Compound Sr Research Articles

Computational analysis of the X2H3I (X=Ca or Sr) compounds for hydrogen storage: A DFT approach

Computational analysis of the X2H3I (X=Ca or Sr) compounds for hydrogen storage: A DFT approach

Hydrogen storage potential of XNiH3 (X= Sr and Ba) compounds: A comprehensive DFT analysis

The increasing need for sustainable energy solutions emphasizes the significance of effective hydrogen storage materials. This work provides a thorough analysis using density functional theory (DFT) to assess the capacity of XNiH3 (X = Sr and Ba) compounds, where X denotes strontium (Sr) and barium (Ba), for storing hydrogen. We employed the Cambridge Serial Total Energy Package (CASTEP) approach to optimize the geometries and determine the structural, electrical, optical, and mechanical properties of SrNiH3 and BaNiH3. The findings indicate that SrNiH3 demonstrates a higher gravimetric hydrogen storage capacity (2.03 %) in comparison to BaNiH3 (1.52 %). Both compounds exhibit metallic behavior, characterized by the absence of band gaps, which indicates a high level of electrical conductivity. The optical investigations reveal prominent absorption peaks at 25.32 eV for SrNiH3 and 18.82 eV for BaNiH3, accompanied by substantial energy loss functions and refractive behaviors. Based on mechanical studies, it has been determined that both compounds are mechanically stable. However, SrNiH3 exhibits a larger bulk modulus and Young's modulus compared to BaNiH3. The results highlight the potential of SrNiH3 and BaNiH3 as suitable options for storing hydrogen, which can contribute to the progress of clean energy technology.

Study of the physical properties of the half-heusler XBrH with (X= sr, Ca and mg) compounds

Half-Heusler alloys are among the most promising thermoelectric materials for medium- and high-temperature waste heat recovery applications. This study investigates the physical properties of Half-Heusler compounds XBrH, with X = Sr, Ca, and Mg. We explored the structural, electronic, optical, and thermoelectric properties of these compounds using density functional theory (DFT) as implemented in the Wien2k package. The Generalized Gradient Approximation (GGA) as proposed by Perdew-Burke-Ernzerhof (PBE) and the modified Becke-Johnson (mBJ) functional were employed to calculate the exchange-correlation interactions. After doing structural optimization for a range of parameters, we discovered that the SrBrH compound is more stable than the CaBrH and MgBrH compounds. Our results show that the density of state calculations indicate semiconductor behavior for the XBrH with (X = Sr, Ca, and Mg) compounds. We also evaluated the real and imaginary parts of the dielectric tensor, the refractive index, the absorption coefficient, the electron energy loss, and the real and imaginary components of the optical conductivity, among other optical parameters. Additionally, we investigated the figure of merit (ZT), electronic and lattice thermal conductivity, Seebeck coefficient, and electrical conductivity. The MgBrH, CaBrH and SrBrH compounds showed p-type behavior, with positive values for the Seebeck coefficient and the greatest value of ≈180 μV/K, according to the thermoelectric data. At 1000 K, the ZT reach their highest values for CaBrH, SrBrH, and MgBrH, respectively, at 2.9, 2.8, and 0.9. The physical properties of the XBrH with (X = Sr, Ca, and Mg) compounds have been studied in detail.

First-principles prediction of antimony based XSbF3 (X = Be, Mg, Ca and Sr) fluoroperovskites: An insight into structural, optoelectronic and thermal properties

First-principles computations have been carried out to explore the structural, optoelectronic and thermodynamic characteristics of antimony-based fluoroperovskites XSbF3 (X = Be, Mg, Ca, Sr) compounds. The optimized lattice constants of 4.46, 4.60, 4.72 and 4.81 Å are obtained for BeSbF3, MgSbF3, CaSbF3 and SrSbF3 compounds, respectively. The negative values of the binding energy of these compounds advocate that these compounds are structurally and thermodynamically stable. The electronic properties such as band structures, density of states and partial density of states reveal the metallic character of the studied compounds. Various optical and thermal parameters have been discussed in detail. To the best of our knowledge, this is the first theoretical attempt to study the physical properties of XSbF3 (X = Be, Mg, Ca, Sr) fluoroperovskite compounds. The findings of this study yield useful insights into the potential implementation of these compounds for the development of lenses, anti-reflection coatings and other valuable optoelectronic devices.

Designing tunable emissions and mechanoluminescence in piezoelectric luminescent ions doped oxysulfide compounds by cations substitution for optical sensing

Piezoelectric mechanoluminescent materials capable of directly converting external mechanical stimulation into light are decisive for the development of optoelectronic sensing devices. However, emission spectral modulation is highly demanded for mechanoluminescent materials, which is important for applications. Here, we have doped luminescent ions into the piezoelectric semiconductor oxysulfide compounds (Sr,Ba)ZnOS using the salt-fusion method to form multi-mode emission materials. The prepared luminescent compounds can simultaneously generate photoluminescence and mechanoluminescence for temperature and stress sensing. The tunable photoluminescence can be obtained for multi-color emissions by controlling concentrations of luminescent ions Mn2+ and Er3+. Subsequently, the materials are combined with polydimethylsiloxane matrix to prepare smart mechanoluminescence films for optical sensing. The mechanoluminescence and tunable emissions from prepared film make this luminescent materials promising in the fields of dynamic imaging of force and anti-counterfeiting.

The Divalent Lanthanoid Triflates Ln(CF3SO3)2(CH3CN) (Ln=Sm, Eu): Structure, Luminescence, and Magnetism.

The reaction of the trivalent lanthanoide triflates Ln(OTf)3 (Ln=Sm, Eu; OTf=CF3SO3 -) with the respective metals in acetonitrile leads to the Ln(II)-triflates Eu(OTf)2(CH3CN) (monoclinic, P21/n, Z=4, a=1053.54(1), b=610.28(5), c=1946.92(2) pm, β =98.611(4)) and Sm(OTf)2(CH3CN) (monoclinic, P21/n, Z=4, a=1054.41(4), b=612.16(2), c=1952.65(7) pm, β =98.524(2)). The isotypic strontium compound Sr(OTf)2(CH3CN) (monoclinic, P21/n, Z=4, a=1056.39(5), b=610.05(3), c=1950.1(1) pm, β =98.900(2)°) has been obtained from SrCO3 and triflic acid. The compounds have been investigated by X-ray diffraction, vibrational spectroscopy, luminescence spectroscopy, cyclic voltammetry, thermal analysis, and magnetic measurements.

First-principles quantum analysis of structural, optoelectronic, thermoelectric and thermodynamic properties of niobium-based pyrochlore oxides A2Nb2O7 (A = Ba, Mg, and Sr) for energy harvesting applications

The present study employed first-principles DFT (density functional theory) computations to investigate the impact of alkaline metal substitutions on the structural, optoelectronic, thermodynamic, and thermoelectric characteristics of Nb-based pyrochlore oxides A2Nb2O7 (A = Ba, Mg and Sr). The PBE-GGA model is employed to calculate the fundamental characteristics of Nb-based pyrochlore oxides. An in-depth analysis of the energy band structures reveals that these Nb-based pyrochlore oxides are semiconductor compounds of A2Nb2O7 (A = Ba, Mg, and Sr) reveals that these Nb-based pyrochlore oxides are semiconductors. The energy bandgap values are around 0.6, 3.05, and 1.4 eV for Ba2Nb2O7, Mg2Nb2O7, and Sr2Nb2O7, respectively. Based on the observed ε2(ω) spectra, it is apparent that the A2Nb2O7 (A = Ba, Mg, and Sr) compound, exhibits a significant absorption of incident photons in the near UV region (at approximately 5.0 eV). The calculated values of n(ω) are 1.71, 1.66 and 1.63 for Ba2Nb2O7, Mg2Nb2O7 and Sr2Nb2O7, respectively. The values of ZT are 0.661, 0.998 and 0.996 for Ba2Nb2O7, Mg2Nb2O7 and Sr2Nb2O7, respectively, which make them favourite for TE device applications. The optoelectronic and thermoelectric properties of Nb-based pyrochlore oxides A2Nb2O7 (A = Ba, Mg, and Sr) indicate their potential as favorable contenders for energy-related applications. The elucidated thermodynamic properties reveal that the Nb-based pyrochlore oxides A2Nb2O7 (A = Ba, Mg, and Sr) display a high degree of thermal stability.

Enhancement in the Rate of CO2 Photoreduction Using Divalent Strontium Cation (Sr2+) Doped TiO2 Nanotube Arrays

The sunlight-assisted conversion of CO2 into portable value-added products has the potential to address both the energy and environmental challenges faced by the world. Therefore, we currently witness intense research activity and substantial progress in the field of CO2 photoreduction. Anatase TiO2 nanotube arrays (TNTAs) formed by electrochemical anodization constitute a well studied semiconductor photocatalyst with excellent optoelectronic properties and photocatalytic behavior [1, 2]. Yet, many aspects related to structure, surface composition, adsorbates, reaction intermediates, rate of reaction, multi-step electron transfer steps, etc. remain poorly understood even for TiO2. This led to our interest in forming surface coatings and bulk nanocomposites of TNTAs with metal oxides of Sr, Mg, Ca, Zn etc, which provide basic sites on the surface of the catalyst for the chemisorption of CO2 molecules. The higher basicity of hydroxyl groups associated with alkaline earth metals generate carbonate and bicarbonate adsorbates which enhance the reactivity of CO2 [3]. Divalent metal cations are also known to influence and modify the crystallographic texture of TiO2 during the annealing treatment step at elevated temperature [4].Here we performed divalent strontium cation (Sr2+) doping of anodically grown TNTAs using two different techniques – an electrochemical cathodic treatment in Sr2+-containing electrolytes and a wet impregnation technique using an aqueoussolution of strontium salts. The X-ray diffraction pattern and Raman spectra indicate the formation of Sr compounds at the TNTA surface. Sr-doping results in modification of the crystallographic texture of anatase phase TNTAs, increased lattice strain, reduced crystal size, and phonon confinement. Subtle changes are observed in the infrared spectra of the CO2 adsorbed on the Sr-doped TNTAs specifying a larger prevalence of monodentate and bidentate carbonate species on the surface. This attributes to the higher alkalinity of surface hydroxyls bound to Sr in comparison to the Ti-bound hydroxyls. In addition to linearly adsorbed CO2, a smaller population of bent CO2 molecules on the surface is observed, which suggests an enhanced stabilization of the carbon dioxide anion radical on the Sr-doped TNTA surfaces. Finally, under AM1.5G one sun illumination, the cathodized TNTAs produce 25 µmolg-1hr-1 whilethe wet impregnated Sr-doped TNTAs produce 17 µmolg-1hr-1 of CO which are nearly 3 and 2 times the amount of CO generated by bare TNTAs (7.7 µmolg-1hr-1) respectively.REFERENCES: Vahidzadeh, Ehsan, et al. "Asymmetric multipole plasmon-mediated catalysis shifts the product selectivity of CO2 photoreduction toward C2+ products." ACS Applied Materials & Interfaces13.6 (2021): 7248-7258.Zeng, Sheng, et al. "Optical control of selectivity of high rate CO2 photoreduction via interband-or hot electron Z-scheme reaction pathways in Au-TiO2 plasmonic photonic crystal photocatalyst." Applied Catalysis B: Environmental267 (2020): 118644.Kwon, Stephanie, et al. "Alkaline-earth metal-oxide overlayers on TiO 2: application toward CO 2 photoreduction." Catalysis Science & Technology6.21 (2016): 7885-7895.Kisslinger, Ryan, et al. "Preferentially oriented TiO2 nanotube arrays on non-native substrates and their improved performance as electron transporting layer in halide perovskite solar cells." Nanotechnology30.20 (2019): 204003.

Enhancement in the optoelectronic and thermoelectric properties of the NaASb (A= Ca, Sr and Ba) Sodium Antimonides via switching from P4/nmm to P62 m symmetry

Structural, opto-electronic and thermoelectric properties of square and butterfly like structured NaASb (A = Ca, Sr and Ba) Sodium Antimonides in tetragonal and hexagonal symmetries (P4/nmm and P62 m) are investigated using of density functional theory (DFT). Structural properties are in good agreement with the reported outcomes. Cohesive energy per atom (−8.233 to −26.1004 for P4/nmm and −8.522 to −28.7306 for P62 m symmetry) and enthalpy of formation per atom (−0.9468 to −2.6800 for P4/nmm and −1.1721 to −2.8034 for P62 m symmetry) for these compounds reveals that these compounds are stable in both P4/nmm and P62 m symmetries and are more stable in P62 m space group as compare to P4/nmm symmetry. Electronic properties show that the transition from indirect to direct band gap nature occurs by replacement of Ca/Sr by Ba in P4/nmm symmetry while P62 m symmetry all the NaASb (A = Ca, Sr and Ba) compounds are direct bandgap semiconductors. The band gap values lie in the range of 0–1.393 in P4/nmm symmetry and 0.542 to 1.547, respectively, in P62 m symmetry. Electrical conductivity also reveals the semiconducting characteristics of these compounds. The study shows that the replacement of Ca by Sr and Ba reduces the band gap and the reduction in bandgap values is greater in P4/nmm symmetry as compared to P62 m. The outcome demonstrates that these compounds NaASb (A = Ca, Sr and Ba) are implicitly active optically in the infrared region and are capable of serving as the primary applicant for optoelectronic devices. Thermoelectric properties like Seebeck coefficient (−138.5 to 154.7 μV/K in P4/nmm, −36.5 to −125.3 μV/K in P62 m at 500 K), Power factor (1.33–3.05 GW/mK2s in P4/nmm, 0.152–0.322 GW/mK2s in P62 m at 500 K) and thermoelectric figure of merit ranges from 0.495 to 0.946 in P4/nmm and 0.016 to 0.260 in P62 m at 500 K shows that these compounds are potential candidates for thermoelectric application in P4/nmm symmetry.

Chalcogenide Perovskite Thin Films with Controlled Phases for Optoelectronics

AbstractChalcogenide perovskites have emerged as promising semiconductor materials due to their appealing properties, including tunable bandgaps, high absorption coefficients, reasonable carrier lifetimes and mobilities, excellent chemical stability, and environmentally benign nature. However, beyond the well‐studied BaZrS3, reports on chalcogenide perovskite thin films with diverse compositions are scarce. In this study, the realization of four different types of chalcogenide perovskite thin films with controlled phases, through CS2 annealing of amorphous chalcogenide precursor films deposited by pulsed laser deposition (PLD), is reported. This achievement is guided by a thorough theoretical investigation of the phase stability of chalcogenide perovskites. Upon crystallization in the distorted perovskite phase, all materials exhibit photoluminescence (PL) with peak positions in the visible range, consistent with their expected bandgap values. However, the full‐width‐at‐half‐maximum (FWHM) of the PL spectra varies significantly across these materials, ranging from 99 meV for SrHfS3 to 231 meV for BaHfS3. The difference is attributed to the difference in kinetic barriers between local structural motifs for the Sr and Ba compounds. The findings underscore the promise of chalcogenide perovskite thin films as an alternative to traditional halide perovskites for optoelectronic applications, while highlighting the challenges in optimizing their synthesis and performance.

Robust half-metallic ferromagnet in doped double perovskite Sr2TiCoO6 by rare-earth elements for photovoltaic and thermoelectric conversion: A DFT method

In this study, we have discovered a novel candidate series of half-metals by replacement of the Ti atom with the rare-earth elements RE (=Dy, Ho, Er, or Tm) in the double perovskite Sr2TiCoO6. We methodically investigated the electronic, magneto-optical, and thermoelectric characteristics of the compounds Sr2(RE)CoO6 using the FP-LAPW method. The spin-polarized electronic structure studied within GGA-WC and GGA + U showed a robust half-metallic character for all compounds. The substitution by the rare-earth elements RE enhanced the magnetic characteristics of Sr2TiCoO6, which exhibits a transition from a total magnetic moment of 1μB for Sr2TiCoO6 to 7μB, 6μB, 5μB, and 4μB for Sr2DyCoO6, Sr2HoCoO6, Sr2ErCoO6, and Sr2TmCoO6, respectively. However, the hybridization between RE-4f, Co-3d, and O-2p is responsible for robust half-metallic ferromagnet in Sr2(RE)CoO6 compounds. We have also studied the effect of spin-orbit coupling (SOC) on electronic structure. The Sr2DyCoO6, Sr2HoCoO6, and Sr2ErCoO6 compounds maintained their half-metallicity under GGA + SOC, whereas Sr2TmCoO6 became a magnetic metal. An in-depth analysis of the optical and thermoelectric characteristics was performed by GGA + U. According to the absorption coefficient and imaginary part of the dielectric function, we have found that the compounds Sr2(RE)CoO6 have better absorption quantities at different frequencies (IR, visible, and UV) than Sr2TiCoO6. Due to their high ZT and good Seebeck coefficient in a spin-up canal, the investigated compounds have excellent thermoelectric efficiency. These characteristics make the double perovskites Sr2(RE)CoO6 as a high absorber an attractive choice for photovoltaic solar cells and thermoelectric applications.

DFT-based computational investigations of structural, mechanical, optoelectronics, and thermoelectric properties of InXF3 (X = Be and Sr) ternary fluoroperovskites compounds

Wide-band gap semiconductors are very interesting due to their high frequency applications. Perovskite have proved to be most stable structures useful for many applications e.g. solar cells detectors etc The current work is based on the prediction of two new materials (InXF3 where X = Be and Sr) for the use of high energy applications. The modelling and simulations were performed through the WIEN2K and BoltzTrap2 packages. The most accurate and precise exchange-correlation of TB-mBJ potential interfaced within WIEN2K is utilized for obtaining better results. The results showed that the selected compounds possess a cubic crystal structure with a space group of Pm-3m (#221). The Goldschmidt’s tolerance factor (τ) is determined and is found to be 0.96 for InBeF3 and 0.92 for InSrF3 which indicates the stability of the compounds in cubic phase. The unit cell crystal structural optimization is done to evaluate the ground state lattice parameters. Both the compounds possess a semiconducting nature having an indirect band gap of 3.06 eV for InBeF3 from M-X symmetry points while a direct band gap from X-X of 3.98 eV for InSrF3 compound. The optical properties are computed and analyzed from the optical dielectric function for both the compounds within the energy range of 0 eV to 40 eV and the results depict that these materials are more sensitive at higher energy range, possess high absorption and optical conductivity in good agreement with electronic band structure. Mechanically these compounds are stable, ductile, anisotropic, and hard to scratch. The thermoelectric properties are evaluated for InXF3 (X = Be and Sr) compounds up to a temperature range of 1000 K. This work can open new opportunities for further exploration in this field.

Mixed ligand approach for novel hydrazide copper(II) complexes: Structural aspects, theoretical investigation and their biological evaluation

In this paper, two novel Cu(II) complexes [CuL(S‐1‐amino‐2‐propanol)](R1)and [CuL(S‐2‐amino‐1‐propanol)](R2)have been synthesized and characterized using Fourier transform infrared (FT‐IR), thermogravimetric analysis (TGA), high‐resolution mass spectrometry (HR‐MS), scanning electron microscopy (SEM) and single crystal X‐ray diffraction (SCXRD) technique. The single‐crystal XRD analyses show that compoundsR1andR2crystallized in triclinic and monoclinic crystal systems with P‐1 and P21space groups, respectively. The τ5 parameter values of R1 and R2 confirmed distorted square pyramidal geometry around Cu(II) centre. The compoundsR1andR2possess 2D polymeric chains with(4,4)IIIaand2C1topology, respectively. The non‐covalent interactions and electrostatic properties were investigated using Hirshfeld surface analysis and density functional theory (DFT). DFT calculations revealed higher stability ofR1overR2. The presence of strong hyper conjugative interactions in carbon–carbon and carbon–nitrogen bonds has been confirmed by natural bond orbital (NBO) analysis. Time‐dependent (TD)‐DFT calculations were also performed to determine the excited state properties. Based on theoretical calculations, the simulated spectra showed absorption maxima at 506 and 743 nm for both complexes. Antimicrobial assays revealed that R1 is significantly antimicrobial againstPseudomonas aeruginosaat 512 and 256 μg/mL forStaphylococcus aureus, correspondingly. Serum binding studies ofR1confirm the existence of instinctive bonding interactions due to negative values on account of ∆G, ∆S and ∆H obtained from thermodynamics studies. In silico molecular dynamics and docking approaches have been used to validate the experimental findings of anti‐microbial assay and serum binding studies. A high dock score for R1 over R2 revealed the high binding energy of the former with bacterial protein. It was found that the protein‐ligand complex remained stable throughout the dynamic simulation process, and substantial interactions between R1 and bovine serum albumin were observed.

Structures and hydrogen storage properties of AeVH3 (Ae = Be, Mg, Ca, Sr) perovskite hydrides by DFT calculations

The capability of hydrogen to be an energy source has made the hydrogen storage as one of the most investigated research fields during the recent years, and novel perovskite materials have become the current focus for hydrogen storage applications. Here we study the AeVH3 (Ae = Be, Mg, Ca, Sr) perovskite-type hydrides to explorer their potential for hydrogen storage applications using the density functional theory (DFT) implemented CASTEP code along with exchange correlation potential. The study examines the electronic structure, optical properties, elastic features and mechanical stability of the materials. The crystal structure of AeVH3 compounds is found to be cubic with lattice constant as 3.66, 3.48, 3.76 and 3.83 for Ae = Be, Mg, Ca and Sr compounds, respectively. The calculated electronic structures of these compounds show ionic bonding and no energy bandgap. The mechanical characteristics of compounds are also investigated as to meet the Born stability criterion, these compounds should be mechanically stable. The Cauchy pressure and Pugh criteria revealed that these materials have a brittle character and rather hard. In low energy range, all optical properties are found to be suitable as needed for storing the hydrogen. Furthermore, the gravimetric ratios suggested that all the compounds are suitable for hydrogen storage as a fuel for a longer time and may provide remarkable contributions in diversity of power and transportation applications.

Recent Advance of Strontium Functionalized in Biomaterials for Bone Regeneration.

Bone defect disease causes damage to people's lives and property, and how to effectively promote bone regeneration is still a big clinical challenge. Most of the current repair methods focus on filling the defects, which has a poor effect on bone regeneration. Therefore, how to effectively promote bone regeneration while repairing the defects at the same time has become a challenge for clinicians and researchers. Strontium (Sr) is a trace element required by the human body, which mainly exists in human bones. Due to its unique dual properties of promoting the proliferation and differentiation of osteoblasts and inhibiting osteoclast activity, it has attracted extensive research on bone defect repair in recent years. With the deep development of research, the mechanisms of Sr in the process of bone regeneration in the human body have been clarified, and the effects of Sr on osteoblasts, osteoclasts, mesenchymal stem cells (MSCs), and the inflammatory microenvironment in the process of bone regeneration have been widely recognized. Based on the development of technology such as bioengineering, it is possible that Sr can be better loaded onto biomaterials. Even though the clinical application of Sr is currently limited and relevant clinical research still needs to be developed, Sr-composited bone tissue engineering biomaterials have achieved satisfactory results in vitro and in vivo studies. The Sr compound together with biomaterials to promote bone regeneration will be a development direction in the future. This review will present a brief overview of the relevant mechanisms of Sr in the process of bone regeneration and the related latest studies of Sr combined with biomaterials. The aim of this paper is to highlight the potential prospects of Sr functionalized in biomaterials.

Emergence of bond-dependent highly anisotropic magnetic interactions in Sr4RhO6 : A theoretical study

The quantum spin liquid states as a natural ground state of the Kitaev model has led to a quest for new materials candidates hosting Kitaev physics. Yet, there are very few material candidates in this category. Using a combination of $ab$ $initio$ and model Hamiltonian methods, we propose that Ruddlesden-Popper compound Sr$_4$RhO$_6$ belongs to this category. With a tight-binding model and exact diagonalization approach, we show that despite substantial trigonal-like distortion, the electronic and magnetic properties of Sr$_4$RhO$_6$ can be well described in terms of pseudo-spin = 1/2 states. Magnetic interactions among pseudo-spins, estimated using the second-order perturbation method are highly bond-dependent anisotropic in nature with two particularly noticeable features, antiferromagnetic Kitaev and Dzyaloshinskii-Moriya interactions. The gaped spin-wave spectra of Sr$_4$RhO$_6$ obtained with linear spin-wave theory is consistent with the underlying magnetic frustration. Additional analysis of the role of individual or a particular combination of magnetic interactions reveals that the spin-wave spectra of Sr$_4$RhO$_6$ is a combined effect of the highly anisotropic interactions and a relatively simpler minimal model may not be plausible in the current case. The crucial insights about coupling between the local structural features and magnetic properties of Sr$_4$RhO$_6$ obtained in this study may be helpful for future studies belonging to this class.

Investigation on the crystal structure and mechanical properties of the ternary compound Mg11-xZnxSr combined with experimental measurements and first-principles calculations

A new ternary compound, Mg 11-x Zn x Sr in the Mg-Zn-Sr system was observed and studied using Scanning Electron Microscopy (SEM), Energy-Dispersive Spectroscope (EDS), X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The XRD patterns were refined by the Rietveld refinement method and the results revealed that the crystallized Mg 11-x Zn x Sr phase belonged to tetragonal I41/amd space group and had the Cd 11 Ba prototype. The Mg atoms were successfully doped into Zn 11 Sr crystal lattice by occupying Zn atomic sites. Moreover, the Rietveld refinement and computational results demonstrated a gradual decrease in the a- axis and c -axis lattice parameters with decreasing concentration levels of Mg coordination substitution in the lattice of Mg 11-x Zn x Sr compound. The elastic constants and modulus of the Mg 11-x Zn x Sr compounds calculated by first-principles calculations (FPC) indicated they were increased with the increasing of Zn content. The variation of hardness, d -band widths and the total density of states for Mg 11-x Zn x Sr compounds with Zn content was discussed.

First-principles study of structural, elastic, electronic and optical properties of cubic perovskite AgXF3 (X = Be, Mg, Ca and Sr) compounds

The structural, elastic, electronic and optical properties of cubic fluoroperovskite crystal AgXF3 (X=Be, Mg, Ca and Sr) were studied using the first-principles method. The optimized lattice constant a0 increases by varying the cation from Be to Sr, which is consistent with previous reports. The calculations of electronic band structure show that AgBeF3, AgMgF3 and AgCaF3 have indirect band gaps, while AgSrF3 has direct band gaps. The band gaps of AgBeF3, AgMgF3, AgCaF3 and AgSrF3 are 1.820, 1.901, 2.074 and 1.795 eV, respectively, which all exhibit semiconducting properties. It is further found that as the cation changes from Be to Sr, the top of the valence band approaches the Fermi level. The nature of chemical bonds in these compounds is discussed by the electron localization function. The optical properties of AgXF3 (X=Be, Mg, Ca and Sr), including the reflectance, absorption, refractive index, dielectric function, conductivity and loss function have been studied, and the wide range of absorption energies makes these materials promising for significant applications in semiconductor fields.

Improved capacitive energy storage in sodium niobate-based relaxor antiferroelectric ceramics

Ceramic-based dielectric capacitors have become an attractive issue due to their wide applications in current pulsed-/high-power electronic devices. Antiferroelectric ceramics generally exhibit ultrahigh energy density owing to their giant polarization activated by antiferroelectric–ferroelectric phase transition under a high electric field but suffer from large hysteresis, meanwhile giving rise to low efficiency. Herein, by introducing perovskite compound Sr(Fe0.5Ta0.5)O3 into an antiferroelectric NaNbO3 matrix, a stabilized antiferroelectric phase and an improved relaxor behavior are observed. That is, relaxor antiferroelectric ceramics are constructed. Accordingly, a double polarization–electric field (P–E) loop becomes slimmer with increasing incorporation of dopants, leading to an ultrahigh recoverable energy density of 11.5 J/cm3, an energy storage efficiency of 86.2%, outstanding frequency/cycling/thermal reliability, and charge–discharge properties in 0.90NaNbO3-0.10Sr(Fe0.5Ta0.5)O3 ceramics. This work reveals that inducing the relaxor behavior in antiferroelectric materials is an effective route to improve their capacitive energy storage.

Synthesis and Structure of Heterometallic Compounds with Dimethyl Pyridine-2,6-dicarboxylate

Dimethyl pyridine-2,6-carboxylate (L) was prepared by refluxing pyridine-2,6-dicarbonyl dichloride in methanol. The reactions of L with Ca(II), Sr(II), and Ba(II) salts and with cobalt(II) thiocyanate resulted in the formation of three heterometallic complexes: [CaL3][Co(NCS)4] (I), [SrL3][Co(NCS)4] (II), and [BaCoL3(μ-NCS)2(NCS-κN)2] (III). The composition and structure of compounds L and I–III were determined by elemental analysis, infrared spectroscopy, and X-ray diffraction (CCDC nos. 2166019–2166022, respectively). It was found that isostructural Ca(II) and Sr(II) compounds are ionic and are formed by the [CaL3]2+ and [SrL3]2+ complex cations and [Co(SCN)4]2– complex anion, while the Ba(II) derivative is a molecular complex in which [BaL3]2+ and [Co(NCS)4]2– moieties are linked by two (NCS)– bridging units of the complex anions. In any of the three compounds, three tridentate L ligands are coordinated to the alkaline earth metal ion.