Cr Doping Research Articles

Evolution of ferrimagnetism against Griffiths singularity in calcium ruthenate

The magnetism in the correlated metal CaRuO3 is enigmatic as it is poised near a triple point among the ferromagnetic, antiferromagnetic, and paramagnetic ground states. Here we report a detailed work on structural, spectroscopic, magnetic, and transport properties in CaRu 1−x Cr x O3. We find that Cr doping reduces the orthorhombicity in CaRuO3. Surprisingly, a tiny (x = 0.01) amount of Cr-doping drives the magnetic ground state from ‘paramagnetic-like’ to ferrimagnetic. Slightly higher Cr-doping (x = 0.05) results formation of magnetic clusters which gives rise to Griffiths singularity and power law divergence in magnetic susceptibility. The magnetism in CaRu 1−x Cr x O3 is explained in terms of ‘seven atom’ ferrimagnetic clusters. Electrical transport shows a gradual evolution of a non-metallic state upon Cr-doping. In particular, for x ⩾ 0.1, the temperature-dependent resistivity follows Mott-VRH conduction. The XPS study also supports significant role of disorder and electron correlation which effectively reduces the itinerant character of electrons. Finally, a new T-x phase diagram is constructed depicting the evolution of electronic and magnetic state in CaRu 1−x Cr x O3.

Tuning the electrochemical properties of ZnO through chromium doping and its suitability for supercapacitor application

ZnO nanoparticles doped with chromium (Cr) were synthesized through a simple sol gel route. The successful Cr doping into the ZnO lattice has been evidenced via several characterisation techniques i.e., XRD and XPS. A high oxygen vacancies (OV) density has been located through Photoluminescence (PL) and EPR studies for the Cr doped ZnO (1 %) (ZnCr1) sample. The high density of OV defects induced from Cr doping in ZnO lattice was considered at the origin of the improved electrochemical performances by promoting efficient electron transfer ability with intercalation process of the electrolyte's ions during charge-discharge mechanism. The ZnOCr1 electrode displays an important capacitance value (367 F.g−1), ultrahigh capacitance retention (86 %) while changing the current from 1 to 20 A·g−1, and marvellous stability of 84 % during 4000 cycles. An asymmetric supercapacitor based ZnOCr1 electrode achieves significant potential window up to 1.6 V with encouraging specific energy density. The device showcases a satisfactory specific energy of 27.1 Wh·Kg−1 at specific power of 480 W·Kg−1 and a great retention of 17 % decay after 4000 cycles at current density of 10 A g−1. This opens door to the developed ZnO-Cr1 material for its application in future supercapacitor devices.

Effect of Cr doping and photoresponse properties of photodiode based on CdO thin films

AbstractCadmium oxide (CdO) and chromium (Cr) doped CdO thin films with various Cr wt% contents (0.1, 0.5, 1, 2 at.%) are synthesised on soda lime glass (SLG) substrates. Results from X-ray analysis indicate that all thin films are in cubic nature with (111) preferential orientation. Cr doping does not appear to result in a transition from one crystal phase to another. CdO with the 2.0 wt% Cr doping absorbs much more light than undoped CdO in low wavelength region (< ≈450 nm), giving a maximum absorption peak in the ultraviolet region. Cr doped CdO/p-Si heterojunction shows the Cr wt% content-sensitive rectification property, achieving a high ratio of 105. In addition, Cr doped CdO/p-Si heterojunction exhibits photodiode behavior and possesses an improved photo-to-dark current ratio of ≈153. This work introduces an occasion to develop the optoelectronic devices based on Cr doped CdO thin films.

Effect of metal doping on the laser induced damage of KDP crystals: A first-principles study

KH2PO4 (KDP) crystal is a kind of widely used nonlinear optical material, but its manufacturing process produces various defects which influence the laser induced damage threshold (LIDT) of the KDP crystal. This work studies the influence of the metal doping defects (Na, Cr, Co, Ni, Zn and Pb) on the stability, electronic structure, optical and mechanical properties of KDP crystal by the density functional theory (DFT) calculation. Results show that the change of lattice parameters and bond lengths, and the formation energies of the metal doped KDP have close relationship with the radius of the doped metal atoms. The electronic and optical calculations show that the Na doping defects have little effect on the energy band and optical properties of KDP crystals, but Cr, Zn and Pb doping defects show large optical absorption peaks. Meanwhile, the Cr, Co, Ni and Pb atoms have great influence on the mechanical properties of the KDP. Therefore, the KDP synthesis process needs to pay particular attention to control Cr and Pb doping defects to avoid decreasing the LIDT of KDP. This work explains the effect of metal doping on the laser damage resistance of KDP crystals and provides a theoretical basis for enhancing the performance of KDP crystals.

Achieving rapid sodiation/desodiation kinetics in NASICON-structured Na3MnTi(PO4)3 via Cr doping

Na3MnTi(PO4)3 is one of the most promising cathode candidates for sodium-ion batteries owing to its low cost, high operating voltage, and large reversible capacity. However, its electrochemical performance is significantly impeded by its deteriorative structure and sluggish Na+ diffusion kinetics. Herein, Cr-doping is introduced to tailor the structure of Na3MnTi(PO4)3, which helps to lengthen the Na2-O bond and expand the Na ion diffusion channels. X-ray diffraction, cyclic voltammetry, galvanostatic intermittent titration technique, and first principle calculations confirm the broadened diffusion channel for Na+ and facilitated Na+ diffusion rate after Cr-doping. As a result, the Na3.1MnTi0.9Cr0.1(PO4)3 electrode exhibits superior electrochemical performance with high discharge capacity (167.5 mAh g–1 at 0.1 C), outstanding rate capability (127.5 mAh g–1 at 10 C), and remarkable cyclability (70.56 % retention after 1400 cycles at 5 C). We believe that the results are useful for the design of high-performance NASICON-structured cathode materials for practical sodium-ion batteries.

Cr dopants and S vacancies in ZnS to trigger efficient photocatalytic H2 evolution and CO2 reduction

Driven by endless solar energy, photocatalytic H2 evolution from water splitting and CO2 conversion to hydrocarbon fuels over semiconductor photocatalysts are of great potential to simultaneously settle the greenhouse effect and energy shortage. Herein, Cr-doped zinc sulfide (ZnS) with accompanying sulphur vacancies (Vs) photocatalytic materials is developed by a facile hydrothermal method. The Cr dopants centralize photoinduced holes and Vs trap electrons, forming a synergistic effect for accelerating charge separation and transfer. The reaction energy barrier for both H2 evolution and CO2 reduction has been optimized. Therefore, in the absence of a cocatalyst, the optimal catalyst (Zn0.94Cr0.06S) achieves an outstanding H2 evolution activity of 20.3 mmol g−1 h−1, which is approximately 2.9 times higher than 6.9 mmol g−1 h−1 for pristine ZnS. In addition, in the gas-solid reaction system without co-catalysts or sacrificial agents, the Zn0.94Cr0.06S exhibits a considerable CO evolution rate of 19.56 μmol g−1 h−1, about 10.1 times higher than ZnS (1.94 μmol g−1 h−1). Both the performances for H2 evolution and CO2 reduction of Zn0.94Cr0.06S outperform most of the previously reported photocatalysts. Particularly, the Zn0.94Cr0.06S possesses superior stability, the photoactivity of which exhibits no noticeable deactivation after six cycles’ reactions. This work may shed light on the rational design and fabrication of highly efficient materials via combining individual element doping and defect engineering.

Cr dopant regulating d-orbital electronic configuration of NiFe spinel oxide to improve oxygen evolution reaction in Zn-air battery

Significant advancements towards enhancing the catalytic activity of spinel ferrites in oxygen evolution reaction (OER) have been achieved, however, further studies are required on this regard. In this study, Cr-doped spinel ferrite (NiFe2O4) embedded in N-doped C (Cr-NiFe2O4@NC) was synthesized via a high-temperature treatment using an NiFe Prussian blue analog as a precursor and K2Cr2O7 as a Cr source. Owing to the strong octahedral site preference energy, Cr3+ ions were successfully doped into octahedral sites and tailored the electronic configuration of NiFe2O4, as confirmed by XPS. The Cr-substituted Cr-NiFe2O4@NC exhibited the overpotential of 241 mV at 10 mA cm−2, which was smaller than that of NiFe2O4@NC (266 mV) at the same current density. Meanwhile, the Tafel slope of Cr-NiFe2O4@NC (65.32 mV dec−1) was also lower than that of NiFe2O4@NC (86.96 mV dec−1). Therefore, the Cr substitution can improve the electrocatalytic OER performance of NiFe2O4@NC. In particular, an assembled rechargeable Zn-air battery using Cr-NiFe2O4@NC as the cathode catalyst afforded a high power density (61.1 mA cm−2) together with a high specific capacity (740 mA g−1). Amazingly, it could power light-emitting diodes, demonstrating its real-world application. Density functional theory calculations revealed that Cr ion doping led to electron transfer in NiFe2O4, resulting in a density of electronic states close to the Fermi level, which probably regulated the adsorption/desorption behaviors of oxygenate intermediates (*O and *OOH), thus promoting the reaction kinetics of the OER. This study provides a helpful basis for the development of spinel oxides with high electrocatalytic OER activity and durability via cation doping.

The lattice contraction of UO2 from Cr doping as determined via high resolution synchrotron X-ray powder diffraction

High resolution synchrotron powder X-ray diffraction analysis of Cr-doped UO2 samples with additions of Cr2O3 as 0, 500, 1000, 1500, 2500 to 3500 ppm prepared under sintering conditions of -420 kJ/mol and 1700 °C is reported. The lattice dependence from Cr doping is established through the Rietveld refinement method where the rate of linear lattice parameter contraction from Cr doping, Δacr, was found to be considerably smaller and more subtle than previously described. This investigation highlights the need for high resolution and precise specimen preparation when measuring and interpreting subtle changes to nuclear material crystal structures due to trace doping.

Tunable anomalous resistance and large magnetoresistance in HfTe5 by atom doping

The Dirac layered material HfTe5 renews significant interest due to its exotic band structure, leading to abundant transport properties, such as the anomaly resistance peak and its large magnetoresistance. Here, we prepared single crystals HfTe5 and Cr-doped CrxHf1−xTe5 and carried out their electrical transport measurements to explore the underlying physical origin of the anomaly resistance behavior and the large magnetoresistance. An anomalous resistance peak was observed in both intrinsic HfTe5 and the Cr-doped ones. Specifically, the peak temperature in the doped ones experiences an obvious shift from 52 to 34 K as the doping concentration x increases from 0 to 0.15, as well as the magnitude of the peak resistance is significantly enhanced. Furthermore, the magnetoresistance of CrxHf1−xTe5 is reduced by more than one order of magnitude compared with the intrinsic one. The significant reduction in magnetoresistance after Cr doping is attributed to the breaking of the balance between electron and hole carriers, which is confirmed by Kohler's plots. Meanwhile, in the sample where the magnetoresistance was minimized, we observed Shubnikov–de Haas oscillations. These observations illustrate that the large magnetoresistance is primarily contributed by the compensation of electrons and holes rather than the high mobility. Our findings provide valuable insight into how to engineer HfTe5 to achieve large magnetoresistance and its further applications in magnetic sensors and spintronics.

Cr-induced enhancement of structural stability in δ-MnO2 for aqueous Zn-ion batteries

δ-MnO2 was proposed as a promising cathode material for aqueous Zn-ion batteries. Nonetheless, its potential application has been impeded by its unstable crystal structure and sluggish reaction kinetics with Zn ions. Herein, we utilized Cr to modify δ-MnO2 by a simple hydrothermal method to develop cathode materials for aqueous Zn-ion batteries with better stability and electron transport properties. The introduction of Cr enhanced the specific capacity and cycling stability of δ-MnO2, in particular, the 3% Cr doped δ-MnO2 electrode exhibited a large specific capacity of 229.2 mAh·g−1 at 0.1 A·g−1 and an excellent capacitance retention of 86.0% after performing 300 cycles. The density functional theory (DFT) calculations indicate that the introduction of Cr decreases the band gap of MnO2 and enhances electron migration in the electrode material. Meanwhile, the introduction of Cr substantially improved the Zn ion adsorption and enhanced the binding energy of δ-MnO2, indicating that the addition of Cr promoted the interaction between the Cr doping δ-MnO2 (Cr-MnO2) electrode materials with Zn ions, while making the structure of the electrode materials more stable. As a result, this suppresses the Jahn-Teller distortion and reduces the solvation and phase transition of Mn.

Quaternary layered Cr‐doped modified NCMFe cathode material for Lithium‐Ion Batteries

AbstractA series of cathode materials, Li[Ni0.6Co0.12Mn0.2Fe0.08]1‐xCrxO2 (x=0, 0.02, 0.04, 0.06), are synthesized via the co‐precipitation method. Structural characterization shows that Cr3+ ions are successfully incorporated into the material structure and evenly dispersed on the surface of crystal particles with other metal elements. The Cr‐doped material shows a well‐defined hexagonal layered structure with less cation mixing, and the increase in interionic and interlayer distances is beneficial for the transport of lithium ions. Compared to the pure NCMFe phase, the cyclic and rate performances of the Cr‐doped quaternary materials have been significantly improved. Among them, the 4Cr material exhibits the best electrochemical performance. The capacity retention rate after 50 charge‐discharge cycles at 0.1 C was increased from 74.83 % to 87.32 %. The rate performance has also increased from 87.6 % to 92.69 %. The Cr‐doped cathode can reduce the charge transfer resistance and enhance the stability of the layered structure, which results in outstanding electrochemical performance of the Cr‐doped cathode. CV and EIS tests were conducted on materials with various Cr doping levels, further confirming that Cr doping can reduce the degree of polarization in electrode materials, enhance charge and discharge reversibility, and reduce the charge transfer resistance of materials.

A new noncollinear triangle antiferromagnetic phase in Mn3GaN by Cr doping

The study on spintronic materials with noncollinear antiferromagnetic (AFM) structures is a hot research field. Antiperovskite Mn-based compounds Mn3XN with Kagome lattice have attracted extensive attention, which display abundant physical properties. Particularly, some with non-zero Berry curvature can exhibit anomalous Hall effects or spin Hall effects despite their noncollinear AFM structures. They are expected to have potential applications in AFM spintronic devices. Here a new noncollinear triangle AFM phase besides the well-known Γ5g phase in Mn3GaN was observed with the space group of RI3‾c by Cr doping at Mn sites. By Neutron powder diffraction, the magnetic structure was determined. The spins of Mn at (111) plane in a Kagome lattice not only orient toward in-plane triangle center which is like Γ4g configuration, but also present out-plane rotation. As a result, a magnetic phase diagram was built. Correspondingly, the electronic transport property presents a different behavior accompanied by the transformation of magnetic phase from Γ5g into RI3‾c. And the thermal expansion behavior is tuned on account of the alteration of magnetic phase. Both the electronic transport property and the thermal expansion behavior in Mn3-xCrxGaN compounds correlate with the magnetic structures, indicating a strong coupling between spin-charge-lattice. The appearance of the new noncollinear triangle AFM phase in Mn3XN antiperovskite compounds will provide a possible way for exploring new AFM spintronic materials.

Effect of Magnesium Site Doping on Electrochemical Properties of Mg-Mn Composite Materials and Application of Carpet-Like Sheets Composite Formed by Cr Doping in Aqueous Zinc-Ion Batteries

Manganese based compounds have very stable electrochemical properties, thus they are widely applied in aqueous zinc-ion battery. However, it is easy to dissolve manganese in the process of charge and discharge, which leads to the collapse of the cathode material structure. In this paper, the composite materials of manganese carbonate and magnesium carbonate were synthesized by hydrothermal method, and its properties were optimized by doping modification. According to the electrochemical tests, the electrochemical performance of the material synthesized with 5% Cr doping is relatively stable. Moreover, with the increase of Cr content, the charge transfer impedance of the material can be significantly reduced. In the cyclic tests, after 60 cycles of charge and discharge under different current densities, and another several cycles at the current density of 50 mA g−1, the capacity rises to 212.01 mAh g−1, higher than the first discharge capacity. SEM tests are also conducted to survey the micro-structure of the material, besides the cube unit, there are also carpet-like sheets made of nano-sized joined petal-like unit, which greatly increases the specific surface area of the material. According to the data of EDS and XPS, the fact that that the types and valence states of elements in the composites were consistent with those in manganese carbonate and magnesium carbonate are confirmed. Through the infrared and Raman tests, the functional groups in the synthesized material are proven to correspond to the molecular formula. From the XRD pattern, no obvious impurity peaks can be observed. With all the data obtained from physical characterization, it can be concluded that the material is mainly composed of manganese carbonate and magnesium carbonate.

Comparison of Cr and Sr doping into TiO2 for photocatalytic removal of gaseous 1,2 dichloroethane

1,2-dichloroethane/DCE, a volatile organic compounds (VOCs), can carry out damage to human health and be emitted from various industrial activities. Therefore, development of an eco-friendly process for removal of DCE is critical to improve the air quality index and further protect human health. Photocatalytic activity has been recognized as an efficient strategy in removing various types of VOCs. Owing to its compatibility to be conducted under mild condition, photocatalytic reaction is also favorable. Performance of TiO2, a widely applied photocatalyst, can be improved by the doping of various metal elements, like Sr and Cr. Besides, the doping process might also promote the suitability of photocatalyst to be operated under visible light. This study explored performance of various ratios of Sr/TiO2 and Cr/TiO2 under illumination of UV light. 0.01 %Sr/TiO2 achieved the best DCE removal and was further applied examination using various temperatures, along with concentration of DCE and O2. The presence of O2 played an important role during the photocatalytic reaction. Characterization, reaction kinetics study, and analysis of byproducts were also investigated in this study. A short-extended assessment was also applied to examine the performance under blue light and white light illumination. Contrary, Cr performed the best DCE photocatalytic removal under the supply of visible light.

Precisely tuning the Ni3N/Pt interface to boost the catalytic activity of alkaline hydrogen evolution reaction

The hydrogen evolution reaction (HER) in alkaline solutions does not access H* directly, resulting in a slower reaction kinetics compared to that in acidic solutions. Here, we report a Cr-doped Ni3N/Pt heterostructure that provides additional active sites to produce H* via the water-cleaving step, in addition to the intrinsic active Pt site for H* absorption. It is demonstrated that the Cr dopant can modulate the charge redistribution between Ni3N and Pt interface, lowering the energy barrier of both the Volmer step and the following Heyrovsky step. As a result, the prepared Cr-Ni3N/Pt catalyst achieves an extreme low overpotential of 20 mV to deliver a current density of 10 mA/cm2 under alkaline conditions, which is significantly better than the commercial Pt/C catalyst (45 mV). Density Functional Theory (DFT) further reveals that the Cr-modified Ni3N/Pt interface undergoes electronic orbital hybridization, enhancing the water adsorption and dissociation processes on the Ni sites. This work presents the feasibility of the electronic structure modulation in low-platinum catalysts, which provides an effective strategy for the design of electrocatalysts used in multi-step reactions.

Epitaxial Growth and Characterization of Nanoscale Magnetic Topological Insulators: Cr-Doped (Bi0.4Sb0.6)2Te3.

The exploration initiated by the discovery of the topological insulator (BixSb1-x)2Te3 has extended to unlock the potential of quantum anomalous Hall effects (QAHEs), marking a revolutionary era for topological quantum devices, low-power electronics, and spintronic applications. In this study, we present the epitaxial growth of Cr-doped (Bi0.4Sb0.6)2Te3 (Cr:BST) thin films via molecular beam epitaxy, incorporating various Cr doping concentrations with varying Cr/Sb ratios (0.025, 0.05, 0.075, and 0.1). High-quality crystalline of the Cr:BST thin films deposited on a c-plane sapphire substrate has been rigorously confirmed through reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM) analyses. The existence of a Cr dopant has been identified with a reduction in the lattice parameter of BST from 30.53 ± 0.05 to 30.06 ± 0.04 Å confirmed by X-ray diffraction, and the valence state of Cr verified by X-ray photoemission (XPS) at binding energies of ~573.1 and ~583.5 eV. Additionally, the influence of Cr doping on lattice vibration was qualitatively examined by Raman spectroscopy, revealing a blue shift in peaks with increased Cr concentration. Surface characteristics, crucial for the functionality of topological insulators, were explored via Atomic Force Microscopy (AFM), illustrating a sevenfold reduction in surface roughness as the Cr concentration increased from 0 to 0.1. The ferromagnetic properties of Cr:BST were examined by a superconducting quantum interference device (SQUID) with a magnetic field applied in out-of-plane and in-plane directions. The Cr:BST samples exhibited a Curie temperature (Tc) above 50 K, accompanied by increased magnetization and coercivity with increasing Cr doping levels. The introduction of the Cr dopant induces a transition from n-type ((Bi0.4Sb0.6)2Te3) to p-type (Cr:(Bi0.4Sb0.6)2Te3) carriers, demonstrating a remarkable suppression of carrier density up to one order of magnitude, concurrently enhancing carrier mobility up to a factor of 5. This pivotal outcome is poised to significantly influence the development of QAHE studies and spintronic applications.

Ab-initio calculation of magnetic properties of doped methylammonium lead chloride

ABSTRACT Magnetic properties of 3d transition metal ion doped methylammonium lead chloride (MAPbCl3) have been studied by ab-initio calculations in the framework of density functional theory. The study of spin–spin interactions reveals that doping (about 2%) of Ti, V, Cr, Mn and Fe at the Pb site of MAPbCl3 shows stable ferromagnetic ordering along with the half-metallic behaviour. 3d orbital electrons of the dopants are primarily responsible for the origin of the magnetic moment and the remaining part comes from the p-d exchange interaction between the 3d orbital electrons of the dopants and the 6p orbital electrons of Pb in the vicinity of the doping position. Additionally, the band structure calculations suggest that the doped system shows n/p-type semiconducting behaviour. Ferromagnetism, along with semiconducting behaviour in transition metal ion-doped MAPbCl3, will be suitable for spintronic applications.

Reusable porous chromium- zinc oxide nano-sheets for efficient detoxification of xenobiotics through integrated advanced oxidation water clean-up process

An integrated approach of acoustic, ultraviolet, and sunlight-driven Advanced Oxidation Process (AOP) is an excellent choice in the quest for a water-cleaning process. This research delves into the realization of chromium-doped zinc oxide (Cr/ZnO) nanopores as a low energy, eco-friendly, efficient, and exhibiting stable photocatalysis for the AOP process. Ultrasonic-aided co-precipitation technique was used for the synthesis of porous Cr-ZnO nanostructures. X-ray diffraction patterns and FTIR spectra of the synthesized samples revealed that chromium ions were effectively intruded into the ZnO lattice. Tauc's equation and Kubella Munk plots have explored that the incorporation of Cr dopants in ZnO reduces the optical band energy. The formation of porous structures was evinced in SEM, TEM, HRTEM, and BET studies. The presence of abundant mesoporous structures was confirmed by the adsorption/desorption isotherms of type IV hysteresis. The antimicrobial efficacy of Cr-ZnO against aqueous bacteria, Staphylococcus aureus, and Escherichia coli was comparatively as effective as the control. The integrated AOP approach enhances the electron trapping characteristics of nanoporous Cr-ZnO catalysts to generate self-sustained in-situ reactive oxygen species on the aqueous matrix. In the current research, methylene orange and nitro phenol were detoxified up to 99 % and 98.2 %, and their half-life degradation rate constant was 22 min and 26 min, respectively. The total organic contaminants (TOC) test on the resultant treated water has confirmed the effective detoxification of xenobiotic molecules and the possibility of reusing the treated water. The ecotoxicology research using treated water on flora and primary aquatic microfauna has supported the possibility of practical utilization of Cr-ZnO in harmless environmental adaptation in the foreseeable future.

Resilience of the Aurivillius structure upon La and Cr doping in a Bi5Ti3FeO15 multiferroic.

Combining the experimental techniques of high-resolution X-ray diffraction, magnetometry, specific heat measurement, and X-ray photoelectron, Raman and dielectric spectroscopy techniques, we have studied the influence of La and Cr doping on the crystal structure and magnetism of the room temperature Aurivillius multiferroic Bi5Ti3FeO15 by investigating the physical properties of (Bi4La)Ti3FeO15 and Bi5Ti3 (Fe0.5Cr0.5)O15. The parent (Bi5Ti3FeO15) and the doped ((Bi4La)Ti3FeO15 and Bi5Ti3(Fe0.5Cr0.5)O15) compounds crystallize in the A21am space group, which is confirmed through our analysis of high-resolution synchrotron X-ray diffraction data obtained on phase-pure polycrystalline powders. We determined the oxidation states of the metal atoms in the studied compounds as Fe3+, Ti4+, Cr3+, and La3+ through the analysis of X-ray photoelectron spectroscopy data. The magnetic susceptibilities of the three compounds are marked by the absence of a long-range ordered ground state, but dominated by superparamagnetic clusters with dominant antiferromagnetic interactions. This signature of short-range magnetism is also seen in specific heat as a low temperature enhancement which is suppressed upon the application of external magnetic fields up to 8 T. Our dielectric spectroscopy experiments showed that the three studied compounds display similar features in the dielectric constant measured as a function of frequency. However, upon doping La at the Bi site, the width of the ferroelectric hysteresis loop increases for (Bi4La)Ti3FeO15 compared to that of the parent compound Bi5Ti3FeO15, and with Cr doping, Bi5Ti3(Fe0.5Cr0.5)O15 becomes a leaky dielectric. The resilience of the Aurivillius crystal structure towards doping of La at the Bi site and Cr at the Fe site is clearly seen in the bulk properties of magnetic susceptibility, specific heat and the average crystal structure. The relevance of changes in the local structure is evident from our Raman spectroscopy and X-ray pair distribution function studies.

A judicious injection and abstraction of a hetero-dopant in a Co3O4 catalyst for efficient methane oxidation

Cr doping and partial Cr de-doping of Co3O4 was utilized to give a catalyst with promising methane oxidation activity.