text] = 0.60 and 0.70, and their magnitude of conductivity is nearly six orders larger than that of pure [Formula: see text].

Effect of Sr and Al or Fe co-doping on the sinterability and conductivity of lanthanum silicate oxyapatite electrolytes for solid oxide fuel cells

The effect of co-doping of Sr and Al or Fe on the microstructure, sinterability and oxide-ion conductivity of lanthanum silicate oxyapatites is investigated in detail at 300–800 °C by the electrochemical impedance spectroscopy. The oxide-ion conductivity is 1.46 × 10−2 S cm−1 for La9.5Sr0.5Si5.5Fe0.5O26.5 (LSSFO) and 1.34 × 10−2 S cm−1 at 800 °C for La9.5Sr0.5Si5.5Al0.5O26.5 (LSSAO), respectively, which is one order of magnitude higher than 6.16 × 10−3 S cm−1 measured on La9.67Si6O26.5 (LSO) oxyapatite under the identical test conditions. The grain bulk and grain boundary resistances of co-doped oxyapatite are significantly smaller than that of LSO oxyapatite, and decrease significantly with the increase of the sintering temperature. LSSFO and LSSAO also show significantly higher density as compared to that of LSO. The results indicate that co-doping of Sr and Al or Fe significantly improves the densification, sinterability and oxide-ion conductivity of lanthanum silicate oxyapatites.

Effects of Gd and Sr co-doping in CeO2 for electrolyte application in solid oxide fuel cell (SOFC)

Rare earth doped ceria is a key composition for electrolyte application in SOFC. The present trend is to investigate the co-doping approach in ceria either to improve further the electrical conductivity or sintering property. In this study, nano-structured Gd and Sr co-doped ceria (GSDC) powders have been prepared by gel combustion route. In all the compositions, total dopant cation concentration has been kept at 0.20 atom fraction having general formulae Ce0.8Gd0.2−xSrxO1.9−x/2. XRD patterns of GSDC powders calcined at 600°C revealed the phase pure cubic fluorite structure with no Gd2O3 or SrO phase within detection limit. The combustion synthesized powders after sintering at 1350°C resulted in pellets with density more than 96% of theoretical density. The total ionic conductivities have been evaluated from impedance data as a function of temperature in the range of 200–800°C. The results indicate that ionic conductivity increases with small addition (~1mol%) of SrO. At higher SrO concentration ionic conductivity decreases and beyond about 5mol% SrO concentration the ionic conductivity becomes lower than that of CeO2 doped with only Gd2O3. The decrease in ionic conductivity at higher SrO concentration has been attributed to the increase in the enthalpy of oxygen vacancy association. The initial increase in conductivity could be due to scavenging of siliceous phase likely to be present in the grain boundary.