JPS6128620B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a high dielectric constant ceramic composition, in which Pb (Mg1/3
Nb2/3) O ₃ -PbTiO ₃ -based oxide, expressed as ABO ₃ where Pb element is A, Mg, Nb, and Ti element is B, and the A/B molar ratio is 0.9200≦A/B≦1.0000.
The present invention relates to a high dielectric constant ceramic composition which has a significantly improved dielectric constant, can be sintered at a particularly low temperature, has a small dielectric loss, and has an excellent temperature change rate. Conventionally, high-permittivity ceramic compositions have been made with barium titanate BaTiO ₃ as the main component, barium stannate BaSnO ₃ , calcium titanate CaTiO ₃ , PbTiO _{3 ,} etc., and their substituted solid solutions or other crystal structures. Composite dielectric ceramics with compounds having the above are widely put into practical use to meet various required characteristics. For these porcelain dielectrics, if the dielectric constant at room temperature is maximized to improve the characteristics, the temperature change in the dielectric constant becomes large, while if the temperature change in the dielectric constant is made small, the maximum value of the dielectric constant decreases. There are various problems in practical use, and improvements have been desired. Furthermore, since it is mainly composed of BaTiO ₃ , it requires sintering at a high temperature range of usually around 1200 to 1400℃, which requires a large amount of thermal energy during sintering. There were drawbacks such as severe thermal deterioration loss of the furnace material and therefore increased maintenance costs for the firing equipment. Furthermore, in the case of multilayer porcelain capacitors, which are rapidly becoming popular these days, the manufacturing method requires that the internal electrodes be sintered while being embedded in a porcelain dielectric, which is different from conventional porcelain capacitors whose sintering temperature exceeds 1200°C. For the dielectric, it was necessary to use precious metals such as platinum, palladium, or alloys of these, which are stable at high temperatures of 1,300°C or higher, but are expensive. If it is possible to use a ceramic dielectric material that can be sintered at a low temperature of about 1000℃ as a multilayer ceramic capacitor, use an inexpensive metal material such as silver, nickel, or aluminum for the embedded internal electrode. This is extremely advantageous in terms of manufacturing costs. Of course, the porcelain dielectric obtained by low-temperature sintering is required to have high insulation resistance, relatively large dielectric constant, small dielectric loss, and excellent temperature change rate. Hitherto, there have been few stable porcelain dielectrics produced by low-temperature sintering that meet these conditions, and the realization of such materials has been desired. In view of the above _- mentioned demands, the present inventors have arrived at the present invention as a result of _intensive research. Pb (Mg1/3Nb2/3)O ₃ ...... 88.0 to 99.0 mol% PbTiO ₃ ...... 1.0 to 12.0 mol% Pb element is mixed with A, Mg, Nb,
The chemical formulas of these complex compounds are as follows, with Ti element as B:
When expressed as ABO ₃ , the molar ratio of A/B is 0.9200
The present invention relates to a high dielectric constant ceramic composition characterized in that ≦A/B≦1.0000. That is, the present inventors have already proposed a binary high permittivity ceramic composition consisting of Pb(Mg1/3Nb2/3)O ₃ -PbTiO ₃ system that can be sintered at low temperatures, but the present invention Within this composition, the Pb element is A, Mg, Nb,
When the Ti element is B and the chemical formula is expressed as ABO ₃ , the A/B mole is due to excessive addition of the B site element.
It has been discovered that the dielectric constant is significantly improved by setting 0.9200≦A/B≦1.0000,
The present invention also relates to a high dielectric constant ceramic composition that has extremely good dielectric loss and excellent sinterability. That is, the present invention provides a high dielectric constant ceramic composition that can be sintered at a low temperature around 850 to 1100°C and has excellent properties. The present invention will be explained in detail below with reference to Examples. Lead oxide (PbO), niobium oxide (Nb ₂ O ₅ ), magnesium oxide (MgO), and titanium oxide (TiO ₂ ) were used as starting materials and were weighed so as to have the compounding ratios shown in Table 1. These raw material mixtures were wet mixed in a synthetic resin ball mill and then calcined at 700 to 850°C for 2 hours to cause a chemical reaction. This reaction product is pulverized and mixed again using a ball mill to a particle size of about several μm. An appropriate amount of polyvinyl alcohol (PVA) was added as a binder to this mixture, and a disc-shaped molded product with a diameter of 16.5 mm and a thickness of 0.6 mm was produced at a molding pressure of about 3 tons/cm ² . The molded product is sealed in a magnesia porcelain container to prevent the lead component from evaporating at high temperatures.
Main firing at ~1100℃ for 2 hours. Silver electrodes are baked onto both end faces of the porcelain body thus obtained. Table 1 shows the results of measuring the electrical properties of the samples produced in this way. Here, permittivity εs and dielectric loss (tanδ)
was measured at a frequency of 1KHz. Temperature characteristics are -25℃ and +25℃ based on room temperature 20℃.
The rate of change in capacity at 85°C was determined.

【table】

[Table] In Table 1, Samples Nos. 6 and 10 are outside the scope of the present invention and are shown for comparison. As is clear from Table 1, those within the range of the present invention exhibit a high relative dielectric constant (εs) of about 20,300 to 29,800, and a very small dielectric loss (tan δ) of 0.8 to 1.7%. 1100℃ as shown
Sintering is possible at low temperatures below. That is, if the composition deviated from this range, it was not possible to obtain the desired properties as shown in Table 1. The reason for this limitation will be explained in detail. In a region where the A/B molar ratio is smaller than 0.9200, there is no improvement in the dielectric constant (εs) and there is no feature that limits the A/B molar ratio. In the examples, MgO and the like were used in the form of carbonate, but it is clear that other forms such as nitrate are also included in the technical idea of the present invention. As described above, the Pb(Mg1/3Nb2/3)O ₃ − of the present invention
PbTiO is a ₃ -based oxide that contains Pb elements such as A, Mg, Nb,
When the Ti element is B and the chemical formula is expressed as ABO ₃ ,
By setting the A/B molar ratio to 0.9200≦A/B≦1.0000, the dielectric constant is significantly improved, and a new ceramic composition with extremely good dielectric loss (tan δ) and capacitance change rate can be obtained. In addition, when used in a multilayer ceramic capacitor, the embedded internal electrode contains silver, nickel, or
It became possible to use low melting point metals such as aluminum. Therefore, compared to conventional sintered materials in high-temperature ranges, high-permittivity porcelain is extremely effective in terms of cost from the perspective of energy saving, as it is significantly effective in reducing the amount of thermal energy and maintenance costs for firing furnace materials, etc. There are great industrial benefits as a result of the ability to provide compositions.

Claims (1)

[Scope of Claims] 1. A composition mainly containing Pb(Mg1/3Nb2/3)O ₃ -PbTiO ₃ , wherein Pb(Mg1/3Nb2/3)O ₃ ......88.0 to 99.0 mol% PbTiO ₃ ...... Pb element is added to A, Mg, Nb, Ti in a composition range of 1.0 to 12.0 mol%.
Let the element be B, and the chemical formula of these complex compounds is
When ABO ₃ is expressed, the molar ratio of A/B is 0.9200≦
A high dielectric constant ceramic composition characterized in that A/B is within the range of 1.0000.