A high temperature (700 degrees C) lithium ion-based CO2 sensor was fabricated using Li2CO3-BaCO3 binary carbonate and SiO2:B2O3:P2O5 (1:2:1 mol%) amorphous glassy ceramic oxide as sensing electrode. The sensor works efficiently at 700 degrees C without any degradation of the sensing material. The electro motive force (EMF) of the sensor is very stable and follows perfect Nernstian behavior with the logarithm of CO2 concentration in the range 500-5000 ppm. It is revealed that Li2Si2O5, Ba-3(PO4)(2) and quartz were formed at high temperatures (500-700 degrees C) due to the reaction of Li2CO3 and BaCO3 with glassy ceramic oxide. The time taken by the sensor to reach a change in 90% CO2 is 10 s. The sensor does not show significant cross-sensitivity to the interfering gases like NO2 and SO2 at 500 degrees C. TG-DTA, XRD, SEM and FT-IR studies were employed to characterize and suggest a probable mechanism. The increase in EMF of the sensor may be due to the easier movement of Lithium ion in to the glass in the sensing electrode. (C) 2008 Elsevier B.V. All rights reserved.