新文速递 - 9.1/9.8

晶格畸变诱导CsPbI3钙钛矿量子点中激子分裂和相干量子拍频

Halide perovskites feature highly dynamic lattices, but their impact on exciton fine structure remains unexplored. Here, the authors show that these lattices lead to a bright-exciton fine structure gap, enabling observation of quantum beats in a non-uniform ensemble.

Lattice distortion inducing exciton splitting and coherent quantum beating in CsPbI3 perovskite quantum dots

Anisotropic exchange splitting in semiconductor quantum dots results in bright-exciton fine-structure splitting important for quantum information processing. Direct measurement of fine-structure splitting usually requires single/few quantum dots at liquid-helium temperature because of its sensitivity to quantum dot size and shape, whereas measuring and controlling fine-structure splitting at an ensemble level seem to be impossible unless all the dots are made to be nearly identical. Here we report strong bright-exciton fine-structure splitting up to 1.6 meV in solution-processed CsPbI3 perovskite quantum dots, manifested as quantum beats in ensemble-level transient absorption at liquid-nitrogen to room temperature. The splitting is robust to quantum dot size and shape heterogeneity, and increases with decreasing temperature, pointing towards a mechanism associated with orthorhombic distortion of the perovskite lattice. Effective-mass-approximation calculations reveal an intrinsic ‘fine-structure gap’ that agrees well with the observed fine-structure splitting. This gap stems from an avoided crossing of bright excitons confined in orthorhombically distorted quantum dots that are bounded by the pseudocubic {100} family of planes.

Principle of FSS and sample information.

Yaoyao Han, Wenfei Liang, Xuyang Lin, Yulu Li, Fengke Sun, Fan Zhang, Peter C. Sercel & Kaifeng Wu doi: 10.1038/s41563-022-01349-4 Article

Linked News and Views: Locking exciton fine-structure splitting Gabriele Rainò & Maksym V. Kovalenko  doi: 10.1038/s41563-022-01372-5

低氧稀土钢

The variation in the properties of rare earth (RE) steels is shown to stem from the presence of oxygen-based inclusions, and only under very-low-oxygen conditions can RE elements perform a vital role in purifying, modifying and micro-alloying steels.

Low-oxygen rare earth steels

Rare earth (RE) addition to steels to produce RE steels has been widely applied when aiming to improve steel properties. However, RE steels have exhibited extremely variable mechanical performances, which has become a bottleneck in the past few decades for their production, utilization and related study. Here in this work, we discovered that the property variation of RE steels stems from the presence of oxygen-based inclusions. We proposed a dual low-oxygen technology, and keeping low levels of oxygen content in steel melts and particularly in the raw RE materials, which have long been ignored, to achieve impressively stable and favourable RE effects. The fatigue life is greatly improved by only parts-per-million-level RE addition, with a 40-fold improvement for the tension–compression fatigue life and a 40% enhancement of the rolling contact fatigue life. We find that RE appears to act by lowering the carbon diffusion rate and by retarding ferrite nucleation at the austenite grain boundaries. Our study reveals that only under very low-oxygen conditions can RE perform a vital role in purifying, modifying and micro-alloying steels, to improve the performance of RE steels.

The superior effects of RE addition on the tensile–compression and rolling contact fatigue lives of 52100 steels.

Dianzhong Li, Pei Wang, Xing-Qiu Chen, Paixian Fu, Yikun Luan, Xiaoqiang Hu, Hongwei Liu, Mingyue Sun, Yun Chen, Yanfei Cao, Leigang Zheng, Jinzhu Gao, Yangtao Zhou, Lei Zhang, Xiuliang Ma, Chunli Dai, Chaoyun Yang, Zhonghua Jiang, Yang Liu & Yiyi Li  doi: 10.1038/s41563-022-01352-9 Article

石榴石固体电解质的多晶形及其对晶粒尺度化学力学性的影响

Understanding and mitigating filament formation, short-circuit and solid electrolyte fracture is necessary for advanced all-solid-state batteries. The effect of polymorphism on the grain-level chemo-mechanical behaviour of dense and polycrystalline garnet solid electrolytes is now investigated.

Polymorphism of garnet solid electrolytes and its implications for grain-level chemo-mechanics

Understanding and mitigating filament formation, short-circuit and solid electrolyte fracture is necessary for advanced all-solid-state batteries. Here, we employ a coupled far-field high-energy diffraction microscopy and tomography approach for assessing the chemo-mechanical behaviour for dense, polycrystalline garnet (Li7La3Zr2O12) solid electrolytes with grain-level resolution. In situ monitoring of grain-level stress responses reveals that the failure mechanism is stochastic and affected by local microstructural heterogeneity. Coupling high-energy X-ray diffraction and far-field high-energy diffraction microscopy measurements reveals the presence of phase heterogeneity that can alter local chemo-mechanics within the bulk solid electrolyte. These local regions are proposed to be regions with the presence of a cubic polymorph of LLZO, potentially arising from local dopant concentration variation. The coupled tomography and FF-HEDM experiments are combined with transport and mechanics modelling to illustrate the degradation of polycrystalline garnet solid electrolytes. The results showcase the pathways for processing high-performing solid-state batteries.

Mechanical response of a polycrystalline LLZO material.

Marm B. Dixit, Bairav S. Vishugopi, Wahid Zaman, Peter Kenesei, Jun-Sang Park, Jonathan Almer, Partha P. Mukherjee & Kelsey B. Hatzell  doi: 10.1038/s41563-022-01333-y Article

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