Complex Oxides Research Articles

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.

Combustion features of dispersed aluminum and boron in high-energy composition

Combustion of dispersed metals in an oxidizing environment is of practical interest, which is related to the prediction of characteristics of high-energy compositions (HECs) containing metal powders, as well as the characteristics of various propulsion systems and gas generators. The research studies peculiarities of ignition and combustion of dispersed systems of Al, B and Al-B mixture in gas products formed during thermal decomposition and combustion of HEC components. In the study of the characteristics of ignition and combustion, the development of flame processes, a continuous CO2 laser (high-speed radiant heating) and a continuous-pressure flow bomb (stationary combustion), including the filter system for the capture of condensed combustion products (CCPs) were applied. It was found that the high reactivity of dispersed Al reduces the ignition time and increases the burning rate of HECs, and increases the volume fraction of fine condensed particles. The use of amorphous B or Al-B mixture (17.2/82.8 mass ratio) increases the ignition time (up to 62%) and significantly reduces the burning rate of HECs, at the same time, the volume share of large CCPs increases due to the melting of the oxide layer on the surface of B particles and their increased cohesion. Analysis of CCPs showed that fine and large agglomerate particles were formed on the surface of the reactive HEC layer, which contain oxides of the metals used. When Al particles are burned together with B particles, complex oxides (aluminum borates) can be formed.

Chemiluminescence and electrochemiluminescence of water-soluble iridium(III) complexes containing a tetraethylene-glycol functionalised triazolylpyridine ligand

BackgroundIridium(III) complexes, exhibiting high luminescence quantum yields and a wide range of emission colours, are promising alternatives to tris(2,2ʹ-bipyridine)ruthenium(II) for chemiluminescence (CL) and electrochemiluminescence (ECL) detection. This emerging class of reagent, however, is limited by the poor solubility of many iridium(III) complexes in aqueous solution, and lack of understanding of their remarkably variable selectivities towards different analytes. ResultsSeven [Ir(CˆN)2(pt-TEG)]+ complexes, exhibiting a wide range of reduction potentials and emission energies, were examined with six model analytes. For CL, cerium(IV) was used as the oxidant. The alkylamine analytes generally produced greater CL and ECL with the more readily oxidised Ir(III) complexes (CˆN = piq, bt, ppy), predominantly through the ‘direct’ pathway requiring oxidation of both metal complex and analyte. Aniline derivatives that did not also contain secondary or tertiary alkylamines elicited CL from the less readily oxidised complexes (CˆN = df-ppy-CF3, df-ppy) via energy transfer. The most difficult to oxidise complexes (CˆN = df(CF3)-ppy-Me, df(CN)-ppy) gave poor responses due to the limited potential window of the solvent and inefficiency of energy transfer to their high energy excited states. Greater CL and/or ECL intensities were generally obtained for each analyte with at least one Ir(III) complex than with [Ru(bpy)3]2+; superior limits of detection for two analytes were demonstrated. SignificanceThis exploration of CL/ECL in which the properties of luminophore, analyte and oxidant are all varied provides a new understanding of the influence of the metal-complex potentials and excited state energy on the light-producing and quenching pathways, and consequently, their distinct selectivity towards different analytes. These findings will guide the development of water-soluble Ir(III) complexes as CL and ECL reagents.

Enhanced Mechanical and Electromechanical Properties of Compositionally Complex Zirconia Zr1-x(Gd1/5Pr1/5Nd1/5Sm1/5Y1/5)xO2-δ Ceramics.

Compositionally complex oxides (CCOs) or high-entropy oxides (HEOs) are new multielement oxides with unexplored physical and functional properties. In this work, we report fluorite structure-derived compositionally complex zirconia with composition Zr1-x(Gd1/5Pr1/5Nd1/5Sm1/5Y1/5)xO2-δ (x = 0.1 and 0.2) synthesized in solid-state reaction route and sintered via hot pressing at 1350 °C. We explore the evolution of these oxides' structural, microstructural, mechanical, electrical, and electromechanical properties regarding phase separation and sintering mechanisms. Highly dense ceramics are achieved by bimodal mass diffusion, composing nanometric tetragonal and micrometric cubic grains microstructure. The material exhibits an anomalously large electrostriction response exceeding the M33 value of 10-17 m2/V2 at room temperature and viscoelastic properties of primary creep in nanoindentation measurement under fast loading. These findings are strikingly similar to those reported for doped ceria and bismuth oxide derivates, highlighting the presence of a large concentration of point defects linked to structural distortion and anelastic behavior, which are characteristics of nonclassical ionic electrostrictors.

High-mobility spin-polarized quasi-two-dimensional electron gas and large low-field magnetoresistance at the interface of EuTiO3/SrTiO3 (110) heterostructures

High-mobility spin-polarized two-dimensional electron gas (2DEG) at the interfaces of complex oxide heterostructures provide great potential for spintronic device applications. Unfortunately, the interfacial ferromagnetism and its associated spin polarization of mobile electrons and negative magnetoresistance (MR) are too weak. As of now, obtaining enhanced interfacial ferromagnetism and MR and strong spin-polarized 2DEG is still a great challenge. In this paper, we report on the realization of strong spin-polarized 2DEG at the interface of EuTiO3/SrTiO3 (110) heterostructures, which were prepared by directly depositing 39-nm EuTiO3 films onto as-received SrTiO3 (110) substrates. Hall and Kondo effects, low-field MR, Shubnikov–de Haas (SdH) oscillation, and magnetic hysteresis loop measurements demonstrate that high mobility electrons (1.4 × 104 cm2 V−1 s−1) accumulate at the interface of the heterostructures, which are not only highly conducting and show SdH oscillations with a non-zero Berry phase but also show a large out-of-plane and in-plane butterfly-like negative low-field MR whose magnitude is unprecedentedly large (46%–59% at 500 Oe and 1.8 K), approximately one to two orders higher than those of previously reported spin-polarized 2DEG systems. The strong spin polarization of the interfacial 2DEG is attributed to the presence of interfacial Eu2+ 4f (3.6–4 μB/f.u.) and Ti3+ 3d moments. Our results may provide guidance for exploring strong spin-polarized 2DEG at the interface of rare-earth titanate–strontium titanate heterostructures.

Influence of swift heavy ion irradiation on structure and morphology of La0.25Pr0.375Ca0.375MnO3 film

The effects of Ag15+ (120 MeV) swift heavy ion (SHI) irradiation on the structural and morphological properties of epitaxial La0.25Pr0.375Ca0.375MnO3 (LPCMO) thin films were investigated by x-ray scattering and atomic force microscopy (AFM) techniques. LPCMO films of thickness ∼ 280 Å were irradiated with an Ag15+ ion beam at different fluences of 1 × 1011, 5 × 1011, and 1 × 1012 ions cm−2. XRD results suggested the development of the tensile stress along the out-of-plane direction of the LPCMO film upon ion irradiation, which increases on increasing the ion fluence. The morphology of the film was also modified with the irradiation and an increase in the fluence of the ion beam enhanced the in-plane height-height correlation length scale (grain size) with a loss of the fractal behaviours. The linear variation of microstrain with ion irradiation fluence in thin LPCMO film can be considered for a possible strain-driven application in modifying functional properties of such a phase separated complex oxide.

Transition Metal‐Oxide Nanomembranes Assembly by Direct Heteroepitaxial Growth

AbstractThe integration of complex oxides with a wide range of functionalities on conventional semiconductor platforms is highly demanded for functional applications. Despite continuous efforts to integrate complex oxides on Si, it is still challenging to harvest epitaxial layers using standard deposition processes. Here, a novel method is demonstrated to create high‐quality complex heterostructures on Si integrated with SrTiO3 membranes as a universal platform. The STO membrane successfully bridges a broad spectrum of complex heterostructures such as SrNbO3, SrVO3, TiO2, and dichalcogenide 2D superconducting FeSe toward semiconducting wafers (Si). Through electronic structures measured by angle‐resolved photoemission spectroscopy, the high quality and functionality of the heterostructures are verified. This study demonstrated a new pathway toward realizing electronic devices with multifunctional physical properties incorporated into Si.

Unique photothermal material: Copper phosphate (Cu3P2O8) with broadband visible-to-near-infrared absorption properties for efficient solar steam generation

Effective harnessing of renewable solar energy in interfacial solar steam generation (ISSG) is a promising solution for addressing freshwater scarcity worldwide. Therefore, the development of photothermal materials plays a pivotal role in achieving efficient ISSG performance. This paper reports on an innovative photothermal material, copper phosphate (Cu3P2O8; CuPO), with broadband visible-to-near-infrared (Vis-to-NIR) absorption for ISSG. CuPO exhibited favorable characteristics, including extensive light absorption across the Vis to NIR spectrum (500–2200 nm), low thermal conductivity (0.64 W/m·K), high photon-to-heat conversion efficiency (87.9 %), and inherent hydrophilicity. When subjected to simulated sunlight (AM1.5G, 100 mW/cm2), the CuPO-coated polyurethane membrane demonstrated remarkable water evaporation performance (2.05 kg/m2·h) and ISSG efficiency (95.0 %). Notably, employing an ultraviolet cutoff filter (< 450 nm) revealed a substantial NIR absorption contribution of CuPO, surpassing 80 % of its overall performance. Moreover, the CuPO photothermal membrane exhibited durable ISSG performance over 25 cycles, underscoring the structural robustness and resilience of CuPO. Our findings offer a promising foundation for designing cost-effective, high-performance ISSG systems utilizing copper-based complex oxides.

Band gap tuning in samarium-modified bismuth titanate ferroelectric via iron doping for photovoltaic applications

The wide band gap of complex oxides is one of the critical challenges restricting their usage in photovoltaic cells. Therefore, examinations of their photoelectric characteristics have increasingly concentrated on materials with a low band gap. This work investigated the effects of iron doping on samarium-modified Bi4Ti3O12-based oxides (BSmT) made via a solid reaction approach to control the band gap of complex oxides. X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-Vis), and X-ray photoelectron spectroscopy (XPS) were used to study the synthesized materials’ structural, optical, and oxygen vacancies. Doping with Fe atoms significantly increased the tunability of the band gap from 3.20 eV to 1.81 eV without violating symmetry. The tuning of bandgap energy in this system was explained based on structural distortion and the formation of oxygen vacancies. This work examined the ferromagnetism and ferroelectricity ordering of the sintered BSmT:F0% and BSmT:F10% samples at room temperature to demonstrate the multiferroelectricity behavior. The findings indicate unsaturated P-E hysteresis loops driven by domain pinning caused by oxygen vacancy formation near domain boundaries. Simultaneously, significant S-type M-H hysteresis loops showed weak ferromagnetic ordering. The findings in this study are encouraging for the development of intrinsic multiferroics for photovoltaic devices for future applications.

Ionic‐Liquid‐Gating‐Induced Hydrogenation in Epitaxial Strontium Ferrite

AbstractIncorporating hydrogen into complex oxides holds promise for discovering exotic phenomena and novel functionalities by promoting couplings between ion and lattice/charge/spin/orbital degrees of freedom. Here, electrolyte gating‐driven hydrogenation is investigated in epitaxial brownmillerite SrFeO2.5 thin films in which the hydrogenation‐induced lattice distortion is qualitatively different from its counterpart SrCoO2.5. The achievable lattice expansion in hydrogenated SrFeO2.5 is weaker than in SrCoO2.5 and primarily occurs along the normal of the stacked octahedral FeO6 and tetrahedral FeO4 layers. Upon the substitution of Fe with Co, the lattice expansion monotonically increases with increase of Co/Fe ratio, implying an intrinsic difference in accommodating hydrogen between Fe‐ and Co‐based brownmillerites. Moreover, a net magnetic moment in hydrogenated SrFeO2.5 films is observed above room temperature, which gradually weakens with the increase of Co substitution, suggesting a stronger canted magnetism in Fe‐based hydrogenated brownmillerites. This work clarifies the electrolyte gating‐driven hydrogenation mechanisms in brownmillerite SrFeO2.5 epitaxial thin films and those with Co substitution, particularly the deterministic role of Co/Fe ratio in the evolution of structure and properties upon hydrogenation.

Improvement of Microwave Dielectric Properties by Impact of Sodium Ion Doping in Complex Oxides for Polymer Composites

The research presented in this study focuses on the dielectric properties of complex oxide-filled epoxy, polyurethane, and silicone rubber composites. Specifically, we investigated various compositions of (1-x) CaWO4-xNa2WO4 (x = 0, 0.2, 0.4), in addition to Na0.5Bi0.5Mo0.5W0.5O4 and Bi2Mo0.5W0.5O6. These complex oxide materials were meticulously synthesized through a solid-state reaction, and their distinct phases were confirmed via rigorous X-ray diffraction (XRD) characterization. We then proceeded to create the composites by manually blending these complex oxides with epoxy, polyurethane, and silicone rubber matrices. The central focus of the study was to examine the impact of varying volume fractions of the complex oxide fillers on the dielectric properties of the composites in the frequency range of 4 – 8 GHz.Our observations revealed a direct correlation between the content of the complex oxide filler and the dielectric properties, including the dielectric constant and dielectric loss. Specifically, the addition of 10 % by volume fraction of (1-x) CaWO4-xNa2WO4 (x = 0, 0.4), Na0.5Bi0.5Mo0.5W0.5O4, or Bi2Mo0.5W0.5O6 fillers to the respective polymer matrices led to a significant enhancement in both the dielectric constant and the loss tangent. Promising results were particularly evident in three composite formulations: the 10 % 0.4Na2WO4-0.6CaWO4/silicone rubber composite demonstrated a dielectric constant (εr) of 2.02 ´ 102 and a loss tangent (tanδ) of -4.07 ´ 10-1 at 7.1 GHz; the 10 % Na0.5Bi0.5Mo0.5W0.5O4/epoxy composite exhibited a dielectric constant of 1.37 ´ 102 and a loss tangent of -6.43 ´ 10-1 at 7.22 GHz; and the 10 % Bi2W0.5Mo0.5O6/polyurethane composite displayed favorable properties with a dielectric constant (ϵr) of 8.37x101 and a loss tangent (tanδ) of -3.4 ´ 10-1 at 7.12 GHz.These results suggest the suitability of these composite materials for a wide range of microwave technology applications, including wireless communication, radar systems, and various microwave devices.