Interfacial structure of NASICON-based sensor attached with Li2CO3-CaCO3 auxiliary phase for detection of CO2

Potentiometric devices combining NASICON (Na+ conductor, Na3Zr2Si2PO12) wit h a series of Li2CO3-CaCO3 auxiliary phases were investigated for CO2 sensi ng properties as well as hetero-junction structure involved. It was reveale d that an addition of proper amount of CaCO3 to Li2CO3 auxiliary phase was effective for improving CO2 sensing capability at lower temperatures; Li2CO 3-CaCO3 (1:2) allowed normal operation down to 350 degreesC, while Li2CO3 d id down to 400 degreesC. The analysis of fractured surfaces by means of an electron-probe micro-analyzer (EPMA) and SEM indicated the formation of an interfacial layer between NASICON and carbonates, the thickness and structu re of which depended on the carbonate composition used. As revealed by X-ra y diffraction analysis, CaZrO3 was formed between NASICON and Li2CO3-CaCO3 (1:2), suggesting its relevance to the lower temperature sensing capability . (C) 2000 Elsevier Science B.V. All rights reserved.