Chen Chunhua

Study on SnO2-Fe2O3 gas-sensing system by a.c. impedance technique

Abstract A.c. complex impedance measurement has been used in a mixed system of tin oxide and iron oxide in an attempt to obtain more information about the gas-sensitive mechanism of semiconducting metallic oxide gas sensors. The impedance spectra in air, liquid petroleum gas (LPG) and acetylene have been obtained for the thick-film elements at different temperatures. A simple equivalent circuit, which contains the contributions from grain bulks and grain boundaries, is proposed to account for the spectra. The results show that both the grain bulks and grain boundaries of tin oxide (doped with a small amount of antimony oxide) are responsible for the reducing-gas sensitivities. For the iron oxide sample, the grain-boundary resistance is dominant in the total resistance and its change in various atmospheres is the main origin of the sensitivity to reducing gases. For the mixed system, the role of grain boundaries is also found to be more important than that of grain bulks. Some structural analyses and direct-current (d.c.) measurement have also been performed. This preliminary study indicates that a.c. complex impedance measurement might be a powerful tool in studying chemical sensors.

Research progress in ternary cathode materials Li(Ni,Co,Mn)O 2 for lithium ion batteries

As the most promising commercial lithium-ion battery, the ternary transition metal oxides Li(Ni,Co,Mn)O2 have been widespread concerned by researchers and companies in recent years. They are expected to become a series of major cathode active material for EV batteries. The latest research progress on Li(Ni,Co,Mn)O2 is reviewed in terms of synthetic methods, property modifications and suitable electrolyte functional additives. Finally, its commercial application prospects are discussed and evaluated.As the most promising commercial lithium-ion battery, the ternary transition metal oxides Li(Ni,Co,Mn)O 2 have been widespread concerned by researchers and companies in recent years. They are expected to become a series of major cathode active material for EV batteries. The latest research progress on Li(Ni,Co,Mn)O 2 is reviewed in terms of synthetic methods, property modifications and suitable electrolyte functional additives. Finally, its commercial application prospects are discussed and evaluated.

Gas sensitivity of SnO2 doped with YBa2Cu3O7−x

Abstract This paper describes the sensitivities of tin oxide thick-film elements doped with the recently discovered high- T c superconductor YBa 2 Cu 3 O 7− x (YBCO) to some reducing gases (carbon monoxide, hydrogen and acetylene). Orthorhombic YBCO is prepared by a dry process. The sensitivities of several elements with different YBCO contents and sintered at different temperatures are measured. Some structural analyses (XRD, SEM and EPR) have also been performed. The results show that YBCO actually acts as an additive and can prohibit the growth of tin oxide grains during sintering, thus enhancing the chemisorption of oxygen on the tin oxide surface. The addition of YBCO with a content less than 10 wt.% can increase the gas sensitivity of the elements and the optimal sintering temperature is around 600 °C. The unusual response to a high concentration of acetylene might imply a different operation mechanism.