Sintered electrically conductive oxide for oxygen sensor electrode, and oxygen sensor using the same

An oxygen sensor for measuring a concentration of a gas to be measured, the oxygen sensor comprising:

• a closed-bottomed tubular substrate formed of ceramic and extending in a longitudinal direction;
• an external electrode formed of a noble metal and disposed on an outer surface of the substrate;
• and
• a reference electrode disposed on an inner surface of the substrate,
• wherein
• the reference electrode is an electrically conductive layer formed of a sintered electrically conductive oxide,
• the sintered electrically conductive oxide comprises a crystal phase formed of a perovskite-type electrically conductive oxide having a crystal structure expressed by following formula (1):
• LaaCobFecNidOx (1),
• wherein, in formula (1):
• a+b+c+d=1,
• 1.25≤x≤1.75,
• 0.474≤a≤0.512,
• 0≤b≤0.225,
• 0<c≤0.300,and
• 0.2005≤d≤50.350;
• and
• the sintered electrically conductive oxide has an absolute value of thermoelectromotive force at 770° C. of 21.0 μV/K or less.