Enhancement of Thermoelectric Performance of Sr0.9Ba0.1Ti0.8Nb0.2O3 Ceramics by A-Site Cation Nonstoichiometry

Sr0.9Ba0.1Ti0.8Nb0.2O3 ceramics （x=0, 0.01, 0.02 and 0.05） are prepared by solid state reaction, whose thermoelectric properties are investigated from 323K to 1073K. By introducing A-site nonstoichiometry, the absolute Seebeck coefficient is enhanced, while the electrical resistivity is surprisingly reduced due to the significantly enhanced carrier mobility. These results are dramatic in thermoelectric materials, effectively enhancing the power factor. Moreover, the thermal conductivity is reduced, thus the thermoelectric performance of Sr0.9Ba0.1Ti0.8Nb0.2O3 ceramic is significantly enhanced by A-site nonstoiehiometry.

Enhanced perovskite electronic properties via A-site cation engineering

Organic-inorganic halide perovskites have emerged as excellent candidates for low-cost photovoltaics and optoelectronics.While the predominant recent trend in designing perovskites for efficient and stable solar cells has been to mix different A-site cations,the role of A-site cations is still limited to tune the lattice and bandgap of perovskites.Herein we compare the optoelectronic properties of acetamidinum(Ace)and guanidinium(Gua)mixed methylammonium lead iodide perovskites and shed a light on the hidden role of A-site cation on the carrier mobility of mixed-cation lead iodide perovskites.The cations do not affect the bandgap of the perovskites since the orbitals from Ace and Gua do not contribute to the band edges of the material.However,the mobility of the Ace mixed perovskite is significantly enhanced to be an order of magnitude higher than that of the pristine perovskite.We apply the Ace mixed perovskite in hole-conductor-free printable mesoscopic perovskite solar cells and obtain a stabilized PCE of over 18%(certified 17.7%),which is the highest certified efficiency so far.

A-site Cation Defects(Ba_(0.5)Sr_(0.5))_(1-x)Co_(0.8)Fe_(0.2)O_(3-δ)Perovskites as Active Oxygen Evolution Reaction Catalyst in Alkaline Electrolyte

Main observation and conclusion Perovskites(Ba_(0.5)Sr_(0.5))_(1-x)Co_(0.8)Fe_(0.2)O_(3-δ)(x=0.02,0.05,0.1 denoted as BSCF-0.98,BSCF-0.95,BSCF-0.9,respectively)with A-site cation defects are synthesized by simple and efficient sol-gel method and are proved to have better OER catalytic effect than the well-known(Ba_(0.5)Sr_(0.5))_(1-x)Co_(0.8)Fe_(0.2)O_(3-δ)(BSCF)oxides.BSCF-0.95 exhibits the best OER catalytic activity in the series perovskite.The current density of BSCF-0.95 is about 56%higher than that of BSCF oxide at a potential of 1.7 V.The experimental studies have shown that compared with BSCF,BSCF-0.95 oxide has a larger electrochemical surface area(ECSA),a higher content of O_(2)^(2–)species related to surface oxygen vacancies,and faster charge transfer rate,which may be the factors for the enhancement of OER activity.The theoretical calculation results prove that the center positions of the O 2p-band of perovskite with A-site cation defects are closer to the Fermi level than BSCF oxide,which agrees with the OER performance trend of the material.

Enhancing Direct Electrochemical CO_(2)Electrolysis by Introducing A-Site Deficiency for the Dual-Phase Pr(Ca)Fe(Ni)O_(3-δ)Cathode

High-temperature CO_(2)electrolysis via solid oxide electrolysis cells(CO_(2)-SOECs)has drawn special attention due to the high energy convention efficiency,fast electrode kinetics,and great potential in carbon cycling.However,the development of cathode materials with high catalytic activity and chemical stability for pure CO_(2)electrolysis is still a great challenge.In this work,A-site cation deficient dual-phase material,namely(Pr_(0.4)Ca_(0.6))_(x)Fe_(0.8)Ni_(0.2)O_(3-δ)(PCFN,x=1,0.95,and 0.9),has been designed as the fuel electrode for a pure CO_(2)-SOEC,which presents superior electrochemical performance.Among all these compositions,(Pr_(0.4)Ca_(0.6))_(0.95)Fe_(0.8)Ni_(0.2)O_(3-δ)(PCFN95)exhibited the lowest polarization resistance of 0.458Ωcm^(2)at open-circuit voltage and 800℃.The application of PCFN95 as the cathode in a single cell yields an impressive electrolysis current density of 1.76 A cm^(-2)at 1.5 V and 800℃,which is 76%higher than that of single cells with stoichiometric Pr_(0.4)Ca_(0.6)Fe_(0.8)Ni_(0.2)O_(3-δ)(PCFN100)cathode.The effects of A-site deficiency on materials'phase structure and physicochemical properties are also systematically investigated.Such an enhancement in electrochemical performance is attributed to the promotion of effective CO_(2)adsorption,as well as the improved electrode kinetics resulting from the A-site deficiency.

Effect of the Cation Size Disorder at the A-Site on the Structural Properties of SrAFeTiO<SUB>6</SUB>Double Perovskites (A = La, Pr or Nd)

In this paper, the cation size disorder effect of the A-site on the structural properties of the SrAFe- TiO6 (A = La, Pr or Nd) was investigated. The compounds were synthesized—as the best of our knowledge—for the first time by conventional and precursor method to get crystalline materials. The results obtained from the experimental measurements carried out on new double perovskite materials were presented. The data of X-ray diffraction (XRD), Fourier Transform Infra Red FTIR were measured at room temperature. From the X-ray diffraction, and by means of standard Rietiveld method, all the samples have the same structure (orthorhombic) with Pnma space group. The difference in the tolerance factor is clearly noticed and refers to the cation size disorder at the A-sites. The Fourier Transform Infra Red FTIR measurement has been done;the results of it confirm the double perovskite structure and the difference between the samples were noticed. The tolerance factors for the samples altered from SrLaFeTiO6 up to SrNdFeTiO6 and this difference return to ionic radius and cation size effect.

A-site phase segregation in mixed cation perovskite

Mixed cation strategy greatly benefits the enhancement of device performance and chemical stability.However,adverse impact also accompanies the mixed cation system simultaneously.It brings the compositional instability,wherein the homogeneous film is likely to segregate into multi-phases during the fabrication and ageing process,thus resulting in the efficiency reduction of perovskite solar cells(PSCs)devices.This review focuses on the cation induced phase segregation,and elucidates the segregation mechanisms from the perspectives of film formation and ageing process,respectively.Furthermore,the influence of cation segregation on device performance and operational stability are discussed.And based on these understandings,viable strategies are proposed for the design of phase-stable mixed composition halide perovskites and for suppressing segregation to benefit its development towards commercial applications.

R-site cation randomness effect in the A-site ordered Y_(0.5)La_(0.5)BaMn_2O_6 compound

The R/Ba-ordered and R-site mixed compound Y0.5La0.5BaMn2O6 is synthesized, in which （Y, La） and Ba are regularly arranged, while Y and La randomly occupy the R-site. Y0.5La0.5BaMn2O6 has a tetragonal unit cell with a space group of P4/mmm. A structural transition between tetragonal and orthorhombic is observed at about 325 K by X-ray powder diffraction （XRD）. Thermal magnetic measurement shows the occurrence of an antiferromagnetic transition at the temperature TN～190 K. Anomalies in magnetization, resistivity and lattice parameters observed around 340 K indicate a charge/orbital order transition accompanying the structural phase transition. The R-site randomness effect is discussed to interpret the different properties of Y0.5La0.5BaMn2O6 between NdBaMn2O6 and SmBaMn2O6.

Structural Modal Parameter Recognition and Related Damage Identification Methods under Environmental Excitations: A Review

Modal parameters can accurately characterize the structural dynamic properties and assess the physical state of the structure.Therefore,it is particularly significant to identify the structural modal parameters according to the monitoring data information in the structural health monitoring(SHM)system,so as to provide a scientific basis for structural damage identification and dynamic model modification.In view of this,this paper reviews methods for identifying structural modal parameters under environmental excitation and briefly describes how to identify structural damages based on the derived modal parameters.The paper primarily introduces data-driven modal parameter recognition methods(e.g.,time-domain,frequency-domain,and time-frequency-domain methods,etc.),briefly describes damage identification methods based on the variations of modal parameters(e.g.,natural frequency,modal shapes,and curvature modal shapes,etc.)and modal validation methods(e.g.,Stability Diagram and Modal Assurance Criterion,etc.).The current status of the application of artificial intelligence(AI)methods in the direction of modal parameter recognition and damage identification is further discussed.Based on the pre-vious analysis,the main development trends of structural modal parameter recognition and damage identification methods are given to provide scientific references for the optimized design and functional upgrading of SHM systems.

A-site cation engineering enables oriented Ruddlesden-Popper perovskites towards efficient solar cells

Quasi two-dimensional(Q-2D)perovskites with favorable environment stability and satisfied device performance are attracting great attention and becoming star materials.The unique characteristics of more wide range of Goldschmidt tolerance factor endow Q-2D perovskites with exceptional composition tunability and great potential.Herein,Guanidinium(Gua)was firstly introduced into the octahedral cation site of BA_(2)MA_(3)Pb_(4)I_(13) perovskite to partially replace methylammonium(MA).With the incorporation of Gua,the XRD intensity ratio of(202)/(111)increased nearly 100%for control and 0.10Gua-mixed Q-2D perovskite,from1.49 to 2.84,indicating that the layered perovskite crystallization orientation is significantly regulated.Coupling with GIWAXS results,a preferential orientation Q-2D perovskite film was obtained.Meanwhile,the Gua-based Q-2D perovskite exhibits significantly reduced nonradiative recombination,which greatly promotes the efficient transport of carriers leading to a high efficiency of 15.41%in the BA_(2)(MA_(0.9)GA_(0.1))_(3)Pb_(4)I_(13)-based solar cell.Moreover,the solar cells display superior environmental stability at an average humidity of 35%±5%in the air for 1200 h.This work points the way to the regulation of crystal orientation for enhancing the performance of Q-2D perovskite by the A-site cation engineering.

Oxygen permeation and phase structure properties of partially A-site substituted BaCo_(0.7)Fe_(0.225)Ta_(0.075)O_(3-δ) perovskites

Ba0.9R0.1Co0.TFe0.225Ta0.07503-δ （BRCFT, R = Ca, La or Sr） membranes were synthesized by a solid-state reaction. Metal cation Ca2＋, La3＋ or Sr2＋ doping on A-site partially substituted Ba2＋ in BaCoo.TFe0.225Ta0.07503-δ oxides, and its subsequent effects on phase structure stability, oxygen permeability and oxygen desorption were systematically investigated by XRD, TG-DSC, Hz-TPR, O2-TPD techniques and oxygen permeation experiments. The partial substitution with Ca2＋, La3＋ or Sr2＋, whose ionic radii are smaller than that of Ba2＋, succeeded in stabilizing the cubic perovskite structure without formation of impurity phases, as revealed by XRD analysis. Oxygen-involving experi- ments showed that BRCFT with A-site fully occupied by Ba2＋ exhibited good oxygen permeation flux under He flow, reaching about 2.3 mL.min-l .cm-2 at 900 with I mm thickness. Of all the membranes, BLCFT membrane showed better chemical stability in CO2, owing to the reduction in alkalinity of the mixed conductor oxide by La doping. In addition, we also found the stability of the perovskite structure under reducing atmospheres was strengthened by increasing the size of A-site cation （Ba2＋〉La3＋〉SrZ＋〉Ca2＋）.

A-site ordered quadruple perovskite oxides AA＇_3B_4O_(12)

The A-site ordered perovskite oxides with chemical formula AA＇3B4O（12）display many intriguing physical properties due to the introduction of transition metals at both A and B sites. Here, research on the recently discovered intermetallic charge transfer occurring between A-site Cu and B-site Fe ions in La Cu3Fe4O（12） and its analogues is reviewed, along with work on the magnetoelectric multiferroicity observed in La Mn3Cr4O（12） with cubic perovskite structure. The Cu–Fe intermetallic charge transfer（LaCu3（3＋）Fe4（3＋）O（12）→ LaCu3（2＋）Fe4（3.75＋）O（12）） leads to a first-order isostructural phase transition accompanied by drastic variations in magnetism and electrical transport properties. The La Mn3Cr4O（12） is a novel spindriven multiferroic system with strong magnetoelectric coupling effects. The compound is the first example of cubic perovskite multiferroics to be found. It opens up a new arena for studying unexpected multiferroic mechanisms.

A-site ordered perovskite CaCu3Cu2Ir2O(12-δ) with square-planar and octahedral coordinated Cu ions

A novel CaCu_3Cu_2Ir_2O_（12-δ） polycrystalline sample was synthesized at 8 GPa and 1373 K.Rietveld structural analysis shows that this compound crystallizes in an AA＇_3B_4O_（12）-type A-site ordered perovskite structure with space group Im-3.Xray absorption spectra reveal a ＋2-charge state for both the square-planar and octahedral coordinated Cu ions,and the valence state of Ir is found to be about ＋5.Although the A-site Ca and the A＇-site Cu^（2＋） are 1：3 ordered at fixed atomic positions,the distribution of B-site Cu^（2＋） and Ir^（5＋） is disorderly.As a result,no long-range magnetic ordering is observed at temperatures down to 2 K.Electrical transport and heat capacity measurements demonstrate itinerant electronic behavior.The crystal structure is stable with pressure up to 35.7 GPa at room temperature.

Characterization of A-site excessive perovskite La_(0.7-x)Sm_(x+0.02)Ca_(0.3)CrO_(3-δ)

La0.7-xSmx＋0.02Ca0.3CrO3-δ （0≤x≤0.4） powders with A-site excessive perovskite structure were synthesized by auto-ignition process and characterized. X-ray diffraction （XRD） patterns of samples after sintering at 1400℃ for 4 h were indexed as tetragonal structure. The relative densities were all above 96% although decreased slightly with the increasing content of samarium, indicating that the excessive A-site element was helpful to enhance their sinterability. Conductivities of the specimens in air increased with increasing content of samarium. The conductivity of La0.6Sm0.12Ca0.3CrO3_swas 33.6 S/cm in air at 700℃ which was about 1.7 times as high as that of La0.7Ca0.3CrO3-δ （20.1 S/cm）. Average thermal expansion coefficients （TECS） of the specimens increased from 11.06×10^-6 to 12.72×10^-6 K^-1 when x increased from 0 to 0.4, and they were close to that of Y doped ZrO2 （YSZ）.La0.7-xSmx＋0.02Ca0.3CrO3-δ （0.1≤x≤0.3） were good choices for intermediate temperature solid oxide fuel cells （IT-SOFCs） interconnect materials.

Enabling an Inorganic-Rich Interface via Cationic Surfactant for High-Performance Lithium Metal Batteries

An anion-rich electric double layer(EDL)region is favorable for fabricating an inorganic-rich solid-electrolyte interphase(SEI)towards stable lithium metal anode in ester electrolyte.Herein,cetyltrimethylammonium bromide(CTAB),a cationic surfactant,is adopted to draw more anions into EDL by ionic interactions that shield the repelling force on anions during lithium plating.In situ electrochemical surface-enhanced Raman spectroscopy results combined with molecular dynamics simulations validate the enrichment of NO_(3)^(−)/FSI−anions in the EDL region due to the positively charged CTA^(+).In-depth analysis of SEI structure by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry results confirmed the formation of the inorganic-rich SEI,which helps improve the kinetics of Li^(+)transfer,lower the charge transfer activation energy,and homogenize Li deposition.As a result,the Li||Li symmetric cell in the designed electrolyte displays a prolongated cycling time from 500 to 1300 h compared to that in the blank electrolyte at 0.5 mA cm^(-2) with a capacity of 1 mAh cm^(-2).Moreover,Li||LiFePO_(4) and Li||LiCoO_(2) with a high cathode mass loading of>10 mg cm^(-2) can be stably cycled over 180 cycles.

Cation effects in electrocatalytic reduction reactions:Recent advances

Electrocatalytic reduction reactions,powered by clean energy sources such as solar energy and wind,offer a sustainable method for converting inexpensive feedstocks(e.g.,CO_(2),N_(2)/NO_(x),organics,and O_(2))into high-value-added chemicals or fuels.The design and modification of electrocatalysts have been widely implemented to improve their performance in these reactions.However,bottle-necks are encountered,making it challenging to further improve performance through catalyst development alone.Recently,cations in the electrolyte have emerged as critical factors for tuning both the activity and product selectivity of reduction reactions.This review summarizes recent advances in understanding the role of cation effects in electrocatalytic reduction reactions.First,we introduce the mechanisms underlying cation effects.We then provide a comprehensive overview of their application in electroreduction reactions.Characterization techniques and theoretical calcula-tion methods for studying cation effects are also discussed.Finally,we address remaining challeng-es and future perspectives in this field.We hope that this review offers fundamental insights and design guidance for utilizing cation effects,thereby advancing their development.

Exploring the mechanism of a novel cationic surfactant in bastnaesite flotation via the integration of DFT calculations,in-situ AFM and electrochemistry

Effectively separating bastnaesite from calcium-bearing gangue minerals(particularly calcite)presents a formidable challenge,making the development of efficient collectors crucial.To achieve this,we have designed and synthesized a novel,highly efficient,water-soluble cationic collector,N-dodecylisopropanolamine(NDIA),for use in the bastnaesite-calcite flotation process.Density functional theory(DFT)calculations identified the amine nitrogen atom in NDIA as the site most susceptible to electrophilic attack and electron loss.By introducing an OH group into the traditional collector dodecylamine(DDA)structure,NDIA provided additional adsorption sites,enabling synergistic adsorption on the surface of bastnaesite,thereby significantly enhancing both the floatability and selectivity of these minerals.The recovery of bastnaesite was 76.02%,while the calcite was 1.26%.The NDIA markedly affected the zeta potential of bastnaesite,while its impact on calcite was relatively minor.Detailed Fourier-transform infrared spectroscopy(FTIR)and X-ray photoelectron spectroscopy(XPS)results elucidated that the―NH―and―OH groups in NDIA anchored onto the bastnaesite surface through robust electrostatic and hydrogen bonding interactions,thereby enhancing bastnaesite's affinity for NDIA.Furthermore,in situ atomic force microscopy(AFM)provided conclusive evidence of NDIA aggregation on the bastnaesite surface,improving contact angle and hydrophobicity,and significantly boosting the flotation recovery of bastnaesite.

Waste acid recovery utilizing monovalent cation permselective membranes through selective electrodialysis

Selective electrodialysis(SED)has surfaced as a highly promising membrane separation technique in the realm of acid recovery owing to its ability to effectively separate monovalent ions through the utilization of a potential difference.However,the current SED process is limited by conventional commercial monovalent cation permselective membranes(MCPMs).This study systematically investigates the use of an independently developed MCPM in the SED process for acid recovery.Various factors such as current density,volume ratio,initial ion concentration,and waste acid systems are considered.The independently developed MCPM offers several advantages over the commercial monovalent selective cation-exchange membrane(CIMS),including higher recovered acid concentration,better ion flux ratio,improved acid recovery efficiency,increased recovered acid purity,and higher current efficiency.The SED process with the MCPM achieves a recovered acid of 95.9%and a concentration of 2.3 mol·L^(–1) in the HCl/FeCl_(2) system,when a current density of 20 mA·cm^(-2) and a volume ratio of 1:2 are applied.Similarly,in the H_(2)SO_(4)/FeSO_(4) system,a purity of over 99%and a concentration of 2.1 mol·L^(–1) can be achieved in the recovered acid.This study thoroughly examines the impact of operation conditions on acid recovery performance in the SED process.The independently developed MCPM demonstrates outstanding acid recovery performance,highlighting its potential for future commercial utilization.

Fabrication and Properties of a New Reactive Diluent for Cationic UV Curing

The reactive diluent prepared by siloxane modified Trimethylene oxide can improve the performance of the UV curing system.Therefore,1,7-bis[(3-ethyl-3-methoxyoxacylobutane)propyl]octadecylosiloxane(BEMOPOMTS)was synthesized from diethyl carbonate,trimethylopropanes,allyl bromide,and 1,1,3,3,5,5,7,7-octadecylosiloxane as the main raw materials.BEMOPOMTS can be used as reactive diluents in the field of cationic UV curing.It has good thermal stability,and the addition of BEMOPOMTS significantly improves the tensile strength and elongation at break of epoxy resin.Compared with the pure epoxy resin,adding 20%BEMOPOMTS increased the elastic modulus by 25%to 677 MPa.

Lithium cation-doped tungsten oxide as a bidirectional nanocatalyst for lithium-sulfur batteries with high areal capacity

Lithium-sulfur(Li-S) batteries are promising for high energy-storage applications but suffer from sluggish conversion reaction kinetics and substantial lithium sulfide(Li_(2)S) oxidation barrier,especially under high sulfur loadings.Here,we report a Li cation-doped tungsten oxide(Li_(x)WO_(x)) electrocatalyst that efficiently accelerates the S■HLi_(2)S interconversion kinetics.The incorporation of Li dopants into WO_(x) cationic vacancies enables bidirectional electrocatalytic activity for both polysulfide reduction and Li_(2)S oxidation,along with enhanced Li^(+) diffusion.In conjunction with theoretical calculations,it is discovered that the improved electrocatalytic activity originates from the Li dopant-induced geometric and electronic structural optimization of the Li_(x)WO_(x),which promotes the anchoring of sulfur species at favourable adsorption sites while facilitating the charge transfer kinetics.Consequently,Li-S cells with the Li_(x)WO_(x) bidirectional electrocatalyst show stable cycling performance and high sulfur utilization under high sulfur loadings.Our approach provides insights into cation engineering as an effective electrocatalyst design strategy for advancing high-performance Li-S batteries.

Exploring the Cation Regulation Mechanism for Interfacial Water Involved in the Hydrogen Evolution Reaction by In Situ Raman Spectroscopy

Interfacial water molecules are the most important participants in the hydrogen evolution reaction(HER).Hence,understanding the behavior and role that interfacial water plays will ultimately reveal the HER mechanism.Unfortunately,investigating interfacial water is extremely challenging owing to the interference caused by bulk water molecules and complexity of the interfacial environment.Here,the behaviors of interfacial water in different cationic electrolytes on Pd surfaces were investigated by the electrochemistry,in situ core-shell nanostructure enhanced Raman spectroscopy and theoretical simulation techniques.Direct spectral evidence reveals a red shift in the frequency and a decrease in the intensity of interfacial water as the potential is shifted in the positively direction.When comparing the different cation electrolyte systems at a given potential,the frequency of the interfacial water peak increases in the specified order:Li+<Na^(+)<K^(+)<Ca^(2+)<Sr^(2+).The structure of interfacial water was optimized by adjusting the radius,valence,and concentration of cation to form the two-H down structure.This unique interfacial water structure will improve the charge transfer efficiency between the water and electrode further enhancing the HER performance.Therefore,local cation tuning strategies can be used to improve the HER performance by optimizing the interfacial water structure.