Presence of Delocalized Ti 3d Electrons in Ultrathin Single-Crystal SrTiO3.

Strontium titanate (STO), with a wide spectrum of emergent properties such as ferroelectricity and superconductivity, has received significant attention in the community of strongly correlated materials. In the strain-free STO film grown on the SrRuO3 buffer layer, the existing polar nanoregions can facilitate room-temperature ferroelectricity when the STO film thickness approaches 10 nm. Here we show that around this thickness scale, the freestanding STO films without the influence of a substrate show the tetragonal structure at room temperature, contrasting with the cubic structure seen in bulk form. The spectroscopic measurements reveal the modified Ti-O orbital hybridization that causes the Ti ion to deviate from its nominal 4+ valency (3d0 configuration) with excess delocalized 3d electrons. Additionally, the Ti ion in TiO6 octahedron exhibits an off-center displacement. The inherent symmetry lowering in ultrathin freestanding films offers an alternative way to achieve tunable electronic structures that are of paramount importance for future technological applications.

2D Janus Polarization Functioned by Mechanical Force.

2D polarization materials have emerged as promising candidates for meeting the demands of device miniaturization, attributed to their unique electronic configurations and transport characteristics. Although the existing inherent and sliding mechanisms are increasingly investigated in recent years, strategies for inducing 2D polarization with innovative mechanisms remain rare. This study introduces a novel 2D Janus state by modulating the puckered structure. Combining scanning probe microscopy, transmission electron microscopy, and density functional theory calculations, this work realizes force-triggered out-of-plane and in-plane dipoles with distorted smaller warping in GeSe. The Janus state is preserved after removing the external mechanical perturbation, which could be switched by modulating the sliding direction. This work offers a versatile method to break the space inversion symmetry in a 2D system to trigger polarization in the atomic scale, which may open an innovative insight into configuring novel 2D polarization materials.

Efficient degradation of micropollutants in CoCaAl-LDO/peracetic acid (PAA) system: An organic radical dominant degradation process.

As a novel strategy, peracetic acid (PAA) based advanced oxidation processes (AOPs) are being used in micropollutant elimination due to their high oxidation and low toxicity. In this study, Co2Ca1Al1-LDO as a kind of layered double oxides (LDOs) was successfully synthesized, and it is the first time to apply Co2Ca1Al1-LDO for activating PAA. The Co2Ca1Al1-LDO/PAA system showed excellent removal efficiencies for various micropollutants with removal ratios ranging from 90.4% to 100% and k values from 0.087 min-1 to 0.298 min-1. In the degradation period, various reactive oxygen species (ROS) are involved in the system, while organic radicals (R-O•) with a high concentration of 5.52 × 10-13 M are the dominant ROS in the contaminants degradation process. Compared to other ROS, R-O• had the largest contribution ratio (more than 85%) to pollutant degradation. Further analysis demonstrated that C1, C2, C3, C4, C5, C6 and N11 concentrated on the aniline group of SMX are the main attack sites based on the density functional theory (DFT) results, which is consistent with the degradation products. The toxicity of contaminants was obviously reduced after removing in this system. Furthermore, Co2Ca1Al1-LDO showed good reusability and stability, and Co2Ca1Al1-LDO/PAA system had excellent removal ability in actual water bodies containing inorganic anions, showing good application potential. Importantly, this study explored the feasibility of applying LDO catalysts in PAA-based AOPs for micropollutants elimination, providing new insights for subsequent research.

Antiferroelectric PbSnO3 Epitaxial Thin Films.

In condensed matter physics, oxide materials show various intriguing physical properties. Therefore, many efforts are made in this field to develop functional oxides. Due to the excellent potential for tin-based perovskite oxides, an expansion of new related functional compounds is crucial. This work uses a heteroepitaxial approach supported by theoretical calculation to stabilize PbSnO3 thin films with different orientations. The analyses of X-ray diffraction and transmission electron microscopy unveil the structural information. A typical antiferroelectric feature with double hysteresis and butterfly loops is observed through electrical characterizations consistent with the theoretical prediction. The phase transition is monitored, and the transition temperatures are determined based on temperature-dependent structural and electrical characterizations. Furthermore, the microscopic antiferroelectric order is noticed under atomic resolution images via scanning transmission electron microscopy. This work offers a breakthrough in synthesizing epitaxial PbSnO3 thin films and comprehensively understanding its anisotropic antiferroelectric behavior.

Electronic metal-support interaction modulates single-atom platinum catalysis for hydrogen evolution reaction.

Tuning metal-support interaction has been considered as an effective approach to modulate the electronic structure and catalytic activity of supported metal catalysts. At the atomic level, the understanding of the structure-activity relationship still remains obscure in heterogeneous catalysis, such as the conversion of water (alkaline) or hydronium ions (acid) to hydrogen (hydrogen evolution reaction, HER). Here, we reveal that the fine control over the oxidation states of single-atom Pt catalysts through electronic metal-support interaction significantly modulates the catalytic activities in either acidic or alkaline HER. Combined with detailed spectroscopic and electrochemical characterizations, the structure-activity relationship is established by correlating the acidic/alkaline HER activity with the average oxidation state of single-atom Pt and the Pt-H/Pt-OH interaction. This study sheds light on the atomic-level mechanistic understanding of acidic and alkaline HER, and further provides guidelines for the rational design of high-performance single-atom catalysts.