Properties Of Sr Research Articles

Improvement on properties of Sr2+ doped perovskite-type ceramic for thermal protective coating: A comprehensive evaluation

Perovskite-type aluminates hold significant promise for applications as thermal protective coatings (TPCs), but their inferior properties necessitate further optimization. In this study, PrAlO3+δ (PA) and Sr2+ doped Pr1-xSrxAlO3+δ (PSA, x = 1, 2, 5 mol%) were fabricated using the solid-state reaction method. The effects of Sr2+ substitution on properties were thoroughly investigated. The results demonstrated pronounced effects of Sr2+ substitution. PSA exhibited significant lattice volume expansion and enhanced sintering resistance with increasing doping concentration. Also, doping strategy effectively decreased thermal conductivity of PSA 4.38 W/(m·K) at room temperature to 3.48 W/(m·K) at 900 °C, decreasing by about 15 % in comparison to that of PA (6.21–4.07 W/(m·K)). Moreover, mechanical properties of PSA were improved, presenting the lowest elastic modulus (118.7 GPa) in contrast to that of PA (344.3 GPa). Most importantly, despite the lattice distortion caused by doping leading to limited improvement in infrared emissivity in the range of 8–14 μm, the infrared emissivity of PSA was significantly enhanced in the range of 3–5 μm. A highest average emissivity of 0.875 was achieved with x = 2 mol%, representing a 10 % enhancement compared to that of PA (0.796). Furthermore, the enhancement mechanisms were systematically elucidated.

Exploring beta irradiation responses in Sr2+-Doped hydroxyapatite: A thermoluminescence study

This research investigates the structural and thermoluminescence (TL) properties of Sr2+-doped Ca5(PO4)3OH (HAp) phosphors. X-ray diffraction (XRD) analysis confirms that HAp has a hexagonal structure with a P63/m space group. The TL behaviour of HAp:Sr2+ phosphors is examined under beta irradiation in the temperature range of 25–500 °C. The study reveals three TL glow peaks at temperatures of 75, 212, and 296 °C. Investigation of TL responses across heating rates (HR) ranging from 0.1 to 5 °C/s shows that higher HRs result in increased maximum TL peak temperatures and reduced TL intensities. This trend suggests an augmented contribution from non-radiative transitions as the heating rate increases. Importantly, no evidence of thermal quenching is found in the HAp samples. Two different methods, Hoogenstraaten's and Booth-Bohun-Porfianovitch, yield consistent activation energy values of 0.50, 1.22, 1.67 eV, and 0.48, 1.19, 1.63 eV, respectively. Reusability assessments indicate a standard deviation of less than 5 %, confirming the reliability of the materials. Tm−Tstop analysis reveals a continuous distribution of trap levels. TL properties in HAp samples have been comprehensively characterized, contributing not only to enhancing our understanding of their behaviour, but also highlighting their potential applications in various areas. The findings of this study have provided valuable insight into the development of efficient catalysts that are suitable for a variety of applications.

Phase composition, crystal structure and ferroelectric properties of Sr0.6Ba0.4Nb2O6/Ba2NdFeNb4O15/si(001) heterostructures

Phase composition, nanostructure and properties of Sr0.6Ba0.4Nb2O6/Ba2NdFeNb4O15/Si(001) heterostructures have been studied by X-ray diffraction, scanning probe microscopy, and dielectric spectroscopy. Sr0.6Ba0.4Nb2O6 and Ba2NdFeNb4O15 films were fabricated under identical conditions by RF cathode sputtering in an oxygen atmosphere. It was shown that the obtained heterostructures were pure, the Sr0.6Ba0.4Nb2O6 and Ba2NdFeNb4O15 layers were polycrystalline textured, and the layer thickness did not affect the unit cell strain. The heterostructure exhibited a ferroelectric-like response, but the polarized regions arising under the application of electric field were unstable at room temperature. The reasons for the identified regularities are discussed.

The Structure, Magnetic and Magnetotransport Properties of Sr 1− x Y x CoO 3− δ Layered Cobaltites

The properties of Sr1−xYxCoO3−δ layered cobaltites are determined by synchrotron X-ray and neutron powder diffraction studies, by measurements of magnetic and magnetotransport properties. It is shown that the crystal structure changes from tetragonal P4/mmm (ap × ap × 2ap) to monoclinic A2/m (4√2ap × 2√2ap×4ap up to the magnetic ordering temperature and 2√2ap ×2√2ap × 4ap above) through the intermediate tetragonal I4/mmm (2ap × 2ap × 4ap) with alternating layers of CoO6 and CoO4+δ. The basic magnetic structure is G-type antiferromagnetic with Co3+ ions in a high spin/low spin (HS/LS) state mixture in both structural layers. The Co3+ magnetic moments in the CoO6 and CoO4+δ layers are 1.5 μB/Co and 2 μB/Co for x = 0.1 and 1.8 μB/Co and 2.7 μB/Co for x = 0.2, respectively. The antiferromagnetic–“ferromagnetic” transition in compounds with x > 0.2 is associated with the structural and orbital disorder. Magnetic transitions are accompanied by structural phase transitions. The presence of the ferromagnetic component is associated with the monoclinic distortions and canting of magnetic moments in anion-deficient layers due to orbital ordering. A sharp drop of the magnetization for x > 0.2 is caused by the LS Co3+ stabilization and orbital disordering. No spontaneous magnetization is found for compounds with x > 27%.

Fabrication and characterization of Sr0.8Bi2.2Ta2O9 /Al2O3 gate stack for ferroelectric field effect transistors

We analyze and report the structural, electrical and ferroelectric properties of Sr0.8Bi2.2Ta2O9/Al2O3/silicon gate stack for ferroelectric field effect transistors (FETs). RF sputtering and plasma-enhanced atomic layer deposition (PEALD) have been used for the deposition of Sr0.8Bi2.2Ta2O9 (SBT) and Al2O3 film, respectively. Different deposition and process parameters of the SBT and Al2O3 films were optimized by obtaining the structural properties of the deposited film, and electrical properties of metal/ferroelectric/silicon (MFeS), metal/insulator/silicon (MIS), and metal/ferroelectric/metal (MFeM) structures. X-ray diffraction analysis reveals the polycrystalline perovskite structure of the SBT film having a dominant intensity peak along direction at different annealing temperatures. Crystalline film morphology with a maximum grain size of 45 nm was confirmed at the annealing temperature of 500 °C by the field emission scanning electron microscopy. Ellipsometric analysis of the SBT film reveals the maximum refractive index of 3.46 at the annealing temperature of 500 °C. Introduction of a 10 nm buffer layer between ferroelectric and silicon substrate shows the improved memory window of 6.07 V in metal/ferroelectric/insulator/silicon (MFeIS) structure as compared to the 3.07 V in the MFeS structure. MFeI(10 nm)S structure also shows improved leakage current characteristics as compared to MFeS structures and endurance greater than 1013 read/write cycles with the data retention time of higher than 10 years.

The elastic, magnetic, and electrical properties of Sr1–уYуCoO3–x cobaltites in the composition range 0.2 ≤ y ≤ 0.3

Anion-deficient layered cobaltites Sr0.75Ln0.25CoO3–x (Ln is a lanthanide) have attracted the special attention of the scientists who study the nature of phase transformations in perovskite-like cobaltites, the anomalous behavior of the temperature magnetization of which is still the subject of scientific discussion. The purpose of this work is to investigate the regularity of changes in the elastic, magnetic, and electrical properties of layered cobaltites Sr1–уYуCoO3–x in the composition range 0.2 ≤ y ≤ 0.3 over a wide temperature range. The studied polycrystalline samples were obtained by the known ceramic technology in the air. Electron microscopic studies were performed on a LEO 1455 PV scanning electron microscope. The temperature dependence of the Young’s modulus was studied by the method of resonance vibrations in the frequency range 1000–6000 Hz and in the temperature range 100–450 K. X-ray phase analysis was performed on a DRON-3M diffractometer under Cu-Kα radiation. Magnetic measurements were performed using a physical property measurement system (Cryogenic Ltd.) in the temperature range 5–325 K. As a result of the studies, it was found that in the temperature range 25–300 K, Sr1–уYуCoO3–x solid solutions (0.2 ≤ y ≤ 0.3) are characterized by the semiconductor-like conductivity. No significant magnetoresistive effect was observed in this temperature range for the studied compositions. It was shown that the Sr1–уYуCoO3–x solid solution (у = 0.25) exhibits two magnetic phase transformations: low-temperature near 220 K and high-temperature at 350 K. The nearby compositions of the concentration range 0.2 ≤ y ≤ 0.3 exhibit magnetic phase transformations at temperatures above room temperature. No low-temperature phase transitions were detected in them. It has been established that magnetic phase transformations are accompanied by structural transitions at corresponding temperatures.

Detection of Negative Thermal Expansion in a Single Crystal of Sr0.75Ba0.25Nb6O2 Relaxor Ferroelectric by X-Ray Diffraction Analysis

The atomic structure of a single crystal of Sr0.75Ba0.25Nb6O2 representing a relaxor ferroelectric is determined from X-ray diffraction data. At nine temperatures within a range of 93–480 K, 12 experiments are performed. The experimental facilities (area detector, goniometer, and sample cooling system) are calibrated. The region of negative thermal expansion with respect to the unit-cell parameter с is revealed at 272–324 K. In the same region, an electrical resistance anomaly is observed. It is found that the structural parameters have a singularity at 296 K, in particular, an unusual thermal motion of atoms is observed. This correlates with a kink in the resistance–temperature curve at 297.5 K. The obtained results and analysis of published data indicate that, near room temperature, several physical properties of Sr0.75Ba0.25Nb6O2 relaxor at once have singularities, which can be explained by the revealed lattice instability.

DFT prediction of structural, electronic and magnetic properties of Sr0.75TM0.25S (TM is 3d transition metals)

ABSTRACTIn recent years, the scientific community has done great efforts to search for new materials suitable for spintronics applications. Diluted magnetic semiconductors have been considered as prospective candidates to be used in spintronic devices. In this paper, we have used the full-potential linearised augmented plane wave (FP-LAPW) method within density functional theory framework to study the structural, electronic and magnetic properties of the strontium sulfide SrS doped with 3d transition metals (TM) with TM concentration (). The generalised gradient approximation proposed by Wu-Cohen (GGA-WC) was adopted to deal with the exchange-correlation effect and the Tran–Blaha modified Becke–Johnson exchange potential was also employed to calculate the electronic and magnetic properties in order to obtain accurate results. Our calculations show that the SrS doped with Ti, V, Cr, Mn, Fe and Ni are half-metallic with relatively wide ferromagnetic band gap E. However only five materials, namely, , , , and may be candidates for spintronic applications as they exhibit a wide half-metallic band gap of 1.002, 0.587, 1.201, 0.533 and 0.661 eV, respectively. Finally, results indicate that TM atoms are those that determine the magnetic properties of materials at hand.

The Effects of Dwell Sintering Time on the Densification and Microwave Dielectric Properties of Sr0.5Ca0.5La4Ti5O17 Ceramic

The effects of dwell sintering time on the densification and microwave dielectric properties of Sr0.5Ca0.5La4Ti5O17 ceramic were investigated. The ceramic was fabricated using the conventional solid-state mixed oxide route using high-purity raw materials which was characterized using X-ray diffraction, scanning electron microscopy and vector network analyzer for phase, microstructure and microwave dielectric properties analysis, respectively. The XRD findings showed single-phase ceramics for all sintered samples. The microstructure was observed to be comprised of compacted elongated plate like grains. The grain size was observed to increase with increase in sintering time from 2 to 7 h. Abnormal grain growth is observed for sintering time > 5 h. Thus, the dwell sintering times effected the density, and hence the microwave dielectric properties of Sr0.5Ca0.5La4Ti5O17 ceramic. er ~ 57.1, Qufo ~ 13,250 GHz and τf ~ 5.1 ppm/°C were obtained for Sr0.5Ca0.5La4Ti5O17 ceramic sintered at 1550 °C for 5 h in the present study.

Cytocompatibility and Dielectric Properties of Sr2+ Substituted Nano-Hydroxyapatite for Triggered Drug Release

Hydroxyapatite (Ca5(PO4)3OH) is a well-known bioceramics material used in medical applications because of its ability to form direct chemical bonds with living tissues. In this context, we investigate the biocompatibility and dielectric properties of Sr2+-substituted hydroxyapatite nanoparticles were synthesized by sol-gel method. The influence of strontium on the crystal structure, functional group, morphological, electrical properties, and biocompatibility of as-synthesized nano-hydroxyapatite samples was analyzed using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FE-SEM). Dielectrical properties of the bioactive Sr-HA sample were investigated by a dielectric impedance spectroscopy method. The observed results illustrate the incorporation of Sr2+ ions in the apatite lattice could influence the pure HA properties, by reducing the crystallite size and crystallinity quite consistent with the morphology variation. The ac conductivity (σac) increased with an increasing applied frequency confirmed that prepared HA sample exhibited the universal power law nature. Further, the in vitro drug loading and release studies using doxycycline as a model drug demonstrate that the Sr2+ -HA nanoparticles show high drug adsorption capacity and sustained drug release. Thus, the improved bioceramics system could be a promising candidate for future biomedical applications.

Effects of synthesis temperature on the microstructures and photoluminescent properties of Eu2O3-doped Sr2−xBaxSiO4 phosphors

In this study, Sr2−xBaxSiO4 (x = 0, 0.2, and 0.4) was used as the host material and Eu2O3 was used as the activator to produce commercial Sr2SiO4:Eu, Sr1.8Ba0.2SiO4:Eu, and Sr1.6Ba0.4SiO4:Eu phosphors by a solid-state reaction method. All the Sr2−xBaxSiO4–Eu phosphors were synthesized in the temperature range of 1000–1300 °C for 2 h. XRD patterns revealed that when different BaO contents and synthesis temperatures were used, all the Sr2−xBaxSiO4–Eu phosphors had similarly crystalline properties. The mainly crystalline phase changed from the (121) to the (103) plane as the BaO content changed from 0 to 0.2. In the case of all Sr2−xBaxSiO4–Eu powders, secondary or unknown phases were not observed if the synthesis temperature was lower than 1000 °C, and only the precursor SiO2 phase was observed in the 1000 °C-synthesized Sr2SiO4–Eu powder. This study also thoroughly investigated the effects of different BaO contents and synthesis temperatures on the photoluminescent properties of Sr2−xBaxSiO4–Eu phosphors. We show that the photoluminescent properties of Sr2−xBaxSiO4–Eu phosphors are dependent on the BaO content and synthesis temperature.

Thermooptical and Dielectric Studies of a Calcium-Induced Ferroelectric Phase in a SrTiO3 Incipient Ferroelectric

We have examined temperature changes of the light refraction, birefringence, dielectric permittivity, and dielectric hysteresis loops in Sr1 – xCaxTiO3 single crystals with x = 0.014 (SCT-1.4). The dielectric properties of Sr1 – xCaxTiO3 with x = 0.007 (SCT-0.7) have been studied. We have performed ab initio calculations of equilibrium structures and total energies for three low-temperature phases of SrTiO3 and CaTiO3, based on which we have determined an expected symmetry of the ground state of their solid solution and spontaneous polarization directions in a calcium-induced ferroelectric phase in Sr1 – xCaxTiO3. In SCT-1.4, we have separated a spontaneous contribution to the light refraction, which arises due to the spontaneous electrooptical effect caused by the spontaneous polarization and its fluctuations. From the spontaneous contribution to the light refraction, based on a previously developed our phenological approach, we have quantitatively determined for the first time the values and temperature dependences of root-mean-square fluctuations of the order parameter—the polarization Psh = 〈P fl 2 〉1/2(short-range, local polar order) in the ferroelectric phase. From optical and dielectric measurements in SCT-1.4, the average value of spontaneous polarization Ps (the contribution from the long-range order) has been determined. We have estimated the values of Psh and Ps, which characterize the short- and long-range orders in the ferroelectric phase of SCT-0.7. Separate determination of the values and temperature dependences of Ps and Psh (which considerably exceeds the value of Ps in the ordered phase) has allowed us to reveal on a quantitative level new particular features of the formation of the induced polar phase in Sr1 – xCaxTiO3.

Auto-Combustion 방법으로 합성한 Sr1−xCaxFe12O19(x = 0, 0.5)의 결정학적 및 자기적 특성

Auto-Combustion 방법으로 합성한 Sr1−xCaxFe12O19(x = 0, 0.5)의 결정학적 및 자기적 특성

Effects of potassium interstitial doping on thermoelectric properties of Sr0.7Ba0.3Nb2O6−δ ceramics

The thermoelectric properties of potassium interstitial doped Sr0.7Ba0.3KxNb2O6−δ ceramics were investigated in the temperature range from 323 to 1073 K. The thermoelectric power factor is improved enormously due to the potassium interstitial doping combined with a reductive calcination method. The potassium dopants not only act as carrier donors but also modulate the electronic structures. Thus, the electrical conductivity increases remarkably, and the Seebeck coefficient, meanwhile, maintains considerable values at high temperatures. Only the moderate doping content x = 0.10 contributes to reducing the lattice thermal conductivity. Thus, the sample Sr0.7Ba0.3K0.1Nb2O6−δ shows the highest ZT value of 0.23 at 1073 K.

Enhanced thermoelectric properties of Sr2Nb2O7 ceramics with barium substitution

Properties of Sr1.9−xBa0.1LaxNb2O7 (SBNL; x = 0.1–0.3) thermoelectric ceramics were investigated in this study. SBNL ceramics were prepared by a reaction–sintering process with the calcinations and subsequent pulverization stages bypassed. Resistivity logρ = 8.5–9.13 Ω cm at 450 °C and logρ = 6.8–7.1 Ωcm at 700 °C were observed. Addition of Ba into Sr2Nb2O7 ceramics dramatically enhances the Seebeck coefficient S. S = −66 to −58 μV K−1 at 200 °C and S = −182 to −80 μV K−1 at temperatures around 470 °C for SBNL ceramics. The maximum S = −182 μV K−1 appears at 472 °C for Sr1.6Ba0.1La0.3Nb2O7. κ values at 500 °C are 0.91–1.215 W m−1 K−1 for SBNL ceramics. Enhanced thermoelectric properties of Sr2Nb2O7 ceramics could be obtained with barium substitution.

Local structure, electrical and magnetic properties of Fe-doped Sr2(Ni,Mo)O6 double perovskite

Abstract Double perovskite material of 10 mol% Fe-doped Sr 2 (Ni,Mo)O 6 was prepared by solid-state reaction. The NiMoO 4 precursor was first synthesized as a starting material with calcination temperature at 1100 °C in air. Effects of FeO, Fe 2 O 3 and Fe 3 O 4 dopant on phase formation, morphology, electrical and magnetic properties of the specimens were investigated and discussed. The XRD technique was used to analyze the phase formation of the samples. It can be clearly seen that phase formation of pure Sr 2 (Ni,Mo)O 6 indicated the cubic phase structure, while the tetragonal phase was found with FeO, Fe 2 O 3 and Fe 3 O 4 dopant. All XANES spectra were collected at the ambient temperature and atmospheric pressure. The result demonstrated that the oxidation state of Fe is 3 + , indicating the occurrence of γ-Fe 2 O 3 phase for all samples. In addition, the room temperature ferroelectric and ferromagnetic properties were determined using a simple Sawyer–Tower circuit (at fixed measuring frequency of 50 Hz) and Vibrating Sample Magnetometer (VSM), respectively. The maximum ferroelectric and ferromagnetic properties were seen with Fe 2 O 3 dopant. Interestingly, the ferroelectric and ferromagnetic properties of Sr 2 (Ni,Mo) 0.9 Fe 0.1 O 6 ceramics were affected by iron oxide doping.

Synthesis, photoluminescence properties of Sr1.95Ba0.05CeO4:Eu3+ for LED applications

The Sr1.95Ba0.05 CeO4:Eu3+ phosphors are synthesized by the solid-state reaction method. The samples are characterized using X-ray diffraction (XRD), diffuse reflectance spectroscopy and photoluminescence (PL) spectra. The XRD results reveal that the synthesized phosphors are genuine crystalline and belong to the orthorhombic structure. The intense PL emission is optimized from the PL spectra at various doping concentrations of europium ions. The results indicates that the phosphor can be effectively excited under 264 nm wavelength producing on intense emission spectrum of the synthesis material at 484 nm (blue region). The color purity of the phosphor is confirmed by CIE coordinates (x = 0.217, y = 0.265). The experimental data indicate that the prepared phosphors can be used as blue-emitting material in the field of illuminations and display devices.

Structure and Fluorescent Properties of Sr0.69La0.31(1–x)F2.31:xEu3+ Phosphors

Structure and Fluorescent Properties of Sr_0.69La_{0.31(1–<i>x</i>)}F_2.31:<i>x</i>Eu³⁺ Phosphors

Properties of Sr2.13Ba0.8SiO5:0.07Eu2+ phosphor synthesized by microwave assisted with SiC method

Nano-sized Sr2.13Ba0.8SiO5:0.07Eu2+ yellow phosphor was synthesized by microwave assisted with SiC method (MASM). The phase, morphology, luminescence properties and formation mechanism of nano-particles were studied. Results indicate that the phosphor is a tetragonal system with space group P4/ncc (130). The SEM shows a smooth surface and regular morphology with homogeneous size distributed from 80 to 100 nm. The formation of nano-sized particles ascribed to the interaction of microwave and reactive material, and that is the high speed vibration of product particles induced by microwave interaction inhibits the growth of the crystal grain size. The excitation spectrum is a broad band spectrum from 250 to 550 nm, which attributed to 4f–5d transition of Eu2+ ions. The emission spectrum excited at 460 nm is a broad band peaking at 577 nm attributed to the transition of 4f65d → 4f7(8S7/2) of Eu2+ ions. The color temperature and color coordinate of white LED prepared with the phosphor are 2658 K and (x = 0.3976, y = 0.2955) respectively.

Luminescence properties of Ca2+ and Si4+ co-doped strontium molybdate red phosphors for white LEDs

Sr0.85−xCaxMoO4:Eu0.153+ (0.15 ≤ x ≤ 0.45) and Sr0.6Ca0.25(Mo1−ySiy)O4:Eu0.153+ (0 ≤ y ≤ 0.08) red phosphors materials for white LEDs were synthesized by the high temperature solid state reaction. The properties were characterized by means of X-ray diffraction (XRD) and photoluminescence spectra. The XRD pattern shows that the Sr0.85−xCaxMoO4:Eu0.153+ and Sr0.6Ca0.25(Mo1−ySiy)O4:Eu0.153+ phosphors sintered at 800 °C for 5 h are SrMoO4 phase. And the samples are crystallized well with the scheelite structure. The luminescent properties of Sr0.85−xCax(Mo1−ySiy)O4:Eu0.153+ with various concentration of Ca2+ and Si4+ were investigated in detail. The results indicate that Sr0.85−xCaxMoO4:Eu0.153+ and Sr0.6Ca0.25(Mo1−ySiy)O4:Eu0.153+ phosphors can be excited by 394 and 464 nm lights and their light emitting properties were improved by co-doping Si4+ and Ca2+ ions. The emission spectra exhibit the most intense emission at 611 and 615 nm, and the latter is corresponding to the 5D0 → 7F2 transition of the Eu3+. Compared with Sr0.85−xCaxMoO4:Eu0.153+, the emission intensity of Sr0.6Ca0.25(Mo1−ySiy)O4:Eu0.153+ is increased obviously. It is found that appropriate Ca2+ and Si4+ concentration can enhance the luminescent intensity and improve crystallization, and the highest emission intensity on the 615 nm is exhibited when x = 0.25 and y = 0.05. Moreover, the CIE chromaticity (x, y) of Sr0.85−xCax(Mo1−ySiy)O4:Eu0.153+ excited by 394 nm light are analyzed. When the doping x of Ca2+ is 0.02 and y of Si4+ is 0.05, phosphors of the samples turn from pink to red. These results present that the Sr0.85−xCax(Mo1−ySiy)O4:Eu0.153+ is an efficient red emitting phosphor for white LED applications.