Sr-doped Samples Research Articles

Dielectric relaxation and Hopping conduction mechanism in Ni1-xSrxO nanostructures

Electrical transport and conduction characteristics of sol-gel prepared Ni1-xSrxO (x = 0.00, 0.02, 0.04) nanostructures have been investigated systematically through DC and AC conduction measurements. The phase purity and structure of the samples have been studied using X-ray diffraction refinement and transmission electron microscope (TEM) analysis. It is observed that metal to semiconductor transition takes place in pure NiO sample whereas, it is suppressed on Sr insertion into NiO lattice. The activation energy (Ea) of the DC conduction have been found between 0.18 and 0.49 meV. Further, we have also observed relaxation process in doped NiO samples which are established by peaking behavior of dielectric constant. To discuss the conduction mechanism, the AC conductivity and temperature dependence of frequency exponent ‘n’ have been analysed using quantum mechanical tunnelling based Non-Overlapping Small Polaron (NSPT) model. Simultaneously, correlated AC conductivity data with NSPT model was used to calculate the value of maximum barrier height (binding energy) (Wm), AC activation energy, tunnelling distance (Rw) and density of states at Fermi level N (EF). Also, impedance spectroscopy suggests that the pure and Sr doped samples exhibit high order insulating behavior at the temperatures of 30 °C and 150 °C.

Synthesis of La1-xSrxAlO3 Perovskites by Reverse Strike Co-Precipitation Method and Its Soot Oxidation Activity

La1-xSrxAlO3 (x=0 to 0.4) perovskite materials were synthesized by reverse strike co-precipitation method and their soot oxidation activity were evaluated. All the catalysts synthesized were characterized using XRD, BET specific surface area, FESEM and XPS techniques. As analyzed by XRD, La1-xSrxAlO3 perovskite from x=0 to 0.35 showed the formation of the rhombohedral phase, while for La0.6Sr0.4AlO3 sample the secondary phases SrO, La2O3, and Al2O3 were also noticed. Sr-doped samples exhibited higher BET specific surface area when compared to pure LaAlO3. FESEM analysis showed that there is a change in morphology upon doping of Sr into LaAlO3 lattice. The O1s spectra observed from XPS analysis showed that the La0.75Sr0.25AlO3 sample contained higher amounts of adsorbed oxygen. La, Sr, and Al existed in +3, +2 and +3 oxidation states respectively in all the synthesized samples as confirmed by XPS. Soot oxidation activity tests showed that La0.75Sr0.25AlO3 exhibited higher catalytic activity relative to other catalysts due to the enhanced amount of reactive adsorbed oxygen species.

Dielectric and Raman spectroscopy study of structural phase transformation of Sr-doped La2CoMnO6 double perovskite

Doping at rare earth site by divalent alkaline-earth ions in the double pervoskite system have noticed a variety of magnetic and electronic orders with spatially correlated charge, spin and orbital degree of freedom. In present report, we aim to study the structural, dielectric and magnetic properties of La2−xSrxCoMnO6 $$\left( {x=0,{\text{ }}0.1,{\text{ }}0.3,{\text{ }}0.5} \right)$$ samples synthesized by the solid-state reaction technique. Using powder X-ray diffraction and data analysis with Rietveld refinement a structural identification has been carried out. From high-temperature Raman spectra, a clear structural phase transformation from monoclinic with P21/n symmetry to a rhombohedral phase with R-3 symmetry was evidenced from the softening and an anomalous change in peak widths of both stretching (A1g) and anti-stretching (B1g) modes around 365K. The dielectric measurement is carried out for all the synthesized samples, a sudden change in dielectric constant (e′) and corresponding dielectric loss (tanδ) around 365 K in x = 0, x = 0.1, and x = 0.5 composition samples reflects a remarkable change in the tilts in oxygen octahedra which is because of the structural phase transformation. The susceptibility measurement was also performed to observe the ferromagnetic transitions. In partially ordered undoped and Sr-doped ceramic samples, relaxor-like behavior combined with a large dielectric constant (> 103) is observed. In this paper, successful attempts have been made to observe the structural phase transition through dielectric properties.

Effects of Sr doping on biodegradation and bone regeneration of magnesium phosphate bioceramics

The present work reports the effects of strontium (Sr) addition on in vitro degradability, cytocompatibility, and in vivo bone regeneration of magnesium phosphate (MgP) bioceramics. Pure and Sr doped MgP bioceramis were prepared by solid state sintering at 1200 °C. Nearly 50% reduction in degradability of MgP ceramics was noticed for 1 wt.% Sr doped samples which was further confirmed by both FESEM and micro computed tomography (µ-CT) analysis. In vitro cell-materials interactions were studied using human osteoblast like cells (MG-63) and it was found that 2 wt.% Sr doped samples had highest cell proliferation as indicated by both alamar blue assay and Live/Dead imaging. Biocompatibility and degradability was further studied by implanting the samples in rabbit femur. µ-CT analysis of the retrieved bone samples showed an enhanced in vivo degradability of higher Sr doped samples whereas bone regeneration was optimum for 2 wt.% Sr doped MgP samples. Quantitative analysis using oxytetracycline labeling indicated 82±3% bone regeneration for MgP-2Sr samples compared to 56±3% for pure MgP samples, after 90 days of implantation. The present results indicated that MgP ceramics has good biocompatibility and suitable degradability to be used for bone regeneration that can further be tuned by Sr doping to make it more patient specific.

In Vitro Biodegradation and In Vivo Biocompatibility of Forsterite Bio-Ceramics: Effects of Strontium Substitution.

The present study investigates the potential use of forsterite as an orthopedic biomaterial along with the role of strontium oxide (SrO) as a dopant. The in vitro degradation behavior was measured as a function of immersion time in simulated body fluid (SBF) for up to 8 weeks and was analyzed by micro computed tomography (μ-CT) and scanning electron microscopy (SEM). All the doped samples showed higher degradation than pure sample. The in vitro cytocompatibility study showed good cytocompatibility and proliferation of MC3T3-E1 cells on Sr-doped MgS samples. The in vivo experiments were carried out by implanting the ceramics in a rabbit femur for 30 and 90 days. The 3D μ-CT and SEM images of 2 and 3 wt % Sr-doped MgS showed increased bone regeneration around the implant materials compared with pure and 1 wt % Sr-doped MgS, which was further confirmed by quantitative oxytetracycline labeling. The histological examination of three major organs of heart, kidney, and liver confirmed that the degradation product of the MgS ceramics, with or without doping, had no toxicological side effects. These results indicate that Sr-doped MgS bioceramics exhibit enhanced degradability with the potential to be used for temporary bone regeneration.

Exchange bias and magnetoresistance effects in La2-xSrxCoMnO6 (0.05 ≤ x ≤ 0.5)

Double perovskites with Sr2+-doping at the A-site in La2-xSrxCoMnO6 (0.05 ≤ x ≤ 0.5) are synthesized by the standard solid-state reaction method. X-ray diffraction indicates that the initial monoclinic crystal structure transforms to rhombohedra with the increasing Sr-doping from x = 0.05 to 0.5. The Sr-doped samples (0.1 ≤ x ≤ 0.3) possess mixed crystallographic phases with monoclinic and rhombohedra structure. The appropriate amount of Sr-doping (x = 0.3) can effectively increase exchange bias effect to reach a maximum value of 6.5 kOe (at 5 K) under the 10 kOe cooled magnetic field. The exchange coupling of uncompensated magnetic moment at the interface between ferromagnetic and antiferromagnetic phases is responsible for the variation trend of exchange bias effect. A large enhanced negative magnetoresistance effect (approximately 67.1%) of the x = 0.3 sample is observed at 85 K and 70 kOe. The reduction of the density of spin polarization states at Fermi level caused by disorder of Co/Mn ions is the reason for the decreasing magnetoresistance effect in the multiple Sr-doping (x > 0.3).

A comparative study of Sr-doped LaMnO3 synthesised via solid-state reaction and sol–gel methods

ABSTRACTThis work deals with the synthesis of hole-doped La1-xSrxMnO3 (x = 0.25 and 0.33) perovskite via two different ways, namely a solid-state reaction method and a sol–gel process. Various properties of the samples have been investigated and compared by means of different techniques, namely X-ray diffraction (XRD), temperature-dependent resistivity measurements in the temperature range 25–300 K using a closed cycle refrigerator and vibrating sample magnetometry (VSM). All samples have orthorhombic crystal symmetry and an irregular variation in unit-cell volume with increase in Sr content. The average crystallite size was determined from the XRD data and found to lie in the range 19–22 nm. Metal–insulator transitions (MIT) were observed in all the samples via low-temperature electrical characterisations. The magnetic measurements confirm that the magnetisation does not saturate for the 25% Sr doped samples up to the available field of 10 kOe. The magnetic response also supports the interpretation of XRD and resistivity data. The obtained results are explained on the basis of double-exchange and super-exchange mechanisms.

Strontium-doped Hydroxyapatite Coatings Deposited on Mg-4Zn Alloy: Physical-chemical Properties and in vitro Cell Response

Biodegradable magnesium (Mg)-based biomaterials have draw extensively attention, due to the high strength-to-weight ratio, low elastic modulus and good biocompatibility. However, the high corrosion rate is still a major obstacle for the potential clinical applications. Therefore, the highly biocompatible hydroxyapatite (HA) coatings are usually introduced to restrain the interactions between Mg-based substrate and the body fluid environment. In the present paper, HA and strontium (Sr)-doped HA coatings were prepared on Mg-4Zn substrates by electrochemical deposition. The surface properties of the samples were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), three-dimensional laser scanning microscopy (3D LSM) and a contact angle video system. The dynamic ion release, protein adsorption, cell adhesion, proliferation and differentiation behavior of the samples were also evaluated. The results reveal that the incorporation of Sr in the HA coatings leads to lattice distortion and decreased crystallinity. The smaller amount of Mg ion release of the Sr-doped HA coated samples suggests a better corrosion resistance. The improved protein adsorption and initial adhesion of mesenchymal stem cells (MSCs) of the Sr-doped samples should be due to their higher surface roughness and wettability. The introduction of Sr leads to comparable cell proliferation behavior, but significantly improved osteogenic differentiation. It is concluded that the Sr-doped HA coatings are promising candidates for the protective biocompatible coating on Mg-based implants.

Unique magnetic properties of perovskite manganites La0.95T0.05CrxMn1−xO3 (T = Ca, Sr)

Powder samples of La0.95T0.05CrxMn1−xO3 (T = Ca or Sr, 0.00 ≤ x ≤ 0.30), two series of ABO3 perovskite manganites, were synthesized using the sol–gel method. X-ray diffraction analysis showed that all the samples had a single ABO3 perovskite phase with space group R3‾c. Unique magnetic properties were obtained for the oxides: (i) the Curie temperature of each series of samples first increased and then decreased with increasing Cr content (x); (ii) the average molecular magnetic moment reached the maximum value when x = 0.08 for the Ca-doped samples, but it monotonically decreased with increasing x for the Sr-doped samples. This behavior was explained using an O 2p itinerant-electron model for magnetic oxides.

Synthesis and Characterization of (Ca1−xSrx)12Al14O33 Electrides

AbstractThe Sr doped (Ca1−xSrx)12Al14O33[(C1‐xSx)12A7] (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) polycrystals were successfully prepared by the melt‐solidification combining spark plasma sintering (SPS) process. The electrides were obtained by thermal treatment with Ti particles at 1100 °C for 20h. The electrical properties and electronic structure were systematically studied. The free oxygen ions of Sr doped samples were easier substituted by electrons. (Ca0.96Sr0.04)12Al14O33:e‐ sample possesses the highest electrical conductivity at room temperature (RT) (∼1136S/cm) and electron concentration [∼(2.13±0.11) × 1021cm−3] was obtained, which was above one magnitude higher than that of nondoped sample. The calculated electronic structure showed that Sr‐doping increased the density of state near the Fermi level of (C0.96S0.04)12A7:e‐. The level of frame conduction band (FCB) decreased compared to Ca12Al14O33:e‐.The large density of state of (C0.96S0.04)12A7:e‐ was mainly contributed by Sr 4p,5s, Ca 3d,4s and Al 3p.

Dielectric, ferroelectric and piezoelectric properties of (Ba0.98−xSrxCa0.02) (Ti0.95Zr0.05)O3 lead-free ceramics

Piezoelectric compositions associated with the chemical formula (Ba0.98−xSrx Ca0.02)(Ti0.95Zr0.05)O3 where x = 0, 0.05, 0.10 and 0.15, were synthesized successfully via solid-state reaction route. The dielectric, ferroelectric, piezoelectric and strain properties of the ceramics of these compositions were studied. X-ray diffraction studies confirmed the presence of pure tetragonal structure and the cell volume was found to decrease with the increase in Sr content. Scanning electron microscopy showed increase in grain size for Sr doped samples when compared to undoped ceramics. Interestingly, the sample with x = 0.10 mol of Sr content exhibited excellent piezoelectric properties. The polarization and strain behaviour for the aforementioned sample showed high piezoelectric strain of 0.22% at 40 kV/cm. The remnant polarization of 13.45 μC/cm2 associated with high piezoelectric coefficient (d33) of 320 pC/N were obtained for the ceramic with x = 0.10 mol of Sr content. These results confirmed that the (Ba0.88 Sr0.10Ca0.02)(Ti0.95Zr0.05)O3 system is a promising lead-free high piezoelectric strain material for piezoelectric based device applications.

Synthesis, structure and magnetic properties of nanostructured La1−xAxFe0.5Mn0.5O3 (A = Ca, Sr and Pb; x = 0 & 0.25) perovskites

The effect of hole doping on magnetic properties of LaFe0.5Mn0.5O3 have been investigated. All the ceramics samples La1−xAxFe0.5Mn0.5O3 (A=Ca, Sr and Pb; x=0 & 0.25) were synthesized at 500°C by sol-gel method and the particles size were found to be in nanodimension. The samples were characterized by X-ray and electron diffraction, HRTEM and both dc and ac-magnetization measurements. The X-ray and electron diffraction patterns were indexed by cubic Pm-3m space group. The particle size of the LaFe0.5Mn0.5O3 is ∼100nm, whereas the Pb-doped sample is ∼50nm and for Ca or Sr doped samples the size is ∼10–30nm. Both dc and ac-susceptibility measurements suggest that the effect of hole doping and A-site cationic radius in LaFe0.5Mn0.5O3 have no significant role on magnetic properties. However, the particle size plays an important role on magnetic property due to the development of surface ferromagnetic cluster at nanoscale. The competing interactions lead to magnetic phase separation where local ferromagnetic clusters coexist within the antiferromagentic matrix in all the samples.

Effect of Sr-doping on sinterability, morphology, structure, photocatalytic activity and AC conductivity of ZnO ceramics

The change in morphology, structure, catalytic activity and ac electrical conductivity of the Sr-doped ZnO (Zn1−xSrxO, x = 0, 0.01, 0.02 and 0.03) ceramic powders was investigated after sintering. The sintering of the Sr-doped samples results in faster growth in particle-size and the shape becomes spherical by dissolution of the sharp edges in order to reduce the strain produced by Sr-doping and to reduce the surface energy. The growth in particle-size reduces the photocatalytic activity. Sr-doping reduces the band gap of ZnO by a small value (~0.1 eV). The ac conductivity values decrease with increase in Sr-concentration, but increase with temperature and frequency. This behavior is due to the conduction by small polarons created by Sr-doping. Our results may facilitate a way for the easy fabrication of monolithic ZnO based devices with improved dielectric and semiconducting properties of ZnO ceramics by doping a small amount of Sr.

Influence of single and binary doping of strontium and lithium on in vivo biological properties of bioactive glass scaffolds

Effects of strontium and lithium ion doping on the biological properties of bioactive glass (BAG) porous scaffolds have been checked in vitro and in vivo. BAG scaffolds were prepared by conventional glass melting route and subsequently, scaffolds were produced by evaporation of fugitive pore formers. After thorough physico-chemical and in vitro cell characterization, scaffolds were used for pre-clinical study. Soft and hard tissue formation in a rabbit femoral defect model after 2 and 4 months, were assessed using different tools. Histological observations showed excellent osseous tissue formation in Sr and Li + Sr scaffolds and moderate bone regeneration in Li scaffolds. Fluorochrome labeling studies showed wide regions of new bone formation in Sr and Li + Sr doped samples as compared to Li doped samples. SEM revealed abundant collagenous network and minimal or no interfacial gap between bone and implant in Sr and Li + Sr doped samples compared to Li doped samples. Micro CT of Li + Sr samples showed highest degree of peripheral cancellous tissue formation on periphery and cortical tissues inside implanted samples and vascularity among four compositions. Our findings suggest that addition of Sr and/or Li alters physico-chemical properties of BAG and promotes early stage in vivo osseointegration and bone remodeling that may offer new insight in bone tissue engineering.

Charge Transfer Mechanism and Superconductivity in Tl0.5Cu0.5 (Ba1−x Sr x )Ca2Cu3O y (x = 0, 0.15,0.25,0.35) Samples

Tl0.5Cu0.5(Ba1−x Sr x )Ca2Cu3O y (x = 0, 0.15,0.25,0.35) superconductors are prepared by a two-step solid-state reaction method, and their superconducting properties are studied by resistivity, susceptibility, FTIR, XRD, and excess conductivity analyses. The samples have shown an orthorhombic crystal structure in which the c-axis length and the volume of the unit cell increase with Sr doping. The normal-state resistivity is appreciably suppressed, and the zero resistivity critical temperature observed between 97 and 104 K. The magnitude of the superconductivity is enhanced in Sr-doped samples. In the Fourier transform infrared (FTIR) absorption measurements, the apical oxygen phonon mode is observed to be softened with Sr doping whereas the peak position of planar oxygen stays unaltered in Sr-incorporated samples. The excess conductivity analyses of Tl0.5Cu0.5(Ba1−x Sr x )Ca2Cu3O y (x = 0, 0.15,0.25,0.35) samples have shown that the values of ξ c(0), the inter-layer coupling J, are not appreciably altered whereas the Fermi velocity v F of superconducting carriers and the phase relaxation increase with Sr doping. The values of parameters such as B c0(T), B c1(T), J c(0) are, however, enhanced with the doping of Sr in the final compound. These studies have shown that Sr doping promotes efficient transfer of the carriers from charge reservoir layer to the conducting CuO2 planes thereby promoting enhancement in the density of carriers and hence increase in the values of aforementioned superconductivity parameters.

Low Sr doping effects on critical current density and pinning mechanism of YBa2Cu3O7-δ single crystals

We report on isotherm dc magnetization hysteresis loops, M(H) to 70K ≤ T ≤ 82.5K of YBa2-xSrxCu3O7-δ (x = 0, 0.02 and 0.1) single crystals with the purpose to study the influence of the low Sr doping effects on the YBa2Cu3O7-δ critical current density, JC(H) and normalized flux pinning force density, f(h). The M(H) measurements were performed in a commercial SQUID magnetometer with H ≤ 50kOe applied parallel to the c axis of the samples. The extended Bean critical state model was applied to JC(H) determination. The magnetic irreversibility fields, Hirr(T) were obtained from M(H) loops. The f(h) behavior was determined from FP/FP,max versus H/Hirr plots where FP is the pinning force density (FP = J × μ0H). The results show that the low Sr doped samples transport higher JC(H) than the pure one. The application of the Dew-Hughes scaling functions to the f(h) plots designates the core normal punctual type as majority pinning mechanism of samples. We suggest that the core normal punctual pinning mechanism, responsible to the enhancement of the JC(H) transported by YBa2-xSrxCu3O7-δ samples, is possibly connected to the segregation of Sr atoms precipitates at the crystalline structure of these samples.

Doping of Strontium into Natural Bone Powder and Further Cell Experiment

Abstract Superior bone repairing materials can shorten bone healing periods and lower the incidence of nonunion. Strontium ions are known for enhancing a bone forming effect. Doping of strontium into bone powder will be able to make an attractive bone repairing material. In this study an ion exchange method was tried to dope strontium into bone powder in vitro. The capability to dope strontium into bone tissue was also observed. The cytotoxicity of novel material was investigated by MTT (Methyl thiazolyl tetrazolium assay) method. And further primarily cultured osteoblast was used to evaluate the biocompatibility of novel strontium doped bone sample. It is found that more than 10% exchange ratio of Sr/Ca can be achieved in bone powder. The Sr-doped bone shows no cytotoxicity. Compared with untreated bone samples, osteoblasts show higher proliferation rate (129%) on Sr-doped bone samples. And ALP (Alkaline phosphatase) is 132% higher on Sr-doped bone samples. Thus it is feasible to develop a Sr-doped allograft bone graft by this method.

Preparation of LaXCoO3 (X = Mg, Ca, Sr, Ce) catalysts and their performance for steam reforming of ethanol to hydrogen

Perovskite nanocomposite catalysts LaXCoO3 (X = Mg, Ca, Sr, or Ce; n(La):n(X) = 3:2) have been prepared by a citric acid-complexing method and used for steam reforming of ethanol (SRE), leading to hydrogen generation. The samples were characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, N2 adsorption-desorption, and H2 temperature-programmed reduction. The effects of elemental substitution in the LaCoO3 perovskite were studied, and the catalytic performance and primary stability of the hydrogen production from SRE were investigated. In the highly substituted samples, only the Ce-doped sample was isolated as the pure perovskite phase. The presence of a Co3O4 phase in the Ca-doped or Sr-doped samples was beneficial for the reduction of the active Co component, while Sr-doped or Ce-doped samples showed good activity and stability. The sample incorporating Sr demonstrated better catalytic performance than those of other samples.

Induced modifications in the properties of Sr doped BiFeO3 multiferroics

Multiferroics exhibit unique combination of ferroic properties, simultaneously. For instance, in BiFeO3, magnetic and electric properties co-exist. In this work, BiFeO3 and Sr-doped BiFeO3 samples with general formula, Bi1−xSrxFeO3 (x=0.00, 0.05, 0.10, 0.20, and 0.30) were synthesized by sol–gel auto-combustion technique, in order to investigate these ferroic properties. The samples were confirmed to have perovskite type rhombohedral structure, characteristic of BiFeO3. A dilute phase of Bi2Fe4O9 was also found in all the Sr-doped samples. The micrographs of the palletized samples revealed that minutely doped Sr might not have any effect on the morphology of the samples. Frequency dependent dielectric measurements were carried out at room temperature for all the samples from 100Hz to 1MHz. The dielectric constant of un-doped sample at low frequency was 52 which decreased with increasing Sr doping. An enhancement of magnetic properties was observed with increasing the Sr contents. Pure BiFeO3 material was observed to have the least value of remanent magnetization. As the Sr2+ ions were doped in BiFeO3, its magnetization and remanence were increased to 0.867emu/g and 0.175emu/g, respectively, at x=0.30.

XANES study of the role of Sr doping in LaCoO3

With the comparisons of experimental XAFS data of Sr doped LaCoO3 samples taken at room temperature and LDA+U (with U = 0,4eV and 8eV, respectively) model calculations of LaCoO3, it is found that the experimental XAFS data of Sr doped samples can be well reconstructed if the samples are phase separated. When U takes 4eV or 8eV, the ground state of LaCoO3 is Mott insulator and the curve shape of calculated XAFS data is even the same as that of the experimental data; when U=0 the HOMO-LUMO band gap vanishes and the calculated XAFS data gets an extra peak. The curve can be well fitted with experimental data of Sr doped LaCoO3 sample. It shows that the doped LaCoO3 sample is not traditional Mott insulator but with some properties of charge transfer type, that is, when Sr ions are doped in LaCoO3, the trivalent Co ions become tetravalent and leave an extra hole in each Co eg orbital. The charge carriers can hop back and forth between trivalent Co ions and tetravalent ones in which way close the band gap.