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Scientists at Tokyo Institute of Technology and collaborators have shown the overbonding of channel oxygens in La-rich apatite-type lanthanum silicates, rather than the presence of the interstitial oxygens, to be responsible for the high oxide-ion conductivity. This concept of "high oxide-ion conductivity by overbonding" opens the door for designing better ion conductors, which could be useful in energy conversion and environmental protection.
Solid oxide electrolytes have been extensively studied due to their wide range of applications in solid oxide fuel cells (SOFCs), oxygen membranes, catalysts, and gas sensors. Electrolytes with high oxide-ion conductivity at temperatures below 600 degrees C are required to decrease the operation temperature of SOFCs. Professor Susumu Nakayama at National Institute of Technology, Niihama College has discovered in 1995 the extremely high oxide-ion conductivity in the intermediate temperature range below 600°C, which has encouraged many researchers to study the structural origin of this phenomenon.
Oxide-ion - Conductivity - Materials - Oxygens - Novel
It was believed that the high oxide-ion conductivity of apatite-type materials is due to interstitial oxygens. However, in this novel study, Professor Masatomo Yashima, Dr. Kotaro Fujii at Tokyo Institute of Technology (Tokyo Tech), and their colleagues have shown that apatite-type materials contain Si vacancies, but not oxygen interstitials. The Si vacancies in the materials have originally been proposed by Professor Koichiro Fukuda at Nagoya Institute of Technology.
Through single-crystal neutron diffraction studies using the SENJU diffractometer installed at MLF, J-PARC facility (Figure 1), they were able to accurately determine the crystal structures of the apatite materials La9.333Si6O26 and La-rich...
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