JP2005119904A - Bismuth oxide based ceramics - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide bismuth oxide based ceramics having low ordinary temperature electric resistivity and having the rapid reduction properties of electric resistivity that reaches ≤1/1000 when temperature becomes higher than the Curie point. <P>SOLUTION: The bismuth oxide based ceramics are expressed by the formula of (Bi<SB>2</SB>O<SB>2</SB>)<SP>2+</SP>(A<SB>n-1</SB>B<SB>n</SB>O<SB>3n+1</SB>)<SP>2-</SP>wherein, A is one or more kinds of metals selected from K, Na, Ca, Ba, Sr, Pb and Bi; B is one or more kinds of metals selected from Ti, Nb, V, Ta, W and Mo; and n is all numbers satisfying 1≤n≤8. In the bismuth oxide based ceramics having a layered crystal structure, one or more kinds of metal oxides selected from NiO, V<SB>2</SB>O<SB>5</SB>, Cr<SB>2</SB>O<SB>3</SB>, Fe<SB>2</SB>O<SB>3</SB>, MnO<SB>2</SB>, WO<SB>3</SB>, TiO<SB>2</SB>, Nb<SB>2</SB>O<SB>5</SB>, SnO<SB>2</SB>and In<SB>2</SB>O<SB>3</SB>are added by 0.01 to 10wt%, or, a part of the constituent elements in the above chemical formula is substituted with these oxides. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a bismuth oxide ceramic useful as an electronic material such as a conductive material, a sensor material, and a switching material.

  In recent years, electronic components have been highly integrated and densified, and high performance and miniaturization are simultaneously required. On the other hand, bismuth oxide ceramics and similar bismuth titanate ceramic compounds inherently have a high dielectric constant, and the compounds also have a high Curie point, so there is a merit that there is little fluctuation in dielectric characteristics when used at room temperature. However, the electrical conductivity and electrical characteristics have not been investigated in detail.

Conventionally, when an oxide has conductivity, a method of substituting a + 1-valent or -1-valent element having a close ionic radius for the constituent elements has been taken, and various substances have been made into semiconductors. However, bismuth oxide ceramics and similar bismuth titanate ceramic compounds have hardly been improved or applied so far.
On the other hand, as a sensor material, there is a conventional thermistor material made of transition metal oxides such as Mn, Ni, Co, Fe, and Cu, which have NTC characteristics. It is used in relationships. However, these materials have a firing temperature as high as 1300 to 1500 ° C., and in order to improve responsiveness, improvement has been desired from the viewpoint of non-matching when performing simultaneous firing with an insulating substrate.
As a method therefor, there is a film type thermistor that forms an NTC thermistor by forming a temperature-sensitive resistance film on an electrically insulating substrate and arranging a pair of electrodes so as to be electrically connected to the temperature-sensitive resistance film. Compared with the bulk type NTC thermistor, the response speed can be greatly improved.

  As an example, a composition for an NTC thermistor in which a metal oxide having thermistor characteristics and glass powder are mixed and heated and fired to form a thick film on an insulating substrate as shown in Patent Document 1 is known. However, since the insulating substrate and the NTC thermistor composition are fixed by the glass component, the resistance variation of the conductive material occurs, the components vary, and the yield decreases.

By the way, as a switching material, in a material such as VO ₂ , V ₂ O ₃ , V ₄ O ₇ , V ₆ O ₁₁ , and V ₅ O ₉ , if the Curie point exceeds 140 to 340 K, the electric resistance is 1/1000 or less. Some of them exhibit characteristics such as CTR that shows a sudden drop in electrical resistance, and are used for some special applications such as liquid level gauges and temperature sensors. However, the upper limit of temperature is about 340K, and its application is extremely limited.
JP 2001-261450 A

  The present invention is not only for the dielectric properties and piezoelectric properties of conventional bismuth oxide ceramics and similar bismuth titanate ceramic compounds, but also for semiconductor properties that have conductivity different from the previous properties, as well as rapidly exceeding the Curie point. An object of the present invention is to provide a bismuth oxide-based ceramic having a unique characteristic in which electric resistance is lowered.

  The present invention improves conductivity by adding a trace amount of transition metal to bismuth oxide ceramics and has NTC characteristics over a wide range. Depending on the additive, when the Curie point is exceeded, the electrical resistance decreases sharply to 1/1000 or less, and switching characteristics are exhibited even in a high temperature range of 100 ° C. or higher. Since the main component of bismuth oxide ceramics is Bi, the firing temperature is low and a thick film can be easily formed on the insulating substrate.

The present invention according to claim 1 has a composition represented by the formula (Bi ₂ O ₂ ) ²⁺ (A _n-1 B _n O _{3n + 1} ) ^2- , wherein A is Ca, Ba, Sr. , Pb, Bi selected from one or more, B in the formula consists of one, two or more selected from Ti, Nb, Ta, n in the formula is 1 ≦ n ≦ 1 or selected from NiO, V ₂ O ₅ , Cr ₂ O ₃ , Fe ₂ O ₃ , MnO ₂ , WO ₃ , TiO ₂ , Nb ₂ O ₅ , SnO ₂ , In ₂ O ₃ It is a bismuth oxide ceramics characterized in that two or more kinds are added or substituted with a part of the compound constituent elements, and the Curie point can be adjusted by the substitution amount of the A element.

For example, the Curie point of Bi ₄ Ti ₃ O ₁₂ is 675 ° C., SrBi ₄ Ti ₄ O ₁₅ is 530 ° C., BaBi ₄ Ti ₄ O ₁₅ is 395 ° C., BaBi ₂ Ta ₂ O ₉ is 110 ° C., and Sr ₂ Bi ₄ Ti ₅ O ₁₈ is 285 ° C., but when it is set to 463 ° C., (Sr _0.5 Ba _0.5 ) Ti ₄ O ₁₅ may be used. Further, transition metal oxides can be made into semiconductors by adding or replacing 0.01 wt% or more, and semiconductors cannot be made sufficiently if the amount is less than this. On the other hand, if it becomes 10 wt%, many different phases other than the main component are generated, and the room temperature electrical resistivity increases or the intended characteristics cannot be obtained.

  A is composed of one or more selected from Ca, Ba, Sr, Pb, Bi, and B is composed of one or more selected from Ti, Nb, Ta, depending on the type of the element. You can change the point. The elements that enter A and B can be selected depending on the size, stability, and reactivity of the ions, and are limited.

  A and B in the chemical formula may deviate from the stoichiometric composition, and if it is 1 or less, sinterability can be improved and more stable conductive properties can be obtained, which is preferable. The composition and the composition of oxygen are determined from the stoichiometric composition, and may deviate from the stoichiometric composition.

Manufacturing conditions vary depending on conditions such as firing temperature and synthesis temperature. The element of A or B may be partially substituted with other elements, but the compound can be selected depending on the application as shown in Table 1. An element different from Bi may be substituted for A and Bi as in Bi ₃ TiNbO ₉ , and Na _0.5 and Bi _2.5 may not be substituted as Na _0.5 Bi _2.5 Ti ₄ O _15. It may be replaced with a stoichiometric ratio, and a part of A is replaced with a non-stoichiometric ratio, such as Ca _0.5 Bi _4.5 of Ca _0.5 Bi _4.5 Ti ₄ O _15. You may do it. That is, the desired Curie point and resistance value can be selected by adjusting the composition of the material according to the application and specifications. That is, n may be a number other than a natural number. When n is a value from 1 to 8, sufficient PTC characteristics are obtained and the crystal is stable. When n is smaller than 1, the crystal is not stable. On the other hand, when n is larger than 8, the crystal orientation becomes too strong, the crystal structure becomes unstable, and the sinterability deteriorates.

The invention according to claim 2 is a bismuth oxide ceramic having a characteristic of room temperature electrical resistivity of 10 ⁷ Ω · cm or less, and the room temperature electrical resistivity of 10 ⁹ to 10 of the conventional bismuth oxide ceramics. Compared with ¹² Ω · cm, the electrical resistivity can be lowered by three orders of magnitude or more, so even when used in a temperature sensor, the operating voltage is low, the application is wide, and accurate characteristics are exhibited with low power.

  The present invention according to claim 3 is a bismuth oxide-based ceramic characterized by exhibiting a rapid resistance decreasing characteristic that is 1/1000 or less when the Curie point is exceeded, and when the compound is used as a sensor. It has switching characteristics at a set Curie temperature, and can function as a switch at a predetermined temperature.

  The present invention according to claim 4 is a bismuth oxide-based ceramic characterized in that the crystal structure has a partly perovskite structure, and is partly perovskite structure in adjusting characteristics including setting of the Curie point. It becomes possible to replace atoms in the crystal in a wide range, and it can be applied to various uses.

  The crystal structure of the compound in the present invention is mainly composed of a layered structure. That is, in order to have a layered structure, valence control can be performed by substituting a transition metal element for an element constituting part of A and B in the above formula, and the electrical conductivity can be imparted. At the same time, the conductivity varies depending on the orientation of the crystal, and by utilizing the orientation, new applications and characteristics can be improved.

Further, SiO ₂ , Al ₂ O ₃ , B ₂ O _3, etc. are added separately, or the constituent elements such as TiO ₂ , Bi ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ are made excessive, Various properties such as resistance-temperature characteristics and withstand voltage characteristics can be improved by reacting to produce a liquid phase, controlling the particle size, and stabilizing the composition.

1. The bismuth oxide ceramics according to the present invention include not only the dielectric properties and piezoelectric properties of conventional bismuth oxide ceramics and similar bismuth titanate ceramic compounds, but also the Curie point as well as the semiconductor properties having conductivity different from the previous properties. It has a unique characteristic that the electric resistance suddenly drops when exceeding.
2. The bismuth oxide ceramics of the present invention have switching characteristics with respect to temperature.
3. The bismuth oxide ceramics of the present invention can be used as a temperature sensor or a switching element.

The present invention improves conductivity by adding a trace amount of transition metal to bismuth oxide ceramics and has NTC characteristics over a wide range. Depending on the additive, when the Curie point is exceeded, the electrical resistance decreases sharply to 1/1000 or less, and switching characteristics are exhibited even in a high temperature range of 100 ° C. or higher. (Bi ₂ O ₂ ) ²⁺ (A _n-1 B _n O _{3n + 1} ) ² has a composition represented by the formula ^2- , wherein A is one selected from Ca, Ba, Sr, Pb, Bi Or B in the formula consists of one or more selected from Ti, Nb, Ta, n in the formula satisfies 1 ≦ n ≦ 8, and NiO, V ₂ O ₅ , one or more selected from Cr ₂ O ₃ , Fe ₂ O ₃ , MnO ₂ , WO ₃ , TiO ₂ , Nb ₂ O ₅ , SnO ₂ , In ₂ O ₃ are added or the above-mentioned compound constituent elements The Curie point can be adjusted by the amount of substitution of the A element.

Bi ₂ O ₃ powder and TiO ₂ powder each having a purity of 99.9% or more are mixed as raw materials, and further added so that the atomic number ratio of Bi and Ti contained in these mixed powders is 4: 3. After preparing 0.1 wt% of transition metal element MnO ₂ as a product, zirconia balls were used and mixed in an alcohol solvent by a ball mill for 18 hours. After drying the obtained mixed slurry, so-called calcination was performed in the atmosphere at 800 ° C. for 3 hours. 3 wt% of PVA (polyvinyl alcohol) as a binder was added to the obtained synthetic powder, granulated with a spray dryer, and then pressure molded at 1 MPa to obtain a molded body. The obtained molded body was fired at 1150 ° C. in an air atmosphere. As a result of measuring the density of the obtained sintered body after firing, it was 5.52 g / cm ³ . Furthermore, as a result of measuring electric conductivity, room temperature resistance of about 10 ¹⁰ Ω · cm was shown. As a result of measuring the resistance temperature characteristics from room temperature to 600 ° C, the resistance suddenly decreases when the Curie point exceeds 550 ° C as shown in Fig. 1, and the characteristic is less than 1Ω · cm which is the limit of the measuring instrument used this time. showed that.

In the same manner as in Example 1, SrCO ₃ powder, Bi ₂ O ₃ powder, and TiO ₂ powder each having a purity of 99.9% or more were mixed, and the number of atoms of each of Sr, Bi, and Ti contained in these mixed powders The ratio was adjusted to 1: 4: 4 and mixed for 18 hours by a ball mill. The obtained slurry was dried, and after granulation, so-called calcination was performed in the atmosphere at 850 ° C. for 3 hours. To the obtained powder, 0.5 wt% of Nb ₂ O ₅ and ₅ wt% of PVA (polyvinyl alcohol) as a binder were added, and after granulation, uniaxial molding was performed at 10 MPa to obtain a molded body. The obtained molded body was fired in air at 1180 ° C. for 2 hours. As a result of measuring the density of the obtained sintered body, it was 6.79 g / cm ³ . Moreover, as a result of measuring electrical conductivity, it showed a normal temperature resistance value of 10 ⁸ Ω · cm, and as a result of measuring resistance temperature characteristics, NTC characteristics were shown.

In addition, Table 1 shows the results of producing materials of other compositions and measuring the density and electrical characteristics in the same manner as in Examples 1 and 2 together with the results of Examples. The porcelain composition of the present invention shown in the examples is a bismuth oxide ceramic compound, which has a room temperature resistance value of 10 ⁷ to 10 ¹⁰ Ω · cm as compared with a series of conventional bismuth oxide ceramic compounds. Compared with the compound, the conductivity was improved by about 2 to 3 digits.

  Not only the dielectric properties and piezoelectric properties of conventional bismuth oxide ceramics and similar bismuth titanate ceramic compounds, but also the semiconductor properties with conductivity different from the previous properties, as well as the electrical resistance decreases rapidly when the Curie point is exceeded It is an object of the present invention to provide a bismuth oxide-based ceramic having unique characteristics. It can be used as a temperature sensor or a switching element.

The resistance-temperature characteristic of Example 1 is shown. The resistance-temperature characteristic and NTC characteristic of Example 2 are shown.

Claims (4)

(Bi ₂ O ₂ ) ²⁺ (A _n-1 B _n O _{3n + 1} ) ₁ having a basic composition represented by the formula ^2- , wherein A is selected from Ca, Ba, Sr, Pb, Bi It consists of seeds or two or more, and B in the formula consists of one or more selected from Ti, Nb, Ta, and n in the formula is 1 ≦ n ≦ 8 (n includes other than natural numbers) filled, _NiO to the basic _{composition, V 2 O 5, Cr 2} O 3, Fe 2 O 3, MnO 2, WO 3, TiO 2, Nb 2 O 5, SnO 2, 1 or more kinds of _in 2 _{O 3} Is added in a total of 0.01 wt% to 10 wt%, or a part of the constituent elements of the basic composition is replaced. 2. The bismuth oxide ceramics according to claim 1, wherein the electrical resistivity at room temperature is 10 ⁷ Ω · cm or less. The bismuth oxide ceramics according to claim 1 or 2, wherein the electrical resistivity decreases to 1/1000 or less when the Curie point is exceeded. The bismuth oxide ceramics according to any one of claims 1 to 3, wherein a part of the crystal structure of the basic composition is a perovskite structure.

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