Ca Substitution Research Articles

The Influence of Zn on Superconducting Properties of Bi2Sr2Ca1Cu2OX

It was investigated that the influence of Ca substitution by Zn on the specific resistivity, thermal power, and excess conductivity of Bi2Sr2CaCu2OX, Bi2Sr2Ca0.8Zn0.2Cu2OX, and Bi2Sr2Ca0.4Zn0.6Cu2OX polycrystalline samples in the 70–300 K temperature interval. The fluctuation-induced conductivity is analyzed using the Aslamasov and Larkin and Lawrence and Doniach models. The microscopic parameters such as dimensional crossover temperature (Tcr), interlayer coupling strength (J), and zero temperature coherence length along c axis (ξ0) are estimated.

Mechanical and chemical pressure effects on the AeFe2As2 (Ae = Ba, Sr, Ca) compounds: Density functional theory

We have studied the pressure-induced structural, magnetic and electronic properties of AeFe2As2 (Ae = Ba, Sr, Ca) compounds in the framework of density functional theory within the GGA-PBE method. The effects of chemical pressure generated by Sr and Ca substitutions in BaFe2As2 have been investigated. We have found a magnetic transition at the same primitive unit cell volume, around 81 Å3 for the (Ba⧹Ca)Fe2As2 compounds, which predicts a magnetic transition pressure of 12 GPa for SrFe2As2. The structural parameters of FeAs4 tetrahedra are obtained after ionic relaxation and compared with the existing experimental results. The change of these internal parameters is ascribed to pressure-induced charge transfer, i.e., as the As-Ae bonds absorb electrons, the Fe-As bonds are depleted, and thus the number of holes in the Fe-As layers increases. The changes of the density of states, the band structure and the hole- and electron- pockets of Fermi surface by pressure have been discussed.

Structural, electronic and magnetic properties of Ca, Sr and Ba heterovalent A-site ion substitution in BiFeO3 with different Fe oxidation states

A comparative study of structural, electronic and magnetic Ca2+, Sr2+ and Ba2+ A-site ion substitution of BiFeO3 with different Fe oxidation states was carried out. Calculation shows doped compounds favours energy stability in Fe oxidation states of 2+ and 4+ compared to 3+ charge. Electronic band gap makes significant changes with value of 1.32 eV, 1.36 eV and 1.31 eV for Ca, Sr and Ba doped respectively, compared to pure BiFeO3 of 1.41 eV. The net magnetization shows improvement with use of the dopant elements compared to pure BiFeO3. These changes indicate the role of the heterovalent dopant in BiFeO3.

Peculiarities of synthesis of Ag-doped hydroxyapatite ceramics

The study is devoted to the preparation of antimicrobial Ag-containing bioactive calcium phosphate ceramics based on carbonated hydroxyapatite and to the determination of the dependence of its phase composition and microstructure on the synthesis temperature. Composite ceramics was obtained by sintering powders of carbonated hydroxyapatite (CHA), synthesized as a result of a reaction between calcium carbonate and phosphoric acid, with the addition of silver nitrate. Ceramics were sintered at 900 and 1000 °C temperatures, i.e., temperatures below and above the melting point of silver. X-ray analysis, electron microscopy, and infrared spectroscopy showed that synthesis at a 900 °C temperature (below the melting point of metallic silver) produces a two-phase composite based on CHA with inclusions of silver nanoparticles smaller than 50 nm in size. From X-ray analysis, with an increase in silver concentration, the lattice constant a remains practically unchanged, while the constant c ‒ increases. This behavior, due to the significant difference in the ionic radii of calcium and silver (Ca2+ ‒ 0.99 Å, Ag+ ‒ 1.28 Å), usually leads to the preferential substitution of Ca(1) sites in the CHA and a linear increasing in the lattice parameters of the CHA with the Ag concentration. That is, even at relatively low temperatures, as a result of the solid-phase reaction in CHA, partial replacement of calcium ions by silver ions occurs and Ag-substituted ceramics are formed. At temperatures above 1000 °C, a single-phase silver-substituted product is synthesized where part of the Ca2+ ions is replaced by Ag+ ions. At the same time, the lattice constant c continues to increase, and in the electron microscopic images only the apatite grain structure is visible without any inclusions. Sintering of composite ceramics at a temperature when silver is in the liquid phase and more easily dissociates into ions compared to the solid phase, results in a single-phase silver-substituted ceramic.

Delicate lattice modulation enables superior Na storage performance of Na3V2(PO4)3 as both an anode and cathode material for sodium-ion batteries: understanding the role of calcium substitution for vanadium

High-performance sodium storage in Na3V2(PO4)3 is realized by elaborate lattice modulation by Ca substitution for V.

Carrier doping effect of magnetic and transport properties on the geometrically frustrated iridate Ca5Ir3O12

Abstract We show the carrier doping effect on magnetic and transport properties of Ca 5 Ir 3 O 12 , indicating semiconductivity and an antiferromagnetic ordering below Neel temperature T N = 7.8 K. The average valence of Ir ions in Ca 5 Ir 3 O 12 is +4.67. Carrier doping for 5 d electrons of Ir ions is achieved by substitution of Ca 2 + by Na + , La 3 + , and Bi 3 + ; Na substitution leads to hole doping, and La or Bi substitution leads to electron doping. The electrical resistivity decreases in both case of the hole doping or the electron doping. For La10% doped samples, T N does not change but Curie–Weiss temperature Θ CW becomes 3.5 times larger than 9.9 K for Ca 5 Ir 3 O 12 . For Bi10% doped samples, T N decreases to 5 K but Θ CW becomes 3 times larger than that of undoped compound. On the other hand, for Na10% doped samples, T N decreases to 4 K and Θ CW decreases to 8.3 K. The frustration index f which is defined by | Θ CW | / T N is enhanced by electron doping. The magnetic frustration becomes stronger with increase of filling of Ir 5 d electrons on the triangular lattice.

Enhanced electrical properties of NaBi modified CaBi2Nb2O9-based Aurivillius piezoceramics via structural distortion

Two-layer structured ferroelectric ceramics, Ca1-x(NaBi)0.5xBi2Nb2O9 (x = 0.0–0.5; CNBN-x), were prepared by solid-state sintering. An artificial pseudo-morphotropic phase boundary was formed by the substitution of Ca with NaBi, and the crystal structure tended to crystallise in the pseudo-tetragonal phase as the increase of NaBi content. Curie temperature (Tc) slightly reduce and remain high value with the increase of NaBi content, which is in the range of 880–935 °C. Moreover, enhanced piezoactivity (d33) and ferroelectricity (Pr) accompanying with decreased dielectric loss can be acquired in NaBi-modified CaBi2Nb2O9. The CNBN-0.1 had the best performance, and its Tc, d33 and Pr was 925 °C, 14.4 pC/N and 6.0 μC/cm2, respectively. Thermal annealing measurement exhibited that the piezoelectric properties of Ca1-x(NaBi)0.5xBi2Nb2O9 had good temperature stability up to 800 °C. Therefore, the NaBi-modified CaBi2Nb2O9 ceramics are perceived to be of promising candidates for high-temperature applications.

Calcium-Substituted Y3Ba5Cu8O18 Ceramics Synthesized via Thermal Treatment Method: Structural and Superconducting Properties

In this work, Y3(Ba1−xCax)5Cu8O18 compounds with x = 0.00, 0.01, 0.02, 0.03 and 0.05 were synthesized by thermal treatment of aqueous solution of metal nitrates and polyvinylpyrrolidone (PVP). The effects of Ca substitution on the crystal structure, electrical resistance and the microstructure of samples were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), four-point probe measurement and AC susceptibility. FESEM analysis showed that there was an increase in the grain size and compactness. The zero-resistance critical temperature decreased from 92 K for the pure sample to 83 K for sample x = 0.05. From AC susceptibility result, the intra- and inter-granular loss peaks shifted toward lower temperature and become wider and broader with the increase of Ca substitution due to the weakening of grain coupling. On the other hand, the inter-granular critical current density (Jcm) was found to increase with Ca substitution and has the highest value Jcm = 35 A cm− 2 at x = 0.05, indicating that the Ca substitution was associated with the formation of pinning centres in the Y-358 matrix.

Divalent ion substitution effect on Yb-site in Kondo insulator YbB12

YbB12 has been investigated energetically as a typical Kondo insulator. To study detailed formation mechanism of Kondo energy gap, we have investigated transport and magnetic properties of Yb1-xR3+xB12 (R3+ = non-magnetic trivalent ions). Recently, we have recently succeeded in substitution of Ca2+ for Yb site in YbB12 by high-pressure synthesis. In Ca- and Lu-substituted alloys both of magnetic susceptibility and specific heat C/T at low temperatures, remarkably show larger increase than those of powdered YbB12. These increases are due to giant increase of density of state in an in-gap state.

Magnetic phase diagram of Ca-substituted EuFe2As2

The simultaneous presence of a Fe-related spin-density wave and antiferromagnetic order of Eu$^{2+}$ moments ranks EuFe$_2$As$_2$ among the most interesting parent compounds of iron-based pnictide superconductors. Here we explore the consequences of the dilution of Eu$^{2+}$ magnetic lattice through on-site Ca substitution. By employing macro- and microscopic techniques, including electrical transport and magnetometry, as well as muon-spin spectroscopy, we study the evolution of Eu magnetic order in both the weak and strong dilution regimes, achieved for Ca concentration $x(\mathrm{Ca}) = 0.12$ and 0.43, respectively. We demonstrate the localized character of the Eu antiferromagnetism mediated via RKKY interactions, in contrast with the largely itinerant nature of Fe magnetic interactions. Our results suggest a weak coupling between the Fe and Eu magnetic sublattices and a rapid decrease of the Eu magnetic interaction strength upon Ca substitution. The latter is confirmed both by the depression of the ordering temperature of the Eu$^{2+}$ moments, $T_\mathrm{N}$, and the decrease of magnetic volume fraction with increasing $x(\mathrm{Ca})$. We establish that, similarly to the EuFe$_2$As$_2$ parent compound, the investigated Ca-doped compounds have a twinned structure and undergo a permanent detwinning upon applying an external magnetic field.

Study of the properties of SBT ceramics doped with different concentrations of Ca

This study investigated how Ca doping affects the electrical properties of Sr2Bi4Ti5O18 (SBT) ceramics. Among the samples tested, a sample with a substitution level of 0.15 showed the highest a-axis orientation and the largest lattice distortion. Through XPS analysis, it was found that the formation of oxygen vacancies is suppressed by Ca substitution in SBT. A large remnant polarization (2Pr) of 17.7 μC/cm2 and small coercive field (2Ec) of 91 kV/cm was observed for the Ca0.15Sr1.85Bi4Ti5O18 (CSBT-0.15) ceramic, which indicated that this sample possessed the best ferroelectric properties. As the substitution level increased, the variation of the leakage current density first decreased and then increased, and the sample with the substitution level of 0.15 showed the smallest leakage current density of J= 1.1 × 10−6A/cm2 at ~80 kV/cm. For the investigated CaxSr2-xBi4Ti5O18 (CSBT) ceramic samples, space-charge-limited conduction (SCLC) was determined to be the main conduction mechanism.

Effect of Ca and La substitution on the structure and magnetic properties of M-type Sr-hexaferrites

Ca- and La-substituted M-type Sr-hexaferrites with the formulae Sr1-xCaxFe12O19, SrFe12-xCaxO19, Sr1-xLaxFe12O19, and SrFe12-xLaxO19 (x = 0, 0.1, 0.2, 0.3, and 0.4) were prepared by conventional solid-state reaction routes. Based on the changes in the lattice parameter with different x, it can be concluded that Ca substitutes into both Sr and Fe sites, whereas La substitutes only into the Sr site in the M-type hexaferrite structure. Ca substitution promotes the densification of the hexaferrites with the growth of large grains at the doping level of x ≥ 0.3 for Sr1-xCaxFe12O19 and x ≥ 0.1 for SrFe12-xCaxO19 samples. La substitution into the Sr site in the Sr1-xLaxFe12O19 samples (x ≥ 0.1) was effective in controlling grain growth in the samples. The saturation magnetization value decreased with increasing x in the SrFe12-xCaxO19, Sr1-xLaxFe12O19, and SrFe12-xLaxO19 samples, whereas it remained almost constant in the Sr1-xCaxFe12O19 samples.

Enhanced thermoelectric performance in Ca-substituted Sr3SnO

First-principles calculations were performed to study the electronic and thermoelectric transport properties of Ca-substituted Sr3SnO (Sr3−xCaxSnO, 3 ≥ x ≥ 0). The effects of Ca substitution on the bandgap are studied, and detailed mechanisms are proposed to explain the results obtained. We found that an increase of the hole concentration reduces the effective mass and the Seebeck coefficient of Ca-substituted Sr3SnO. The optimum hole concentration was obtained for Sr2CaSnO, and the corresponding maximum Seebeck coefficient of 219 μV/K was obtained at 500 K. The electrical conductivity of Sr3SnO and its alloys has a semiconducting nature, which contradicts experimental results for Ca3SnO. We found that Ca-deficient Ca3SnO exhibits metallic conductivity, and this removes the contradiction with our results. The lattice thermal conductivities (κl) of Sr3SnO and Ca3SnO were calculated by use of both the Perdew-Burke-Ernzerhof functional and the GW functional. The total thermal conductivity for Sr3SnO and Ca3SnO at 300 K is 3.03 and 2.06 W/(m K), respectively. The figure of merit (ZT) for Sr2CaSnO at 500 K is 0.6, making it promising for thermoelectric applications.

Thermal Expansion of Ca1-xSrxZr4(PO4)6 Ceramics

Ceramics with the formula Ca1-xSrxZr4(PO4)6 (x=0.4, 0.45, 0.5, 0.55) have been synthesized by coprecipitation method, an. their structures, phase transitions, thermal expansion properties have been studied by differential sanning calorimetry, scanning electron microscope, X-ray diffraction and dilatometer. The results show that Ca1-xSrxZr4(PO4)6 ceramics sintered at 1400°C had good sintering condition. Unit cell volume basically had no change with substitution of Ca by Sr. The coprecipitation method saved energy and time. It was introduced to increase the relative density of Ca0.5Sr0.5Zr4(PO4)6 ceramic. The coefficient of thermal expansion was about 1.447×10-6/°C.

Influence of Ca Doping on the Performance of Ruddlesden-Popper Oxides Sr3.2-XCaxLn0.8Fe1.5Co1.5O10-δ as Cathode Materials for It-SOFCs

Solid oxide fuel cell (SOFC) is an attractive electrochemical device for energy conversion with high efficiency and fuel flexibility at high operating temperatures (~1000 °C). Current operating temperatures of SOFC technology limit its wide commercialization due to the selection of materials used and degradation of cell components. This challenge has generated enormous interest in SOFCs operating at intermediate temperatures (600 – 800 oC). However, the catalytic activity of the conventional La1-xSrxMnO3 perovskite cathode drops significantly at temperatures < 800 °C. Mixed ionic-electronic conducting perovskites are widely investigated as cathodes for SOFCs due to their high catalytic activity for oxygen reduction reaction (ORR) at intermediate operating temperatures. Cobalt-based perovskite oxides exhibit good mixed ionic-electronic conductivity and catalytic activity at 600 – 800 oC, but they suffer from a huge thermal expansion mismatch between the electrolyte and electrode. Another class of materials with mixed ionic and electronic conducting property and catalytic activity for ORR is the perovskite-related intergrowth oxides belong to the Ruddlesden-Popper (R-P) series. Here we present R-P oxides of the n = 3 series Sr3.2-xCaxLn0.8Fe1.5Co1.5O10-δ with x = 0 and 0.4 and Ln = La, Pr, and Nd as potential cathodes for intermediate temperature SOFCs. Specifically, the effects of Ca substitution for Sr on the crystal chemistry, oxygen content, thermal expansion coefficient (TEC), and electrocatalytic activity in SOFC are presented. The substitution of Ca for Sr in Sr3.2-xCaxLn0.8Fe1.5Co1.5O10-δ enhances the stability of phase at the operating temperatures and decreases the amount of oxygen loss on heating. Comparing different lanthanides with and without Ca in Sr3.2-xCaxLn0.8Fe1.5Co1.5O10-δ, the Ln = Nd samples exhibit superior cathode performance which is ascribed to the high concentration of oxygen vacancies. Among the different compositions studied, the composite cathode Sr2.8Ca0.4Nd0.8Fe1.5Co1.5O10-δ + GDC exhibits an enhanced performance with good phase stability due to high oxygen vacancy concentration and enhanced oxide-ion transport.

Magnetic properties and magnetocaloric effect of Sr-doped Pr0.7Ca0.3MnO3 compounds

In this work, we pointed out that Sr substitution for Ca leads to modify the magnetic and magnetocaloric properties of Pr0.7Ca0.3-xSrxMnO3 compounds. Analyzing temperature dependence of magnetization, M(T), proves that the Curie temperature (TC) increased with increasing Sr content (x); TC value is found to be 130–260 K for x = 0.0–0.3, respectively. Using the phenomenological model and M(T,H) data measured at several applied magnetic field, the magnetocaloric effect of Pr0.7Ca0.3-xSrxMnO3 compounds has been investigated through their temperature and magnetic field dependences of magnetic entropy change ΔSm(T,H) and the change of the specific heat change ΔCP(T,H). Under an applied magnetic field change of 10 kOe, the maximum value of -ΔSm is found to be about 3 J/kg·K, and the maximum and minimum values of ΔCP(T) calculated to be about ±60 J/kg·K for x = 0.3 sample. Additionally, the critical behaviors of Pr0.7Ca0.3-xSrxMnO3 compounds around their TC have been also analyzed. Results suggested a coexistence of the ferromagnetic short- and long-range interactions in samples. Moreover, Sr-doping favors establishing the short-range interactions.

Effect of thermoelectric material of Ca or Fe-doped LaCoO3

As the Perovskite-type Lanthanum Cobalt Oxide of LaCoO3 is nontoxic and thermally stable even at high temperature, this material is expected as a candidate for thermoelectric applications. The thermoelectric performance of a material is often evaluated by the dimensionless figure-of-merit, ZT (=S[Formula: see text]T/[Formula: see text]), or S[Formula: see text] in the ZT equation. S[Formula: see text] shows the electrical characteristic as a Power factor (PF). It has been reported Seebeck coefficient of LaCoO3 is higher than other oxide materials at room temperature even though electrical conductivity and ZT are lower values. In this study, calcium-doped lanthanum cobaltite La[Formula: see text]Ca[Formula: see text]CoO3 (x = 0.00, 0.05, 0.10 and 0.15) and iron-doped lanthanum cobaltite LaCo[Formula: see text]Fe[Formula: see text]O3 (y = 0.05, 0.10 and 0.15) have been prepared by solid-phase process. The X-ray diffraction patterns of the calcium-doped samples and iron-doped samples show cubic perovskite structure. Electric conductivities were improved by Ca or Fe substitution and showed a tendency to increase with increasing the temperature. The sample substituted with Fe 5 mol.% showed the maximum PF, 0.510 ([Formula: see text] W/K2m) at 548 K, and the sample substituted with Ca 15 mol.% showed the maximum PF, 0.152 ([Formula: see text] W/K2m) at 498 K.

Effect of Tb-doped Concentration Variation on the Electrical and Dielectric Properties of CaF₂ Nanoparticles.

Calcium fluoride (CaF2) nanoparticles with various terbium (Tb) doping concentrations were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and alternating current (AC) impedance measurement. The original shape and structure of CaF2 nanoparticles were retained after doping. In all the samples, the dominant charge carriers were electrons, and the F− ion transference number increased with increasing Tb concentration. The defects in the grain region considerably contributed to the electron transportation process. When the Tb concentration was less than 3%, the effect of the ionic radius variation dominated and led to the diffusion of the F− ions and facilitated electron transportation. When the Tb concentration was greater than 3%, the increasing deformation potential scattering dominated, impeding F− ion diffusion and electron transportation. The substitution of Ca2+ by Tb3+ enables the electron and ion hopping in CaF2 nanocrystals, resulting in increased permittivity.

High-Frequency Magnetic Properties of Ca-Substituted Co2Z and Co2W Barium Hexaferrite Composites

A series of Ca-substituted Z-type hexaferrites having nominal composition Ba3– x Ca x Co2Fe24O41 ( $x = 0$ –1.5) was studied for their high-frequency magnetic properties, including measurement of the permeability spectra and magnetic loss over a frequency range of 0.1–10 GHz. Analyses of crystal composition and microstructure reveal that hexaferrite composites consist of the Z-type phase and increasing amounts of the W-type phase were obtained as the Ca content was increased. Correspondingly, the permeability $\mu ^\prime $ displays a near linear decrease with x varying from 0 to 1.5, from ~8 to ~4.1 at 0.1 GHz. The relationship between permeability and variations in intrinsic magnetic parameters, i.e., saturation magnetization $M_{s}$ and coercivity $H_{c}$ , follows the Globus model. Compared with the undoped Z-type hexaferrite, the sample with $x = 0.2$ has lower magnetic loss over a broad frequency range, and higher levels of Ca substitutions ( ${x} \ge 1$ ) lead to low magnetic loss at high frequencies. The dual-phase composite of Co2Z and Co2W in proper ratio is an effective technique to improve the homogeneity of grain and microstructure, and thus reduce the high-frequency magnetic loss of the sintering hexaferrites.

Research Update: Ca doping effect on the Li-ion conductivity in NASICON-type solid electrolyte LiZr2(PO4)3: A first-principles molecular dynamics study

In this work, we used a density functional theory-based molecular dynamics simulation to investigate the Ca content-dependent Li-ion conductivity of NASICON-type Li1+2xCaxZr2-x(PO4)3 (LCZP) solid electrolytes (0.063 ≤ x ≤ 0.375) which exhibit a Li-excess chemical composition. The LCZP systems show a higher room temperature Li-ion conductivity and a lower activation energy than pristine LiZr2(PO4)3 (LZP), and the tendencies of those properties agree with the experimental results. In addition, the Li-ion conduction mechanisms in LCZP were clarified by analyzing the radial distribution functions and site displacement functions obtained from our molecular dynamics simulations. For minimal Ca substitution for LZP, the Li-ion conductivity is enhanced because of the creation of interstitial Li ions by Ca doping in the LCZP systems; the frequency of collisions with Li ions dramatically increases. For substantial Ca substitution for LZP, the Li-ion conductivity gradually worsened because some Li ions were trapped at the M1 (most stable) and M2 (metastable) sites near Ca atoms.