Chemical Substitution Research Articles

Recent progress in MnBi2nTe3n+1 intrinsic magnetic topological insulators: crystal growth, magnetism and chemical disorder.

The search for magnetic topological materials has been at the forefront of condensed matter research for their potential to host exotic states such as axion insulators, magnetic Weyl semimetals, Chern insulators, etc. To date, the MnBi2nTe3n+1 family is the only group of materials showcasing van der Waals-layered structures, intrinsic magnetism and non-trivial band topology without trivial bands at the Fermi level. The interplay between magnetism and band topology in this family has led to the proposal of various topological phenomena, including the quantum anomalous Hall effect, quantum spin Hall effect and quantum magnetoelectric effect. Among these, the quantum anomalous Hall effect has been experimentally observed at record-high temperatures, highlighting the unprecedented potential of this family of materials in fundamental science and technological innovation. In this paper, we provide a comprehensive review of the research progress in this intrinsic magnetic topological insulator family, with a focus on single-crystal growth, characterization of chemical disorder, manipulation of magnetism through chemical substitution and external pressure, and important questions that remain to be conclusively answered.

Magnetic and transformation properties of Ni2MnGa combinatorically substituted with 5 at.% of transition elements from Cr to Cu – Experimental insight

Heusler Ni–Mn–Ga alloys with martensitic transformation being multiferroic materials exhibit magnetic shape memory (MSM) phenomena and moreover, these are touted for magneto– and multi–caloric effect (MCE). MCE benefits from high saturation magnetization and also large variability and sensitivity of transformation temperatures on alloying. In contrast, MSM phenomena are limited by low temperatures of both ferromagnetic and ferroelastic transformations. In an attempt to increase or modify the transformation temperatures and to understand the physical fundamentals beyond transformation variations and magnetic ordering, we experimentally investigate the magnetic and transformation properties in Ni2MnGa alloyed with transitional elements spanning from Cr to Cu. These elements are consecutively substituted on Ni, Mn, and Ga sites, to establish the effect of chemical substitution and elemental evolution. The elemental dependence of saturation magnetization, magnetocrystalline anisotropy, Curie temperature, and martensitic transformation temperatures are compared with (non–)stoichiometric Ni–Mn–Ga Heusler compounds. The observed behavior is complex and there are no clear trends of transformation temperatures as a function of the number of valence electrons or of non–bonding electrons per atom. The saturation magnetization at 10 K seems to follow the Slater–Pauling curve particularly for Ni substitution. Obtained results can serve as useful rectification for the theoretical prediction of new Ni–Mn–Ga–X Heusler alloys.

Optimized electromechanical performance in Aurivillius compounds via hot-pressing

Bismuth layer-structured ferroelectrics (BLSFs) are widely demanded in high-temperature piezoelectric sensors, while their low piezoelectricity-induced low sensitivity of piezoelectric sensors is not appropriate for practical operation conditions. Texturing is an effective way to engineer the performance of piezoelectric ceramics by aligning the polar vectors and increasing poling efficiency. Herein, chemical substitution together with the hot-pressing technique is utilized to improve the piezoelectricity of BTN-based ceramics. Characterizations demonstrate that the grains with (100) orientation as shown in the {001} pole figure and the improved domain switching are the main causes of excellent ferroelectricity (Pr∼17.7 μC/cm2) and large piezoelectric coefficient (d33∼27 pC/N) in the textured BCTNTW-Per ceramic. The BCTNTW-Per ceramic also exhibits high TC (890 °C), low dielectric loss, high electrical resistivity (1.6 ×105 Ω•cm at 600 °C), and excellent thermal stability, demonstrating that the combination of the hot-pressing technique and traditional doping strategy is an effective way to prepare high-performance of BLSFs.

Insight into structure-activity relationships of hydroxycinnamic acids modified porous starch: The effect of phenolic hydroxy groups.

Antioxidant capacity of hydroxycinnamic acids-modified starch mainly depends on their chemical structure. Herein, cinnamic acid as well as meta-substituted and para-substituted cinnamic acid were selected for esterification with porous starch (labelled as CA@PS, m-CA@PS and p-CA@PS), with the successful formation of porous starch (labelled as PS) esters then confirmed by 1H NMR, 13C solid-state NMR and FT-IR spectroscopy. Three PS esters with almost same degrees of substitution (DS) were obtained, and antioxidant assays, including DPPH radical scavenging, reducing power and hydroxyl radical scavenging tests, were subsequently used to evaluate the antioxidant activity of the esterified PS. Overall, CA@PS showed weak antioxidant activity because of the absence of phenolic hydroxy, while p-CA@PS displayed better antioxidant capacity. Because its conjugated structure offered the stronger electron-donating effect, that could enhance antioxidant capacity. Therefore, antioxidant capacity depended significantly on overall chemical structure, including numbers and substitution positions of phenolic hydroxy groups.

Crystal structure, morphology and optical properties of orange red emitting (Y1–xLnx)2Ti2O7 (Ln = Eu, Sm) solid solutions

The present work reports a comparative study of two phosphors families; (Y1-xEux)2Ti2O7 and (Y1-xSmx)2Ti2O7 with (0 ≤ x ≤ 1), prepared by solid-state reaction. XRD, SEM, and Raman spectroscopy combined characterization confirms the phase structure, morphology and purity of the prepared phosphors. XRD analysis had revealed the formation of solid solutions with cubic pyrochlore structure with the space group Fd3m. Rietveld refinement of the XRD data shows that the substitution of Y3+ ion with rare earth ions (Ln3+), having larger ionic radii, causes a systematic increase in the lattice parameter a with the value of x, in (Y1-xLnx)2Ti2O7. Characteristic vibration modes (A1g + Eg + 3F2g) for pyrochlore structure are evidenced using Raman spectroscopy. A clear variation of peak positions was observed for Eg and A1g modes with Ln3+ substitution. The great ability of the host matrix, Y2Ti2O7, for chemical substitution, with lanthanide ions, gives rise to new emitting phosphors. The effect of rare earth Ln3+ concentration on the luminescence performance of the (Y1-xLnx)2Ti2O7 phosphors was studied, by photoluminescence (PL) spectroscopy, and discussed in details. The most intense Eu3+ red emission was obtained with a substitution ratio x = 0.25, while the strongest Sm3+ orange-reddish emission was observed for a ratio x = 0.05. These results prove that the prepared phosphors are promising for applications in solid-state white light emitting diodes (W-LEDs) and orange-red emitting components.

Investigations on structural, morphological, dielectric, and ferroelectric properties of BiFeO3/BiMnO3 composite ceramics prepared via sol–gel synthesis route

In this work, we report the preparation of BiFeO3/BiMnO3 (BFO/BMO) composite material, via the chemical substitution method, by adopting the sol–gel method. The X-ray diffraction studies confirmed the formation of two distinct phases in the prepared sample. Field emission scanning electron microscopic images revealed the two different morphologies, and the compositional studies verified the presence of the respective elements in these different grains. The dielectric constant value almost doubled in the composite sample than the single-phase BFO sample. The dielectric constant values at a frequency of 105 Hz were found to be 46 and 73 for the BFO and BFO/BMO samples, respectively. The remnant polarization value was found to reduce from 8.3 µC/cm2 (for BFO) to 0.3 µC/cm2 for biphasic BFO/BMO samples.

Flexible Anionic Groups-Activated Structure Dissymmetry for Strong Nonlinearity in Ln2 Ae3 MIV 3 S12 Family.

Structural dissymmetry and strong second-harmonic generation (SHG) responses are key conditions for nonlinear optical (NLO) crystals, and targeted combinatorial screening of suitable anionic groups has become extremely effective. Herein, optimal combination of flexible SnSn (n=5, 6) groups and highly electropositive cations (lanthanides (Ln3+ ) and alkaline earth (Ae2+ : Sr, Ca) metals) affords the successful synthesis of 12 NLO thiostannates including Ln2 Sr3 Sn3 S12 (Pmc21 ) and Ln2 Ca3 Sn3 S12 (P-62m); whereas 17 rigid GeS4 or SiS4 tetrahedra-constructed Ln2 Ae3 Ge3 S12 and Ln2 Ae3 Si3 S12 crystallize in the centrosymmetric (CS) Pnma. This unprecedented CS to noncentrosymmetric (NCS) structural transformation (Pnma to P-62m to Pmc21 ) in the Ln2 Ae3 MIV 3 S12 family indicates that chemical substitution of the tetrahedral GeS4 /SiS4 units with SnSn breaks the original symmetry to form the requisite NCS structures. Remarkably, strong polarization anisotropy and hyperpolarizability of the Sn(4+) S5 unit afford huge performance improvement from the nonphase-matching (NPM) SHG response (1.4×AgGaS2 and Δn=0.008) of La2 Ca3 Sn3 S12 to the strong phase-matching (PM) SHG effect (3.0×AgGaS2 and Δn=0.086) of La2 Sr3 Sn3 S12 . Therefore, Sn(4+) S5 is proven to be a promising "NLO-active unit." This study verifies that the coupling of flexible SnSn building blocks into structures opens a feasible path for designing targeted NCS crystals with strong nonlinearity and optical anisotropy.

Effect of fluorine substitution on the electronic states and conductance of CuPc on Cu(100)

The electronic states and conductance of CuPc, F8CuPc, and F16CuPc on Cu(100) were studied by using scanning tunneling microscopy (STM) and the density functional theory (DFT) calculations. For all molecules, the lowest unoccupied molecular orbital (LUMO) was observed around the Fermi level (EF), regardless of the difference in the original LUMO levels of the free molecules. This indicates that the strong interaction causes the pinning of EF at LUMO levels. Meanwhile, the differential conductance at EF is drastically affected by the substitution: it increases and decreases for CuPc and F16CuPc, respectively, suggesting that the Fano effect plays a major role in the conductance. This finding provides a new strategy for the control of molecular conductance by chemical substitution.

Effect of heterogeneity on the diffusion of Pb in apatite for petrochronological applications: A multiscale approach to characterizing the influence of apatite chemistry and anisotropy on Pb diffusion

The investigation of various factors effecting the Lead (Pb) diffusion in phosphate minerals such as apatite is still challenging in the interpretation of (UTh)/Pb geochronology. For (UTh)/Pb system, apatite minerals have closure temperatures in the range of 375 to 600 °C and therefore can be used for the investigation of mid-temperature thermochronological and/or petrochronological questions i.e., the reconstruction of thermal events in Earth's crust. There is still uncertainty whether Pb diffusion in apatite is characterized by thermally activated volume and/or anisotropic diffusion profiles or is instead impacted by novel growth processes and recrystallization (chemical substitutions). As the apatite structure support extensive compositional variability, including partial or total substitution of both the cationic and anionic sites and forms solid solutions therefore, it necessitates a thorough examination of these effects and anisotropy on Pb diffusivity and (UTh)/Pb geochronometric system. For this, a multi-scale study is carried out to examine the effects of chemical composition, anisotropy, and growth structure on the diffusion of Pb in order to better understand the behaviour of Pb diffusion in apatite. This study employed computational techniques like Density Functional Theory (DFT) and Transition State Theory (TST) at the atomic level and integrates it with the Kinetic Monte Carlo (KMC) simulations at the macroscopic level. Models of this study shows that Pb diffusion is completely anisotropic along the preferred z-axis or [001] direction and Pb readily escapes faster from Na-substituted apatite when compared to pure F-apatite and Cl-substituted apatite. Because of this anisotropy and chemical substitutions, Pb diffusivity in apatite either increases by opening of diffusion channels or decreases by blocking the diffusion channels depending on the site and type of chemical substitution. Further, in case of blocking effect the Pb diffusion occurs through workaround pathways and approaches towards the isotropic diffusion. For Na-substituted apatite, the impact of Na occupation on anisotropic Pb diffusion is significantly greater while in case of Cl-substituted apatite the Cl occupation mostly leads towards isotropic diffusion by opening the diffusion paths along other directions (mostly along the in-plane direction). Furthermore, the high closure temperatures (Tc) (e.g., ∼1370 °C) of the modelled apatites (except the perfect Na-substituted apatite e.g., ∼500 °C) of this study when compared to the Tc of Durango apatite obtained experimentally for the effective grain size of 100 μm and cooling rates of 10 °C/Ma indicate that the effective closure temperature dominantly depends on the degree and types of chemical substitutions and play a crucial role for the closure or opening of Pb diffusion/loss in apatites.

Epitaxy and transport properties of alkali-earth palladate thin films

ABSTRACT Topological insulators and semimetals are an interesting class of materials for new electronic and optical applications owing to their characteristic electromagnetic responses originating from the spin-orbit coupled band structures. However, topological electronic structures are rare in oxide materials despite their chemical stability being preferable for applications. In this study, given the theoretical prediction of Dirac bands in CaPd3O4, we investigate the fabrication and transport properties of SrPd3O4 and CaPd3O4 thin films as candidates of oxide Dirac semimetals. We have found that these materials are epitaxially grown on MgO (100) substrate under limited growth conditions by pulsed laser deposition. The transport properties show a weak temperature dependence, suggestive of narrow-gap properties, although unintentionally doped holes hinder us from revealing the presence of the Dirac band. Our study establishes the basic thermodynamics of thin-film fabrication of these materials and will lead to interesting properties characteristic of topological band structure by modulating the electronic structure by, for example, chemical substitutions or pressure.

Li2GeS3: Lithium Ionic Conductor with an Unprecedented Structural Type.

Lithium-ion batteries (LIBs) are widely used in electric vehicles, mobile electronic devices, and large-scale stationary energy storage systems. However, their liquid electrolytes present significant safety concerns due to their inherent flammability. To address this, the focus has shifted toward all-solid-state batteries (ASSBs) utilizing inorganic solid electrolytes that promise enhanced safety. In this work, we report the discovery of a new crystal structural type of Li-ion conductor, Li2GeS3, with a unique structure, synthesized by a solid-state reaction from Li2S and GeS2. It was first reported in 2000 with an orthorhombic unit cell, but its detailed crystal structure remains veiled. We have unveiled its structure for the first time, employing an ab initio structure determination technique from powder X-ray and time-of-flight neutron diffraction data. The compound has an unprecedented crystal structural type with a hexagonal P61 symmetry and a unit cell of a = 6.79364(4) Å and c = 17.90724(14) Å. Its structure is comprised of a distorted hexagonal close-packed arrangement of sulfur anions with three asymmetric metal atoms: Li1, Li2, and Ge are in tetrahedral cavities surrounded by sulfur atoms. The ionic conductivity of Li2GeS3 was measured to be 1.63 × 10-8 S cm-1 at 303 K and 2.45 × 10-7 S cm-1 at 383 K. Bond valence energy landscape calculations revealed three-dimensional lithium diffusion pathways within the structure. This novel crystal structure in Li2GeS3 holds the potential for developing high-performance ionic conductors through suitable chemical substitution and offers valuable insights into designing new ionic conductors for ASSBs.

Interplay of magnetism and band topology in Eu[formula omitted]Ca[formula omitted]Mg[formula omitted]Bi[formula omitted] (x=0, 0.5, 0.67) from first principles study

Recent discovery of the time reversal symmetry breaking magnetic Weyl semimetals (WSMs) has created a huge surge of activities in the field of quantum topological materials. In this work, we have studied systematically various magnetic orders, electronic structure and the interplay between the magnetic order and band topology in one such material, EuMg2Bi2 (EMB) and its Ca doped variant using first principle methods within the framework of density functional theory (DFT). Our thorough investigation reveals the existence of various magnetic order driven topological phases (for example, topological insulator in the A-type antiferromagnetic (A-AFM) phase with Eu moments aligned along the crystallographic a or b direction, Dirac semimetal in the A-AFM phase when Eu moments are parallel to c direction and Weyl semimetal in the ferromagnetic (FM) phase with Eu moments pointing along the c direction) in this material. These phases are found to be energetically very close and hence are expected to be tunable from one to the other by an external handle such as magnetic field or chemical substitution. Most importantly, we observe the existence of a single pair of Weyl points (WPs) connecting valence and conduction band very close to the Fermi level (FL) along Γ-A direction in the FM state of EuMg2Bi2 with Eu moments aligned along the c direction making it an ideal Weyl semimetal in its FM state exactly similar to EuCd2As2. On doping 50% and 67% Ca at Eu sites, we observe the single pair of WPs to move even closer to the FL which is highly desirable for application purposes. Further, we observe that the separation between the WPs in the pair decreases in doped compounds compared to that in the parent compound which has direct consequence on anomalous Hall conductivity (AHC). Our first principles calculation of AHC shows high peak values exactly at these WPs and the peak height decreases when we dope the system with Ca. Therefore, Ca doping can be a good external handle to tune AHC in this system.

Tuning Colossal Magnetoresistance Effect Through Chemical Substitution In Perovskite Manganites

Objective: This research is focused on the colossal magnetoresistance (CMR) effect tunability via chemical substitution in perovskite manganites. The objective is to learn how changing the chemical structure of these compounds affect their magnetic and electronic characteristics particularly the CMR effect. Methods: Perovskite manganite materials were prepared by the chemical substitution method to tune the composition of transition metal ions and rare-earth elements. The structural, magnetic, and electronic characterizations were done by the means of X-ray diffraction, magnetization measurements, and electrical transport measurements. Results: The study showed that the selective chemical substitution within the perovskite structure could be used to modulate the CMR effect in manganite materials. Due to the differences in chemical structure the magnetic ordering, charge carrier concentration and electronic band structure are altered which in turn influence the magnitude of the CMR effect. For example, specific chemical substitutions were shown to remarkably strengthen the CMR effect, leading to better magnetoresistance characteristics. Conclusion: This study demonstrates the possibility of tuning the CMR effect by the chemical substitution of Mn perovskite materials. By manipulating the chemical composition, it is achievable to fine-tune the magnetic and electronic characteristics for various spintronics, magnetic sensors and other devices that need high magnetoresistance effects. The results help to gain more knowledge about CMR in manganite systems and provide the guidance for the research on improving their performance.

Synthesis and spectroscopic characterization of thioparacetamol: Evidence for solvent-dependent changes in conformational equilibrium

The search for analogs of compounds with proved pharmacological activity frequently starts by obtaining those that result from simple chemical substitutions, have structural and mechanical characteristics suitable for inclusion in a formulation and close similarity with related lead compounds. With this aim, the isosteric replacement of the carbonyl functional group of paracetamol to obtain solid thioparacetamol was achieved through microwave mediated thionation of parent compound in very good yield (85 %). A thorough characterization of the compound prepared was performed by GC/MS spectrometry, FTIR and NMR (1H, 13C, COSY, HSQC and HMBC) spectroscopies and quantum chemical calculations derived from density functional theory. From the experimental and theoretical spectra, it was evidenced that the structural, vibrational and conformational properties of this compound vary whether the sample is solved in a solvent or not. The anti form (anti of the CS and NH bonds) was the preferred conformational isomer in the solid phase, while a conformational equilibrium of anti and syn forms was found for samples solved in different solvents. As polarity of solvents increased, proportion of the anti isomer increased as well.

Structural, relaxor behavior, and energy storage performance of BaTiO3–Bi (Mg2/3Nb1/3)O3 solid solutions for potential MLCC application

In the discussed work, (1-x) BaTiO3 (BT)-x Bi(Mg2/3Nb1/3)O3 (BMN) solid-combinations have been synthesized via the solid-state process; and both corresponding dielectric and ferroelectric behavior have been learned for possible Multilayer Ceramic Capacitor (MLCC) applications. The phase confirmation has been identified utilizing X-ray diffraction; and Rietveld refinement technique has been used for structural analysis that unveils the formation of pure perovskite structure of the prepared ceramics. Rietveld refinement results reveal the structural changeover from tetragonal to pseudo-cubic for x≥0.125. Raman spectroscopy measurements confirm the structural phase changes and lattice modifications due to the chemical substitutions. Microstructural analysis has been done with the help of electron micrograph. Dielectric performance of the synthesized (1-x)BaTiO3(BT)-xBi(Mg2/3Nb1/3)O3(BMN) solid solutions has been examined within a temperature range of 173K–473K at different applied frequencies. A broad phase transition and relaxor character is detected from dielectric investigation. The relaxor behavior has been quantified by the Vogel-Fulcher fitting. The thermal stability of the prepared samples was calculated by means of standard formula of Temperature Coefficient of Capacitance (TCC). Hysteresis loop was undertaken to identify the ferroelectric properties and energy storage capacity. Among all the compositions, x = 0.10 shows good thermal stability, an elevated recoverable energy density; and a remarkable efficiency that makes it suitable for MLCC applications.

Excellent Nonlinear Optical M[M4 Cl][Ga11 S20 ] (M = A/Ba, A = K, Rb) Achieved by Unusual Cationic Substitution Strategy.

The typical chalcopyrite AgGaQ2 (Q = S, Se) are commercial infrared (IR) second-order nonlinear optical (NLO) materials; however, they suffer from unexpected laser-induced damage thresholds (LIDTs) primairy due to their narrow band gaps. Herein, what sets this apart from previously reported chemical substitutions is the utilization of an unusual cationic substitution strategy, represented by [[SZn4 ]S12 + [S4 Zn13 ]S24 + 11ZnS4 ⇒ MS12 + [M4 Cl]S24 + 11GaS4 ], in which the covalent Sx Zny units in the diamond-like sphalerite ZnS are synergistically replaced by cationic Mx Cly units, resulting in two novel salt-inclusion sulfides, M[M4 Cl][Ga11 S20 ] (M = A/Ba, A = K, 1; Rb, 2). As expected, the introduction of mixed cations in the GaS4 anionic frameworks of 1 and 2 leads to wide band gaps (3.04 and 3.01 eV), which exceeds the value of AgGaS2 , facilitating the improvement of high LIDTs (9.4 and 10.3 × AgGaS2 @1.06 µm, respectively). Furthermore, compounds 1 and 2 exhibit moderate second-harmonic generation intensities (0.84 and 0.78 × AgGaS2 @2.9 µm, respectively), mainly originating from the orderly packing tetrahedral GaS4 units. Importantly, this study demonstrates the successful application of the cationic substitution strategy based on diamond-like structures to provide a feasible chemical design insight for constructing high-performance NLO materials.

Synergistic Effect between Fe<sup>4+</sup> and Co<sup>4+</sup> on Oxygen Evolution Reaction Catalysis for CaFe<sub>1−</sub><i><sub>x</sub></i>Co<i><sub>x</sub></i>O<sub>3</sub>

Chemical substitution is an effective way to improve electrocatalytic properties in transition metal oxides. We investigate the synergistic effect between Fe4+ and Co4+ ions on the catalytic activity for oxygen evolution reaction (OER) in the Fe-Co-mixed perovskite oxide CaFe1–xCoxO3. The OER activity of CaFe1–xCoxO3 is substantially increased by small amounts of Co (Fe) doping into CaFeO3 (CaCoO3), leading to the superiority compared to the pure Fe and Co perovskite oxides. The x dependences of the OER overpotential and specific activity for CaFe1–xCoxO3 (0.05 ≦ x ≦ 0.95) are expressed by constant offset from the weighted average between CaFeO3 and CaCoO3, which can be interpreted to be the synergistic effect between Fe4+ and Co4+ ions on OER activity. The absence of the optimum x for the highest activity for CaFe1–xCoxO3 contrasts with the volcano-like plots reported in various mixed-metal oxides. First-principle calculations using the special quasirandom structure models on CaFe1–xCoxO3 (x = 0.03–0.5) demonstrate that about half the amount of Fe4+ is electronically activated to possess smaller charge-transfer energies, corroborating the enhancement of catalytic activity in CaFe1–xCoxO3. These findings provide new insight into the synergistic effects in complex transition metal oxide catalysts.

Biomineralization of mantis shrimp dactyl club following molting: Apatite formation and brominated organic components

The stomatopod Odontodactylus scyllarus uses weaponized club-like appendages to attack its prey. These clubs are made of apatite, chitin, amorphous calcium carbonate, and amorphous calcium phosphate organized in a highly hierarchical structure with multiple regions and layers. We follow the development of the biomineralized club as a function of time using clubs harvested at specific times since molting. The clubs are investigated using a broad suite of techniques to unravel the biomineralization history of the clubs. Nano focus synchrotron x-ray diffraction and x-ray fluorescence experiments reveal that the club structure is more organized with more sub-regions than previously thought. The recently discovered impact surface has crystallites in a different size and orientation than those in the impact region. The crystal unit cell parameters vary to a large degree across individual samples, which indicates a spatial variation in the degree of chemical substitution. Energy dispersive spectroscopy and Raman spectroscopy show that this variation cannot be explained by carbonation and fluoridation of the lattice alone. X-ray fluorescence and mass spectroscopy show that the impact surface is coated with a thin membrane rich in bromine that forms at very initial stages of club formation. Proteomic studies show that a fraction of the club mineralization protein-1 has brominated tyrosine suggesting that bromination of club proteins at the club surface is an integral component of the club design. Taken together, the data unravel the spatio-temporal changes in biomineral structure during club formation. Statement of significanceMantis shrimp hunt using club-like appendages that contain apatite, chitin, amorphous calcium carbonate, and amorphous calcium phosphate ordered in a highly hierarchical structure. To understand the formation process of the club we analyze clubs harvested at specific times since molting thereby constructing a club formation map. By combining several methods ranging from position resolved synchrotron X-ray diffraction to proteomics, we reveal that clubs form from an organic membrane with brominated protein and that crystalline apatite phases are present from the very onset of club formation and grow in relative importance over time. This reveals a complex biomineralization process leading to these fascinating biomineralized tools.

Crystal Structure and Magnetic Properties of Bi1-yBa(Sr)Fe1-yTiyO3 Solid Solutions

Abstract: Usages of various chemical substitution schemes of the initial multiferroic BiFeO3 can significantly reduce known drawbacks specific for the functional oxides based of iron ions and thus foster a creation of novel magnetoelectric compounds perspective for various technological applications. In the present study the co-doped compounds of the system Bi1-y(Ba1- xSrx)yFe1-yTiyO3 (x = 0.0 – 1.0; y ≤ 0.4) synthesized using sol-gel technique were analyzed focusing on the crystal structure stability and the correlation between the structure and magnetic properties. The concentration driven evolution of the crystal structure as well as the unit cell parameters were investigated based on the X-ray diffraction data, the correlation between the crystal structure and the magnetic properties of the compounds has been studied by magnetometry techniques. The compounds Bi1-y(Ba1- xSrx)yFe1-yTiyO3 with x = 0; y = ≤ 0.2 are characterized by single-phase rhombohedral structure, and increase in the dopant concentration to y = 0.4 leads to the stabilization of the pseudocubic phase. An increase in the Sr content leads to the phase transition in the compounds to the single phase state with the cubic structure which is accompanied by an increase in the value of the remanent magnetization.

The Fermi energy as common parameter to describe charge compensation mechanisms: A path to Fermi level engineering of oxide electroceramics

Chemical substitution, which can be iso- or heterovalent, is the primary strategy to tailor material properties. There are various ways how a material can react to substitution. Isovalent substitution changes the density of states while heterovalent substitution, i.e. doping, can induce electronic compensation, ionic compensation, valence changes of cations or anions, or result in the segregation or neutralization of the dopant. While all these can, in principle, occur simultaneously, it is often desirable to select a certain mechanism in order to determine material properties. Being able to predict and control the individual compensation mechanism should therefore be a key target of materials science. This contribution outlines the perspective that this could be achieved by taking the Fermi energy as a common descriptor for the different compensation mechanisms. This generalization becomes possible since the formation enthalpies of the defects involved in the various compensation mechanisms do all depend on the Fermi energy. In order to control material properties, it is then necessary to adjust the formation enthalpies and charge transition levels of the involved defects. Understanding how these depend on material composition will open up a new path for the design of materials by Fermi level engineering.