Effects of strontium doping on the degradation and Sr ion release behaviors of α‐tricalcium phosphate bone cement

Strontium plays important physicochemical and biological roles in the applications of bone repair materials. The available methods of Sr doping in bone cements were believed to make a key effect on the biodegradation and Sr ion release behaviors of cements. In this work, Sr‐doped octacalcium phosphate (Sr‐OCP), Sr‐doped α‐tricalcium phosphate (Sr‐α‐TCP), SrCO₃, and SrCl₂ with different actual availability of Sr²⁺ were imported into α‐TCP bone cements, and their effects on the biodegradation and ions release of cements were comparatively investigated. Incorporation of different Sr carriers had led to distinct hydration morphologies, crystal evolutions, degradation rates, and microenvironments of bone cements during their in vitro biodegradation. Compared with other Sr carriers, Sr‐OCP facilitated the hydration reaction of α‐TCP, which induced the enhanced degradation and Sr ion release behaviors. In conclusion, Sr‐OCP was supposed to be a more potential Sr carrier applied in the synthesis of biodegradable Sr‐doped calcium phosphate bone cements.     

Influence of magnesium and silver ions on rheological properties of hydroxyapatite/chitosan/calcium sulphate based bone cements

Rheology of bioceramic bone cements is usually described as properties of ceramic slurries, neglecting the self-setting character of these materials. In our studies calcium sulphate based bone cements with Ag⁺, Mg²⁺ and Mg²⁺/CO₃^2- modified hydroxyapatite were investigated. Despite of expectations, it has been proven that the presence of magnesium ions significantly influence the rheological properties of cement pastes. Changes in rheological properties were connected with (I) chemical interactions between Mg²⁺ and sulphate ions (II) chemical interaction between Mg²⁺ and chitosan. These effects were not observed for silver additive. Most of the developed calcium sulphate based pastes, except material containing MgHA and chitosan, have been categorized as thick pastes applicable with the spatula. It has been found that the chitosan present around and at the calcium sulphate grains acted as a lubricant and prolong the period of quasi-constant viscosity of the pastes.     

Drug and ion releasing tetracalcium phosphate based dual action cement for regenerative treatment of infected bone defects

Calcium phosphate cements (CPCs) are ideally suited for the local delivery of antibiotics in infected bone defects as they have multiple binding sites for loading various drugs. CPCs can also be substituted with ions such as Ag⁺, Zn²⁺, Mg²⁺, Sr²⁺, etc., to exhibit extended broad-spectrum antimicrobial activity. Strontium (Sr) in particular is known to enhance the new bone formation and decrease bone resorption. The current work aims to develop a dual action tetracalcium phosphate (TTCP) based cement which releases both the Sr²⁺ ion and ornidazole antibiotic drug for the treatment of bone infections. The TTCP with Sr²⁺ ion substitution was prepared by the solid state reaction method and it was used to form ornidazole loaded CPC. The ornidazole loaded cement prepared using 8?at% Sr substituted TTCP (8SCPC-O) showed complete hydroxyapatite (HA) formation in phosphate buffered solution at the end of 1 week. Fine needle-shaped HA crystals were observed in 8SCPC-O cement. In vitro drug release studies showed an accelerated ornidazole release from the 8SCPC-O sample when compared to samples without Sr substitution. Ornidazole releasing cements were found to be biocompatible with skeletal myoblast (L6) cells. Antibacterial activity of ornidazole releasing cement was evident from day 1 onwards against E. coli. The above results suggest 8SCPC-O as a good candidate for treating local bone infections.     

Mg2+, Sr2+, Ag+, and Cu2+ co-doped β-tricalcium phosphate: Improved thermal stability and mechanical and biological properties

β-tricalcium phosphate (β-TCP, β-Ca₃(PO₄)₂) is an attractive biomaterial for bone repair applications. However, its sintering and mechanical properties are limited by a problematic phase transition to α-TCP. Cationic doping of β-TCP is able to postpone the formation of α-TCP allowing higher sintering temperatures and better mechanical properties. The co-doping of β-TCP with Mg²⁺ and Sr²⁺ has already been studied in detail, but the addition of antibacterial cations (Ag⁺ and Cu²⁺) on the Mg–Sr β-TCP co-doped composition remains unexplored. Thus, two co-doped β-TCP compositions were realized by aqueous precipitation technique without any secondary phase and compared with undoped β-TCP: Mg–Sr (2.0–2.0 mol%) and Mg–Sr–Ag–Cu (2.0–2.0–0.1–0.1 mol%). Differential thermal analysis and dilatometry analyses showed a slight decrease of the β-TCP → α-TCP phase transition temperature for the Mg–Sr–Ag–Cu (2.0–2.0–0.1–0.1% mol) composition as compared to the Mg–Sr (2.0–2.0 mol%). However, both exhibited much higher transition temperatures than undoped β-TCP. The addition of Ag⁺ and Cu²⁺ slightly reduces the grain size after sintering compared to the Mg–Sr (2.0–2.0 mol%) and the undoped compositions. The co-doped compositions also exhibited improved mechanical properties, specifically a higher Vickers hardness and elastic modulus. Finally, cell proliferation assays showed that the presence of dopants, even Ag⁺ and Cu²⁺, does not affect the survival and proliferation of cells. Thus, the use of Mg²⁺, Sr²⁺, Ag⁺, and Cu²⁺ co-doped β-TCP could be very promising for biomedical applications due to the improvements of these dopants on the thermal stability and mechanical and biological properties.     

Chloride‐Ion‐Stabilized Strontium Mayenite: Expansion of Versatile Material Family

Sr‐mayenite (S₁₂A₇) incorporating Cl^? ions in its crystallographic cages up to the theoretical maximum occupancy, Sr₁₂Al₁₄O₃₂Cl₂, is reported in our study. The addition of a stoichiometric amount of SrCl₂ to the starting mixture is effective for the formation of Sr₁₂Al₁₄O₃₂Cl₂ with high phase purity. Almost 100% densification is achieved using spark plasma sintering (SPS). Evaporation of SrCl₂ from Sr₁₂Al₁₄O₃₂Cl₂, which becomes significant at sintering temperatures above ~1300°C, degrades the phase purity. However, SrCl₂ effusion is significantly suppressed in the samples fully densified by SPS, impeding the decomposition of Sr₁₂Al₁₄O₃₂Cl₂ up to temperature as high as ~1400°C. The crystal structure of Sr₁₂Al₁₄O₃₂Cl₂ was investigated by Rietveld analysis of the X‐ray diffraction pattern. It is found that the Cl^? ion is incorporated in the center of the inner cage with nearly theoretical maximum occupancy, which is responsible for the phase stability. Porous Sr₁₂Al₁₄O₃₂Cl₂ exhibits humidity‐sensitive surface protonic conductivity. Dense Sr₁₂Al₁₄O₃₂Cl₂ prepared under reducing conditions such as SPS exhibits electronic conductivity. Sr‐mayenite has various potential applications derived from its multifunctionalities.     

Effect of codoping Ce3+ on the luminescence properties of Sr9Mg1.5(PO4)7:Eu2+ orange–yellow phosphor

Sr₉Mg_1.5(PO₄)₇:Eu²⁺ has recently been reported as a promising blue light-excited orange–yellow phosphor that can be used in white LED device. Here, Ce³⁺-codoping is found to be an effective strategy to improve the luminescence performance of Sr₉Mg_1.5(PO₄)₇:Eu²⁺ phosphor. The coexistence of Eu²⁺ and Eu³⁺ ions has been verified via photoluminescence spectral analysis. The reduction of Eu³⁺ to Eu²⁺ in Sr₉Mg_1.5(PO₄)₇ lattice cannot be completed in a reducing atmosphere, but can be promoted through codoping with Ce³⁺ ions to a great extent, which finally increase the effective concentration of Eu²⁺ in the crystal lattice. The Eu³⁺−Eu²⁺ reduction mechanism is analyzed using a charge compensation model. This work not only achieves enhanced luminescence of the Sr₉Mg_1.5(PO₄)₇:Eu²⁺ phosphor by codoping with Ce³⁺ ions, but also provides new insights into the design of Ce³⁺/Eu²⁺ codoped luminescent materials.     

Synthesis and characterisation of nanophase hydroxyapatite co-substituted with strontium and zinc

In order to develop new bioactive calcium phosphate (CaP) materials to repair bone defects, it is important to ensure these materials more closely mimic the non-stoichiometric nature of biological hydroxyapatite (HA). Typically, biological HA combines various CaP phases with different impurity ions, which substitute within the HA lattice, including strontium (Sr²⁺), zinc (Zn²⁺), magnesium (Mg²⁺), carbonate (CO₃^2-) and fluoride (F^-), but to name a few. In addition to this biological HA have dimensions in the nanometre (nm) range, usually 60?nm in length by 5–20?nm wide. Both the effects of ion substitution and the nano-size crystals are seen as important factors for enhancing their potential biofunctionality. The driving hypothesis was to successfully synthesise nanoscale hydroxyapatite (nHA), co-substituted with strontium (Sr²⁺) and zinc (Zn²⁺) ions in varying concentrations using an aqueous precipitation method and to understand their chemical and physical properties. The materials were characterised using Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM) techniques. The FTIR, XRD and XPS results confirmed that the nHA was successfully co-substituted with Sr²⁺ and Zn²⁺, replacing Ca²⁺ within the nHA lattice at varying concentrations. The FTIR results confirmed that all of the samples were carbonated, with a significant loss of hydroxylation as a consequence of the incorporation of Sr²⁺ and Zn²⁺ into the nHA lattice. The TEM results showed that each sample produced was nano-sized, with the Sr/Zn-10%nHA having the smallest sized crystals approximately 17.6 ± 3.3?nm long and 10.2 ± 1.4?nm wide. None of the materials synthesised here in this study contained any other impurity CaP phases. Therefore, this study has shown that co-substituted nHA can be prepared, and that the degree of substitution (and the substituting ion) can have a profound effect on the attendant materials’ properties.     

Study on the new bone cement based on calcium sulfate and Mg,CO3 doped hydroxyapatite

In order to improve some features of bone substitutes the new self-setting composite-type implant material based on Mg²⁺/CO₃^2? co-substituted hydroxyapatite (Mg-CHA) and calcium sulfate hemihydrate (CSH) was developed. Synthetic hydroxyapatites doped with small amounts of additives found in natural bone (e.g. Mg²⁺ and CO₃^2?) are regarded as promising components of calcium phosphate bone cements (CPCs). The CPCs, now available on the market, due to low resorption rate are too stable to permit material degradation and are slowly replaced by the newly formed bone. To improve cement resorption we used calcium sulfate which is a well-known biodegradable and biocompatible bone defect filler. Combining properties of Mg-CHA and CSH allowed developing a new, promising, easy shapeable implant material with high potential for bone regeneration.     

Adsorption Kinetics and Equilibria of Strontium onto Kaolinite

Adsorption of Sr²⁺ onto kaolinite has been studied by means of a radiotracer technique using the ⁹⁰Sr isotope. Bangham’s and McKay models have been applied to kinetic results in Sr²⁺ concentrations between trace ?0.1 mol.L^?1. The magnitudes of film and intra-particle diffusion coefficients are 10?10 and 10?14 m²·s^?1, respectively. Concentration dependence of diffusion coefficients indicated that Sr²⁺ ions are adsorbed on two different adsorption sites by an exothermic and spontaneous process. The Freundlich isotherm parameters and exchange equilibrium constants derived from selectivity coefficients indicate that Sr adsorption are depressed by competing cations in the order of Na⁺< Mg²⁺< Al³⁺.     

Influence of Sr2+ on Calcium‐Deficient Hydroxyapatite Formation Kinetics and Morphology in Partially Amorphized α‐TCP

Hydration of partially amorphized α‐TCP powders with Sr²⁺ concentrations ranging from 0 to 10 mol% substitution for Ca²⁺ was analyzed by isothermal calorimetry and quantitative in‐situ XRD. Hydration of both crystalline α‐TCP and amorphous TCP (ATCP) forming CDHA was retarded to an increasing extent with increasing Sr²⁺ content. Sr²⁺ slightly reduced the crystallite size (XRD coherent scattering domains) of the CDHA formed during hydration, while the size of crystals visible under SEM was not noticeably affected. Reaction enthalpies of ΔH_{R(Sr‐α‐TCP→Sr‐CDHA)} = 122 ± 8 J/g_TCP and ΔH_{R(Sr‐ATCP→Sr‐CDHA)} = 257 ± 8 J/g_TCP were determined for the hydration of crystalline α‐TCP and ATCP containing 5 mol% Sr²⁺ substitution for Ca²⁺. This is comparable with the corresponding reaction enthalpies previously obtained for undoped samples, which are 106 ± 7 J/g_TCP for α‐TCP and 250 ± 7 J/g_TCP for ATCP.     

Adsorption from aqueous solution by δ-manganese dioxide I. Adsorption of the alkaline-earth cations

The adsorption isotherms of M²⁺ ions (M = Mg, Ca, Sr or Ba) were determined at pH 7.0 and at different temperatures. The adsorbent, δ-MnO₂, was converted to the K⁺ form prior to adsorption and about 1.5 mol K⁺ ions were released per mol of M²⁺ ions adsorbed. The adsorption capacity at a given temperature increased in the series: Mg²⁺ < Ca²⁺ ≦ Sr²⁺ < Ba²⁺. This was explained by an ion exchange mechanism between hydrated ions: K⁺ ions in the outer Helmholtz layer and M²⁺ ions in the bulk of the solution. The radii of the hydrated ions decreased in the series: Mg²⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺. The adsorption of M²⁺ ions at pH values below the point of zero charge (pH 3.3) was significant for Mg²⁺ ions only. Although adsorption was not strictly reversible, the results fitted the Langmuir isotherm and ‘apparent heats of adsorption’, Q, were calculated. The endothermic heats (Q = 20,18, 11 and 5 kJ mol^?1 for Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ adsorption respectively) indicated positive entropy contributions which are expected for the adsorption mechanism suggested. The decrease in Q down the alkaline-earth group was correlated to the entropy effects and to the hydration numbers of the cations.     

Broadband emission phosphor Sr3Al2O5Cl2:Bi3+: Luminescence modulation and application for a white-light-emitting diode

Bi³⁺ ions can regulate and control the fluorescence of a phosphor by transferring energy to the activating agent or occupying different luminescent centers, which is important for modifying phosphors and revealing fluorescence mechanisms. As a base material, Sr₃Al₂O₅Cl₂ has three types of Sr sites (Sr 1, Sr 2, and Sr 3) that may be occupied by Bi³⁺ ions (Sr²⁺ has a similar radius to Bi³⁺). Herein, we successfully synthesized a series of Sr₃Al₂O₅Cl₂:x%Bi³⁺ phosphors using the high-temperature solid-state method and determined a two-site-occupying emission mechanism. X-ray diffraction patterns indicated that the samples were synthesized well, and Rietveld refinement results provided their structural information. Photoluminescence spectra showed 490 nm (λ_ex = 345 nm) and 556 nm (λ_ex = 376 nm) emission peaks, which might arise from different luminescent centers. The concentration quenching study, peak separation analysis, fluorescence lifetime spectra, and diffuse reflection spectra indicated that the Bi³⁺ ions occupied two of the three Sr sites. Calculations of relative system energies and distortion index proved that the occupation only occurred in the Sr 1 and Sr 3 sites, and crystal splitting analysis determined that Sr 1 site generated 490 nm emission light and Sr 3 site generated 556 nm emission light. The charge compensator and flux were added to enhance the fluorescence intensity of the phosphor, and 5% K⁺ along with 1% BaF₂ is the optimal dosage. Finally, the SrAlSiN₃:Eu²⁺, BaMgAl₁₀O₁₇:Eu²⁺, and optimized Sr₃Al₂O₅Cl₂:5%Bi³⁺ phosphors were combined as a luminous layer and a warm-white light-emitting diode was realized; the color rendering indices were 84.3, 85.8, 86.4, and 86.2 under working currents of 20, 30, 40, and 50 mA, respectively.     

Effect of divalent cation addition on structure,conductivity and grain boundary properties in La doped ceria oxygen ion conductors

The aim of this work is to investigate the effect of divalent cations on the structure and electrical properties of Ce_0.85La_0.1D_0.05O_2-δ (D = Ca, Sr and Ba) oxygen ion conductors. The X-Ray structural analysis confirms the presence of CeDO₃ minor phase in addition to cubic fluorite phase of ceria in Sr²⁺ and Ba²⁺ added compositions. The lattice parameter of the compositions significantly depends on the ionic radius of dopants and the presence of D²⁺ ions in ceria lattice. The Ca²⁺ added composition shows the highest free oxygen vacancy concentration due to its lowest association energy and complete dissolution of Ca²⁺ ions into ceria lattice. The dopant-vacancy association energy and grain interior conductivity changes with the ionic radii of the divalent dopants. The grain boundary capacitance depends on dielectric constant, grain size and grain boundary thickness. The grain boundary conductivity shows 46% over total conductivity for Sr²⁺ added composition. The presence of CeDO₃ phase and space charge layer promotes the grain boundary resistances and affects the ion dynamics. Schematic models are proposed to understand the ion migration in grain boundaries. The scavenging effect is found to be highest in Sr²⁺ ions added composition. The defect structures, the presence of CeDO3 phase and electrical properties are correlated with each other.     

Partial cation substitution of tunable blue-cyan-emitting Ba2B2O5:Ce3+ for near-UV white LEDs

In this study, Sr²⁺, Ca²⁺, Zn²⁺, and Mg²⁺ ions act to tune the emission band to the blue-cyan region in Ba_xSr_yB₂O₅:Ce³⁺ (BSBO), Ba_xCa_zB₂O₅:Ce³⁺ (BCBO), Ba_xZn_uB₂O₅:Ce³⁺ (BZBO), and Ba_xMg_vB₂O₅:Ce³⁺ (BMBO) phosphors. A red shift occurs with the increase of Sr²⁺, Ca²⁺, Zn²⁺, and Mg²⁺ concentration, and a blue shift occurs when the concentrations of Sr²⁺, Ca²⁺, Zn²⁺, and Mg²⁺ exceed the critical value. The emission color can be tuned from deep blue (0.15, 0.12) to cyan (0.16, 0.27) upon 365 nm UV lamp excitation due to the crystal field splitting and centroid shifts. The excitation band shift to long wavelength by introducing ions, so that the synthesized phosphor can be better matched with the n-UV chip. The emission intensity slowly decreases with the temperature increasing. Therefore, the BMBO:Ce³⁺, BZBO:Ce³⁺, BCBO:Ce³⁺, and BSBO:Ce³⁺ phosphors with relatively good thermal stability were synthesized, which could have potential applications in the n-UV white LEDs.     

Optical Energy Storage Properties of (Ca1−xSrx)2Si5N8: Eu2+, Tm3+ Solid Solutions

While the reddish‐orange emitting phosphors M₂Si₅N₈:Eu²⁺(M = Ca, Sr) have been intensively investigated as potential materials for white‐light‐emitting diodes, in this study, optical energy storage properties of (Ca_1?xSr_x)₂Si₅N₈: Eu²⁺, Tm³⁺ (x = 0–1) solid solutions were tuned by cation substitution, which was commonly used to tune color point for improving w‐LEDs. Partial substitution of either Ca by Sr or Sr by Ca resulted in a redshifted Eu²⁺ emission which had a demarcation point at x = 0.5. Furthermore, the (Ca_1?xSr_x)₂Si₅N₈: Eu²⁺, Tm³⁺ materials exhibited similar persistent‐ and photostimulated luminescence behaviors with a maximum intensity at about x = 0.2. Such optical energy storage characters of the samples were attributed to the more appropriate trap depths (322–333 K) and higher density of energy level traps indicated by the thermoluminescence analysis.     

Light‐induced electrons suppressed by Eu3+ ions doped in Ca11.94−xSrxAl14O33 caged phosphors for LED and FEDs

Control of light‐induced electron generation is of vital importance for the application of caged phosphors. For Eu‐doped Ca_11.94?xSr_xAl₁₄O₃₃ caged phosphors, the suppressed effect of strontium doping on the light‐induced electrons is observed compared to the europium‐free Ca_11.94?xSr_xAl₁₄O₃₃ phosphors. In the presence of europium ions, Sr doping will promote the reduction of Eu³⁺ to Eu²⁺. The Rietveld refinement suggests that unit cell volumes of the Ca_11.94?xSr_xAl₁₄O₃₃:Eu_0.06 samples are expanded when Ca²⁺ ions are replaced by Sr²⁺ ions. The absorption and FTIR transmittance spectra confirm that the competitive reaction of encaged O^2? anions with H₂ is suppressed. For the sample (x=0.48), the higher thermal activation energy (~0.40 eV) for luminescence quenching can be attributed to the more rigid framework structure after Sr doping. For Ca_11.94?xSr_xAl₁₄O₃₃:Eu_0.06 phosphors, their emission colours are tuned from red to purple upon 254 nm excitation and from pink to blue under electron beam excitation through Sr substitution. The insight gained from this work may have a significant guiding to design new phosphors for LED and FEDs and novel nanocaged mutifunctional materials.     

Luminescence properties of Eu2+ and Mn2+ doped Sr1.7Mg0.3SiO4 phosphors

Eu²⁺, Mn²⁺ doped Sr_1.7Mg_0.3SiO₄ phosphors were prepared by high temperature solid-state reaction method. Their luminescence properties were studied. The emission spectra of Eu²⁺ singly doped Sr_1.7Mg_0.3SiO₄ consist of a blue band (455 nm) and a green band (550 nm). The relative intensities of two emissions varied with Eu²⁺ concentration. Eu²⁺ and Mn²⁺ co-doped Sr_1.7Mg_0.3SiO₄ phosphors emit three color lights and present whitish color. The blue (455 nm) and green (550 nm) emissions are attributed to the transitions of Eu²⁺, while the red (670 nm) emission is originated from the transition of Mn²⁺ ion. The results indicate the energy transfer from Eu²⁺ to Mn²⁺. The mechanism of the energy transfer is resonance-type energy transfer due to the spectral overlap between the emission of Eu²⁺and the absorption of Mn²⁺.     

Microwave hydrothermal synthesis of Sr doped ZnO crystallites with enhanced photocatalytic properties

Pure and Sr²⁺ doped ZnO crystallites were successfully synthesized via a microwave hydrothermal method using Zn(NO₃)₂·6H₂O and Sr(NO₃)₂·6H₂O as source materials. The phase and microstructure of the as-prepared Zn_1−xSr_xO crystallites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Ultraviolet–visible spectrum (UV–vis) and photochemical reaction instrument were used to analyze the photocatalytic properties of the particles. XRD results show that the diffraction peaks of the as-prepared Zn_1−xSr_xO crystallites shifted slightly toward lower 2θ angle with the increasing of Sr²⁺ doping concentration from 0% to 0.3%. The pure ZnO crystallites with lamellar structure are found transforming to a hexagonal columnar morphology with the increase of Sr²⁺ doping concentration. UV–vis analysis shows that the particles have a higher absorption in UV region with a slightly decreased of optical band (E_g) gap. The photocatalytic activity of Sr²⁺ doped ZnO crystallites was evaluated by the Rhodamine B (RhB) degradation in aqueous solution under visible-light irradiation. Compared with the pure ZnO particles, the photocatalytic properties of the Sr²⁺ doped ZnO crystallites are obviously improved. The photocatalysis experiment results demonstrate that the 0.1% Sr²⁺ doped ZnO exhibits the best photocatalytic activity for the degradation of Rhodamine B.     

Effects of Sr doping on the structure,magnetic properties and microwave absorption properties of LaFeO3 nanoparticles

Lightweight, broadband microwave absorbing materials, with strong absorption capacities, are an urgent demand for practical applications. The microstructural and microwave absorption properties of LaFeO₃ samples prepared by a sol-gel method using different amounts of Sr are investigated systematically. X-ray diffraction and Rietveld refinement studies showed that Sr²⁺ doping can distort the crystal structure of LaFeO₃, leading to lattice expansion and spin tilt of the Fe-O-Fe bond angle. The improvement of magnetic properties mainly originates from the synergistic effect of the bond angle spin tilt and crystal structure defects. Oxygen vacancies will be generated due to the fluctuations in the valence state of Fe³⁺ resulting from the substitution of La³⁺ by Sr²⁺ as deduced from the X-ray photoelectron spectroscopy analysis. The generation of oxygen vacancies, electronic hopping and polarization loss may be one of the main reasons for changes in the electromagnetic parameters. The minimum reflection loss (RL) of La_1–xSr_xFeO₃ nanoparticles with the Sr doping of 0.2 can reach approximately -39.3 dB at 10 GHz for the thickness of 2.2 mm, and the effective absorption bandwidth (RL ≤ -10 dB) can reach approximately 2.56 GHz. In addition, the La_1–xSr_xFeO₃ nanoparticles also can obtain better microwave absorbing performance in the C-band (4–8 GHz) with the minimum RL of -36.8 dB for the matching thickness of 3.0 mm and Sr content of 0.3. Consequently, La_1–xSr_xFeO₃ nanoparticles are promising materials for use in a high-performance and adjustable electromagnetic wave absorber, particularly in C-band and X-band.     

Structural,optical, electrical and dielectric properties of (Sr1-xMgx)(Sn0.5Ti0.5)O3 (X=0.00, 0.25, 0.50, 0.75) ceramics via solid state route

We have prepared (Sr_1-xMg_x)(Sn_0.5Ti_0.5)O₃, (X = 0.00, 0.25, 0.50, 0.75) samples by the solid state reaction method and studied the structural, optical, electrical modulus and the other dielectric properties of the samples with respect to variation in frequencies (1 × 10⁹ to 2 × 10⁹ Hz) using Impedance Analyzer. This study suggests that the XRD patterns of the samples have shown that this possesses cubic perovskite structure in space group Pm-3m and scanning electron microscope was used to analyze the grain size distribution and porosity of the ceramic. The dielectric properties of these materials were strongly dependent upon on concentration X as well as amount of frequencies. The existence of metal oxygen bonds of Sr–Ti–O was verified by Fourier Transform Infra Red (FTIR) spectrum at 540 cm⁻¹. The highest PL intensity of 716.38 that exhibits the green emission (508.5 nm) was obtained for the composition of (Sr_0.25Mg_0.75)(Sn_0.5Ti_0.5)O₃. AC conductivity slowly decreases with increasing Mg substitution and also the sample (Sr_0.25Mg_0.75)(Sn_0.5Ti_0.5)O₃ having the lowest (constant) value of conductivity at 1 GHz–2GHz.