Complex Oxides Research Articles

Domains with Varying Conductance in Tensile Strained SrMnO3 Thin Films Using Out‐of‐Plane Electric Fields

AbstractDomains and domain wall engineering have been extensively explored in ferroic materials for a wide range of applications in nanoelectronics and spintronics. Complex oxides exhibiting strongly correlated properties are model platforms for such studies where response to strain or external stimuli such as electric field, temperature and light can be probed. Here, domains in strained SrMnO3 films, grown on a degenerate semiconductor, allowing for conduction in an out‐of‐plane geometry, are studied using a combination of microscopy probes. Using conductive atomic force microscopy, electrically isolated domains with varying conductance are found and their temporal evolution is investigated. Further, their formation and microstructure are studied using scanning transmission electron microscopy and secondary electron contrast in scanning electron microscopy. An important contribution is establishing that the observed domains are formed by cracks, driven by inhomogeneous strain relaxation throughout the film, resulting in significantly high strain planes. The potential of secondary electrons to detect domain dependent contrast over a large area, ensuing due to the use of a degenerate semiconductor correlates with the conductive properties of the domains and serves as a new direction to probe domains and domain walls in ferroic materials.

Electronic and Structural Disorder of the Epitaxial La0.67Sr0.33MnO3 Surface.

Understanding and tuning epitaxial complex oxide films are crucial in controlling the behavior of devices and catalytic processes. Substrate-induced strain, doping, and layer growth are known to influence the electronic and magnetic properties of the bulk of the film. In this study, we demonstrate a clear distinction between the bulk and surface of thin films of La0.67Sr0.33MnO3 in terms of chemical composition, electronic disorder, and surface morphology. We use a combined experimental approach of X-ray-based characterization methods and scanning probe microscopy. Using X-ray diffraction and resonant X-ray reflectivity, we uncover surface nonstoichiometry in the strontium and lanthanum alongside an accumulation of oxygen vacancies. With scanning tunneling microscopy, we observed an electronic phase separation (EPS) on the surface related to this nonstoichiometry. The EPS is likely driving the temperature-dependent resistivity transition and is a cause of proposed mixed-phase ferromagnetic and paramagnetic states near room temperature in these thin films.

Particle-based Photoelectrodes for PEC Water Splitting: Concepts and Perspectives.

This comprehensive review delves into the intricacies of the photoelectrochemical (PEC) water splitting process, specifically focusing on the design, fabrication, and optimization of particle-based photoelectrodes for efficient green hydrogen production. These photoelectrodes, composed of semiconductor materials, potentially harness light energy and generate charge carriers, driving water oxidation and reduction reactions. The versatility of particle-based photoelectrodes as a platform for investigating and enhancing various semiconductor candidates is explored, particularly the emerging complex oxides with compelling charge transfer properties. However, the challenges presented by many factors influencing the performance and stability of these photoelectrodes, including particle size, shape, composition, morphology, surface modification, and electrode configuration, are highlighted. The review introduces the fundamental principles of semiconductor photoelectrodes for PEC water splitting, presents an exhaustive overview of different synthesis methods for semiconductor powders and their assembly into photoelectrodes, and discusses recent advances and challenges in photoelectrode material development. It concludes by offering promising strategies for improving photoelectrode performance and stability, such as the adoption of novel architectures and heterojunctions. This article is protected by copyright. All rights reserved.

Structure and phase transitions in niobium and tantalum derived nanoscale transition metal perovskites, Ba(Ti,MV)O3, M=Nb,Ta.

The prospect of creating ferroelectric or high permittivity nanomaterials provides motivation for investigating complex transition metal oxides of the form Ba(Ti, MV)O3, where M = Nb or Ta. Solid state processing typically produces mixtures of crystalline phases, rarely beyond minimally doped Nb/Ta. Using a modified sol-gel method, we prepared single phase nanocrystals of Ba(Ti, M)O3. Compositional and elemental analysis puts the empirical formulas close to BaTi0.5Nb0.5O3-δ and BaTi0.5Ta0.5O3-δ. For both materials, a reversible temperature dependent phase transition (non-centrosymmetric to symmetric) is observed in the Raman spectrum in the region 533-583K (260-310°C); for Ba(Ti, Nb)O3, the onset is at 543K (270°C); and for Ba(Ti, Ta)O3, the onset is at 533K (260°C), which are comparable with 390-393K (117-120°C) for bulk BaTiO3. The crystal structure was resolved by examination of the powder x-ray diffraction and atomic pair distribution function (PDF) analysis of synchrotron total scattering data. It was postulated whether the structure adopted at the nanoscale was single or double perovskite. Double perovskites (A2B'B″O6) are characterized by the type and extent of cation ordering, which gives rise to higher symmetry crystal structures. PDF analysis was used to examine all likely candidate structures and to look for evidence of higher symmetry. The feasible phase space that evolves includes the ordered double perovskite structure Ba2(Ti, MV)O6 (M = Nb, Ta) Fm-3m, a disordered cubic structure, as a suitable high temperature analog, Ba(Ti, MV)O3Pm-3m, and an orthorhombic Ba(Ti, MV)O3Amm2, a room temperature structure that presents an unusually high level of lattice displacement, possibly due to octahedral tilting, and indication of a highly polarized crystal.

Organic carbon sequestration by Fe oxides in aggregates in a Pinus massoniana conifer-broadleaf mixed forest

Stand conversion and Fe/Al oxides are potential variables that collectively determine soil organic carbon (SOC) sequestration. However, the mechanism of SOC sequestration provided by Fe/Al oxides in the conversion of Pinus massoniana plantations (PMs) into mixed conifer-broadleaf forests remains unknown. The increase in SOC content (4.08–151.80%) in PM-converted mixed forest was related to the significant increase in the content of all OC fractions. Light fraction (LF) contents were generally higher in larger aggregates and mixed forest aggregates, reflecting the greater plant C input and the driving effect of soil aggregation in mixed conifer-broadleaf forests. This plant C input to the soil as the core of aggregate formation provides physical protection from particulate organic carbon (POC), but this physical protection was achieved by the greater free Fe oxides (FeD) and amorphous Fe oxides (FeO) content in the mixed forests acting as an aggregate stabiliser. Potential processes are driven by pH-driven FeD and FeO binding to silt to improve aggregate stability and pore occlusion, which promotes physical protection of coarse intra-aggregate particulate organic carbon (c-iPOC). Moreover, this process reduces macroaggregate turnover (c-iPOC/f-iPOC ratio), allowing the transfer of c-iPOC in macroaggregates to microaggregate-associated fine intra-aggregate particulate organic carbon (f-iPOC). The higher mineral-associated organic carbon (MOC) content of conifer-broadleaf mixed forest soils was mainly derived from silt+clay and controlled by chemisorption of Fe/Al oxides (especially complex Fe oxides, FeP), but Fe/Al oxides do not provide physical protection for MOC. In addition, LF, c-iPOC and f-iPOC were significantly positively correlated with SOC content, reflecting the sensitivity of aggregate structure development and stabilization in predicting SOC sequestration, but these OC fractions will shift more towards MOC as conifer-broadleaf mixed forests develop. Overall, Fe oxides provide SOC accumulation and long-term stability by OC fractions associated with physical protection and chemisorption in the conversion of PM into mixed conifer-broadleaf forests.

Zirconium-based hydrophobic-MOFs as innovative electrode modifiers for flibanserin determination: Exploring the electrooxidation mechanism using a comprehensive spectroelectrochemical study.

Threedifferent types of Zr-based MOFs derived from benzene dicarboxylic acid (BDC) and naphthalene dicarboxylic acid as organic linkers (ZrBDC, 2,6-ZrNDC, and 1,4-ZrNDC) were synthesized. They were characterized using X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform IR spectroscopy (FT-IR), and Transmission electron microscopy (TEM). Their hydrophilic/hydrophobic nature was investigated via contact angle measurements; ZrBDC MOF was hydrophilic and the other two (ZrNDC) MOFs were hydrophobic. The three MOFs were combined with MWCNTs as electrode modifiers for the determinationof a hydrophobic analyte, flibanserin (FLB), as a proof-of-concept analyte. Under the optimized experimental conditions, a significant enhancement in the oxidation peak current of FLB was observed when utilizing 2,6-ZrNDC and 1,4-ZrNDC, being the highest when using 1,4-ZrNDC. Furthermore, a thorough investigation of the complex oxidation pathway of FLB was performed by carrying out simultaneous spectroelectrochemical measurements. Based on the obtained results, it was verified that the piperazine moiety of FLB is the primary site for electrochemical oxidation. The fabricated sensor based on 1,4-ZrNDC/MW/CPE showed an oxidation peak of FLB at 0.8V vs Ag/AgCl. Moreover, it showed excellent linearity for the determinationof FLB in the range 0.05 to 0.80μmol L-1 with a correlation coefficient (r) = 0.9973 and limit of detection of 3.0nmol L-1. The applicability of the developed approach was demonstrated by determinationof FLB in pharmaceutical tablets and human urine samples with acceptable repeatability (% RSD values were below 1.9% and 2.1%, respectively) and reasonable recovery values (ranged between 97 and 103% for pharmaceutical tablets and between 96 and 102% for human urine samples). The outcomes of the suggested methodology can be utilized for the determinationof other hydrophobic compounds of pharmaceutical or biological interest with the aim of achieving low detection limits of these compounds in various matrices.

Magnetic anisotropy driven by ligand in 4d transition-metal oxide SrRuO3

The origin of magnetic anisotropy in magnetic compounds is a longstanding issue in materials science, and nonmagnetic ligand ions are considered to contribute little to magnetic anisotropy. Here, we introduce the concept of ligand-driven magnetic anisotropy in a complex transition-metal oxide. We conducted x-ray magnetic circular dichroism spectroscopies at the Ru and O edges in the 4d ferromagnetic metal SrRuO3. Systematic variation of the sample thickness in the range of ≤10 nm allowed us to control the localization of Ru 4d t2g states, which affects the magnetic coupling between the Ru and O ions. We observe that the orbital magnetic moment of the ligand O 2p orbitals induced through the charge transfer to the Ru 4d t2g states becomes anisotropic first, and the anisotropic magnetic moment of Ru and, therefore, the entire system is induced via magnetic coupling between Ru 4d and O 2p orbitals.

Ultrasound-assisted synthesis of Dy2Mo3O12-Dy2O3 nanostructures for enhanced electrochemical hydrogen storage

Among the major challenges facing the hydrogen economy is the issue of hydrogen storage. In terms of "future energy needs", electrochemical hydrogen storage in solid-state materials is an accepted perspective that could mitigate the discontinuation of primary energy sources. In this study, we demonstrate the electrochemical properties of a complex metal oxide that contains the molybdate group, Dy2Mo3O12. Wet-chemical synthesis of nanostructured Dy2Mo3O12 is primarily carried out using ultrasound-assisted wet-chemical methods in the presence of a variety of surfactants. The structural and morphological observations of the samples confirm a pure and highly crystalline structure obtained in the presence of CTAB surfactant at 900 °C and 30 min of sonication, with an average crystalline size of 29 nm. Based on the FTIR spectrum of this sample, it can be concluded that there are significant absorptions indicating the formation of oxygen-metal bonds. The specific surface area and pore volume of the selected sample are 4.543 m2/g and 0.0284 cm3/g, respectively, demonstrating its porous structure. Electrochemical studies of this sample at various temperatures have revealed an enhanced discharge capacity (5100 mAh/g at 65 °C) with a capacity retention rate of 97%. Based on these findings, mixed metal oxides containing at least one active charge transfer species (Red./Ox.) are suitable for use in solid-state hydrogen storage devices.

High temperature oxidation behaviors of TaCrTiW and TaCrTiZrW alloy coatings

The high-temperature oxidation behaviors of a series of refractory high entropy alloys TaCrTiW and TaCrTiZrW alloy coatings at 1073 K in air were studied. A complex protective oxide layer consisting of Cr2O3, TiO2, and CrTaO4 oxides was generated on the alloys surface. Among the TaCrTiW alloy coatings, the presence of TiO2 inhibited the generation of unfavorable oxides and promoted the generation of CrTaO4. The Ta41.7Cr50.3Ti4.5Zr1.6W1.9 exhibits excellent oxidation resistance. The addition of Zr not only accelerated the initial oxide formation but also promoted the rapid formation of Cr2O3

Predicting solvation energies of free radicals and their mixtures: A robust approach coupling the Peng-Robinson and COSMO-RS models

Detailed kinetic models are valuable tools for a clear understanding of the dynamics of complex reacting systems based on radical-chain mechanisms, such as combustion and oxidation. Gas-phase automatic kinetic generators, such as EXGAS, RMG, MAMOX, NetGen, REACTION, and GENESYS can be used to establish a detailed network of reaction pathways and the rates associated with each reaction. The range of applications of these gas-phase kinetic generators can be extended to liquids through diffusional and solvation corrections directly applied to the gas-phase thermo-kinetic data. In this work, a flexible framework is proposed for the calculation of the solvation correction involving closed-shell (i.e., non-free radical) and open-shell (i.e., free radicals) molecules. This novel model relies on the Peng-Robinson cubic equation of state (EoS) combined with a quantum-based continuum solvation model (COSMO-RS) through an advanced mixing rule. Unlike most predictive equations of state, the proposed model requires only pure compound inputs: critical temperature (Tc,i), critical pressure (Pc,i), acentric factor (ωi), and the screening charge distribution (σ-profile). These inputs were obtained for C/H/O free radicals using group corrections applied to the known values of the associated closed-shell molecules (parent molecules). The resulting EoS is able to provide fast predictions of solvation quantities of closed-shell molecules and C/H/O free radicals with a mean unsigned error of around 0.30 kcal/mol. The great advantage of this method is that it allows high-throughput computation of solvation quantities in pure solvents and mixtures at any temperature (including the supercritical domain), which could enable the simulation of complex oxidation kinetics in a wide range of applications.

Room temperature atomic layer deposition of zinc titanium oxide using sequential adsorption of dimethyl zinc and tetrakis(dimethylamino)titanium

Complex oxide films of TiO2 and ZnO are deposited by RT atomic layer deposition (ALD) with a sequential adsorption process. In this ALD, a Zn precursor of dimethyl zinc (DMZ) and a Ti precursor of tetrakis(dimethylamino)titanium (TDMAT) are used. In the sequential adsorption step, the DMZ saturation on the surface is followed by partial adsorption of TDMAT. It is assumed that the TDMAT molecule is adsorbed on the DMZ uncovered area. The mixed layer of DMZ and TDMAT is formed in the adsorption step, followed by being oxidized with the plasma-excited humidified Ar. All the ALD processes are performed at RT without any sample heating in the ALD chamber. The growth per cycle of the balanced Zn and Ti oxide deposition is recorded at 0.086 nm/cycle. The mixing ratio of Zn and Ti is controlled by the TDMAT exposure in the adsorption step. In this study, the reaction model and the related rate equations to calculate the mixing concentration ratio are proposed based on the in situ observation of the surface reaction by IR absorption spectroscopy.

Photostrictive Actuators Based on Freestanding Ferroelectric Membranes.

Complex oxides offer a wide range of functional properties, and recent advances in fabrication of freestanding membranes of these oxides are adding new mechanical degrees of freedom to this already rich functional ecosystem. Here, we demonstrate photoactuation in freestanding thin film resonators of ferroelectric Barium Titanate (BaTiO3) and paraelectric Strontium Titanate (SrTiO3). The free-standing films, transferred onto perforated supports, act as nano-drums, oscillating at their natural resonance frequency when illuminated by a frequency-modulated laser. The light-induced deflections in the ferroelectric BaTiO3 membranes are two orders of magnitude larger than in the paraelectric SrTiO3 ones. Time-resolved X-ray micro-diffraction under illumination and temperature-dependent and holographic interferometry provide combined evidence for the photostrictive strain in BaTiO3 originating from partial screening of ferroelectric polarization by photo-excited carriers, which decreases the tetragonality of the unit cell. These findings showcase the potential of photostrictive freestanding ferroelectric films as wireless actuators operated bylight. This article is protected by copyright. All rights reserved.

The Inhibition Action of Some Brij-Type Nonionic Surfactants on the Corrosion of OLC 45 in Various Aggressive Environments.

The corrosion protection property of three Brij-type surfactants, namely, Brij 35, Brij 56 and Brij 58P, was considered on OLC 45 carbon steel in a 0.5 M H2SO4 medium. The efficacy for these organic compounds was examined using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods, scanning electron microscopy (SEM) procedures, and Fourier transform infrared (FT-IR) spectroscopy. We hypothesized that these surfactants hinder the corrosion for OLC 45 samples through a protecting mechanism owing to the adsorption of organic molecules that form an inhibitive film or through the formation of complex oxides. These surfactants exhibited an appreciable protective effect against OLC 45 corrosion, operating as mixed inhibitors, as could be demonstrated by their influence on the electrochemical characteristics of the metallic substrates. The adsorption of surfactants over the substrates zone conformed to the representation of the Langmuir isotherm. The effect of temperature on the electrochemical comportment of the OLC 45 specimens in H2SO4 without and with Brij at 800 ppm was examined in the temperature interval of 293 to 333 K. The negative estimate of thermodynamic attributed as Gibbs free energy of adsorption presented the spontaneity of the adsorption activity. The investigation with FT-IR and SEM established the adsorption of Brij and the constitution of the corrosive components on the OLC 45 surface. Electrochemical determinations of these surfactants indicated its anticorrosion inhibition performance and the highest inhibition of 96% was reached when the Brij 35 concentration was at 800 or 1000 ppm, while for Brij 56 and Brij 58P, the highest inhibition was obtained when their concentrations were 500, 800, or 1000 ppm.

Hydrothermal Synthesis and Catalytic Activity of a Nanosized Fe2V4O13 Material in Heterogeneous Fenton-like Reaction for Degradation of Organic Compounds

In this research, the nanosized Fe2V4O13 complex oxide material was synthesized by the hydrothermal method. Its structure, morphology characterization, and other properties were determined using X-ray, SEM, EDX, and DTA-TG methods. The catalytic activity of the material was evaluated in terms of the decolorization and the degradation of the Indigo carmine dye. The optimal condition for the degradation and the reusability of the catalyst were determined. The results showed that the heterogeneous Fenton-like catalyst is a promise for wastewater treatment.

Remote epitaxy-based atmospherically stable hybrid graphene template for fast and versatile transfer of complex ferroelectric oxides onto Si

Heterogenous integration of complex epitaxial oxides onto Si and other target substrates is recently gaining traction. One of the popular methods involves growing a water-soluble and highly reactive sacrificial buffer layer, such as Sr3Al2O6 (SAO), at the interface and a functional oxide on top of this. To improve the versatility of layer transfer techniques, it is desired to utilize stable (less reactive) sacrificial layers without compromising on the transfer rates. In this study, we utilized a combination of chemical vapor deposited (CVD) graphene as a 2D material at the interface and pulsed laser deposited (PLD) water-soluble SrVO3 (SVO) as a sacrificial buffer layer. We then exploit the well-known enhancement of liquid diffusivities by monolayer graphene to enhance the dissolution rate of SVO over ten times without compromising its atmospheric stability. We demonstrate the versatility of our hybrid- graphene-SVO- template by growing ferroelectric BaTiO3 (BTO) via PLD and Pb(Zr, Ti)O3 (PZT) via Chemical Solution Deposition (CSD) technique and transferring them onto the target substrates and establishing their ferroelectric properties. Our hybrid templates allow for the realization of the potential of complex oxides in a plethora of device applications for MEMS, electro-optics, and flexible electronics.

The effect of B – site cation on the supercapacitive properties of LaBO3 (B = Cr, Mn, Fe and Co) porous perovskites

Perovskite oxides have attracted great attention as favorable electrode materials for supercapacitors due to their sole structure, intrinsic oxygen vacancy and compositional flexibility. However, a facile synthetic route which is simple and economical is a challenging issue related to the synthesis of such complex functional oxides. We present a facile and ultrafast way to synthesize LaBO3 (B = Cr, Mn, Fe and Co) perovskite nanocrystallites using glycine-nitrate autocombustion followed by annealing. The structure, phase purity, thermal stability, morphology and surface features of thus synthesized perovskite oxides were analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, Field emission scanning electron microscopy, High resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Brunauer-Emmet-Teller measurements. The role of B – site cation on the electrochemical performance has been investigated by cyclic voltammetry, galvanostatic charge discharge measurements and electrochemical impedance spectroscopy. Electrochemical measurements showed that, among the synthesized materials, LaBO3 nanoparticles with smallest transition metal cation at its B – site, that is LaCoO3 delivered highest value of specific capacitance (750 F/g) and the value of specific capacitance decreases in the order LaCoO3 ˃ LaMnO3 ˃ LaCrO3 ˃ LaFeO3. Therefore, B – site transition metal cation holds the key to regulate perovskite's properties which are essential prerequisites for supercapacitors. An asymmetric device fabricated using LaCoO3 and activated carbon as the positive and negative electrode respectively acted in broad potential window (1.7 V) and delivered an energy density of 22.2 Wh/kg at a power density of 997.7 W/kg and two supercapacitors connected in series could power a red light emitting diode efficiently.

Reactivity of Organoiridium Tungsten Oxide Clusters with Transition Metal Aquo Cations.

Organometallic-polyoxometalate (POM) complexes form a unique class of molecular organometallic oxides characterized by the dynamic behavior of the organometallic cations. Herein, we investigated the reactivity of Cp*Ir-octatungstate clusters (where Cp* represents pentamethylcyclopentadienyl, C5Me5-) with Werner-type transition-metal aquo cations. The addition of Ag+, Co2+, Ni2+, and M3+ (M = Cr, Fe, or In) cations to the aqueous solution of Cp*Ir-octatungstate clusters resulted in the formation of [{Ag(OH2)2}2{Cp*Ir(OH2)}2{Cp*IrW3O12(OH)}2(WO2)2] (1), Co1.5K0.8Na0.2[{trans-Co(OH2)2}{Cp*IrW3O12(OH)}2(WO2)1.3{cis-Co(OH2)2}0.7] (2-Co), Ni0.2K1.4Na0.2[{Ni(OH2)4}2{Cp*IrW3O12(OH)}2(WO2)1.1{cis-Ni(OH2)2}0.9] (2-Ni), and [{M(OH2)4}2{Cp*IrW3O12(OH)}2{cis-M(OH2)2}2](NO3)2 (M = Cr, 3-Cr; Fe, 3-Fe; or In, 3-In), respectively. All clusters share the same cubane-type {Cp*IrW3O12(OH)}5- building block, representing the first examples of organoiridium-POMs functionalized by transition-metal aquo cations. These compounds are insoluble in water, facilitating the evaluation of their heterogeneous water-oxidation properties. Notably, 2-Co generates the highest catalytic water oxidation current. This work provides a new synthetic method to introduce metal-aquo complexes on an organometallic oxide cluster, producing multimetallic molecules that model the catalytic sites of complex oxides.

High performance Pt/Nb2W3O14 catalyst for glycerol valorization to 1,3-propanediol

Glycerol hydrogenolysis to 1,3-propanediol (1,3-PDO) is of significance in promoting the biomass valorization. To achieve the efficient conversion, the selective activation of the secondary C–O bonds in the glycerol is vital. In this work, we comparatively investigated the catalytic performances of Pt/Nb2W3O14 catalyst for glycerol hydrogenolysis controlled at the reacting conditions of 140 °C and 40 bar. Compared to Pt/WO3 and Pt/NbOx, the space–time yield (STY) of 1,3-PDO over Pt/Nb2W3O14 catalyst can be improved by a factor of 13, reaching 596.4 mg gcat−1 h−1. The cation ordering of Nb and W on atomic-scale were fully synergized their unique advantages, showing preferential adsorption of the secondary C–O bond under in-situ DRIFTS tracking. The prepared Nb2W3O14 is a tetragonal tungsten bronze (TTB) type complex oxides which can effectively promote the dispersion and reduction of Pt nanoparticles. Such strong interaction between Nb2W3O14 and Pt can coordinate the precise adsorption and activation of the secondary C–O bond, simultaneously triggering subsequent hydrogenation. Pt/Nb2W3O14 affords an ultrahigh activity in glycerol hydrogenolysis to produce 1,3-PDO, tripling the record productivity that was previously reported of these Pt-W based catalysts. This study reported the development of highly synergistic catalyst based on efficient and selective activation of the secondary C–O bond, which can be extended to catalyst design for other biomass valorization.

2024 Roadmap on Magnetic Microscopy Techniques and Their Applications in Materials Science

Abstract Considering the growing interest in magnetic materials for unconventional computing, data storage, and sensor applications, there is active research not only on material synthesis but also characterisation of their properties. In addition to structural and integral magnetic characterisations, imaging of magnetization patterns, current distributions and magnetic fields at nano- and microscale is of major importance to understand the material responses and qualify them for specific applications. In this roadmap, we aim to cover a broad portfolio of techniques to perform nano- and microscale magnetic imaging using SQUIDs, spin center and Hall effect magnetometries, scanning probe microscopies, x-ray- and electron-based methods as well as magnetooptics and nanoMRI. The roadmap is aimed as a single access point of information for experts in the field as well as the young generation of students outlining prospects of the development of magnetic imaging technologies for the upcoming decade with a focus on physics, materials science, and chemistry of planar, 3D and geometrically curved objects of different material classes including 2D materials, complex oxides, semi-metals, multiferroics, skyrmions, antiferromagnets, frustrated magnets, magnetic molecules/nanoparticles, ionic conductors, superconductors, spintronic and spinorbitronic materials.

Comparison of Structure and Reactivity of Hydrothermally Prepared Bi−Mo−Co−Fe−O Catalysts in Selective Propylene and Isobutene Oxidation

AbstractThe elucidation of structure‐activity correlations in selective oxidation of propylene and isobutene over mixed metal oxides (MMO) is attractive for knowledge‐based catalyst design and process optimisation. Particularly, 4‐component Bi−Mo−Co−Fe−O catalysts need to be studied since their complex metal oxide phase mixture leads to higher activity and selectivity than 2‐component Bi−Mo−O. Hence, three Bi−Mo−Co−Fe‐oxides with different metal ratios were prepared by hydrothermal synthesis and compared during selective oxidation tests with propylene and isobutene. The active phases after several days on stream were investigated by synchrotron X‐ray diffraction (XRD) and Raman spectroscopy, while the structural evolution under reaction conditions was followed by operando Raman spectroscopy, synchrotron XRD, and multi‐edge X‐ray absorption spectroscopy. Similar structural transformations were observed during selective oxidation of propylene and isobutene, with similar influence on catalytic performance. A phase mixture of β‐CoMoO4/β‐Co0.7Fe0.3MoO4, γ‐Bi2MoO6, Fe3O4 and Bi3FeMo2O12 was observed, whereby high amounts of β‐CoMoO4/β‐Co0.7Fe0.3MoO4 increased selectivity to acrolein/methacrolein. In contrast, high amounts of γ‐Bi2MoO6 and Fe3O4 favoured total oxidation to CO and CO2. The simultaneous presence of β‐CoMoO4/β‐Co0.7Fe0.3MoO4, Bi3FeMo2O12 and Fe2O3 increased selectivity to methacrolein in isobutene oxidation, whereas no comparative increase in acrolein selectivity was observed in propylene oxidation. This suggests different key active phases in both reactions.