Effect Of Cation Substitution Research Articles

Effect of B-site cationic substitution on the structural, spectroscopic, and conductivity behaviour of Ho2(Hf1-xZrx)2O7 (x=0 and 1)

Ideally, a solid electrolyte which is a central component of SOFC should exhibit high anionic or cationic ionic conductivity at the proposed operating temperatures. In most cases, the performance is compromised when operating above 1000 °C due to poor mechanical, thermal and chemical stability of selected functional and non-functional materials. In this context, pyrochlores are one of the potential candidates due to their high conductivity, flexibility to accommodate large cations, and high mechanical, thermal and chemical stability. In this study, we report the synthesis of nano-powders of Ho2Hf2O7 (HH) and Ho2Zr2O7 (HZ) pyrochlore ceramics by eco-friendly alginate mediated ion-exchange process also known as Leeds Alginate Process (LAP) and provide further insight into the structure - conductivity relationship of HH and HZ compounds by EXAFS studies. Both the compositions were sintered at temperatures, ranging from 1100 °C-1500 °C at 2 h dwell time to achieve the desired high-density ceramic with stable pyrochlore structure. X-ray diffraction and Extended X-ray absorption fine structural (EXAFS) analysis showed superlattice reflections and complex coordination geometry of these oxides. The coordination number and disorder factor in the case of HZ were found to be more stable than the HH sample, as evident from the EXAFS. Impedance spectroscopy and dc-conductivity analysis showed a better charge transport behavior in HZ ceramics than in HH making HZ as a preferred solid electrolyte for SOFC. The conductivity of Ho2Zr2O7 is comparable with the best-known fluorite oxide-ion conductor such as Sc2O3-stabilized ZrO2 at 500 °C.

Cation substitution effects (Mn, Ni, and Zn) on ZIF-67 derived spinel modified with 3DGO for the detection of NO2 gas with high sensitivity and selectivity

Detailed cation substitution studies of MCo2O4 (M = Mn, Ni, Zn) spinel structures supported on 3D graphene oxide via solvothermal method have been carried out and used as a highly sensitive and selective NO2 gas sensor at room temperature.

Insights into P-Type Iron- and Manganese-Based Layered Sodium Cathodes

Sodium-ion batteries are a low-cost alternative to lithium-ion batteries in large-scale electric energy storage applications due to the natural-abundant sodium resources and similar working principle to LIBs during cycling [1]. Until now, many different cathodes for SIBs have been studied, including layered transition metal oxides (NaxTMO2, x<1), Prussian blue-type compounds, polyanionic and organic compounds [2]. Among them, NaxTMO2 has been extensively reported, due to its layered structure, easy synthesis, promising electrochemical properties, and feasibility for commercial production [3]. According to the occupation of Na ions and oxygen stacking, NaxTMO2 can be classified into P2 and O3 types, where P2 structure contasins trigonal prismatic sites of sodium ions and ABBA oxygen stacking sequence and O3 structure represents octahedral sites of sodium ions and ABCABC oxygen stacking sequence [4]. At low potentials (<2.0V), there is a phase transition P2-P2’ connected with the manganese redox activity and the Jahn-Teller distortion [5]. Compared with O3-type structure, P2-type NaxTMO2 provides higher specific capacity and better structural stability due to the lower diffusion barriers through Na-ion prismatic sites [6].Iron- and manganese-based layered oxides for sodium-ion batteries have attracted renewed interest due to their low cost and environmental friendliness. However, the phase change at high voltage and the Jahn-Teller effect lead to shortening cycle life and poor rate capability. We design a structure optimization of the Na2/3Mn1/2Fe1/2O2 cathode through a partial substitution of Fe3+ to explore the mechanism of redox activity of P2-type Mn/Fe-based layered cathodes. We present the investigation of the effect of simultaneous cationic substitution on the electrochemical performance and structural stability of P2-Na2/3Mn1/2Fe1/2O2. The obtained material exhibits a solid solution mechanism during desodiation/resodiation process and delivers an initial discharge capacity of 168 mA h g-1 at 0.1C and a capacity retention of 80% after 50 cycles. The modified P2 composition has stable cycle performance in the potential window from 1.5V to 4.5V. The main focus here is to understand the fundamental electrochemical mechanism of this layered cathode material by exploring the redox processes of transition metal cations and oxygen anions upon cycling. In situ X-ray synchrotron radiation diffraction is used to explore the structural changes during cycling. In situ X-ray Absorption Near Edge Spectroscopy is used to elucidate the local electronic structure of Fe and Mn atoms as it evolves throughout this electrochemical process. 23Na solid-state nuclear magnetic resonance spectroscopy is used to investigate Na coordination environments during desodiation/resodiation. Ex situ soft X-ray absorption spectroscopy results reveal the participation of oxygen anions in the electrochemical reactions. Thus, we explore the redox reactions of transition metals and oxygen to explain the mechanism and the electrochemical performance for the P2-type Mn/Fe-based layered cathodes.

Dehydration performance of a novel solid solution library of mixed Tutton salts as thermochemical heat storage materials

To improve energy efficiency and reduce greenhouse gas emissions, energy storage technologies are of paramount importance. Thermochemical energy storage (TCES) materials offer high energy storage densities, and systems based on the dehydration of common salt hydrates like MgSO4·7H2O have been extensively investigated, though frequent problems such as agglomeration and unfavorable kinetics highlight the need for further material development. We consulted our VIENNA TCES-database and became aware of the Tutton salts, A2M(XO4)2·6H2O, (X = S or Se) which have also been previously investigated as TCES materials, although the effects of cation substitution on reactivity had remained poorly characterized. Herein, we report the synthesis and characterization of 41 mixed Tutton salts with the composition K2Zn1-xMx (SO4)2·6H2O (M = Mg, Co, Ni, Cu). Two trends were readily apparent: increasing the amount of nickel leads to a predictable increase in the dehydration onset temperature while preserving the simple form of the single dehydration step observed, while the use of copper leads to a predictable decrease in dehydration onset.

Effects of rubidium substitution of Cs2−xRbxAgBiBr6 double halide perovskites on resistive switching characteristics for memory applications

Cation substitution technique in halide perovskites (HPs) is one of the famous schemes to enhance the characteristics of HPs-based electronic and optoelectronic devices. Here, we fabricated rubidium (Rb) substituted inorganic double halide perovskites (HPs) Cs2−xRbxAgBiBr6 (x = 0, 0.05, 0.1, 0.2, and 0.3) film-based resistive switching (RS) devices and investigated effects of Rb cation substitution on characteristics of RS devices. Grain sizes of the formed Cs2−xRbxAgBiBr6 films gradually increased as increase of Rb contents in the precursor. All of the fabricated RS devices demonstrated non-volatile bipolar RS behavior, device with the Rb content x = 0.1 showed a particularly high on/off ratio (9.29 × 102) of about 30 times greater than pristine Cs2AgBiBr6-based ones (3.09 × 10). In addition, it has been shown that an appropriate amount of Rb substitution at the level of x = 0.1 can effectively prevent the appearance of other crystalline phases at high humidity condition of > 80 %. Through various analytical techniques including SEM, XPS, and SCLC measurement, it was confirmed that an enlargement in grain size resulting in a decrease in defects such as Br vacancies in the fabricated film can lead to an increase in resistance at a high resistance state (HRS) and high on/off resistance ratio. This study provides a facile and feasible way to enhance performances of HPs-based RS devices for practical electronic memory applications.

Structural transition and magnetization reversal in rare earth doped R0.5Sr0.5Fe0.5Cr0.5O3 (R[dbnd]La, Nd and Sm) perovskite oxides containing mixed valent cations at B site: Magnetic, optical and transport properties

In the current paper, the effect of lanthanide metal cation substitution on structural, magnetic, optical and transport properties of R0.5Sr0.5Fe0.5Cr0.5O3 (RLa, Nd and Sm) perovskite oxides have been investigated. Structural investigations reveal that there is a phase transition from cubic to orthorhombic symmetry with the doping of heavier rare earth ion. The findings of XPS studies point to the existence of mixed valence states of Cr and Fe ions. The change in magnetization in response to an external magnetic field reveals that the phases have a mostly antiferromagnetic character with some trace amounts of ferromagnetic components. In temperature dependent magnetization studies, magnetic reversal has been observed in Nd doped sample, while La and Sm doped samples only show positive magnetization. The band gap energies of the synthesized materials determined from the UV–vis reflectance spectroscopy lie in the range of 1.60–1.78 eV indicating the semi-conducting nature of the samples. The temperature-dependent resistivity measurements show semi-conducting behaviour of the samples with decreasing temperature which finally become insulating at low temperature. It has been shown that the VRH model provides the best fit for the resistivity data when compared to the other transport mechanism models that were used to describe the electrical conduction process of synthesized phases.

Effect of Cation Substitution on the Formation of Microcracks in Ni-Rich Layered Oxides

Effect of Cation Substitution on the Formation of Microcracks in Ni-Rich Layered Oxides

Study of the effect of cation substitution on the formation of microcracks in Ni-rich layered oxides

Study of the effect of cation substitution on the formation of microcracks in Ni-rich layered oxides

Cation substitution and size confinement effects on structure, magnetism and magnetic hyperthermia of BiFeO3-based multiferroic nanoparticles and hydrogels

Highly crystalline BiFeO3 (BFO), Bi0.97Sm0.03FeO3 and BiFe0.97Co0.03O3 nanoparticles are synthesized via the chemical co-precipitation method after calcination at 600 °C in air for 2 h. The effect of cation substitution, Sm for Bi and Co for Fe, on the structural and magnetic properties of BFO nanoparticles is investigated, whereas their magnetically induced heating efficiency in radio frequency alternating magnetic fields is examined. X-ray diffraction indicates the formation of the R3c phase in all compounds, while the corresponding Rietveld refinement reveals a variation of the lattice parameters upon doping, suggesting structural distortion within the BFO lattice due to the ionic radii mismatch between doped and host elements. Transmission electron microscopy unveils smaller particle sizes for the doped nanoparticles, owing to the frustrated particle growth induced by the dopants, whose presence is verified by X-ray photoelectron spectroscopy and energy dispersive X-ray analysis. The combined effect of cation substitution and size confinement results in the suppression of the spiral spin structure of BFO, leading to the significantly enhanced magnetic features of the doped nanoparticles at room temperature. For possible applications in the biomedical sector, we tested them as heating agents in magnetic hyperthermia. The dispersion of BiFe0.97Co0.03O3 nanoparticles in water at a concentration of 4 mg/mL could reach the therapeutic window of 41–45 °C for cancer treatment in 50 mT at 375 kHz, whereas the remarkable temperature increase of the BFO-based multiferroic hydrogels, under the same conditions, is auspicious for an effective local treatment at reduced toxicity.

Cation Substitution Strategy for Developing Perovskite Oxide with Rich Oxygen Vacancy-Mediated Charge Redistribution Enables Highly Efficient Nitrate Electroreduction to Ammonia.

The electrocatalytic nitrate (NO3-) reduction reaction (eNITRR) is a promising method for ammonia synthesis. However, its efficacy is currently limited due to poor selectivity, largely caused by the inherent complexity of the multiple-electron processes involved. To address these issues, oxygen-vacancy-rich LaFe0.9M0.1O3-δ (M = Co, Ni, and Cu) perovskite submicrofibers have been designed from the starting material LaFeO3-δ (LF) by a B-site substitution strategy and used as the eNITRR electrocatalyst. Consequently, the LaFe0.9Cu0.1O3-δ (LF0.9Cu0.1) submicrofibers with a stronger Fe-O hybridization, more oxygen vacancies, and more positive surface potential exhibit a higher ammonia yield rate of 349 ± 15 μg h-1 mg-1cat. and a Faradaic efficiency of 48 ± 2% than LF submicrofibers. The COMSOL Multiphysics simulations demonstrate that the more positive surface of LF0.9Cu0.1 submicrofibers can induce NO3- enrichment and suppress the competing hydrogen evolution reaction. By combining a variety of in situ characterizations and density functional theory calculations, the eNITRR mechanism is revealed, where the first proton-electron coupling step (*NO3 + H+ + e- → *HNO3) is the rate-determining step with a reduced energy barrier of 1.83 eV. This work highlights the positive effect of cation substitution in promoting eNITRR properties of perovskites and provides new insights into the studies of perovskite-type electrocatalytic ammonia synthesis catalysts.

Coke-resistant NdFe0.7Ni0.3O3 perovskite catalyst with superior stability for dry reforming of ethane

Effects of A-site cation substitution and B-site active metal doping-segregation on physicochemical properties of Ni-doped perovskite-structured LnFe0.7Ni0.3O3 (Ln = La, Nd, Sm, Eu) catalysts and their catalytic performance for dry reforming of ethane (DRE) were studied. The DRE activity follows the trend: NdFe0.7Ni0.3O3 > SmFe0.7Ni0.3O3 > EuFe0.7Ni0.3O3 > LaFe0.7Ni0.3O3. The doping-segregation process of Ni was demonstrated by in-situ X-ray Diffraction (XRD) and X-ray Absorption Fine Structure (XAFS) measurements, which significantly improves the dispersion of Ni and enhance the interaction between metal and support. The results of temperature-programmed surface reactions (TPSR) and pulse reactions indicate that oxygen vacancies generated by the exsolution of Ni play an important role in the elimination of coke and shift the product from surface carbon to gaseous CO. According to the in-situ Raman experiments, the superior catalytic stability (no coke deposition or activity loss over 100 h) of NdFe0.7Ni0.3O3 is ascribed to its strong resistance towards carbon deposition.

Novel Red Phosphor of Gd3+, Sm3+ co-Activated AgxGd((2-x)/3)-0.3-ySmyEu3+0.30☐(1-2x-2y)/3WO4 Scheelites for LED Lighting.

Gd3+ and Sm3+ co-activation, the effect of cation substitutions and the creation of cation vacancies in the scheelite-type framework are investigated as factors influencing luminescence properties. AgxGd((2-x)/3)-0.3-ySmyEu3+0.3☐(1-2x)/3WO4 (x = 0.50, 0.286, 0.20; y = 0.01, 0.02, 0.03, 0.3) scheelite-type phases (AxGSyE) have been synthesized by a solid-state method. A powder X-ray diffraction study of AxGSyE (x = 0.286, 0.2; y = 0.01, 0.02, 0.03) shows that the crystal structures have an incommensurately modulated character similar to other cation-deficient scheelite-related phases. Luminescence properties have been evaluated under near-ultraviolet (n-UV) light. The photoluminescence excitation spectra of AxGSyE demonstrate the strongest absorption at 395 nm, which matches well with commercially available UV-emitting GaN-based LED chips. Gd3+ and Sm3+ co-activation leads to a notable decreasing intensity of the charge transfer band in comparison with Gd3+ single-doped phases. The main absorption is the 7F0 → 5L6 transition of Eu3+ at 395 nm and the 6H5/2 → 4F7/2 transition of Sm3+ at 405 nm. The photoluminescence emission spectra of all the samples indicate intense red emission due to the 5D0 → 7F2 transition of Eu3+. The intensity of the 5D0 → 7F2 emission increases from ~2 times (x = 0.2, y = 0.01 and x = 0.286, y = 0.02) to ~4 times (x = 0.5, y = 0.01) in the Gd3+ and Sm3+ co-doped samples. The integral emission intensity of Ag0.20Gd0.29Sm0.01Eu0.30WO4 in the red visible spectral range (the 5D0 → 7F2 transition) is higher by ~20% than that of the commercially used red phosphor of Gd2O2S:Eu3+. A thermal quenching study of the luminescence of the Eu3+ emission reveals the influence of the structure of compounds and the Sm3+ concentration on the temperature dependence and behavior of the synthesized crystals. Ag0.286Gd0.252Sm0.02Eu0.30WO4 and Ag0.20Gd0.29Sm0.01Eu0.30WO4, with the incommensurately modulated (3 + 1)D monoclinic structure, are very attractive as near-UV converting phosphors applied as red-emitting phosphors for LEDs.

Salt-flux synthesis of bismuth layer-structured Ca-doped Sr2Bi2Nb2TiO12: the effect of cation substitution on structure, ferroelectric and optical properties

Salt-flux synthesis of bismuth layer-structured Ca-doped Sr2Bi2Nb2TiO12: the effect of cation substitution on structure, ferroelectric and optical properties

Effects of cation and anion substitution in KVPO4F for K-ion batteries

The effects of cation (Ti4+) and anion (O2−) substitution on the electrochemical properties of KVPO4F cathodes are investigated in this work. Both forms of substitution lead to smoothing of the associated voltage profile as well as reduced charging time at high voltage (>4.8 V vs. K/K+). These changes effectively suppress electrolyte decomposition, thereby enhancing the capacity retention in the ion-substituted KV(1−x)TixPO4+yF1−y materials. Ionic substitution also enables the intercalation of excess K ions at a reasonably high voltage (∼1.8 V vs. K/K+) relative to that required in pure KVPO4F (<1.0 V vs. K/K+). Finally, this study reveals that detours in the synthesis reaction pathways can be created by using a pre-reacted precursor, VPO4, rather than the conventional precursors V2O3 and NH4H2PO4 to form stoichiometric (or non-substituted) KVPO4F. These results highlight several design criteria that can be used to optimize KVPO4F and related compositions to prepare K-ion batteries with high capacity, good cyclability, and fast rate capability.

Effects of Spin Transition and Cation Substitution on the Optical Properties and Iron Partitioning in Carbonate Minerals

AbstractThe high‐pressure behavior of deep carbonate dictates the state and dynamics of oxidized carbon in the Earth's mantle, playing a vital role in the global carbon cycle and potentially influencing long‐term climate change. Optical absorption and Raman spectroscopic measurements were carried out on two natural carbonate samples in diamond‐anvil cells up to 60 GPa. Mg‐substitution in high‐spin siderite FeCO3 increases the crystal field absorption band position by approximately 1000 cm–1 but such an effect is marginal at &gt;40 GPa when entering the low‐spin state. The crystal field absorption band of dolomite cannot be recognized upon compression to 45.8 GPa at room temperature but, in contrast, the high‐pressure polymorph of dolomite exhibits a strong absorption band at frequencies higher than (Mg,Fe)CO3 in the low‐spin state by 2000–2500 cm–1. Additionally, these carbonate minerals show more complicated features for the absorption edge, decreasing with pressure and undergoing a dramatic change through the spin crossover. The optical and vibrational properties of carbonate minerals are highly correlated with iron content and spin transition, indicating that iron is preferentially partitioned into low‐spin carbonates. These results shed new light on how carbonate minerals evolve in the mantle, which is crucial to decode the deep carbon cycle.

A theoretical exploration of the structural feature, mechanical, and optoelectronic properties of Au-based halide perovskites A2AuIAuIIIX6 (A = Rb, Cs; X = Cl, Br, I).

As a possible alternative to lead halide perovskites, inorganic mixed-valence Au-based halide perovskites have drawn much attention. In the current research, we have conducted comprehensive theoretical calculations to reveal the structural feature, thermodynamic and dynamic stability, mechanical behavior, optoelectronic properties, and photovoltaic performance of Au-based halide perovskites A2AuIAuIIIX6 (A = Rb, Cs; X = Cl, Br, I). The structural parameters of these compounds are carefully analyzed. Our calculations indicate that the thermodynamic, dynamic, and mechanical stability of monoclinic Rb2AuIAuIIIX6 and tetragonal Cs2AuIAuIIIX6 are ensured, and they are all ductile. The electronic band structure analysis shows that Rb2AuIAuIIII6 illustrates a direct-gap feature, while Rb2AuIAuIIIX6 (X = Cl, Br) and Cs2AuIAuIIIX6 (X = Cl, Br, I) are indirect-gap materials. The effect of A-site cation substitution on the optical band gaps of the Au-based halide perovskites is elucidated. Our results further suggest that Rb2AuIAuIIIX6 (X = Br, I) and Cs2AuIAuIIIX6 (X = Cl, Br, I) are more suitable for single-junction solar cells due to their suitable band gaps within 1.1-1.5 eV. Furthermore, four compounds A2AuIAuIIIX6 (A = Rb, Cs; X = Br, I) not only have high absorption coefficients in the visible region but also show excellent photovoltaic performance, especially for A2AuIAuIIII6 (A = Rb, Cs), whose efficiency can reach over 29% with a film thickness of 0.5 μm. Our study suggests that inorganic Au-based halide perovskites are potential alternatives for optoelectronic devices in solar cells.

Hydroxyfluorooxoborate (NH4)[C(NH2)3][B3O3F4(OH)] for exploring the effects of cation substitution on structure and optical properties.

Cation substitution is a straightforward but effective technique for improving the structure and properties; however, controlling directed substitution still poses significant difficulties. Herein, a metal-free hydroxyfluorooxoborate (NH4)[C(NH2)3][B3O3F4(OH)] has been synthesized using the strategy of heterologous substitution based on the template of A2[B3O3F4(OH)]. Tunable structure and optical properties have been achieved via varied A-site cation substitution. The intrinsic mechanism for this tunability was established by crystallography and theoretical research.

Structure-Activity Relationship Studies of Substitutions of Cationic Amino Acid Residues on Antimicrobial Peptides.

Antimicrobial peptides (AMPs) have received considerable attention as next-generation drugs for infectious diseases. Amphipathicity and the formation of a stabilized secondary structure are required to exert their antimicrobial activity by insertion into the microbial membrane, resulting in lysis of the bacteria. We previously reported the development of a novel antimicrobial peptide, 17KKV, based on the Magainin 2 sequence. The peptide was obtained by increasing the amphipathicity due to the replacement of amino acid residues. Moreover, we studied the structural development of 17KKV and revealed that the secondary structural control of 17KKV by the introduction of non-proteinogenic amino acids such as α,α-disubstituted amino acids or side-chain stapling enhanced its antimicrobial activity. Among them, peptide 1, which contains 2-aminobutyric acid residues in the 17KKV sequence, showed potent antimicrobial activity against multidrug-resistant Pseudomonus aeruginosa (MDRP) without significant hemolytic activity against human red blood cells. However, the effects of cationic amino acid substitutions on secondary structures and antimicrobial activity remain unclear. In this study, we designed and synthesized a series of peptide 1 by the replacement of Lys residues with several types of cationic amino acids and evaluated their secondary structures, antimicrobial activity, hemolytic activity, and resistance against digestive enzymes.

A high-pressure structural transition of norsethite-type BaFe(CO3)2: Comparison with BaMg(CO3)2 and BaMn(CO3)2

Abstract Investigations on the phase stability of the norsethite-type family [BaMg(CO3)2, BaMn(CO3)2, BaFe(CO3)2] under high-pressure conditions are of great significance for understanding the structure and metal cationic (Mg2+, Fe2+, Mn2+) substitution mechanism in double divalent metal carbonates. The structural evolution and equation of state of BaFe(CO3)2 were studied at high pressure up to ~7.3 GPa by synchrotron X-ray diffraction (XRD) in diamond-anvil cell (DAC) in this study. BaFe(CO3)2 undergoes a reversible phase transition from R3m (α-phase) to C2/c (γ-phase) space groups at ~3.0 GPa. The fitted elastic parameters are V0 = 377.79(2) Å3 and K0 = 40.3(7) GPa for α-BaFe(CO3)2, V0 = 483.24(5) Å3 and K0 = 91.2(24) GPa for γ-BaFe(CO3)2 using second-order Birch-Murnaghan equation of state (BM2-EoS). Besides, the vibrational properties and structural stability of complete norsethite-type minerals were also investigated first by Raman spectroscopy combined with DAC up to 11.1 GPa. Similar structural phase transitions occur in BaMg(CO3)2, BaFe(CO3)2, BaMn(CO3)2 at 2.2–2.6, 2.6–3.7, and 3.7–4.1 GPa, respectively. The onset phase transition pressures of the norsethite-type family are much lower than that of dolomite-type Ca(Mg,Fe,Mn)(CO3)2 and calcite-type (Mg,Fe,Mn)CO3 carbonates. These results provide new insights into the divalent cation substitution effects on the stability and structural evolution of carbonates under high-pressure conditions.

Basic crystal field theory—A simple and useful tool to understand the structure–property relationship in luminescent materials

Crystal field theory has been widely adopted to study the structure–property relationships in luminescent materials. It has the advantage of simplicity and clarity, i.e., the total crystal field splitting is reciprocally proportional to the 5th power of bond length. Yet this rule fails many times, especially in phosphors with low-symmetry sites. In order to provide an intact and practical framework of how to use crystal field theory, we address two main questions in this short review, i.e., how the 5th power rule is produced and why it fails. The regular octahedron potential is selected to show the procedure of crystal field calculations. Then the symmetry limitations on crystal field parameters are discussed considering the contribution from every ligand. After the set up of basic formula, two distinct cases, the reverse garnet effect and neutralization of cationic substitution on peak shifts are selected to show the effectiveness and validity of basic crystal field theory. It is hoped that this work could clarify some misconceptions and help the phosphor researchers in using crystal field theory.