Ca Substitution Research Articles

Structural transformation and investigation of dielectric properties of Ca substituted (Na0.5Bi0.5)0.95−xBa0.05CaxTiO3 ceramics

Polycrystalline samples of composition (Na0.5Bi0.5)0.95−xBa0.05CaxTiO3 (x = 0.05, 0.075 and 0.1) were synthesized with the purpose of fabricating ceramics having morphotropic phase boundary by well known solid state reaction method. X-ray diffraction along with Rietveld-refinement showed a gradual change in crystal structure from rhombohedral to orthorhombic with increasing Ca doping in the host-matrix compound. The effect of Ca substitution on the electrical properties was studied by impedance spectroscopy in the temperature range 303 K723 K. The dielectric properties of the synthesized ceramics were characterized by a strong temperature and frequency dependence. Complex impedance analysis distinguished the grain, grain boundary and electrode contribution and suggested that the systems are undergoing a polydispersive Non-Debye type relaxation. The equivalent circuit model was used to find a correlation between the response of real system and discrete electrical components. Combined study of imaginary part of electric impedance and modulus as a function of frequency was taken as additional evidence of electrical heterogeneous microstructure of the polycrystalline ceramics as explained by the Nyquist plots. The ac conductivity variation with frequency and temperature was investigated, which showed qualitative similarities as that of dielectric spectra. The dc conductivity was measured by extrapolating the conductivity spectra at different temperatures to the zero frequency values, from which thermal activation energies <1 eV was inferred indicating the conduction is probably induced by the migration of oxide ions and oxygen vacancies.

Crystal chemistry and dielectric properties of (Bi1.5Zn0.4M0.1)(Nb1.5Zn0.5)O7 (M = Sr, Ca, Mn, Zn) pyrochlore oxides

As a potentially attractive candidate of LTCC material, Bi1.5Zn1.0Nb1.5O7 ceramics with substituted Zn2+ were synthesized by a conventional mixed oxide route. For the first time, the effect of the chemical ionic substitution of Sr, Ca and Mn cations on the microstructure, bond energy and dielectric properties of bismuth-based pyrochlores was discussed systematically for Bi1.5Zn1.0Nb1.5O7. Rietveld refinement was carried to analyze the structure variation of the sintered specimens. The solid solubility limits of in the Bi1.5Zn1.0Nb1.5O7 system with Sr, Ca and Mn incorportion were discussed. The samples presented single cubic phase that were used to study the dielectric properties of Bi1.5Zn1.0Nb1.5O7 based on the crystallization and microstructure. The dielectric constant er was mainly related to relative density not the ionic polarizability. The relative density and the dielectric constant er showed the same decreased trend as a function of different ionic dopant. And the change of the grain size and grain boundaries had a significant influence on the loss tangent tanδ in this system. The A-site cation bond energy of (Bi1.5Zn0.4M0.1)(Nb1.5Zn0.5)O7 (M = Sr, Ca, Mn, Zn) ceramics was performed to explain the relationship between the temperature coefficient of the dielectric constant τe and the crystal microstructure in a new way. With the decrease of |τe| values as a function of the substitution, the Zn–O bond energy of A-site became strong. This indicated that the (Bi1.5Zn0.4M0.1)(Nb1.5Zn0.5)O7 system tended to be stable.

Synthesis and characterization of strontium-substituted hydroxyapatite nanoparticles for bone regeneration

The production of stable suspensions of strontium-substituted hydroxyapatite (Sr-HA) nanopowders, as Sr ions vector for bone tissue regeneration, was carried out in the present work. Sr-HA nanopowders were synthesized via aqueous precipitation methods using Sr2+ amount from 0 to 100mol% and were characterized by several complementary techniques such as solid-state Nuclear Magnetic Resonance spectroscopy, X-ray diffraction, Infrared spectroscopy, N2 physisorption and Transmission Electron Microscopy.The substitution of Ca2+ with Sr2+ in HA is always isomorphic with gradual evolution between the two limit compositions (containing 100% Ca and 100% Sr), this pointing out the homogeneity of the synthesized nanopowders and the complete solubility of strontium in HA lattice. Strontium addition is responsible for an increasing c/a ratio in the triclinic unit cell. A significant variation of the nanopowders shape and dimension is also observed, a preferential growth along the c-axis direction being evident at higher strontium loads. Modifications in the local chemical environment of phosphate and hydroxyl groups in the apatite lattice are also observed.Stable suspensions were produced by dispersing the synthesized nanopowders in bovine serum albumin. Characterization by Dynamic Light Scattering and ζ-potential determination allowed to show that Ca2+→Sr2+ substitution influences the hydrodynamic diameter, which is always twice the particles size determined by TEM, the nanoparticles being always negatively charged as a result from the albumin rearrangement upon the interaction with nanoparticles surface.The biocompatibility of the suspensions was studied in terms of cell viability, apoptosis, proliferation and morphology, using osteosarcoma cell line SAOS-2. The data pointed out an increased cell proliferation for HA nanoparticles containing larger Sr2+ load, the cells morphology remaining essentially unaffected.

Synthesis, Crystal Structure Analysis and Electrochemical Properties of MgxNi1-XO2.

INTRODUCTION Currently, the secondary battery having a high energy density as a high performance secondary battery has been developed. Although polyvalent cations secondary batteries such as Mg and Ca batteries are a promising candidate, polyvalent cations secondary battery as alternative to lithium ion batteries has not been reported. In the lithium-ion battery, LiNi0.5Mn1.5O4 was well known to show two-electron reaction from Ni2 + to Ni4+ and high potential of 4.7 V. Interestingly, the electrochemical characteristic of LiNi0.5Mn1.5O4 was due to firing temperature changes. Therefore, the oxides consisted of Mg and Ni can be expected to be high potential and capacity from a viewpoint of the combination with divalent cations and two-electron reaction. However, synthesis of the oxides consisting of Mg and Ni has been only reported in the limited chemical composition, MgNiO2 and Mg0.67Ni1.33O2, and not reported the synthesis of other Mg / Ni ratio1,2). The present study was aimed at examination of difference in the electrochemical properties due to the difference in the firing temperature, controlling the rock-salt type MgxNi1-xO2 to Mg/Ni ratio, and evaluation as a magnesium ion battery cathode material. EXPERIMENTAL MgxNi1-xO2 was synthesized by a reverse coprecipitation synthesis1). MgxNi1-xO2 synthesized by nitrate aqueous solution of Mg and Ni were mixed to Na2CO3 solution while heating to 80° C, and the precursor dried (100 ° C, Air, 24h), and firing (550 - 950° C, Air, 24h). It was examined that the change in Mg/Ni ratio by changing the concentration of Na2CO3 solution. The samples were characterized by powder X-ray diffraction and ICP measurements. We also examined the valence of Ni by XAFS analysis (BL14B2, SPring-8). Before Charge-discharge test, active material and conductive agent in a weight ratio of 10:3 carbon coating (300rpm, 2h) by a planetary ball-mill. The positive electrodes were mixed active material and a conductive carbon and a binder (PTFE) at 5: 5: 1 weight ratio. Negative electrode used Mg metal or AZ31, electrolyte used 0.5 mol/L-Mg(N(CF3SO2)2)2/Acetonitrile (AN) or 1.0 mol/L-Mg(N(CF3SO2)2)2/Triglyme (G3). We attempted the Rietveld analysis (RIETAN-FP) and MEM analysis (Dysnamia) using the measured synchrotron X-ray diffraction data(BL19B2, SPring-8) RESULTS AND DISCUSSION The synthesized samples were identified as Rock-salt structure with space group Fd-3m by powder X-ray diffraction. To refine the crystal structure of the samples, we performed the Rietveld analysis using the synchrotron X-ray diffraction (e.g. R wp=5.60%, R e=2.35%). In addition, the results of ICP analyses for the compounds revealed that Mg/Ni ratio of the samples were ranged from 0.28 to 0.48 by changing Na2CO3 aq. concentration. The XAFS analysis, the valence state of Ni was determined to be divalent (Fig.1). The intensity ratio of d 111/d 200increased with the increasing the Mg/Ni ratio in the X-ray diffraction. We performed a charge-discharge test. Results of the charge-discharge test using AN showed 217mAh/g for the sample fired at 950 °C . The sample being higher Mg/Ni ratio tended to show higher capacity. However, the capacity might increase by a side reaction because of the electrochemical reaction occurred at extremely low voltage. To solve this reaction, electrolyte was changed from AN to G3 and the current collector was changed from Pt to Ni. As a result for such condition, it showed high reversibility and suppressed the side reactions. We examined the elimination of Mg by an oxidizing agent of NO2BF4. Since the lattice constants did not change before and after treatment, it was suggested elimination of Mg by chemical treatment was difficult. Therefore, we partly replaced Mg with Ca for the improvement of electrochemical property.We confirmed that (Mg,Ca)xNi1-xO2 was synthesized from the increase of the lattice parameter. As a result of the charge-discharge test for (Mg,Ca)xNi1-xO2, discharge potential was increased from 0.5V to 0.8V. Therefore, it may be possible to significantly improve the properties of Mg secondary battery of rock-salt type by Ca substitution. It was performed by help of ALCA-SPRING and shows thanks to the members concerned. References 1)S. Yagi et al., Jpn. J. Appl. Phys., 52,025501 (2013). 2)T. Ichitsubo, T. Adachi, S. Yagi, T. Doi, J.Mater.Chem., 21, 11764(2011). Figure 1

In-situ LA-ICP-MS trace elements analysis of scheelites from the giant Beiya gold–polymetallic deposit in Yunnan Province, Southwest China and its metallogenic implications

The Beiya gold–polymetallic deposit, located in the middle of the Jinshajiang–Ailaoshan alkaline porphyry metallogenic belt, is the largest skarn gold deposit in China. Scheelite is a typical hydrothermal mineral which can serve as mineralization process tracer and is significant for the hydrothermal deposit study. In this paper, we present in-situ LA-ICP-MS scheelite geochemical data from the different parts of the skarn mineralization in the Beiya deposit. The data indicate that the Beiya scheelite has high Mo (average: 38,943ppm) and high LREE/HREE (average: 29.6), resembling typical skarn-type scheelite. The mechanism of REE substitution of Ca in the Beiya scheelite was probably 3Ca2+=2REE3++□Ca, which implies that the scheelite inherited its REE composition from magma-derived ore-forming fluids. The scheelite from near the marble shows negative Eu anomaly (average δEu: 0.45), indicating an oxidizing condition, whereas that from near the porphyry shows positive Eu anomaly (average δEu: 3.58), indicating a reducing environment. Scheelite from the sandstone-hosted stratiform orebody shows slight and variable Eu anomalies (δEu: 0.66–1.47), indicating possible fluctuating physicochemical conditions. Our data demonstrate an increasing oxygen fugacity (fO2) trend from the ore-related intrusion to the surrounding carbonates at Beiya. The Rb/Sr, Nb/Ta and Zr/Hf ratios of the Beiya scheelite suggest an addition of mantle-derived components to the ore-forming materials of the Beiya deposit.

Spectroscopic study for a chromium-adsorbed montmorillonite

Samples of purified montmorillonite with trace amounts of quartz were subjected to different concentrations of chromium sulphate solutions for one week to allow cation exchange. The chromium-bearing montmorillonites were verified and tested using powder X-ray diffractometry (XRD), X-ray fluorescence spectrometry, electron spin resonance (ESR) spectrometry and Fourier transformation infrared (FTIR) spectroscopy to explore the occupation sites of the chromium. The ESR spectra recorded before and after the chromium exchange show clear differences: a strong and broad resonance with two shoulders at the lower magnetic field side was present to start, and its intensity as well as that of the ferric iron resonance, increased with the concentration of added chromium. The signals introduced by the chromium, for example at g=1.975 and 2.510 etc., suggested that the chromium had several occupational sites. The ESR peak with g=2.510 in the second derivative spectrum suggested that Cr3+ was weakly bounded to TOT with the form of [Cr(H2O)3]3+ in hexagonal cavities. This was verified by comparing the FTIR spectra of the pure and modified montmorillonite. The main resonance centred at g=1.975 indicated that the majority of Cr3+ occupied the interlayer region as [Cr(H2O)6]3+. The substitution of Ca2+ by Cr3+ also greatly affected the vibration of the hydrogens associate to water, ranged from 3500 to 2600cm-1 in FTIR. Furthermore, the presence of two diffraction lines in the XRD results (specifically those with d-values of 1.5171 and 1.2673nm) and the calculations of the size of the interlayer space suggested the presence of two types of montmorillonite with different hydration cations in the sample exposed to 0.2M chromium sulphate. The two diffraction lines were assigned to [Cr(H2O)6]3+ and [Cr(H2O)3O3]3+, respectively. This also suggested that the species of hydration cation was constrained by the concentration of the chromium solution.

Effect of charge compensator ion on dysprosium doped di-calcium magnesium di-silicate phosphors

In the present article, effect of charge compensator ions (R+ = Li+, Na+ and K+) on dysprosium doped di-calcium magnesium di-silicate (Ca2MgSi2O7:Dy3+) phosphors were investigated. The Ca2MgSi2O7:Dy3+ and Ca2MgSi2O7:Dy3+, R+ (R+ = Li+, Na+ and K+) phosphors were prepared by the traditional high temperature solid state reaction method. The crystal structures of sintered phosphors were an akermanite type structure which belongs to the tetragonal crystallography. Thremoluminescence kinetic parameters such as activation energy (E), order of kinetics (b), and the frequency factor (s) of synthesized phosphors has been calculated by the peak shape method. The prepared Ca2MgSi2O7:Dy3+ and Ca2MgSi2O7:Dy3+, R+ phosphors were excited at 350 nm and their corresponding emission spectrum were recorded at blue (481 nm) and yellow (574 nm) region due to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions respectively of Dy3+ ions. The combination of these two emissions constituted as white light; confirmed by the Commission Internationale de L’Eclairage chromaticity diagram. The possible mechanism of white light emitting Ca2MgSi2O7:Dy3+ and Ca2MgSi2O7:Dy3+, R+ phosphors were also investigated. The addition of charge compensator ions enhances the luminescence intensity of prepared Ca2MgSi2O7:Dy3+ phosphors because they neutralize the charge generated by Dy3+ substitution for Ca2+ ions. The role of Li+ ions among all charge compensator ions (Na+ or K+) used was found to be most effective for enhanced Dy3+ ion emission.

Evaluation of europium-doped HA/β-TCP ratio fluorescence in biphasic calcium phosphate nanocomposites controlled by the pH value during the synthesis

Europium-doped hydroxyapatite (HA), beta-tricalcium phosphate (β-TCP) and biphasic phosphate nanopowders were synthesized by co-precipitation method and their crystal structures and fluorescence properties were investigated depending on the pH of the starting solution. In the range of pH 6–10, HA and β-TCP phases coexist. The β-TCP proportion increased as the pH of the solution decreased, while HA yields decreased. At pH below 6, monophasic β-TCP powder was obtained after thermal treatment. In particular, HA and β-TCP can be used as luminescent materials when activated by Eu3+ ions in substitution of Ca2+ ions. Herein, the Eu3+ ions doped HA and β-TCP phase composition were analyzed in order to investigate the fluorescence emission of the HA, β-TCP and biphasic compounds. Eu-doped HA exhibited a red-orange emission at 575nm with several minor peaks at 610–640nm, while Eu-doped β-TCP had an unexpected strong red emission at 610–620nm and a secondary band at 590–600nm. In fact, the Eu:β-TCP integrated emission area is almost 20-fold higher than Eu:HA for the same europium ion concentration. These results demonstrate the potential of Eu:β-TCP as biomarker for medical applications, as drug release and targeting based on their luminescent properties.

Synthesis, structure and photoluminescence properties of (Sr,Ca)AlSiN3:Eu2+ phosphor for white light emitting diodes with controllable optical performance

A series of SryCa1−x−yAlSiN3:xEu2+ (x = 0–0.01, y = 0–0.8) phosphors have been successfully prepared by solid state reaction under atmospheric pressure. All the phosphors exhibit orthorhombic crystal structure similar with CaAlSiN3 structure. It is found that the emission bands for all Ca1−xAlSiN3:xEu2+ phosphors are centered at ~650 nm and fluorescence quenching has been observed along with the increase of Eu2+ concentration in host materials. Through substitution of Ca2+ by Sr2+, an expected red emission peak (625 nm) and enhanced luminescent intensity can be achieved. The obtained Sr0.8Ca0.192AlSiN3:0.008Eu2+ phosphor was further used as efficient red component to fabricate white light emitting diodes (LEDs). Under the optimized condition of LED packaging, the white LEDs own the excellent optical properties with luminous efficiency of 90.6 lm/W and an ideal color rendering index (Ra = 82). Furthermore, the color correlated temperature of white LEDs can be simply adjusted through changing the red phosphor concentration and dispensing package saves time.

Effect of chemical doping on the visible emission in Cu ions doped perovskite zirconates

We investigated the effect of the chemical doping on the visible emission of the Cu-ion-doped perovskite zirconates. We synthesized the Cu-ion-doped Sr1−x Ca x ZrO3 (SCZO:Cu) compounds (x = 0 − 1), where the structural distortion and the chemical disorder were tuned due to the ionic size difference between Sr2+ and Ca2+. The nominal doping concentration of Cu ion was chosen to be 1%. We found that the visible emission in SCZO:Cu was suppressed dramatically with the substitution of Ca2+ for Sr2+ (x > 0). The violet emission was more susceptible to the structural distortion than the orange and the green emissions. These experimental findings were discussed in relation to the electronic properties of SCZO:Cu.

Enhancement of the mechanoluminescence properties on Ca2MgSi2O7:Dy3+ phosphor by co-doping of charge compensator ions

In the present article, effect of charge compensator ions (R+ = Li+, Na+ and K+) on dysprosium-doped di-calcium magnesium di-silicate (Ca2MgSi2O7:Dy3+) phosphors were investigated. The Ca2MgSi2O7:Dy3+ and Ca2MgSi2O7:Dy3+, R+ phosphors, were prepared by solid-state reaction method. The crystal structures of sintered phosphors were an akermanite-type structure which belongs to the tetragonal crystallography. The peaks of mechanoluminescence (ML) intensity were increased linearly with increasing impact velocity of the moving piston. Thus, present investigation indicates that the piezoelectricity was responsible to produce ML in prepared phosphors. The time of the peak ML intensity and the decay rate did not change significantly with respect to increasing impact velocity. Addition of charge compensator ions enhances the luminescence intensity of prepared Ca2MgSi2O7:Dy3+ phosphors, because they neutralize the charge generated by Dy3+ substitution for Ca2+ ions. The role of Li+ ions among all charge compensator ions (Na+ or K+) used was found to be most effective for enhanced Dy3+ ion emission. These ML materials can be used in the devices such as stress sensor, fracture sensor, impact sensor, damage sensors, safety management monitoring system and fuse system for army warheads.

Possibility of adjusting photoluminescence spectra of Ca scheelites (CaMoO4: Eu3+ and CaWO4: Eu3+) to the emission spectrum of incandescent lamps

The peculiarities of the photoluminescence of compounds CaMoO4: Eu3+ and CaWO4: Eu3+ with the scheelite structure associated with a change in the short- and long-range orders of the crystal lattice upon a change in the activator (Eu3+) of the photoluminescence range in the interval 1–4 mol %, in which the photoluminescence of the matrix is preserved in the range 484–557 nm, are investigated using X-ray phase analysis as well as photoluminescence, Raman, and diffuse reflection spectroscopies. The introduction of Eu3+ ions leads to the reconstruction of the lattice so that up to 10% of these ions stimulate the formation of centrosymmetric localization upon the substitution of Ca2+ ions in the noncentrosymmetric positions. It is found that the spectral radiant emittance of the more effective luminophore CaMoO4: Eu3+ can be adjusted to this parameter for an incandescent lamp for the Eu3+ concentration of 1–2 mol %.

Color-Tunable and Highly Luminous N(3-)-Doped Ba2-xCaxSiO4-δN2/3δ:Eu(2+) (0.0 ≤ x ≤ 1.0) Phosphors for White NUV-LED.

In the search for well-defined phosphor materials for white NUV-LEDs, the highly enhanced luminous efficacy by N(3-) doping as well as color tunability via Ca substitution has been successfully obtained in Ba2-xCaxSiO4-δN2/3δ:Eu(2+) (x = 0.0, 0.5, 0.8, 1.0) phosphors. With increasing Ca-substitution rate, the crystal structures of the phosphor materials are changed from the primitive orthorhombic structure to the hexagonal one, so that the CIE coordinates move from bluish-green (at Ca = 0.0), to blue (at Ca = 0.5), and finally to near white region (at Ca = 0.8 and 1.0) in these materials. In combination with the results from X-ray photoelectron spectroscopy (XPS) and infrared (IR) spectroscopy, the elemental distribution of the phosphor materials found from secondary-ion mass spectrometry (SIMS) directly indicates that the N(3-) ions are partially substituted for O(2-) ions into the crystal lattice of alkaline-earth orthosilicates and thus critically improves the color-tunable photoluminescence (PL) and electroluminescence (EL) efficiency of the phosphor materials for white NUV-LEDs. The newly found "the N(3-) doping and color-tunable effect" on large PL and EL enhancement may provide a platform in the discovery of new efficient phosphors for solid state lighting.

Preparation of Sr1−xCaxLiAl3N4:Eu2+ Solid Solutions and Their Photoluminescence Properties

A series of quaternary nitride solid solutions with a general formula of Sr1−xCaxLiAl3N4:0.5%Eu2+ was synthesized by a solid‐state reaction method. The experimental results showed that a proper amount of Ca‐doping can improve the crystallinity and the photoluminescence properties of the produced phosphors. Rietveld refinement showed that the volume of the unit cell shrank with the increase of Ca substitution for Sr, which resulted in a red shift of the emission spectra from 654 to 665 nm under blue excitation at 475 nm. Rietveld refinement and CASTPE calculations suggested that Ca2+ ions prefer to occupy the smaller Sr(I) sites in the crystal lattice, which increases the amount of Eu2+ ions in Sr(II) sites and enables the tuning of the chromaticity coordinates of the obtained phosphors. The thermal stability of the produced phosphors is better than that of commercial Sr2Si5N8:Eu2+ phosphor. The experimental results qualify the solid‐solution Sr1−xCaxLiAl3N4:0.5%Eu2+ for consideration as a potential candidate for application in white LEDs.

Chemical pressure effects on crystal and magnetic structures of bilayer manganites PrA2Mn2O7 (A = Sr or Ca)

The crystal and magnetic structures of the bilayer manganites PrSr2Mn2O7 (PSMO) and PrCa2Mn2O7 (PCMO) have been studied by neutron powder diffraction. It was found that PSMO crystallizes in space group I4/mmm, while PCMO adopts space group Cmc21 at room temperature. The difference in the structure arises from chemical pressure induced by the Ca substitution for Sr on the A sites, which causes different Jahn-Teller distortions. In PSMO, the MnO6 octahedra suffer a small elongated distortion, while those in PCMO adopt strong compressed distortion along the axial direction. In addition, the octahedra in PCMO show a+b0c0 rotation and a0b+c+ tilting in the Glazer notation in comparison to PSMO. As a result, these two compounds adopt very different magnetic structures: The magnetic structure of PSMO is an A-type magnetic structure (Im'm'm) with propagation vector k = (0, 0, 1) and magnetic moments in the ab plane. In contrast, a C-type antiferromagnetic magnetic structure (Cm'c2′1) with the multiple propagation vectors (k = (0, 12, 12) and (0, 12, 0)) and magnetic moments mainly along the b axis is found in PCMO. The critical exponent of the magnetic phase transition is around 0.345 for PSMO and 0.235 for PCMO, indicating 3D and 2D XY transitions, respectively. The strong Jahn-Teller distortion induced by the chemical pressure is believed to suppress the double exchange and favour super-exchange in PCMO, leading to the dramatic difference in the magnetic structure.

Degradation and hemostatic properties of polyphosphate coacervates

Sodium polyphosphate is a linear polymer formed from phosphate units linked together by sharing oxygen atoms. Addition of calcium to a solution of sodium polyphosphate results in phase separation and formation of a polyphosphate coacervate best described as a polymeric rich viscoelastic material. Polyphosphate coacervate is an interesting candidate as a biomaterial based on its ability to bind with different cations and to be loaded with drugs. Here, in vitro degradation and hemostatic properties of polyphosphate coacervates are comprehensively evaluated. We show that polyphosphate coacervates degrade and dissolve at a fast rate, losing half of their original mass in a week and transforming to mainly pyrophosphate after 4weeks. This burst dissolution phase happens earlier for the coacervate prepared from very short chain polyphosphate but overall using longer polyphosphate chains does not increase the coacervate longevity significantly. Substitution of Ca with Sr or Ba does not affect the hydrolysis of coacervates but slows down their dissolution into the media. In a whole blood clotting assay, coacervates profoundly decrease the clotting time especially when very long chain polyphosphates are used. While coacervate chain length and divalent cation type were found to significantly affect prothrombin time and thromboplastin time compared to the control, no discernible trends were observed. Platelets adhere in large numbers to coacervates, especially those containing long chain polyphosphate, but the cell morphology observed suggests that they might not to be fully activated. Overall, the long chain polyphosphate coacervate holds a great potential as a resorbable hemostatic agent. Statement of SignificanceDivalent cation additions to a sodium polyphosphate solution result in polyphosphate coacervates, or highly viscous gel-like materials, having great potential in bio-applications such as drug delivery and hemostasis. As these coacervates degrade in aqueous environments, we undertook a comprehensive evaluation to better understand the impact of polyphosphate chain length and divalent cation substitution on this hydrolytic response in order to better predict degradation behavior in the body. Furthermore, there is great interest in the role of polyphosphates in hemostasis following recent publications showing that platelets secrete polyphosphates upon thrombin stimulation. In this paper, we evaluate the hemostatic potential of polyphosphate coacervates as bulk constructs, demonstrating that indeed these materials hold great potential as a degradable hemostatic agent.

Calcium-induced cation ordering and large resistivity decrease in Pr0.3CoO2

Structure of layered cobaltates Pr0.3CoO2 and (PrCa)0.3CoO2 were investigated by electron diffraction tomography and powder X-ray diffraction. The effect of the calcium substitution on thermoelectric properties was evaluated. The structure consists of hexagonal sheets of edge-sharing CoO6 octahedra interleaved by cationic monolayers. The cations form a 2-dimensional a√3×a√3 superstructure in the a–b plane. While Pr0.3CoO2 showed no layer order in the [001] direction, introduction of calcium resulted in the formation of a superstructure spanning over six cationic layers along the [001]. This superstructure model appears to be valid also for the description of the superstructures of CaxCoO2 and SrxCoO2 with x about 1/3. Thanks to the increased number of charge carriers, the substitution of Ca2+ for Pr3+ significantly lowers the electric resistivity, while keeping quite high thermopower around 100μVK−1, though the character of resistivity remained semiconducting.

Calcium and strontium substituted lanthanum manganite–cobaltite [La1−x(Ca,Sr)xMn0.5Co0.5O3] nano-catalysts for low temperature CO oxidation

In this work, structural and catalytic properties of La1−xCaxMn0.5Co0.5O3 and La1−xSrxMn0.5Co0.5O3 nano-catalysts in the concentration range of 0.00≤x≤1.00 are investigated. The structural characterization of the compounds obtained by X-ray powder diffraction and using X′Pert package and Fullprof program is an evidence for structural phase transition of the samples that can be described by variation of tolerance factor. The obtained results also have been confirmed by FTIR measurements. The structural results, and the non-uniformly changes of activation energy, band gap energy and electrical conductivity values suggest the presence of different concentration of various cations Co+2, Co+3, Co+4, Mn+4 and Mn+3 in the compounds studied. The decrease of the crystallite size with increasing Ca and Sr substitution for x up to 0.5 in La1−x(Sr, Ca)xMn0.5Co0.5O3 can be related to the increase and decrease of micro-strain, respectively. Substituting Sr having higher ionic radius with respect to La in LaMn0.5Co0.5O3 shifts the catalytic activity of CO oxidation to lower temperature, whereas, for Ca substitution the catalytic activity shifts to higher temperature. The trend of catalytic activity observed for Ca- and Sr-substituted samples can be related to different morphology observed in SEM micrographs due to different types of micro-strain. La0.5Sr0.5Mn0.5Co0.5O3 nano-catalyst exhibits excellent CO conversion rate of 95% at 175°C.

Rapid and efficient visible light photocatalytic dye degradation using AFe2O4 (A = Ba, Ca and Sr) complex oxides

Photocatalytic activity of spinel type complex oxides has been investigated in this study. Alkaline earth ferrites AFe2O4 (A = Ba, Ca, Sr) were synthesized by sol–gel method. Structural characterizations reveal that the synthesized ferrites have orthorhombic crystal structures with different space groups and cell dimensions when they have different alkaline earth metals in their A site. All the synthesized ferrites exhibited their bandgap in the range 2.14–2.19 eV. Their photocatalytic activities were studied using congo red dye under sunlight and xenon lamp radiation. The substitution of Ba, Ca and Sr at A site of these ferrites had varying impact on dye degradation process. Under xenon lamp irradiation, BaFe2O4 exhibited the highest percentage of dye degradation (92% after 75 min). However, CaFe2O4 showed the fastest degradation of the dye (70% within 15 min). In the absence of irradiation, SrFe2O4 showed the highest dye adsorption (44% after 75 min).

A-site calcium-doped Pr1−xCaxBaCo2O5+δ double perovskites as cathodes for intermediate-temperature solid oxide fuel cells

The LnBaCo2O5+δ (Ln = rare earth) double perovskite cathodes possess superior electrochemical performance in intermediate-temperature solid oxide fuel cells (IT-SOFCs). However, high thermal expansion coefficients (TECs) and material costs are major challenges to their widespread applications. In this paper, a novel A-site Ca doping strategy that can suppress the spin-state transition of Co3+ is proposed to reduce the TECs and material costs of Pr1−xCaxBaCo2O5+δ (x = 0.1–0.4; PCBCO). Substitution of Ca for Pr effectively reduces the TEC from 22.2 × 10−6 K−1 at x = 0.1 to 19.1 × 10−6 K−1 at x = 0.3 between 100 and 800 °C. PCBCO exhibits good chemical compatibility with the Sm0.2Ce0.8O1.9 (SDC) electrolyte. The area-specific resistances of PCBCO cathodes with x = 0.1, 0.2, and 0.3 are 0.081, 0.082, and 0.089 Ω cm2, respectively, at 700 °C on the SDC electrolyte. The maximum power densities of a single cell on a 0.3 mm-thick SDC electrolyte reach 646.5, 636.8, and 620.6 mW cm−2 at 800 °C for cathodes with x = 0.1, 0.2, and 0.3, respectively. The PCBCO double perovskites exhibit excellent chemical compatibility and electrochemical performance while reducing the TECs and material costs; thus, these double perovskites are promising cathode materials for applications in IT-SOFCs.