- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Structural, Electronic and Mechanical Properties of Perovskite Oxides LaMO<sub>3</sub> (M = Mn, Ni) Compounds in the High and Low Symmetric Phases by First Principle Calculation
摘要： The widely investigated perovskite oxides has attracted for a long time a great interest on the physical properties, in their bulk structures as well as the heterostructures components. The Lanthanum transition metal oxides LaMO3 (M= Transition metal) is part of, due to their potential use in advanced technology (including superconductivity, magnetoresistance, ionic conductivity, and a multitude of dielectric properties). Despite the broad exploration of the physical properties, we found a considerable lack in the investigation of the mechanical properties of the LaMO3 compounds. By applying the Density Functional Theory (DFT), we shed light on the structural, electronic, and especially mechanical properties of the experimentally verified phases of The LaMnO3, and LaNiO3. We first calculated the structural and electronic properties, then we continue with the single-crystal elastic constants and mechanical properties, where the bulk, shear and Young’s moduli, and the Anisotropy indexes were deduced, in order to remedy the existing gap of the theoretical knowledge about the mechanical behavior of the LaMnO3, and LaNiO3 compounds.
关键词： Density Functional Theory,Mechanical properties,Perovskite oxides,Electronic properties
更新于2025-09-23 15:23:52
-
Interaction between in-gap states and carriers at the conductive interface between perovskite oxides
摘要： The 2D electron systems of SrTiO3/NdGaO3 (STO/NGO) and amorphous-LaAlO3/SrTiO3/NdGaO3 (a-LAO/STO/NGO) heterojunctions were explored. An obvious interaction between in-gap states (IGSs) and carriers was found. The IGSs can trap a large number of carriers and enhance carrier scattering. As a result of the high density of IGSs in STO, the conductivity of STO/NGO was severely weakened. However, for a-LAO/STO/NGO heterojunctions, the high carrier density can reduce the effect of IGSs through the electrostatic screening effect. The competition between IGSs and the screening effect of carriers results in an insulator–metal transition and a strange temperature dependence of carrier density. We also explored the interaction between IGSs and carriers theoretically. A mathematical description was proposed and the calculated results showed good agreement with experimental findings.
关键词： in-gap states,perovskite oxides interface,2D electron system,electrostatic screening effect
更新于2025-09-23 15:23:52
-
The effects of the oxygen content on the photoelectrochemical properties of LaFeO3 perovskite thin films obtained by pulsed laser deposition
摘要： The physical properties of perovskite oxides are strongly influenced by their stoichiometry and one of the key features of these materials is the tunability of their functionality by controlling the interplay between the compositional and structural properties. Here, the effects on the photoelectrochemical (PEC) water splitting properties of ferroelectric LaFeO3 thin films obtained at different oxygen partial pressures during growth are reported in conjunction with the morphological, optical and structural features. The LaFeO3 thin films have been deposited by pulsed laser deposition on Nb:SrTiO3 substrates. The strong dependence of the photocurrent values Jphoto on the growth conditions is revealed by the photoelectrochemical measurements. Strong variations of the lateral coherence lengths L‖ of LaFeO3/Nb:SrTiO3 with the oxygen partial pressure values are noticed from the X-ray diffraction (XRD) analysis. All the films are heteroepitaxial with small tensile strain levels detected in the crystalline structure, but only for a narrow interval of oxygen partial pressures the LFO/STON thin films show high quality crystalline structure with large lateral coherence length L‖ and photoelectrochemical currents.
关键词： oxygen partial pressure,perovskite oxides,photoelectrochemical,pulsed laser deposition,water splitting
更新于2025-09-12 10:27:22
-
Controlled synthesis of nanocrystalline Nb:SrTiO <sub/>3</sub> electron transport layers for robust interfaces and stable high photovoltaic energy conversion efficiency in perovskite halide solar cells
摘要： Perovskite halides are of great attraction as efficient light absorption materials for solid-state solar cells, but the stability and photovoltaic energy conversion efficiency of perovskite solar cells (PSCs) are still limited by the interface structures and defects between their light-absorbing perovskite halides and electron transport layers (ETLs). Here, we report the ultraviolet (UV) light-induced degradation mechanism at the interfaces between perovskite halide and conventional TiO2 ETL materials, and provide a solution to overcome this drawback. UV-induced degradation is shown to be attributed to the formation of oxygen vacancies formed at the perovskite halide-ETL interface under UV light illumination, where the oxygen atoms released at the interface accelerate the decomposition of perovskite halide by inducing chemical reactions. Meanwhile, nanocrystalline SrTiO3 (STO) ETLs are revealed to be tunable in enabling high performance in PSCs under UV light illumination. Indeed, tuning the electronic structure of STO ETLs by Nb doping, in combination with the controllable removal of SrO phases segregated on the Nb-doped STO ETL surfaces, is exhibited to enable robust interface stability and stable high photovoltaic energy conversion efficiency for PSCs. Furthermore, we demonstrate that STO-based PSCs have no hysteresis due to low defect concentrations at the perovskite halide-STO ETL interfaces.
关键词： oxygen vacancy formation,electron transfer layer,perovskite oxides,photo stability,Perovskite solar cells
更新于2025-09-11 14:15:04
-
European Microscopy Congress 2016: Proceedings || Direct mapping of Li-enabled octahedral tilt ordering and associated strain in nanostructured perovskites
摘要： Self-assembled nanostructures are promising for creating 2D and 3D superlattices with exceptional functionalities. Understanding the mechanisms driving the superlattice formation demands the underlying structural information. However, nanoscale structural modulations intrinsic to these superlattices are difficult to be characterized by conventional diffraction-based structure determination. A real-space, direct imaging method is necessary to probe the local structure characteristics, providing essential information for theoretical understanding and subsequent design of structure-property correlations. Using the aberration-corrected scanning transmission electron microscopy (STEM), we developed an optimized atomic-level bright-field (BF) condition to image the oxygen octahedra in perovskite oxides. We used multislice calculations to determine detector collection angles that allow oxygen octahedra to be imaged sensitively and robustly over large specimen thicknesses. These calculations also provided a calibration by which the octahedral-tilt angle can be measured quantitatively from the image of each octahedron. Applying this real-space octahedral-tilt mapping on Li0.5–3xNd0.5+xTiO3, a promising solid electrolyte in Li-ion batteries, we directly revealed an unconventional superlattices with 2D modulated octahedral tilting. A mathematical description of the octahedral-tilt modulation was derived based on the quantitative tilt maps, which explicitly identified the high-order harmonic character of the modulation. Using simultaneous annular-dark-field (ADF) imaging, we also mapped the lattice parameters unit-cell by unit-cell, uncovering highly-localized strain associated with the tilt modulation. Furthermore, we demonstrate the tunability of the tilt modulation by changing Li stoichiometry. Fascinatingly, we observe a reversible annihilation/reconstruction of the tilt modulation correlated with delithiation/lithiation process, suggesting the structural transformation that is associated with Li-ion conduction in this promising Li-ion conductor. The above observations are largely inaccessible from conventional diffraction analysis, and lead to an unprecedented mechanically-coupled tilting competition model to explain the superlattice formation. Our real-space approach to quantify local octahedral structure and correlate it with strain can be applied to other advanced oxide systems.
关键词： 2D modulated structure,STEM,Li-ion solid electrolyte,perovskite oxides,oxygen octahedral tilting
更新于2025-09-11 14:15:04
-
Design for Highly Piezoelectric and Visible/Near-Infrared Photoresponsive Perovskite Oxides
摘要： Defect-engineered perovskite oxides that exhibit ferroelectric and photovoltaic properties are promising multifunctional materials. Though introducing gap states by transition metal doping on the perovskite B-site can obtain low bandgap (i.e., 1.1–3.8 eV), the electrically leaky perovskite oxides generally lose piezoelectricity mainly due to oxygen vacancies. Therefore, the development of highly piezoelectric ferroelectric semiconductor remains challenging. Here, inspired by point-defect-mediated large piezoelectricity in ferroelectrics especially at the morphotropic phase boundary (MPB) region, an efficient strategy is proposed by judiciously introducing the gap states at the MPB where defect-induced local polar heterogeneities are thermodynamically coupled with the host polarization to simultaneously achieve high piezoelectricity and low bandgap. A concrete example, Ni2+-mediated (1–x)Na0.5Bi0.5TiO3-xBa(Ti0.5Ni0.5)O3–δ (x = 0.02–0.08) composition is presented, which can show excellent piezoelectricity and unprecedented visible/near-infrared light absorption with a lowest ever bandgap ≈0.9 eV at room temperature. In particular, the MPB composition x = 0.05 shows the best ferroelectricity/piezoelectricity (d33 = 151 pC N–1, Pr = 31.2 μC cm–2) and a largely enhanced photocurrent density approximately two orders of magnitude higher compared with classic ferroelectric (Pb,La)(Zr,Ti)O3. This research provides a new paradigm for designing highly piezoelectric and visible/near-infrared photoresponsive perovskite oxides for solar energy conversion, near-infrared detection, and other multifunctional applications.
关键词： photovoltaics,ceramics,ferroelectrics,perovskite oxides,semiconductors
更新于2025-09-10 09:29:36
-
Detection of oxygen sub-lattice ordering in A-site deficient perovskites through monochromated core-loss EELS mapping
摘要： Perovskite oxides are widely studied for a variety of applications, from thermoelectrics to fuel cells. Part of the attraction lies in the fact that perovskite ceramics are relatively easy to dope chemically over a wide range of compositions, resulting in various degrees of structural ordering. As a consequence, the properties and functionalities of such materials can be readily tailored. For instance in systems proposed for thermoelectric applications, the presence of superlattices, or domain boundaries vacancies can suppress the thermal conductivity due to increased phonon scattering. Understanding therefore the mechanisms behind the formation of such types of ordering in ceramic systems is crucial for their implementation in engineering applications. Here, we report on an A-site deficient perovskite system based on the Nd2/3xTiO3 double perovskite. This system, a candidate for thermoelectric applications, has attracted significant attention due to the presence of a peculiar superstructure originating in part in A-site cation vacancy ordering. Using aberration corrected Scanning Transmission Electron Microscopy we investigate a series of Nd2/3xTiO3 ceramics engineered to possess different degrees of A-site cation-vacancy ordering and as a result vastly different thermoelectric properties. Annular Bright Field Imaging of the [110] orientation, preformed in the Nion UltraSTEM 100TM reveals the presence of tilting domains in the TiO6 sub lattice, dependent on the A-site occupancy. Furthermore, advanced image analysis of the electron micrographs was used to measure local distortions in the TiO6 lattice. The presence of these octahedral distortions was further investigated by employing atomically resolved monochromated core loss Electron Energy Loss measurements, acquired with an energy resolution better than 0.100eV, using the Nion UltraSTEM 100MC TM instrument. With this approach it is not only possible to map individual components of the Ti L2,3 near edge fine structure, but also fine local changes in the ELNES; subtle changes Ti L2,3 pre-peak intensity – usually not discernible in conventional EELS measurements as well as changes in the Ti L3 eg/tg and tg L3/L2 intensity ratios all indicative of local TiO6 distortions.
关键词： Annular Bright Field Imaging,aberration corrected Scanning Transmission Electron Microscopy,Nd2/3xTiO3,structural ordering,Electron Energy Loss measurements,thermoelectrics,fuel cells,A-site deficient perovskite,phonon scattering,perovskite oxides
更新于2025-09-09 09:28:46
-
Spin Dimer Formation in BaTi0.67?xMn0.33 + xO3 (x = - 0.02, - 0.01, 0, 0.01, and 0.02)
摘要： Mn concentration of 6H-Ba3Ti2MnO9 was adjusted slightly to deviate from stoichiometric ratios. Our structural analysis shows that the spin dimer may form with Mn concentration slightly higher than stoichiometric. The magnetic properties are explored by combining DC magnetization and X-band (9.4 GHz) electron spin resonance (ESR). DC magnetization shows the signature of combination of frustrated spin and short-range spin. ESR shows that spin dimer can be formed in BaTi0.65Mn0.35O3, while no signature of spin dimer can be found in BaTi0.69Mn0.31O3 and Ba3Ti2MnO9.
关键词： Low-dimensional magnet,Spin dimer,Magnetic materials,Ceramic composites,Perovskite oxides
更新于2025-09-09 09:28:46