Orthorhombic Phase Research Articles

Symmetry Engineering of Epitaxial Hf0.5Zr0.5O2 Ultrathin Films.

Robust ferroelectricity in HfO2-based ultrathin films has the potential to revolutionize nonvolatile memory applications in nanoscale electronic devices because of their compatibility with the existing Si technology. However, to fully exploit the potential of ferroelectric HfO2-based thin films, it is crucial to develop strategies for the controlled stabilization of various HfO2-based polymorphs in nanoscale heterostructures. This study demonstrates how substrate-orientation-induced anisotropic strain can engineer the crystal symmetry, structural domain morphology, and growth orientation of ultrathin Hf0.5Zr0.5O2 (HZO) films. Epitaxial ultrathin HZO films were grown on the heterostructures of (001)- and (110)-oriented La2/3Sr1/3MnO3/SrTiO3 (LSMO/STO) substrate. Various structural analyses revealed that the (110)-oriented substrate promotes a higher degree of structural order (crystallinity) with improved stability of the (111)-oriented orthorhombic phase (Pca21) of HZO. Conversely, the (001)-oriented substrate not only induces a distorted orthorhombic structure but also facilitates the partial stabilization of nonpolar phases. Electrical measurements revealed robust ferroelectric properties in epitaxial thin films without any wake-up effect, where the well-ordered crystal symmetry stabilized by STO(110) facilitated better ferroelectric characteristics. This study suggests that tuning the epitaxial growth of ferroelectric HZO through substrate orientation can improve the stability of the metastable ferroelectric orthorhombic phase and thereby offer a better understanding of device applications.

Observations on “Mg” incorporated oxides of tungsten for superconducting applications

The present work involves in the synthesis and characterization of pristine and "Mg" associated WO3.H2O nano powders by a high yield irradiation technique using microwaves. The diffraction patterns present phased orthorhombic phase and retained even after annealing process. Clear evidence noticed for pure and doped samples in morphological behavior of the samples. The change in optical properties in terms of energy values revealed the contribution of dopants with the evident at 360 nm wavelength blue shift. The obtained magnetic behavior on the annealed samples revealed the transition offer magnetic state to diamagnetic state may be investigated for super conducting applications.

Precise determination of oxygen content in SmBa2Cu3O7-δ thin film samples using x-ray diffraction

Abstract The superconducting properties of SmBa2Cu3O7-δ (SmBCO) thin films are predominantly influenced by the oxygen deficiency δ. Yet, the established methods to determine δ such as iodometric titration or thermogravimetry cannot be applied to thin films due to their very small volume.
Therefore, an alternative way to determine δ for SmBCO thin film samples using X-ray diffraction (XRD) is presented. Main point of this analysis is the structural relationship between the a, b and c lattice parameters and δ. A linear relationship between c and δ is found in SmBCO powder samples for both the orthorhombic and tetragonal phases.
Furthermore, an attempt is made to quantify the chemical composition using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). This attempt was inconclusive because of drastically changing ion yields due to δ influencing the valence state of the analyzed ions.
The found crystal structural relationship gathered from the powder samples is applied to thin film samples. Thereby, it becomes clear that thermal strain is affecting the crystal structure of the thin films. A simple correction model is used to correct for thermal strain and a good match between powder, literature and thin film data is achieved and thus a non-destructive way for the determination of δ using XRD.


Contribution of (Bi0.45Y0.05)Na0.5ZrO3 to induced multiphase coexistence and enhanced piezoelectric properties of K0.5Na0.5NbO3 lead-free ceramics

In this study, new lead-free piezoelectric ceramics (1 − x)(K0.5Na0.5)NbO3 (KNN)–x(Bi0.45Y0.05)Na0.5ZrO3 (BYNZ) were prepared using the conventional solid-state method, and the relation between the doping amount of (Bi0.45Y0.05)Na0.5ZrO3 and its structural and electrical properties was investigated. Material characterization and structural analyses conducted using X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy revealed that KNN–BYNZ ceramics formed single perovskite structures at 0 ≤ x ≤ 0.05 and a polycrystalline phase boundary (PPB) for the coexisting orthorhombic and tetragonal phases at 0.03 ≤ x ≤ 0.05. The ceramics exhibited desirable electrical properties at x = 0.04 (d33 = 305 pC/N, kp = 45.8 %, εr = 1316, tanδ = 2.4 %, Tc = 332 °C, Pr = 28.2 μC/cm2, and Ec = 1.07 kV/mm). These findings reveal that the introduction of BYNZ enables the effective formation of a PPB in the KNN-based ceramics to improve their electrical properties, and they exhibit potential for replacing lead-based piezoelectric ceramics in the market.

Pt Nanoparticles Embedded Polypyrrole‐Carbon Black/SrSnO3 Photocatalyst with Stable and Superior Photodegradation Performance

AbstractCurrently, the primary focus for scientific authorities and regulatory departments revolves around water pollution. In this regard, photocatalysis has emerged as a highly effective, affordable, and goal‐oriented approach. Thus, recognizing the urgency of this issue, we focused our efforts towards developing a novel ternary photocatalytic structure based on mesoporous SrSnO3, combined with polypyrrole‐doped carbon black (PPC) and platinum nanoparticles (Pt NPs). Pt NPs, PPC and SrSnO3‐based nanocomposite photocatalyst was developed through a very simple chemical method followed by ultrasonication and photoreduction techniques. XRD analysis confirmed orthorhombic phase of SrSnO3, while the formation of the ternary nanocomposite among Pt NPs, PPC and SrSnO3 has been confirmed by X‐ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared (FTIR) spectroscopy. Transmission electron microscopy (TEM) revealed the presence of Pt NPs (5–15 nm), beads/dense cocoon like structures of PPC along with rod, spherical and needle shape nanostructures of SrSnO3 in newly created ternary photocatalyst. Diffuse reflectance spectroscopy (DRS) showed lowering of band gap energy in case of Pt@PPC/SrSnO3. Newly developed Pt@PPC/SrSnO3 nanocomposite worked efficiently when employed on colorless insecticide imidacloprid (IMD) and on colored methylene blue (MB) dye under UV‐light. Pt@PPC/SrSnO3 photocatalyst exhibited excellent performance with 96.03 % removal of pollutant IMD in only 20 min, almost 296 % more efficient than bare SrSnO3. Furthermore, the Pt@PPC/SrSnO3 ternary photocatalyst showed rapid removal of MB with almost total elimination of dye molecule in just 16 min.

Hot-Injection Synthesis of Cesium Lead Halide Perovskite Nanowires with Tunable Optical Properties

Metal halide perovskite semiconductors have emerged as promising materials for various optoelectronic applications due to their unique crystal structure and outstanding properties. Among different forms, perovskite nanowires (NWs) offer distinct advantages, including a high aspect ratio, superior crystallinity, excellent light absorption, and carrier transport properties, as well as unique anisotropic luminescence properties. Understanding the formation mechanism and structure–property relationship of perovskite NWs is crucial for exploring their potential in optoelectronic devices. In this study, we successfully synthesized all-inorganic halide perovskite NWs with high aspect ratios and an orthorhombic crystal phase using the hot-injection method with controlled reaction conditions and surface ligands. These NWs exhibit excellent optical and electrical properties. Moreover, precise control over the halogen composition through a simple anion exchange process enables the tuning of the bandgap, leading to fluorescence emission, covering a wide range of colors across the visible spectrum. Consequently, these perovskite NWs hold great potential for efficient energy conversion and catalytic applications in photoelectrocatalysis.

Non-centrosymmetric crystallization in ferroelectric hafnium zirconium oxide via photon-assisted defect modulation

Ferroelectricity in Hf1-xZrxO2 (HZO) thin films has garnered significant attention for advanced memory devices. However, the challenge in understanding nanoscale polymorphism and the absence of non-centrosymmetric crystallization techniques compatible with back-end-of-line processes have restricted its broader application to various types of information storage systems. In this study, we report a novel method to generate the ferroelectric orthorhombic phase (o-phase) in HZO films via photon-assisted non-centrosymmetric crystallization. As-prepared HZO films (8 nm) prepare by atomic layer deposition underwent thermal annealing and subsequent deep ultraviolet (DUV) irradiation. The DUV treatment successfully triggered ferroelectricity in HZO films annealed at 300 °C. Moreover, the same post-treatment applied to HZO films annealed at 400 °C led to a further enhanced polarization up to 29.2 μC cm−2 under high bipolar triangular pulses and outstanding reliability for up to 106 bias stress cycles. Finally, based on in-depth microscopic and structural analyses, we proposed the mechanism on the symmetry-breaking phase transformation to the o-phase HZO with advanced ferroelectricity via oxygen vacancy-driven lattice rearrangement.

Ultrahigh strain and superior temperature stability in lead-free ceramics via synergetic texture technique and phase structure engineering

Lead-free piezoelectric ceramics with large strain response and good temperature stability are highly required for actuator applications. However, the search for lead-free ceramics with both enhanced strain and reduced thermal-dependent behavior is a great challenge. In this work, by employing templated grain growth technique and elaborately modulate the phase structure, large unipolar strain of 0.30%, low strain hysteresis Hs~12%, along with small strain variation 11.8% between 20-100oC are achieved in (001)C-oriented (Ba0.95Ca0.05)(Sn0.04Ti0.96)O3 ceramics, being the optimal level of BaTiO3 family. It is revealed the ceramics exhibit a coexistence of orthorhombic and tetragonal phases. The inherent piezoelectric anisotropy of orthorhombic phase, the reversible a→c domain switch, along with the refined non-180o domain structures contribute to the remarkable electrostrain characteristic. This study proposed a promising strategy to develop high performance piezoelectric materials for actuator applications.

Investigating the Potential of ZrO2/MoO3 Nanocomposites for Efficient Hydrogen Generation through NaBH4 Methanolysis

This work investigates the potential of ZrO2/MoO3 nanocomposites as catalysts for hydrogen production through NaBH4 methanolysis. The samples were prepared by controlled thermal calcination and characterized using various techniques like XRD, FTIR, Raman, SEM, and surface area BET analysis. Rietveld refinements verified the presence of the ZrO2 monoclinic phase with the space group P21/c in all samples and a second orthorhombic MoO3 phase with the space group Pnma. The average crystal size decreased from 44 to 40 nm. FTIR and Raman spectroscopy confirmed the successful preparation of ZrO2/MoO3 nanocomposites. SEM analysis showed ZrO2 particles and MoO3 nanoparticles adhered to the ZrO2 surface, potentially creating a rougher texture. The results confirmed the formation of ZrO2/MoO3 nanocomposites with increasing MoO3 content, leading to an increased surface area of 19 - 23 m2/g. The catalytic performance evaluation revealed that the sample containing 30% MoO3 (ZM3) exhibited the highest hydrogen generation rate of 18451 mL/g.min at 30 °C. The calculated activation energy for ZM3 was 18.78 kJ/mol, suggesting efficient hydrogen generation at moderate temperatures.

Enhanced electrochemical performance of Ba0.5Sr0.5Co0.8Fe0.2O3-δ cathode by Zr4+, Sm3+ and Yb3+ tri-doped BaCeO3 compositing for intermediate-temperature thin-film fuel cells

In this study, Zr4+, Sm3+ and Yb3+ tri-doped BaCeO3 (BaCe0.7Zr0.1Sm0.1Yb0.1O3-α) was prepared using a citric acid-EDTA combined complexing sol-gel method. The influence of sintering aid (CuO) content on structure, sinter-ability and conductivity of BaCe0.7Zr0.1Sm0.1Yb0.1O3-α (BCZSY) was studied using XRD, SEM and AC impedance. XRD patterns of different sintering aid contents and temperatures showed that all samples formed a pure BaCeO3 orthorhombic phase without any impurities. The conductivity of 1500-BCZSY reached 1.8×10-2 S.cm-1 and 1.9×10-2 S.cm-1 in dry nitrogen and hydrogen atmospheres at 700 °C, respectively. The anode-supported membrane fuel cells of NiO-BCZSY | BCZSY (13 μm) | Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) and NiO-BCZSY | BCZSY (15 μm) | BCZSY-BSCF were fabricated, respectively. SEM results showed that the cathode, anode-support and electrolyte had good adhesion. The polarization resistance (Rp) of BCZSY-BSCF was significantly reduced by 34%, 44% and 55% compared to BSCF at 500 °C, 550 °C and 600 °C, respectively. The maximum power density (Pmax) using BCZSY-BSCF as the cathode increased by 18%, 17% and 22% compared to BSCF at 500 °C, 550 °C and 600 °C under the condition of slightly higher electrolyte film thickness, correspondingly.

Zr/Hf-containing metallocene-based ceramic precursors

Polymer-derived-ceramic (PDC) route is an excellent strategy to tailor components at the molecular level, while existing synthetic methods face various problems such as complex preparation, multi-step reaction, and high conversion temperature, etc. Here, we propose an approach to prepare Zr-, Hf-, or Zr/Hf-containing metallocene-based ceramic precursors, which are constructed by the alkylation reaction between cyclopentadienyl ligand and methylene. Through the homogeneous and one-pot reaction occurs, we collect the target products. The reaction condition is mild, and the conversion temperature (1400 °C) is relatively low, and with a high ceramic yield (57.50–66.34%). The obtained metal-containing polymers are further converted to the orthorhombic phase (M7O8.79F9.71, M = Zr, Hf) after pyrolysis at 800 °C. Annealing at an intermediate temperature of 1400 °C in an argon atmosphere results in cubic crystalline ZrC or HfC nanoparticles embedded in a ceramic matrix. The free carbons are in-situ formed after high-temperature treatment, and higher disorder of carbons is observed with increasing temperature. This work provides a good strategy for the potential precursor of ultrahigh-temperature ceramics.

Enhancement of ferroelectricity in chemical-solution-deposited ZrO2 thin films through fine phase transition control

Recent studies have highlighted the ferroelectric potential of ZrO2 thin films, which offer advantages over HfO2-based ferroelectric materials, such as lower thermal budget and greater natural abundance. In this research, pure ZrO2 ferroelectric thin films were fabricated on Si substrates using chemical solution deposition with all-inorganic precursors. We explored the impacts of film thickness and HfO2 seed layers on phase transition and ferroelectric properties. Notably, an 11 nm thick ZrO2 film exhibited ferroelectric behavior with a remanent polarization of 12.6 μC/cm2. Due to the combined effects of tensile stress and surface energy, the increase in thickness to 30 nm led to a phase transition from the orthorhombic phase to the monoclinic phase and a resultant decrease in remanent polarization. Additionally, the introduction of an HfO2 seed layer facilitated the crystallization of the ferroelectric o-phase, enhancing the remanent polarization to 16.5 μC/cm2 in our ∼8 nm thick ZrO2 thin film with a ∼2 nm thick HfO2 seed layer. These findings provide valuable insights into optimizing ferroelectric properties in ZrO2 thin films through phase transition control.

Semi-wet synthesis of high-performance Li1.6Mn1.6O4 for selective lithium extraction from Salt Lakes Brine

Among the manganese-based lithium-ion sieves, Li1.6Mn1.6O4 has a high theoretical lithium adsorption capacity as a spinel ion sieve material. Small particle size orthogonal phase purity LiMnO2 powders were prepared by a semi-wet method and calcined in air at 400 °C to obtain Li1.6Mn1.6O4 a lithium-ion sieve precursor. The synergistic effects of oxygen atmosphere, heat treatment conditions and lithium/manganese molar ratio on the crystal structure of LiMnO2 and the lithium adsorption/desorption characteristics of Li1.6Mn1.6O4 were comprehensively investigated with XRD, SEM, TEM, XPS, Raman, DTA-TG and capacity retention study. Notably, when the initial lithium/manganese molar ratio was set at 1.1, and the sample underwent a calcination at 120 °C for 48 h under carefully controlled deoxygenation conditions, we observed the exclusive presence of the desired orthorhombic phase in the LiMnO2 sample. In contrast, when the synthesis conditions deviated from the optimized parameters led to the presence of the monoclinic phase of Li2MnO3. This highlights the sensitivity of Li1.6Mn1.6O4 properties to the synthesis conditions. The results of adsorption-desorption cycles show that the ion sieve Li1.6Mn1.6O4 prepared by heat treatment of ordered o-LiMnO2 is more stable, the structural stability of Li1.6Mn1.6O4 were characterized by high-temperature in-situ XRD experiments during heating from 30 to 800 °C. The equilibrium adsorption capacity was 34 mg g−1 in Qarhan Salt Lake brine at 10th cycle, and a remarkably low Mn dissolution loss rate of 0.6 %. The results have significant potential to advance the development of high-performance adsorbent in the Li-Mn-O system and contribute to the advances in lithium separation technology.

Exploring Layered Disorder in Lithium-Ion-Conducting Li3Y1-xInxCl6.

Li3Y1-xInxCl6 undergoes a phase transition from trigonal to monoclinic via an intermediate orthorhombic phase. Although the trigonal yttrium containing the end member phase, Li3YCl6, synthesized by a mechanochemical route, is known to exhibit stacking fault disorder, not much is known about the monoclinic phases of the serial composition Li3Y1-xInxCl6. This work aims to shed light on the influence of the indium substitution on the phase evolution, along with the evolution of stacking fault disorder using X-ray and neutron powder diffraction together with solid-state nuclear magnetic resonance spectroscopy, studying the lithium-ion diffusion. Although Li3Y1-xInxCl6 with x ≤ 0.1 exhibits an ordered trigonal structure like Li3YCl6, a large degree of stacking fault disorder is observed in the monoclinic phases for the x ≥ 0.3 compositions. The stacking fault disorder materializes as a crystallographic intergrowth of faultless domains with staggered layers stacked in a uniform layer stacking, along with faulted domains with randomized staggered layer stacking. This work shows how structurally complex even the "simple" series of solid solutions can be in this class of halide-based lithium-ion conductors, as apparent from difficulties in finding a consistent structural descriptor for the ionic transport.

Monolithic three-dimensional hafnia-based artificial nerve system

Artificial nerve systems that mimic the tactile perception ability of human skin could be adopted in the realization of devices for a hyperconnected society, including prosthetic devices, interfaces for virtual reality, and smart sensors. The system consists of a pressure sensor, memory, and signal processing circuit, which possess the capability of generating sensory neuron-like signals. Although technological advances have been made in semiconductor-based memory and transistors over the decades, sensor technology is still relying on micro-electromechanical systems, which are hard to realize miniaturization/high-density and high-performance technology. Here, we demonstrate a monolithic three-dimensional integrated artificial nerve on the basis of ferroelectric HfxZr1-xO2 for use in the core element of neuromorphic memory and a self-powered piezoelectric pressure sensor. The morphotropic phase boundary (MPB) state of hafnia film was formed between orthorhombic and tetragonal phases for high piezoelectric performance. The MPB-based sensor was integrated with self-rectifying ferroelectric tunnel junction memory and silicon-based ring oscillator. We realized a frequency-modulated pulse-like synaptic signal with pressure detection ability over a wide range of 1–50 kPa and a good sensitivity of 0.35 mV/kPa. Also, we demonstrate the real-time frequency-modulated operation of the artificial nerve system by adjusting the functional properties of the hafnia films.

Exploring the effect of concentration on hydrothermally synthesized mesoporous spherical nanoflowers of bismuth tungstate for hybrid supercapacitor and water-splitting applications

This paper describes how the synergistic effect of concentration changes the electrode conductivity and enhances the electrochemical and electrocatalytic activities of bismuth tungstate nanoflowers (BWO NFs). This research mainly aims to develop mesoporous spherical BWO NFs using a hydrothermal route. The structural analysis of the BWO NFs revealed the presence of an orthorhombic phase with a regular atomic arrangement. Scanning electron microscopy revealed that the different BWO NFs samples had nonuniform spherical NFs, which play an important role in supercapacitor and electrocatalytic applications. The identification of functional groups and stretching–bending vibrations of Bi–W–O bonds are revealed by FT-IR and Raman spectroscopy respectively. Additionally, the transmission electron microscopy and X-ray photoelectron spectroscopy confirmed the morphological, structural, and electronic states of the BWO NFs. Furthermore, the supercapacitive and electrocatalytic activity of BWO–nickel foam (NF) electrodes were investigated using an aqueous 1 M KOH electrolyte. The results revealed that the BWO-2 electrode exhibited an improved specific capacity (Csp) of (647 F/g) 72 mAh/g and excellent capacitive retention of 81 % over 5000 cycles. An asymmetrical hybrid device was fabricated using a two-electrode cell with BWO–NF and reduced graphene oxide acting as the positive and negative electrodes, respectively. The device demonstrated favorable electrochemical properties: a Csp of 52 mAh/g at 5 mV/s as well as a Csp of 46 mAh/g, the highest energy density of 32 Wh/kg, and the highest power density of 2330 W/kg at 5 mA/cm2. Furthermore, the BWO NFs were investigated for water-splitting activity, and the BWO-2 electrode was found to exhibit better electrocatalytic performance (overpotential: 328 mV, Tafel slope: 80.9 mV/dec, and electrochemical surface area: 41.2 cm2) and stability than the other electrodes. The designed asymmetric structure offers a suitable cathode material for energy storage and electrocatalytic applications.

Irregular α-V2O5 nanodiscs fabrication for highly sensitive and responsive ethanol vapours detection

The current study presents a template-free hydrothermal approach for synthesizing nanodiscs resembling vanadium pentoxide (V2O5) nanostructures, highlighting their potential as ethanol gas sensing materials. X-ray diffraction (XRD) analysis confirms the presence of a highly crystallized orthorhombic phase of V2O5 (JCPDS file no 85–0601). The morphological features of V2O5, resembling irregular nanodiscs, were investigated using field-emission scanning electron microscopy (FE-SEM). Fourier-transform infrared (FTIR) spectroscopy was employed to explore the chemical structure and bonding of V2O5. High-resolution transmission electron microscopy (HRTEM) confirmed the crystalline nature of the material, with lattice spacing at 0.57 nm corresponding to the (020) crystal planes. Elemental chemical composition analysis of V2O5 was conducted via energy-dispersive X-ray spectroscopy (EDX). The V2O5 sample exhibited a BET surface area of 15.32 m2/g and a BJH desorption average pore width of 28.76 nm, providing essential insights into its surface availability for gas adsorption. In ethanol vapor environments, the sensing capabilities of the V2O5 sensor were evaluated at room temperature. The prepared V2O5-based sensor demonstrated exceptional selectivity towards ethanol over other volatile organic compounds (VOCs), with a sensing response of 74.88 % towards 1000 ppm ethanol at room temperature (30 °C). These findings underscore the efficacy of the V2O5-based sensor in ethanol atmospheres, exhibiting rapid response and recovery times of 36s and 12s, respectively, at room temperature.

Novel Indium nanocomposites for Photonic applications

In the present communication, MgO:In2O3- 1:1 (MIO), SrO/MgO/In2O3 (1:1:1) (SMIO), SrO/Al2O3/In2O3 (1:1:1) (SAIO) and CeO2/ZnO/In2O3 (1:1:1) (CZIO) NCs are synthesized by Punicagranatum juice extract as a reducing agent followed by calcination at 600 °C for 3 h. The Bragg reflections confirm that Magnesium indate, SrO, Al2O3, ZnO crystallizes in orthorhombic, trigonal, rhombohedral and hexagonal crystalline phases whereas CeO2, In2O3 and MgO crystallizes in cubic phase. Surface morphology consists large number of irregularly sized and shaped nanoparticles along with few pores and hallows. The direct energy band gap was determined using Wood and Tauc’s plot. The direct energy band gap was found to be 3.12, 3.15, 3.18 and 3.05 eV. The optical nonlinearity of the specimens was investigated using the open aperture Z-scan technique. With the exception of SAIO, the synthesized samples exhibited reverse saturable absorption attributed to a two-photon absorption (2PA) process. The nonlinear absorption coefficient follows the order CZIO > MIO > SMIO. However, the optical limiting threshold follows the order SMIO > MIO > CZIO NCs. These findings distinctly highlight the superior potential of CZIO binary NCs for optical limiting applications. This characteristic is advantageous for shielding sensors and the human eye, providing protection against the detrimental effects of intense green laser radiation. Unexpectedly, the SAIO NCs displayed Q-switching behavior. This behavior holds potential applications in optical discriminators, spatial light filters, optical isolation, and other photonic mode-locking devices.

Manganese substitution effect on physical properties of sol-gel derived DyFeO3 orthoferrite

A simple composite DyFe(1-x)MnxO3 (x = 0, 0.1, 0.3, 0.5) powders were successfully prepared by the sol–gel method. The effect of Mn modification on the structure, thermal and phase transition behaviour of DyFeO3 orthoferrite was investigated. Mn modification didn't show any structural change and all the samples confirmed the pure orthorhombic phase with Pbnm space group. However, a contradicting trend in the variation of lattice parameters were observed due to the presence of mixed oxidation state of Dy, Fe and Mn in the sample leading to oxygen vacancies. The presence of mixed oxidation state was confirmed through X-ray photoemission spectra (XPS). Scanning electron microscopy (SEM) and Williamson Hall (WH) plot confirmed a decrease in particle sizes with increasing Mn concentration leading to an increase in the specific surface area which suggested an inhibition of grain growth with Mn modification. The defects-initiated change in physical behaviour in terms of structural, thermal, microstructural and dielectric are analyzed and discussed in detail.

Cation doping and oxygen vacancies in the orthorhombic FeNbO4 material for solid oxide fuel cell applications: A density functional theory study.

The orthorhombic phase of FeNbO4, a promising anode material for solid oxide fuel cells (SOFCs), exhibits good catalytic activity toward hydrogen oxidation. However, the low electronic conductivity of the material specifically in the pure structure without defects or dopants limits its practical applications as an SOFC anode. In this study, we have employed density functional theory (DFT + U) calculations to explore the bulk and electronic properties of two types of doped structures, Fe0.9375A0.0625NbO4 and FeNb0.9375B0.0625O4 (A, B = Ti, V, Cr, Mn, Co, Ni) and the oxygen-deficient structures Fe0.9375A0.0625NbO3.9375 and FeNb0.9375B0.0625O3.9375, where the dopant is positioned in the first nearest neighbor site to the oxygen vacancy. Our DFT simulations have revealed that doping in the Fe sites is energetically favorable compared to doping in the Nb site, resulting in significant volume expansion. The doping process generally requires less energy when the O-vacancy is surrounded by one Fe and two Nb ions. The simulated projected density of states of the oxygen-deficient structures indicates that doping in the Fe site, particularly with Ti and V, considerably narrows the bandgap to ∼0.5eV, whereas doping with Co at the Nb sites generates acceptor levels close to 0eV. Both doping schemes, therefore, enhance electron conduction during SOFC operation.