Sintered electrically conductive oxide for oxygen sensor electrode, and oxygen sensor using the same
A sintered electrically conductive oxide for an oxygen sensor electrode includes a crystal phase formed of a perovskite-type electrically conductive oxide containing at least La, Fe and Ni. The oxide has an absolute value of thermoelectromotive force at 770° C. of 21.0 μV/K or less.
1. 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):
La a Co b Fe c Ni d O x (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.
2. The oxygen sensor as claimed in claim 1 , wherein, in formula (1):
0.474≤ a< 0.512.
3. The oxygen sensor as claimed in claim 1 , wherein the sintered electrically conductive oxide contains substantially no alkaline earth metal elements.
4. The oxygen sensor as claimed in claim 1 , wherein the external electrode is configured for contact with the gas to be measured, and the reference electrode is configured for contact with a gas serving as a reference for detecting the oxygen concentration of the gas to be measured.
5. The oxygen sensor as claimed in claim 1 , wherein the reference electrode has a length in the longitudinal direction from 1 cm to 10 cm.
6. The oxygen sensor as claimed in claim 1 , wherein the substrate is formed of zirconia doped with yttria.
7. The oxygen sensor as claimed in claim 1 , wherein the crystal phase formed of the perovskite-type electrically conductive oxide has the crystal structure expressed by following formula (2):
La a Fe c Ni d O x (2),
wherein, in formula (2):
a+c+d= 1,
1.25≤ x≤ 1.75,
0.474≤ a≤ 0.512,
0< c≤ 0.300,and
0.200≤ d≤ 0.350.
8. The oxygen sensor as claimed in claim 1 , wherein a and b satisfy
0.474≤ a< 0.512, and
0≤ b< 0.100.
9. The oxygen sensor as claimed in claim 1 , wherein b satisfies
0< b< 0.100.