Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userAlerts in High-resolution TEM characterization of perovskite material
487
0
0.0
(
0
)
Authors
Yu-Hao Deng
Ask ChatGPT about the research
No Arabic abstract
High-resolution TEM (HRTEM) is a powerful tool for structure characterization. However, methylammonium lead iodide (MAPbI3) perovskite is highly sensitive to electron beams and easily decompose into lead iodide (PbI2). Universal misidentifications that PbI2 is incorrectly labeled as perovskite are widely exist in HRTEM characterization, which would negatively affect the development of perovskite research field. Here misidentifications in MAPbI3 perovskite calibration are summarized, classified and corrected based on corresponding electron diffraction (ED) simulations. Corresponding crystallographic parameters of intrinsic tetragonal MAPbI3 and the confusable hexagonal PbI2 are also presented clearly. Finally, the method of proper phase identification and some ways to control the radiation damage in HRTEM are provided. This work paves the way to avoid misleadings in HRTEM characterization of perovskite and other electron beam-sensitive materials in the future.
rate research
Read More
Organic-inorganic hybrid perovskites (OIHPs) have recently emerged as groundbreaking semiconductor materials owing to their remarkable properties. Transmission electron microscopy (TEM), as a very powerful characterization tool, has been widely used in perovskite materials for structural analysis and phase identification. However, the perovskites are highly sensitive to electron beams and easily decompose into PbX2 (X= I, Br, Cl) and metallic Pb. The electron dose of general high-resolution TEM is much higher than the critical dose of MAPbI3, which results in universal misidentifications that PbI2 and Pb are incorrectly labeled as perovskite. The widely existed mistakes have negatively affected the development of perovskite research fields. Here misidentifications of the best-known MAPbI3 perovskite are summarized and corrected, then the causes of mistakes are classified and ascertained. Above all, a solid method for phase identification and practical strategies to reduce the radiation damage for perovskite materials have also been proposed. This review aims to provide the causes of mistakes and avoid misinterpretations in perovskite research fields in the future.
AVO4 vanadates are materials of technological importance due to their variety of functional properties. They have applications as scintillators, thermophosphors, photocatalysts, cathodoluminescence, and laser-host materials. Studies at HP-HT are helpful for understanding the physical properties of the solid state, in special, the phase behavior of AVO4 materials. For instance, they have contributed to understand the macroscopic properties of vanadates in terms of microscopic mechanisms. A great progress has been made in the last decade towards the study of the pressure-effects on the structural, vibrational, and electronic properties of AVO4 compounds. Thanks to the combination of experimental and theoretical studies, novel metastable phases with interesting physical properties have been discovered and the HP structural sequence followed by AVO4 oxides has been understood. Here, we will review HP studies carried out on the phase behavior of different AVO4 compounds. The studied materials include rare-earth vanadates and other compounds; for example, BiVO4, FeVO4, CrVO4, and InVO4. In particular, we will focus on discussing the results obtained by different research groups, who have extensively studied vanadates up to pressures exceeding 50 GPa. We will make a systematic presentation and discussion of the results reported in the literature. In addition, with the aim of contributing to the improvement of the actual understanding of the high-pressure properties of ternary oxides, the HP behavior of vanadates will be compared with related compounds; including phosphates, chromates, and arsenates. The behavior of nanomaterials under compression will also be briefly described and compared with their bulk counterpart. Finally, the implications of the reported studies on technological developments and geophysics will be commented and possible directions for the future studies will be proposed.
Morphological measures are introduced to probe the complex procedure of shock wave reaction on porous material. They characterize the geometry and topology of the pixelized map of a state variable like the temperature. Relevance of them to thermodynamical properties of material is revealed and various experimental conditions are simulated. Numerical results indicate that, the shock wave reaction results in a complicated sequence of compressions and rarefactions in porous material. The increasing rate of the total fractional white area $A$ roughly gives the velocity $D$ of a compressive-wave-series. When a velocity $D$ is mentioned, the corresponding threshold contour-level of the state variable, like the temperature, should also be stated. When the threshold contour-level increases, $D$ becomes smaller. The area $A$ increases parabolically with time $t$ during the initial period. The $A(t)$ curve goes back to be linear in the following three cases: (i) when the porosity $delta$ approaches 1, (ii) when the initial shock becomes stronger, (iii) when the contour-level approaches the minimum value of the state variable. The area with high-temperature may continue to increase even after the early compressive-waves have arrived at the downstream free surface and some rarefactive-waves have come back into the target body. In the case of energetic material ... (see the full text)
The existence of a very special ratcheting regime has recently been reported in a granular packing subjected to cyclic loading cite{alonso04}. In this state, the system accumulates a small permanent deformation after each cycle. After a short transient regime, the value of this permanent strain accumulation becomes independent on the number of cycles. We show that a characterization of the material response in this peculiar state is possible in terms of three simple macroscopic variables. They are defined that, they can be easily measured both in the experiments and in the simulations. We have carried out a thorough investigation of the micro- and macro-mechanical factors affecting these variables, by means of Molecular Dynamics simulations of a polydisperse disk packing, as a simple model system for granular material. Biaxial test boundary conditions with a periodically cycling load were implemented. The effect on the plastic response of the confining pressure, the deviatoric stress and the number of cycles has been investigated. The stiffness of the contacts and friction has been shown to play an important role in the overall response of the system. Specially elucidating is the influence of the particular hysteretical behavior in the stress-strain space on the accumulation of permanent strain and the energy dissipation.
High-spatial-resolution secondary ion mass spectrometry offers a method for mapping lithium at nanoscale lateral resolution. Practical implementation of this technique offers significant potential for revealing the distribution of Li in many materials with exceptional lateral resolution and elemental sensitivity. Here, two state-of-the-art methods are demonstrated on an aluminium-lithium alloy to visualise nanoscale Li-rich phases by mapping the 7Li+ secondary ion. NanoSIMS 50L analysis with a radio frequency O- plasma ion source enabled visualisation of needle-shaped T1 (Al2CuLi) phases as small as 75 nm in width. A compact time-of-flight secondary ion mass spectrometry detector added to a focused ion beam scanning electron microscope facilitated mapping of the T1 phases down to 45 nm in width using a Ga+ ion beam. Correlation with high resolution electron microscopy confirms the identification of T1 precipitates, their sizes and distribution observed during SIMS mapping.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
