Defect physics of intrinsic point defects in BiPO4 photocatalysts: a hybrid functional study

In this work, the intrinsic point defect properties of bulk BiPO4 under different growth conditions are intensively investigated and explored using first-principles hybrid functional calculations. It is found that Bi vacancies and O vacancies are the primary native defects in BiPO4. Under O-poor conditions, BiPO4 acts as an intrinsic insulator because the O vacancy defects (donor) and the Bi vacancy defects (acceptor) compensate for each other. Under Bi-poor conditions, good p-type conductivity is observed in BiPO4, which affirms the observed p-type conductivity behavior in experiments. Bi vacancies in BiPO4 are very shallow, which make it an excellent acceptor and are mostly responsible for the p-type character. In addition, it is found that the primary Bi vacancy defects of BiPO4 hardly affect its electronic structure and optical absorption spectrum regardless of the charge states. In contrast, the neutral O vacancy defects in BiPO4 introduce an impurity energy level near the VBM and induce a new optical absorption peak at around 370 nm. Furthermore, the O vacancies should be favorable for enhancing the production and separation efficiencies of the photo-generated electrons and holes in BiPO4. While Bi vacancies easily provide p-type carriers, simultaneously, they could become the active sites for the photocatalytic reactions because of their dominant -3 charge state. Therefore, understanding the defect physics in BiPO4 photocatalysts is believed to be beneficial for more research in developing BiPO4 or BiPO4-based photocatalysts.

Pressure-Induced Structural Phase Transition and Metallization of CrCl3 under Different Hydrostatic Environments up to 50.0 GPa

High-pressure structural, vibrational, and electrical transport properties of CrCl₃ were investigated by means of Raman spectroscopy, electrical conductivity, and high-resolution transmission electron microscopy under different hydrostatic environments using the diamond anvil cell in conjunction with the first-principles theoretical calculations up to 50.0 GPa. The isostructural phase transition of CrCl₃ occurred at 9.9 GPa under nonhydrostatic conditions. As pressure was increased up to 29.8 GPa, CrCl₃ underwent an electronic topological transition accompanied by a metallization transformation due to the discontinuities in the Raman scattering and electrical conductivity, which is possibly belonging to a typical first-order metallization phase transition as deduced from first-principles theoretical calculations. As for the hydrostatic condition, a ∼2.0 GPa pressure delay in the occurrence of two corresponding transformations of CrCl₃ was observed owing to the different deviatoric stress. Upon decompression, we found that the phase transformation from the metal to semiconductor in CrCl₃ is of good reversibility, and the obvious pressure hysteresis effect is observed under different hydrostatic environments. All of the obtained results on the structural, vibrational, and electrical transport characterizations of CrCl₃ under high pressure can provide a new insight into the high-pressure behaviors of representative chromium trihalides CrX₃ (X = Br and I) under different hydrostatic environments.

The Zintl phases compound AEIn2As2 (AE=Ca, Sr, Ba): topological phase transition under pressure

AEIn2As2 (AE=Ca, Sr, Ba), as a new crucial nonmagnetic thermoelectric candidate, is desired to be understood in terms of its potential physical properties and controversial structural phases in both experimental...

Degradation of formaldehyde aqueous solution by Bi based catalyst and its activity evaluation

Bi based catalysts have attracted continuous attention from the scientific community because of their excellent photochemical properties and wide application in photocatalytic treatment of environmental pollution. A series of Bi based catalysts with good crystallinity and high purity were prepared by calcination and hydrothermal synthesis. In the application of degrading formaldehyde aqueous solution in a mercury lamp and xenon lamp atmosphere, it was found that BiVO₄ and Bi₂WO₆ showed excellent photochemical properties under ultraviolet and visible light. The tests of PL, UV-Vis and EIS confirmed their high activity. In the calculation based on density functional theory (DFT), through the analysis of the energy band structure, density of states (DOS) and partial wave density of states (PDOS), it is found that the d orbital of V and W elements has a great influence on the position and size of the energy band of the catalyst, which makes it have high activity and excellent electrochemical properties.

Bi based catalysts have attracted continuous attention from the scientific community because of their excellent photochemical properties and wide application in photocatalytic treatment of environmental pollution.

Unraveling High-Yield Phase-Transition Dynamics in Transition Metal Dichalcogenides on Metallic Substrates

2D transition metal dichalcogenides (2D-TMDs) and their unique polymorphic features such as the semiconducting 1H and quasi-metallic 1T' phases exhibit intriguing optical and electronic properties, which can be used in novel electronic and photonic device applications. With the favorable quasi-metallic nature of 1T'-phase 2D-TMDs, the 1H-to-1T' phase engineering processes are an immensely vital discipline exploited for novel device applications. Here, a high-yield 1H-to-1T' phase transition of monolayer-MoS2 on Cu and monolayer-WSe2 on Au via an annealing-based process is reported. A comprehensive experimental and first-principles study is performed to unravel the underlying mechanism and derive the general trends for the high-yield phase transition process of 2D-TMDs on metallic substrates. While each 2D-TMD possesses different intrinsic 1H-1T' energy barriers, the option of metallic substrates with higher chemical reactivity plays a significantly pivotal role in enhancing the 1H-1T' phase transition yield. The yield increase is achieved via the enhancement of the interfacial hybridizations by the means of increased interfacial binding energy, larger charge transfer, shorter interfacial spacing, and weaker bond strength. Fundamentally, this study opens up the field of 2D-TMD/metal-like systems to further scientific investigation and research, thereby creating new possibilities for 2D-TMDs-based device applications.