Ion Vacancies Research Articles

Unconventional Ferroelectricity with Quantized Polarizations in Ionic Conductors: High-Throughput Screening.

Ferroelectricity is generally a displacive phenomenon within a unit cell in which ions are placed asymmetrically. In ionic conductors, ions can also be electrically displaced but by much longer distances. They are mostly nonpolar with symmetrical lattices due to the nondirectional character of ionic bondings. Here we propose that the combination of two such displacive modes may give rise to unconventional ferroelectricity with quantized polarizations, where even one local vacancy may induce giant polarization in ubiquitous ionic conductors. Such systems should be insulating with ion vacancies inclined to aggregate at one side. Our high-throughput screening combined with ab initio calculations provided 35 candidates, from which we select KSnS4 and Na4SnS4 to show the existence of such long ion displacement ferroelectricity with a change in integer quantum number in polarizations during switching. The polarizations can be unprecedentedly large with a moderate density of ion vacancies that can be experimentally achieved via ion deintercalation.

Resistive Switching in Ag2Te Semiconductor Modulated by Ag+‐Ion Diffusion and Phase Transition

AbstractMemristors are considered to be the fourth circuit element and have great potential in areas like logic operations, information storage, and neuromorphic computing. The functional material in a memristor, which has a nonlinear resistance, is the key component to be developed. Herein, resistive switching is demonstrated and the structural evolutions in Ag2Te are examined under an external electric field. It is shown that the electroresistance effect is originating from an electronically triggered phase transition together with directional Ag+‐ion diffusion. Using in situ transmission electron microscopy, the phase transition from the monoclinic α‐Ag2Te into the face‐centered cubic b‐Ag2Te, accompanied by a change in resistance, is directly observed. Diffusion of Ag+‐ions modulates the localized density of Ag+‐ion vacancies, leading to a change in electrical conductivity and influences the threshold voltage to trigger the phase transition. During the electric field‐driven phase transition, the spontaneous and localized multiple polarizations from the low‐symmetry α‐Ag2Te (referring to an antiferroelectric structure) are vanishing in the cubic b‐Ag2Te (referring to a paraelectric structure). The abrupt resistance change of thin Ag2Te caused by the phase transition and modulated by the applied electric field demonstrates its great potential as functional material in volatile memory and memristors with a low‐energy consumption.

Prevention of Noise Current Generation in Tin‐Based Lead‐Free Perovskites for Highly Sensitive Photodetection

AbstractLead (Pb) halide perovskites have attracted significant attention in the field of optoelectronics. However, due to the disadvantages associated with the presence of Pb in perovskite, its use should be minimized, if not completely eliminated. Herein, an efficient Pb‐free Sn‐based halide perovskite photodetector (PD) that is sensitive to visible and near‐infrared light is developed. The Sn perovskite is characterized with low toxicity and a narrow bandgap, and exhibits lower shunt leakage and a higher built‐in potential compared with a Pb‐based perovskite. Also, the relatively stronger bond strength between Sn and iodine ions in comparison with that observed in the Pb‐based perovskite effectively prevents charge injections that are vulnerable to dark current suppression. The Sn‐based perovskite PD demonstrates a high signal‐to‐noise ratio (SNR) of 51.12 dB, as well as an excellent cut‐off frequency of 763 kHz. To the best knowledge, this device is one of the fastest and most efficient photodiode‐type Sn‐based perovskite PDs developed to date. Unlike the Pb‐based perovskite device, the Sn‐based perovskite PD retains its high SNR over time. This effect may be attributed to the low movement of ion vacancies and degree of vertical shunt leakage in the perovskite material.

Impact of Polymeric Hole‐Selective Layers on Chemical Inductance in Inverted Perovskite Solar Cells

An essential role is played by the charge selective layers, in particular, the hole transport layer (HTL) in determining the performance of perovskite solar cells (PSCs). HTL contribution is even more substantial in the inverted PSCs (p‐i‐n) as it also affects the crystallization process of the overlayer perovskite deposition. The influence of HTL on inverted PSCs was probed, the role through admittance spectroscopy quantified, and the photovoltaic performance correlation with the microstructure of the perovskite established. By measuring the low‐frequency impedance responses of inverted PSCs, the photo‐induced charge transfer dynamics in the PSCs were deciphered, revealing negative chemical inductor features at low frequencies in the Nyquist plots. The noted additional recombination pathways are attributed to the ionic vacancies in the interfacial states. The PSCs fabricated with poly(triaryl amine) showed a higher open‐circuit voltage, lower recombination, and higher charge carrier lifetime. The chemical inductance behavior was supported through variable temperature frequency‐dependent capacitance measurements.

Erratum to: “Nanobubble formation from ionic vacancies in an electrode reaction on a fringed disk electrode under a uniform vertical magnetic field −1. Formation process in a vertical magnetohydrodynamic (MHD) flow” [J. Electroanal. Chem. 914 (2022) 116291

Erratum to: “Nanobubble formation from ionic vacancies in an electrode reaction on a fringed disk electrode under a uniform vertical magnetic field −1. Formation process in a vertical magnetohydrodynamic (MHD) flow” [J. Electroanal. Chem. 914 (2022) 116291

A study of Cr3+-substitution induced defects restructuring in BiFeO3 by positron annihilation and other supportive methods

The effects of Cr3+ ion substitution in place of Fe3+ ions in BiFe1-xCrxO3 nanocrystallites are reported in this work. Due to the smaller radii of Cr3+ ions, the nanocrystallite sizes and lattice parameters decreased during the substitution. The band gap energy decreased due to the increased conduction band edge tailing. The ionic concentrations, estimated from the energy-dispersive analysis of X-rays, indicated that there is only partial replacement of Fe3+ ions and a fraction of the Cr3+ ions either occupied the pre-existed Bi3+ ion vacancies or replaced some of the Bi3+ ions. Positron annihilation studies proved that, with increasing doping by Cr3+ ions, Bi3+- and O2− ion vacancies were generated. The diffusion of positrons to the surfaces of the nanocrystallites, however, continued to enhance the mean positron lifetimes. Coincidence Doppler broadened spectra also hinted at the generation of divacancies of Bi3+ and O2− ions. Dielectric measurements showed that the charge excess of the VBi3--VO2+ divacancies got balanced by a reduction of the Fe3+ ions to Fe2+ states. Magneto-electric coupling enhanced due to the quenching of the cycloidal-spiral spin structure and the increased Fe–O–Fe/Cr bond-bending. No structural transformation was observed unlike in the case of lanthanide ion substitution of Bi3+ ions.

Photoluminescence quenching of CVD grown WS2 monolayers treated with low-power Ar plasma

Defect engineering in two-dimensional materials is of high importance to improve a specific property of such materials. By introducing defects directly in the lattice, by means of ion doping or vacancies, it is possible to optimize the structure for a target application, such as high-performance batteries, catalysis, or optoelectronics. Herein, monolayer WS2 was synthesized by chemical vapor deposition and was subsequently subjected to Ar plasma treatment. The changes in properties were monitored using Raman spectroscopy, photoluminescence (PL) spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. The influence of defects resulted in a variation in the intensity of the PL signal, as well as a progressive redshift owing to an increase in the defect density with increasing plasma treatment time, and through the analysis of the PL and Raman spectra one can quantify the evolution of defects in the WS2 monolayers due to the treatment.

Point defect creation by proton and carbon irradiation of α-Ga2O3

Films of α-Ga2O3 grown by Halide Vapor Phase Epitaxy (HVPE) were irradiated with protons at energies of 330, 400, and 460 keV with fluences 6 × 1015 cm−2 and with 7 MeV C4+ ions with a fluence of 1.3 × 1013 cm−2 and characterized by a suite of measurements, including Photoinduced Transient Current Spectroscopy (PICTS), Thermally Stimulated Current (TSC), Microcathodoluminescence (MCL), Capacitance–frequency (C–f), photocapacitance and Admittance Spectroscopy (AS), as well as by Positron Annihilation Spectroscopy (PAS). Proton irradiation creates a conducting layer near the peak of the ion distribution and vacancy defects distribution and introduces deep traps at Ec-0.25, 0.8, and 1.4 eV associated with Ga interstitials, gallium–oxygen divacancies VGa–VO, and oxygen vacancies VO. Similar defects were observed in C implanted samples. The PAS results can also be interpreted by assuming that the observed changes are due to the introduction of VGa and VGa–VO.

Effects of Sm and Cr co-doping on structural, magnetic, optical and photocatalytic properties of BiFeO3 nanoparticles

In this paper, bismuth ferrite and co-doped nanoparticle were synthesized by the tartaric acid modified sol–gel method. The XRD and Raman spectroscopy indicated that the structural phase changed from rhombohedral to orthorhombic. The nanocrystalline nature, grain size and morphology of the samples were confirmed using field emission scanning electron microscopy (FESEM) techniques. The ferromagnetic parameters increase with an increase in Sm-Cr co-doping concentration. Improved ferromagnetic properties Bi0.85Sm0.15Fe1-xCrxO3 VSM studies match with the EPR studies. The optical band gap energy of BFO and Bi0.85Sm0.15Fe1-xCrxO3 is 2.24 eV to 1.96 eV using UV–Visible spectroscopy. Compared to pristine BiFeO3, co-doped BiFeO3 nanoparticles exhibited the outstanding photocatalytic properties of methylene blue (MB) exposed to UV–Visible light irradiation. Bi0.85Sm0.15Fe0.95Cr0.05O3 nanoparticles showed 99.16 percent degradation at 90 min of radiation. The enhancement in BFO and Bi0.85Sm0.15Fe1-xCrxO3 nanoparticles' photocatalytic behaviors are contributed to changes in ionic radii, oxygen vacancies and narrow bandgap.

Nanobubble formation from ionic vacancies in an electrode reaction on a fringed disk electrode under a uniform vertical magnetic field – 2. Measurement of the angular velocity of a vertical magnetohydrodynamic (MHD) flow by the microbubbles originating from ionic vacancies

• Microbubble clusters are originated from ionic vacancies via nanobubbles. • Microbubble clusters are used as tracers for the flow visualization of the vertical MHD flow. • We examined the mechanism of the vertical MHD flow by measuring the motion of microbubble clusters. • Experimental results presented that microbubbles are created from the collisions of the nanobubbles. In an electrode reaction under a uniform vertical magnetic field, due to the tangential Lorentz force by the interaction of the current lines and the magnetic field, a tornado-like rotation accompanied by a radial secondary flow and numerous microscopic vortexes (micro-magnetohydrodynamic (MHD) flows (micro-MHD flows)) emerges over a disk electrode with an insulator fringe (fringed vertical MHD electrode (fringed-VMHDE)). By utilizing as tracers, the microbubble clusters originating from the ionic vacancies created in a solution phase, the angular velocity of the rotation was measured for copper cathodic deposition. As a result, not always the contribution of the current lines to the rotation but also the contribution of the micro-vortexes to the mass transfer at the electrode were exactly determined. Namely, 4.71% of the whole current lines drives the rotation, and 4.67% of the mass flux density of the radial secondary flow is converted to the diffusion current by the mixing effect of the micro-MHD flows. Within the experimental error, the product of both values 2.20 × 10 - 3 was in good agreement with the value ( 1.76 ± 0.45 ) × 10 - 3 obtained by the measurement of the limiting-diffusion-current in Part 1.

Influence of Ion Vacancy Migration on Short‐Circuit Current of Perovskite Solar Cells

For perovskite solar cells (PSCs), the effect of ion vacancy motion on the short‐circuit current (Jsc) in the reverse and forward J–V scans is investigated. To reveal its mechanism, all the components of current (carrier current, ionic current, displacement current) at the short‐circuit working point are calculated and the action of mobile ion vacancy on them is explored. By adjusting the parameters determining the ion vacancy mobility μI, the effect of parameter μI on Jsc is discussed. The finding provides a great supplement for the theory of short‐circuit current.

Oxygen Vacancy‐Induced Dielectric Polarization Prevails in the Electromagnetic Wave‐Absorbing Mechanism for Mn‐Based MOFs‐Derived Composites

AbstractPolymeric metal‐organic framework (MOF)‐derived composites are promising functional materials because of their exceptional chemical homogeneity, designable components, and adjustable pore size. The modulation of oxygen and Mn vacancies via the introduction of heteroatoms and changes in the annealing temperature in MOFs‐derived composites can be a possible solution to investigate the polarization loss mechanism, which facilitates the improvement of electromagnetic loss capacity. Herein, the design of laminate‐stacked sphere‐shaped trimetallic CoNiMn‐MOFs is presented. The derived CoNi/MnO@C composites retain the original topography of the MOFs. The concentration of oxygen vacancies increases with the incorporation of heteroatoms, but decreases with annealing temperature, which prevails in the polarization loss mechanism rather than the contribution of Mn2+ vacancies and heterogeneous interfaces. Therefore, the minimum reflection loss of the CoNi/MnO@C sample demonstrates −55.2 dB at 2.6 mm and the broad effective absorption bandwidth reaches 8.0 GHz at 2.1 mm. This work is expected to provide meaningful insights into the significant effect of ion vacancy modulation on the EM wave‐absorbing performance of Mn‐based MOFs‐derived composites.

Nanobubble formation from ionic vacancies in an electrode reaction on a fringed disk electrode under a uniform vertical magnetic field −1. Formation process in a vertical magnetohydrodynamic (MHD) flow

Under a uniform vertical magnetic field, the collision process of ionic vacancies created on a disk-electrode with an insulator fringe (fringed vertical magnetohydrodynamic (MHD) electrode (fringed-VMHDE)) was clarified by measuring the diffusion current of copper cathodic deposition. Due to the repulsion of Coulomb’s force, ionic vacancies with the same sign do not collide in a vacancy layer formed on the electrode, but collide in the upward microscopic vortexes ascending from the vacancy layer, forming stable nanobubbles. After emitted from the tops of the vortexes, the nanobubbles are changed to microbubbles by further collisions in the tornado-like rotation called vertical MHD flow.

RETRACTED: Oxygen vacancy induced high specific capacitance in Sr2CoSbO6

Sr2CoSbO6, a double perovskite compound known to have oxide ion vacancies, is not well explored for its electrical properties. In the present article, we study the effect of the aliovalent doping of Na+ at Sr site in Sr2CoSbO6 on their electrochemical performance. The X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) techniques confirm the phase formation and reveal particle-like morphologies for all the samples. The cyclic voltammetry study reveals the specific capacitance increases with increasing Na concentration and a specific capacitance value of 228 F/g is obtained for the maximum dopant composition. Excellent cycling stability of 92% of initial capacitance retention even after 2000 continuous cycles at a high scan rate of 100 mVs-1 in an aqueous 1 M KOH electrolyte solution and a 98% of coulombic efficiency at a current density of 1 A/g is observed. These values suggest that the Na doped Sr2CoSbO6 can find application as supercapacitors material.

Influence of implanted 150 keV Fe ion and 100 keV Mg ions on hydrogen absorption by Pd/Ti/V/Pd/Ti multilayer films on Ti substrate

The effect of implanted 150 keV Fe ion and 100 keV Mg ions on hydrogen (H) absorption by Pd/Ti/V/Pd/Ti multilayer films, prepared on Ti substrate, was investigated using the H profiling analytical technique, energy recoil detection analysis (ERDA). The stability of the multilayer stack system at 550 °C was investigated using Rutherford backscattering spectrometry for the investigation of possible intermixing of layers and X-ray diffraction for crystal structure and any possible new phase formation due to elevated temperatures. SEM was used for surface topography investigation. Ion penetration, distribution, and vacancy distribution inside the system, under investigation, were achieved using the Monte Carlo semi-empirical simulation code, Stopping and Range of Ions in Matter, and found to be 700 and 1055 Å for 150 keV Fe ions and 100 keV Mg ions implantations, respectively. ERDA revealed a maximum H amount of ∼ 4.8 at.% at a depth of ∼ 1.8 µm, with ∼ 2.6 at.% average H content over the probed depth in the non-implanted hydrogenated sample. The average H amount values in the 150 keV Fe ions implanted samples, over a probed depth, were found to be ∼ 1.32, ∼1.19 and ∼ 1.09 at.% in samples implanted up to a fluence of 1 × 1014, 1 × 1015, and 1 × 1016 ions/cm2, respectively, with H content, restricted to the surface and near the surface and constantly decreased into the bulk. The average H amount values, over a probed depth, in the 100 keV Mg ions implanted samples, up to 1 × 1014, 1 × 1015, and 1 × 1016 ions/cm2 fluence, were found to be ∼ 1.26, ∼1.25, and ∼ 1.17 at.%, respectively. These results suggest the entrapment of the H atoms by the implanted species and the ineffectiveness of Fe and Mg ion implantation in the enhancement of H absorption and diffusion in these films; at least at the energies and fluence used in this investigation. No indication of intermixing, suggesting that the system was stable up to 500 °C in an H2 environment.

Efficiently Improved Corrosion Resistance of Electrodeposition Ni–Cu Coatings via Site‐Blocking Effect of Ce

Cerium is a rare‐earth element that is often utilized as a corrosion inhibitor to improve the corrosion resistance of materials. However, it is rarely used in electrodeposition. Herein, Ce‐modified Ni–Cu coatings are prepared using a pulse current (PC) electrodeposition technique. This modification of Ni–Cu coatings with Ce is investigated via scanning electron microscopy, cyclic voltammetry, potentiodynamic polarization, and Mott–Schottky measurements. It is demonstrated in the results that Ce modification alters the reduction potential of Cu, causing an underpotential deposition effect, which is beneficial for Cu electrodeposition. In addition, Ce accumulates close to the coating/passive film interface and gives rise to a “site‐blocking” effect, which reduces the transmission rate of cation and oxygen ion vacancies. Finally, Ce accumulation noticeably decreases the concentration of point defects and enhances the corrosion resistance of Ni–Cu coatings.

Downward Homogenized Crystallization for Inverted Wide‐Bandgap Mixed‐Halide Perovskite Solar Cells with 21% Efficiency and Suppressed Photo‐Induced Halide Segregation

AbstractMixed‐halide perovskite has an irreplaceable role as wide‐bandgap absorber in multi‐junction tandem solar cells. However, large open‐circuit voltage (Voc) loss due to non‐uniform halide distribution and compromised device stability due to photo‐induced halide segregation has significantly limited the applications. Here, it is introduced 4‐(2‐aminoethyl)‐benzenesulfonyl fluoride hydrochloride (ABF) with multifunctional groups (sulfonyl, ammonium, and fluoride) to the mixed‐halide precursor to demonstrate a downward homogenized crystallization strategy for suppressing the initial vertical halide phase separation during perovskite crystallization and reducing Voc loss. Furthermore, fluoride with strong electronegativity effectively fixes anions and cations, while sulfonyl and ammonium are used to passivate positive charged (halide vacancies) and negative charged (FA/MA vacancies) defects, respectively, thereby reducing the generation of ion vacancies that lead to subsequent photo‐induced halide segregation. As a result, the 1.63 and 1.68 eV wide‐bandgap perovskite solar cells with inverted structures exhibit the champion power conversion efficiency (PCE) of 21.76% and 20.11% with Voc of 1.18 and 1.21 V, respectively. Most importantly, the optimized devices without encapsulation preserve 86% of initial efficiency after 240 h of continuous illumination under AM 1.5G, showing excellent light stability. Thus, the homogenized crystallization strategy provides highly efficient performance and stability for future tandem solar cell applications.

High-Temperature Impedance, Modulus Spectroscopy, and Conductivity Study of Nd Modified Barium Stannate Titanate Electroceramics

(Nd1−2x/3Bax)(Ti0.95Sn0.05)O3: NBTS electroceramics with different concentrations of Nd doping, i.e. x = 0.00 - 1.5 mol % are prepared. Structural characterization reveals the formation of single-phase tetragonal symmetry. Highly dense microstructures are observed in FE-SEM micrographs. Impedance, modulus, and conductivity studies are done at 350-500°C temperature. Negative temperature coefficient: NTC resistance nature is confirmed from the Nyquist analysis. Impedance spectra analysis reveals that grain resistance (Rg ) and grain boundary resistance (Rgb ) are dependent on temperature and Nd concentration in the NBTS ceramics. The frequency-dependent imaginary part of impedance (Z′′ ) and electrical modulus (M′′ ) reveal the localization of relaxation in NBTS ceramics at high temperatures. The activation energy obtained from the relaxation peak and the scaling formalism reveals that the conductivity is attributed to the oxygen ion vacancies. Conductivity study suggests the variation of frequency exponent, which follows correlated barrier hopping (CBH) model. These studies suggest that NBTS ceramics are potential candidates for future power electronics applications at high temperatures.

Amorphous calcium phosphate nanoparticles allow fingerprint detection via self-activated luminescence

Herein, stable activator-free photoluminescent nanoparticles based on amorphous calcium phosphate (ACP) were obtained for the first time, and their performance for latent fingerprint imaging was investigated. ACP nanoparticles with irregular rounded shape and diameters in 10–40 nm range were prepared by a rapid and simple chemical precipitation followed by heat treatment at 400 °C for 4 h. Notably, diffuse reflectance spectroscopy, photoluminescence excitation and emission measurements reveal a high density of localized energy states within the wide optical band gap of heat-treated ACP (Eg = 5.25–5.42 eV). This behavior allowed the excitation of ACP in near-ultraviolet region (λexc = 450 nm, 2.75 eV), leading to an intense defect-related broadband (490–890 nm) photoluminescence emission centered at 540 nm (2.30 eV), 50 times more intense than untreated nanoparticles. The effect of lattice shrinkage due to structural water elimination, the presence of ionic vacancies (VCa and VO in PO43-) and carbonate groups (CO32-), on the luminescent properties of ACP were discussed in detail, as well as investigated after aqueous-mediated ACP crystallization into hydroxyapatite (HA). ACP nanoparticles were non-cytotoxic, as determined by MTT assay in Human Dermal Fibroblast neonatal (HDFn) cell line, with cell viabilities superior to 95% in all tested concentrations (20–320 μg/mL), after incubation for 24 and 48 h. Latent fingerprint images were obtained using the ACP nanoparticles under near-ultraviolet irradiation (λexc = 450 nm) in tweezers and LCD smartphone and successfully validated by the Integrated Automated Fingerprint Identification System used by Scientific Police in Spain. The present results evidenced that the new luminescent ACP nanoparticles are safe to be used and agree with the forensic requirements for future legal actions.

Reduction of operation temperature in SOFCs utilizing perovskites: Review

Fuel cells are electrochemical devices utilized for converting chemical energy to electrical energy. Solid Oxide Fuel Cells (SOFCs) have several advantages over other kinds. For instance, high energy efficiency expanded fuel flexibility, low environmental pollutant emission are the properties of SOFCs that make them superior to other fuel cell types. Due to these special characteristics, SOFCs are gained a great deal of attraction. These fuel cells consist of different main operating parts, a cathode, an anode, and electrolyte which each of them demands special materials to operate with the most efficiency. SOFCs mostly operate in high temperatures (800-1000 ᵒC). Reducing the operating temperature to lower than 600 ᵒC or intermediate temperatures 600-800 ᵒC is one of the methods that can make them more practical devices. Perovskite oxides can be used effectively as all main parts of SOFCs because of their excellent properties like electrical and ionic conductivities, oxygen ion vacancies, great catalytic properties, thermal durability, and chemical stability to decrease the operating temperature. In this review, numerous perovskite-based materials utilized in the anode and the cathode electrodes of SOFCs are investigated in the most recent, advanced, and novel works. The perovskite materials, their properties, and their influence on the fuel cell’s performance, and in some cases the sulfur tolerance of the materials when H2S co-exists in the fuel of the fuel cell are reviewed in this paper Adding different dopants in A-site and B-site of the perovskite oxides is the most effective way to modify the characteristics of the materials. This review can provide great data on the possible perovskite oxides with the capability of enhancing the efficiency of SOFCs by reducing the operating temperature, and their most decisive and significant characteristics, like composition, structure, electrical conductivity, electrochemical and mechanical properties for research groups working on solid oxide fuel cells.