Ion Vacancies Research Articles

Vertically Oriented Quasi-2D Perovskite Grown In-Situ by Carbonyl Array-Synergized Crystallization for Direct X-Ray Detectors.

Quasi-2D perovskite quantum wells are increasingly recognized as promising candidates for direct-conversion X-ray detection. However, the fabrication of oriented and uniformly thick quasi-2D perovskite films, crucial for effective high-energy X-ray detection, is hindered by the inherent challenges of preferential crystallization at the gas-liquid interface, resulting in poor film quality. In addressing this limitation, a carbonyl array-synergized crystallization (CSC) strategy is employed for the fabrication of thick films of a quasi-2D Ruddlesden-Popper (RP) phase perovskite, specifically PEA2MA4Pb5I16. The CSC strategy involves incorporating two forms of carbonyls in the perovskite precursor, generating large and dense intermediates. This design reduces the nucleation rate at the gas-liquid interface, enhances the binding energies of Pb2+ at (202) and (111) planes, and passivates ion vacancy defects. Consequently, the construction of high-quality thick films of PEA2MA4Pb5I16 RP perovskite quantum wells is achieved and characterized by vertical orientation and a pure well-width distribution. The corresponding PEA2MA4Pb5I16 RP perovskite X-ray detectors exhibit multi-dimensional advantages in performance compared to previous approaches and commercially available a-Se detectors. This CSC strategy promotes 2D perovskites as a candidate for next-generation large-area flat-panel X-ray detection systems.

Influence of excess sodium and phosphorus on the ionic conductivity of NASICON-structured Na3Zr2(SiO4)2PO4 ceramic solid electrolyte

NASICON-structured Na3Zr2(SiO4)2PO4 (NZSP) is regarded as one of the most promising solid-state electrolytes (SSEs) for all-solid-state Na-ion batteries mainly due to its high thermal stability and wide electrochemical window. However, the existing NZSP tends to exhibit lower ionic conductivity at room temperature. Thus, in order to solve this issue, NaH2PO4 was chosen as a novel phosphate source for the synthesis of NZSP via solid-state reaction method. On top of that, excess sodium (Na) and phosphorus (P) were also added into parent NZSP SSE with different weight percentage ratios to investigate their effects on Na+ ion activation energy. Structural study reveals NZSP with either excess Na or P have the same crystal structure morphology but are dissimilar in terms of the presence of impurities and grain size. NZSP with the excess of Na shows the highest ionic conductivity (1.05 × 10−3 S cm−1) and electrode polarization contributed by the increasing of Na+ carriers and the excess Na+ ion vacancies. These results authenticate that the excess of Na can be an effective way to improve the performance of NZSP SSE for energy storage application.

Effect of copper addition on passivation film of TC18 titanium alloy

TC18 and TC18–0.5Cu alloys were prepared by vacuum arc furnace melting. The properties of its passivation film in 5 % NaCl solution were investigated using constant potential polarization, electrochemical impedance spectroscopy, Mott-Schottky and XPS analysis. The corrosion resistance of TC18 passivation films was found to be superior to that of TC18–0.5Cu alloy. The passivation films formed on both alloys displayed n-type semiconductor behavior. In the TC18–0.5Cu alloy, the presence of copper as a form of copper interstitial segregation Cuix+ was observed, which was subsequently replaced by low-mobility titanium ionic vacancies in the form of a cationic sublattice CuTix′, as a small defect.

Enhanced corrosion protection of rebars in alkaline solutions by ferroporphyrin and the mechanisms of electron consumption and lattice reconstruction

Abstract Reinforced concretes are the primary materials in coastal and offshore engineering. In alkaline environment of concrete, the anodic process is passivation of rebars and the conjugated cathodic process is oxygen reduction reaction (ORR). It is proposed that a novel approach to enhance the passivation films through catalyzed ORR by iron meso-tetra(4-carboxyphenyl)porphine (FeTCPP). The ORR catalyst FeTCPP promotes the formation of passivation film, as it accelerates the consumption of abundant electrons generated and accumulated by the anodic formation of passivation films. The passivation films of rebars are highly defective Fe3O4 semiconductor. The dissolution of interstitial ferrous ions and lattice iron ions produces defects of O ion vacancies, Fe ion vacancies and interstitial Fe ions, and they further cause the formation and accumulation of Fe atom vacancies on the metal surface, leading to the collapse of the passivation films. The FeTCPP adsorbs on the surface of passivation films, hindering the dissolution of lattice iron ions and interstitial ferrous ions, thereby inhibiting the generation and accumulation of Fe atom vacancies and improving the integrity and protective ability of the passivation films.

Surface Crystallization Enhancement and Defect Passivation for Efficiency and Stability Enhancement of Inverted Wide-Bandgap Perovskite Solar Cells.

Wide-bandgap (WBG) inverted perovskite solar cells (PSCs) are used as the top cell for tandem solar cells, which is an effective way to outperform the Shockley-Queisser limit. However, the low efficiency and poor phase stability still seriously restrict the application of WBG inverted PSCs. Here, the surface of the WBG perovskite film was passivated by the synthesized 1,2,4-tris(3-thienyl)benzene (THB). The THB size well matches with the halogen ion vacancy on the perovskite surface, and the S atom in THB can strongly interact with Pb2+ on the surface of the WBG perovskite film to the greatest extent, which effectively passivates surface defects and suppresses the recombination of carriers caused by these defects. At the same time, the S atom in THB occupied the migration site of the halogen ions, which inhibits the migration of halogen ions. Due to the strong conjugation effect and stability of THB, it can be locked on the surface of perovskite to increase the lattice strength and inhibit the segregation of photoinduced halide, thus improving the performance and operational stability of PSCs. The THB-modified WBG (Eg = 1.71 eV) PSC achieves a maximum power conversion efficiency of 20.75%, and its 99.0% is retained after 1512 h at a relative humidity of 10-25%. Under the irradiation of 1000 lx LED light, the indoor power conversion efficiency of the THB-modified WBG PSC reaches 34.15%.

Low-electric-field-induced high electrocaloric properties via defect regulation in samarium-doped BaTiO3 ceramics

A small electrocaloric effect (ECE) is usually observed in aliovalent doped ferroelectric ceramics since decreased polarization is usually present. In this work, the high ECE is achieved in a barium titanate [BaTiO3 (BT)]-based ceramic by introducing defect polarization to enhance the ferroelectric polarization and polarization change. The defect dipoles consisting of donor ion and barium vacancy, or barium and oxygen vacancies were formed in samarium-doped (Ba1−1.5xSmx)TiO3 ceramics. The phase and defect structures, and dielectric and ferroelectric properties are analyzed to confirm the evolution of charge compensation states and defect structures, and the influences of defects on polarization rotation and ECE. An enhanced ferroelectric polarization and high internal bias field are present in the ceramic with a suitable defect dipole effect, leading to a high polarization change before/after applying an electric field, causing an enhanced ECE. Finally, a high electrocaloric temperature change of ∼1.11 K and a large electrocaloric strength of ∼0.037 K·cm kV−1 were achieved under a low electric field of 30 kV/cm, indicating that forming suitable defect dipoles can optimize the ECE. This work provides a significant paradigm for tuning ECE in ferroelectric materials via defect regulation.

Theory of Chiral Electrodeposition by Micro-Nano-Vortexes under a Vertical Magnetic Field-2: Chiral Three-Dimensional (3D) Nucleation by Nano-Vortexes

The contributions of magnetohydrodynamic (MHD) vortexes to chiral electrodeposition in a vertical magnetic field were theoretically examined based on the three-generation model of the 2D nucleus, 3D nucleus, and screw dislocation; for the vortexes to rotate in the second and third-generation, the kinematic viscosity must be at least 10−18 and 10−30 times lower than the ordinary value in the first generation, i.e., almost equal to zero. This implies that the ionic vacancy created on the electrode surface works as an atomic-scale lubricant. At the same time, the vortexes played three roles: promotion and suppression of nucleation, and transport of the chirality from the upper generation to the lower generation through precessional motion. Then, the rule of the chirality transfer was established, and finally, the relationship between the chiral activity and magnetic field was clarified in the presence and absence of chloride ions.

Tailoring of Interface Quality of MoOx/Si Solar Cells

Transition metal oxide films (TMO) as passivating contacts with improved opto-electronic characteristics play an important role in improving the silicon solar cell device efficiency. In this report, the effect of sputtering power on the optical properties of MoOx and the quality of MoOx/n-Si interface for its application in a silicon solar cell as carrier selective contacts has been reported. The optical transmittance of the film greater than 80 % in the visible and near infrared region of the spectrum is observed, which further improved with sputtering power. The creation of oxygen ion vacancies, which acts as positively charged structural defects able to capture one or two electrons led to the decrease of optical band gap from 3.70 eV to 3.23 eV at higher power. The oxygen vacancies occupied by electrons acts as donor centers, which lies close to the valence band, were responsible for modulation in electrical properties. The electrical properties of MoOx/n-Si interface was analyzed using current-voltage (I-V) measurements for its application as selective contact. A significant change in the selectivity parameters, like barrier height, I0 and series resistance of MoOx, has been observed with dc power. These extracted parameters showed that the sputtering power has a great influence on the selectivity of the charge carriers.

Enhancing sintering behavior and conductivity of YSZ electrolyte by co-doping of ZnO and MnO2

This study aimed to enhance the sinterability and conductivity of yttria fully stabilized zirconia electrolyte through co-doping by 2 mol% of ZnO and different contents of MnO2 (0, 0.5, 1, 1.5 mol%) at two sintering temperatures of 1300 and 1400 °C. Phase composition identification, density, microstructure, and conductivity of the samples were evaluated using X-ray diffraction (XRD), Archimedes' method, field emission scanning electron microscopy (FESEM), and electrochemical impedance spectroscopy (EIS), respectively. The XRD results revealed that ZnO and MnO2 are successfully doped in the fluorite structure of YSZ sintered at 1400 °C, and the cubic structure is completely preserved. However, at a sintering temperature of 1300 °C, the (111) peaks of doped samples were slightly split, which implied a slight phase transformation of YSZ from cubic to a tetragonal structure. The co-doped samples, at both sintering temperatures, showed higher relative density and grain size compared with pure YSZ. The addition of 2 mol% of ZnO and 0.5 mol% of MnO2 at 1400 °C increased the relative density of YSZ from 81.6% to 95.1%. The increase in relative density and grain size, while maintaining the cubic structure, caused an increase in the conductivity of the mentioned sample. Compared with pure YSZ, the sample's total conductivity increased from 7.37 to 10.03 S m−1 at 800 °C. The proposed composition showed better sintering behavior, lower activation energy of grain conductivity, and higher conductivity than pure YSZ. This behavior is thought to be due to the facilitating rearrangement of atoms during sintering and an increase in oxygen ion vacancy concentration due to co-doping with the appropriate amount of ZnO and MnO2.

Phase formation, microstructural and dielectric properties of bismuth ferrite nanoceramics synthesized by low-temperature molten salt flux route

BiFeO3 nano-ceramics were synthesized using the low-temperature molten salt synthesis route to study the influence of calcination temperature and salt ratios. The Rietveld refinement revealed the distorted perovskite structure of BFO. These granular-shaped BFO samples’ grains morphology was studied using the FESEM. The FTIR revealed the presence of Metal-Oxygen bonds in the BFO ceramics. The XPS studies exhibited the respective constituent elements’ oxidation states and validated the presence of oxygen ion vacancies. The frequency-dependent dielectric properties were measured at various temperatures. The electrical conductivity measurement showed a linear variation as a function of frequency which validated Jonscher’s power law.

Synthesis and electrical characterization of Sb modified lithium bismuth titanate

Sb-modified lithium bismuth titanate Li0.5Bi0.3Sb0.2TiO3 is prepared following the mixed oxide method. The development of a new compound with a single-phase orthorhombic crystal structure is approved from the XRD analysis at environmental temperature. The electrical behavior like dielectric and electrical conductivity are analyzed in a wide temperature as well as frequency range by the impedance analyzer, which exhibits that these properties effectively depend on frequency and temperature. The ac conductivity versus temperatures plots obeys the Arrhenius relation and confirm the presence of the mixed type of conductivity process like space charge conductivity created from oxygen ion vacancies, ionic-polaronic conductivity, and so on, in the sample. Ac conductivity versus frequency spectra is as per Jonscher’s Universal Power law.

Investigating the effects of varying sulfur concentration on ZnSxSe1-x (0 ≤ x ≤ 1.0) thin films prepared by photo-assisted chemical bath method

Zinc sulfur-selenide (ZnSxSe1-x) (0 ≤ x ≤ 1.0) thin films were grown on glass substrates using photo-assisted chemical bath deposition technique and the deposited samples were annealed in an open-air furnace at 250 ℃ for 3 h. X-ray diffraction analysis revealed a phase transition from hexagonal ZnSe to cubic ZnS as x changes from 0 to 1.0. Raman scattering showed two longitudinal optical modes due to ZnSe structure. The effects of S and Se ions variation is observed by the change in surface morphology from nanoflakes to spherical particles as x increased. The presence of the expected elementary composition was confirmed by the energy dispersive x-ray spectroscopy. The bandgap of the films was found to increase from 2.68 to 3.50 eV with a corresponding decrease in crystallite size (11.9 – 7.1 nm) as x varied from 0 to 1.0. Photoluminescence excitation and emission showed defect emission peaks ascribed to intrinsic and extrinsic deep level defects such as Zn2+ or S2- ions vacancies and interstitials. The emission colours were tuned from red to yellowish-green with increased x values as confirmed from Commission Internationale de L’Eclairage analysis. The tunability of the ZnSxSe1-x structural, optical and morphological properties makes it a good candidate for optoelectronic applications.

Effect of sintering temperature on structural, elastic, and hyperfine features of nickel ferrite nanoparticles

Temperature is one of the key parameters in the synthesis of a system of magnetic nanoparticles and can affect considerably the arrangement of atoms in the crystal structure. Consequently, the magnetic, elastic, and structural properties are strongly impacted. In the magnetically soft NiFe1.8O4 spinel ferrite, the relative number of Ni and Fe ions in each of the two possible different geometries, tetrahedral (T) and octahedral (O), is of extreme importance. In this work, this material was studied on products of co-precipitation synthesis followed by a temperature dependent sintering. We performed 57Fe Mössbauer spectroscopy (MS), X-ray diffraction (XRD), scanning and transmission electron microscopies (SEM and TEM), X-ray absorption spectroscopy (XAS) using synchrotron radiation at Ni K- and L2-edge, and vibrating sample magnetometry (VSM) measurements. From XAS measurements it was found that Ni atoms prefer an octahedral coordination when the sintering temperature is increased. MS showed that the T-sites are more populated by Fe ions than the O-sites, a fact that can be explained by the presence of Fe ion vacancies in the O- sites. However, as the sintering temperature increases, we found that there is also a migration of Fe atom to the O-sites. Additionally, based on MS measurements in 78–292 K region, we estimated the Debye temperatures of the Fe ions in the tetra- and octahedral geometries and found that the recoiless f-factor depends on the sintering temperature of the nickel ferrite powders. The ratio fO/fT is about 0.98 and 0.95 at room temperature for the samples sintered at 1000 °C and 600 °C, respectively.

Excess heat production of the pair annihilation of ionic vacancies in a copper redox reaction using a double bipolar MHD electrode.

Through a copper double bipolar magnetohydrodynamic (MHD) electrode (MHDE) producing twice the amounts of ionic vacancies than a conventional single MHDE, the molar excess heat of the pair annihilation of ionic vacancies, 702kJmol-1 at 10T on average was obtained in a copper redox reaction. It was about twice as large as that of a single MHDE, 387kJmol-1 at the same magnetic field. This result strongly suggests that a multi-channel bipolar MHDE will produce much greater excess heat. To conserve the linear momentum and electric charge during electron transfer in an electrode reaction, ionic vacancies are created, storing the solvation energy in the polarized core of the order of 0.1nm, and the pair annihilation of the vacancies with opposite charges liberates the energy as excess heat. The promoted excess heat by the double bipolar MHDE with a diffuser at 10T was 710 ± 144kJmol-1, whereas as mentioned above, 702 ± 426kJmol-1 was obtained by the same electrode without such a diffuser. From the theoretical excess heat of 1140kJmol-1, the collision efficiencies in pair annihilation were 0.623 ± 0.126 and 0.616 ± 0.374, respectively. From these results, the reproducibility of the thermal measurement was experimentally validated. At the same time, it was concluded that at magnetic fields beyond 10T, the concentration of ionic vacancy and the collision efficiency take constant uppermost values.

Ion transport induced room-temperature insulator-metal transition in single-crystalline Cu2Se.

Cu2Se is a superionic conductor above 414 K, with ionic conductivities reaching that of molten salts. The superionic behavior results from hopping Cu ions between different crystallographic sites within the Se scaffold. However, the properties of Cu2Se below 414 K are far less known due to experimental limitations imposed by the bulk or polycrystalline samples that have been available so far. Here, we report the synthesis of ultra-thin, large-area single crystalline Cu2Se samples using a chemical vapor deposition method. The as-synthesized Cu2Se crystals exhibit optically and electrically detectable and controllable robust phases at room temperature and above. We demonstrate that Cu ion vacancies can be manipulated to induce an insulator-metal transition, which exhibits 6 orders of magnitude change in the electrical resistance of two terminal devices, accompanied by an optical change in the phase configuration. Our experiments show that the high mobility of the liquid-like Cu ion vacancies in Cu2Se causes macroscopic ordering in the Cu vacancies. Consequently, phase distribution over the crystals is not dictated by the diffusive motion of the ions but by the local energy minima formed due to the phase transition. As a result, long-range vacancy ordering of the crystal below 414 K becomes optically observable at a micrometer scale. This work demonstrates that Cu2Se could be a prototypical system where long-range ordering properties can be studied via electrical and optical methods.

Efficient oxygen evolution activity of CoFe-PBA heterojunctions using a bimetallic probe (Mo/Cu) at room temperature: construction of multilayered activated structures and cationic vacancies

Multilayer active heterojunctions and Co ionic vacancies (VCo) were successfully constructed by bimetallic probes (Mo/Cu) in CoFe-PBA precursors. This makes it a new strategy for doping various types of isotropic metals at room temperature.

Understanding oxide ion transport in cation-ordered yttria-stabilized zirconia.

Classical molecular dynamics simulations are carried out on cationically ordered yttria-doped zirconia, YxZr1-xO2-x/2, at the dopant (Y3+) concentration of x = 12.5%. A variety of Zr4+/Y3+ ordered structures are examined for local migration pathways and microscopic energetics governing oxide ion transport in the system. Starting from a layer of cubic Y2O3 spanning the basal plane, the number of Y3+ layers in the simulation cell is multiplied systematically, at the expense of their coverage per layer. The study reveals that cationic ordering in YxZr1-xO2-x/2 can produce a profound impact on the oxide ion transport in the framework, wherein with the maximal dispersion of the dopant a four-fold enhancement in the ionic conductivity is observed relative to the cationically disordered matrix. We demonstrate that this improvement in ion mobility is due to the homogenization of oxide ion vacancies across the matrix. This study thus provides valuable insights for the enhancement of the electrochemical performance of solid oxide fuel cells.

Dopant clustering and vacancy ordering in neodymium doped ceria

Reverse Monte Carlo analysis of total neutron scattering data on neodymium doped ceria reveals details of local structure including dopant–oxide ion vacancy association, dopant clustering and oxide ion vacancy pair ordering in the 〈100〉 direction.

Development and performance evaluation of (Sm1-xNdx)0.2O2-δ electrolyte for low-temperature solid oxide fuel cell application

Major hurdle for SOFC operation at lower temperature is it’s ion migration through electrolyte crystal lattice reduces as more energy required and lowered number of ion vacancies. In order, researchers from all over the world trying to develop SOFC which operates at lower temperature which let to erupt the electrolyte performance. Currently available electrolyte YSZ (Yttria Stabilized Zirconia) shows high efficiency above 1100 °C. Fluorite structure doped/codoped ceria electrolyte shows better ionic conductivity below the 1000 °C. In current study ceria co doped with the Sm+3 and Nd+3 having ionic radius close to host ceria through oxalate co precipitation route. Crystallite size and structure is observed through X-ray diffraction for purity of doping with nano crystallite size transpose from 13.21 to 22.21 nm. Furthermore, Energy dispersive X-ray spectroscopy (EDXS) validates maximum 0.2 Codoping achieved through oxalate rought. Moreover grain size and grain boundary compaction enhances with sintering electrolyte pellet at 1300˚C for 2 h observed under FE-SEM. AC and DC conductive properties are studied with diverse codoping percentage and it is analyzed through Electrochemical Impedance Spectroscopy (EIS). Ce with 0.1 codoping Sm+3 and Nd+3 respectively enhances ion migration with minimum activation energy and relaxation time in lattice site.

First-Principles Calculations on Diffusion and Association Behavior of Fluoride Ions in Ba-Doped LaF3 Solid Electrolyte

Fluoride ion batteries, which generate electrical energy through the fluorination/de-fluorination reaction of electrode active materials, are expected to be the next-generation storage batteries with high energy density. LaF3 with a tysonite-type structure is known as one of the representative solid-state fluoride ion conductors. Substitutional solid solution of divalent cations such as Ba or Sr ions at La sites forms fluoride ion vacancies as charge compensation, resulting in fluoride ion conductivity. The main objective of this study is to analyze the formation behavior of point defects in LaF3 through quantitative evaluation of their formation energies using first-principles calculations, and to elucidate the conduction mechanism of fluoride ions in LaF3.The plane-wave basis PAW method implemented in VASP code was used for the electronic structure calculations. The electron correlation treatment uses the PBEsol-type potential based on the generalized gradient approximation. Calculations for given point defects were performed. The cutoff energy of the plane wave basis sets was set to 420 eV, and the structure optimization calculations were performed until the Hellmann-Feynman force acting on each atom was less than 0.02 eV/Å.There are three fluoride ion sites (12g, 4d, and 2a) in the unit cell of LaF3. Using the supercell model, we calculated the defect formation energies of fluoride ion vacancies at each site. The formation energies at the 12g, 4d, and 2a sites are 0.17 eV, 0.52 eV, and 0.52 eV, respectively. According to the defect formation energies, fluoride ion vacancies are most likely to form at the 12g sites.To elucidate the elementary processes of fluoride ion transfer between 12g sites by the vacancy mechanism, we performed first-principles calculations and transition state search using the Nudged Elastic Band method. From symmetry, four different pathways exist in the lattice of undoped LaF3. The pathway with the highest energy barrier is shown to have very low transfer energies, 0.17 eV, and the energy barriers of the other pathways are less than 0.1 eV. These results suggest that LaF3 has a potential for very fast fluoride ionic conductivity by the vacancy mechanism. In the presentation, the mechanism of fluoride ion conduction in Ba-doped LaF3 will also be reported. This work was supported by the RISING2 (JPNP16001) and the RISING3 (JPNP21006) projects from the New Energy and Industrial Technology Development Organization (NEDO), Japan.