Breakthrough in Phase Transitions

Phase transition is the transformation between different forms of materials, which is the research focus in the field of materials science and of great value for study of material structure and properties. Through phase transition control, the microstructure of advanced functional materials can be fine-regulated, so as to achieve near-perfect performance. Recently, researchers from School of Materials Science and Engineering/Herbert Gleiter Institute of Nanoscinece in Nanjing University of Schence and Technology (NJUST) have made great breakthroughs in the frontier of phase transition field. Related research work are reported by Nature Photonics and Nature Materials in succession.


White LEDs, as the key component in lighting and display field, have attracted people’s wide attention. Recently, Zeng group from School of Materials Science and Engineering reported a CsPbI3 single emissive layer with both α and δ phases acting as unique emitter for perovskite white LEDs (Pe-WLEDs), which has just been published with title of "Efficient and bright white light-emitting diodes based on single-layer hetero-phase halide perovskites" on Nature Photonics. This material combines the superior electronic transport and red emission of α-CsPbI3 with the broad-white, self-trapped emission of δ-CsPbI3.


The efficient white electroluminescence originates from the superior charge injection into α phase, α-to-δ charge transfer, and α-δ balanced radiative recombination, so-called hetero-phase optics-electronics synergistic effect. Such effects at the α/δ-heterophase interface endows the Pe-WLED with relatively high efficiency and brightness: luminance of 12200 cd·m−2 and EQE of 6.5%. This work will have great impact on broad optoelectronic device fields and greatly decrease the cost and motivate the development of the next-generation lighting/display with flexibility and transparency features.


To reveal the evolution of structural units during the phase transition process of amorphous materials, Prof. Si Lan's group from the School of Materials Science and Engineering has reported a chiral medium-range order building block which can link the amorphous and crystalline states, published in the latest issue of Nature Materials with the title of "A medium-range structure motif linking amorphous and crystalline state". The NJUST is the first correspondingaffiliation, and Prof. Si Lan is the first and co-corresponding author of the paper. Prof. Xun-Li Wang of the City University of Hong Kong and senior physicist Prof. Yang Ren of Argonne National Laboratory are the co-corresponding authors.


What is the nature of the glassy state” is one of the frontier scientific problems in condensed matter physics. In order to solve the above scientific problem, one needs to know whether there are structural building blocks of certain spatial length scale in amorphous matters, and how to pack to form a locally ordered but long-range disordered amorphous structure. In this work, a metastable phase with a layered periodic cubic structure was captured in a classical Pd-Ni-P bulk metallic glass system. A chiral six-membered tricapped trigonal prism cluster (named 6M-TTP) with a length scale of 12.5 Å, which exists in both the cubic phase and the amorphous matrix, was revealed in Pd-Ni-P bulk metallic glasses by a suite of advanced structural characterization techniques.


Prof. Lin Gu, professor of the Institute of Physics of the Chinese Academy of Sciences, Dr. Zhenduo Wu, professor of the City University of Hong Kong Dongguan Research Institute, and Mr. Li Zhu, Ph.D student of Nanjing University of Aeronautics and Astronautics, are the co-first-authors of this paper. The other co-authors involved in this work from NJUSTare Prof. Wei Liu, Prof. Huihui Kong, Prof. Jizi Liu, Ph.D student from Prof. Lan’s group Mr. Sinan Liu and Prof. Gang Sha.


This work is supported by the National Natural Science Foundation of China, the Outstanding Youth Fund of the Natural Science Foundation of Jiangsu Province, the Joint Laboratory of Guangdong, Hong Kong and Macao, the Hong Kong Croucher Foundation, the Hong Kong Research Foundation, and the Fundamental Research Funds for the Central Universities.



Figure a. A team photo of Zeng group and Lan group. b. Structure and performance of white LED device. c. The direct experimental evidence revealing the medium-range ordered structure motif linking the amorphous and the crystalline states


Links

J.W. Chen#, J. Wang#, X.B. Xu*, J.H. Li, J.Z. Song*, S. Lan, S.N. Liu, B. Cai, B.N. Han, J.T. Precht, D. Ginger*, H.B. Zeng*. Efficient and bright white light-emitting diodes based on single-layer heterophase halide perovskites. Nat. Photonics 15, 238244 (2021).

DOI: 10.1038/s41566-020-00743-1.

(https://www.nature.com/articles/s41566-020-00743-1)


S.Lan*#, L. Zhu#, Z.D. Wu#, L. Gu#, Q.H. Zhang, H.H. Kong, J.Z. Liu, R.Y. Song, S.N. Liu, G. Sha, Y.G. Wang, Q. Liu, W. Liu, P.Y. Wang, C.-T. Liu, Y. Ren*, X.-L. Wang*, A medium-range structure motif linking amorphous and crystalline states, Nature Materials. 2021.

DOI: 10.1038/s41563-021-01011-5.

(https://www.nature.com/articles/s41563-021-01011-5)