Ca Substitution Research Articles

Study of magnetization of ferrite with Rare Earth and Ca substitutions

Study of magnetization of ferrite with Rare Earth and Ca substitutions

Crystal Field Engineering of Pr-Activated Gehlenite with Near Golden Ultraviolet C Emission for 100% Sterilization Efficiency.

Ultraviolet C (UVC) sterilization has the advantages of high efficiency, broad spectrum, and no secondary pollution. However, the emission wavelength of UVC phosphors still suffers from a large deviation from the golden sterilization wavelength of 265 nm and a low luminescence intensity. Herein, we report UVC emission near the golden sterilization wavelength as well as a long afterglow through crystal field engineering, which can lead to 100% sterilization efficiency. Combined with theoretical calculation and experimental studies, substitution of Ca2+ with large-sized Sr2+ could obtain slight expansion and distortion of cationic sites, resulting in a decrease in crystal field intensity and blue shift of Ca1.5Sr0.5Al2SiO7:1%Pr3+, and produce near golden UVC emission. Ca1.5Sr0.5Al2SiO7:1%Pr3+ phosphor can effectively inactivate Staphylococcus aureus within 10 min, showing more efficiency than the traditional mercury lamp. This work provides an effective solution for the design and preparation of UVC phosphors using crystal field engineering toward near golden UVC emission.

Yb Substitution and Ultralow Thermal Conductivity of the Ca3–xYbxAlSb3 (0 ≤ x ≤ 0.81(1)) System

A series of Yb-substituted Zintl phases in the Ca3-xYbxAlSb3 (0 ≤ x ≤ 0.81(1)) system has been synthesized by initial arc melting and post-heat treatment, and their isotypic crystal structures were characterized by both powder and single crystal X-ray diffraction analysis. All four title compounds adopted the Ca3AlAs3-type structure (space group Pnma, Pearson code oP28, Z = 4). The overall structure can be described as a combination of the 1-dimensional (1D) infinite chain of ∞1[Al(Sb2Sb2/2)] formed by two vertices sharing [AlSb4] tetrahedral moieties and three Ca2+/Yb2+ mixed sites located in between these 1D chains. The charge balance and the resultant independency of the 1D chains in the title system were explained by the Zintl-Klemm formalism [Ca2+/Yb2+]3[(4b-Al1-)(1b-Sb2-)2(2b-Sb1-)2/2]. A series of DFT calculations proved that (1) the band overlap between the d-orbital states from two types of cations and the p-orbital states from Sb at the high symmetry Γ point implied a heavily doped degenerate semiconducting behavior of the quaternary Ca2YbAlSb3 model and (2) the site preference of Yb for the M1 site was due to the electronic-factor criterion based on the Q values of each atomic site. The electron localization function calculations also proved that the two different shapes of lone pairs of the Sb atoms─the "umbrella-shape" and the "C-shape"─are determined by local geometry and the coordination environment on the anionic frameworks. Thermoelectric measurements of the quaternary title compound Ca2.19(1)Yb0.81AlSb3 showed an approximately two times larger ZT value than that of ternary Ca3AlSb3 at 623 K due to increased electrical conductivity and ultralow thermal conductivity originated from Yb substitution for Ca.

The Effect of Full-Scale Exchange of Ca2+ with Co2+ Ions on the Crystal Structure and Phase Composition of CaHPO4·2H2O

The influence of ionic substitution in the Ca1−xCoxHPO4·nH2O compound was studied systematically for the first time. Among the fascinating features of these biomaterials is that they can be easily tailored for specific applications, for example, as biocements and bioceramics. Different molar concentrations of Co(NO3)2·6H2O, Ca(NO3)2·4H2O, and NaH2PO4·2H2O compounds were employed in determining the starting solutions utilized in the present study. The experimental findings reveal that, when the Co/Ca molar ratio is below 0.67 (BCo4), Co doping (the partial substitution of Ca by Co) takes place in brushite as a monophase. However, in the Co/Ca 0.67–1.5 molar ratio range (BCo4–BCo6), biphasic Co3(PO4)2·8H2O/CaHPO4·2H2O crystals start to precipitate. Full Ca replacement by Co results in the precipitation of nanostructured monoclinic cobalt phosphate and orthorhombic ammonium cobalt phosphate hydrate. Subsequent X-ray photoelectron spectroscopy (XPS), powdered X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) analyses, along with thermogravimetric analysis (TGA), confirmed that the starting solution ratio of Co/Ca had a significant influence on the material’s microstructure, while tuning this ratio ultimately tailored the desired properties of the material for the intended applications.

Synthesis, Characterization and Impedance Analysis of CalciumDoped Zinc Oxide Nanoparticles

The calcium-doped ZnO nanoparticles, Zn1-xCaxO (x = 0, 0.025, 0.05, 0.075) were prepared by the solution combustion method. The synthesized nanoparticles were characterized by various techniques such as XRD, FTIR, Raman, FESEM-EDX, PL, Impedance, and UV-Vis. The Rietveld refinement of the X-ray diffractogram yields the crystalline structure and lattice parameters. Also, the XRD analysis shows that the substitution of Ca into ZnO does not alter the Wurtzite structure of ZnO. The crystallite size of the samples, calculated using the Scherer equation, was found to be between 46 nm and 92 nm. FTIR spectra detect the ZnO-related vibration modes of the samples. The FESEM morphological images suggest the spherical shape of the synthesized nanoparticles. The EDAX spectra identify the presence of Zn, Ca, and O atoms in the samples. The Raman active modes of the ZnO phase were identified by Raman spectral analysis. The analysis of Photoluminescence (PL) spectra gives information about the UV emission and other visible bands corresponding to violet, blue, and green emission representing different intrinsic defects in synthesized nanoparticles. Using UV-vis spectroscopy, the optical transparency and band gap values were examined. The energy band gap obtained by Tauc’s plot was decreased with the increase in Ca doping. Impedance analysis shows that the grain conductivity increased with the increase in dopant concentration. Contrarily, the total conductivity decreased with the increasing doping concentration due to increased grain boundary resistance. The proposed work demonstrates the changes in microstructure, electrical conductivity, and optical bandgap energy with Ca-doping. These synthesized Ca-doped ZnO nanoparticles could be promising materials for photocatalytic applications.

Onset of Antiferromagnetic Insulator‐to‐Ferromagnetic Half Metal‐to‐Antiferromagnetic Metal Transitions in La1−xCaxCrO3 and their Microscopic Origin

The magnetic ground state of LaCrO3 and CaCrO3 solid solution is investigated in the complete miscibility range, that is, La1−xCaxCrO3 with 0 ≤ x ≤ 1 at the interval of x = 0.25 to understand the magnetic phase transitions with Ca substitutional fraction. The density functional theory is used with Hubbard correction to account for Cr exchange interaction. The isostructural La1−xCaxCrO3 system exhibits antiferromagnetic insulator (x = 0, i.e., LaCrO3) to ferromagnetic half metal (x = 0.75, i.e., La0.25Ca0.75CrO3) to antiferromagnetic metal (x = 1, i.e., CaCrO3) phase transitions. Cr changes its oxidation state from 3+ in LaCrO3 to 4+ in CaCrO3, showing both 3+ and 4+ states for intermediate compositions. Interestingly, the introduction of Hubbard energy U and Ca substitution affects Cr–O hybridization, as observed in partial density of states. A compositional phase diagram with magnetic ground state is presented for the La1−xCaxCrO3 (0 ≤ x ≤ 1) system.

Crystal Structure, Thermal Expansion and Luminescence of Ca10.5−xNix(VO4)7

The structural and luminescence properties of a new material, Ca10.5−xNix(VO4)7, formed by substitution of a fraction of calcium by nickel, are studied as a function of the Ni content (x). The powder X-ray diffraction results for the polycrystals, synthesized using a solid-state reaction method, show that in the studied temperature range (300–1150 K), the structure of the unsubstituted material (space group R3c, whitlockite-β-Ca3(PO4)2 structure type) is conserved up to the solubility limit, x = 0.72(2), determined on the basis of variation of unit cell size with x. The samples of nominal composition exceeding this limit contain a significant amount of the impurity phase.The structural refinements demonstrate that Ni atoms preferentially occupy the M5 site (one of the five independent Ca sites, M1–M5). The unit cell size was equally studied in the range of 300–1150 K, leading to the determination of the thermal expansion coefficients. It was found that with rising Ni content, the room temperature volumetric thermal expansion decreases from 41.80 MK−1 (x = 0.16) to 39.24 MK−1 (x = 0.66) and to 38.92 MK−1 at the solubility limit, this reduction being in line with earlier reported data for x=0. In the unit cell variation, around 800–900 K, a weak anomaly is observed, detectable most clearly for the axial ratio; it is also visible at thermal expansion coefficient temperature dependence. Substitution of Ca by Ni ions reduces the optical band gap of Ca10.5−xNix(VO4)7 from 3.56 (x = 0) to 3.29 and 3.16 eV observed for Ni-containing samples (x = 0.33 and 0.66, respectively). Observed bands in the absorption and photoluminescence spectra are assigned to electronic transitions in both VO43− groups and Ni2+ ions, confirming that Ni mainly occupies the M5 site. The band gap narrowing and decrease in photoluminescence intensity when the Ni concentration increases makes Ni-substituted compounds attractive for application, e.g., as photocatalysts.

Mechanistic study of HER and OER catalyzing performance of Ca incorporated [formula omitted] perovskite: A computational approach

This study investigates the potential for improving the efficiency of hydrogen production via photocatalytic water-splitting by examining the effects of Ca substitution in ultra-wide bandgap KMgO3 perovskite. We used density functional theory to conduct a comprehensive comparative theoretical study of structural, electronic, optical, mechanical, and photocatalytic properties of KMg1−xCaxO3(x=0,0.25,0.50,0.75,1). With increasing Ca concentration, the bandgap gradually decreased from 6.56 eV to 5.31 eV, indicating an ultra-wide bandgap. The reason for this trend was revealed through analysis of the total density of states and elemental partial density of states. Ca inclusion increases thermodynamic stability, as evidenced by the negative formation energy values (x=0(-1.528 eV), x=0.25(-259.601 eV), x=0.5(-243.063 eV), x=0.75(-235.106 eV) and x=1(-222.864 eV)). To explore optical transitions, real and imaginary components of dielectric function are analyzed. These materials' high static values (dielectric constant) make them suitable for optoelectronic applications. All compositions have a dual absorption range (both visible and ultraviolet) while KMg0.75Ca0.25O3 reveal the highest absorption coefficient (α). Remarkable α approaching 105cm−1 in the visible range with the maximum value in the UV region for mixed perovskites (x = 0.25, 0.5, 0.75). Make them an appropriate candidate for harvesting light energy. These compounds exhibit favorable mechanical properties and are elastically anisotropic, which makes them highly desirable for photocatalysis. Further, results showed suitable band edge positions for redox reactions. The photocatalytic activity of the doped materials significantly improved in the visible and ultraviolet irradiation range, which is an essential requirement for photocatalytic energy harvesting. The results support the potential implementation of Ca-incorporated KMgO3 perovskites as they offer the possibility of higher output as energy harvesting materials for HER and OER applications.

Effects of Ca substitution on magnetic and magnetocaloric properties in PrBa1-xCaxMn2O6 system

In this study, we have examined the effect of Ba substitution by Ca on the magnetic, and magnetocaloric properties of PrBa1-xCaxMn2O6 (x = 0, 0.2 and 0.3) double perovskite manganites produced using sol-gel method. The samples were indexed in orthorhombic structure (with space group of Pbnm). The temperature-dependent magnetization, M(T), measurements indicate that all samples have a magnetic phase transition from ferromagnetic (FM) to paramagnetic (PM) state with increasing temperature. Curie temperature (TC) decreases with increasing Ca content in the main lattice. From the magnetic field dependence of magnetization measurements, M(H), maximum magnetic entropy change (−ΔSMmax) values were calculated as 4.07, 4.12, and 5.04 Jkg−1K−1 under 5 T for PrBaCaMn2O6, PrBa0.8Ca0·2Mn2O6, and PrBa0.7Ca0·3Mn2O6 samples, respectively. Relative cooling power (RCP) values below 5 T were determined as 214.16, 227.14 and 279.62 Jkg-1 based on the increasing Ca content. The −ΔSMmax and RCP values enhance with increasing Ca content, respectively. The nature of the phase transition, checked by Banerjee criterion and Franco's universal master curves, was found to be second order magnetic phase transition (SOMT).

Lanthanide and yttrium substitution in natural fluorite

Fluorite is one of the most common minerals in the crust and is of widespread economic importance. It shows strong UV-excited luminescence, variously attributed to defects within the fluorite structure and lanthanide substitutions. We present here a detailed chemical characterisation of a suite of natural fluorite samples, chosen to represent the range of compositions observed in nature. We perform X-ray excited luminescence spectroscopy on the samples as a function of temperature (20–673 K) in the wavelength range 250–800 nm to provide insights into physical defects in the lattice and their interactions with lanthanide substituents in natural fluorite. Most broad bands in the UV are attributed to electronic defects in the fluorite lattice, whereas sharp emissions are attributed to intra-ion energy cascades in trivalent lanthanides. Lanthanides are accommodated in fluorite by substitution for Ca2+ coupled with interstitial F−, O2− (substituting for F−) and a variety of electronic defect structures which provide local charge balance. The chondrite-normalised lanthanide profiles show that fluorite accommodates a greater proportion of heavy lanthanides (and Y) as the total Rare Earth Element (REE) concentration increases; whereas cell parameters decrease and then increase as substitution continues. Luminescence intensity also goes through a maximum and then decreases as a function of REE concentration. All three datasets are consistent with a model whereby lanthanides initially act as isolated centres, but, beyond a critical threshold (~ 1000 ppm), cluster into lanthanide-rich domains. Clustering results in shorter REE-O bond distances (favouring smaller heavier ions), a larger unit cell but more efficient energy transfer between lanthanides, thereby promoting non-radiative energy loss and a drop in the intensity of lanthanide emission.

Composition design of (LaCeCa)1(NiMnAl)5 alloys by uniform design method and their hydrogen storage performance

Rare-earth-based AB5-type alloys are strong candidates for use in solid state hydrogen storage applications; however, their capacity needs to be improved. To efficiently optimize the hydrogen storage performance of AB5-type alloys, the effects of the substitution of Ce and Ca for La (A side) and Mn and Al for Ni (B side) on the structural properties and hydrogenation/dehydrogenation performance of the (LaCeCa)1(NiMnAl)5 alloy series were studied systematically using the uniform design method. X-ray diffraction analysis and scanning electron microscopy showed that all the designed alloys consisted of a single uniform LaNi5 phase. The atomic radii and contents of the constituent elements had a determining effect on the cell volume and properties of the alloys. The maximum hydrogen storage capacity of the (LaCeCa)1(NiMnAl)5 alloy series is approximately 1.7 wt%, which is much higher than the theoretical hydrogen storage capacity of LaNi5 (1.39 wt%).

Luminescence Temperature Sensing and First Principles Calculation of Photoelectric Properties in C12A7 Co-Doped Eu3+ Ions.

Developing high-resolution, high-accuracy fluorescent thermometers is challenging. In this study, the optical properties and thermal sensing of Yb-, Tm-, and Eu-co-doped C12A7 (C12A7:Yb/Eu/Tm), with flower-like structure upconversion microparticles, were studied. Eu3+ doping induced an approximately 6-fold change in the upconversion luminescence (UCL) output in comparison with C12A7:Yb/Tm microparticles. The maximum relative temperature sensitivity (S) of C12A7:Yb/Eu/Tm reached 3.0% K-1, representing an approximately 5-fold difference compared with the value of C12A7:Yb/Tm. In particular, the multicolor upconversion emission of C12A7:Yb/Eu/Tm can easily change from blue to white UCL with increasing temperature. Moreover, the band structure, total density, and optical coefficient of C12A7:Yb/Eu/Tm were investigated via density functional theory. The total density of O atoms increased in comparison with the total density of pure C12A7, indicating that substitution of Ca2+ by Yb/Eu/Tm produced positive vacancies on the cage structure. The optical coefficient of C12A7 was improved by the Yb/Eu/Tm dopant. The thermally regulated multicolor characteristics and thermally coupled energy levels of Tm3+ provide "dual adjustment temperature sensing", which is a promising strategy for realizing accurate and effective temperature sensors.

Magnetic Properties and Magnetocaloric Effect of Polycrystalline and Nano-Manganites Pr0.65Sr(0.35-x)CaxMnO3 (x ≤ 0.3).

Here we report investigations of bulk and nano-sized Pr0.65Sr(0.35-x)CaxMnO3 compounds (x ≤ 0.3). Solid-state reaction was implemented for polycrystalline compounds and a modified sol-gel method was used for nanocrystalline compounds. X-ray diffraction disclosed diminishing cell volume with increasing Ca substitution in Pbnm space group for all samples. Optical microscopy was used for bulk surface morphology and transmission electron microscopy was utilized for nano-sized samples. Iodometric titration showed oxygen deficiency for bulk compounds and oxygen excess for nano-sized particles. Measurements of resistivity of bulk samples revealed features at temperatures associated with grain boundary condition and with ferromagnetic (FM)/paramagnetic (PM) transition. All samples exhibited negative magnetoresistivity. Magnetic critical behavior analysis suggested the polycrystalline samples are governed by a tricritical mean field model while nanocrystalline samples are governed by a mean field model. Curie temperatures values lower with increasing Ca substitution from 295 K for the parent compound to 201 K for x = 0.2. Bulk compounds exhibit high entropy change, with the highest value of 9.21 J/kgK for x = 0.2. Magnetocaloric effect and the possibility of tuning the Curie temperature by Ca substitution of Sr make the investigated bulk polycrystalline compounds promising for application in magnetic refrigeration. Nano-sized samples possess wider effective entropy change temperature (ΔTfwhm) and lower entropy changes of around 4 J/kgK which, however, puts in doubt their straightforward potential for applications as magnetocaloric materials.

Optimal Raman-scattering signal for estimating the Fe3+ content on the clinozoisite–epidote join

Abstract. To provide a tool for fast estimation of the Fe3+ content in Ca2(Al, Fe3+)3Si3O12(OH) epidote grains, including in thin sections and crude-rock samples, we applied Raman spectroscopy to 33 areas from 15 natural samples with Fe3+ ranging from 0.22 to 1.13 atoms per formula unit (apfu), the chemistry of which was independently determined by wavelength-dispersive electron microprobe analysis (WD-EPMA). The Raman spectra were collected from the very areas subjected to WD-EPMA. We have analysed both the OH-stretching region (3215–3615 cm−1) and the spectral range generated by the framework vibrations (15–1215 cm−1). Similarly to the IR spectra, the Raman peaks in the OH-stretching region shift toward higher wavenumbers with increasing Fe. However, the quantification of Fe3+ based on OH-stretching Raman peaks can be hindered by the multicomponent overlapping and significant intensity variations with the crystal orientation. Among the Raman signals generated by framework vibrations, the position of four peaks (near 250, 570, 600, and 1090 cm−1) exhibit a steady linear regression with the increase in Fe content (in apfu). However, the peak near 250 cm−1 attributed to MO6 vibrations also depends on the crystal orientation and therefore is not always well resolved, which worsens the accuracy in Fe-content determination based on its position. The peaks near 570, 600, and 1090 cm−1 arise from Si2O7 vibrational modes, and although their intensities also vary with the crystal orientation, all three signals are well resolved in a random orientation. However, among the three Si2O7-related signals, the 570 cm−1 peak is the sharpest (peak width <10 cm−1) and is easily recognized as a separate peak. Hence, we propose to use the position of this peak as a highly reliable parameter to estimate the Fe content, via the linear trend given as ω570=577.1(3)-12.7(4)x, where ω is the wavenumber (cm−1) and x is Fe content (apfu), with accuracy ± 0.04 Fe3+ apfu. The peaks near 600 and 1090 cm−1 may be complementarily used for the Fe estimate, based on the following relations: ω600=611.6(2)-13.8(4)x and ω1090=1098.8(3)-13.5(5)x. Analyses of the effect of Sr as a substitution for Ca and Cr at the octahedral sites indicate that contents of Sr <0.12 apfu do not interfere with the quantification of Fe via the ω570 (x) relation, whereas Cr >0.16 apfu leads to overestimation of Fe; Cr presence can be recognized however by the broadening of the peaks near 95 and 250 cm−1.

Crystal Structure of Gd(Ca3.319Sr0.681)O[BO3]3 and Gd(Ca2.592Sr1.408)O[BO3]3

AbstractThe structure family of the rare‐earth calcium oxoborates O[BO3]3 (RCOB) has been investigated mainly with regard to their optical characteristics. Due to their monoclinic‐domatic structure they exhibit pyro‐ and piezoelectric properties, which is not dependent on the numerous possible substitutions of the rare‐earth cation site R. The rare‐earth cations are known to show partial disorder with the earth alkaline cation positions X and Z. To study whether a stabilization of the cation occupation is possible without disorder, calcium oxoborates are chemically modified using the Ca substitutes, Sr, Na, Y, Gd on the X and Z positions. No oxoborate phases can be synthesized by coupled substitution of Ca with Sr, Na, and a rare‐earth element. Only with single substitution of Sr the oxoborate phases can be synthesized. It is found that up to 35% Sr can be incorporated into the structure. From the synthesized Gd(CaSrx)O[BO3]3 precursor material, single crystals have been grown and used for the refinement of the first structure model. The structures have been refined in space group . A replacing only of Ca with Sr, mainly on the X position, has been observed. The stoichiometry resulting from the refinement is Gd(Ca3.319Sr0.681)O[BO3]3 and Gd(Ca2.592Sr1.408)O[BO3]3.

Super-stable mineralization of Cu, Cd, Zn and Pb by CaAl-layered double hydroxide: Performance, mechanism, and large-scale application in agriculture soil remediation

The synthesized CaAl-layered double hydroxide (CaAl-LDH) shows excellent performance in potentially toxic metals (PTMs) removal, and the removal capacity of CaAl-LDH toward Cu2+, Zn2+ and Pb2+ in aqueous solution is 502.4, 315.2 and 600.0 mg/g respectively. Cu2+ and Zn2+ are removed through isomorphic substitution of laminate Ca and dissolution-reprecipitation, leading to the formation of CuAl-LDH and ZnAl-LDH mineralization products. Pb2+ is removed by the complexation and precipitation to form Pb3(CO3)2(OH)2. The application of CaAl-LDH in laboratory-scale soil remediation shows that target PTMs are gradually mineralized into relatively stable oxidizable and residual state, and the immobilization efficiency of available Cu, Zn, Cd and Pb reaches 84.62 %, 98.66 %, 96.81 % and 70.27 % respectively. In addition, practical application in farmland results in the significant reduction of available Cu, Zn, Cd and Pb with the immobilization efficiency of 30.15 %, 67.30 % and 57.80 % and 38.71 % respectively. Owing to the super-stable mineralization effect of CaAl-LDH, the content of PTMs in the roots, stems and grains of cultivated buckwheat also decreases obviously, and the growth and yield of buckwheat are not adversely affected but improved. The above prove that the super-stable mineralization based on CaAl-LDH is a promising scheme for the remediation of PTMs contaminated agriculture soil.

Substitution of Ca2+ and changes in the H-bond network near the oxygen-evolving complex of photosystem II.

Ca2+, which provides binding sites for ligand water molecules W3 and W4 in the Mn4CaO5 cluster, is a prerequisite for O2 evolution in photosystem II (PSII). We report structural changes in the H-bond network and the catalytic cluster itself upon the replacement of Ca2+ with other alkaline earth metals, using a quantum mechanical/molecular mechanical approach. The small radius of Mg2+ makes W3 donate an H-bond to D1-Glu189 in Mg2+-PSII. If an additional water molecule binds at the large surface of Ba2+, it donates H-bonds to D1-Glu189 and the ligand water molecule at the dangling Mn, altering the H-bond network. The potential energy profiles of the H-bond between D1-Tyr161 (TyrZ) and D1-His190 and the interconversion between the open- and closed-cubane S2 conformations remain substantially unaltered upon the replacement of Ca2+. Remarkably, the O5⋯Ca2+ distance is shortest among all O5⋯metal distances irrespective of the radius being larger than that of Mg2+. Furthermore, Ca2+ is the only alkaline earth metal that equalizes the O5⋯metal and O2⋯metal distances and facilitates the formation of the symmetric cubane structure.

Crystallographic stability and improved magnetic anisotropy of La0.57Sm0.1Sr0.33−xCaxMnO3 manganites nanoparticles

Herein, we are reporting a systematic study of Sm and Ca substituted La0.57Sm0.1Sr0.33−xCaxMnO3 manganites synthesized by sol–gel method. We kept the concentration of rare-earth Sm ion constant whereas the substitution of Ca cation was varied in the range of x = 0.0, 0.05, 0.1, 0.20 and 0.33. Thermogravimetric/differential thermal analysis was carried out to investigate the thermal stability of the prepared samples. X-ray diffraction (XRD) patterns, transmission electron microscopy (TEM), scanning electron microscopy (SEM) etc. were employed to investigate the crystallographic structure. Rietveld refined XRD analysis confirm the crystallographic stability upon Ca substitution in La0.57Sm0.1Sr0.33MnO3, where no secondary phase was detected. TEM analysis confirmed the particle size in the range of 25–35 nm, grain size obtained by SEM also support the TEM observation. Magnetization of the prepared samples increased with the substation of Ca ions in La0.57Sm0.1Sr0.33MnO3. TG-DTA data was used to investigate the crystallization temperature.

KCoO2-type layered nitrides Ca1-xEuxTiN2: structural stability, electrical properties and Eu coordination chemistry.

Eu2+ was used to substitute Ca in the orthorhombic KCoO2-type layered CaTiN2 to form a Ca1-xEuxTiN2 solid solution, which showed a limited substitution around x = 0.35 with the tetragonality enhanced but the orthorhombic symmetry retained and inaccessibility for the end member EuTiN2. This was in contrast with the full solid solution Ca1-xSrxTiN2, which realized a structural transition from orthorhombic to tetragonal at x = 0.5, even though Eu2+ and Sr2+ ions have similar sizes. The Eu substitution for Ca reduced the dielectric permittivity of CaTiN2 owing to the reduced structural distortion arising from the enhanced tetragonality with the substitution. First-principle theoretical calculations on the total energies and formation energies considering the 4f electrons of Eu ions and the related magnetism were performed to understand the structural stability of the hypothetical EuTiN2. Compared with CaTiN2 and SrTiN2, EuTiN2 has much higher formation energies, making it inaccessible at high temperature. The evolutions of the experimentally observed and calculated lattice parameters of the Ca1-xEuxTiN2 solid solution showed a preference for the orthorhombic phase over the tetragonal phase for the hypothetical EuTiN2, revealing a different coordination chemistry of Eu2+-N to Eu2+-O through the comparison of the structural variations of ATiN2 and ATiO3 (A = Ca, Sr, Eu).

Ca substitution improves the catalytic activity of perovskite LaCoO3 toward toluene: comprehension of electronic structure alteration.

For perovskite La1-xCaxCoO3 (Ca-x, x = 0-0.3), Ca-0.2 with the closest O p band center to the Fermi level, displays the best catalytic activity for toluene oxidation. The O p band center determines the reducibility and active oxygen content. This finding is beneficial for the design of highly active perovskite catalysts.