Search results for "PEROVSKITE"

Surface properties and catalytic performance for ethane combustion of La1−xKxMnO3+δ perovskites

2001

Abstract The influence of K substitution in LaMnO3 perovskite on the surface properties and catalytic oxidation of ethane has been studied. La1−xKxMnO3+δ perovskites (x=0.05, 0.10, 0.15, 0.20 and 0.25) with BET surface area of 20–26 m2 g−1 have been prepared by the freeze-drying method and characterized by X-ray diffraction patterns (XRD), TPR, TPD and XPS. The XRD analyses showed the presence of a single crystalline phase (x≤0.15) with the linear increase of the lattice parameter corroborating the incorporation of potassium in the perovskite structure. The XPS studies revealed an enrichment of the perovskite surface with potassium accompanied by an increase in the surface Mn4+/Mn3+ ratio. …

Covalent and Ionic Functionalization of HLN Layered Perovskite by Sonochemical Methods

2017

We describe the functionalization of the layered perovskite HLaNb2O7 with n-propanol, n-decanol, 3-mercaptopropyl-trimethoxysilane, imidazole, n-decylamine, and histamine. The use of sonication is found to significantly improve the reaction yield and to reduce the reaction time, compared to conventional thermal treatment under reflux. The obtained intercalates are thoroughly characterized through the use of several complementary experimental techniques (scanning electron microscopy, IR spectroscopy, X-ray diffraction, thermogravimetric analysis, magic-angle spinning NMR), clarifying their structure and chemical bonding. The implications for the design of inorganic–organic composite material…

Comparison of Permeation Measurements and Hybrid Density Functional Calculations on Oxygen Vacancy Transport in Complex Perovskite Oxides

2014

The oxygen vacancy (VO••) formation enthalpy (ΔHF) was determined from the effective activation energies obtained in the permeation measurements on a series of solid solutions La0.98–xSrxCo0.2Fe0.8O3−δ (x = 0.125–0.8) and compared with the results of ab initio calculations at finite temperatures based on the hybrid (PBE0) and GGA+U calculations, as well as previous thermogravimetric experiments. The Mulliken atomic charges, magnetic moments, and the Fe-VO•• and Sr-VO•• distances are analyzed. The strong dependence of formation enthalpy of VO•• on the Fe oxidation state due to variation in Sr and VO•• concentrations is discussed.

Fabrication and Characterisation of Titania Photonic Nanostructures

2015

In this work, we report about the preparation and morphological characterization of photonic nanopatterned titania films (~ 200 nm).

Trap-Assisted Non-Radiative Recombination in Organic-Inorganic Perovskite Solar Cells

2015

Luminescent perovskites: From materials to light-emitting devices

2019

The thesis describes the preparation of efficient and simple bright halide perovskite materials and light-emitting devices. In the different chapters, several perovskite types are described and studied: Perovskites with different crystal sizes, from nanosized perovskites (Chapter 2, 3 and 4) to bulk perovskites (Chapter 5) all with a 3D crystal structure; and perovskites with different crystal structure dimensionalities, such as 3D or nanoplatelets with 2D (Chapter 3) and even quasi-2D structures (Chapter 2). Photoluminescence and electroluminescence with colours ranging from red to green and blue are reported. Chapter 2 focuses on obtaining stable and very PL efficient red-emitting hybrid …

Structural and magnetic properties of the solid solution series Sr2Fe1–xMxReO6(M = Cr, Zn)

2005

Strong correlations between the electronic, structural and magnetic properties have been found during the study of doped double perovskites Sr2Fe1−xMxReO6 (0 ≤ x ≤ 1, M = Zn, Cr). The interplay between the van Hove singularity and the Fermi level plays a crucial role for the magnetic properties. Cr doping of the parent compound Sr2FeReO6 leads to a non-monotonic behaviour of the saturation magnetization and an enhancement for doping levels up to 10%. The Curie temperatures monotonically increase from 401 to 616 K. In contrast, Zn doping leads to a continuous decrease in the saturation magnetization and the Curie temperatures. Superimposed on the electronic effects is the structural influenc…

Zero-Dimensional Hybrid Organic−Inorganic Lead Halides and Their Post-Synthesis Reversible Transformation into Three-Dimensional Perovskites

2021

Zero-dimensional (0D) mixed-halide hybrid organic-inorganic MA4PbX6·2H2O (MA = CH3NH3+; X = Br1 - xIx with 0 < x < 1) has been synthesized by a solvent-free mechanochemical approach. It has been shown that this 0D phase with sharp absorption features in the near-UV is a hydrated structure, which can be reversibly transformed into the three-dimensional perovskite phase MAPbX3 by simple thermal annealing (dehydration) in air. This work reveals a new approach to hybrid organic-inorganic perovskites and related 0D structures, which have so far only been thoroughly studied for the inorganic Cs4PbX6 compounds. Hetero-structures for Efficient Luminescent Devices (HELD) REFERENCIA: 834431 PCIN-2019…

Interfacial Modification for High-Efficiency Vapor-Phase-Deposited Perovskite Solar Cells Based on a Metal Oxide Buffer Layer.

2018

Vacuum deposition is one of the most technologically relevant techniques for the fabrication of perovskite solar cells. The most efficient vacuum-based devices rely on doped organic contacts, compromising the long-term stability of the system. Here, we introduce an inorganic electron-transporting material to obtain power conversion efficiencies matching the best performing vacuum-deposited devices, with open-circuit potential close to the thermodynamic limit. We analyze the leakage current reduction and the interfacial recombination improvement upon use of a thin (<10 nm) interlayer of C60, as well as a more favorable band alignment after a bias/ultraviolet light activation process. This wo…

Excitonic States in Semiconducting Two-dimensional Perovskites

2018

Hybrid organic/inorganic perovskites have emerged as efficient semiconductor materials for applications in photovoltaic solar cells with conversion efficiency above 20 \%. Recent experiments have synthesized ultra-thin two-dimensional (2D) organic perovskites with optical properties similar to those of 2D materials like monolayer MoS$_2$: large exciton binding energy and excitonic effects at room temperature. In addition, 2D perovskites are synthesized with a simple fabrication process with potential low-cost and large-scale manufacture. Up to now, state-of-the-art simulations of the excitonic states have been limited to the study of bulk organic perovskites. A large number of atoms in the …