JP2015030641A - Gas sensor element, and gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor element using a zirconia sintered body capable of achieving both of improvement in sinterability and suppression of highly increasing in electric resistance, as a solid electrolyte, and to provide a gas sensor including the same.SOLUTION: A gas sensor element 1 includes a partially stabilized or stabilized zirconia sintered body used as a solid electrolyte. In the partially stabilized or stabilized zirconia sintered body, a composite oxide having a chemical composition of ZrOof 15-35 mol% and NbOof 85-65 mol% is added. An added amount of the composite oxide with respect to 100 pts.mass of the total amount of the partially stabilized or stabilized zirconia and the composite oxide can be within a range of 0.1-5 pts.mass. A gas sensor 3 includes the gas sensor element 1.

Description

  The present invention relates to a gas sensor element and a gas sensor.

  Conventionally, a gas sensor having a gas sensor element using a zirconia sintered body as a solid electrolyte in an internal combustion engine for an automobile or the like is known.

  For example, Patent Document 1 discloses an oxygen sensor element using a partially stabilized zirconia sintered body to which a sintering aid made of silica and alumina is added as a solid electrolyte. In this document, a stabilizer is added to stabilize the crystal structure of zirconia that undergoes phase transformation at high temperatures. Further, in this document, the amount of the sintering aid added is in the range of 0.1 to 0.6 parts by mass of silica and 1 to 10 parts by mass of alumina with respect to 100 parts by mass of the solid electrolyte. As a result, the sintering temperature is set to a range of 1350 ° C. to 1500 ° C. by the interaction between silica and alumina, and sufficient strength can be obtained by suppressing excessive grain growth while obtaining a desired crystal composition. ing.

JP-A-9-124365

  However, the conventional technology has room for improvement in the following points. That is, since the zirconia sintered body has a high melting point and poor sinterability, it is difficult to improve the relative density. Therefore, it is a common practice to improve the sinterability by adding a sintering aid as in the prior art. However, when silica and alumina, which are insulating materials, are added to the zirconia sintered body as sintering aids in order to improve the sinterability, the oxygen ion conductivity at the grain boundary decreases and the electrical resistance increases.

  The present invention has been made in view of the above background, and a gas sensor element using a zirconia sintered body as a solid electrolyte capable of achieving both improvement of sinterability and suppression of high electrical resistance, and A gas sensor is provided.

One aspect of the present invention is a gas sensor element using a partially stabilized or stabilized zirconia sintered body as a solid electrolyte,
To the partially stabilized or stabilized zirconia sintered _body, in the gas sensor element, wherein the composite oxide is added with a chemical composition of _{15~35mol% ZrO 2 -85~65mol% Nb 2} O 5 .

  Another aspect of the present invention is a gas sensor including the gas sensor element.

The gas sensor element uses a partially stabilized or stabilized zirconia sintered body to which a composite oxide of ZrO ₂ —Nb ₂ O ₅ having the specific chemical composition is added as a solid electrolyte. The melting point of zirconia alone is about 2700 ° C., and the melting point of silica conventionally used as a sintering aid is 1650 ° C., whereas the composite oxide has a lower melting point. Therefore, the partially stabilized or stabilized zirconia sintered body to which the composite oxide is added is sintered at a lower temperature, and the sinterability is improved. By improving the relative density of the sintered body by improving the sinterability, the electric resistance of the solid electrolyte can be reduced. In addition, the partially stabilized or stabilized zirconia sintered body to which the composite oxide is added is obtained by adding the powder of the composite oxide to a zirconia powder in which a stabilizer is dissolved in advance and firing the powder. be able to. The composite oxide can be partly dissolved in the zirconia grains, but hardly dissolves in the zirconia grains, and is present mainly at the zirconia grain boundaries. Moreover, since the addition of the complex oxide is only a small amount relative to the partially stabilized or stabilized zirconia powder, the complex oxide hardly functions as a zirconia stabilizer. Therefore, partial stabilization or expression of electronic conductivity of stabilized zirconia, which is a concern when Nb ₂ O ₅ described in the prior art is added as a stabilizer, hardly occurs. Conventionally, since silica used as a sintering aid is an insulating material, if it is present at a zirconia grain boundary, it inhibits oxygen ion conductivity and increases the electrical resistance of the solid electrolyte. On the other hand, since the composite oxide contains ZrO _{2 in} its chemical composition, it does not inhibit oxygen ion conductivity even when present at the zirconia grain boundary, and suppresses high electrical resistance of the solid electrolyte. Can do.

  The gas sensor has the gas sensor element. Therefore, the gas sensor is effective in that it can be operated at a low temperature.

  Therefore, according to the present invention, it is possible to provide a gas sensor element using a zirconia sintered body that can achieve both improvement of sinterability and suppression of high electrical resistance as a solid electrolyte, and a gas sensor having the gas sensor element. it can.

3 is a cross-sectional view showing a part of the gas sensor element of Example 1. FIG. It is a phase diagram of ZrO ₂ —Nb ₂ O ₅ . 1 is a cross-sectional view of a gas sensor of Example 1. FIG. It is the figure which showed the microstructure of the sample 1 in Experimental example 1, (a) is a secondary electron image, (b) is a reflected electron image. FIG. 5 is a diagram showing the phase density (%) of Samples 2 to 4 in Experimental Example 1. It is the figure which showed the electrical conductivity with respect to the temperature of the samples 2-4 in Experimental example 1. FIG. FIG. 6 is a diagram showing the phase density (%) of Samples 1, 5, and 6 in Experimental Example 1. It is the figure which showed the oxygen ion transport number (-) in 700 degreeC of the samples 1, 5, and 6 in Experimental example 1. FIG.

  The gas sensor element is, for example, a solid electrolyte made of a partially stabilized or stabilized zirconia sintered body, an inner electrode provided on the inner surface of the solid electrolyte, an outer surface of the solid electrolyte, and exposed to a gas to be measured. And having an outer electrode. The shape of the solid electrolyte in the gas sensor element is not particularly limited. For example, the solid electrolyte may have a cup shape or a flat plate shape having an inner chamber in which one end is closed and the other end is opened. As the gas sensor element, a solid electrolyte made of a partially stabilized zirconia sintered body can be suitably used from the viewpoint of element strength.

A composite oxide having a chemical composition of _{15 to} 35 mol% ZrO ₂ -85 to 65 mol% Nb ₂ O ₅ is added to the partially stabilized or stabilized zirconia sintered body forming the solid electrolyte. Thereby, since melting | fusing point of complex oxide becomes 1500 degrees C or less and becomes a liquid phase at the temperature of 1500 degrees C or less, the sinterability improvement of a partially stabilized or stabilized zirconia sintered compact is achieved. Note that 1500 ° C. is a temperature that can be fired in a general firing furnace. Moreover, since the said complex oxide contains a zirconia moderately, even if a complex oxide exists in a zirconia grain boundary, oxygen ion conductivity is not inhibited and the high electrical resistance increase of a solid electrolyte is suppressed. When ZrO ₂ in the composite oxide is less than 15 mol% and Nb ₂ O ₅ exceeds 85 mol%, the melting point is lowered and a liquid phase is generated, but a part of the grain boundary of the partially stabilized or stabilized zirconia sintered body is produced. There exists a possibility that it may precipitate unreacted and the sinterability may be reduced. When ZrO ₂ in the composite oxide exceeds 35 mol% and Nb ₂ O ₅ is less than 65 mol%, the melting point of the composite oxide monotonously increases with the increase in the composition amount of ZrO ₂ , and partially stabilized or stabilized zirconia There is a possibility that the sinterability of the sintered body will not be improved, and it will be precipitated unreacted at the grain boundary of the partially stabilized or stabilized zirconia sintered body, thereby reducing the sinterability. The range of the chemical composition of ZrO ₂ and Nb ₂ O ₅ in the composite oxide is preferably 17 to 33 mol% for ZrO ₂ , 83 to 67 mol% for Nb ₂ O ₅ , more preferably ₂₀ to 30 mol for ZrO ₂ . %, _Nb 2 _{O 5} is 80~70mol%, more preferably, ZrO ₂ is 22~28mol%, _Nb 2 _{O 5} is 78~72mol%, and most preferably, ZrO ₂ is 25 mol%, the _Nb 2 _{O 5} 75 mol % Is good. This is because it becomes close to the eutectic point and the melting point of the composite oxide is lowered, so that the above-described effect can be easily obtained.

  In the gas sensor element, the amount of the composite oxide added to 100 parts by mass of the partially stabilized or stabilized zirconia and the composite oxide is preferably in the range of 0.1 to 5 parts by mass. In addition, the said addition amount points out the value in the raw material powder time at the time of obtaining the partially stabilized zirconia or stabilized zirconia sintered compact to which the said complex oxide was added by baking.

  In this case, sufficient sinterability can be improved, oxygen ion conductivity of partially stabilized or stabilized zirconia is hardly inhibited, and high electrical resistance of the solid electrolyte can be easily suppressed.

  The amount of the composite oxide added is preferably 0.1 parts by mass or more, more preferably 0.15 parts by mass or more, and still more preferably 0. It is good that it is 2 parts by mass or more. In addition, the amount of the composite oxide added is preferably 5 parts by mass or less, more preferably 3 parts by mass from the viewpoint of partially stabilizing or reducing the conductivity of stabilized zirconia and easily suppressing the oxygen ion transport number. It is good in it being below 1 mass part, More preferably, it is 2 mass parts or less, More preferably, it is good in it being 1 mass part or less. When the addition amount of the composite oxide is less than 0.1 parts by mass, the tendency to make it difficult to improve the sinterability of partially stabilized zirconia or stabilized zirconia is observed, and the addition amount of the composite oxide is 5 parts by mass. When it is larger, the electronic conductivity of partially stabilized zirconia or stabilized zirconia due to the addition of Nb increases, and it tends to be difficult to obtain a sufficient electromotive force.

In the gas sensor element, Al ₂ O ₃ may be further added to the partially stabilized or stabilized zirconia sintered body. In this case, the strength of the solid electrolyte made of the partially stabilized or stabilized zirconia sintered body can be improved by the dispersed Al ₂ O ₃ . Therefore, a gas sensor element excellent in structural reliability can be obtained.

In the gas sensor element, the amount of Al ₂ O ₃ added to 100 parts by mass of partially stabilized or stabilized zirconia, composite oxide, and Al ₂ O ₃ is preferably in the range of 0.1 to 15 parts by mass. More preferably, it should be in the range of 0.2 to 13 parts by mass. Incidentally, the additive amount refers to the value in the raw material powder when in obtaining the composite oxide, the Al ₂ O ₃ is added partially stabilized zirconia or stabilized zirconia sintered body by firing.

In this case, the effect of improving the strength of the solid electrolyte by adding Al ₂ O ₃ is ensured. Moreover, since the thermal stress resulting from the difference in thermal expansion coefficient between partially stabilized or stabilized zirconia and Al ₂ O ₃ does not become excessive and cracks of the sintered body are easily suppressed, excessive Al ₂ O ₃ This is advantageous because it is difficult to cause a decrease in strength due to the addition of.

In the gas sensor element, the partially stabilized or stabilized zirconia is, for example, one or more stabilizers selected from CaO, MgO, Y ₂ O ₃ , Yb ₂ O ₃ , and Nb ₂ O _5. Can be included. Depending on the type of stabilizer added, the composition to be partially stabilized or stabilized zirconia varies, but the content of the stabilizer can be in the range of about 3 to 15 mol.

  The partially stabilized or stabilized zirconia is preferably partially stabilized or stabilized by either or both of CaO and MgO stabilizers.

Partially stabilized or stabilized zirconia containing CaO and / or MgO as a stabilizer is less sinterable than partially stabilized or stabilized zirconia containing other stabilizers such as Y ₂ O ₃ It is a material that makes it difficult to increase the relative density of the sintered body. However, since the gas sensor element uses the composite oxide, the sinterability can be improved even with partially stabilized or stabilized zirconia containing CaO and / or MgO. The density can be improved. In addition, CaO and MgO do not contain rare earth like Y ₂ O ₃ , Yb ₂ O _3, etc., and thus have excellent resource supply stability. Therefore, in this case, it can contribute to the improvement of the production stability of the gas sensor element. Moreover, since the gas sensor element does not contain a rare earth, it is advantageous for cost reduction. The partially stabilized or stabilized zirconia is particularly preferably partially stabilized or stabilized by CaO. In this case, there are advantages such as partially stabilized or stabilized zirconia containing no rare earth and having the highest conductivity.

In the gas sensor element, the phase density of the partially stabilized or stabilized zirconia sintered body is preferably 90% or more, more preferably 90.5% or more, and further preferably 91% or more. In this case, gas densification is not a problem due to densification, and there are advantages such as improved material strength. The relative density can be 96% or less from the viewpoint of crystal grain growth, manufacturability, and the like. The relative density (%) is a value obtained by dividing the density (g / cm ³ ) obtained from the mass and volume of the sintered body by the theoretical density of partially stabilized or stabilized zirconia constituting the sintered body. A value obtained by multiplying by 100.

  Specifically, the gas sensor element can be configured as an air-fuel ratio sensor element (A / F sensor element) or an oxygen sensor element. In particular, the gas sensor element can be suitably used as an air-fuel ratio sensor element. Since the air-fuel ratio sensor is used by passing a current through the element, the electric resistance of the solid electrolyte is preferably small. Since the gas sensor element can suppress the increase in the electrical resistance of the solid electrolyte, it is advantageous for improving the sensor performance by using it as an air-fuel ratio sensor.

  In addition, each structure mentioned above can be arbitrarily combined as needed, in order to acquire each effect etc. which were mentioned above.

  Hereinafter, the gas sensor element and gas sensor of an example are explained using a drawing. In addition, about the same member, it demonstrates using the same code | symbol.

Example 1
As shown in FIG. 1, the gas sensor element 1 of this example uses a partially stabilized or stabilized zirconia sintered body as the solid electrolyte 10. In the gas sensor element 1 of this example, a composite oxide having a chemical composition of _{15 to} 35 mol% ZrO _{2 to} 85 to 65 mol% Nb ₂ O ₅ is added to a partially stabilized or stabilized zirconia sintered body that is a solid electrolyte. ing. Further, in the gas sensor element 1 of this example, Al ₂ O ₃ is further added to the partially stabilized or stabilized zirconia sintered body that is a solid electrolyte.

In this example, specifically, the partially stabilized or stabilized zirconia sintered body is a partially stabilized zirconia sintered body containing 12 mol% of CaO as a stabilizer. The composite oxide has a chemical composition of 25 mol% ZrO ₂ -75 mol% Nb ₂ O ₅ . That is, as shown in FIG. 2, the composite oxide in this example has a chemical composition constituting the eutectic point in the phase diagram of ZrO ₂ —Nb ₂ O ₅ , and its melting point is 1450 ° C. The addition amount of the composite oxide with respect to 100 parts by mass in total of the partially stabilized zirconia and the composite oxide is 0.2 parts by mass. The amount of Al ₂ O ₃ added is 10 parts by mass with respect to a total of 100 parts by mass of partially stabilized zirconia, composite oxide, and Al ₂ O ₃ .

  As shown in FIG. 1, the gas sensor element 1 of this example is specifically an air-fuel ratio sensor element, and is made of the cup-shaped sintered body having an inner chamber 101 with one end closed and the other end open. It has a solid electrolyte 10, an outer electrode 11 provided on the outer surface of the solid electrolyte 10, and an inner electrode 12 provided on the inner surface of the inner chamber 101. In this example, a diffusion resistance layer 13 made of porous ceramic is further provided outside the outer electrode 11, and a poisoning substance trap layer 14 is provided outside the diffusion resistance layer 13.

Next, the structure of the gas sensor of this example using the gas sensor element 1 of this example will be described.
As shown in FIG. 3, the gas sensor 3 of this example includes a housing 30, and the gas sensor element 1 is fixed to the housing 30 with a seal. A measured gas chamber 310 is formed at the front end side of the housing 30, and double measured gas side covers 311 and 312 for protecting the gas sensor element 1 are provided. In addition, on the base end side of the housing 30, three stages of atmospheric side covers 321, 322, and 323 are provided.

  An elastic insulating member 35 into which lead wires 371, 381, 391 are inserted is provided on the base end side of the atmosphere side covers 322, 323. In the inner chamber 101 of the gas sensor element 1, a rod-shaped heater 2 containing a heating element is inserted and disposed. The lead wire 371 is for energizing the heater 2 to generate heat. The lead wires 381 and 391 are for taking out the sensor output to the outside. Connection terminals 382 and 392 are provided on the leading ends of the lead wires 381 and 391. The connection terminals 382 and 392 are in contact with and electrically connected to the metal terminals 383 and 393 fixed to the gas sensor element 1. Further, the metal terminals 383 and 393 are fixed in contact with an outer terminal portion (not shown) and an inner terminal portion (not shown) of the gas sensor element 1, respectively. The outer terminal portion is electrically connected to the outer electrode 11 via an outer lead (not shown), and the inner terminal portion is electrically connected to the inner electrode 12 via an inner lead (not shown).

Next, the effects of the gas sensor element 1 and the gas sensor 3 of this example will be described.
The gas sensor element 1 uses a partially stabilized or stabilized zirconia sintered body to which a composite oxide of ZrO ₂ —Nb ₂ O ₅ having the above specific chemical composition is added as a solid electrolyte. The melting point of zirconia alone is about 2700 ° C., and the melting point of silica conventionally used as a sintering aid is 1650 ° C., whereas the composite oxide has a lower melting point. Therefore, the partially stabilized or stabilized zirconia sintered body to which the composite oxide is added is sintered at a lower temperature, and the sinterability is improved. By improving the relative density of the sintered body by improving the sinterability, the electric resistance of the solid electrolyte can be reduced. In addition, the partially stabilized or stabilized zirconia sintered body to which the composite oxide is added is obtained by adding the powder of the composite oxide to a zirconia powder in which a stabilizer is dissolved in advance and firing the powder. be able to. The composite oxide can be partly dissolved in the zirconia grains, but hardly dissolves in the zirconia grains, and is present mainly at the zirconia grain boundaries. Moreover, since the addition of the complex oxide is only a small amount relative to the partially stabilized or stabilized zirconia powder, the complex oxide hardly functions as a zirconia stabilizer. Therefore, partial stabilization or expression of electronic conductivity of stabilized zirconia, which is a concern when Nb ₂ O ₅ described in the prior art is added as a stabilizer, hardly occurs. Conventionally, since silica used as a sintering aid is an insulating material, if it is present at a zirconia grain boundary, it inhibits oxygen ion conductivity and increases the electrical resistance of the solid electrolyte. On the other hand, since the composite oxide contains ZrO _{2 in} its chemical composition, it does not inhibit oxygen ion conductivity even when present at the zirconia grain boundary, and suppresses high electrical resistance of the solid electrolyte. Can do.

  The gas sensor 3 has a gas sensor element 1. Therefore, the gas sensor 3 is effective in that it can be operated at a low temperature.

(Experimental example 1)
Hereinafter, it demonstrates more concretely using an experiment example.

<Preparation of complex oxide>
After mixing ZrO ₂ powder and Nb ₂ O ₅ powder so as to have a chemical composition of 25 mol% ZrO ₂ -75 mol% Nb ₂ O ₅ , the mixture was heated at 1100 ° C. for 2 hours and pulverized in a mortar to obtain 25 mol% A powdery composite oxide having a chemical composition of ZrO ₂ -75 mol% Nb ₂ O ₅ was obtained.

<Preparation of Solid Electrolyte Consisting of Zirconia Sinters of Samples 1-6>
The raw material powder was prepared by fully mixing the partially stabilized zirconia powder in which 12 mol% of CaO was dissolved and the prepared composite oxide powder with a high-pressure homogenizer (dispersion medium: water). Subsequently, the obtained raw material powder was pressure-molded with a uniaxial molding machine. Next, the obtained molded body was fired at 1600 ° C. for 10 hours. As a result, a solid electrolyte of Sample 1 was obtained. In addition, the addition amount of the composite oxide powder with respect to a total of 100 parts by mass of the partially stabilized zirconia powder and the composite oxide powder was 0.2 parts by mass.

By fully mixing the partially stabilized zirconia powder in which 12 mol% of CaO is dissolved, the composite oxide powder prepared above, and the Al ₂ O ₃ powder with a high-pressure homogenizer (dispersion medium: water), the raw material powder Was prepared. Subsequently, the obtained raw material powder was pressure-molded with a uniaxial molding machine. Next, the obtained molded body was fired at 1600 ° C. for 10 hours. As a result, a solid electrolyte of Sample 2 was obtained. The portion addition amount of _Al 2 _{O 3} powder to the total 100 parts by weight of stabilized zirconia powder and the composite oxide powder and _Al 2 _{O 3} powder was 10 mass parts.

A solid electrolyte of Sample 3 was obtained in the same manner except that the composite oxide was not added in the preparation of Sample 2. In addition, a solid electrolyte of Sample 4 was obtained in the same manner as Sample 2 except that SiO ₂ was added instead of the composite oxide.

  A solid electrolyte of Sample 5 was obtained in the same manner except that the amount of the composite oxide powder added was 0.1 parts by mass in the preparation of Sample 1. Further, a solid electrolyte of Sample 6 was obtained in the same manner as in the preparation of Sample 1, except that the amount of the composite oxide powder added was 3 parts by mass.

<Composition analysis of sintered body of sample 1>
The composition of the sintered body of Sample 1 was measured by the following method. That is, the sintered compact pellet of the sample 1 obtained by producing the sample was cut in the thickness direction and polished. Thereafter, the polished surface was vapor-deposited with Pt, and EDS analysis was performed with a scanning electron microscope. Table 1 shows chemical compositions of the analysis points A1 to A6.

<Measurement of relative density>
The value obtained by dividing the density (g / cm ³ ) obtained from the mass and volume of each sample by the theoretical density of partially stabilized zirconia in which CaO is dissolved, and multiplying by 100, the density of each phase of each sample (%).

<Measurement of conductivity>
The electrical conductivity σ (S / cm) of each sample 2 to 4 was measured by the following method. That is, Pt paste was printed with a diameter of 12 mm on both sides of the sintered pellet obtained by the preparation of the above sample, dried at 70 ° C. for 30 minutes, and then fired at 1200 ° C. for 2 hours. A Pt lead wire was attached on the fired Pt electrode, dried at 70 ° C. for 30 minutes, and then fired at 900 ° C. for 30 minutes. The obtained evaluation sample was put into an electric furnace, and the electrolyte resistance and the electrode reaction resistance were separated by an AC four-terminal method. The conductivity was obtained from the electrolyte resistance obtained by the measurement. The measurement was performed in the range of 500 to 800 ° C. for each sample.

<Measurement of oxygen ion transport number>
The oxygen ion transport number (−) of Samples 1, 5, and 6 was measured by the following method. That is, Pt paste was printed with a diameter of 12 mm on both sides of the sintered pellet obtained by the preparation of the above sample, dried at 70 ° C. for 30 minutes, and then fired at 1200 ° C. for 2 hours. The sintered pellet is placed in a gas flow jig that can change the atmosphere of the gas in contact with the first and second surfaces of the formed Pt electrode, and the oxygen concentration of the gas flowing through the one surface of the Pt electrode The electromotive force of the sintered compact pellet when changing was measured to determine the oxygen ion transport number. The second surface of the Pt electrode was an air atmosphere. The measurement was performed at 700 ° C.

  According to the measurement results, the following can be said. First, as shown in FIG. 4 and Table 1, it was confirmed that the composite oxide was hardly present in the zirconia grains and was mainly present at the zirconia grain boundaries.

Next, as shown in FIG. 5, the sample 3 fired without adding the composite oxide having the specific chemical composition has a low relative density of 88.0% and is inferior in sinterability. Recognize. Thus, it can be seen that partially stabilized or stabilized zirconia containing CaO as a stabilizer is a hardly sinterable material. The same applies to partially stabilized or stabilized zirconia containing MgO as a stabilizer. Next, Sample 4 fired with the addition of SiO ₂ has a relative density of 88.9%, which is slightly better than Sample 3 in terms of sinterability. On the other hand, Sample 2 fired by adding a complex oxide having the above specific chemical composition has a relative density of 92.0%, which is significantly improved in sinterability compared to Samples 3 and 4. I understand that. From this result, it can be seen that the composite oxide is useful for SiO ₂ or more which is a conventional sintering aid.

Next, as shown in FIG. 6, the sample 3 fired without adding the complex oxide having the above specific chemical composition had a conductivity σ at 700 ° C. of 8.8 × 10 ⁻⁴ S / cm. It was. On the basis of this, Sample 4 has a conductivity σ at 700 ° C. of 4.0 × 10 ⁻⁴ S / cm, and it can be seen that the conductivity is greatly reduced. This is because SiO ₂ added as a sintering aid is an insulating material. Thus, although the sample 4 was able to improve the sinterability although it was slight, the electrical resistance became high, and as a result, it was difficult to achieve both improvement of sinterability and suppression of high electrical resistance. It can be said that there is. On the other hand, Sample 2 has a conductivity σ at 700 ° C. of 7.4 × 10 ⁻⁴ S / cm, and it can be seen that the conductivity does not decrease greatly even when the complex oxide is added. That is, it can be seen from the results of FIGS. 5 and 6 that the sample 2 can achieve both improvement in sinterability and suppression of high electrical resistance. Therefore, it can be said that the gas sensor element 1 and the gas sensor 3 can exhibit the above-described effects.

Next, FIG. 7 examines the addition amount of 25 mol% ZrO ₂ -75 mol% Nb ₂ O ₅ . As shown in FIG. 7, the relative density of Sample 1 to which 0.2 parts by mass of 25 mol% ZrO ₂ -75 mol% Nb ₂ O ₅ composite oxide was added was 92.0%. On the other hand, the relative density of Sample 5 to which 0.1 part by mass of the composite oxide was added was 89.0%, and the effect of the addition of the composite oxide was relatively small. On the other hand, the relative density of Sample 6 to which 3 parts by mass of the composite oxide was added was 92.1%, which was almost the same as Sample 1. From this, it was confirmed that the composite oxide has an effect of improving the sinterability by adding a small amount to the partially stabilized or stabilized zirconia powder.

Further, as shown in FIG. 8, the oxygen ion transport number of Sample 1 to which 0.2 parts by mass of 25 mol% ZrO ₂ -75 mol% Nb ₂ O ₅ composite oxide was added was 1. The oxygen ion transport number of Sample 5 to which 0.1 part by mass of the composite oxide was added was 1 as in Sample 1. On the other hand, the sample 6 to which 3 parts by mass of the complex oxide was added had an oxygen ion transport number of 0.9, and it was found that the oxygen ion transport number tended to decrease when the amount of the complex oxide added was increased. . That is, from the results of FIG. 7 and FIG. 8, since the phase density can be improved even if the amount of the composite oxide added is relatively small, the amount added is from the viewpoint of ensuring the effect of the present application. It can be said that the content is preferably 0.1 parts by mass or more. On the other hand, if the addition amount of the composite oxide is excessively increased, the sinterability is not significantly improved. If the addition amount is excessively increased, the oxygen ion transport number of the solid electrolyte is lowered, which is disadvantageous. Therefore, from this point, it was confirmed that the addition amount is sufficient if it is 5 parts by mass.

  As mentioned above, although the Example of this invention was described in detail, this invention is not limited to the said Example, A various change is possible within the range which does not impair the meaning of this invention.

  In the said Example, it illustrated about the case where the solid electrolyte which consists of the said sintered compact is a cup-shaped shape. Without being limited thereto, the solid electrolyte made of the sintered body can be formed into a flat plate shape to be configured as a stacked gas sensor element or gas sensor.

DESCRIPTION OF SYMBOLS 1 Gas sensor element 10 Solid electrolyte 3 Gas sensor

Claims (7)

A gas sensor element (1) using a partially stabilized or stabilized zirconia sintered body as a solid electrolyte (10),
To the partially stabilized or stabilized zirconia sintered _body, the gas sensor element (1, wherein the composite oxide is added with a chemical composition of _{15~35mol% ZrO 2 -85~65mol% Nb 2} O 5 ).   The addition amount of the composite oxide with respect to a total of 100 parts by mass of the partially stabilized or stabilized zirconia and the composite oxide is within a range of 0.1 to 5 parts by mass. The gas sensor element (1) according to 1. The gas sensor element (1) according to claim 1 or 2, wherein Al ₂ O ₃ is added to the partially stabilized or stabilized zirconia sintered body. The amount of Al ₂ O ₃ added to a total of 100 parts by mass of the partially stabilized or stabilized zirconia, the composite oxide, and the Al ₂ O ₃ is in the range of 0.1 to 15 parts by mass. Gas sensor element (1) according to claim 3, characterized in that. The partially stabilized or stabilized zirconia includes one or more stabilizers selected from CaO, MgO, Y ₂ O ₃ , Yb ₂ O ₃ , and Nb ₂ O ₅ , Gas sensor element (1)   The gas sensor element (1) according to any one of claims 1 to 5, wherein the gas sensor element (1) is an air-fuel ratio sensor element.   A gas sensor (3) comprising the gas sensor element (1) according to any one of claims 1 to 6.