Development of Neutron Radiography Technique to Visuslize Lithium Ions in Solod Electrolytes

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(1) An electric heater using IR beam was installed in the NR facility of Kyoto University Reactor for in-situ measurements of Li^+ movement in solid electrolytes under high temperature. The performance of the heater and its influence to the facility were experimentally evaluated using some simulated samples(ceramic materials wet with water).(2) Neutron radiography was used to study the transfer of lithium ions in the high temperature-type ionic conductor, Li_<1.33>Ti_<1.67>O_4. After dc current was passed for electrolysis through specially prepared xides with different isotope ratios(^6Li/^7Li), a set of NR images was obtained, which confirmed the lithium ion conduction in the oxides. Analysis of the imagesclarified that the lithium ion transport number of the oxide is almost equal to 1.0 and that lithium ions in the Li_<1.33>Ti_<1.67>O_4 were transferred almost reversibly according to the polarity of the electric field applied.(3) Cold neutron radiography was applied to study the lithium ion conduction in the substituted scheelite-type oxide of Ca_<0.95>Li_<0.10>WO_4. The lithium ion distribution profile were obtained from a set of neutron radiography images of the electrolyzed oxides having different ^6Li/^7Li ratios. They showed that the lithium ion transport number of the oxide is 0.99, which coincided with the result of electrochemical measurements. Furthermore, they denoted that only a half of all lithium ions in Ca_<0.95>Li_<0.10>WO_4 can move with charge transfer, but another half stays at the calcium sites. Therefore, it can be considered that the lithium ion conduction would be due to the 50% of the interstitial lithium ions.(4) It was confirmed that the combination of cold neutron radiography and an imaging plate was effective to improve the accuracy of the technique to measure Li^+ in the oxides.