The development of novel trivalent ion conducting solids and their application for gas sensors

An exceptionally high Al³⁺ ion conducting polycrystalline solid based on the NASICON type structure was successfully realized within the system (Al_xZr_1−x)_4/(4−x)Nb(PO₄)₃. The partial substitution of the smaller higher valent Nb⁵⁺ ion for Zr⁴⁺ helped stabilize and accommodate the mobile Al³⁺ ion into the NASICON like structure. The addition of boron oxide to the Al³⁺ ion conducting solid electrolyte, as a sintering additive, aided in the achievement of satisfactory mechanical strength and density for practical use. Environmental gas sensors were fabricated by combining the (Al_xZr_1−x)_4/(4−x)Nb(PO₄)₃ solid electrolyte with yttria stabilized zirconia (YSZ) and appropriate auxiliary electrodes. The Nernst-like electrochemical sensors demonstrated rapid and reproducible response to CO₂ and NOx, thereby promising excellent potential for environmental monitoring applications.