Increasing Sr Content Research Articles

Structural and Magnetic Properties Control of Pr0.7Ba0.3MnO3 with Sr-Doping

Structural and magnetic properties of Sr-doped Pr0.7Ba0.3MnO3 polycrystallines prepared by solid state reaction are presented. Samples were in monoclinic structure P21/n without structural phase transition when Ba was gradually replaced by Sr. Parameters a, b, and c of a unit cell monotonously decrease with increasing Sr content, while β angle has increased from 89.981° to 90.007°. The X-ray absorption spectra show the co-existence of Mn3+ and Mn4+ ions in materials and the number of Mn4+ ions increases in the presence of Sr. The thermal magnetization data indicate that the Curie temperature shifts toward room temperature from 190, 210, 232 to 267 K with increasing Sr content x from 0 to 0.3.

Microstructural evolution, segregation and fracture behavior of A390 alloy prepared by combined Rheo-HPDC processing and Sr-modifier

Abstract The microstructural evolution, segregation behavior and fracture mechanism of the hypereutectic A390 alloy prepared by Rheo-HPDC processing with Sr-modifier were investigated by morphology analysis and electron probe microanalysis technique (EPMA). The results indicate that the Rheo-HPDC processing with Sr-modifier can simultaneously refine the primary Si particles (PSPs) and modify the eutectic Si. Strontium reduces the formation tendency of α-Al dendritic halo around the PSPs by narrowing the constitutional undercooled zone in the solid-liquid interface front, which leads to the nucleation of eutectic Si on the primary Si. The liquid segregation causes the PSPs to concentrate toward the center of the sample and other elements to segregate toward the edge of the sample. The trace amounts of Sr intensify the degree of element segregation by increasing the melt viscosity. With the increase in Sr content, the melt viscosity gradually decreases. The fracture mechanisms of the A390 alloy without and with the addition of Sr-modifier are quasi-cleavage fracture. Strontium atom increases the internal stress within the PSPs to promote its cracking.

Enhanced thermoelectric properties of Ca3Co4O9+δ ceramics by Sr substitution

Ca3-xSrxCo4O9+δ (CCO-Srx) with varying strontium (Sr) content (x = 0.4, 0.5, 0.6, and 0.7) were synthesized by solid-state method. The crystal structures and morphologies of Ca3-xSrxCo4O9+δ thermoelectric ceramics were analyzed by XRD and SEM. Micro structural characterizations have shown that all samples are composed by the same oriented plate-like grains with similar sizes about 1–3 μm diameters and 0.2–0.5 μm thicknesses. The results of XRD have shown that no secondary phases have been produced, which indicated that Sr has been incorporated into the Ca3Co4O9 phase. The diffraction peak (00l) shifted to a lower angle and the offset is increasing with the increase of Sr content, which indicated that the Sr cations can enter the Ca-sites of the Ca3-xSrxCo4O9+δ, and cause increase of the length of the C axis. Slight improvements in the Seebeck coefficient (S) and electrical resistivity (ρ) were observed across all Sr-substitution samples when the mol% of Sr was adjusted. The improvement in both electrical resistivity and Seebeck coefficient leads to higher power factor (PF) values for the ceramics. The measured results show that the highest power factor value around 0.21 mW m−1K−2 can be obtained in Ca2.4Sr0.6Co4O9+δ at 650 °C, which is 16.7% higher than the undoped sample, The ZT value of 0.37 at 650°Cfor the CCO–Sr0.6 sample is significantly higher than that of the pure CCO sample. The results show that Sr can be as an effective doping element to reduce the thermal conductivity and enhance the Seebeck coefficient for the CCO system. It can be concluded that x = 0.6 is the optimal Sr for Ca substitution in this material system.

Magnetic and electric behaviors of [formula omitted]: Effect of hole doping

DyMn2O5 is an intriguing multiferroic material showing multiple magnetic, electric and structural transitions. We present here the systematic study on the effect of Sr doping at the Dy site of DyMn2O5 through magnetic and dielectric measurements. Doping of divalent Sr at the Dy site is expected to enhance the Mn4+:Mn3+ ratio and it will also dilute the Dy site. Our study indicates large enhancement in the magnetic anomaly observed close to 43 K, which we believe to be related to the increased ferromagnetic correlations on Sr doping. Gradual increase in coercive field at 3 K with the Sr doping and decrease in bond length of adjacent Mn4+ ions further support the enhancement of ferromagnetic correlations in the system. The parent sample shows a large magnetocaloric effect around 12 K, the magnitude of which found to decrease with increasing Sr concentration. The doping also enhances the anomaly at around 28 K observed in the dielectric permittivity versus temperature data, and this anomaly was earlier claimed to be associated with the spin reorientation as well as a simultaneous transition from one ferroelectric state to other. The electric orderings observed below 25 K are found to be susceptible to the applied magnetic field, and supports the view of Ratcliff II et al. (Phys. Rev. B 72, 060407(R) (2005)) of concomitant changes in the magnetic structure associated with the multiple electric transitions.

Effects of Sr addition on microstructures and mechanical properties of Mg-1Zn-1Ca-xSr alloys

The Sr-containing magnesium alloys have unique characteristics and demonstrate potentials to broaden the application of magnesium alloys. The microstructures and room temperature tensile properties of the as-cast Mg-1Zn-1Ca-xSr (x = 0.1, 0.5, 1.5, 2.5 weight%) alloys were investigated in this study. The results indicated that the grains of the Sr-containing alloys were gradually refined and the quantity of second phases was obviously increased with increasing the Sr content. In addition, the phase constituents of the alloys were found to be α-Mg, Mg2Ca, Mg6Ca2Zn3 and Mg17Sr2. The tensile results at room temperature showed that the tensile strength and elongation increased for low Sr-content alloys, but didn’t change or even decreased a little for high Sr-content alloys. The yield strength changed little with increasing Sr content. The alloy with 0.1% Sr exhibited the best comprehensive properties, with yield strength of 65.69 MPa, tensile strength of 118.23 MPa and elongation of 2.45%. Fracture analysis showed that the fracture mode of the alloys was mainly quasi-cleavage mechanism.

Effect of Strontium Doping Into CaBi2Nb2O9 Aurivillius Oxide Nanoceramics: Structural and Electrical Properties

Herein, we report the synthesis and characterization of Ca1-xSrxBi2Nb2O9 (CSBNO) (0 ≤ x ≤ 1) nanoceramics prepared using sucrose-assisted sol–gel combustion methods. The synthesized nanoceramics were characterized by different tools like differential thermal and thermogravimetric analyzer (DTA-TG), high resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR) spectrometer, X-ray powder diffraction (XRD), and impedance analyzer. DTA-TG reveals that the optimum temperature of calcination of CBN is higher than 1000 °C. The FTIR revealed the formation of CaBi2Nb2O9 (CBNO) at 614 cm-1. The XRD confirmed that all samples exhibited orthorhombic crystal structure. Increased orthorhombic distortion was spotted for doped CBNO and the structure acquires extra orthorhombicity through Sr doping. The TEM measurement inspected the increase of the grain size due to the inclusion of strontium into the orthorhombic crystal structure of CBNO from 56 nm to 76 nm. The dielectric constant measurement demonstrated that the increase in Sr content is associated with steady decrease in Curie temperature from 1207 K up to 720 K. The dielectric loss exhibited a minimum value at x = 0.5 and high stability along the temperature range of 300–850 K. Such property may enable this nanocomposite to be used for the application of FeRAM.

Thermomechanical properties of zero thermal expansion materials from theory and experiments.

Origin and composition dependence of the anisotropic thermomechanical properties are elucidated for Ba1-xSrxZn2Si2O7 (BZS) solid solutions. The high-temperature phase of BZS shows negative thermal expansion (NTE) along one crystallographic axis and highly anisotropic elastic properties characterized by X-ray diffraction experiments and simulations at the density functional theory level. Ab initio molecular dynamics simulations provide accurate predictions of the anisotropic thermal expansion in excellent agreement with experimental observations. The NTE considerably decreases with increasing Sr content x. This is connected with the composition dependence of the vibrational density of states (VDOS) and the anisotropic Grüneisen parameters. The VDOS shifts to higher frequencies between 0-5 THz due to substitution of Ba with Sr. In the same frequency range, vibrational modes contributing most to the NTE are found. In addition, phonon calculations using the quasi-harmonic approximation revealed that the NTE is mainly connected with deformation of four-membered rings formed by SiO4 and ZnO4 tetrahedra. The thermomechanical and vibrational properties obtained in this work provide the basis for future studies facilitating the targeted design of BZS solid solutions as zero or negative thermal expansion material.

Effect of Substitution Sr Cations on the Structure in the Gd<sub>1</sub>(Ba<sub>2</sub><sub>−<i>x</i></sub>Sr<sub><i>x</i></sub>)Cu<sub>3</sub>O<sub>7−<i>δ</i></sub> Phases

In an effort to improve the performance of superconductors in the field and high temperatures it is important to study the superconducting mechanism. For this reason, the cation substitution can be conducted. One of the high Tc superconductors Gd1Ba2Cu3O7−δ phase with Sr substitution has been synthesized, i.e. Gd1(Ba2−xSrx)Cu3O7−δ compound. The sample was synthesized by using a solid-state reaction method with a wet mixing, sintered for 12 hours at temperature 900°C. The synthesis results are characterized by using XRD. The results of Match-3 software analysis showed high (higher 85%) Gd1Ba2Cu3O7−δ phase was formed. The Sr substitution causes changes to the structure, i.e. the lattice parameters a, b and c, where the orthorhombicity tends to decrease with increasing Sr content. Refinement results show that based on the oxygen occupancy, the total oxygen content tends to increase.

The influence of co-doping strontium and zirconium on structure and ionic conductivities of Li6+yLa3−ySryNbZrO12 solid electrolytes

To enhance the ionic conductivity of lithium garnets, a co-doping strategy was adopted with both strontium and zirconium for [Formula: see text] ([Formula: see text], 0.25, 0.5, 0.75 and 1.0) (LLSNZO). By increasing the content of Sr, lithium garnet ceramics maintain cubic structure when [Formula: see text] is in the range of 0–0.75. A secondary phase of [Formula: see text] appeared in the ceramic when [Formula: see text]. We also studied the cross-section of lithium garnets with silver electrode. Results showed that the density of LLSNZO ceramics increased continuously against the increase of Sr content, while their total ionic conductivity enhanced initially and then reduced, with the maximum reached when [Formula: see text]. It is indicated that ionic conductivity of lithium garnets is not only decided by the density but also decided by the concentration and the mobility of [Formula: see text].

Analisa Perkembangan Struktur Aluminum (AC2B) dengan Pengaruh Penambahan Stronsium pada Part Transmisi Sub Assy Menggunakan Metode Pengecoran Gravity Dies Casting

Recently, one of the problems faced by the automotive industry is the frequent failure parts produced by casting processes such as uncomplete filling, low mechanical properties, shrinkage (non-uniform shrinkage), and porosity. In this research, the modification method with the addition of strontium while aluminum being melted is held. This experiment was made to solve either the shrinkage problem or porosity. The improvement of the mechanical properties of aluminum also become one of the purposes of the experiment. The concentration of strontium added was 0 wt.% Sr, 0.005wt.% Sr, 0.0075wt.% Sr, and 0.01 wt.%. The results show that the increased Sr content on AC2B will increase the mechanical properties, while the optimum value occurred by addition value 0.01wt. % Sr. However the results also show that the concentration of strontium has no effect on reducing shrinkage porosity, and can reduce the size of aluminum dendrites.

CO2 dry reforming of CH4 with Sr and Ni co-doped LaCrO3 perovskite catalysts

Catalysts La0.8−xSrxCr0.85Ni0.15O3 (x = 0, 0.1, 0.2 and 0.3; P-80, P-71, P-62 and P-53) are prepared and reduced (R-80, R-71, R-62 and R-53) in H2 for CO2-dry reforming of methane (CO2-DRM). P-80, P-71 and P-62 are single-phase perovskite; P-53 contains additional NiO and SrCrO4. Ni particles are exsolved in R-80, R-71 and R-62 with a strong interfacial interaction; whereas those in R-53 are produced by NiO reduction. Increasing Sr concentration increases basicity and oxygen vacancy concentration of the support. R-53 demonstrates the highest conversion of CH4 and CO2 below 650 °C, which decreases to the lowest above 650 °C due to carbon deposition, while R-62 shows the highest performance with CH4 and CO2 conversions on the level of 90% at 800 °C because of the strong exsolved Ni particle/support interfacial interaction and the high basicity and oxygen vacancy concentration of the support. The performance of R-62 increases with the decrease of gas hourly space velocity (GHSV) from 1.2 to 0.3 × 104 ml g−1 h−1, and remains stable at 750 °C and 0.3 × 104 ml g−1 h−1 with conversions of CH4 and CO2 near 90% and selectivities of H2 and CO above 95%.

Structural characterization and ZFC/FC magnetization study of La0.6Ca0.4−xSrxMnO3 nanoparticle compounds

Structural and magnetic properties of La0.6Ca0.4−xSrxMnO3 manganites have been investigated for x = 0.0, 0.1 and 0.4. The Rietveld analysis of X-ray diffraction data indicates that, with increasing Sr content, a structural phase transition from rhombohedral to orthorhombic is occurred. Structural parameters are calculated and found to be dependent upon the composition. The nanometric size of our samples estimated using Debye–Scherrer equation is confirmed by SEM images. Magnetic measurements according to the zero-field cooled and field cooled procedures are performed. The observed irreversibility between the two modes is assigned to the presence of magnetic anisotropy which has been explained as arising from the surface effects. The blocking temperature (TB) is estimated and found to increase as the particle size increases. Above TB, the materials show a superparamagnetic (SPM) behavior where the coercivity and remanence magnetizations are almost zero that favors their application in the biomedical field. Studying the thermal variation of dc susceptibility confirms the SPM nature of the studied compounds. The good fit of the magnetization vs. magnetic field curves with Langevin function supports our findings. From this simulation, the saturation magnetization is calculated and found to increase as particle size increases which is explained in terms of Core–shell model. With the reduction of particle size to the nanometric scale, single domain structure and SPM regime structure are detected.

Study on microstructure and dynamic corrosion behavior of degradable Mg–Y–Zn–Zr alloy with different Sr contents

Microstructure and corrosion behaviors of cast Mg-2Y-1Zn-0.4Zr-xSr alloys were investigated by using OM, SEM, immersion and electrochemical tests. The results show that the addition of Sr refines the grain, the grain size of Mg-2Y-1Zn-0.4Zr-0.3Sr alloy is the thinnest. the addition of Sr also changes the morphology and distribution of the second phase. The precipitation of W-phase at grain boundary decreases, while the precipitation of punctate W-phase and Mg0.97Zn0.03 phase in the grain increased. In addition, both immersion and electrochemical tests illustrates Mg-2Y-1Zn-0.4Zr-0.3Sr alloy has the best corrosion performance among the four investigated alloys, and shows a relatively uniform corrosion morphology on the surface. Moreover, as the Sr content increases, the corrosion mode of the alloy changes from intergranular corrosion to intragranular corrosion.

Tuning magnetoelectric effect in Pb(1−x)SrxTiO3/CoFe2O4 multiferroic nanocomposites by varying Sr content

Effect of chemical compositions in ferroelectric phase on magnetoelectric (ME) coupling is investigated for (3-1) multiferroic Pb(1−x)SrxTiO3/CoFe2O4 nanocomposites, via phase field model. The Sr content in ferroelectric phase varies in a wide range of 0 ≤ x ≤ 0.4. Stripe polarization domain structure is stably formed in the ferroelectric matrix, while rectilinear magnetization domain appears in each ferromagnetic nanowire. Average sizes of polarization domains strongly depend on the Sr content in the ferroelectric matrix. The magnitude of polarization in the ferroelectric matrix monotonically decreases with increasing Sr content. Interestingly, the ME coupling of the multiferroic nanocomposites depends non-monotonically on the Sr content. In particular, the ME coefficient increases with the Sr content x < 0.15 and decreases with x > 0.15. The largest ME coefficient is obtained in the multiferroic nanocomposite with x = 0.15. On the other hand, we show that the ME coupling is dependent of both the density of polarization domain walls and elastic energy of the nanocomposites. Importantly, as the Sr content increases, the density of polarization domain walls and elastic energy vary oppositely, which results in the non-monotonic change of ME coupling. The change of ME coupling with the Sr content is governed by the increase of elastic energy as x < 0.15, but dominated by the decrease of domain wall density as x > 0.15. The obtained results suggest an optimized range of chemical compositions in the ferroelectric matrix of multiferroic nanocomposites to obtain a high ME coupling.

Enhanced room-temperature TCR of La0.67Ca0.33-xSrxMnO3 (0.06 ≤ x ≤ 0.11) polycrystalline ceramics by Sr content adjustment

Herein, the influence of Sr doping on chemical composition, microstructure, and electrical transport properties of La0.67Ca0.33-xSrxMnO3 (LCSMO, 0.06 ≤ x ≤ 0.11) polycrystalline ceramics is systematically investigated. The study was performed by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), elemental mapping, energy dispersive spectrometry (EDS), X-ray photoemission spectroscopy (XPS), and four-probe method (ρ-T). XRD results verified the synthesis of high-purity orthogonal perovskite structure with Pnma space group. EDS and XPS results confirmed presence and uniform distribution of La, Ca, Sr, Mn and O. Furthermore, ρ-T curves indicated that the resistivity decreased with increasing Sr content, whereas metal-insulator transition temperature (TMI) gradually increased. Moreover, cell volume (V) and electron bandwidth (W) increased with the increase in Sr content, which effectively reduced the resistivity of LCSMO ceramics. One should note that double exchange (DE) enhancement between Mn3+ and Mn4+ is responsible for gradually increasing TMI. Finally, maximum TCR value of 14.3% K−1 was achieved at x = 0.08, which rendered TCR peak temperature of 299.0 K. High room-temperature TCR of LCSMO ceramics is promising for next-generation infrared bolometers, operating at room-temperature.

(Ba,Sr)TiO3 solid solutions sintered from sol-gel derived powders: An insight into the composition and temperature dependent dielectric behavior

Single-phase Ba1-xSrxTiO3 (BST) perovskite ceramics with 0.3 ≤ x ≤ 0.4 were prepared from powders synthesized via sol-gel route. The compositions have the ferroelectric-paraelectric phase transition close to room temperature. At 20 °C the BST ceramics are ferroelectric for 0.3 ≤ x ≤ 0.35 and paraelectric for x = 0.375 and x = 0.40. The study follows the relation between the structural changes produced when increasing the Sr content and the dielectric properties at low intensity electric fields. It is found that the grain size and tetragonality decreases as the Sr content increases. Analyses of complex permittivity and impedance spectroscopy reveal the temperature and frequency dependencies of the dielectric properties. The phase transitions seem to be of first order for all compositions, with a thermal hysteresis that decreases with increasing the Sr content, fact attributed to the corresponding increase of the grain boundaries weight allowing a more efficient stress relaxation in the structure during the change of the symmetry from cubic to tetragonal. The diffusiveness degree during the phase transition is increasing with Sr content, suggesting some relaxor-type contribution attributed to smaller grain size. The ac conductivity follows the universal Jonscher law, with an ac component having the power parameter s independent of Sr content, and a dc component that it is thermally activated with an activation energy of about 0.7–0.77 eV attributed to oxygen vacancies acting as donor-like defects. The fit of impedance spectra at different temperatures and frequencies is obtained by using an equivalent circuit accounting the grains, grain boundaries, electrode interfaces and the local contributions produced by reorientation of defect dipoles or defect clusters. All the component circuits have significant variations around phase transitions. These are discussed in relation to structural changes occurring during transition and considering the changes in the distribution of various charges when polarization vanishes.

Fabrication and characterization of strontium-hydroxyapatite/silk fibroin biocomposite nanospheres for bone-tissue engineering applications

Osteoinductive bone filling biomaterials are in high demand for effective bone defect reconstruction. In this study, we aimed to design both organic and inorganic substances containing strontium-doped hydroxyapatite/silk fibroin (SrHA/SF) biocomposite nanospheres as an osteoinductive bone defect-filling biomaterial. SrHA/SF nanospheres were prepared with different concentration of Sr using ultrasonic coprecipitation method. The nanospheres were characterized using XRD, FTIR, SEM, TEM, ICP-AES and TGA. Solid and dense SrHA/SF nanospheres with 500–700 nm size and rough surfaces were synthesized successfully. Higher crystallinity and HA/SF phase were observed with the increase in Sr-concentration. The doping of different concentration of Sr did not affect the size and surface characteristics of the nanospheres. ICP-AES data showed that Sr/Ca ratio in SrHA/SF is very close to the nominal value. Nanospheres with higher concentration of Sr did not negatively affect the biocompatibility, but enhanced viability of mesenchymal stem cells (MSCs). Moreover, SrHA/SF nanospheres showed higher osteogenic differentiation potential compared to HA/SF nanospheres as indicated by the results from ALP staining, ALP activity, and Runx2, Alp, Col-1 and Opn gene expression assay in MSCs culture. Our findings suggest this novel design of biocompatible and osteoinductive SrHA/SF biocomposite nanospheres as a potential bone defect-filling biomaterial for bone regenerative applications.

Study of A-site disorder dependent structural properties and magnetic ordering in polycrystalline perovskite Sm0.5Ca0.5−xSrxMnO3

This paper reports the studies on the effect of A-site substitution by strontium on the structural properties and magnetic ordering in polycrystalline perovskite Sm0.5Ca0.5−xSrxMnO3 (x = 0.1, 0.2 and 0.3). The investigated samples are prepared by conventional solid-state reaction technique. XRD analysis at room temperature has confirmed orthorhombic structure of the sample with space group Pnma. The dependence of structural parameter, Curie temperature and coercivity on Sr doping content has been thoroughly investigated. It is observed that substitution of Sr2+ for Ca2+ increases lattice parameter, tolerance factor and the Curie temperature. However, the coercivity (Hc) decreases with increasing Sr content while the charge ordering process is weakened with increasing Sr content. Field cooled (FC) and zero-field cooled (ZFC) dc magnetizations measurements at low field and low temperature indicate that there is a spin-glass (SG) like state occurred. Temperature dependent ac susceptibility at different frequency indicates a spin-glass-like transition of the sample.

Doping Strontium into Neodymium Manganites Nanocomposites for Enhanced Visible light Driven Photocatalysis

Nd1−xSrxMnO3 nanocomposites perovskites were synthesized using sol gel method at different Sr content x = 0.3, 0.5, 0.7, and 0.9. The photocatalytic performance of the Nd1−xSrxMnO3 nanocomposites for photodegradation of Acridine orange dye (AO) was evaluated over visible light illumination. The single phase of orthorhombic pbnm was formed for x = 0.3 and 0.5; however monoclinic and orthorhombic were observed at x = 0.7 and 0.9. The Energy gap of the Nd1−xSrxMnO3 nanocomposites were estimated for all concentrations to be in the range of 3 ± 0.05 eV. The photocatalytic efficiency of Nd0.3Sr0.7MnO3 nanocomposite was 95% of the initial AO dye concentration within 3 h illumination time. The linear increase of the photodegradation rate was found in our samples as a result of the increase of Sr contents from 0.3 to 0.7wt %. Interestingly, the Nd0.3Sr0.7MnO3 content has the highest degradation rate of AO which is two times faster than undoped NdMnO3. This superior behavior in photocatalytic activity of Nd0.3Sr0.7MnO3 nanocomposite emerges from large surface area, structural anisotropy, and small particle size. These findings shows convincingly that the Nd1−xSrxMnO3 photocatalysts possess great promise for visible light driven photodegradation of AO dye.

Optical and magnetic properties of Gd1−xSrxCrO3 (0 ⩽ x ⩽ 0.15)

Optical and magnetic properties of Gd1−xSrxCrO3 (0 ⩽ x ⩽ 0.15) polycrystalline samples have been investigated to identify the role of Sr2+ ion in GdCrO3 compound. Quantitative structural analysis using Rietveld refinement suggests the formation of single orthorhombic phase up to x = 0.1 composition, and in addition, a secondary monazite-type structure of SrCrO4 arises for x = 0.15 composition. Raman and Fourier transform infrared spectra also confirm the presence of SrCrO4 component for higher concentration of Sr2+ ion. Mixed valence state of Cr such as Cr3+ and Cr4+ is obtained from x-ray photoelectron spectroscopy. The presence of Cr4+ ion induces a reduction of optical band gap with increase of Sr content. The unoccupied states originate from Cr4+ modify d–d transitions. Larger cell volume and breaking of magnetic exchange pathways through nonmagnetic element (Sr) weaken the strength of interaction and consequently lower Néel and spin reorientation temperatures.