Dislocations as line defects in crystalline solids play a crucial role in controlling the mechanical and functional properties of materials. Yet, for functional ceramic oxides, it is very difficult to introduce dense dislocations because of the strong chemical bonds. In this work, the introduction of high-density dislocations is demonstrated by ultrahigh-pressure sintering into a typical ceramic oxide, BiCuSeO, for thermoelectric applications. The ultrahigh-pressure induces shear stresses that surpass the critical strength for dislocation nucleation, followed by dislocation glide and profuse multiplication, leading to a high dislocation density of ≈9.1 × 10 16 m −2 in Bi 0.96 Pb 0.04 CuSeO ceramic. These dislocations greatly suppress the phonon transport to reduce the lattice thermal conductivity, reaching 0.13 Wm −1 K −1 at 767 K and resulting in a record-high zT of 1.69 in this oxide thermoelectric ceramic. This study demonstrates the feasibility of generating dense dislocations in ceramic oxides via ultrahigh-pressure sintering for tuning functional properties.
Fangming Liu,Jiawei Zhang,Pingping Liu,Qihuang Deng,Duanwei He
High pressure obviously decreased the sintering temperature of high melting point ceramics and produced bulks with excellent mechanical and thermal properties. In this study, the effect of pressure alone on the densification process of alumina ceramics was demonstrated. The translucent alumina bulks with unexpected hardness were obtained by compressing α-Al 2 O 3 powder under ultra-high pressure at room temperature. Through analyzing microstructure and hardness of cold compressed samples, the results reveal that ultra-high pressure could crush alumina grains under appropriate pressure, and initiate plastic deformation of grains when the applied pressure exceeds the yield strength of alumina. Thus to enhance the hardness of the samples by grain boundary strengthening and plastic deformation at higher pressure.
Fu Xianwei,Liu Yang,Liu Zhi,Dong Ning,Zhao Tianyu,Zhao Dan,Lian Gang,Wang Qilong,Cui Deliang
Although organic semiconductors have attracted extensive interest and been utilized to fabricate a variety of optoelectronic devices, their electrical transportation characteristics under high pressure have rarely been investigated. However, the weak intermolecular interaction of organic semiconductors endows them with a pressure-sensitive crystal structure and electrical transportation performance, especially the latter. Herein, a new pressure-sensitive transistor was fabricated from an organic semiconductor 1,1′-dibutyl-4,4′-bipyridinium diiodide. It was found that this transistor exhibited increasing resistance as the pressure gradually increased and that it eventually shut off under a pressure of 288 MPa. Such a characteristic makes this organic semiconductor a potential candidate for the use in the fabrication of pressure-sensitive switches and regulators. In addition, these results shed light on the electrical performance of flexible organic optoelectronic devices working under high pressure levels resulted from the bending force.
Yang Jiawei,Zeng Tong,Xu Huimin,Ni Yonghao,Huang Liulian,Chen Lihui,Hu Hui-Chao
This paper aims to improve the signal response in headspace (HS) analysis over than the GC analysis with a classical splitless injection mode, and this was achieved by the development of high-pressure headspace (HP-HS) analysis method. Based on the theoretical analysis on the sampling principle of HS, the HP-HS concept was proposed in section one, indicative of possibility to achieve excellent signal response. In the proposed HP-HS technology, the complete transfer of gas sample from HS to GC column is achieved in a very short purge-off time in the splitless injection of GC using the high-pressure carrier gas. The sampling size was increased by adopting high-pressure auxiliary gas. The dilution effect of venting process on detected substance was greatly reduced by controlling the terminal pressure of venting process at a high level. With the HP-HS analysis technology, the optimal equilibration temperature and signal response for analytes with high or medium volatility in ten common solvents was determined, and the results showed that the HP-HS-GC method can achieve very high signal response and very low solvent effect on GC. For aqueous samples, the signal response of HP-HS-GC can be up to three times than that of the splitless GC analysis. The present technology has a great potential, in particular, in high sensitivity analysis of complicated samples with serious substrate effect.
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