JP2948124B2 - Oxygen sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor used for detecting an oxygen concentration in a temperature range from room temperature to a high temperature of about 800.degree. It is used as an oxygen concentration detector for combustion control (lean burn) of combustion equipment such as engines and stoves.

[0002]

2. Description of the Related Art As a method of measuring or detecting an oxygen concentration, a semiconductor type and an electrolyte type are roughly classified according to materials.
The semiconductor type using a material such as TiO ₂ or SnO ₂ utilizes the fact that the electric conductivity of the entire oxide bulk changes depending on the oxygen concentration in the gas phase. The conductivity σ of an n-type TiO ₂ sintered element at 700 ° C. is proportional to PO ₂ ^-1/4 . The conductivity σ changes in a stepwise manner at the stoichiometric air-fuel ratio, and is used for controlling the air-fuel ratio of an automobile engine used at a high temperature.
SnO ₂ has attracted attention for monitoring the complete combustion of oil and gas stoves and for monitoring the combustion of water heaters and the like. In addition, materials such as Co _1-x Mg _x O are also of semiconductor type. However, the stoichiometric air-fuel ratio (the semiconductor type that changes stepwise at an oxygen concentration of 15% is useful for lean burn control and combustion control at an oxygen concentration of about 15%. Difficult to grasp and lacks quantitative ability.

On the other hand, the electrolyte type is classified into a solid electrolyte type and a solution electrolyte type depending on the type of the electrolyte. Further, it is classified into a current measurement type and a potential measurement type depending on whether the detection is made by battery current or by battery electromotive force. The solution electrolyte type is
It is generally called a galvanic cell type and is used near room temperature. Therefore, it is not applicable to high temperature oxygen sensors such as combustion equipment. At present, a zirconia-based solid electrolyte sensor is partially used as an oxygen sensor at around 800 ° C. or a lean burn sensor for an automobile engine. Zirconia-based oxides are chemically stable under a hydrocarbon gas or a reducing atmosphere and are high-oxide ion conductors, and are therefore used in a wide range of fields. Since it is a pure oxide ion conductor, the oxygen concentration can be accurately detected by the electromotive force of the concentration cell. However, in the electromotive force type, the potential change sharply changes at an oxygen concentration of 14.5%, which is the stoichiometric air-fuel ratio, and becomes flat in a lean burn region of a higher concentration.

[0004] The limiting current type is drawing attention as a sensor in the lean burn region. It is an electrochemical type using a cathode reaction, in which a constant voltage is applied between both electrodes sandwiching a solid electrolyte, and the current change is read. In a galvanic electrochemical sensor using a solution, a current corresponding to the concentration can be obtained by forming a diffusion layer of the test component on the electrode surface as in the case of polarography, but oxidizing in a solid electrolyte Since the substance ion concentration becomes constant, a current change with respect to the oxygen concentration in the gas phase is obtained by providing a structure in which a diffusion layer is formed in the oxygen in the gas phase on the electrode. The sensor output is linear with respect to the excess air ratio λ,
It has higher sensitivity than semiconductor type and can be used up to high air-fuel ratio. However, the operating temperature is high (700
C), and reducing the operating temperature is an issue.
An oxygen sensor that has a simple structure and operates at low temperature is desired. The electrodes of the solid electrolyte type sensor are hot (800
C.) for long-term stability.

[0005]

SUMMARY OF THE INVENTION As an oxygen concentration detector for detecting oxygen concentration in a living environment and controlling the combustion (lean burn) of combustion equipment such as an engine and a stove, it has high sensitivity, high reliability and small size. A simple and low-cost sensor is desired. Semiconductor and limiting current sensors using conventional oxides, including zirconia-based oxides, must be operated at high temperatures. Therefore, the test environment is 40
When the temperature is about 0 ° C. or less, a heater is required. Further, although the zirconia and platinum electrodes are stable for a long period of time, there is a problem that the interface resistance between the zirconia and platinum electrodes is considerably large and the rate of resistance increase is also large. Further, in the limiting current method using platinum-platinum for an electrode, a layer for suppressing diffusion of oxygen is required. Therefore, low temperature 200 ° C
Has high conductivity up to the vicinity, and is chemically stable,
Desirably, there is a demand for a solid electrolyte in which the interface resistance is reduced even with a platinum electrode, and an electrode that is stable for a long period of time. In addition, for downsizing and cost reduction, there is a demand for a sensor that does not require a heater, a resistance plate for suppressing diffusion of oxygen, or a porous layer.

In view of the above problems, an object of the present invention is to provide an oxygen sensor which can be operated at a low temperature, requires no heater, is small in size, is low in cost, and can easily measure the oxygen concentration. Another object of the present invention is to provide an oxygen sensor capable of easily and simply measuring the oxygen concentration without the need for a resistor plate for suppressing the diffusion of oxygen.

[0007]

SUMMARY OF THE INVENTION The present invention provides an oxygen sensor comprising a layer of barium-cerium-based oxide, an anode and a cathode formed on the same or different surfaces of said layer. The oxide preferably contains at least one rare earth element as a third element. More preferably, the oxide of the formula _{BaCe 1-x M x O 3-} α
(Where M is La, Pr, Nd, Pm, Sm, Eu, G
at least one rare earth element selected from the group consisting of d, Tb, Dy, Ho, Er, Y and Yb, 0.16
≦ x ≦ 0.23, 0 <α <1). Among them, M is preferably Gd. In the oxygen sensor according to one embodiment of the present invention, the oxide is a conductor of at least one ion selected from the group consisting of a proton and an oxide ion, and the electrical conductivity of the oxide between the anode and the cathode. This is a semiconductor type oxygen sensor that detects the oxygen concentration by changing the degree. In this semiconductor type oxygen sensor, it is possible to adopt a configuration in which an anode and a cathode are provided on the same surface of the oxide layer.
An oxygen sensor according to another aspect of the present invention is a limiting current type oxygen sensor in which the oxide is a solid electrolyte and an oxygen concentration is detected by a change in an output current when a constant voltage is applied between the two electrodes. This limiting current type oxygen sensor has means for suppressing diffusion of oxygen into the solid electrolyte on the cathode side. In this limiting current type oxygen sensor, at least one of the anode and the cathode can be made of platinum or a material containing platinum as a main component. Further, at least one of the anode and the cathode can be made of silver or a material containing silver as a main component.

Further, the present invention comprises a solid electrolyte layer, a cathode and an anode formed on the same surface or different surfaces of the solid electrolyte layer, wherein the anode is made of a material mainly composed of platinum, silver or any one of them. Wherein the cathode is made of gold or a material containing gold as a main component. Further, the present invention provides
A solid electrolyte layer, comprising a cathode and an anode formed on the same surface or different surfaces of the solid electrolyte layer,
An oxygen sensor is provided in which the anode is made of silver or a material containing silver as a main component and the cathode is made of platinum or a material containing platinum as a main component. The present invention also provides an oxygen sensor comprising a solid electrolyte layer, a cathode and an anode formed on the same surface or different surfaces of the solid electrolyte layer, wherein the cathode is a mixed conductor of electrons (holes) and ions. I do. 90% of the mixed conductor
It is preferred that the dense body has a true density of more than.

[0009]

According to the present invention, a barium-cerium-based oxide is used as the oxide constituting the oxygen sensor element. Above all, formula Ba
Ce _{1 over x} M x O _3- α (M in the formula, La, Pr, Nd, P
at least one rare earth element selected from the group consisting of m, Sm, Eu, Gd, Tb, Dy, Ho, Er, Y and Yb, α is the amount of oxygen deficiency, and 0.16 ≦ x ≦ 0.
The oxide represented by 23, 0 <α <1) is an excellent conductor of protons and oxide ions, and thus effectively functions as an element of a semiconductor sensor and a limiting current sensor. That is, in the conventional semiconductor sensor,
The fact that oxides such as TiO ₂ and SiO ₂ change their electrical conductivity near the stoichiometric air-fuel ratio has been used. However, in the lean burn region, the change in electrical conductivity was extremely small and could not be used for sensors. The oxide has a large change in electric conductivity even in the lean burn region. Therefore, the sensor of the present invention can detect oxygen not only in the stoichiometric air-fuel ratio but also in the lean burn region.

A typical oxide used in a conventional limiting current type oxygen sensor is a zirconia-based oxide, and its oxide ion has a conductivity of about 2 × 10 3 at 700 ° C. ^-2 S / cm, and about ^10-3 S / cm at 500 ° C. On the other hand, the above-mentioned barium-cerium-based oxide has an oxide ion conductivity at 500 ° C. that is approximately 100 times that of the zirconia-based oxide, and thus provides a highly sensitive sensor. Further, since it has a sufficient oxygen pumping ability even at a low temperature of about 200 ° C., it can be used at a lower temperature than before. In the limiting current type oxygen sensor, it is usually necessary to provide a means such as a resistance plate for suppressing diffusion of oxygen on the cathode side. In the oxygen sensor of the present invention, a material having a lower activity for oxygen than the anode such as platinum or silver for the anode, gold for the cathode, or silver for the anode and platinum for the cathode is used for the cathode, so that the oxygen on the cathode side is reduced. Dissociation can be suppressed and additional elements such as the resistor plate can be omitted. Further, by constituting the cathode with a mixed conductor of electrons (holes) and ions, the means for suppressing oxygen diffusion can be omitted. In this case, there is no particular limitation on the anode material.

The present invention also provides a long-term stable oxygen sensor having a low interfacial resistance by using silver for the anode or the cathode. Conventionally, platinum has been used for electrodes of oxygen pumps operating at high temperatures. this is,
Although it is expensive, it is stable at a high temperature of 500 ° C. or more. However, at a temperature lower than 500 ° C., silver has a higher activity with respect to oxygen, has a lower interfacial resistance with the electrolyte, and can smoothly perform oxygen pumping.
It is difficult to use silver at a temperature exceeding 800 ° C. As described above, a small, simple, and low-cost oxygen sensor with high sensitivity and high reliability can be manufactured. When the barium-cerium-based oxide is used as the oxide, the oxygen sensor of the present invention detects indoor oxygen concentration and controls combustion of combustion equipment such as an engine or a stove in a temperature range from room temperature to a high temperature of about 800 ° C. It can be used as an oxygen concentration detector for (lean burn).

[0012]

The present invention will be described below in detail with reference to examples. [Embodiment 1] In this embodiment, an example of a semiconductor type oxygen sensor will be described. Ba-cerium-based oxide, Ba
Ce _0.8 Y _0.2 O _3- α or BaCe _{0. 75} Eu _0.25 O _3- α
A disk having a thickness of 0.5 mm and a diameter of 13 mm was used. Platinum electrodes were provided on both sides of this disk. The sensor element was placed in an electric furnace, and the atmosphere in the furnace was changed from a nitrogen atmosphere containing 1% oxygen to air at a predetermined temperature, and the change in resistance of the oxide element was examined. The results are shown in Table 1 in comparison with the conventional zirconia.

[0013]

[Table 1]

The resistance value ratio represents (resistance in air atmosphere) / (resistance value in 1% oxygen atmosphere). From Table 1,
It can be seen that the barium-cerium-based oxide has a large change in resistance due to a change in oxygen concentration, and has high sensitivity to oxygen. The device according to the present embodiment has a low temperature of 250 to 300 ° C.
It turns out that it is about 2 to 4 times active to oxygen compared with the conventional material. Also, when expressed barium-cerium oxide in the formula BaCe _{1 over x} M x O _3- α, M is Gd, D
It was also found that y, Yb and the like were similarly highly sensitive to oxygen. When the value of x exceeds 0.4, it was difficult to synthesize an oxide. As is clear from this example, the oxygen sensor using barium-cerium-based oxide has higher sensitivity than that using a conventional oxide and can be detected at a low temperature, and has a heater-free component structure. Simple and cheap.

[Embodiment 2] FIG. 1 shows the structure of an oxygen sensor according to the present invention. The oxide 1 contains BaCe _0.8 Gd _0.2 which is a mixed ion conductor of protons and oxide ions.
O _3- α is used. This oxide is a perovskite-type oxide and is thermally stable. Usually, this kind of oxide is often unstable in a reducing atmosphere, but is stable in a reducing atmosphere. The size of the oxide 1 is 10 mm in size.
It has a size of 10 mm, a thickness of 0.4 mm, and platinum electrodes 2 attached to both sides of the oxide 1.

The temperature of the sensor element was maintained at 300 to 500 ° C., and a test gas of each oxygen concentration was flowed to examine the characteristics of the sensor. FIG. 2 shows the characteristics at 500 ° C. As a comparative example, the characteristics at 900 ° C. of an oxygen sensor using the oxide semiconductor Co _0.3 Mg _0.7 O are also shown. As can be seen from FIG. 2, the difference in electrical conductivity in the lean burn region can be increased at a lower temperature by using the oxygen sensor of the present example than when using the semiconductor Co _0.3 Mg _0.7 O of the comparative example. Thus, the oxygen concentration can be detected more accurately. In addition, since it can be used at low temperatures, it is determined that it can be used for a wide range of applications.

[Embodiment 3] FIG. 3 shows the structure of an oxygen sensor according to this embodiment. As in Embodiment 2, the oxide 1 contains Ba, which is a mixed ionic conductor of protons and oxide ions.
Ce _0.8 Gd _0.2 O _3- α is used. The oxide 1 has a size of 5 mm × 15 mm and a thickness of 0.4 mm, and a pair of platinum electrodes 2 is attached to one surface of the oxide 1.
The sensor element was maintained at a temperature of 300 to 500 ° C., and a test gas of each oxygen concentration was flowed to examine the characteristics of the sensor. FIG.
9 shows the characteristics at 500 ° C. together with the characteristics of the sensor of Example 2. FIG. 4 shows that even if a pair of electrodes are attached to the same surface, the sensor has the same performance as that of the sensor according to the second embodiment. This sensor attaches electrodes to the same surface,
The manufacturing process of the sensor can be reduced, and a simple and high-performance oxygen sensor can be obtained. In addition, BaCe _0.8 Nd _0.2 O _3- α
It has been found that the sensor using the same has the same performance as the sensor using BaCe _0.8 Gd _0.2 O _3- α.

Embodiment 4 FIGS. 5 and 6 show the structure of a limiting current type oxygen sensor of this embodiment. The solid electrolyte 11 in the sensor section is made of a BaCe _0.8 Gd _0.2 O _3- α sintered body having a size of 10 mm × 10 mm and a thickness of 0.5 mm. A fritless Pt paste in which platinum fine powder was made into a paste with terpineol was applied to both surfaces of the solid electrolyte 11 and baked at 900 ° C. for 1 hour to form an anode 12 and a cathode 13. On the cathode side, a resistance plate 14 made of an alumina plate having a size of 10 mm × 10 mm and a thickness of 0.5 mm was sealed with a ceramic adhesive 15 except for a gas intake port having a diameter of 2 mm. 16 and 17 are leads of the anode 12 and the cathode 13, respectively.

The limiting current characteristics of the sensor at various temperatures were examined by a cyclic voltammetry (CV) method. Air, 10% oxygen, and 0% oxygen were supplied as test gases in a nitrogen gas balance, and the relationship between the oxygen concentration and the limiting current value was examined. FIG. 7 shows 500 of the sensor (a) of the present invention and the zirconia sensor (b) of the comparative example.
4 shows current-voltage characteristics at ° C. It can be seen that the sensor (a) of the present invention is clearly superior in relative sensitivity to the zirconia type. FIG. 8 shows the sensor (a) of the present invention.
4 shows current-voltage characteristics at 200 ° C., 300 ° C., 350 ° C., and 400 ° C. FIG. 8 also shows the current-voltage characteristics at 200 ° C. of the zirconia sensor (b).
It can be seen that the sensor of the present invention can sufficiently detect a difference in oxygen concentration with a limiting current even at a low temperature of 200 ° C. The solid electrolyte BaCe _0.8 Gd _0.2 O _3- α has been proven to be stable even in hydrocarbons and reducing gases in a fuel cell test for 5000 hours.

As is clear from this embodiment, the oxygen sensor using barium-cerium-based oxide as the solid electrolyte has higher sensitivity than the conventional zirconia type, can directly detect even at low temperature, and requires no heater. The structure becomes simple and inexpensive. The interface resistance between the zirconia-platinum electrode and the interface resistance between the BaCe _0.8 Gd _0.2 O ₃ -α-platinum electrode was measured by the AC impedance method. As a result, at 500 ° C., the interface resistance between zirconia and platinum was several MΩcm, while BaCe _0.8 Gd _0.2 O
The interface resistance between _3- α and platinum was several tens Ωcm. Therefore, it is understood that the interface resistance can be suppressed by the combination of the barium-cerium-based oxide and platinum.

Embodiment 5 This embodiment is an example of an oxygen sensor using a mixed conductor of electrons (holes) and ions for electrodes. In this sensor, the electrode (cathode) itself has a function of suppressing oxide ion conduction, and an oxygen diffusion resistance plate is not required. The structure of the sensor is a solid electrolyte with a size of 10 mm x 10 mm and a thickness of 0.5 mm Ba.
Ce _0.8 Gd _0.2 O ₃ -α sintered body, platinum on the anode, La _0.5 Sr _0.5 Co _0.8 Mn _0.2 which is a mixed conductor on the cathode
It was composed using O ₃ . First, paste powder La _0.5 Sr
_0.5 Co _0.8 Mn _0.2 O ₃ was applied to the solid electrolyte so as to form a thick film, sintered at 1300 ° C., and then a platinum electrode was baked. At this time, the cathode La _0.5 Sr _0.5
Co _0.8 Mn _0.2 O ₃ was a dense electrode with a true density of 92%, and had almost no gas permeation.

In the same manner as in Example 4, the limiting current characteristics were examined by the cyclic voltammetry (CV) method.
Air, 10% oxygen, and 0% oxygen were supplied as test gases in a nitrogen gas balance, and the relationship between the oxygen concentration and the limiting current value was examined. FIG. 9 shows sensor 7 of the present invention (c).
The current-voltage characteristics at 00 ° C. are shown. As is evident from the results, according to the sensor of the present invention, the oxygen concentration difference can be sensed by the limiting current. It can be seen that the oxygen sensor of the present invention using a mixed conductor for the cathode eliminates the need for an oxygen diffusion resistance plate and can provide a simple and low-cost oxygen sensor. When the current-voltage characteristics of the sensor using a cathode having a density of 90% of the true density were examined in the same manner, no remarkable difference in the limit current density due to the oxygen concentration difference was observed. It turned out to be difficult.

La _0.4 Sr _0.6 Co _0.8 Fe _0.2 O ₃ , La
_{0.5 Sr 0.5 Co 0.8 Ni 0.2 O} 3, La 0. 5 Sr 0.5 Co 0.6
Similarly, when a mixed conductor such as Cu _0.4 O ₃ was used for the cathode, the oxygen concentration could be measured by the limiting current method without using an oxygen diffusion resistance plate. In this embodiment, an example in which a LaSrCoMnO-based mixed conductor is used for the electrode is shown. However, a BaSrCoO-based or LaBaFeO-based mixed conductor may be used as long as it is a mixed conductor of electrons (holes) and ions.

[Embodiment 6] This embodiment is an example of an oxygen sensor in which the anode and the cathode are made of different electrode materials. In the same manner as in Example 5, BaC having a size of 10 mm × 10 mm and a thickness of 0.5 mm was formed on the solid electrolyte.
An oxygen sensor was constructed by using e _0.8 Dy _0.2 O ₃ -α sintered body, using platinum for the anode and gold for the cathode. The limit current characteristics were examined by the cyclic voltammetry (CV) method in the same manner as in Example 5. As test gas, air,
10% oxygen and 0% oxygen were supplied in a nitrogen gas balance, and the relationship between the oxygen concentration and the limiting current value was examined. FIG. 10 shows a current-voltage characteristic at 500 ° C. of the sensor (d) of the present invention. As is apparent from this result, it is understood that the difference in oxygen concentration can be sensed by the limit current. The difference in the activity of the electrode surface causes the diffusion of oxygen to be different, and has the same effect as the addition of a resistance plate that suppresses the diffusion of oxygen to one electrode (cathode). It can be seen that the oxygen sensor of the present invention in which the anode and the cathode are made of different kinds of electrode materials can eliminate the need for an oxygen diffusion resistance plate and provide a simple and low-cost oxygen sensor. Further, in this embodiment, an example is shown in which platinum is used for the anode and gold is used for the cathode, but silver may be used for the anode and gold may be used for the cathode.

[Embodiment 7] This embodiment is an example of an oxygen sensor using silver or a material containing silver as a main component for at least one of an anode and a cathode. In the same manner as in Example 4, the solid electrolyte of the sensor portion was 10 mm × 10
A stabilized zirconia sintered body having a thickness of 8 mm and a thickness of 0.5 mm was used. A fritless Ag paste in which silver fine powder was made into a paste with terpineol was applied to both surfaces of the solid electrolyte and baked at 800 ° C. for 1 hour to form an anode and a cathode. On the cathode side,
An oxygen diffusion resistance plate made of a forsterite plate having a size of 10 mm × 10 mm and a thickness of 0.5 mm was sealed with glass 5 except for a gas inlet of 2 mm.

At this time, the interfacial resistance of the electrode was measured by an AC impedance method, and compared with that of a conventional platinum electrode. At 800 ° C. and 700 ° C., no remarkable difference in interface resistance was observed, but it was found that the difference increased at 600 ° C. or less. FIG. 11 shows the results of Cole-Cole plots of the platinum electrode and the silver electrode at 500 ° C. The vertical axis in FIG. 11 represents the resistance (lie number), and the horizontal axis represents the resistance (real number). As is clear from FIG. 11, the silver electrode has lower interface resistance. In addition, when the life cycle was examined by repeating a heat cycle from room temperature to 500 ° C. to room temperature 200 times for 1000 hours, the interface resistance was increased by 7% for the platinum electrode, but was about 1% for the silver electrode. Was. Thus, it is clear that the silver electrode has a lower interface resistance than the platinum electrode with respect to the zirconia-based solid electrolyte, has high sensitivity, and is excellent in long-term stability. Also, when a BaCe _0.8 Gd _0.2 O _3- α sintered body is used for the solid electrolyte,
Similar results were obtained, indicating that the silver electrode is superior to the platinum electrode.

In Examples 4 to 7, B was added to the solid electrolyte.
aCe _0.8 Gd _0.2 O _3- α, BaCe _0.8 Dy _0.2 O _3- α,
An example using a zirconia-based solid electrolyte was shown,
BaCe _0.8 Y _0.2 O _3- α or BaCe _0.8 Tb _0.2 O _3- α may be used. In addition, solid electrolytes such as ceria-based, hafnia-based, and bismuth-based, which are used in this kind of limiting current type oxygen sensor can be used. Of course, the platinum, silver and gold electrodes used in the examples may be mixtures with other components. In addition, the synthesis and manufacturing methods of the electrolyte and the mixed conductor include coating, vapor deposition, sputtering, and C.I. V. The D method may be used.

[Embodiment 8] In this embodiment, BaCe which is a mixed ionic conductor of proton and oxide ion is used as the oxide.
_0.8 Nd _0.2 O _3- α is used. The oxide has a size of 5 mm × 15 mm and a thickness of 0.4 mm, and a pair of silver electrodes is attached to one surface of the oxide. The configuration of the sensor is the same as that of the third embodiment except for the electrodes. The sensor element was maintained at a temperature of 300 to 500 ° C., and a test gas of each oxygen concentration was flowed to examine the characteristics of the sensor. FIG. 12 shows the characteristics at 500 ° C. of the sensors of this embodiment and the third embodiment. From FIG. 12, it can be seen that even when silver is used as the electrode, the sensor has the same performance as a sensor using platinum. In the present embodiment, BaCe _0.8 Nd _0.2 O _3- α, which is a mixed ion conductor of protons and oxide ions, was used as the electrolyte. _0.9 Gd _0.1 O _3-
α, BaCe _0.9 Y _0.1 O _3- α or the like can also be used.
Also, the pair of electrodes need not be the same, and the electrode material may be Pt, Ag, Au, or the like.

[0029]

According to the present invention, a small, simple and low-cost oxygen sensor having high sensitivity and high reliability can be realized. INDUSTRIAL APPLICABILITY The oxygen sensor of the present invention is excellent in detecting oxygen concentration especially at a low temperature of around 200 ° C., and realizes a compact, simple, and low-cost oxygen concentration detector for controlling combustion (lean burn) of combustion equipment such as an engine and a stove. I do.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an oxygen sensor according to a second embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between oxygen partial pressure and electric resistance of the oxygen sensor.

FIG. 3 is a longitudinal sectional view of an oxygen sensor according to a third embodiment.

FIG. 4 is a diagram showing a relationship between oxygen partial pressure and electric resistance of the oxygen sensor.

FIG. 5 is a longitudinal sectional view of a limiting current type oxygen sensor according to a fourth embodiment.

FIG. 6 is a plan view of the oxygen sensor.

FIG. 7 is a diagram showing a comparison of current-voltage characteristics at 500 ° C. between the sensor of Example 4 and a zirconia sensor.

FIG. 8 is a diagram showing a comparison of current-voltage characteristics at 200 ° C. between the sensor of Example 4 and a zirconia sensor.

FIG. 9 is a diagram showing current-voltage characteristics at 700 ° C. of the sensor of Example 5.

FIG. 10 is a diagram showing current-voltage characteristics at 500 ° C. of the sensor of Example 6.

FIG. 11 is a view showing a Cole-Cole plot of a platinum electrode and a silver electrode at 500 ° C. of the sensor of Example 7;

FIG. 12 is a diagram showing the relationship between the oxygen partial pressure and the electrical resistance of the oxygen sensor in Example 8.

Continued on the front page (72) Kunihiro Tsuruta, 1006 Kadoma Kadoma, Kadoma, Osaka Pref., Matsushita Electric Industrial Co., Ltd. References JP-A-63-234604 (JP, A) JP-A-5-234604 (JP, A) JP-A-64-28549 (JP, A) JP-A-1-97848 (JP, A) 2-167461 (JP, A) JP-A-5-249072 (JP, A) JP-A-52-2491 (JP, A) JP-A-55-162052 (JP, A) JP-A-58-123446 (JP, A A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G01N 27/409 G01N 27/12 G01N 27/41

Claims (9)

(57) [Claims] 1. The formula BaCe _1-x M _x O _3-α (wherein M
Are La, Pr, Nd, Pm, Sm, Eu, Gd, T
b, Dy, Ho, Er, Y and Yb.
At least one rare earth element selected, 0.16 ≦ x ≦
0.23,0 <α <1 layer of oxide represented by), Ri Na than the anode and cathode formed on the same surface or different surfaces of the layer, be operated at 500 ° C. or less
Oxygen sensors that characterized the. 2. The oxygen sensor according to claim 1, wherein the anode and the cathode are provided on the same surface of the oxide layer. 3. The oxygen sensor according to claim 1, wherein the oxide is a solid electrolyte, and the oxygen concentration is detected by a change in an output current when a constant voltage is applied between the two electrodes. 4. The oxygen sensor according to claim 1, further comprising means for suppressing diffusion of oxygen into the solid electrolyte on the cathode side. 5. The method according to claim 1, wherein at least one of the anode and the cathode is made of silver or a material containing silver as a main component.
5. The oxygen sensor according to any one of 4. 6. The cathode is a mixed conductor of electrons (holes) and ions, and the mixed conductor has a true density of 9%.
The oxygen sensor according to any one of claims 1 to 4, wherein the oxygen sensor is a dense body exceeding 0%. 7. The oxygen according to claim 1, wherein the anode is made of platinum, silver or a material mainly containing one of them, and the cathode is made of gold or a material mainly containing gold. sensor. 8. The oxygen sensor according to claim 1, wherein the anode is made of silver or a material containing silver as a main component, and the cathode is made of platinum or a material containing platinum as a main component. 9. The oxygen sensor according to claim 1, wherein M is Gd.