Ruddlesden-Popper System Research Articles

Two-Dimensional Quantum-Confined CsPbBr3 in Silicene for LED Applications

Perovskites with reduced dimensions are very attractive for LED applications due to their improved stability and efficient energy transfer. This is exemplified by 2D perovskites reported in the literature, predominantly either Dion-Jacobson or Ruddlesden–Popper systems, which typically use long chain alkyl moieties as spacers in order to form 2D layers. Here, we report an approach which uses an inorganic 2D material─silicene─as a template to form two-dimensional quantum-confined CsPbBr3 (qc-CsPbBr3) layers of less than 5 nm in thickness. This approach can be further generalized to synthesize other types of perovskites with reduced dimensionality. The structural and optical properties of the qc-CsPbBr3 layers inside silicene were characterized. The qc-CsPbBr3-based LEDs demonstrate improved stability under ambient conditions, along with a current efficiency of 13.7 Cd A–1 and external quantum efficiency of 8.5%.

Oxygen deficiency in Sr2FeO4-x: electrochemical control and impact on magnetic properties.

The oxygen-deficient system Sr2FeO4-x was explored by heating the stoichiometric Fe4+ oxide Sr2FeO4 in well-defined oxygen partial pressures which were controlled electrochemically by solid-state electrolyte coulometry. Samples with x up to about 0.2 were obtained by this route. X-ray diffraction analysis reveals that the K2NiF4-type crystal structure (space group I4/mmm) of the parent compound is retained. The lattice parameter a slightly decreases while the c-parameter increases with increasing x, which is in contrast to the Ruddlesden-Popper system Sr3Fe2O7-x and suggests removal of oxygen atoms from FeO2 lattice planes. The magnetic properties were studied by magnetization, 57Fe Mössbauer, and powder neutron diffraction experiments. The results suggest that extraction of oxygen atoms from the lattice progressively changes the elliptical spiral spin ordering of the parent compound to an inhomogeneous magnetic state with coexistence of long-range ordered regions adopting a circular spin spiral and smaller magnetic clusters.

Multiple perovskite layered lanthanum nickelate Ruddlesden-Popper systems as highly active bifunctional oxygen catalysts

A systematic study of the Ruddlesden-Popper structured Lan+1NinO3n+1 (n = 1, 2, 3, and 4) and its catalytic performance in oxygen evolution (OER) and oxygen reduction reactions (ORR) is carried out with a view to design a highly-efficient and cost-effective electrocatalyst. In particular, we introduce for the first time a novel La5Ni4O13-δ with a 4-layered perovskite structure (n = 4) for use as a highly active and durable bifunctional oxygen catalyst for OER/ORR. Concretely, La5Ni4O13-δ catalysts has demonstrated performance of 1.65 V at 10 mA·cm−2 and 0.66 V at near half-wave potential (–3 mA·cm−2) for OER and ORR, respectively, this indicates excellent intrinsic OER/ORR kinetics. Furthermore, by controlling the fuel-to-oxidizer ratio (using extremely fuel-rich conditions) in the glycine-nitrate combustion technique, the 4-layered perovskite La5Ni4O13-δ catalysts are synthesized as a single Ruddlesden–Popper phase with various dopants to further boost its bifunctional oxygen electrode activity. Among OER/ORR catalysts, La5Ni3CoO13-δ catalysts exhibit exceptional electrocatalytic activity with low overpotential and Tafel slope (35/76 mV‧dec-1 for OER/ORR). Outstandingly, the La5Ni3CoO13-δ is able to achieve an extremely low overpotential of 370 mV at 10 mA‧cm−2 in 0.1 M KOH for OER, surpassing Ir/C catalysts and any metal oxide catalyst ever reported. The high catalytic performance of La5Ni3CoO13-δ can be attributed to its favorable electronic structure enriched with oxygen defects and electronic charge carriers (increased Ni oxidation state) as well as to the promoted lattice-oxygen oxidation mechanism pathway that comes from strong metal–oxygen covalency (high oxygen-ion diffusion rate).

Unraveling the Suppression of Oxygen Octahedra Rotations in A_{3}B_{2}O_{7} Ruddlesden-Popper Compounds: Engineering Multiferroicity and Beyond.

The competition between polar distortions and BO_{6} octahedra rotations is well known to be critical in explaining the ground state of various ABO_{3} perovskites. Here, we show from first-principles calculations that a similar competition between interlayer rumpling and rotations is playing a key role in layered Ruddlesden-Popper (RP) perovskites. This competition explains the suppression of oxygen octahedra rotations and hybrid improper ferroelectricity in A_{3}B_{2}O_{7} compounds with rare-earth ions in the rocksalt layer and also appears relevant to other phenomena like negative thermal expansion and the dimensionality determined band gap in RP systems. Moreover, we highlight that RP perovskites offer more flexibility than ABO_{3} perovskites in controlling such a competition and four distinct strategies are proposed to tune it. These strategies are shown to be promising for designing new multiferroics. They are generic and might also be exploited for tuning negative thermal expansion and band gap.

Synthesis and characterisation of Sr4Fe3-xCrxO10-δ: Stabilisation of n=3 Ruddlesden-Popper phases through Cr doping

Ruddlesden-Popper type compounds have the general formula, An+1MnO3n+1±x (typically A is a rare earth, alkaline earth, M is a transition metal), and are constructed of perovskite-type layers separated by rock salt type blocks. While n ​= ​1, 2 phases are typically straightforward to prepare, the synthesis of higher order (n ​> ​2) systems is difficult. In this paper we show that chromate (CrO42−) doping can be exploited to stabilise new n ​= ​3 Ruddlesden-Popper systems, Sr4Fe3-xCrxO10-δ: without chromate doping, a mixture of the n ​= ​2 phase Sr3Fe2O7-x and perovskite-type SrFeO3-x is obtained. This can be explained by the stabilisation of the central perovskite building block by chromate incorporation, similar to prior work on sulfate and carbonate doping in this system. The structure, and Fe/Cr oxidation states were evaluated by X-ray diffraction, 57Fe Mössbauer spectroscopy and X-ray absorption spectroscopy supporting the incorporation of Cr as CrO42−. In order to examine the potential of these new systems for use as a SOFC cathode material, conductivity studies were carried out, which showed semiconducting behaviour with slightly higher conductivities than the sulfate doped counterparts.

Synthesis and characterization of Ruddlesden-Popper system (Ba1−xSrx)2SnO4

The samples of (Ba1−xSrx)2SnO4 with x = 0, 0.10, 0.20, 0.40, 0.80, 1.00 were synthesized by a high-temperature solid state ceramic route. Lattice parameters obtained from the Rietveld profile analysis; decreased with increasing Sr. The decreasing nature of lattice parameters indicated the complete solubility of Sr at Ba-site. Further, incorporation of Sr at Ba-site has been studied by Fourier transform infrared (FTIR) spectroscopy. The dielectric constant and dissipation factor increases with increasing Sr. Contribution of grain and grain boundary were resolved by complex modulus spectroscopy analysis. AC conductivity spectra of the entire sample follow Universal Jonscher's power law. The similar value of activation energy obtained from relaxation frequency and dc conductivity implies that the origin of conduction and relaxation mechanisms remains the same throughout the samples. The modulus and conductivity spectra of solid solutions nicely follow the time-temperature superposition (TTSP) principle. Further, conductivity spectra of solid solutions were studied by Ghosh and Summerfield scaling.

Introduction of Sulfate to Stabilize the n = 3 Ruddlesden-Popper System Sr4Fe3O10-δ, as a Potential SOFC Cathode

In this paper we report the successful incorporation of sulfate into the triple layer (n = 3) Ruddlesden-Popper system Sr4Fe3O10-δ, with characterisation of these materials by X-ray diffraction, Mössbauer spectroscopy, and conductivity measurements. Significantly, the incorporation of SO4 2- into the middle perovskite layer leads to the stabilization of this Ruddlesden-Popper phase, which cannot be prepared without sulfate doping, thus highlighting the potential of oxyanion doping as a strategy to synthesise new phases of interest for solid oxide fuel cells.

Hybrid Improper Ferroelectricity in (Sr,Ca)3Sn2O7 and Beyond: Universal Relationship between Ferroelectric Transition Temperature and Tolerance Factor in n = 2 Ruddlesden-Popper Phases.

Hybrid improper ferroelectricity, which utilizes nonpolar but ubiquitous rotational/tilting distortions to create polarization, offers an attractive route to the discovery of new ferroelectric and multiferroic materials because its activity derives from geometric rather than electronic origins. Design approachesblending group theory and first principles can be utilized to explore the crystal symmetries of ferroelectric ground states, but in general, they do not make accurate predictions for some important parameters of ferroelectrics, such as Curie temperature ( TC). Here, we establish a predictive and quantitative relationship between TC and the Goldschmidt tolerance factor, t, by employing n = 2 Ruddlesden-Popper (RP) A3B2O7 as a prototypical example of hybrid improper ferroelectrics. The focus is placed on an RP system, (Sr1- xCa x)3Sn2O7 ( x = 0, 0.1, and 0.2), which allows for the investigation of the purely geometric (ionic size) effect on ferroelectric transitions, due to the absence of the second-order Jahn-Teller active (d0 and 6s2) cations that often lead to ferroelectric distortions through electronic mechanisms. We observe a ferroelectric-to-paraelectric transition with TC = 410 K for Sr3Sn2O7. We also find that the TC increases linearly up to 800 K upon increasing the Ca2+ content, i.e., upon decreasing the value of t. Remarkably, this linear relationship is applicable to the suite of all known A3B2O7hybrid improperferroelectrics, indicating that the TC correlates with the simple crystal chemistry descriptor, t, based on the ionic size mismatch. This study provides a predictive guideline for estimating the TC of a given material, which would complement the convergentgroup-theoretical and first-principles design approach.

Landau theory of tilting of oxygen octahedra in perovskites

The list of possible commensurate phases obtained from the parent tetragonal phase of Ruddlesden-Popper (RP) systems, ${A}_{n+1}{B}_{n}{C}_{3n+1}$ for general $n$ due to a single phase transition involving the reorienting of octahedra of $C$ (oxygen) ions is reexamined using a Landau expansion. This expansion allows for the nonlinearity of the octahedral rotations and the rotation-strain coupling. It is found that most structures allowed by symmetry are inconsistent with the constraint of rigid octahedra, which dictates the form of the quartic terms in the Landau free energy. For ${A}_{2}B{C}_{4}$ our analysis allows only 10 of the 41 structures which satisfy the general symmetry arguments of Hatch et al. [Phys. Rev. B 39, 9282 (1989)]. The symmetry of rotations for RP systems with $n>2$ is clarified. Our list of possible structures for general $n$ excludes many structures allowed in previous studies.

ELNES study of chemical solution deposited [formula omitted] Ruddlesden–Popper films: Experiment and simulation

This article analyzes electron energy-loss near-edge fine structures of the SrO(SrTiO3)n=1 Ruddlesden–Popper system and of the parent compounds SrTiO3 and SrO by comparison with first principles calculations. For that, the fine structures of chemical solution deposited Ruddlesden–Popper films have been experimentally recorded by means of transmission electron microscopy. Moreover, density of states computations using an all-electron density-functional code have been performed. It is shown that the appearance and shape of the experimental O–K and Ti–L2,3 fine structure features result from the crystallography-dependent electronic structure of the investigated oxides, which display technologically interesting dielectric as well as lattice–structural properties.

Universal Parameters in the Response of Unconventional Superconductors

This paper is devoted to a unified description of a large class of clean unconventional superconductors within a generalized weak coupling BCS model,applicable to the superfluid phases of liquid 3He, heavy Fermion and cuprate superconductors as well as the Ruddlesden–Popper system Sr2RuO4. Gap nodes, leading to low energy (nodal) Bogoliubov quasiparticles do not only modify the two universal so-called Muhlschlegel-BCS parameters, namely the specific heat discontinuity ΔC/CN at the transition and the gap maximum Δ0(0)/kBTc at zero temperature. They give rise also to the existence ofa certain number of further universal parameters, namely the slopes or curvatures in the temperature dependence of the local response functions the low temperature limit, which vanish altogether in a conventional BCS description of isotropic s-wave pairing. All these parameters are calculated analyticallyfor a large variety of model pairing states and discussed with respect to their experimental observability.

Structural and Physical Property Trends of the Hyperstoichiometric Series, La2Ni(1-x)CoxO4+δ

ABSTRACTMembers of the Ruddlesden-Popper system, La2Ni(1-x)CoxO4+δ (0.00 ≤ × ≤ 1.00), were synthesized and studied for their potential use as cathodes for solid-oxide fuel cells. An unusual structural trend has been noted across the series, which appears to correlate with the oxygen-hyperstoichiometry observed. Details of the structural variance by x-ray and neutron diffraction, as well as selected physical properties for this system will be presented.

Antiferromagnetism, Ferromagnetism, and Phase Separation in the GMR System Sr2-xLa1+xMn2O7

Neutron and synchrotron X-ray powder diffraction techniques have been used to refine the crystal and magnetic structures of the n = 2 Ruddlesden−Popper (RP) system Sr2LaMn2O7. The sample is shown to be biphasic, although both phases are of the RP type and have similar structural parameters. The majority phase (81%) adopts a collinear antiferromagnetic structure below ∼210 K whereas the minority phase is ferromagnetically ordered below ∼125 K. The ordered magnetic moments lie in the xy plane in both phases. The behavior observed is discussed in terms of the interplay between structural and electronic factors. Comparison with data obtained previously by other workers leads to the conclusion that our results have some general significance in the study of n = 2 RP systems.