Simple Perovskite Research Articles

Unveiling the key factor for the phase reconstruction and exsolved metallic particle distribution in perovskites

To significantly increase the amount of exsolved particles, the complete phase reconstruction from simple perovskite to Ruddlesden-Popper (R-P) perovskite is greatly desirable. However, a comprehensive understanding of key parameters affecting the phase reconstruction to R-P perovskite is still unexplored. Herein, we propose the Gibbs free energy for oxygen vacancy formation in Pr0.5(Ba/Sr)0.5TO3-δ (T = Mn, Fe, Co, and Ni) as the important factor in determining the type of phase reconstruction. Furthermore, using in-situ temperature & environment-controlled X-ray diffraction measurements, we report the phase diagram and optimum ‘x’ range required for the complete phase reconstruction to R-P perovskite in Pr0.5Ba0.5-xSrxFeO3-δ system. Among the Pr0.5Ba0.5-xSrxFeO3-δ, (Pr0.5Ba0.2Sr0.3)2FeO4+δ – Fe metal demonstrates the smallest size of exsolved Fe metal particles when the phase reconstruction occurs under reducing condition. The exsolved nano-Fe metal particles exhibit high particle density and are well-distributed on the perovskite surface, showing great catalytic activity in fuel cell and syngas production.

Sc3Ir4Si13+x and Sc4Ir7Ge6 – the perovskite-related crystal structures

Abstract The crystal structure of Sc3Ir4Si13+x (x = 0.22) [space group P m 3 ‾ n $Pm\bar{3}n$ , a = 8.4651(1) Å] is found to be a new disordered variant of the primitive cubic Yb3Rh4Sn13 Remeika prototype. The silicide is stable in the narrow temperature range of 1283–1397 °C and reveals metallic properties. The crystal structure of Sc4Ir7Ge6 [U4Re7Si6 type, space group I m 3 ‾ m $Im\bar{3}m$ , a = 8.1397(8) Å] is refined for the first time. The electronic band structure calculations reveal that the properties of this germanide can be explained based on the free electron gas model. Both compounds reveal close structural relationships to the simple perovskite structure.

Evaluation of carbonate precursors in manganite coprecipitation synthesis by Fourier transform infrared (FTIR) spectroscopy

The simple perovskite oxides, manganites, are nowadays subject of extensive research because of their electrical, magnetic and photocatalytic properties. In this paper, manganites described with general formula A1-xSrxMnO3 (A = Ca, Ba, La) were prepared by the coprecipitation method. Precursors and calcined powders were analyzed by Fourier transform infrared (FTIR) spectroscopy and crystallization was studied by X-ray diffraction. In all systems, successfully doped manganites were obtained by coprecipitation. Positions and shapes of carbonate bands in carbonate precursors FTIR spectra were shown to be useful for screening successful syntheses of doped manganites, particularly in Ca1-xSrxMnO3 and La1-xSrxMnO3 systems.

Understanding Oxygen Anion Transport in Nb-Doped La0.7Sr0.3CoO3 Perovskite Materials

Simple perovskite structured electrode materials of the series (LaxSr1-xCoO3- δ) are commonly utilised for high-temperature solid-state electrochemical cells and Li-air batteries with some limitations observed on prolong operations due to the structural instability associated with the segregation of strontium ions. In order to overcome this structural incompatibility, doping of heterovalent dopant at the B-site is proposed which could possibly improve upon the stability by controlling the segregation of surface cations. In addition, the doped structure is likely to provide faster oxygen anion transport through the vacancies in the structure, thereby improving its electrochemical performance. Herein, oxygen anion diffusion in pure La0.7Sr0.3CoO3-- δ (LSC) and Nb-doped La0.7Sr0.3Co0.95Nb0.05O3- δ (LCSN) perovskite structure is calculated using molecular dynamics (MD) simulations. Self diffusion coefficient of oxygen ions in the LSCN structure is observed to increase by an order of magnitude (1.356×10-8 cm2/s) on Nb doping as compared to the undoped LSC structure (6.499×10-9 cm2/s) at 1073 K. On varying the Nb concentration from 0.05 to 0.15 and optimum Nb concentration is estimated to be 0.05 corresponding to a maximum oxygen anion diffusivity in the structure (1.356×10-8 cm2/s) at 1073 K.

Unique octahedral rotation pattern in the oxygen-deficient Ruddlesden-Popper compound Gd3Ba2Fe4O12.

A novel Ruddlesden-Popper-related compound, Gd3Ba2Fe4O12, was discovered and its crystal structure was determined via single-crystal X-ray diffraction. The structure has an ordered structure of octahedra and pyramids along the c axis. Gd3Ba2Fe4O12 belongs to the tetragonal system P42/ncm, with a = 5.59040 (10) Å and c = 35.1899 (10) Å. The A-site ions in the Ruddlesden-Popper structure, i.e. Gd3+ and Ba2+, exhibit an ordering along the c axis. The perfect oxygen deficiency is accommodated at the GdO layers in the proper Ruddlesden-Popper structure. Using the bond-valence-sum method, the Fe ions in the FeO6 octahedra and FeO5 pyramids represent valence states of +3 and +2.5, respectively, demonstrating a two-dimensional charge disproportionation. The corner-sharing FeO6 octahedra and FeO5 pyramids are tilted in opposite directions, with the neighbours around one axis of the simple perovskite configuration, which, using Glazer's notation, can be represented as a-b0c0/b0a-c0. In the perovskite blocks, the facing FeO5 pyramids across the Gd layer rotate in the same sense, which is a unique rotation feature related to oxygen deficiency.

B-site La, Ce, and Pr-doped Ba0.5Sr0.5Co0.7Fe0.3O3-δ perovskite cathodes for intermediate-temperature solid oxide fuel cells: Effectively promoted oxygen reduction activity and operating stability

Highly active cathode materials are crucial to accelerating the commercialization of intermediate-temperature solid oxide fuel cells (IT-SOFCs). Herein, a facile doping strategy is proposed to promote the electrode performance of simple perovskite oxides by introducing the lanthanide (Ln = La, Ce, and Pr) ions into B-site. These materials are evaluated as promising cathodes for IT-SOFCs and characterized by electrochemical test between 500 and 700 °C. Among all Ba0.5Sr0.5Co0.7Fe0.28Ln0.02O3-δ perovskites, the Ba0.5Sr0.5Co0.7Fe0.28Pr0.02O3-δ (BSCFP) cathode exhibits the lowest polarization resistance (Rp) of 0.026 Ω cm2 at 700 °C, approximately 50% lower than that of the pristine Ba0.5Sr0.5Co0.7Fe0.3O3-δ (BSCF0.3). The BSCFP cathode-based fuel cell delivers a peak power density of 1083 mW cm−2 at 700 °C, along with exceptional operating stability for 150 h. Such performance may benefit from increased electrical conductivity and optimized surface oxygen process based on experiments and density-functional theory (DFT) calculations. The DFT calculations indicate that the Pr doping not only promotes the adsorption of oxygen species but also enhances the p-d hybridization of O 2p and Co/Fe/Pr 3d bands. The findings endow the performance modulation of the perovskite cathode systems involving the lanthanide doping at B-site.

Non-collinear magnetism & multiferroicity: the perovskite case

Abstract The most important types of non-collinear magnetic orders that are realized in simple perovskite oxides are outlined in relation to multiferroicity. These orders are classified and rationalized in terms of a mimimal spin Hamiltonian, based on which the notion of spin-driven ferroelectricity is illustrated. These concepts find direct application in reference materials such as BiFeO3, GdFeO3 and TbMnO3 whose multiferroic properties are briefly reviewed.

The hydrogen-containing bronzes H0.23WO3 and H0.10ReO3 synthesized via a polymer route

We report the synthesis of two hydrogen-containing perovskite-type bronzes H0.23WO3 and H0.10ReO3 utilizing an unconventional solid-state synthetic approach, involving the use of the polymer Poly(vinylidene fluoride) (CH2CF2)n. Powder neutron diffraction at ambient temperature shows that H0.23WO3 crystallizes in a tetragonal symmetry distortion of the simple perovskite structure (space group P4/nmm), with lattice parameters a ​= ​5.2279(2) Å, and c ​= ​3.8763(1) Å. H0.10ReO3, in contrast, crystallizes in a monoclinic distortion of a simple cubic perovskite (space group P2/m), with lattice parameters a ​= ​5.3125(1) Å, b ​= ​5.3155(3) Å, c ​= ​3.7045(3) Å, and γ ​= ​90.43(1)°. Both H0.23WO3 and H0.10ReO3 exhibit intrinsically diamagnetic behavior, with low temperature paramagnetic upturns and no signs of bulk superconductivity down to 0.35 ​K.

Extended B-Site Vacancy Content Range and Cation Ordering in Twinned Hexagonal Perovskites Ba8Cr4-xTa4+0.6xO24.

The new 8-layer twinned hexagonal solid solution Ba8Cr4-xTa4+0.6xO24 (x = 0.0-3.0) was isolated through the aliovalent substitution of Ta5+ for Cr3+ in Ba2CrTaO6, showing the widest B-site vacancy content range among the 8-layer twinned hexagonal perovskites. Ba8Cr4-xTa4+0.6xO24 forms a simple 8-layer hexagonal perovskite structure within 0.0 ≤ x < 2.4 and a tripled 8-layer hexagonal perovskite superstructure within 2.4 ≤ x ≤ 3.0. The latter shows expanded a and b axes by times in comparison to the simple 8-layer hexagonal perovskite structure owing to the partial face-sharing octahedral (FSO) B cation ordering along the ab plane. The B-cation and vacancy distributions in the tripled superstructure were characterized by neutron and X-ray powder diffraction and further confirmed by a scanning transmission electron microscopy-high angle annular dark field imaging and intensity profile analysis. The formation of 8-layer twinned hexagonal perovskites Ba8Cr4-xTa4+0.6xO24 in an extended solid solution range can be attributed to the presence of both covalent B-B and B-O-B bonding and B-site vacancies in the FSO sites. This work provides an effective way of combining covalent B-B and B-O-B bonding and vacancy creation as well as the cationic ordering in the FSO sites to reduce electrostatic repulsion, which could further enable the stabilization of new hexagonal perovskite compounds.

Simple and Efficient Perovskite Solar Cells with Multi‐Functional Mixed Interfacial Layers

AbstractRecently, hybrid organic–inorganic perovskite solar cells (PVSCs) have attracted significant attention owing to their simple solution processability and high efficiency for the next generation of low‐cost solar cell technology. Herein, a multi‐functional interfacial layer (IFL) composed of a mixture of poly(oxyethylene tridecyl ether) (PTE) and ethanolamine (EA) is introduced between a CH3NH3PbI3 perovskite light‐absorbing layer and a nickel oxide (NiOx) hole transport layer to improve the photovoltaic (PV) performance of PVSCs. With the solution‐coated IFL of mixed PTE:EA, a highly improved film‐forming capability of the perovskite layer is realized together with large‐sized grains and fewer film defects. Moreover, the IFL also improved the charge carrier separation and hole‐extraction capabilities at the interface between the CH3NH3PbI3 and the NiOx layers. The results here successfully demonstrate that the CH3NH3PbI3 PVSC with IFL exhibits greatly improved PV performance, in this case a much higher power conversion efficiency (15.1%), greatly exceeding that (12.3%) of a reference device without an IFL. The author's study demonstrates that a multi‐functional mixed IFL can be used as a solid foundation for efficient and cost‐effective PVSCs, thus providing a platform for the realization of a new generation of highly efficient solution‐processable PVSCs.

Effect of Cd2+ element substitution at the Nd3+ site on the magnetic, the magnetocaloric and hysteresis properties of Nd1-xCdxMnO3 perovskite: Monte Carlo study

In this work, we use the Monte Carlo simulations (MCS) based on the heat bath algorithm to study the magnetic properties, the magnetocaloric effect (MCE) and the hysteresis loops behavior of Cd2+ element substitution at the Nd3+ site in the NdMnO3 simple perovskite. The thermal variation of the total magnetization and the total susceptibility in the presence of the external magnetic field h is given for different values of x (from 0.0 to 0.5) in order to examine the effect of the dilution on the magnetic properties. From the variation of the magnetization as a function of temperature, the transition temperature Tc of the compound NdMnO3 from the ferromagnetic phase to the paramagnetic one has been deduced and it depends on the value of the x. The magnetic entropy change ΔSm, the adiabatic temperature change ΔTad are obtained for different values of the external magnetic field. The isothermal magnetizations versus magnetic field are obtained at different temperatures. Finally, the magnetic hysteresis cycles have been obtained for different values of x and temperature. The remanent magnetization and the magnetic coercive field of the system decreases with increasing the value of x and the temperature.

Strain-induced creation and switching of anion vacancy layers in perovskite oxynitrides

Perovskite oxides can host various anion-vacancy orders, which greatly change their properties, but the order pattern is still difficult to manipulate. Separately, lattice strain between thin film oxides and a substrate induces improved functions and novel states of matter, while little attention has been paid to changes in chemical composition. Here we combine these two aspects to achieve strain-induced creation and switching of anion-vacancy patterns in perovskite films. Epitaxial SrVO3 films are topochemically converted to anion-deficient oxynitrides by ammonia treatment, where the direction or periodicity of defect planes is altered depending on the substrate employed, unlike the known change in crystal orientation. First-principles calculations verified its biaxial strain effect. Like oxide heterostructures, the oxynitride has a superlattice of insulating and metallic blocks. Given the abundance of perovskite families, this study provides new opportunities to design superlattices by chemically modifying simple perovskite oxides with tunable anion-vacancy patterns through epitaxial lattice strain.

Development of chemically synthesized lead-free double perovskite compound: BiBaFeCeO6

In this communication, preliminary structural and detailed electrical (impedance, and conductivity) along with multiferroic (ferroelectric and ferromagnetisc) characteristics of a cost effective chemically processed double perovskite compound, BiBaFeCeO6, have been reported. By analyzing the X-ray diffraction data, the orthorhombic crystal structure of the compound with a single-phase characteristic is obtained. Combining the two simple perovskite materials, BiFeO3 with BaCeO3, in equal ratio produces a new double perovskite compound BibaFeCeO6 with the enhanced dielectric constant (as compared to that of individual perovskite). The shift in the dielectric peak and increase of peak broadening with increase in frequency suggest the existence of relaxation process and relaxor characterizes in the studied compound. The variation of the characteristic of dc conductivity with temperature displays the presence of semiconductor (negative temperature coefficient of resistance) behavior in the compound. Analysis of frequency dependence of ac conductivity data shows that the studied compound obeys the Jonscher’s universal power law. The analysis of complex impedance and modulus spectroscopy data exhibits the non-Debye type of relaxation mechanisms in the compound. The multiferroicity in the compound has been confirmed from the P–E, M–H hysteresis loop and M–E coupling characteristics.

A Sequential Electron Doping for Quadruple Perovskite Oxides ACu3Co4O12 (A = Ca, Y, Ce).

A novel quadruple perovskite oxide CeCu3Co4O12 has been synthesized in high-pressure and high-temperature conditions of 12 GPa and 1273 K. Rietveld refinement of the synchrotron X-ray powder diffraction pattern reveals that this oxide crystallizes in a cubic quadruple perovskite structure with the 1:3-type ordering of Ce and Cu ions at the A-site. X-ray absorption spectroscopy analysis demonstrates the valence-state transitions in the ACu3Co4O12 series (A = Ca, Y, Ce) from Ca2+Cu3+3Co3.25+4O12 to Y3+Cu3+3Co3+4O12 to Ce4+Cu2.67+3Co3+4O12, where the electrons are doped in the order from B-site (Co3.25+ → Co3+) to A'-site (Cu3+ → Cu2.67+). This electron-doping sequence is in stark contrast to the typical B-site electron doping for simple ABO3-type perovskite and quadruple perovskites CaCu3B4O12 (B = V, Cr, Mn), further differing from the monotonical A'-site electron doping for Na1-xLaxMn3Ti4O12 and A'- and B-site electron doping for AMn3V4O12 (A = Na, Ca, La). The differences in the electron-doping sequences are interpreted by rigid-band models, proposing a wide variety of electronic states for the complex transition-metal oxides containing the multiple valence-variable ions.

Photocatalytic La4Ti3O12 nanoparticles fabricated by liquid-feed flame spray pyrolysis

Hexagonal plate-like nanoparticles (NPs) of the layered perovskite La4Ti3O12 were fabricated using liquid-feed flame spray pyrolysis (LF-FSP) followed by subsequent heat-treatments. Their photocatalytic activity was evaluated using decolorization of methyl orange solutions under Uv irradiation. LF-FSP combusts metalloorganic precursor aerosols to produce mixtures of cubic simple perovskite (ABO3) phase and lanthanum oxycarbonate (La2O4·846C0.846) phase with very low agglomeration and average particle sizes (APSs) of 23 nm (as-produced NPs). Rietveld refinement of synchrotron XRD powder patterns verified that the simple perovskite in the as-produced NPs is LaTiO3 (originally cubic Pm-3m-type space group) and heat-treating gives NPs of the trigonal layered perovskite La4Ti3O12 (R-3-type space group). La4Ti3O12 NPs heat-treated at 1100 °C/3-6h/air exhibits hexagonal plate-like morphology and high crystallinity offering enhanced photocatalytic degradation of methyl orange solutions compared to the as-produced NPs. The LF-FSP approach to obtaining layered perovskite La4Ti3O12 NPs provides a simple route to photocatalytic materials in reasonable quantities.

Unraveling the Impact of Hole Transport Materials on Photostability of Perovskite Films and p-i-n Solar Cells.

We investigated the impact of a series of hole transport layer (HTL) materials such as Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), NiOx, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA), and polytriarylamine (PTA) on photostability of thin films and solar cells based on MAPbI3, Cs0.15FA0.85PbI3, Cs0.1MA0.15FA0.75PbI3, Cs0.1MA0.15FA0.75Pb(Br0.15I0.85)3, and Cs0.15FA0.85Pb(Br0.15I0.85)3 complex lead halides. Mixed halide perovskites showed reduced photostability in comparison with similar iodide-only compositions. In particular, we observed light-induced recrystallization of all perovskite films except MAPbI3 with the strongest effects revealed for Br-containing systems. Moreover, halide and β FAPbI3 phase segregations were also observed mostly in mixed-halide systems. Interestingly, coating perovskite films with the PCBM layer spectacularly suppressed light-induced growth of crystalline domains as well as segregation of Br-rich and I-rich phases or β FAPbI3. We strongly believe that all three effects are promoted by the light-induced formation of surface defects, which are healed by adjacent PCBM coating. While comparing different hole-transport materials, we found that NiOx and PEDOT:PSS are the least suitable HTLs because of their interfacial (photo)chemical interactions with perovskite absorbers. On the contrary, polyarylamine-type HTLs PTA and PTAA form rather stable interfaces, which makes them the best candidates for durable p-i-n perovskite solar cells. Indeed, multilayered ITO/PTA(A)/MAPbI3/PCBM stacks revealed no aging effects within 1000 h of continuous light soaking and delivered stable and high power conversion efficiencies in solar cells. The obtained results suggest that using polyarylamine-type HTLs and simple single-phase perovskite compositions pave a way for designing stable and efficient perovskite solar cells.

High-performance La0.5(Ba0.75Ca0.25)0.5Co0.8Fe0.2O3-δ cathode for proton-conducting solid oxide fuel cells

La0.5(Ba0.75Ca0.25)0.5Co0.8Fe0.2O3-δ, a simple perovskite cathode material with high electrical conductivity (940 S cm−1 at 600 °C) and impressive surface catalytic activity, was prepared and used in proton-conducting solid oxide fuel cells. As its thermal expansion coefficient is higher than that of the electrolyte material BaZr0.1Ce0.7Y0.1Yb0.1O3-δ, they were combined and used as a composite cathode. The crystal structure, chemical compatibility, electrical conductivity, cell performance, and the oxygen reduction reaction of the cathode material were explored, and we found that the single fuel cell developed with the composite cathode achieved excellent electrochemical performance, with both a low polarization resistance and high peak power density (0.044 Ω cm2 and 1102 mW cm−2 at 750 °C, respectively). Outstanding stability was also achieved, as indicated by a long-term 100-h test. Additionally, the rate-limiting steps of the oxygen reduction reaction were the oxygen adsorption, dissociation, and diffusion processes.

Red luminescent Eu2+ in K2MgH4 and comparison with KMgH3

A Ruddlesden–Popper (n = 1) hydride perovskite, K2MgH4:Eu2+, shows longer wavelength luminescence compared with the KMgH3:Eu2+ simple perovskite by crystal field engineering.

Effective promotion of oxygen reduction activity by rare earth doping in simple perovskite cathodes for intermediate-temperature solid oxide fuel cells

The development of highly efficient cathode materials at intermediate temperatures is critical to realize the large-scale commercialization of solid oxide fuel cells (SOFCs). Here, a facile way is presented to tune both the crystal structure and the electrochemical performance of simple perovskite oxides as cathode materials by doping rare earth cations (La, Pr, Nd) in A site. The obtained cubic perovskites LnxBa1−xCo0.7Fe0.3O3−δ (Ln = La, Pr, Nd, x = 0.1, 0.2) exhibit enhanced electrocatalytic activity in comparison with their parent compound BaCo0.7Fe0.3O3−δ, with Pr0.1Ba0.9Co0.7Fe0.3O3−δ reaching area specific resistance of 0.038 and 0.026 Ω cm2 and peak power densities of 905.9 and 1236.4 mW cm−2 at 650 and 700 °C, respectively. Such enhancement is a result of the stabilized cubic structure and the promoted oxygen vacancy formation and oxygen adsorption-dissociation process due to rare-earth doping (Pr is more effective for its redox-active character) by the combination of experimental characterization and first-principles calculation. Furthermore, Pr-doped materials also maintain favorable durability at 600 °C (800 mA cm−2 for ~150 h). These findings in this work may provide new insights into the design of cathode materials for other perovskite systems in SOFCs, especially those involving rare earths.

Study of a Promising Co-Doped Double Perovskite Cathode Material for IT-SOFCs

Based on the high catalytic activity and mixed ionic and electronic conductivity, double layered perovskites have been recognized as advanced cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). A recent study has outlined that the synergic effect of co-doping high valence cations (Nb5+ and Ta5+) on a simple perovskite (SrCo1.8Ta0.1Nb0.1O5+δ) has created an optimal balance of oxygen vacancies, ionic mobility and surface electron transfer which results with a drop of the ASR and a promising power density of the fuel cell. In this study, a co-doped double layered perovskite, LnBa0.5Sr0.5Co1.8Ta0.1Nb0.1O5+δ (Ln = Sm and Pr), was evaluated as IT-SOFC cathode material. The properties of the materials were analyzed with yttria stabilized zirconia and gadolinium-doped ceria electrolytes. As result, the Ta-Nb co-doped materials exhibits excellent chemical compatibility with typical electrolyte material and good electrochemical performance over 100 hours, making them as a promising cathode material for applications in IT-SOFCs.