Shanghai silicate conductive ceramic research progress
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Recently, Li Guorong, a research fellow at the Shanghai Institute of Ceramics, Chinese Academy of Sciences, has made new progress in the research of ZnO conductive ceramics. The team successfully eliminated the Schottky barrier at the grain boundary of ZnO through grain and grain boundary defect design methods, and fabricated a highly conductive ZnO ceramic with conductivity as high as 1.9×105 Sm-1 at room temperature. The defect design also reduces the lattice thermal conductivity of the material, making the ceramic exhibit good high-temperature thermoelectric properties. Its power factor at 980 K has reached 8.2×10-4 W m-1 K-2, which is better than ZnO without defects. Ceramics increased 55 times. The study was published in Acta Materialia (2016, 119: 136-144). The paper was highly evaluated by the reviewers of the journal. The reviewers thought that the results have important implications for the regulation of the grain boundary barrier and conductance of ZnO.
ZnO has the advantages of abundant source, low price, no pollution and good chemical stability, and has wide application prospects in the fields of optoelectronics, piezoelectrics, pressure-sensitive and thermoelectric. Trivalent donor doping is often used to improve the conductivity of ZnO materials, but due to the limited solid solubility of trivalent elements such as Al3+ in ZnO, the conductivity cannot be greatly improved; at the same time, ZnO ceramics have their intrinsic defects. The grain boundary Schottky barrier also further reduces its conductivity. Therefore, improving the grain resistance and eliminating the grain boundary Schottky barrier is a difficult problem in the research field of ZnO conductive and thermoelectric materials.
The research team conducted an innovative exploration in the preparation of high-conductivity ZnO ceramics and the regulation of the grain boundary barriers: Through sintering in a reducing atmosphere, the acceptor defects at the grain boundaries of ZnO were successfully eliminated, and their grain boundaries were eliminated. At the same time, the reducing atmosphere sintering also improves the solid solubility of the trivalent donor doping elements in the ZnO grains, and the carrier concentration and mobility of the materials are greatly improved. In this study, high-resolution transmission electron microscopy (HRTEM), cathodoluminescence (CL) emission spectroscopy, and electron backscatter diffraction (EBSD) were used to further confirm the distribution of crystal grain boundary defects after acceptor doping. Miscellaneous impurities are introduced into the grains of ZnO ceramics, which can reduce the lattice thermal conductivity of ZnO at the same time. It has successfully achieved its own regulation of electrical and thermal properties, and has a good application prospect in conductive and thermoelectric ceramics.
At present, related research work on high-conductivity ZnO ceramics has applied for two national invention patents. In addition, the team also established a structure-performance model, which provides a good basis for research on the grain boundary barrier and electrical properties of ZnO ceramics.
Relevant research work has been funded by the National "863" Project (2013AA030801) and the International Science and Technology Cooperation Project (2013DFG51570) of the Ministry of Science and Technology.
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