Sr-doped Samples Research Articles

Synthesis and characterization of hierarchical Sr-doped ZnO hexagonal nanodisks as an efficient photocatalyst for the degradation of methylene blue dye under sunlight irradiation

This study presents the synthesis and comprehensive characterization of hierarchical hexagonal nanodisks of zinc oxide (ZnO) and strontium (Sr) doped ZnO, prepared via a hydrothermal method. The experimental synthesis procedure involved dissolving zinc nitrate in a water–ethanol mixture, followed by the addition of polyethylene glycol (PEG 200), sonication, and subsequent hydrothermal treatment. Different concentrations of Sr were introduced into the ZnO lattice to generate Sr-doped ZnO samples. Analysis of the obtained results revealed successful incorporation of Sr, evidenced by shifts in the X-ray diffraction (XRD) pattern and alterations in lattice parameters. Moreover, the Williamson-Hall plot indicated minimal strain and high structural stability in both pristine ZnO and Sr-doped ZnO. The morphology of the synthesized Sr-doped ZnO was confirmed through field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), revealing a hexagonal nano disk-shaped morphology akin to pristine ZnO. Elemental composition analysis conducted via X-ray photoelectron spectroscopy (XPS) further confirmed the presence of Sr in the doped ZnO samples. Evaluation of photocatalytic activity against methylene blue dye demonstrated superior performance of the 5 % Sr-doped ZnO catalyst, attributed to its increased surface area compared to pristine ZnO. Notably, the highest degradation rate constant (k) of 0.0389 min−1 was observed for the 5 % Sr-doped ZnO catalyst, emphasizing its efficacy in environmental remediation applications. This research underscores the potential of Sr-doped ZnO as a promising photocatalyst, offering stability, reusability, and effective utilization of UV and visible light for catalytic processes.

Tailoring optical and dielectric properties of TiO2 through mono- and co-doping with Ag and Sr

In this study, we applied a direct and incipient wetness impregnation technique to synthesize titanium dioxide (TiO2) doped with silver (Ag), strontium (Sr), and a combination of the two elements. The purpose was to further our understanding of doped TiO2 materials. The results of scanning electron microscopy (SEM) analysis showed that the agglomerated particles of the doped composites had smaller sizes than those of pure TiO2. The incorporation of Ag–Sr bimetallic doping led to a more pronounced reduction in the particle size. The SEM images revealed no significant morphological alterations in the TiO2, Ag/TiO2, Sr/TiO2, and Ag–Sr/TiO2 composites. We also examined the dielectric characteristics of composites within a range of temperature of 25 °C–120 °C and a range of frequency of 100 Hz to 0.3 MHz. The electrical conductivity and dielectric permittivity of TiO2 were enhanced as a result of doping. The optical characteristics of the composites indicated that the introduction of Ag, Sr, and Ag–Sr into TiO2 led to an increase in both their refractive index and Urbach energy. This led in turn to a progressive reduction in the energy band gap (Eg) from the Ag-doped samples to the Ag–Sr-doped samples, with the Sr-doped samples exhibiting an intermediate reduction in Eg. The findings of this study indicate that the introduction of Ag, Sr, and Ag–Sr into TiO2 enhanced its refractive index. Notably, the Ag–Sr/TiO2 composite exhibited the most significant increase in the refractive index of all the composites considered. This phenomenon can be attributed to the increased level of polarization and crystallinity of the compound. By contrast, the incorporation of Ag, Sr, and Ag–Sr into composite materials composed of TiO2 led to a reduction in the values of Eg, where this renders these materials suitable for various optical applications.

A comparative study of structural, magnetic and catalytic properties of half doped nanocrystalline La0.5A0.5Mn0.5Fe0.5O3 (A = Ca, Sr) perovskite oxides: Highly efficient and versatile candidates for enhanced oxidative degradation of hazardous organic dyes at ambient conditions

This work presents a systematic study of half doped nanocrystalline La0.5A0.5Mn0.5Fe0.5O3 (A = Ca, Sr) perovskite oxides to examine the effect of A-site cation radius on structural, magnetic and catalytic properties via different characterization techniques. Rietveld refinements of powder X-ray diffraction data confirmed the orthorhombic symmetry for both the samples with Pbnm space group. The results show an increase in lattice parameters and unit cell volume with doping of larger A cation. The BET surface area for Ca and Sr-doped samples has been found to be 32.3 m2/g and 33.8 m2/g respectively. The magnetic properties of nano structured samples show magnetic inhomogeneity due to coexistence of ferromagnetic and antiferromagnetic interactions. The magnetization has enhanced in Sr-doped sample which may be associated with increase in double exchange interactions between mixed valence manganese ions through oxygen. Moreover, the synthesized nano samples have been employed to catalytic degradation of rhodamine B dye as model pollutant under normal atmospheric conditions and it has been found that Sr-doped sample has shown better catalytic dye degradation than Ca-doped (99% degradation in 25 min) due to the presence of greater number of Mn3+/Mn4+ redox couples as determined by iodometric titration. Additionally, methylene blue and methyl orange dyes were also tested for catalytic degradation by more active Sr-doped catalyst in order to check its versability.

The structural, biological and dielectric properties of Sr, Mg and Zn doped silicate ceramics

The current work examines the structural and biological characteristics of doped Zn, Mg, and Sr. Na2O–CaO–Si2O–P2O5 silicate ceramics synthesized by the solid state method. The undoped sample showed amorphous behavior after sintering at the 800 OC while doping of SrO, MgO and ZnO induce crystal growth; and a single phase of Parawollastonite (JCPDS# 00-043-1460) was identified in both doped samples. The strontium doped sample showed the highest value of the dielectric as compared to other three samples. The Sr doped sample had higher dielectric value because the size of Sr2+ is greater than Ca+2 so it will possess the higher polarizing power. Conductivity of Zn and Sr doped samples increased with increase in frequency and Mg doped decrease with increase in frequency. Bioactivity test confirmed that doped samples were more bioactive as compared to undoped samples, and Sr doped sample showed superior bioactivity as compared to other samples.

Comparative studies by X-ray diffraction, Raman, vibrating sample magnetometer and Mössbauer spectroscopy of pure, Sr doped and Sr, Co co-doped BiFeO3 ceramic synthesized via tartaric acid-assisted technique

Pure BiFeO3 (BFO), Sr-doped Bi0.97Sr0.03FeO3 (BSFO) and Sr, Co co-doped Bi0.97Sr0.03Fe0.8Co0.2O3 (BSFCO) samples have been prepared via a tartaric acid-assisted sol-gel technique. Investigation of the structure, lattice dynamics, magnetization and hyperfine interaction have been performed through X–ray diffraction (XRD), transmission electron microscope (TEM), Raman spectroscopy (RS), vibrating sample magnetometer (VSM) and Mössbauer spectroscopy (MS). The TEM images show that the particle sizes <D> of BFO, BSFO and BSFCO are respectively 11.4, 12.1 and 8.8 nm. The XRD analysis reflects a structural phase transition from rhombohedral R3c structure in case of BFO and BSFO samples to two phase coexistence (rhombohedral R3c and trigonal R–3m:R) in case of BSFCO sample. This structural phase transition has been strongly confirmed by the alterations in the vibration modes observed in Raman spectra (expansion, shift, merge, and reduced intensity). Second order vibration modes, corresponding to the two-phonon scattering in the range 650–1000 cm−1, have been recorded for all samples. Investigation of magnetic properties reveals that pure and Sr doped samples possess considerably high magnetic saturations (Ms = 5.61 and 5.79 emu/g respectively). Additionally, BSFCO sample shows enhancement in Ms (Ms rises to 8.26 emu/g). Suppression of spiral spin structure caused by the small nano-size has been assumed. The destruction of the spiral spin has been also suggested through M össbauer studies. The hyperfine parameters reveal that only Fe3+ is observed in two different nonequivalent trigonal distorted octahedral environments. The outcome of this work suggests the potentiality of Sr, Co co-doping to improve the structure and ferromagnetism of BiFeO3 ceramic making it feasible to be employed in enormous applications.

The structural and magnetic features of perovskite oxides La1–xSrxMnO3+δ (x = 0.05, 0.10, 0.20) depending on the strontium doping content and heat treatment

Sr-doped (0<x < 0.2) ceramic samples of the lanthanum manganite oxides were obtained via sol-gel method to investigate the influence of doping on structural, magnetic end electronic responses, and their correlations. Synthesized samples of non-stoichiometric compositions are rhombohedral single-phase. After annealing the formation of a phase-separated system as a mixture of orthorhombic phases was found. The R-3c and PnmaI, PnmaII* and PnmaII phases have been studied using Mössbauer spectroscopy, XRD, SEM analysis and magnetic measurements. The magnetic temperature-concentration phase diagram of La1–xSrxMnO3+δ (x = 0.05, 0.10, 0.20) was obtained.The Jahn-Teller effect or the orbital order breaking, as well as the competition between Mn3+–O2—Mn4+ double- and Mn3+–O2-–Mn3+ superexchange interaction was demonstrated under the effect of cation doping compound and interstitial oxygen value (δ). The relaxation character of the Mössbauer spectra and the type of magnetization dependences revealed nanosized magnetic clusters with fluctuation of their magnetic moment in all perovskite phases. Results are interpreted in terms of matrix – clusters: regions of sample with ferromagnetic type of ordering (cluster) exist in antiferromagnetically or ferromagnetically (with different exchange parameter) ordered matrix. Exchange interaction frustrations of the cluster with the matrix can lead to relaxation behavior of the magnetic moment of the cluster. The clusters size vary from about 3.9 to 5.7 nm. All samples are characterized by the presence of particles agglometates with a typical size about 0.4–0.8 μm; for annealed samples additional non-conducting regions with 80–220 nm in size were found. It is shown that the annealing time significantly affects the production of materials with determined properties and be useful in the applied field in technological processes.

In vitro and in vivo assessment of decellularized platelet-rich fibrin-loaded strontium doped porous magnesium phosphate scaffolds in bone regeneration

The present work reports the effect of decellularized platelet-rich fibrin (dPRF) loaded strontium (Sr) doped porous magnesium phosphate (MgP) bioceramics on biocompatibility, biodegradability, and bone regeneration. Sustained release of growth factors from dPRF is a major objective here, which conformed to the availability of dPRF on the scaffold surface even after 7 days of in vitro degradation. dPRF-incorporated MgP scaffolds were implanted in the rabbit femoral bone defect and bone rejuvenation was confirmed by radiological examination, histological examination, fluorochrome labeling study, and micro-CT. μ-CT examination of the regained bone samples exhibited that invasion of mature bone in the pores of the MgP2Sr-dPRF sample was higher than the MgP2Sr which indicated better bone maturation capability of this composition. Quantifiable assessment using oxytetracycline labeling showed 73.55 ± 1.12% new osseous tissue regeneration for MgP2Sr-dPRF samples in contrast to 65.47 ± 1.16% for pure MgP2Sr samples, after 3 months of implantation. Histological analysis depicted the presence of abundant osteoblastic and osteoclastic cells in dPRF-loaded Sr-doped MgP samples as compared to other samples. Radiological studies also mimicked similar results in the MgP2Sr-dPRF group with intact periosteal lining and significant bridging callus formation. The present results indicated that dPRF-loaded Sr-doped magnesium phosphate bioceramics have good biocompatibility, bone-forming ability, and suitable biodegradability in bone regeneration.

Synthesis and optimization of green one-part geopolymer from mine tailings and slag: Calcium carbide residue and soda residue as supplementary alkali sources

• Activated tailings acted as an alkaline activator for the one-part geopolymer production. • Waste treatment by waste: Calcium carbide residue was used as a supplementary alkali source. • Waste calcium carbide residue prompted the hydration reaction and increased the sample strength. • This study provides promising guidance for the rational and cost-effective utilization of tailings. The use of mine tailings (MTs) as the precursor for producing geopolymers is an effective way to reduce their storage and mitigate their negative effects on the environment. MTs were firstly activated through hydrothermal pretreatment in the presence of NaOH at 200 °C. Then one-part geopolymer (OPG) samples were synthesized from activated MTs and slag, and calcium carbide residue (CCR) and soda residue (SR), the solid industry wastes, were added as supplementary alkali sources to improve the strength of OPG samples. The effects of alkali sources on the setting time, fluidity, compressive strength, pH, hydration kinetics, hydration products, and microstructure of OPG samples were investigated. Both alkali sources shortened the setting time, decreased the fluidity, and increased the strength of OPG samples, and the CCR showed a more significant effect on these properties than SR. These clear differences in sample performances were associated with the pronounced mineralogical differences between SR and CCR. Compared to SR, CCR rich in Ca(OH) 2 produced a higher pH of the pore solution, which significantly promoted the slag dissolution, shortened the induction period, and accelerated the hydration process. Calcium–sodium aluminosilicate hydrate (C(N)-A S H) gel was the dominant reactant in all samples that enhanced the strength of OPG samples. More geopolymer gel was generated in CCR-doped samples and thus a much higher strength than SR-doped samples. However, the incorporation of excessive alkali sources induced the high carbonization degree of samples, and it was likely responsible for the reduction in strength.

High-performance visible-light active Sr-doped porous LaFeO3 semiconductor prepared via sol–gel method

ABSTRACT In this work, we have successfully fabricated Sr-doped porous LaFeO3 samples via sol–gel method. The results reveal that Sr2+ cation is effectively doped into LaFeO3 crystal lattice substituting La3+ cation. The visible light catalytic performance of the materials was evaluated by the degradation of 2,4-dichlorophenol (2,4-DCP) and Rhodamine B (RhB). The amount-optimized Sr-doped porous LaFeO3 sample exhibited outstanding visible-light catalytic performance for the degradation of the model pollutants compared to the porous LaFeO3 alone. The enhanced performance was accredited to the enlarged surface area, absorption extension via the surface states of the introduced Sr2+ below the conduction band bottom of LaFeO3, and promoted charge carrier’s separation as confirmed by various experiments. Experiments of radical trapping reveal that •OH species are dominant intermediate oxidants involved in the oxidation of 2,4-DCP and RhB over the optimized sample. This research will provide new routes for environmental remediation based on the LaFeO3 semiconductor.

Enhanced cyclic redox reactivity of hematite via Sr doping in chemical looping combustion

Aiming at the problems of low redox activity and easy sintering deactivation of hematite, Sr was used to modify hematite in chemical looping combustion (CLC). The results showed that a low concentration (1 wt%) of Sr dopant could significantly improve the redox activity and cyclic stability of hematite. During the successive redox cycles, the surface sintering was not occurred for the Sr-doped hematite samples, indicating that Sr could significantly intensify the sintering resistance of hematite in CLC. In the first redox cycle, the oxygen carrying capacity of the Sr-doped hematite samples followed the sequence: 10Sr-HM (3.32%) > 5Sr-HM (3.20%) > 1Sr-HM (2.11%). By comparing the redox performance of hematite samples doped with different SrO content, 5 wt% is the best addition ratio of SrO dopant. The results of successive 50 cycles indicated that the hematite sample doped with 5 wt% SrO exhibited very high cyclic stability. For the 5Sr-HM, the CH4 conversion and CO2 selectivity was about 90% and 100%, respectively. In addition, the effect of calcination temperature (950 °C, 1050 °C, 1150 °C) on the redox performance of Sr-doped hematite was also considered. The results indicated that the Sr-doped hematite presented high redox activity after high temperature calcination.

Structural Evolution-Enabled BiFeO3 modulated by strontium doping with enhanced magnetic and photoelectric performance

Ion doping is one of promising methods for enhancing the versatility of bismuth ferrite, BiFeO3. In this work, a structural phase transition of Bi1-xSrxFeO3 (0 < x < 1) nanoparticles (NPs) from rhombohedral to cubic occurs when the doping amount of strontium (Sr) reaches x = 0.25, which leads to a magnetic transformation from antiferromagnetic to ferromagnetic in Bi0.75Sr0.25FeO3 and Bi0.65Sr0.35FeO3. Comparing all the Sr-doped samples, the saturation magnetization and the residual magnetization of Bi0.75Sr0.25FeO3 are increased by approximately one order of magnitude, reaching the maximum of 1.859 emu/g and 0.046 emu/g, respectively. Meanwhile, an unanticipated 3 to 4-times higher photo-conductivity is found in Bi0.75Sr0.25FeO3, which is attributed to the band-gap reduction induced by phase transition and the increase in density of unoccupied oxygen vacancies. This work is beneficial for the study of the tuneable ferromagnetic properties of BiFeO3 at room temperature and opens up one new way to improve the electrical and electrochemical properties.

High proportion strontium-doped micro-arc oxidation coatings enhance early osseointegration of titanium in osteoporosis by anti-oxidative stress pathway

The excessive accumulation of reactive oxygen species (ROS) under osteoporosis precipitates a microenvironment with high levels of oxidative stress (OS). This could significantly interfere with the bioactivity of conventional titanium implants, impeding their early osseointegration with bone. We have prepared a series of strontium (Sr)-doped titanium implants via micro-arc oxidation (MAO) to verify their efficacy and differences in osteoinduction capabilities under normal and osteoporotic (high OS levels) conditions. Apart from the chemical composition, all groups exhibited similar physicochemical properties (morphology, roughness, crystal structure, and wettability). Among the groups, the low Sr group (Sr25%) was more conducive to osteogenesis under normal conditions. In contrast, by increasing the catalase (CAT)/superoxide dismutase (SOD) activity and decreasing ROS levels, the high Sr-doped samples (Sr75% and Sr100%) were superior to Sr25% in inducing osteogenic differentiation of MC3T3-E1 cells and the M2 phenotype polarization of RAW264.7 cells, thus enhancing early osseointegration. Furthermore, the results of both in vitro cell co-culture and in vivo studies also showed that the high Sr-doped samples (especially Sr100%) had positive effects on osteoimmunomodulation under the OS microenvironment. Ultimately, the collated findings indicated that the high proportion Sr-doped MAO coatings were more favorable for osteoporosis patients in implant restorations.

Study of Carrier Transfer Mechanism When Substituting Strontium at Barium Sites in CuTl-1223 Superconducting Phase

Strontium-doped CuTl-1223 phase has been obtained by employing a nonstoichiometric composition of the form Tl1/2Cu1/2(Ba1−xSrx)Ca1Cu4Oy (x = 0, 0.1, 0.2, 0.3). The superconducting properties of the samples were investigated by x-ray diffraction analysis and four-probe resistivity, alternating-current (AC) susceptibility, and Fourier-transform infrared (FTIR) absorption measurements. The effect of doping strontium atoms on the intrinsic superconductor parameters of these samples was studied by excess conductivity analysis. All the samples showed orthorhombic crystal structure in space group Pmmm, and the cell parameters were determined by using all the planar reflections. The c-axis length and the unit cell volume decreased with Sr doping in the final compound. Suppression of the room-temperature resistivity followed by metallic variations in resistivity versus temperature measurements are typical features for these samples. The zero-resistivity critical temperature and the onset of diamagnetism were suppressed with increasing Sr doping in the final compound. The apical oxygen phonon mode of type Cu(1)–OA–Cu(2) observed at around 548 cm−1 hardened with increasing Sr doping. The excess conductivity analysis revealed that the coherence length along the c-axis, the interlayer coupling, and the Fermi velocity of the carriers increased for the Sr doping levels of x = 0.1 and 0.2 but decreased for the sample with x = 0.3. The values of Bc0(T), Bc1(T), and Jc0(0) increased with increasing Sr doping in the final compound. It is proposed that this effect arises due to an increase in the superconducting volume fraction. A decrease in the value of the London penetration depth λp.d. and the Ginzburg–Landau (GL) parameter shows that the flux-pinning characteristics of the samples were improved by Sr doping. An increase in the mean free time of the carriers and a decrease in the energy required to break apart Cooper pairs result from a decrease in the remanent field scattering induced by the increased population of pinning centers in Sr-doped samples.

Comparative investigation on the functional properties of alkaline earth metal (Ca, Ba, Sr) doped Nd2NiO4+δ oxygen electrode material for SOFC applications

Functional properties of Nd2NiO4+δ based materials doped with different alkaline earth metal ions for SOFC applications is studied extensively and compared in this article. Phase pure powders of Nd2NiO4 +δ and Nd1.7A0.3NiO4+δ (A=Ca, Sr and Ba) were synthesized by solid state route at 1250 °C from the constituent precursor oxides and carbonates. Good compatibility of these cathode materials with GDC electrolyte is confirmed through XRD analysis of the composite powder heat treated at 1250 °C. Electrical conductivity of undoped Nd2NiO4+δ is found to attain a maximum at ~470 °C and then decreases noticeably with increase in temperature. The decrease in conductivity at higher temperatures is not significant for alkaline earth metal ion doped systems. In the lower temperature range, electrical conductivity decreases with alkaline earth metal ion doping and this decrement is more as the size of the dopant cation increases with an exception for Sr doped samples. However, at the operating temperature of the fuel cell (say 800 °C) electrical conductivity of Ca and Sr doped Nd2NiO4+δ are higher than the undoped material. Polarization resistance of the cathode materials are evaluated from the measured impedance spectra of symmetric cells and activation energy for oxygen reduction reaction is calculated from the Arrhenius plot of polarization resistance. Activation energy decreases with alkaline earth metal ion doping and this decrease is more in case of Ca doping followed by Sr and Ba doping. Electrolyte supported button cells fabricated under identical processing conditions were tested at 800 °C; highest power density of 188 mW cm−2 is obtained for the cell having Ca doped Nd2NiO4+δ as oxygen electrode.

Magnetic anomalies, chemical and magnetic properties at wide temperature range (15–1000 K) in LiSrxFe5-xO8 (x = 0, 0.025, 0.05)

We report on magnetic anomalies at low temperatures, high Curie temperature values, structural and chemical properties of Sr doped LiFe5O8 bulk material. Micron size LiSrxFe5−xO8 (x = 0, 0.025, 0.05) are seen to crystallize in ordered α-LiFe5O8 phase with the space group of P4332. Chemical states of Li, Fe, Sr and O are confirmed from X-ray photoelectron spectroscopy measurements. Domain wall thickness is calculated to be 60 nm, 59.4 nm and 52.5 nm for x = 0, 0.025, 0.05 samples respectively. Field cooled (FC) and zero field cooled (ZFC) measurements from 300 K to 15 K shows several anomalies in LiSrxFe5−xO8 (x = 0, 0.025, 0.05) samples. Magnetic anomalies are observed at Tm1 (275 K), Tm2 (225 K), Tm3 (125 K), Tm4 (80 K) and Tm5 (30 K) for the pure LiFe5O8 sample and for the Sr doped samples, two sharp jumps in magnetization are observed around Tm6 (250 K) and Tm7 (75 K). Saturation magnetization and Curie temperature values are seen to decrease with the partial substitution of Sr2+ ions for the Fe3+ ions in α-LiFe5O8 structure. Remanent magnetization, magnetocrystalline anisotropy constant (K1) and coercivity values are seen to increase with increasing Sr concentration. LiSrxFe5−xO8 (x = 0, 0.025, 0.05) samples exhibit magnetic anomalies at low temperatures and exhibit hard magnetic behavior with Sr substitution.

Structural Distortion and Dielectric Permittivities of KCoO2-Type Layered Nitrides Ca1-xSrxTiN2.

Among the KCoO2-type phases, the orthorhombic layered nitride CaTiN2 is a newly reported high dielectric permittivity material (εr ∼ 1300-2500 within 104-106 Hz from 80 to 450 K) while the tetragonal SrTiN2 is reported to display an unintentional metallic conduction property. In this work, a Ca1-xSrxTiN2 solid solution was synthesized, in which the insulating SrTiN2 end member and some Sr-doped CaTiN2 samples were successfully obtained, and therefore, the dielectric properties of the Ca1-xSrxTiN2 solid solution were investigated. The Sr substitution for Ca drove an orthorhombic-to-tetragonal phase transformation in Ca1-xSrxTiN2, which reduced the dielectric permittivity significantly. The tetragonal SrTiN2 displays a much lower dielectric permittivity (εr ∼ 20-70 in 105-106 Hz and 10-300 K) than that of CaTiN2. The comparison on the dielectric permittivities and structures of CaTiN2 and SrTiN2 indicates that the structural distortion arising from the splitting of N planes between Ti layers within the TiN2 pyramidal layers could be a plausible structural origin of the high bulk dielectric permittivity of CaTiN2.

Incorporation of Incompatible Strontium and Barium Ions into Calcite (CaCO3) through Amorphous Calcium Carbonate

Calcite is a ubiquitous mineral in nature. Heavy alkaline-earth elements with large ionic radii such as Sr2+ and Ba2+ are highly incompatible to calcite. Our previous study clarified that incompatible Sr2+ ions can be structurally incorporated into calcite through crystallization from amorphous calcium carbonate (ACC). In this study, we synthesized Sr-doped calcite with Sr/(Sr + Ca) up to 30.7 ± 0.6 mol% and Ba-doped calcite with Ba/(Ba + Ca) up to 68.6 ± 1.8 mol%. The obtained Ba-doped calcite samples with Ba concentration higher than Ca can be interpreted as Ca-containing barium carbonates with the calcite structure which have not existed so far because barium carbonate takes the aragonite structure. X-ray diffraction (XRD) patterns of the Sr-doped and Ba-doped calcite samples obtained at room temperature showed that reflection 113 gradually weakened with increasing Sr/(Sr + Ca) or Ba/(Ba + Ca) ratios. The reflection 113 disappeared at Ba/(Ba + Ca) higher than 26.8 ± 1.6 mol%. Extinction of reflection 113 was reported for pure calcite at temperatures higher than 1240 K, which was attributed to the rotational (dynamic) disorder of CO32− in calcite. Our Molecular Dynamics (MD) simulation on Ba-doped calcite clarified that the CO32− ions in Ba-doped calcites are in the static disorder at room temperature. The CO32− ions are notable tilted and displaced from the equilibrium position of pure calcite.

Degradability and in vivo biocompatibility of doped magnesium phosphate bioceramic scaffolds

In the present study, degradability and in vivo biocompatibility of doped magnesium phosphate (MgP) scaffolds were evaluated. 0.5 wt% Zn, 0.5 wt% Si, and 2 wt% Sr doped MgP scaffolds were prepared with up to 47% porosity. Zn doped MgP scaffolds showed nearly 13% weight loss when immersed in SBF for 8 weeks whereas least degradation was noticed for Sr doped samples. In vitro cytocompatibility study, using MC3T3-E1, showed significantly higher cell proliferation at day 5 in a composition independent manner. When implanted in rabbit femur, micro-CT (µ-CT) results showed extensive degradation for Zn doped MgP scaffolds after 2 months while significant bone growth was noticed for both Si and Sr doped scaffolds.

Hydrothermal Synthesis of Sr-doped Hydroxyapatite and Its Antibacterial Activity

In this study, we prepared hydroxyapatite (HAP) samples using hydrothermal method. We investigated the effect of reaction conditions such as phosphate excess applying 1.49 and 1.67 (as stoichiometric) Ca/P ratio, pH (9/ 10/ 11/ 12) and time (4/ 8/ 12/ 24 h). Sample characterization was carried out by XRD and SEM. The results showed, all samples had HAP structure, however, lower Ca/P ratio, larger reaction time and setting the pH to 10 increased the crystallinity. Then, we synthetized Sr-doped HAP samples, varying the Sr concentration using 2, 4, 6, 8 and 10 % Sr/ (Ca+Sr). The Sr content was revealed by EDX. Sr-incorporation did not change the obtained crystalline HAP phase but the unit cell parameters increased. We calculated lattice constants and found that a, b changed from 9.4310 Å to 9.4700 Å, c from 6.8819 Å to 6.9227 Å and the unit cell volume from 530.0951 Å3 to 537.6556 Å3 due to the larger ionic radius of Sr compared to Ca. The pure and doped samples had uniform, mostly needle-like morphology with 100-300 nm length and 25-100 nm. In vitro cytotoxicity tests revealed evident antibacterial activity in the case of doped samples compared to pure HAP against E. coli.

Zero-field-cooled exchange bias effect in phase-segregated La2−xAxCoMnO6−δ (A=Ba,Ca,Sr;x=0,0.5)

In the zero-field-cooled exchange bias (ZEB) effect the unidirectional magnetic anisotropy is set at low temperatures even when the system is cooled in the absence of external magnetic field. La$_{1.5}$Sr$_{0.5}$CoMnO$_{6}$ stands out as presenting the largest ZEB reported so far, while for La$_{1.5}$Ca$_{0.5}$CoMnO$_{6}$ the exchange bias field ($H_{EB}$) is one order of magnitude smaller. Here we show that La$_{1.5}$Ba$_{0.5}$CoMnO$_{6}$ also exhibits a pronounced shift of its magnetic hysteresis loop, with intermediate $H_{EB}$ value in respect to Ca- and Sr-doped samples. In order to figure out the microscopic mechanisms responsible for this phenomena, these compounds were investigated by means of synchrotron X-ray powder diffraction, Raman spectroscopy, muon spin rotation and relaxation, AC and DC magnetization, X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). The parent compound La$_{2}$CoMnO$_{6}$ was also studied for comparison, as a reference of a non-ZEB material. Our results show that the Ba-, Ca- and Sr-doped samples present a small amount of phase segregation, and that the ZEB effect is strongly correlated to the system's structure. We also observed that mixed valence states Co$^{2+}$/Co$^{3+}$ and Mn$^{4+}$/Mn$^{3+}$ are already present at the La$_{2}$CoMnO$_{6}$ parent compound, and that Ba$^{2+}$/Ca$^{2+}$/Sr$^{2+}$ partial substitution at La$^{3+}$ site leads to a large increase of Co average valence, with a subtle augmentation of Mn formal valence. Estimates of the Co and Mn valences from the $L$-edge XAS indicate the presence of oxygen vacancies in all samples (0.05$\leq \delta \leq$0.1). Our XMCD results show a great decrease of Co moment for the doped compounds, and indicate that the shift of the hysteresis curves for these samples is related to uncompensated antiferromagnetic coupling between Co and Mn.