Metal Ion Substitution Research Articles

Exchange-coupled α-Fe/Fe3O4 bi-magnetic nanoparticles with non-core/shell morphology formed by eutectoid decomposition of FeO nanoparticles

A new approach to fabricating ferrite-based bi-magnetic nanoparticles with non-core/shell morphology, generated by a lamella-based phase separation process induced by the eutectoid reaction, is presented. The fabrication process is based on the eutectoid decomposition of chemically synthesized FeO nanoparticles into a nanoscale mixture consisting of a ferromagnetic metal (α-Fe) and a ferrimagnetic spinel ferrite (Fe3O4). It was found that decomposition of FeO was almost fully completed after annealed at 673 K for 1 h in an inert atmosphere. The room-temperature magnetization measurements gave rise to smooth curves with single-phase-like behavior despite the coexistence of two magnetic phases, suggesting that the two magnetic phases could be magnetically exchange-coupled. Since the substitution of constituent metal ions can tune the magnetic properties of the spinel ferrites, the fabrication process described here is expected to provide a potential route to making various kinds of iron-based alloy/ferrite bi-magnetic nanoparticles.

DFT study of ferric ion interaction with passive layer on chalcopyrite surface: Elemental sulfur, defective sulfur and replacement of M2+(M=Cu and Fe) ions

The acidic dissolution of chalcopyrite in the sulfated medium is dependent on the rate of ferric (F3+) ion reduction. Due to the formation of elemental sulfur passive layer on the chalcopyrite surface, the ferric ion reduction rate decreases at the surface and prevents electron transfer from the surface to ferric ion. In this research, the interaction of ferric ion with sulfur passive layer in different modes has been studied using studio material software and density functional theory method. The results showed that the sulfur passive layer is insulated and ferric ion does not react on this surface, but the layer can be activated by changes in the structure. Defects in the passive layer structure (removal of sulfur atoms) or substitution of metal ions (iron and copper) cause surface reactivity, which by interaction with ferric ion will result in electron transfer to 3d orbital of Fe3+ ion. The overlap of 3p orbital surface sulfur atoms and the 3d orbital ferric ion conduction band provide the conditions for electron transfer. Also, the Fe3+ ion adsorption energies for different surface states, structure defects; ferrous and cupric ions substitution were obtained at −244, −229 and −228 kcal/mol, respectively. In addition, energy change (ΔE) due to the reduction of Fe3+ ion for structure defects more than the other two surfaces.

Effects of alkaline earth metal elements and their synergistic roles with Ta for Li7La3Zr2O12

Effects of alkaline earth metal elements and their synergistic roles with Ta for the modified Li7La3Zr2O12 (LLZO) are discussed. Li7.1La3Zr1.95M0.05O12 (M = Mg, Ca, Sr, Ba) with the substitution of alkaline earth metal ions for Zr4+ and Li6.5La3Zr1.35Ta0.6M0.05O12 (M = Mg, Ca, Sr, Ba) with the co-substitution of alkaline earth metal ions and Ta5+ for Zr4+ are prepared. The sole substitution of alkaline earth metal elements for Zr in LLZO have little effects on improving ionic conductivity, while the modified LLZO with synergistically co-doping Ta and alkaline earth metal elements can achieve the great enhancement of ionic conductivity. The order of ionic conductivity influenced by Ta5+ and alkaline earth metal ions (Mg2+, Ca2+, Sr2+, Ba2+) co-substitution for Zr4+ demonstrates a strong correlation with ionic radii of Mg2+/Ca2+/Sr2+/Ba2+. Particularly, the enhanced Li6.5La3Zr1.35Ta0.6Mg0.05O12 with the joint substitution of Mg and Ta delivers a highest ionic conductivity of 3.45 × 10−4 S cm−1 at room temperature.

Signature of Oxide-Ion Conduction in Alkaline-Earth-Metal-Doped Y3GaO6.

We have studied alkaline-earth-metal-doped Y3GaO6 as a new family of oxide-ion conductor. Solid solutions of Y3GaO6 and 2% −Ca2+-, −Sr2+-, and −Ba2+-doped Y3GaO6, i.e., Y(3–0.06)M0.06GaO6−δ (M = Ca2+, Sr2+, and Ba2+), were prepared via a conventional solid-state reaction route. X-ray Rietveld refined diffractograms of all the compositions showed the formation of an orthorhombic structure having the Cmc21 space group. Scanning electron microscopy (SEM) images revealed that the substitution of alkaline-earth metal ions promotes grain growth. Aliovalent doping of Ca2+, Sr2+, and Ba2+ enhanced the conductivity by increasing the oxygen vacancy concentration. However, among all of the studied dopants, 2% Ca2+-doped Y3GaO6 was found to be more effective in increasing the ionic conductivity as ionic radii mismatch is minimum for Y3+/Ca2+. The total conductivity of 2% Ca-doped Y3GaO6 composition calculated using the complex impedance plot was found to be ∼0.14 × 10–3 S cm–1 at 700 °C, which is comparable to many other reported solid electrolytes at the same temperature, making it a potential candidate for future electrolyte material for solid oxide fuel cells (SOFCs). Total electrical conductivity measurement as a function of oxygen partial pressure suggests dominating oxide-ion conduction in a wide range of oxygen partial pressure (ca. 10–20–10–4 atm). The oxygen-ion transport is attributed to the presence of oxygen vacancies that arise from doping and conducting oxide-ion layers of one, two-, or three-dimensional channels within the crystal structure. The oxide-ion migration pathways were analyzed by the bond valence site energy (BVSE)-based approach. Photoluminescence analysis, dilatometry, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy studies were also performed to verify the experimental findings.

Substitution of the Native Zn(II) with Cd(II), Co(II) and Ni(II) Changes the Downhill Unfolding Mechanism of Ros87 to a Completely Different Scenario.

The structural effects of zinc replacement by xenobiotic metal ions have been widely studied in several eukaryotic and prokaryotic zinc-finger-containing proteins. The prokaryotic zinc finger, that presents a bigger βββαα domain with a larger hydrophobic core with respect to its eukaryotic counterpart, represents a valuable model protein to study metal ion interaction with metallo-proteins. Several studies have been conducted on Ros87, the DNA binding domain of the prokaryotic zinc finger Ros, and have demonstrated that the domain appears to structurally tolerate Ni(II), albeit with important structural perturbations, but not Pb(II) and Hg(II), and it is in vitro functional when the zinc ion is replaced by Cd(II). We have previously shown that Ros87 unfolding is a two-step process in which a zinc binding intermediate converts to the native structure thorough a delicate downhill folding transition. Here, we explore the folding/unfolding behaviour of Ros87 coordinated to Co(II), Ni(II) or Cd(II), by UV-Vis, CD, DSC and NMR techniques. Interestingly, we show how the substitution of the native metal ion results in complete different folding scenarios. We found a two-state unfolding mechanism for Cd-Ros87 whose metal affinity Kd is comparable to the one obtained for the native Zn-Ros87, and a more complex mechanism for Co-Ros87 and Ni-Ros87, that show higher Kd values. Our data outline the complex cross-correlation between the protein–metal ion equilibrium and the folding mechanism proposing such an interplay as a key factor in the proper metal ion selection by a specific metallo-protein.

Vanadyl Phosphates AxVOPO4 (A = Li, Na, K) as Multielectron Cathodes for Alkali‐Ion Batteries

AbstractVanadyl phosphates comprise a class of multielectron cathode materials capable of cycling two Li+, about 1.66 Na+, and some K+ ions per redox center. In this review, structures, thermodynamic stabilities, and ion diffusion kinetics of various AxVOPO4 (A = Li, Na, K, NH4) polymorphs are discussed. Both the experimental data and first‐principle calculations indicate kinetic limitations for alkali metal ions cycling, especially between for 0 ≤ x ≤ 1, and metastability of phases with x > 1. This creates challenges for multiple‐ion cycling, as the slow kinetics call for nanosized particles, which being metastable and reactive with organic electrolytes are prone to side reactions. Thus, various synthesis approaches, surface coating, and transition metal ion substitution strategies are discussed here as possible ways to stabilize AxVOPO4 structures and improve alkali metal ion diffusion. The role of advanced characterization techniques, such as X‐ray absorption spectroscopy, diffraction, pair distribution function analysis and 7Li and 31P NMR, in understanding the reaction mechanism from both structural and electronic points of view is emphasized.

Relationship of Various Structural Parameters with Magnetic Behavior of Stoichiometric Tb3+ and Dy3+ Co-substituted NiFe2O4 Nanostructures

In this study, we have successfully controlled the structural parameters of NiFe2-x-y TbxDyyO4 (x + y = 0, 0.1, 0.15, 0.2) of nickel ferrites with the substitution of rare earth metal ions (RE3+ = Tb3+, Dy3+) in order to optimize the magnetic properties. XRD reflections had ensured phase purity and single phase of FCC structure formation for all synthesized samples with no additional impurity peaks. It was found that crystallite size and lattice parameters are found to decrease from 28.13 to 25.2 nm and 8.43 to 8.41 A, respectively, with increasing the amount of dopant ions. The magnetic parameters for NiFe2-x-yTbxDyyO4 (x + y = 0, 0.1, 0.15, 0.2) were measured by tracing the hysteresis curves for all synthesized samples at room temperature. VSM data suggested a decrease in magnetization which is attributed to increase in spin disorder due the decrease of crystallite size which was associated with increase in contents of Tb3+, Dy3+ ions in the host structure. Higher dopant concentrations have greatly reduced coercivity and improve initial permeability. Hence, size and shape of particles are the key features which govern the stability and magnetic properties of ferrite nanoparticles.

Soft magnetic properties of Co–Ni–Fe–Gd/Cu electrodeposited thin film

In this study, Co–Ni–Fe–Gd alloy thin films were coated on the copper substrate with a deposition time of 30 min at room temperature and pH 7. Composition, surface morphology and magnetic behavior of electrodeposited Co–Ni–Fe–Gd/Cu thin film are investigated in comparison with Co–Ni–Gd/Cu and Co–Fe–Gd/Cu thin film. Co–Ni-Gd/Cu thin film is the source of the smallest particle size and soft ferromagnetism with low coercivity. The spherical morphology of the deposited thin films were explored with scanning electron microscope (SEM) and the particle size is found to be smallest for Co–Ni–Gd/Cu thin film. Fourier transform infrared spectroscopy validated the functional group and substitution of metal ions in the thin films. X-ray diffraction and EDAX spectrum confirm the structure and composition of metal ions.

The Effects of the Metal Ion Substitution into the Active Site of Metalloenzymes: A Theoretical Insight on Some Selected Cases

A large number of enzymes need a metal ion to express their catalytic activity. Among the different roles that metal ions can play in the catalytic event, the most common are their ability to orient the substrate correctly for the reaction, to exchange electrons in redox reactions, to stabilize negative charges. In many reactions catalyzed by metal ions, they behave like the proton, essentially as Lewis acids but are often more effective than the proton because they can be present at high concentrations at neutral pH. In an attempt to adapt to drastic environmental conditions, enzymes can take advantage of the presence of many metal species in addition to those defined as native and still be active. In fact, today we know enzymes that contain essential bulk, trace, and ultra-trace elements. In this work, we report theoretical results obtained for three different enzymes each of which contains different metal ions, trying to highlight any differences in their working mechanism as a function of the replacement of the metal center at the active site.

Pentanuclear Scaffold: A Molecular Platform for Small-Molecule Conversions.

Small-molecule conversions involving multielectron transfer processes enable the conversion of earth-abundant materials into valuable chemicals and are regarded as a solution for environmental and energy shortage problems. In this context, the development of artificial catalysts that promote these reactions is an important research target. In nature, metalloenzymes that contain multinuclear metal complexes as active sites are known to efficiently catalyze reactions under mild conditions. Therefore, using multinuclear metal complexes as artificial catalysts can be an attractive strategy for small-molecule conversions involving multielectron transfer processes. However, multinuclear-metal-complex-based catalysts for these reactions have not been well established. In this Account, we describe our recent advances in the development of multinuclear metal complexes as catalysts for small-molecule conversion, mainly focusing on water oxidation. As small-molecule conversions involving multielectron transfer processes consists of two essential processes, (1) the transfer of multiple electrons and (2) the formation/cleavage of covalent bond(s), catalysts for these reactions should facilitate both steps. Therefore, we assumed that the assembly of redox-active metal ions and the cooperative effect of neighboring coordinatively unsaturated metal ions can promote these processes. On the basis of this assumption, we employed a pentanuclear metal complex as a molecular scaffold for the catalyst. The scaffold has a pentanuclear structure with quasi-D3 symmetry and consists of a [M3(μ3-X)] core (X = O2- or OH-) wrapped by two [M(μ-bpp)3] units (Hbpp = 3,5-bis(2-pyridyl)pyrazole). The metal ions in the triangular core are coordinatively unsaturated, whereas the metal ions at the apical positions are coordinatively saturated. In other words, the pentanuclear scaffold possesses multiple redox-active centers and coordinatively unsaturated sites. It should also be noted that the electron transfer ability of the complex changes dramatically depending on the identity of the constituent metal ions. The iron derivative of the pentanuclear scaffold was found to serve as an electrocatalyst for water oxidation (2H2O → O2 + 4e- + 4H+) with a high reaction rate and excellent robustness. The substitution of metal ions in the pentanuclear scaffold to cobalt ions resulted in the development of a catalyst for CO2 reduction. Furthermore, we investigated the effect of substituents on the ligands of the pentanuclear iron complex and succeeded in precisely manipulating the electron transfer possess. These results clearly demonstrate that the pentanuclear scaffold is an attractive platform for catalysts for small-molecule conversions. Additionally, the intrinsic features of the multinuclear catalytic system, which are totally different from those of conventional mononuclear-metal-complex-based catalysts, are disclosed. In reactions mediated by multinuclear complexes, the multinuclear core can initially accumulate the charge required for catalysis to reach the catalytically active state. Subsequently, the catalyst in the active state reacts with the substrate, initiating electron transfer to the substrate and rearrangement of covalent bonds in the substrate to afford the product. In such a mechanism, the desired number of electrons can be transferred to the substrates in an on-demand fashion, and the formation of undesired chemical species in the targeted catalysis may be prevented. This feature of multinuclear-metal-complex-based catalysts will achieve demanding small-molecule conversions with a high reaction rate, selectivity, and durability.

Effect of divalent metal ions substitution on structural and magnetic properties of Li0.25Mn0.5-xMxFe2.25O4 (M = Co2+, Ni2+, Cu2+) spinel ferrites

In the existing study, substitution of different divalent metal ions in Li0.25Mn0.5-xMxFe2.25O4 (where, M = Co2+, Ni2+, Cu2+; x = 0.0, 0.1, 0.3 and 0.5) was performed to improve the magnetic properties. Their structural and magnetic features were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). XRD analysis proved the presence of single phase cubic spinel structure in all prepared compositions. The lattice parameter decreased linearly with increasing doping concentrations. The crystallite size values vary from 60 to 101 nm. VSM studies revealed that saturation magnetization values of Li0.25Mn0.5-xMxFe2.25O4 were strongly affected by different metal ions substitutions, which is credited to the cationic arrangement on the lattice sites. The change in the magnetization with metal substitution was discussed by using Neél's two-sublattice model. Among the three investigated series, Li0.25Mn0.5-xCoxFe2.25O4 ferrite revealed a synergistic effect in improving the magnetic properties making it suitable for applications in microwave devices and magnetic recording media. The initial permeability μi was measured at elevated temperatures from 300 up to 890 K. The composition Li0.25Mn0.4Ni0.1Fe2.25O4 gave the highest value of initial permeability, indicating the material potential utility in TV deflection yokes. Curie temperature increased with the replacement of manganese ions by different metal ions. In general, the replacement of different divalent transition metal ions plays an important role in changing the structural and magnetic properties of Li0.25Mn0.5Fe2.25O4 ferrites.

Construction of Ta-Cu7S4 negative electrode for high-performance all-solid-state asymmetric supercapacitor

Constructing electronic structure of the electrode materials is an effective approach to enhance the electrochemical activity. The substitution of high-valence metal ions can optimize the electronic structure of host materials. And there are few reports using this way to enhance supercapacitor performances. Herein, the isomorphous replacement by tantalum in Cu7S4 (Ta-Cu7S4) materials were fabricated by hard-template method and designed as negative electrode materials for solid-state supercapacitor (SSC). The unique hollow structure increased the specific areas of active materials and enabled the effective contact between electrode and electrolyte. Density functional theory (DFT) calculations indicate that the replacement of Ta element optimized the electronic structure, endowing the Ta-Cu7S4 with good electrical conductivity and more active sites. Moreover, the Ta element acted as an ‘electron reservoir’, which decreased the adsorption energy of OH– on the surface of electrode material, carried the electron to trigger redox reaction on Cu active sites continuously. These factors resulted the obtained Ta-Cu7S4 exhibited the excellent supercapacitor performances. When used as a negative electrode material, the Ta-Cu7S4 had an outstanding specific capacitance (675F g−1 at 1 A g−1) and good rate capacity (363.1F g−1 at 10 A g−1). In addition, the assembled SSC showed high energy density (111.1 Wh kg−1 at power density of 800 W kg−1) and long-term cyclic stability of retaining 83.3% after 5000 charge/discharge cycles. This work reports a low-cost and efficient Cu7S4-based supercapacitor material by Ta incorporating, and infer this new strategy can be used in other energy storage application devices.

The Influence of Various Divalent Metal Ions (Mn2+, Co2+, and Cu2+) Substitution on the Structural and Magnetic Properties of Nickel–Zinc Spinel Ferrite

Ni0.7 – xZn0.3MxFe2O4 (M = Mn2+, Co2+, and Cu2+; x = 0, 0.1, 0.3, 0.5, and 0.7) spinel-type ferrite were fabricated through citrate technique. The X-ray diffraction analysis disclosed the creation of the cubic phase spinel structure in all prepared samples, except for the high concentration of Mn (x = 0.7). As the concentration of dopant ions increased, the structural parameters, such as lattice constant, particle size, X‑ray density, bulk density, and percentage porosity showed interesting changes. The experimental lattice parameter was found in the range from 0.839 to 0.843 nm for the three investigated series. The average particle size ranged from 52 to 107 nm. The density decreased with the addition of Mn and Co, while it improved considerably with the increment of Cu content. Besides, the percentage porosity for Ni–Zn–Cu ferrite was lower than those for the Ni–Zn–Mn and Ni–Zn–Co ferrite series. Several magnetic properties were studied at room temperature. Magnetization curves were measured in the range of magnetizing field up to 6000 A m–1. The magnetization was studied at a constant magnetic field (4500 A m–1) and it was found to rise with Mn2+ ions content up to x = 0.3 followed by a subsequent decline at x = 0.5. Furthermore, a monotonic decrease in the magnetization was observed by the incorporation of Co into Ni–Zn ferrite, while an increase was noticed for Cu-substituted samples. Among the three investigated series, the Ni–Zn–Cu ferrite series exhibited the highest magnetization, making it appropriate for high-density recording media. The initial permeability (μi) was studied as a function of temperature for all samples. The Curie temperature TC was estimated from the μi(T) plot and was determined to decrease with the upsurge in the content of substitute ions (Mn2+, Co2+, and Cu2+).

Broadband free space impedance in Co2Z hexaferrites by substitution of high valency heavy transition metal ions for miniaturized RF devices

Polycrystalline samples of Z-type hexaferrites, having nominal compositions Ba3Co2+xFe24−2xMxO41, where M = Ir, Hf, or Mo and x = 0 and 0.05, were processed via ceramic protocols in pursuit of low magnetic and dielectric losses, as well as equivalent permittivity and permeability over the VHF–UHF band. Fine process control was conducted to ensure optimal magnetic properties. Organic dispersants, i.e., isobutylene and maleic anhydride, were employed to achieve maximum densities. Crystallographic structure, characterized by x-ray diffraction, revealed that the dopants did not adversely affect the crystal structure and phase purity of the Z-type hexaferrite. An increase in permeability and size reduction factor is shown to be linearly proportional to the ionic radii of the dopants. This trend is consistent with local bonding distortions giving rise to increased exchange energy (J) as predicted by the Goodenough–Kanamori–Anderson rules and superexchange theory. We posit that these distortions increase the magnetocrystalline anisotropy energy affecting the frequency dependent complex permeability. For Mo doping of x = 0.05, a bandwidth of 400 MHz exists at a center frequency of 650 MHz where the permittivity and permeability are very nearly equal, i.e., Z = 377 ± 5 Ω. These results give rise to low loss, i.e., tan δε/ε′ = 0.0006 and tan δμ/μ′ = 0.038 at 650 MHz, with considerable size reduction (×9). The miniaturization and optimized performance of magnetodielectric materials for antenna at VHF–UHF frequencies using cost-effective and volumetric processing methodologies are demonstrated.

Fission isotope release kinetics and its sorption on insitu formed MnO2 during the dissolution of fission isotope substituted chromium oxide in HMnO4

Fission isotopes contribute approximately 10% of the total radioactivity removed from the heat transport circuit of reactor systems during the chemical decontamination process. Simulated corrosion products (SCP) (CrFeO3 and MxCrFe1−xO3) and with fission isotope substituted in SCP [MxNiCrFe1−xO4 (M = La, Ce and Zr; x ≤ 0.05)] were synthesised and its dissolution behavior were studied in permanganate medium. Fission isotope metal ion substitution in SCP showed enhanced ‘Cr’ dissolution rates during the permanganate treatment. Among the fission isotope (La, Ce and Zr) substituted oxide dissolution studies, ‘La’ release was more compare to ‘Ce’ and ‘Zr’. The release behavior of fission products studies showed that dissolved lanthanum is getting sorbed onto the insitu formed MnO2.

Mg2+ vs Ca2+ bound active site of group II intron– A MD study

Group II introns are enzymes which undergo self-splicing and remove itself from pre-messenger RNA. X-ray structures of group II intron of Oceanobacillus iheyensis at various stages of the self-splicing pathway (pre-hydrolytic, post-hydrolytic, and ligand-free state) revealed intricate atomic interaction network in the active site of the intron. It has been confirmed that a heteronuclear metal ion cluster consisting of four metal ions (K1, K2 sites with K+ and M1, M2 sites with Mg2+) are crucial for function. Substitution of Mg2+ by Ca2+ results in loss of enzymatic activity. The X-ray structures not only opens up the possibility of modelling Mg2+ and Ca2+ bound active site of group II intron and quantitatively estimate the energetics of Mg2+ vs Ca2+ preference but also explore the relative structural and dynamical differences in response to divalent metal ion substitution. Thus, using X-ray structures as a template we performed molecular dynamics simulations to compare structural and dynamical differences between Mg2+ and Ca2+ bound active site of group II intron at various stages of the splicing pathway (i.e., pre-hydrolytic, post-hydrolytic, and ligand-free state). Quantitative estimation of Mg2+ vs Ca2+ selectivity at the M1, M2 sites confirmed Mg2+ preference at intron active sites relative to Ca2+. Ca2+ is relatively more hydrated in the intron active site relative to Mg2+. The local environment (bound nucleophilic water, interaction with scissile phosphate) around M2 is strikingly different between Mg2+ and Ca2+ bound pre-hydrolytic state. In the post-hydrolytic state, the exon part of the hydrolysis product is involved in direct interaction with the M1, whereas the intron part is highly flexible in our MD trajectories. Solvent exposure of M1, M2 sites are least in the pre-hydrolytic state, highest in the ligand-free state, and intermediate in the post-hydrolytic state.

Recent progress in molecular ferroelectrics with perovskite structure

Discovered in 1920 by Valasek, a molecular crystal of Rochelle salt (potassium sodium tartrate tetrahydrate) displayed abnormal electrical hysteresis, named as ferroelectric effect. After that, ferroelectrics became an important class of functional materials, due to their unique reversible spontaneous polarization characteristics and other fascinating dielectric, thermoelectric and piezoelectric properties. Although the first reported ferroelectric material is an organic material, the later discovered inorganic materials almost dominated the fields of ferroelectrics for both fundamental studies and practical applications. Among them, inorganic perovskite ceramics received rapid development and showed great application potential in a wide-range of applications such as non-volatile memories, capacitors, sensors, energy convertors, etc., due to their high phase transition temperature and excellent ferroelectric/piezoelectric properties. Comparing to inorganics, molecular materials possess advantages as low acoustic impedance, good flexibility of structure design and composition modification, simple solution synthesis and easy realization of functional properties. Thus, molecular ferroelectrics are expected to be an irreplaceable complement to conventional inorganics, especially in applications like flexible electronics and thin film devices. In the large family of molecular materials, some adapt a similar structure of perovskite with partial substitution of metal ions by organic molecules. These hybrid materials have attracted widespread attention because of their extraordinary optoelectronic and photovoltaic performance. Since last decade, the ferroelectric related properties of molecular perovskite materials were also largely improved. The combination of highly adaptive perovskite structures and variable composition attributes hybrid perovskites them unparalleled potential in rational design of ferroelectricity and piezoelectricity. In this review, we firstly introduced the structural characteristics and dimensionalities of different molecular perovskite ferroelectrics. The next part, we focused on the current design strategy toward rational synthesis of molecular perovskite ferroelectrics, especially on how to tune polarization performance and introducing multiple polar axial properties. In the third part, we briefly introduced the latest progress of molecular piezoelectrics and the role of perovskite structure, molecular design, halogen-bonding and morphotropic phase boundary (MPB) in dramatically improving the piezoelectric coefficient d 33. The fourth part of this review is an application-driven example of tuning band gap in molecular perovskite ferroelectrics, for better optoelectronic and photovoltaic performance. In the last part, a new class of perovskite materials, the metal-free perovskite, is introduced. Without the limitation of metal ions, the metal-free system is believed to have more potential with even better related properties. In summary, the ferroelectric, piezoelectric, and optoelectronic properties of perovskite molecular ferroelectric materials have been greatly developed. This article introduces several design strategies of perovskite molecular ferroelectrics, including “quasi-spherical” theory, H/F substitution and hydrogen bonding introduction method. Meanwhile, we combine comprehensive examples to introduce its recent application and the progress made in other functional characteristics such as band gap regulation and photo electricity. This review provides macroscopic view and general introduction of the evolution and recent progress in molecular perovskite ferroelectrics materials and is suitable for readers in a broad area of research.

Geometrical frustration and piezoelectric response in oxide ferroics

Ferroic perovskite oxides remain a major topic of interest in material science and condensed matter physics. Their versatile structure can accommodate many transition metal ions leading to a variety of useful properties, such as, among others, ferroelectricity. Several mechanisms behind the ferroelectricity of perovskites have been proposed. Using advanced x-ray scattering techniques and 3D modeling, the increased piezoelectric response of the exemplary sodium-potassium niobate ferroics is shown to arise from the presence of local fluctuations in the tilt pattern of the constituent niobium-oxygen octahedra. The result implies that the search for perovskite ferroics with increased functionality need not necessarily concentrate on systems exhibiting a morphotropic boundary and/or distinct polar nanodomains. Inducing local structural disorder in a controlled manner, e.g. through measured metal ion substitution, may become worthwhile.

Metal ion substitution and aldehyde exchange for CuII4 aggregates from two types of piperazine-based Schiff base ligands: Synthesis, X-ray structures, magnetic studies and theoretical validation

Two new tetranuclear CuII complexes [Cu4(L2)2(µ2-OH)2(H2O)2]·(ClO4)2·DMF·2H2O (1) and [Cu4(L3)2(µ2-OH)2(H2O)2]·(ClO4)2·DMF·H2O (2) have been synthesized containing piperazine based Schiff base ligands H2L2 (asymmetric) and H2L3 (symmetric). H2L2 contains one o-vanillin and a salicylaldehyde unit while H2L3 has two o-vanillin units. An interesting synthetic methodology involving transition metal ion induced aldehyde exchange reaction between two Schiff base ligands has been explored for the synthesis of H2L2 and H2L3. While the latter can be obtained by direct condensation of the respective amine and aldehyde, the former can only be synthesized by this procedure developed. Both 1 and 2 contain a piperazine ring bridging two CuII centers in chair conformation in the rare axial-equatorial mode of coordination. Two piperazine bridged Cu2 moieties are further connected via two hydroxido and two phenoxido bridges. Of the two Ophenoxido–Cu bonds one is short (basal) and the other is long (apical) while the hydroxido O bridges the two CuII centers symmetrically in basal–basal manner giving rise to a unique [Cu2O2] moiety where, of the four bonds linking the metals, three are basal (short) and one axial (long). Magnetic studies reveal weak antiferromagnetic interactions across the two piperazine bridges with an average exchange constant value of −4.007 cm−1 and −4.507 cm−1 for 1 and 2 respectively. The antiferromagnetic exchanges across the phenoxido–hydroxido bridges were found to be stronger with the average value being −43.036 cm−1 for 1 and −38.031 cm−1 for 2. Computational studies further support the experimental findings and the spin density plots in the HS configuration reveal that the exchange across the piperazine bridge takes place via through space mechanism. The spin density analysis in the HS and BS configurations also reveal that the exchange interaction is propagated mainly through the hydroxido bridge. The unsymmetrical nature of H2L2 leads to greater spin density at the hydroxido bridge in 1 leading to slightly stronger exchange interaction.

Impact of Metal Ion Substitution on the Activity and Stability of Saccharifying Raw Starch Digesting Amylase from Aspergillus carbonarius

Though raw starch digesting amylases can be utilized in numerous bioprocesses, poor activity and stability remain a limiting factor. In this study, the effect of metal ion substitution on the activity and stability of the RSDA from Aspergillus carbonarius was investigated. The amylase was inactivated using the chelating agent ethylene di aminotetraacetic acid (EDTA) and reactivated using different metal ions. The effect of different metal ions on the reactivation of the amylase activity was investigated. Impact of the metal ions on the stability of the amylase was also studied. Kinetic constants of the native enzyme were compared to the metal reactivated holoenzyme. Most efficient was 5 mM concentration of Co2+ with 94.6% activity recovery. Others included 5 mM Zn2+ (77.7%) and 5 mM Ca2+ (68.7%). Incubating the Co2+ activated amylase in 10 mM Mn2+ further stimulated the activity of the amylase to 136.7%. Compared to the metal ions tested, Mn2+ had the most stabilizing effect on the amylase; the amylase exhibited 148.2% and 136.5% activity at 70ºC and 80ºC respectively in the presence of 5 mM Mn2+. Ca2+ inhibited the amylase activity and inhibition rate increased with increasing concentration of Ca2+ concentrations. Km of the reactivated amylase was 0.18 mg/ml.