Scientists have discovered dozens of two-dimensional layered plastic inorganic non-metallic materials

Inorganic non-metallic materials with room temperature plastic deformation ability integrate the mechanical properties of metals and the electrical properties of semiconductors, which greatly expands the application functions and application scenarios of existing materials and becomes a new class of material systems. However, at present, the types of plastic inorganic non-metallic materials are rare, limited to Ag2S, InSe single crystal and some derivatives, and it has become a major challenge to find more new materials with plastic deformation ability.

Recently, researcher Shi Xun, researcher Qiu Pengfei and Chen Lidong of Shanghai Institute of Ceramics, Chinese Academy of Sciences, and associate professor Wei Natural of Shanghai Jiao Tong University cooperated to propose plastic screening indicators for two-dimensional layered materials, design and develop high-throughput algorithms and processes, predict and discover 36 two-dimensional layered plastic inorganic non-metallic materials, and experimentally verify that 7 materials such as MoS2, GaSe and SnSe2 have plastic deformation characteristics, of which the thermoelectric power factor of SnSe2 reaches 10.8 μWm-1K-2, is the highest value of plastic thermoelectric materials at present. The findings were published in Nature Communications and Advanced Science.

Based on the structural characteristics of two-dimensional layered materials, it is proposed that “interlayer cleavage energy ×cross-layer cleavage energy/interlayer slip energy barrier” can be used as plastic screening index factors of two-dimensional layered materials, and an efficient calculation method for each parameter is developed, and a high-throughput automated screening process is designed and developed (Figure 1, Figure 2a), and 36 two-dimensional layered materials may have plastic deformation ability from 3451 binary chalcogenide compounds in ICSD database (Figure 2b). The research team selected 13 materials for preliminary experimental characterization, and found that the theoretical prediction of 7 plastic single crystal materials InSe, GaSe, GaS, SnSe2, SnS2, MoS2 and MoTe2 can withstand 20% strain without rupture under three-point bending, while 6 brittle single crystal materials Bi2Te3, Sb2Te, NiTe2, etc. fracture when bending (Figure 2c), and the experimental results are consistent with the theoretical prediction. Furthermore, the two-dimensional material MoS2 was selected for fine mechanical characterization, and it was found that the single crystal could withstand 6% tensile strain and 50% compressive strain, showing good plastic deformation ability. Based on the fine mechanical characterization of other two-dimensional materials such as GaSe and SnSe2, it is found that layered materials first undergo interlayer slip when plastic deformation occurs, and cross-layer slip occurs after increasing stress, showing strong anisotropy. The possible slip surfaces and slip systems of interlayer and cross-layer slip were theoretically calculated, and the evolution of chemical bonds of the slip surface during the slip process was analyzed, and it was found that whether it was interlayer or cross-layer slip, the continuous fracture and formation of chemical bonds in the crystal was the core of excellent plasticity, and this chemical bond characteristic made the slip surface always have strong interaction during the slip process, thereby inhibiting cleavage fracture and ensuring the integrity of the material during plastic deformation.

Figure 1. High-throughput screening process for two-dimensional layered plastic inorganic non-metallic materials

Figure 2. (a) Plastic deformation and decomposition fracture modes of two-dimensional layered materials; (b) High-throughput screening results for binary chalcogenides; (c) Curved photographs of 7 plastic materials and 6 brittle materials

The results of the relevant research were published in Nature Communications (2022, 13:7491) with the title “High-throughput screening of 2D van der Waals crystals with plastic deformability”, with Gao Zhiqiang, a doctoral student at the Shanghai Institute of Ceramics/ShanghaiTech University, as the first author of the paper. Associate Professor Wei of Shanghai Jiaotong University is the co-corresponding author.

Among them, the SnSe2 single crystal with hexagonal structure can reach 20000 S m-1 at 375 K after doping with halogen group elements, which is two orders of magnitude higher than the matrix, and the power factor is up to 10.8 μWm-1K-2, which is the highest value of plastic thermoelectric materials (Figure 3). The study was published in Advanced Science (2022, 9:29) under the title “Plastic/Ductile Bulk 2D van der Waals Single-Crystalline SnSe2 for Flexible Thermoelectrics”, Shanghai Institute of Ceramics/Deng Tingting, Postdoctoral Fellow, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, and Shanghai Institute of Ceramics/ Zhiqiang Gao, a doctoral student at ShanghaiTech University, is the co-first author, and researcher Shi Xun and researcher Pengfei Qiu are the corresponding authors.

Figure 3.Power factor and conductivity of plastic thermoelectric materials

The above work has expanded the types of plastic inorganic non-metallic materials to dozens of kinds, enriched the types and connotations of plastic inorganic non-metallic materials, and taken an important step in promoting the process of new applications of inorganic plastic materials. The research work was supported by the National Key Research and Development Program of China, the National Natural Science Foundation of China and the Shanghai Municipal Science and Technology Commission. (Source: Shanghai Institute of Ceramics, Chinese Academy of Sciences)

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