Microstructure, Conductivity, and NO ₂ Sensing Characteristics of α‐Al ₂ O ₃ ‐Doped (8 mol% Sc ₂ O ₃ )ZrO ₂ Composite Solid Electrolyte

α‐Al ₂ O ₃ ‐doped (8 mol % Sc ₂ O ₃ )ZrO ₂ composite solid electrolyte has been investigated in the fabrication of solid‐state ceramic gas sensors. The microstructure and electrical conductivity of the composite solid electrolyte have been measured over a range of temperature from 240°C to 596°C. The composite solid electrolyte has been found to exhibit a higher conductivity compared with the commonly used (8 mol% Y ₂ O ₃ )ZrO ₂ at temperatures above ∼448°C. The sensing characteristics for NO ₂ detection have been studied in the temperature range of 500–650°C at the low concentration from 10 to 30 ppm and at high concentration from 100 to 500 ppm of NO ₂ . The NO ₂ sensor was found to respond reproducibly and rapidly to the variations of NO ₂ , concentration, indicating that the composite solid electrolyte has promising application as a solid electrolyte for on‐board exhaust gas monitoring.