Formation Of Ruddlesden-Popper Phases Research Articles

(High-Temperature Energy, Materials, & Processes Division Outstanding Achievement Award Address) Mechanisms of Oxide Exsolution and Electrode Applications in Solid Oxide Cells

Solid oxide cell fuel electrodes based on perovskite oxides are desirable to avoid problems with Ni-based anodes, including coking in hydrocarbon fuels and degradation due to fuel impurities or redox cycling. However, oxide anode electrochemical performance is often lacking, limited by surface processes such as the dissociative adsorption of hydrogen. One way to improve such anodes is by the addition of a reducible cation in the oxide formulation, resulting in cation exsolution and nucleation of metallic nanoparticles on oxide surfaces during cell startup and operation. For example, substitution of small amounts of Ni or Ru on the B-site of Sr(Ti,Fe)O3 results in the formation of Ni-Fe or Ru-Fe nanoparticles, respectively, during exposure of the electrode to fuel during cell operation. This talk will examine the microstructural evolution of these exsolution anodes, making use of in situ x-ray diffraction measurements to detect formation of exsolved metal alloys and oxide phase changes. Exsolved metal nanoparticles enhance electrochemical performance, usually by promoting hydrogen dissociation on electrode surfaces. Changes in perovskite stoichiometry resulting from B-site exsolution can also impact the phase stability of the oxide, in some cases resulting in the formation of Ruddlesden-Popper phases that deleteriously affect electrochemical performance. The application of exsolution in fuel electrodes in novel thin-electrolyte oxygen-electrode-supported cells is discussed; the results indicate that performance in H2/H2O fuel is superior to Ni-YSZ in both electrolysis and fuel cell modes. Electrochemical characteristics of the exsolution electrodes are especially superior to Ni-YSZ when operated in CO/CO2 fuel.

Fully Inorganic Ruddlesden-Popper Double Cl-I and Triple Cl-Br-I Lead Halide Perovskite Nanocrystals.

The vast majority of lead halide perovskite (LHP) nanocrystals (NCs) are currently based on either a single halide composition (CsPbCl3, CsPbBr3, and CsPbI3) or an alloyed mixture of bromide with either Cl– or I– [i.e., CsPb(Br:Cl)3 or CsPb(Br:I)3]. In this work, we present the synthesis as well as a detailed optical and structural study of two halide alloying cases that have not previously been reported for LHP NCs: Cs2PbI2Cl2 NCs and triple halide CsPb(Cl:Br:I)3 NCs. In the case of Cs2PbI2Cl2, we observe for the first time NCs with a fully inorganic Ruddlesden–Popper phase (RPP) crystal structure. Unlike the well-explored organic–inorganic RPP, here, the RPP formation is triggered by the size difference between the halide ions. These NCs exhibit a strong excitonic absorption, albeit with a weak photoluminescence quantum yield (PLQY). In the case of the triple halide CsPb(Cl:Br:I)3 composition, the NCs comprise a CsPbBr2Cl perovskite crystal lattice with only a small amount of incorporated iodide, which segregates at RPP planes’ interfaces within the CsPb(Cl:Br:I)3 NCs. Supported by density functional theory calculations and postsynthetic surface treatments to enhance the PLQY, we show that the combination of iodide segregation and defective RPP interfaces are most likely linked to the strong PL quenching observed in these nanostructures. In summary, this work demonstrates the limits of halide alloying in LHP NCs because a mixture that contains halide ions of very different sizes leads to the formation of defective RPP interfaces and a severe quenching of LHP NC’s optical properties.

Pb2+-stabilized Ruddlesden–Popper (Sr1−xPbx)3Ti2O7 ceramics

Abstract

Ruddlesden-Popper Phase Formation in Pb(Zr,Ti)O3 Thin Films

In this work, we give evidences of Ruddlesden-Popper (RP) phase formation in Pb(Zr,Ti)O 3 thin films deposited by multi-target reactive sputtering at a substrate temperature of 520°C onto oxidized silicon wafers comprising a ZrO 2 buffer layer. X-ray diffraction data of films deposited at 520°C revealed the appearance of a Pb 2 (Zr,Ti)O 4 RP phase. High-resolution transmission electron microscopy (HRTEM) images have proved the presence of a corresponding superstructure with a period of about 1.3 nm. It was nucleated on top of an amorphous, lead-enriched interface layer near the ZrO 2 /PZT interface. At higher substrate temperatures, when this amorphous interface layer disappears, a perovskite structure with a sharp interface was nucleated directly on the ZrO 2 buffer layer.

Investigation of the stability limits of the La(Sr1 − x Ca x )2Mn2O7 solid solution

The stability limits of the solid solutions La(Sr1 − xCax)2Mn2O7 (x = 0−1) are investigated using isothermal annealing-quenching methods in combination with X-ray powder diffraction analysis. It is established that the formation of Ruddlesden-Popper phases occurs in the calcium concentration range x = 0−0.06. The replacement of strontium by calcium in this concentration range leads to an increase in the thermodynamic stability of the structure under investigation.

Reversible Electrical Field-Induced Formation of Ruddlesden-Popper Phases in Strontium Titanate at Room Temperature

ABSTRACTOn base of the structural characteristics of near-surface regions of a SrTiO3 (001) (STO (001)) single-crystal plate revealed by means of wide-angle X-ray scattering (WAXS), X-ray fluorescence spectroscopy and high-resolution transmission electron microscopy, structural changes in the STO (001) single-crystal plate under the influence of an external electric field at room temperature can be described as the tunable and reversible formation of Ruddlesden-Popper-phases of the quasi-binary system SrO-TiO2. The WAXS behavior implies the use of the reversible phase-transition for adaptive X-ray optics.

Kinetics of Ruddlesden-Popper Phase Formation: III. Mechanism of Gd2SrAl2O7 Formation

Studies on phase formation in the system Gd2O3-SrO-Al2O3 in the range 900-1530°C showed that the synthesis of Gd2SrAl2O7 occur by a mechanism differing from the mechanism of Ln2SrAl2O7 formation (Ln = La, Nd, Sm), and the limiting stage is reaction between Gd2O3 and SrAl2O4.

Kinetics of Ruddlesden-Popper Phase Formation: II. Mechanism of Nd2SrAl2O7 and Sm2SrAl2O7 Formation

Phase formation in the Ln2O3-SrO-Al2O3 system (Ln = Nd, Sm) was studied in the range 900-1530°C. Comparative examination of the kinetics of the synthesis of Ln2SrAl2O7 oxides (Ln = La, Nd, Sm) showed that this reaction proceeds by a common mechanism and is substantially faster for neodymium and samarium complex aluminates than for lanthanum aluminate.

Kinetics of formation of ruddlesden-popper phases : I. Mechanism of La2SrAl2O7 formation

Phase formation in the La2O3-SrO-Al2O3 system was studied. Formation of the perovskite LaAlO3 structure and the perovskite-like LaSrAlO4 and La2SrAl2O7 layered structures in solid-phase chemical reactions is activated only after reaching certain critical temperatures which correlate with the temperatures of of the transition of intergranular formations to the liquid-like state (melting points of two-dimensional nonautonomous phases).