scholarly journals Seeing Structural Mechanisms of Optimized Piezoelectric and Thermoelectric Bulk Materials through Structural Defect Engineering

Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 487
Author(s):  
Yang Zhang ◽  
Wanbo Qu ◽  
Guyang Peng ◽  
Chenglong Zhang ◽  
Ziyu Liu ◽  
...  
Keyword(s):  
High Performance ◽  
Structural Characteristics ◽  
Functional Materials ◽  
Atomic Scale ◽  
Structural Defects ◽  
General Strategy ◽  
Defect Engineering ◽  
Scanning Transmission ◽  
Complex Structural ◽  
Manufacturing Platform

Aberration-corrected scanning transmission electron microscopy (AC-STEM) has evolved into the most powerful characterization and manufacturing platform for all materials, especially functional materials with complex structural characteristics that respond dynamically to external fields. It has become possible to directly observe and tune all kinds of defects, including those at the crucial atomic scale. In-depth understanding and technically tailoring structural defects will be of great significance for revealing the structure-performance relation of existing high-property materials, as well as for foreseeing paths to the design of high-performance materials. Insights would be gained from piezoelectrics and thermoelectrics, two representative functional materials. A general strategy is highlighted for optimizing these functional materials’ properties, namely defect engineering at the atomic scale.

scholarly journals The mechanism for the enhanced piezoelectricity in multi-elements doped (K,Na)NbO3 ceramics

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Xiaoyi Gao ◽  
Zhenxiang Cheng ◽  
Zibin Chen ◽  
Yao Liu ◽  
Xiangyu Meng ◽  
...  
Keyword(s):  
High Performance ◽  
Functional Materials ◽  
Atomic Scale ◽  
Ferroelectric Ceramics ◽  
Structure Property ◽  
X Ray Diffraction ◽  
Temperature Dependent ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
High Dielectric

Abstract(K,Na)NbO3 based ceramics are considered to be one of the most promising lead-free ferroelectrics replacing Pb(Zr,Ti)O3. Despite extensive studies over the last two decades, the mechanism for the enhanced piezoelectricity in multi-elements doped (K,Na)NbO3 ceramics has not been fully understood. Here, we combine temperature-dependent synchrotron x-ray diffraction and property measurements, atomic-scale scanning transmission electron microscopy, and first-principle and phase-field calculations to establish the dopant–structure–property relationship for multi-elements doped (K,Na)NbO3 ceramics. Our results indicate that the dopants induced tetragonal phase and the accompanying high-density nanoscale heterostructures with low-angle polar vectors are responsible for the high dielectric and piezoelectric properties. This work explains the mechanism of the high piezoelectricity recently achieved in (K,Na)NbO3 ceramics and provides guidance for the design of high-performance ferroelectric ceramics, which is expected to benefit numerous functional materials.

Direct Imaging of the Atomic Structure and Chemistry of Defects and Interfaces by Z-Contrast Stem

1989 ◽  
Vol 169 ◽  
Author(s):  
S. J. Pennycook ◽  
M. F. Chisholm ◽  
D. E. Jesson ◽  
D. P. Norton ◽  
J. W. Mccamy ◽  
...  
Keyword(s):  
Critical Currents ◽  
Atomic Scale ◽  
Structural Defects ◽  
New Approach ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Resolution Imaging ◽  
Film Substrate ◽  
Z Contrast

AbstractZ-contrast scanning transmission electron microscopy (STEM) is a fundamentally new approach to high-resolution imaging which provides unambiguous, compositionally sensitive images on the atomic scale. Such images are intuitively interpretable, even in thick regions of the sample, tremendously simplifying determination of the structure and chemistry of defects and interfaces. To illustrate this, examples are presented of commonly observed planar defects in laser-ablated thin films of YBa2Cu3O7-x. Film/substrate interfaces are shown to be chemically diffuse on the atomic scale and steps or undulations in the substrate need not result in defects in the film. Low-angle grain boundaries are found to be chemically clean, the drastic reductions in critical currents with tilt angle being due to the array of intrinsic structural defects comprising the boundary.

Complex Atomic-Scale Structures in Solids by a Combination of Theory and Microscopy

1998 ◽  
Vol 4 (S2) ◽  
pp. 760-761
Author(s):  
S. T. Pantelides ◽  
S. J. Pennycook ◽  
M. F. Chisholm ◽  
A. Maiti ◽  
Y. Yan ◽  
...  
Keyword(s):  
High Performance ◽  
Atomic Scale ◽  
Extended Defects ◽  
Atomic Structures ◽  
Spatially Resolved ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Synergistic Approach ◽  
Comprehensive Picture ◽  
Electron Microscopes

Modern high-performance computers are now capable of calculations that can be used to determine the preferred atomic arrangements in complex systems. Both first-principles and semiempirical approaches have been developed with complementary capabilities. At the same time, powerful transmission electron microscopes have been developed that yield direct atomic-scale images of crystals and extended defects such as dislocations, grain boundaries and buried interfaces. This paper presents several examples where a synergistic approach combining theoretical results, Z-contrast scanning transmission electron microscopy, and spatially resolved electron energy loss spectroscopy (EELS) have led to the elucidation of complex atomic structures. In some cases, theory predicts, experiment confirms and expands and theory revisits; in other cases, observations come first and theory helps put together a comprehensive picture or goes beyond the original observations with new predictions. In both cases, equilibrium structures, impurity or stressinduced structural transformations, and dynamical processes such as diffusion, segregation or precipitation are elucidated in great detail.

Defect Structures in Al-Ni-Rh Crystalline Approximants Studied by HREM and HAADF Techniques

2007 ◽  
Vol 561-565 ◽  
pp. 1353-1356 ◽  
Author(s):  
Wei Sun ◽  
Y.H. Chen ◽  
J.P. Wang ◽  
Z. Zhang
Keyword(s):  
Electron Microscopy ◽  
Structural Characteristics ◽  
Symmetry Plane ◽  
High Resolution Electron Microscopy ◽  
Dark Field ◽  
Structural Defects ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Scanning Transmission ◽  
Annular Dark Field

By means of a combination of high-resolution electron microscopy (HREM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) techniques, we have directly revealed that periodic arrangements in different manners for flattened hexagons constructed with atom columnar clusters can form two Al-Ni-Rh crystalline approximant phases. In contrast to periodic arrangements of flattened hexagons, configurations and distributions of various defects in these structurally-complicated alloy phases have been examined and their structural characteristics discussed. HREM observations clearly show that structural defects in Al-Ni-Rh crystalline approximants are of phason type and they are correlated with incorrect arrangements of atom columnar clusters. The distribution of high density planar defects can destroy the long-range periodicity in at least one direction in the pseudo decagonal symmetry plane. By means of the HAADF-STEM imaging technique, the existence of ill-formed atom columnar clusters in the core area of a linear defect, which is usually not visible in HREM observations, has been clearly revealed.

scholarly journals Grain-boundary-rich polycrystalline monolayer WS2 film for attomolar-level Hg2+ sensors

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Lixuan Liu ◽  
Kun Ye ◽  
Changqing Lin ◽  
Zhiyan Jia ◽  
Tianyu Xue ◽  
...  
Keyword(s):  
Active Sites ◽  
High Performance ◽  
2D Materials ◽  
Layered Materials ◽  
High Density ◽  
Structural Defects ◽  
Defect Engineering ◽  
Ion Sensors ◽  
Sensor Performance ◽  
2D Layered Materials

AbstractEmerging two-dimensional (2D) layered materials have been attracting great attention as sensing materials for next-generation high-performance biological and chemical sensors. The sensor performance of 2D materials is strongly dependent on the structural defects as indispensable active sites for analyte adsorption. However, controllable defect engineering in 2D materials is still challenging. In the present work, we propose exploitation of controllably grown polycrystalline films of 2D layered materials with high-density grain boundaries (GBs) for design of ultra-sensitive ion sensors, where abundant structural defects on GBs act as favorable active sites for ion adsorption. As a proof-of-concept, our fabricated surface plasmon resonance sensors with GB-rich polycrystalline monolayer WS2 films have exhibited high selectivity and superior attomolar-level sensitivity in Hg2+ detection owing to high-density GBs. This work provides a promising avenue for design of ultra-sensitive sensors based on GB-rich 2D layered materials.

scholarly journals Octahedral spinel electrocatalysts for alkaline fuel cells

2019 ◽  
Vol 116 (49) ◽  
pp. 24425-24432 ◽  
Author(s):  
Yao Yang ◽  
Yin Xiong ◽  
Megan E. Holtz ◽  
Xinran Feng ◽  
Rui Zeng ◽  
...  
Keyword(s):  
Fuel Cells ◽  
Active Sites ◽  
High Performance ◽  
High Energy ◽  
Reduction Reaction ◽  
Atomic Scale ◽  
High Energy Resolution ◽  
Alkaline Fuel Cells ◽  
Edge Structure ◽  
Scanning Transmission

Designing high-performance nonprecious electrocatalysts to replace Pt for the oxygen reduction reaction (ORR) has been a key challenge for advancing fuel cell technologies. Here, we report a systematic study of 15 different AB2O4/C spinel nanoparticles with well-controlled octahedral morphology. The 3 most active ORR electrocatalysts were MnCo2O4/C, CoMn2O4/C, and CoFe2O4/C. CoMn2O4/C exhibited a half-wave potential of 0.89 V in 1 M KOH, equal to the benchmark activity of Pt/C, which was ascribed to charge transfer between Co and Mn, as evidenced by X-ray absorption spectroscopy. Scanning transmission electron microscopy (STEM) provided atomic-scale, spatially resolved images, and high-energy-resolution electron-loss near-edge structure (ELNES) enabled fingerprinting the local chemical environment around the active sites. The most active MnCo2O4/C was shown to have a unique Co-Mn core–shell structure. ELNES spectra indicate that the Co in the core is predominantly Co2.7+ while in the shell, it is mainly Co2+. Broader Mn ELNES spectra indicate less-ordered nearest oxygen neighbors. Co in the shell occupies mainly tetrahedral sites, which are likely candidates as the active sites for the ORR. Such microscopic-level investigation probes the heterogeneous electronic structure at the single-nanoparticle level, and may provide a more rational basis for the design of electrocatalysts for alkaline fuel cells.

Utilization of electron-beam irradiation under atomic-scale chemical mapping for evaluating the cycling performance of lithium transition metal oxide cathodes

2021 ◽  
Author(s):  
Jae-Hyun Shim ◽  
Hyosik Kang ◽  
Sanghun Lee ◽  
Young-Min Kim
Keyword(s):  
Scanning Transmission Electron Microscopy ◽  
High Performance ◽  
Lithium Ion ◽  
Cycling Performance ◽  
Atomic Scale ◽  
Chemical Mapping ◽  
X Ray ◽  
Transmission Electron ◽  
Oxide Cathodes ◽  
Scanning Transmission

With the development of high-performance lithium ion batteries, scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDX) has been widely applied as a high-precision technique to investigate...

Probing vacancies and structural distortions at individual defects in ceramics using EELS

1996 ◽  
Vol 54 ◽  
pp. 678-679
Author(s):  
D. J. Wallis ◽  
N. D. Browning
Keyword(s):  
Structural Information ◽  
Core Loss ◽  
Nearest Neighbors ◽  
Ceramic Materials ◽  
Scanning Transmission Electron Microscope ◽  
Real Space ◽  
Atomic Scale ◽  
Structure Property ◽  
Scanning Transmission ◽  
Key Issues

In electron energy loss spectroscopy (EELS), the near-edge region of a core-loss edge contains information on high-order atomic correlations. These correlations give details of the 3-D atomic structure which can be elucidated using multiple-scattering (MS) theory. MS calculations use real space clusters making them ideal for use in low-symmetry systems such as defects and interfaces. When coupled with the atomic spatial resolution capabilities of the scanning transmission electron microscope (STEM), there therefore exists the ability to obtain 3-D structural information from individual atomic scale structures. For ceramic materials where the structure-property relationships are dominated by defects and interfaces, this methodology can provide unique information on key issues such as like-ion repulsion and the presence of vacancies, impurities and structural distortion.An example of the use of MS-theory is shown in fig 1, where an experimental oxygen K-edge from SrTiO3 is compared to full MS-calculations for successive shells (a shell consists of neighboring atoms, so that 1 shell includes only nearest neighbors, 2 shells includes first and second-nearest neighbors, and so on).

Electron Microscopy Studies of The Chemistry And Microstructure of BaF2 / YBa2Cu3O7-x Thin Films

1994 ◽  
Vol 52 ◽  
pp. 796-797
Author(s):  
J. L. Lee ◽  
C. A. Weiss ◽  
R. A. Buhrman ◽  
J. Silcox
Keyword(s):  
Thin Film ◽  
Electron Microscopy ◽  
Thin Films ◽  
Scanning Transmission Electron Microscope ◽  
Atomic Scale ◽  
Island Growth ◽  
Multilayer Systems ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Mgo Substrate

BaF2 thin films are being investigated as candidates for use in YBa2Cu3O7-x (YBCO) / BaF2 thin film multilayer systems, given the favorable dielectric properties of BaF2. In this study, the microstructural and chemical compatibility of BaF2 thin films with YBCO thin films is examined using transmission electron microscopy and microanalysis. The specimen was prepared by using laser ablation to first deposit an approximately 2500 Å thick (0 0 1) YBCO thin film onto a (0 0 1) MgO substrate. An approximately 7500 Å thick (0 0 1) BaF2 thin film was subsequendy thermally evaporated onto the YBCO film.Images from a VG HB501A UHV scanning transmission electron microscope (STEM) operating at 100 kV show that the thickness of the BaF2 film is rather uniform, with the BaF2/YBCO interface being quite flat. Relatively few intrinsic defects, such as hillocks and depressions, were evident in the BaF2 film. Moreover, the hillocks and depressions appear to be faceted along {111} planes, suggesting that the surface is smooth and well-ordered on an atomic scale and that an island growth mechanism is involved in the evolution of the BaF2 film.

Tetraphenylbenzene-based AIEgens: the Horizontally Oriented Emitters for highly Efficient Non-doped Deep Blue OLEDs and Host for High-Performance Hybrid WOLEDs

2020 ◽  
Author(s):  
Pengbo Han ◽  
Zeng Xu ◽  
Chengwei Lin ◽  
Dongge Ma ◽  
Anjun Qin ◽  
...  
Keyword(s):  
High Performance ◽  
General Strategy ◽  
Flat Panel Displays ◽  
Light Emitting ◽  
Horizontal Orientation ◽  
Deep Blue ◽  
Full Color ◽  
High Emission ◽  
White Oleds ◽  
Low Efficiency

Deep blue organic-emitting fluorophores are crucial for application in white lighting and full color flat-panel displays but emitters with high color quality and efficiency are rare. Herein, novel deep blue AIE luminogens (AIEgens) with various donor units and an acceptor of cyano substituted tetraphenylbenzene (TPB) cores were developed and used to fabricate non-doped deep blue and hybrid white organic light-emitting diodes (OLEDs). Benefiting from its high emission efficiency and high proportion of horizontally oriented dipoles in the film state, the non-doped deep blue device based on CN-TPB-TPA realized a maximum external quantum efficiency 7.27%, with a low efficiency roll-off and CIE coordinates of (0.15, 0.08). Moreover, efficient two-color hybrid warm white OLEDs (CIE<sub>x,y</sub> = 0.43, 0.45) were achieved using CN-TPB-TPA as the blue-emitting layer and phosphor doped host, which realized maximum current, power, external quantum efficiencies 58.0 cd A<sup>-1</sup>, 60.7 lm W<sup>-1</sup> and 19.1%, respectively. This work provides a general strategy to achieve high performance, stable deep blue and hybrid white OLEDs by construction of AIEgens with excellent horizontal orientation

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