A-site Doping Research Articles

High temperature 0.63BiFeO3-0.37BaTiO3 based ceramics with large electromechanical properties by simple A-site K+ doping

Designing high temperature piezoelectric ceramics with large electromechanical properties is key to the actuators application in harsh environment. BiFeO3-BaTiO3 based piezoelectric ceramics are the promising candidates due to their high electromechanical properties and high Curie temperature. Here, the simple A-site single K+ doped 0.63Bi1−xKxFeO3-0.37BaTiO3 (abbreviated as 0.63B1−xKxF-0.37BT) ceramics with positive temperature dependent electromechanical properties were fabricated via conventional solid phase method. The electromechanical properties in the 0.63B1−xKxF-0.37BT ceramics are closely related to the content of K+ doping. The excellent electromechanical properties of S= 0.26% and d33*=861 pm/V under low electric field of 30 kV/cm at 105 ℃ are achieved in the 0.63B0.9975K0.0025F-0.37BT ceramic, which is conducive to their application at high temperature. Combined with the microstructure and PFM, the optimized electromechanical properties in 0.63B0.9975K0.0025F-0.37BT ceramic are mainly due to more nanodomains switching facilitated by the large grain size and local structural heterogeneity. The site engineering of A-site single ion doping is an efficient and simple strategy for BF-BT based piezoelectric ceramics to achieving excellent electromechanical properties under low electric field at high temperature.

An ab initio study of the oxygen defect formation and oxide ion migration in (Sr1-xPrx)2FeO4±δ

The Sr n+1 Fe n O 3n+1 Ruddlesden-Popper (RP) perovskite family displays promising oxygen permeability and serves as a host stoichiometry for the design of solid oxide electrode materials. A strategy to tune electronic and ionic properties is the introduction of substitutional dopants like Pr 3+ to the A-site. In this study, we investigate the bulk structural, electronic, and oxygen migration properties for the n = 1 RP perovskite (Sr 1-x Pr x ) 2 FeO 4± δ (x = 0, 0.125, 0.25, 0.375, and 0.5). The oxygen partial pressure is adjusted to elucidate how anodic and cathodic operating conditions influence the formation of oxygen defects. Under anodic conditions, the oxygen vacancy is the dominant oxide defect for all dopant-configurations. Under cathodic conditions, oxygen vacancy defects dominate for configurations from x = 0 to x = 0.375 while the oxygen peroxide interstitial defect becomes the primary defect for x = 0.5. Next, we examine the relationship between Pr 3+ concentration, iron oxidation state, and charge compensation with defect formation to explain the trends in vacancy and peroxide interstitial formation energies. Results clarify the role of lanthanide A-site substitutional dopants on the electronic conductivity and oxide defect formation and migration in Sr-based RP perovskites. These atomic-scale insights suggest design directions for RP perovskites in SOFCs. • Doping strategy of Sr 2 FeO 4 with Pr 3+ for targeted electronic and ionic properties. • Mechanism of vacancy defect formation outlined in terms of charge delocalization. • Mechanism of interstitial defect formation outlined in terms of A-site identity. • Studied all non-symmetrical vacancy-mediated migration paths for given Pr 3+ value.

First principles study on organic cation A-site doping in CsPbI3 perovskite

Among all inorganic perovskite, CsPbI3 has the closest ideal bang gap for solar cells. However, the instability of metal halides hinders its commercial application. The doping of A-site organic cations might improve the stability of perovskite and also make the bandgap adjustable, thus enhance its photoelectric properties. In this paper, the structure stability, electronic structure and optical properties of CsPbI3 with five different organic cations (H3NNH2+, CH3NH3+, C3H6NH2+, CH3NH2CH3+, CH3CH2NH3+) partially alternative doping instead the A site cation have been studied by using the first principles within density functional theory. In order to get accurate description of the bandstructure information, different exchange–correlation functions, e. g. PBE, PBE + SOC and HSE were used to describe the calculated systems, our calculation results indicated that the PBE exchange–correlation function can describe the electronic properties of the systems very well in this paper. Formation energy calculation indicates that all the doping systems are thermally stable; and all the doped CsPbI3 show good tolerance factor according Goldschmidt rule. Among the five different doping systems, the bandgap of doped H3NNH2+ will decrease to 1.28 eV, while the bandstructure of other doped cations will widen the bandgap. The maximum bandgap increased to 1.65 eV with doping C3H6NH2+. However, all the band structures are mainly contributed by inorganic framework. The results suggest that the structure doped organic cations can be exited stably, and the band edge of the optical absorption spectrum will be redshifted. These properties can provide research ideas for the subsequent research of A-site doping organic cations.

A-Site Mixing to Adjust the Photovoltaic Performance of a Double-Cation Perovskite: It Is Not Always the Simple Way.

Considerable progress has been made in improving the performance of optoelectronic devices based on hybrid organic-inorganic perovskites of the form ABX3. However, the influences of A-site doping on the structure and dynamics of the inorganic perovskite crystal lattice and, in turn, on the optoelectronic performance of the resulting devices remain poorly understood at an atomic level. This work addresses this issue by combining the results of several experimental characterization methods for three-dimensional MA1-xDMAxPbBr3 perovskite single crystals (MA, methylammonium; DMA, dimethylammonium). The results reveal a two-stage change in lattice with an increase in DMA content, which has completely opposite effects on the optoelectronic performance of the double-cation perovskite. At low DMA concentrations, fast reorientation of incorporated DMA cations strengthens the interaction between MA cations and the lattice without significant lattice distortion, which could suppress lattice fluctuation and thus improve the photovoltaic performance. At high DMA concentrations, the lattice get a severe distortion, leading to poorer photovoltaic performance.

Dielectric and Electrical Properties of Barium and Nickel Doped LaFeO3

In this paper we report the role of barium doping at A-site and nickel doping at B-site in LaFeO3 ceramics synthesised by Co-precipitation route for tailoring its dielectric and electrical properties. Shifts in the X-ray diffraction peaks indicate distortion induced in host lattice due to Ba/Ni doping. The morphology of the ceramics is studied using scanning electron miscropy. Plate-like grains stacked over one another are observed in Ba-doped and Ni-doped LaFeO3 ceramics. Barium doping is found to improve dielectric properties due to the higher polarizability of barium ion. Nickel-doped LFO shows higher ionic conductivity as compared to Ba-doped LFO because of toggling of the ionic state of Fe3+ to Fe4+ for charge compensation. The conduction mechanism in these ceramics is evaluated using Nyquist plots. Grain boundary resistance is found to dominate in all the samples. Barium doping increases the capacitive nature of LaFeO3 with increase in the Ba concentration.

Comprehensive understanding of alkaline-earth elements effects on electrocatalytic activity and stability of LaFe0.8Ni0.2O3 electrode for high-temperature CO2 electrolysis

Symmetrical solid oxide electrolysis cell (SSOEC) is a promising energy conversion device for CO2 electroreduction due to their high efficiency, low cost and good stability. However, electrode materials with lower catalytic activity limit their development. In this work, optimization of LaFe0.8Ni0.2O3 (LFN) electrode using various A-site doping strategies was explored in SSOEC applications. The effect of the A-site doping elements Ca, Sr, Ba on the structure and physic-chemical property of LFN was assessed. The electrochemical performance including half-cell performance and CO2 electrolysis performance has been investigated. The results demonstrated that Ca doped LFN (LCFN) exhibits the best electrolysis performance and superior operation stability. The polarization resistance and the current density of the LCFN single cell at 2.0 V is 0.113 Ω cm2 and 0.876 A cm−2 at 800°C, respectively. Compared with Sr and Ba, Ca doped LFN exhibits appropriate conductivity, suitable oxygen vacancy concentration and high activation performance for O2 and CO2.Therefore, La0.6Ca0.4Fe0.8Ni0.2O3 is a promising material for SSOEC electrode.

Promising Versions of Non-Zero Magnetic Field Optical Sensors for Magnetoencephalography

Among all inorganic perovskite, CsPbI3 has the closest ideal bang gap for solar cells. However, the instability of metal halides hinders its commercial application. The doping of A-site organic cations might improve the stability of perovskite and also make the bandgap adjustable, thus enhance its photoelectric properties. In this paper, the structure stability, electronic structure and optical properties of CsPbI3 with five different organic cations (H3NNH2+, CH3NH3+, C3H6NH2+, CH3NH2CH3+, CH3CH2NH3+) partially alternative doping instead the A site cation have been studied by using the first principles within density functional theory. In order to get accurate description of the bandstructure information, different exchange–correlation functions, e. g. PBE, PBE + SOC and HSE were used to describe the calculated systems, our calculation results indicated that the PBE exchange–correlation function can describe the electronic properties of the systems very well in this paper. Formation energy calculation indicates that all the doping systems are thermally stable; and all the doped CsPbI3 show good tolerance factor according Goldschmidt rule. Among the five different doping systems, the bandgap of doped H3NNH2+ will decrease to 1.28 eV, while the bandstructure of other doped cations will widen the bandgap. The maximum bandgap increased to 1.65 eV with doping C3H6NH2+. However, all the band structures are mainly contributed by inorganic framework. The results suggest that the structure doped organic cations can be exited stably, and the band edge of the optical absorption spectrum will be redshifted. These properties can provide research ideas for the subsequent research of A-site doping organic cations.

Effect of Sr doped the YFeO3 rare earth ortho-ferrite on structure, magnetic properties, and microwave absorption performance

Given the remarkable performances of rare earth multiferroic ortho-ferrites with magnetic optical and dielectric properties, the Y1-xSrxFeO3 (x = 0, 0.05, 0.1, 0.15) perovskite structure microwave absorbing ferrite materials was successfully synthesized by Sr2+ ions A-site doping based on sol-gel technology in this paper. The XRD of all samples was refined with FullProf software, which confirmed the formation of the orthogonal perovskite structure (SG: Pnma). The SEM and TEM results display the average particles size of the samples is distributed between 110 and 160 nm. The increase of Sr doping concentration leads to the increase of particles size, which may be related to the growth of preferred orientation and incomplete substitution. The XPS analysis shows that Fe3+ was accompanied by the presence of Fe2+ with the doping of Sr2+ ions and oxygen vacancies increased significantly. The samples change from weak ferromagnetic state to paramagnetic state with the increase of Sr content. The minimum reflection loss (RL) of the Y0.95Sr0.05FeO3 samples at 12.2 GHz reached −30.87 dB with thickness of 2.2 mm, where its effective absorption bandwidth (EAB, RL ≤ −10 dB) reached 2.4 GHz (11.3–13.7 GHz). Moreover, the EAB of the Y0.85Sr0.15FeO3 samples reached 2.64 GHz, and the corresponding range is 9.0–11.6 GHz (X-band).

Phase Evolution in Lead-Free Cs-Doped FASnI3 Hybrid Perovskites and Optical Properties

Tin halide perovskites are among the candidates having potential to substitute lead-based perovskites due to their environmentally benign components and potential medical usage. Nevertheless, the air stability remains a challenge due to Sn2+ oxidation. The recent developments have shown that adding SnF2 as an additive and A-site cation replacement by an inorganic element such as Cs+ can improve the film stability. However, exploring the structural change through A-site doping in Sn-based perovskites experimentally requires an in-depth investigation. Here, the phase evolution mechanism from the transformation of CsxFA1–xSnI3 to Cs2SnI6 via Cs2–xFAxSnI6 in the presence of the intermediate phase SnI2–(dmf)x due to Cs substitution in FASnI3 and the substitution’s influences on the optical properties were identified and investigated. Introducing a small amount of Cs+ (≤5% CsI) significantly promoted Sn2+ oxidation due to the anharmonic lattice dynamics. Later, at 10% CsI, self-doping was initiated, resulting in the coexistence of Sn2+/Sn4+. However, phase separation of Cs2SnI6 via Cs2–xFAxSnI6 occurred at contents greater than 10% CsI. Notably, the absorption coefficient was amplified along with the increasing Cs content (at 10% CsI, 6 times greater than that of FASnI3). The air stability was also enhanced as a result of Cs substitution. This work demonstrates the structural engineering of A-site cations in order to obtain various material properties for photovoltaic (PV) and non-PV applications.

Synthesis of Chemically Stable Ultrathin SiO2-Coated Core-Shell Perovskite QDs via Modulation of Ligand Binding Energy for All-Solution-Processed Light-Emitting Diodes.

Recently, perovskite quantum dots (QDs) have attracted intensive interest due to their outstanding optical properties, but their extremely poor chemical stability hinders the development of the high-performance perovskite QD-based light-emitting diodes (PeLEDs). In this study, chemically stable SiO2-coated core-shell perovskite QDs are prepared to fabricate all-solution-processed PeLEDs. When the SiO2 shell thickness increases, the chemical stability of perovskite QDs is dramatically improved, while the charge injection efficiency is significantly decreased, which becomes the biggest obstacle for PeLED applications. Thus, controlling the SiO2 thickness is essential to obtain core-shell perovskite QDs optimal for PeLEDs in an aspect of chemical and optoelectrical properties. The 3-aminopropyl-triethoxysilane (APTES)/oleylamine (OAm) volume ratio is found to be a critical factor for obtaining an ultrathin SiO2 shell. Optimization of the APTES/OAm ratio affords A-site-doped CsPbBr3 QDs with an ultrathin SiO2 shell (A-CsPbBr3@SiO2 QDs) that exhibit longer radiative lifetimes and smaller shallow trap fraction than those without A-site doping, resulting in a higher photoluminescence quantum yield. A-CsPbBr3@SiO2 QDs also demonstrate long-term superior chemical stability in polar solvents without loss of optical properties due to passivation by the SiO2 shell and less defects via A-site doping. Consequently, all-solution-processed PeLED is successfully fabricated under ambient conditions, facilitating perovskite QD utilization in low-cost, large-area, flexible next-generation displays.

A DFT+U Study of the Oxygen Defect Formation in (Sr1-xPrx)2FeO4

INTRODUCTION Solid oxide fuel cell (SOFC) electrodes are commonly composed of cermet materials, a composite of ceramic and metal materials. Despite success in electrochemical performance, cermet materials suffer from sulfur poisoning at the triple-phase boundary (TPB), high operating temperatures, and metal coarsening. To mitigate these problems, single-phase mixed ionic-electronic conducting (MIEC) materials have been investigated as alternative electrode materials. One such class of materials is the Ruddlesden-Popper (RP) phase (An+1BnO3n+1), a perovskite composed of n layers of octahedra in a perovskite (ABO3) stack. The RP family of Srn+1FenO3n+1 has found recent use as a base stoichiometry in both cathodes1 and anodes2 with and without A-site trivalent dopants. In order to rationalize the design of RP electrodes, we elaborate on the relationship of MIEC properties as a function of A-site dopant concentration at the atomistic level. In the present study, we used ab initio methods to investigate the relationship between Pr3+ concentration, iron oxidation state, and charge compensation upon defect formation to better understand the role of the A-site on the ionic and electronic properties in (Sr1-xPrx)2FeO4± \U0001d6ff (x = 0, 0.125, 0.25, 0.375, 0.5). COMPUTATIONAL DETAILS All calculations presented in this work were performed using the spin-polarized DFT+U method with periodic boundary conditions as implemented in the VASP 5.4.4 code. We choose the PBE functional to describe exchange and correlation effects. Dudarev’s approach for DFT+U calculations is used to correct the inadequate description of localized 3d electrons on Fe and 4f electrons on Pr with a U-J value of 4.0 and 6.0 eV, respectively. We used the projector-augmented wave (PAW) method to represent the inner core potentials. The kinetic energy cutoff was set for all calculations to 750 eV, and integration over the Brillouin zone was performed with 5×5×3 Monkhorst-Point k-point mesh and the tetrahedron method with Blöchl corrections. RESULTS AND DISCUSSION To sample all possible structural conformations at a given dopant concentration, we tested all non-symmetrical conformers for the lowest relative energy on a model 2×2×1 supercell, as displayed in Figure 1a. A total of 7, 42, 123, and 181 structures were tested for each dopant configuration, respectively. We calculate metallic behavior for x = 0.125 and 0.25 and semi-conducting behavior for x = 0, 0.375 and 0.5, indicating electronic conductivity decreases upon increasing A-site dopant concentration. Figure 1b displays the relationship between the final optimized dopant configurations and defect stability. The interstitial formation energy decreases linearly with Pr concentration with a deviation at x = 0.125. This relationship is primarily a function of the neighboring cation elemental identity and the decreasing interatomic distance between the interstitial defect and the neighboring cations in the rocksalt regime. The vacancy formation energy appears constant with Pr except for a large energy penalty at x = 0.5. The origin of the harsh energy penalty is rooted in the over-reduction of Fe. Upon vacancy formation, the released electrons directly reduce the next-nearest Fe atoms from +3 to +2 as opposed to delocalizing upon the oxide lattice. Figure 1c displays the relationship between the degree of delocalization and the energy of vacancy formation. The degree of delocalization3 is a dimensionless quantity that describes the extent of charge delocalized upon the oxygen sublattice with a vacancy. For x = 0 to 0.375, vacancy formation delocalizes the released electrons onto the lattice as opposed to x = 0.5, where charge from the lattice directly reduces Fe. Covalence between Fe-O bonds is decreased upon the formation of Fe2+, causing a harsh penalty in vacancy formation.In conclusion, tuning MIEC behavior is a balance between reducing Fe and charge delocalization upon the oxide lattice. In terms of electronic conductivity, a small introduction of Pr yielded metallic behavior. In terms of ionic conductivity, a threshold value of Pr yields an unfavorable vacancy formation energy. Future studies will focus on the optimization of the catalytic activity by B-site doping. ACKNOWLEDGMENTS This work has been funded by the Division of Materials Research, a National Science Foundation organization under Award Number 1832809. Computing resources provided by the San Diego Supercomputer Center (SDSC) and Texas Advanced Computing Center (TACC) under XSEDE grant number TG-CTS090100 and USC High-Performance Computing clusters are gratefully acknowledged. REFERENCES T. Hong, M. Zhao, K. Brinkman, F. Chen, C. Xia, ACS Appl. Mater. Interfaces, 9, 8659–8668 (2017)C. Yang, Z. Yang, C. Jin, G. Xiao, F. Chen, Adv. Mater., 11, 1439-1443 (2012)A. M. Ritzmann, J. M. Dieterich, E. A. Carter, Phys. Chem. Chem. Phys., 17, 12260-12269 (2016) Figure 1

Influence of A-site doping barium on structure, magnetic and microwave absorption properties of LaFeO3 ceramics powders

In this paper, the effect of Ba2+ ions A-site doping LaFeO3 on structure, magnetic properties and microwave absorption properties was investigated by the sol–gel method. According to the TEM and FullProf refinement results, the structure of LaFeO3 changes from orthogonal (SG: Pnma) to cubic (SG: Pm-3m) when the Ba doping amount is x = 0.4. The SEM image shows that the particles size tends to decrease with the increase of Ba content. The production of weak ferromagnetism indicates that Ba doping has a significant effect on the magnetic properties of LaFeO3. The Neel temperature (TN) decreases significantly with the increase of Ba doping amount. An appropriate amount of Ba doping can effectively increase the dielectric and magnetic loss of LaFeO3 ceramics powders. The increase permittivity (ε′ and ε″) may be attributed to the hopping of the electrons between the Fe3+ and Fe4+ ions with the Ba2+ ions doping. The minimum reflection loss (RLmin) of La0.9Ba0.1FeO3 at 6.72 GHz reaches −30.04 dB, its effective bandwidth (RL ≤ −10 dB) is 2.1 GHz, and the matching thickness is only 3.2 mm. These results indicate that Ba doping can effectively control the microwave absorption properties of LaFeO3, especially in the C-band.

Influence of A-site doping on properties of lead-free KNN-based perovskite ceramics

Influence of A-site doping with Li+, Ag+, and K+ cations on structure, microstructure, dielectric, ferroelectric, and local piezoelectric properties of potassium niobate (K0.5Na0.5)NbO3 ceramics was studied. Changes in the unit cell parameters correlated with ionic radii changes. Correlations between dielectric and piezoelectric properties were confirmed. The highest effective local d33 piezoelectric coefficient values were observed in Ag+-doped compositions prepared by the sol-gel method.

EA-Directing Formamidinium-Based Perovskite Microwires with A-Site Doping.

One recent development to improve optoelectronic properties of perovskites is to use a larger cation for multication engineering. The chain-like ethylammonium (EA) [(C2H5)NH3]+ cation is more likely to form a one-dimensional perovskite structure; however, there is no remarkable evidence in this connection. Therefore, in this work, for the first time, the EA cation as an alternative cation was introduced into FAPbBr3 cubic crystals to explore the stabilities and optoelectronic properties of mixed FAxEA(1–x)PbBr3 perovskites. The results indicate that replacing FA with EA is a more effective way to realize band gap tuning and morphology transformation between the cubic shape and microwires. The tuned band gap of perovskite is due to the variation of Pb–Br–Pb angles induced by the insertion of the larger EA cation. We highlight that this work provides new physical insights into the correlation between the engineering of organic cations and the formation of perovskite microwires and the tunable band gap. This observation will help us to find new ways to grow perovskite microwires and subsequently study the optoelectronic performance of low-dimensional perovskites devices.

Comparison of structural, ferroelectric, and piezoelectric properties between A-site and B-site acceptor doped 0.93Bi0.5Na0.5TiO3-0.07BaTiO3 lead-free piezoceramics

The effects of A-site Li- or B-site Fe-doping into 0.93(Bi0.5Na0.5)TiO3-0.07BaTiO3 (BNBT) ceramics were systematically investigated for the compositional ranges of (Bi0.465Na0.465Ba0.07)1-xLixTiO3 (BNBT-xLi) and (Bi0.465Na0.465Ba0.07)FexTi1-xO3 (BNBT-xFe) (x = 0.01–0.03). The R3c/P4bm phase ratio remained essentially unchanged across the entire set of Li and Fe doping levels studied. Although some typical characteristics for acceptor doping were observed for both BNBT-xLi and BNBT-xFe, their ferroelectric and piezoelectric properties were different. A clear transition from a slim (BNBT, Ec = 17.0 kV/cm, Pr = 22.9 μC/cm2) to square-like P-E hysteresis loops (Ec = 29.9 kV/cm, Pr = 33.9 μC/cm2) was observed in BNBT-xLi at x≥0.02. In contrast, constricted P-E loops (Ec = 13.0–15.7 kV/cm and Pr = 28.6–31.7 μC/cm2) and deformed butterfly S-E curves were detected in all BNBT-xFe ceramics. These results suggest A-site Li doping as a more effective method for stabilizing the non-ergodic relaxor phase in BNT-BT ceramics, which could help further tailor the piezoelectric properties in other A-site doped Bi-based perovskite systems.

Flexible A-site doping La0.6-xMxSr0.4Co0.2Fe0.8O3 (M=Ca, Ba, Bi; x=0, 0.1, 0.2) as novel cathode material for intermediate-temperature solid oxide fuel cells: A first-principles study and experimental exploration

To address both challenges of insufficient oxygen vacancies and excessive interface resistance in intermediate-temperature solid oxide fuel cells (IT-SOFCs), in this study, we apply the first-principle density functional study to choose the A-site cation doping M(M = Ca, Ba, Bi) for conventional La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) and find that Bi doping could produce the smallest generation energy of oxygen vacancy. Then novel Bi-doped La0.6-xBixSr0.4Co0.2Fe0.8O3 (LBSCFx, x = 0,0.1,0.2) cathode materials are investigated, revealing Bi3+ doping can promote the electrochemical performance of LBSCFx cathode by the enrichment of oxygen vacancies and the triple-phase boundaries. Attributed to the accelerated oxygen transportation and the increased oxygen reduction reaction sites, the effectiveness of Bi3+ doping LSCF on the reduction of polarization resistant (Rp) and activation energy (Ea) is superior than most of other LSCF doping strategies. The Rp and Ea values of LBSCF0.2 are reduced more than 58% and 27% compared to that of undoped LSCF respectively, and the maximum power density of the anode-supported single cells based on LBSCF0.2 outperforms 1 W⋅cm−2 at 750 °C. Both Rp and power density suggest the effectiveness of Bi doping strategy for developing cathode materials in IT-SOFCs.

Recent advances in perovskite oxides as electrode materials for supercapacitors.

Owing to the high power density and ultralong cycle life, supercapacitors represent an alternative to electrochemical batteries in energy storage applications. However, the relatively low energy density is the main challenge for supercapacitors in the current drive to push the entire technology forward to meet the benchmark requirements for commercialization. To effectively solve this issue, it is crucial to develop electrode materials with excellent electrochemical performance since the electrode used is closely related to the specific capacitance and energy density of supercapacitors. With the unique structure, compositional flexibility, and inherent oxygen vacancy, perovskite oxides have attracted wide attention as promising electrode materials for supercapacitors. In this review, we summarize the recent advances in perovskite oxides as electrode materials for supercapacitors. Firstly, the structures and compositions of perovskite oxides are critically reviewed. Following this, the progress in various perovskite oxides, including single perovskite and derivative perovskite oxides, is depicted, focusing on their electrochemical performance. Furthermore, several optimization strategies (i.e., modulating the stoichiometry of the anion or cation, A-site doping, B-site doping, and constructing composites) to improve their electrochemical performance are also discussed. Finally, the significant challenges facing the advancement of perovskite oxide electrodes for supercapacitor applications and future outlook are proposed.

Substitution-site and ambient annealing dependences of upconversion emission of SrTiO3

We investigated the upconversion (UC) emissions and their ambient dependences of SrTiO3 polycrystals co-doped in Er3+ and Yb3+ at different substitution sites. i.e., the A-site and B-sites in ABO3-type perovskite, and its response to H2 and O2 ambient annealing. Under near-infrared excitation at 980 nm, the as-synthesized samples exhibited strong UC emission features in the green (525 and 550 nm) and red (660 nm) region from Er3+ ions owing to sensitization by Yb3+; the emission was much stronger for A-site doping than for B-site doping. Interestingly, annealing in the H2 atmosphere to increase the oxygen vacancies suppressed the photoluminescence and UC emission of the A-site doped samples, but enhanced the emission signals of the B-site doped samples. After subsequent annealing in the O2 atmosphere to decrease the oxygen vacancies, the emission intensities showed a tendency to return to those in the as-synthesized A-site doped and B-site doped samples. These intriguing behaviors were explained in terms of the relationship between the substitution site and charge compensation. We performed the temperature dependent UC emissions and found that the intensity ratio between two green emissions changed significantly with temperature. This strong fluorescence intensity ratio could be used for optical thermometry.

Electronic, structural and optical properties of cerium and zinc co-doped organic-inorganic halide perovskites for photovoltaic application

Organic-inorganic hybrid perovskites have been receiving considerable attention due to their excellent performances. However, the pollution of the lead element and the instability under strong light and high temperatures are still problems to be solved. In this work, we studied the structure and photoelectrical properties of Cs and Zn co-doped organic-inorganic hybrid perovskite by first-principles calculations. Results showed the synergy effects of A-site and B-site doping improved the lattice stability, reduced pollution via the decreased contents of lead elements and also induced an adjustable bandgap of 1.5–2.2 eV. The optical absorption of perovskites with different doping ratios was enhanced in the visible region. The hybridization among Zn 3d4s, Pb 6s6p, and I 5s5p states were observed, clarifying the origin of the enhancement. The Cs and Zn co-doped perovskites with adjustable band gaps are expected to be used in single-junction, multijunction, and tandem solar cells.

Steering the Methane Dry Reforming Reactivity of Ni/La2O3 Catalysts by Controlled In Situ Decomposition of Doped La2NiO4 Precursor Structures.

The influence of A- and/or B-site doping of Ruddlesden–Popper perovskite materials on the crystal structure, stability, and dry reforming of methane (DRM) reactivity of specific A2BO4 phases (A = La, Ba; B = Cu, Ni) has been evaluated by a combination of catalytic experiments, in situ X-ray diffraction, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and aberration-corrected electron microscopy. At room temperature, B-site doping of La2NiO4 with Cu stabilizes the orthorhombic structure (Fmmm) of the perovskite, while A-site doping with Ba yields a tetragonal space group (I4/mmm). We observed the orthorhombic-to-tetragonal transformation above 170 °C for La2Ni0.9Cu0.1O4 and La2Ni0.8Cu0.2O4, slightly higher than for undoped La2NiO4. Loss of oxygen in interstitial sites of the tetragonal structure causes further structure transformations for all samples before decomposition in the temperature range of 400 °C–600 °C. Controlled in situ decomposition of the parent or A/B-site doped perovskite structures in a DRM mixture (CH4:CO2 = 1:1) in all cases yields an active phase consisting of exsolved nanocrystalline metallic Ni particles in contact with hexagonal La2O3 and a mixture of (oxy)carbonate phases (hexagonal and monoclinic La2O2CO3, BaCO3). Differences in the catalytic activity evolve because of (i) the in situ formation of Ni–Cu alloy phases (in a composition of >7:1 = Ni:Cu) for La2Ni0.9Cu0.1O4, La2Ni0.8Cu0.2O4, and La1.8Ba0.2Ni0.9Cu0.1O4, (ii) the resulting Ni particle size and amount of exsolved Ni, and (iii) the inherently different reactivity of the present (oxy)carbonate species. Based on the onset temperature of catalytic DRM activity, the latter decreases in the order of La2Ni0.9Cu0.1O4 ∼ La2Ni0.8Cu0.2O4 ≥ La1.8Ba0.2Ni0.9Cu0.1O4 > La2NiO4 > La1.8Ba0.2NiO4. Simple A-site doped La1.8Ba0.2NiO4 is essentially DRM inactive. The Ni particle size can be efficiently influenced by introducing Ba into the A site of the respective Ruddlesden–Popper structures, allowing us to control the Ni particle size between 10 nm and 30 nm both for simple B-site and A-site doped structures. Hence, it is possible to steer both the extent of the metal-oxide-(oxy)carbonate interface and its chemical composition and reactivity. Counteracting the limitation of the larger Ni particle size, the activity can, however, be improved by additional Cu-doping on the B-site, enhancing the carbon reactivity. Exemplified for the La2NiO4 based systems, we show how the delicate antagonistic balance of doping with Cu (rendering the La2NiO4 structure less stable and suppressing coking by efficiently removing surface carbon) and Ba (rendering the La2NiO4 structure more stable and forming unreactive surface or interfacial carbonates) can be used to tailor prospective DRM-active catalysts.