Oxidation Polymorphism Research Articles

Correlation between crystal structure and magnetism in PLD grown epitaxial films of ε-Fe2O3 on GaN

ABSTRACT In the present paper we discuss correlations between crystal structure and magnetic properties of epitaxial ε-Fe2O3 films grown on GaN. The large magnetocrystalline anisotropy and room temperature multiferroic properties of this exotic iron oxide polymorph, make it a perspective material for the development of low power consumption magnetic media storage devices. Extending our recent progress in PLD growth of ε-Fe2O3 on the surface of technologically important nitride semiconductors, we apply reciprocal space tomography by electron and x-ray diffraction to investigate the break of crystallographic symmetry occurring at the oxide-nitride interface resulting in the appearance of anisotropic crystallographic disorder in the sub-100 nm ε-Fe2O3 films. The orthorhombic-on-hexagonal nucleation scenario is shown responsible for the development of a peculiar columnar structure observed in ε-Fe2O3 by means of HRTEM and AFM. The complementary information on the direct and reciprocal space structure of the columnar ε-Fe2O3 films is obtained by various techniques and correlated to their magnetic properties. The peculiar temperature dependence of magnetization studied by the small-field magnetization derivative method and by neutron diffraction reveals the existence of a magnetic softening below 150 K, similar to the one observed earlier solely in nanoparticles. The magnetization reversal in ε-Fe2O3 films probed by X-ray magnetic circular dichroism is found different from the behavior of the bulk averaged magnetization measured by conventional magnetometry. The presented results fill the gap between the numerous studies performed on randomly oriented ε-Fe2O3 nanoparticles and much less frequent investigations of epitaxial epsilon ferrite films with lattice orientation fixed by the substrate.

Low energy photocatalytic glycerol conversion to high valuable products via Bi2O3 polymorphs in the presence of H[formula omitted]O2

In this study, two polymorphs of bismuth oxide were synthesized via the solution-based route for the aqueous phase glycerol transformation to high valuable compounds with low energy photocatalysis in the presence of hydrogen peroxide as the electron acceptor. The results showed that the hydrogen peroxide was deficient to produce OH• radicals in tetragonal bismuth oxide (β-Bi2O3) photocatalyst because it decomposed very fast to H2O and O2 and unoxidized glycerol, resulting in a low glycerol conversion at almost 6.6 times comparing with that of monoclinic bismuth oxide (α-Bi2O3) photocatalyst. Also, more valuable products could be produced with α-Bi2O3 photocatalyst system. In addition, the possible mechanisms of hydrogen peroxide on the low energy photocatalytic performances of both bismuth oxide polymorphs were discussed.

Thermodynamics of high entropy oxides

With the hype of “high entropy” alloys and more recently, “high entropy” ceramics and “high entropy” oxides (HEOs), there has been a great push to investigate and characterize systems with 5 or more components. This push has been extremely beneficial for the materials community as it has led to the development of many new systems with targeted applications. However, with our desire to find “new” and “exotic” materials, we have not spent enough time to step back and think deeply about the fundamental thermodynamic constraints that will guide design of future HEOs. Here, we present data-driven discussions with examples that have been collected from the fields of geology and materials science over the past 50 years to highlight critical thermodynamic parameters and principles that can be used for the design of HEOs. The goal of HEOs is to push the limit of the number of components in a single-phase solid solution to achieve unique and tunable properties. True single-phase HEOs are stabilized if the positive entropy of formation more than compensates an unfavorable enthalpy of formation above some critical temperature, making the overall ΔGf negative i.e. the HEO phase is “entropy stabilized”. Under ideal mixing, the number of components in a solid solution does not affect the solubility of an additional component. In real systems, the types of additional components, their structural transformations, and their associated non-ideal interactions influence the solubility limit. Non-ideal interactions can lead to short- or long-range ordering that decreases the overall configurational entropy. Due to the ionic-covalent nature of oxides, this ordering is the norm, not the exception. In the limited cases where mixing is ideal, charge coupled substitutions can work to influence overall configurational entropy contributions due to unique crystallographic sites. Long-range ordering can be minimized by mixing oxide components that have similar charge or are isostructural. Most excitingly, is the realization that surface energies will drastically affect the stability of oxide polymorphs and solubility limits. Thus, nano-materials are an interesting and novel approach that will vastly extend the HEO engineering space. As one can see, there are many avenues for the design and development of “HEOs” that thermodynamics will allow, even though they all may not be driven explicitly by entropy.

Formaldehyde in hospitals can still represent a risk factor. Oxidative stress and GSTT1 polymorphism

Abstract Background Nurses employed in operating theatres and pathologists are workers professionally exposed to some environmental xenobiotics, such as drugs and formaldehyde (FA). Through experimental and epidemiological studies, both acute and chronic inhalation of FA has been associated with various health effects, including toxicity in the respiratory tract and cancer. The purpose of this study was to evaluate the relationship between occupational exposure to FA and the intensity of oxidative stress (OS). Methods 87 female hospital workers were enrolled in a Turin hospital in Italy. Each subject filled a questionnaire and provided biological samples to measure OS biomarkers: 15-F2t-Isoprostane, malondialdehyde (MDA) and total glutathione content (GSX) in urine and inflammatory mediators and receptors (sIL-6R, VEGF-R2, TNFR1, TNFa, FGF2, CD30, CD27) in blood. All individuals were genotyped for CYP1A1, GSTT1, GSTM1, TNFa, and IL-6 polymorphisms. A personal passive air sampler, worn for a working shift (8h), assessed personal FA exposure. Results Subjects exposed to FA (27%) resulted to have a significant higher amount of 15-F2t-Isop (p = 0.000), MDA (p = 0.000), GSX (p = 0.001) compared with non-exposed workers. FA concentration was positively correlated with prevalence of reported respiratory symptoms (p = 0.004), 15-F2t-Isop (p = 0.044), GSX (p = 0.000), MDA (p = 0.000), FGF2 (p = 0.000), CD27 (p = 0.000) and negatively with sIL-6R (p = 0.001), VEGF-R2 (p = 0.000). A significant reduction was found in GSTT1 positive subjects concerning MDA levels (p = 0.000). The same relationship was found in the control group (b=-2.25; C.I. 0.21 - 0.516; p = 0.06). Conclusions FA exposure is confirmed to be an OS inductor and to be correlated with inflammatory response, highlighting how daily occupational exposure to this air pollutant can result in measurable biological outcomes. Key messages Daily occupational exposure to FA results in a disruption of oxidative status and inflammatory profile. GSTT1 gene polymorphism is able to influence the MDA levels in the control group.

Association between Dietary Zinc and Selenium Intake, Oxidative Stress-Related Gene Polymorphism, and Colorectal Cancer Risk in Chinese Population - A Case-Control Study

Zinc and selenium may protect against colorectal cancer (CRC) progression through their anti-oxidative effects. This study examined the independent and combined effect of dietary zinc and selenium intake, and polymorphisms of the oxidative stress-related genes (superoxide dismutase 1, superoxide dismutase 2, glutathione peroxidase, and catalase) on CRC risk in a Chinese case-control study. A total of 493 cases and 498 sex and age-matched controls were randomly selected from an ongoing case-control study. Dietary information was assessed through face-to-face interviews using a validated food frequency questionnaire. Multiplex PCR-ligase detection reaction was used for genotyping the target SNPs. Multivariable logistic regression was used to estimate the odds ratios (ORs) and 95% confidence interval (CI). Intake of selenium was found to be inversely associated with CRC risk, while zinc was not associated with CRC risk. The ORs (95% CI) for the highest vs. the lowest quartile were 0.42 (95% CI 0.28, 0.64, P trend < 0.001) for selenium and 0.96 (95% CI 0.63, 1.47, P trend = 0.505) for zinc. Combined effect was observed between zinc and SOD1 rs4998557 on CRC risk (P interaction < 0.05). This study identified a novel diet-gene interaction in the oxidative stress pathway on CRC risk in Chinese population.

Active Learning Accelerated Discovery of Stable Iridium Oxide Polymorphs for the Oxygen Evolution Reaction

The discovery of high-performing and stable materials for sustainable energy applications is a pressing goal in catalysis and materials science. Understanding the relationship between a material’s structure and functionality is an important step in the process, such that viable polymorphs for a given chemical composition need to be identified. Machine-learning-based surrogate models have the potential to accelerate the search for polymorphs that target specific applications. Herein, we report a readily generalizable active-learning (AL) accelerated algorithm for identification of electrochemically stable iridium oxide polymorphs of IrO2 and IrO3. The search is coupled to a subsequent analysis of the electrochemical stability of the discovered structures for the acidic oxygen evolution reaction (OER). Structural candidates are generated by identifying all 956 structurally unique AB2 and AB3 prototypes in existing materials databases (more than 38000). Next, using an active learning approach, we find 196 IrO2 polymorphs within the thermodynamic amorphous synthesizability limit and reaffirm the global stability of the rutile structure. We find 75 synthesizable IrO3 polymorphs and report a previously unknown FeF3-type structure as the most stable, termed α-IrO3. To test the algorithms performance, we compare to a random search of the candidate space and report at least a 2-fold increase in the rate of discovery. Additionally, the AL approach can acquire the most stable polymorphs of IrO2 and IrO3 with fewer than 30 density functional theory optimizations. Analysis of the structural properties of the discovered polymorphs reveals that octahedral local coordination environments are preferred for nearly all low-energy structures. Subsequent Pourbaix Ir–H2O analysis shows that α-IrO3 is the globally stable solid phase under acidic OER conditions and supersedes the stability of rutile IrO2. Calculation of theoretical OER surface activities reveal ideal weaker binding of the OER intermediates on α-IrO3 than on any other considered iridium oxide. We emphasize that the proposed AL algorithm can be easily generalized to search for any binary metal oxide structure with a defined stoichiometry.

Metastability at Defective Metal Oxide Interfaces and Nanoconfined Structures

AbstractMost of the paradigms in materials science and technology firmly rely on equilibrium materials, i.e., phases with the lowest Gibbs energy under thermodynamic conditions. In nature, however, complexity rules, and the other aspect is metastability. This review aims to provide a coherent description of such effects and to formulate hypotheses on the fundamental energetic mechanisms of residual metastability in crystalline metal oxide polymorphs. The authors especially focus on different forms of broken symmetry at the interface, e.g., induced by defects, lattice strain/stress, and elemental diffusion. The discussion also provides perspective on the technological implications and possibilities arising from identifying a general methodology for establishing metastability in polymorphic functional metal oxides for energy applications, catalysis, and electronics.

Lead exposure and its interactions with oxidative stress polymorphisms on lung function impairment: Results from a longitudinal population-based study

Exposure to lead (Pb) and cadmium (Cd) were related to lung function impairment, and this association may be modified by genetic variants in oxidative stress response. Here we enrolled 1243 coke-oven workers in a prospective cohort who were followed up from 2010 to 2014, assessed the associations of Pb and Cd exposure with 4-year lung function impairment, and further explored the interaction effects of Pb with 2664 single nucleotide polymorphisms (SNPs) in 345 oxidative stress related genes. Urinary levels of Pb, Cd, and two oxidative stress biomarkers [8-iso-prostaglandin F2α (8-iso-PGF2α) for lipid peroxidation and 8-hydroxy-2′-deoxyguanosine (8-OHdG) for oxidative DNA damage] were measured at baseline only and their lung function levels were measured both at baseline and at the end of follow-up. Each 10-fold increase in urinary Pb was associated with −159 (95%CI: −254, −64.2) mL and −3.63% (95%CI: −6.48%, −0.78%) changes in FEV1 and percent predicted FEV1 (ppFEV1), respectively. But none significant associations were observed for Cd. NQO1 rs2917670 showed significant interaction with Pb on elevated FEV1 decline after multiple comparison (Pint=1.54 × 10−5). In addition, urinary Pb increased with 8-iso-PGF2α and the rs2917670-C could significantly decrease NQO1 expression in normal lung tissues. These findings suggested the gene-environmental interaction of NQO1 rs2917670 and Pb exposure on the reduction of FEV1. The effect of Pb exposure on elevated oxidative stress and the decreased expression of antioxidant enzyme NQO1 caused by rs2917670-C allele may partly explain the underlying biological mechanism.

Development of highly sensitive [Ru(bpy)3]2+ - Based optical oxygen sensing thin films in the presence with Fe3O4 and Fe3O4@Ag NPs

Optical sensors based on chemically sensitive matrices/dyes have been used for accurate measurements of oxygen levels. In this study, the intensity-based response of highly sensitive tris(2,2′-bipyridyl) ruthenium(II) chloride [Ru(bpy)3]2+ dye to oxygen (O2) was analyzed in the polymeric ethylcellulose matrix (EC) in the presence of two magnetite forms; Fe3O4 and Fe3O4@Ag nanoparticles (NPs). Fe3O4 NPs were synthesized by flame spray pyrolysis (FSP) and then Fe3O4@Ag NPs were prepared by a core-shell coating method. Iron oxide polymorphs were characterized by using X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). It was measured that the particles synthesized by the FSP technique have an average size of ˂60 nm Fe3O4, Fe3O4@Ag NPs, and 1-butyl-3-methylimidazolium tetrafluoroborate; ([BMIM][BF4]) were used as additives for enhancement of the sensitivity of the [Ru(bpy)3]2+ dye to O2 gas. The effects of these additive materials were examined by photoluminescence spectroscopy (PL). [Ru(bpy)3]2+ dye doped nanofiber in the presence with the Fe3O4@Ag NPs additive yielded higher Stern-Volmer constant (KSV) and extended linear response range when compared with the sensing slides in the presence with Fe3O4 NPs and the additive-free forms. The higher response ratio (I0/I100) was found as 3.45 for the ruthenium dye doped EC nanofiber form in the presence with Fe3O4@Ag NPs. Also, KSV values were calculated as 2.41 × 10−2 between the concentration range of 0–100% [O2]. According to our knowledge, it is the first time Fe3O4 and Fe3O4@Ag NPs were used for the enhancement of oxygen sensitivity of the ruthenium dye.

Iron intake, oxidative stress-related genes and breast cancer risk.

Iron has been suggested to contribute to breast cancer development through oxidative stress generation. Our study investigated associations between iron intake and breast cancer risk, overall and by menopausal and estrogen receptor/progesterone receptor (ER/PR) status, and modification by oxidative stress-related genetic polymorphisms (MnSOD, GSTM1 and GSTT1). A population-based case-control study (3,030 cases and 3,402 controls) was conducted in Ontario, Canada. Iron intake (total, dietary, supplemental, heme, nonheme) was assessed using a validated food frequency questionnaire. Odds ratios (OR) and 95% confidence intervals (CI) were estimated from multivariable logistic regression models. Interactions between iron intake and genotypes were assessed among 1,696 cases and 1,761 controls providing DNA. Overall, no associations were observed between iron intake and breast cancer risk. Among premenopausal women, total, dietary and dietary nonheme iron were positively associated with ER-/PR- breast cancer risk (all ptrend < 0.05). Among postmenopausal women, supplemental iron was associated with reduced breast cancer risk (OR>18 vs. 0 mg/day = 0.68, 95% CI: 0.51-0.91), and dietary heme iron was associated with an increased risk, particularly the ER-/PR- subtype (ORhighest vs. lowest quintile = 1.69, 95% CI: 1.16-2.47; ptrend = 0.02). Furthermore, GSTT1 and combined GSTM1/GSTT1 polymorphisms modified some of the associations. For example, higher dietary iron was most strongly associated with increased breast cancer risk among women with GSTT1 deletion or GSTM1/GSTT1 double deletions (pinteraction < 0.05). Findings suggest that iron intake may have different effects on breast cancer risk according to menopausal and hormone receptor status, as well as genotypes affecting antioxidant capacity.

Strategy to control magnetic coercivity by elucidating crystallization pathway-dependent microstructural evolution of magnetite mesocrystals

Mesocrystals are assemblies of smaller crystallites and have attracted attention because of their nonclassical crystallization pathway and emerging collective functionalities. Understanding the mesocrystal crystallization mechanism in chemical routes is essential for precise control of size and microstructure, which influence the function of mesocrystals. However, microstructure evolution from the nucleus stage through various crystallization pathways remains unclear. We propose a unified model on the basis of the observation of two crystallization pathways, with different ferric (oxyhydr)oxide polymorphs appearing as intermediates, producing microstructures of magnetite mesocrystal via different mechanisms. An understanding of the crystallization mechanism enables independent chemical control of the mesocrystal diameter and crystallite size, as manifested by a series of magnetic coercivity measurements. We successfully implement an experimental model system that exhibits a universal crystallite size effect on the magnetic coercivity of mesocrystals. These findings provide a general approach to controlling the microstructure through crystallization pathway selection, thus providing a strategy for controlling magnetic coercivity in magnetite systems.

Oxidative Stress-Related Gene Polymorphisms Are Associated With Hepatitis B Virus-Induced Liver Disease in the Northern Chinese Han Population.

Oxidative stress is closely related to the occurrence and development of various diseases such as cancer, diabetes, and cardiovascular and infectious diseases. We identified six critical genetic variants related to oxidative stress, and evaluated their main effects and their interaction effects on hepatitis B virus (HBV)-induced liver diseases. We enrolled 3,128 Han Chinese subjects into five groups: healthy controls, chronic hepatitis B (CHB), liver cirrhosis (LC), hepatocellular carcinoma (HCC), and natural clearance. We then determined the genotypes in each group for CYBA-rs4673, NCF4-rs1883112, NOX4-rs1836882, rs3017887, SOD2-rs4880, and GCLM-rs41303970, and evaluated the association between these variants and HBV-induced liver diseases. Gene-gene interactions were evaluated using generalized multifactor dimensionality reduction, logistic regression, and four-by-two tables. Significant associations were observed between healthy controls and the CIB group (CHB+LC+HCC). The CYBA-rs4673AG genotype was associated with a 1.356 rate of susceptibility of HBV-induced liver disease compared to the wild type GG genotype. The NCF4-rs1883112G allele occurred more frequently in healthy controls than in the CIB group in all three models (dominant, codominant, and recessive). Nox4-rs1836882 TC showed a protective association, being more frequent in healthy controls compared to the wild type TT genotype. GCLM-rs41303970A was associated with HBV-induced liver disease. The overall best model by multifactor dimensionality reduction was a five factor interaction model that had the highest cross validation consistency (10/10) and test accuracy (0.5669), P = 0.001. Oxidative stress-related gene polymorphisms are likely to be associated with HBV-induced liver disease, suggesting that information on these variations is useful for risk assessment of HBV-induced liver disease.

A Metal-Oxide Contact to ε-Ga2O3 Epitaxial Films and Relevant Conduction Mechanism

In this work, the conduction mechanisms across novel contacts to epitaxial films of pure phase epsilon-Ga2O3 (ε-Ga2O3) were investigated. Different structures made by sputtered metal and oxide thin films were tested as electrical contacts. I-V characteristics show heterogeneous behaviors, revealing different conduction mechanisms according to the applied bias. The results are interesting as they offer a viable method to obtain ohmic contacts on ε-Ga2O3, which is less studied than other gallium oxide polymorphs but may find application in new electronic and optoelectronic devices. The newly developed ohmic contacts allow to fabricate simple test devices and assess the potential of this material.

Structural and morphological tuning of iron oxide polymorphs by ECR plasma-assisted thermal oxidation.

The work presented involves the generation of oxygen plasma species at low pressure utilizing an Electron Cyclotron Resonance (ECR) plasma reactor, and their interactions with micron- and nano-sized iron films (M-Fe and N-Fe film respectively) prepared using ethyl cellulose processed at high temperature. A specially designed radiation heater (RH) was used to raise the surface temperature of the film rapidly, exactly at the film interface, where the plasma species interact with the surface. As a result of the interaction of oxygen plasma species and temperature, iron is oxidized to different polymorphs depending on the operating pressure and hence oxygen gas flow rate. The phase, as well as the morphology of the film was controlled by monitoring the oxygen flow rate using the unique Plasma-Assisted Thermal Oxidation (PATO) process. Different polymorphs, viz., Fe3O4, γ-Fe2O3, α-Fe2O3 and different morphologies, such as polygonal, compact facets, wire-like (1D) nanostructures at the surface were obtained for the films processed using PATO. The selected PATO-processed films were investigated for Field Electron Emission (FEE) properties. The 1D-grown surface of iron oxide obtained from the M-Fe film showed a turn-on field of 3 MV m−1 and emission current of 337 μA cm−2, whereas the pyramidal surface morphology obtained using N-Fe film gives a turn-on field of 3.3 MV m−1 with an emission current of 578 μA cm−2.

Polymorphism in MTHFR (at SNPs 677 and 1298) in Paternal Sperm DNA and Risk of Retinoblastoma in their Children.

Letter to: Oxidative Stress and Polymorphism in MTHFR SNPs (677 and 1298) in Paternal Sperm DNA is Associated with an Increased Risk of Retinoblastoma in Their Children: A Case–Control StudyJ Pediatr Genet 2018; 07(03): 103-113DOI: 10.1055/s-0038-1667037

A Precursor Approach for the Development of Lace-like Fe2O3 Nanocrystallites Triggered by Pressure Dependent Nucleation and Growth of Akaganeite over Clay Based Composites for Toluene Combustion

Embedded catalysts for toluene combustion, featuring iron oxide (FeOx) moieties on the surface of clay derived porous heterostructural supports (PCH) were developed. The nucleation and growth of Fe4Cl0.44O3.56(OH)4.44(H2O)0.2 (akaganeite) in the function of Fe precursor interaction with the support entailed creation of nanostructured Fe oxides on the PCH surface. The hydrothermal forcing of ions migration and thermal transformation of as-synthesized Fe-PCH altered the surface composition and crystallinity of the formed nanostructured Fe oxides, thereby affecting the advantageous effects of donation gauged by electronic transfer. The polymorphism of Fe oxides created on PCH supports resulted in diverse catalytic activity of toluene combustion. Analysis of XPS Fe 2p core excitations showed that elongation of crystallization time of iron moieties on as synthesized Fe-PCH, as well as shortening of the annealing time, led to highly oxidized Fe species, mainly in the form of an α-Fe2O3 phase. Pressure dependent...

Autism Spectrum Disorders and Perinatal Complications-Is Oxidative Stress the Connection?

Background: Autism spectrum disorders (ASD) are complex psychiatric disorders, with gene environment interaction being in the basis of their etiology. The association of perinatal complications and ASD is well established. Recent findings suggested that oxidative stress and polymorphism in genes encoding antioxidant enzymes might be involved in the development of ASD. Glutathione transferases (GSTs) have an important role in the antioxidant defense system. We aimed to establish whether the predictive effects of prenatal and perinatal complications (as possible oxidative stress inducers) on ASD risk are dependent on GST polymorphisms. Methods: The study included 113 ASD cases and 114 age- and sex group-matched healthy controls. All participants were genotyped for GSTA1, GSTM1, GSTT1, and GSTP1 polymorphisms. The questionnaire regarding prenatal and perinatal risk factors and complications was administered for all the subjects in the study. Results: The evaluated perinatal complications as a group significantly increased the risk of ASD [odds ratio (OR) = 9.415; p = 0.000], as well as individual perinatal complications, such as prematurity (OR = 11.42; p = 0.001), neonatal jaundice (OR = 8.774; p = 0.000), respiratory distress syndrome (OR = 4.835; p = 0.047), and the use of any medication during pregnancy (OR = 2.413; p = 0.03). In logistic regression model, adding GST genotypes did not modify the significant effects found for prematurity and neonatal jaundice as risk factors in ASD. However, there was a significant interaction of GST genotype with medication use during pregnancy and the use of tocolytics during pregnancy, which was predictive of ASD risk only in carriers of GSTM1-null, as opposed to carriers of GSTM1-active genotype. Conclusion: Specific perinatal complications may be significant risk factors for ASD. GSTM1 genotype may serve as a moderator of the effect of some prenatal factors on the risk of ASD such as using medication during pregnancy. It may be speculated that different oxidative stress-related genetic and environmental factors could lead to development of ASD. Apart from etiological mechanisms, possible therapeutic implications in ASD are also discussed.

Влияние оксидативного стресса и полиморфизма гена каталазы CAT-262G/A на тяжесть течения язвенного колита

Влияние оксидативного стресса и полиморфизма гена каталазы CAT-262G/A на тяжесть течения язвенного колита

Electronic-reconstruction-enhanced hydrogen evolution catalysis in oxide polymorphs

Transition metal oxides exhibit strong structure-property correlations, which has been extensively investigated and utilized for achieving efficient oxygen electrocatalysts. However, high-performance oxide-based electrocatalysts for hydrogen evolution are quite limited, and the mechanism still remains elusive. Here we demonstrate the strong correlations between the electronic structure and hydrogen electrocatalytic activity within a single oxide system Ti2O3. Taking advantage of the epitaxial stabilization, the polymorphism of Ti2O3 is extended by stabilizing bulk-absent polymorphs in the film-form. Electronic reconstructions are realized in the bulk-absent Ti2O3 polymorphs, which are further correlated to their electrocatalytic activity. We identify that smaller charge-transfer energy leads to a substantial enhancement in the electrocatalytic efficiency with stronger hybridization of Ti 3d and O 2p orbitals. Our study highlights the importance of the electronic structures on the hydrogen evolution activity of oxide electrocatalysts, and also provides a strategy to achieve efficient oxide-based hydrogen electrocatalysts by epitaxial stabilization of bulk-absent polymorphs.

Structure‐Dependent Electrical and Magnetic Properties of Iron Oxide Composites

The physical and chemical properties of polymorphs of iron oxides are utilized for electronic, energy, and biomedical applications. To design a functional material with arresting interplay at the interfaces and boundaries between polymorphs of iron oxide (Fe3O4 – magnetite with Fe2O3 – hematite), two different approaches of synthesis are adopted, namely, mechanical mixing and in situ growth. Unlike mechanically mixed composites, the in situ‐synthesized composites show the development of a highly distinct non‐stoichiometric, Fe21.34O32 phase at the boundary. The atomically diffused composition at boundary is found to govern the fourfold increase in conductivity. By varying the ratio of constituent iron oxide polymorphs, the dielectric constant can be tuned and is found to be highly frequency dependent with minimum loss in tan δ plot. The inherent ferromagnetism of Fe3O4 reveals to be retained in composite samples.