JP2000223352A - Multilayer ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer ceramic capacitor, having a high specific inductive capacity εr and superior temperature characteristic, which can be sintered simultaneously with the internal electrode layer of Ag-Pd alloy which is mainly comprised of Ag, at a temperature of 1,150 deg.C or lower. SOLUTION: In this multilayer ceramic capacitor, having a internal electrode layer consisting of Ag-Pd, a dielectric magnetic layer contains Ba, Ti and Bi as metal elements. When the composition formula by the molar ratio of the metal element oxide is represented by (100-a)BaTiO3.aBi2Ti2O7, the dielectric magnetic layer is composed of the main component, where (a) satisfies 2.5<=a<=6.0, and the supplemental component of Nb of 0.7 to 1.9 mol part in terms of Nb2O5 with respect to the main component of 100 mol part, Zn of 0.8 to 1.9 mol part in terms of ZnO, a rare earth element of 0.4 mol part or less (0 is not included) in terms of RE2O3 (RE is a rare earth element) and Si of 0.4 to 8.3 mol part in terms of SiO2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer ceramic capacitor suitably used for a vehicle.

[0002]

2. Description of the Related Art Conventionally, a multilayer ceramic capacitor generally has a structure in which a plurality of dielectric sheets serving as dielectric ceramic layers each having a main surface coated with a conductive film serving as an internal electrode layer are laminated, and the internal electrode layer of each sheet is formed. The laminate was cut so as to extend to a pair of different ends and fired, and then external connection electrodes were formed at the pair of ends. Such multilayer ceramic capacitors have been rapidly used in a wide variety of electronic circuits due to the rapid progress of miniaturization of electronic components with the development of electronics in recent years.

[0003] In particular, capacitors called X7R characteristics are:
From -55 to 125 [deg.] C., the rate of change in capacity is within. +-. 15%. The dielectric material having this property is B
The main electrode was aTiO ₃ , and the internal electrode layer was made of an alloy of Pd and Ag or Ni, and was simultaneously fired at 1200 to 1350 ° C.

[0004] In recent years, with the computerization of various controls for automobiles, ECUs (engine control units) and the like have been used.
Installation in the engine room is effective. But,
The interior of the engine room is -20 ° C or less at the start of the winter in a cold region, and + 130 ° C in the summer after the engine is started.
And become very hot. However, in the conventional multilayer ceramic capacitor having the X7R characteristic, the capacitance value sharply decreases when the temperature exceeds 125 ° C., and the capacitance change rate becomes −4 at 150 ° C.
It will be as low as 0%.

Further, a dielectric ceramic composition having a flat temperature characteristic up to a high temperature region, for example, 150 ° C., is disclosed in
427, JP-A-7-37428, JP-A-8
The one disclosed in Japanese Patent Application Laid-Open No. 295559/1990 is known. For example, in the dielectric ceramic composition disclosed in JP-A-7-37428, BaT partially substituted with Pb is used.
iO ₃ , ZnO, Bi ₂ O ₃ , Nb ₂ O ₅ , RE ₂ O
₃ (RE is a rare earth element) and a glass mainly composed of SiO ₂ .

In such a dielectric porcelain composition, 116
It can be fired at a low temperature of 0 ° C. or lower and has flat temperature characteristics over a wide temperature range from −55 ° C. to + 150 ° C.

In this dielectric ceramic composition, Ba is used.
_{TiO 3, PbO, TiO 2,} ZnO, Bi 2 O3, N
After b ₂ O ₅ and RE ₂ O ₃ powders are mixed to have a predetermined composition ratio, the mixture is calcined, and the calcined product is mixed with BaO—SrO—
The glass component is added consisting of _{CaO-Li 2 O-SiO 2} , it was fired this.

[0008]

However, each of the above-mentioned dielectric ceramic compositions has a problem that the relative dielectric constant is small.

For this reason, when the dielectric ceramic layer is used for the dielectric ceramic layer of the multilayer ceramic capacitor, it is necessary to take measures such as reducing the thickness of the dielectric ceramic layer and increasing the number of layers.

The present invention has been devised in view of the above-mentioned problems, and has as its object the purpose of using Ag at a low temperature of 1150 ° C. or less.
Can be fired at the same time as the internal electrode layer of an Ag-Pd alloy containing as a main component, a dielectric material having a high relative dielectric constant εr of 2000 or more, and a large capacity, easy to manufacture, small and inexpensive due to a dielectric ceramic having good temperature characteristics. An object of the present invention is to provide a multilayer ceramic capacitor.

[0011]

SUMMARY OF THE INVENTION The present invention is directed to a BaTiO ₃
In a multilayer ceramic capacitor comprising a dielectric ceramic layer mainly composed of: and an internal electrode layer made of Ag-Pd, the dielectric ceramic layer contains Ba, Ti and Bi as metal elements, and The composition formula based on the molar ratio of the element oxide is expressed as (100-a) BaTiO ₃ .aBi ₂ T
When expressed as i ₂ O ₇ , N is defined as Nb with respect to a main component satisfying the condition that a satisfies 2.5 ≦ a ≦ 6.0 and 100 mol parts of the main component.
Is 0.7 to 1.9 mol parts in terms of Nb ₂ O ₅ , and Zn is Zn.
0.8 to 1.9 mol parts in terms of O, the rare earth element is RE ₂ O
_This is a monolithic ceramic capacitor composed of 0.4 mol part or less (excluding 0) in terms of ₃ (RE is a rare earth element) and 0.4 to 8.3 mol parts of Si in terms of SiO ₂ .

That is, there are main crystal grains composed of a perovskite-type composite oxide containing Ba and TiO _3, and crystal grains composed of a composite oxide containing Bi and Ti as a grain boundary phase.

[0013]

The dielectric ceramic of the multilayer ceramic capacitor of the present invention can be fired at a relatively low temperature of 1150 ° C. or less.
Therefore, even if a relatively inexpensive Ag-Pd alloy containing 60% by weight or more of Ag and 40% by weight or less of Pda is used as the internal electrode layer, it can be fired simultaneously with the above-described dielectric ceramic layer.

Further, the dielectric constant is as high as 2,000 or more, and the temperature change of the capacitance on the high temperature side can be reduced.

That is, in the conventional dielectric ceramic composition, Bi
Due to the addition of the Bi ₂ O ₃ powder as in the produced dielectric porcelain, the grain boundary of BaTiO ₃ crystal grains,
Although Bi ₂ O ₃ particles are present, the relative dielectric constant is as small as about 2000 at the maximum, but in the present invention, Bi between the main crystal particles has a higher dielectric constant than Bi ₂ O _3. However, since it is present as crystal particles composed of a complex oxide containing Bi and Ti having a high Curie temperature, the dielectric constant of the dielectric ceramic can be as high as 2000 or more, and the temperature characteristics are improved.

Further, by containing Si and Zn in the grain boundary phase between the main crystal grains of the dielectric ceramic layer, the sinterability of the dielectric ceramic is improved, and the dielectric ceramic can be fired at a relatively low temperature of 1150 ° C. or less. Using the conductive metal of the internal electrode layer of the Ag-Pd alloy containing 60 wt% or more of Ag, it can be co-fired with the dielectric ceramic. Further, the temperature characteristics can be improved by Zn in the grain boundary phase.

In the dielectric porcelain of the present invention, the grain boundary phase Bi
Is a composite oxide containing Bi and Ti, in particular, Bi ₂ Ti
_The presence of only crystal grains composed of ₂ O ₇ can further improve the relative dielectric constant and temperature characteristics.

In the dielectric porcelain of the present invention, the composition formula based on the molar ratio is (100-a) BaTiO ₃ .aBi ₂
When expressed as Ti ₂ O ₇ , N is based on a main component satisfying the condition of 2.5 ≦ a ≦ 6.0 and 100 mole parts of the main component.
b is 0.7 to 1.9 mol parts in terms of Nb ₂ O ₅ , and Zn is Z
0.8 to 1.9 mole parts in terms of nO, rare earth element is RE ₂
0.4 mol parts or less (0 in terms of O ₃ (RE is a rare main element))
), And Si is 0.4 to 8.3 in terms of SiO 2.
By containing a molar part, it can be fired at a low temperature of 1150 ° C. or less, the dielectric constant of the dielectric ceramic can be increased to 2000 or more, the temperature change of the capacitance on the high temperature side can be reduced, and the EIA standard X8R (+25) (Based on the capacitance in ° C, the temperature change rate of the capacitance is within ± 15% over a wide temperature range from -55 ° C to + 150 ° C.)
Can be satisfied.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a multilayer ceramic capacitor according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is an external perspective view of a multilayer ceramic capacitor according to the present invention, and FIG. 2 is a sectional view taken along line AA of FIG.

The multilayer ceramic capacitor of the present invention has a capacitor body 4 in which dielectric ceramic layers 1 and internal electrode layers 2 are alternately stacked, and a terminal electrode 3 formed on a pair of ends of the capacitor body 4. It is composed of

The dielectric ceramic layer 1 is made of Ba as a metal element.
It contains Ti and Bi, and the composition formula based on the molar ratio of these metal element oxides is (100-a) BaTiO ₃ .aB
When expressed as i ₂ Ti ₂ O ₇ , a is 2.5 ≦ a ≦ 6.
0 and 0.7 to 1.9 mol parts of Nb in terms of Nb ₂ O ₅ with respect to 100 mol parts of the main component and Z
n is 0.8 to 1.9 mol parts in terms of ZnO, rare earth elements are 0.4 mol parts or less (excluding 0) in terms of RE ₂ O ₃ (RE is a rare earth element), and Si is 0 in terms of SiO _2. .4 ~
It is configured to contain 8.3 mole parts.

The dielectric porcelain comprises a main crystal grain composed of a perovskite-type composite oxide containing at least Ba and Ti as metal elements, and a grain boundary phase containing at least Si, Zn, Bi and Ti as metal elements. Wherein the grain boundary phase Bi exists as crystal grains made of a complex oxide containing Bi and Ti.

The internal electrode layers 2 are arranged between the dielectric ceramic layers 1. One internal electrode layer 2 adjacent in the thickness direction via the dielectric ceramic layer 1 extends to one of a pair of ends of the capacitor body 4, and the other internal electrode layer 2 It extends to the other of the pair of ends. Such an internal electrode layer 2 is made of an Ag-Pd alloy mainly composed of Ag. Specifically, the weight ratio of Ag is 60
For example, the weight ratio of Pd is 40 wt% or less. When the weight ratio of Ag is increased as described above, the melting point of Ag-Pd is reduced, but it is difficult to co-fire with the dielectric ceramic. Since the dielectric porcelain of the present invention can be fired at 1150 ° C. or lower, an inexpensive conductor material with a higher Ag weight ratio than before can be used.

External terminals are formed at a pair of ends of the capacitor body 4 in which the dielectric ceramic layers 1 and the internal electrode layers 2 are alternately laminated. The external terminal may be, for example, a thick base conductor film containing Ag as a main component, Ni
It has a structure in which plating, soldering, and tin plating are laminated in this order. Alternatively, a conductive resin layer may be provided on the thick underlying conductor film, and the surface thereof may be plated.

In the multilayer ceramic capacitor having the above structure, the dielectric porcelain includes at least Ba as a metal element.
And main crystal particles composed of a perovskite-type composite oxide containing Ti, and at least Si, Zn,
It is composed of a grain boundary phase containing Bi and Ti, and Bi of the grain boundary phase exists as crystal grains composed of a complex oxide containing Bi and Ti.

Here, Bi of the grain boundary phase between the crystal grains has a relative dielectric constant of 4,000 or more at room temperature and a crystal particle composed of a complex oxide containing Bi and Ti having a Curie temperature of 300 ° C. or more. Due to the presence, the dielectric constant of the dielectric ceramic can be improved to 2000 or more, and the temperature characteristics on the high temperature side can be improved.

The Bi of the grain boundary phase is present only as crystal particles composed of a complex oxide containing Bi and Ti, in particular, Bi ₂ Ti ₂ O _7.
Only the peak of the composite oxide containing i and Ti is present,
It means that there is no Bi ₂ O ₃ peak.

The dielectric ceramic constituting the multilayer ceramic capacitor of the present invention has a compositional formula (100-
a) When expressed as BaTiO ₃ + aBi ₂ Ti ₂ O ₇ , a
Satisfying 2.5 ≦ a ≦ 6.0 as a main component.

In this composition formula, the molar ratio a of the titanate containing Bi and Ti is set to 2.5 ≦ a ≦ 6.0 mol% when the molar ratio a is less than 2.5 mol%. This is because the sinterability decreases and the dielectric loss becomes 3.0% or more.

On the other hand, if it exceeds 6.0 mol%, the temperature characteristics and the relative dielectric constant are lowered, or the temperature characteristics, that is,
The absolute maximum value of the capacity change rate at −55 to 150 ° C. is 1
Greater than 5% (minimum value is less than -15%). In particular, 3.5 ≦ a ≦ 4.4 is desirable from the viewpoint of the relative dielectric constant and temperature characteristics of the dielectric ceramic. In addition, such a composition system has a temperature characteristic in which the capacitance change rate of the capacitance at 150 ° C. becomes minimum.

[0032] Then, with respect to the main component as 100 parts by mole, from 0.7 to 1.9 molar parts of Nb calculated as Nb ₂ O _5, Z
n is 0.8 to 1.9 mol parts in terms of ZnO, rare earth elements are 0.4 mol parts or less (excluding 0 mol parts) in terms of RE ₂ O ₃ (RE is a rare earth element), and Si is equivalent to SiO _2. At 0.4
8.3 mol parts.

Here, Nb is converted to Nb ₂ O ₅ by 0.7 to 0.7%.
The reason for containing 1.9 mol parts is that if it is less than 0.7 mol parts, the dielectric loss becomes 3.0% or more, and the sinterability deteriorates.

If it exceeds 1.9 mole parts, the relative dielectric constant becomes small, and the temperature characteristics, ie, -55 to 150 ° C.
Is greater than 15%. Particularly, from the viewpoint of the relative dielectric constant and dielectric loss of the dielectric ceramic, 0.9 to l. 4 mole parts are preferred.

Further, Zn is 0.8 to 1.9 in terms of ZnO.
The molar part was contained when the molar ratio was less than 0.8 molar part.
The sinterability deteriorates, and the temperature characteristics, ie, -55 to 150 ° C
Is greater than 15%. On the other hand, if the amount exceeds 1.9 mol part, the dielectric constant loss becomes 3.0% or more, and the sinterability deteriorates.

In particular, from the viewpoint of the temperature characteristics of the dielectric porcelain, 1.2 to 1.5 mol parts is preferable.

[0037] In addition, the Si in terms of SiO ₂ 0.4
The reason for containing 8.3 parts by mole is that if it is less than 0.4 parts by mole, the sinterability deteriorates, and if it exceeds 8.3 parts by mole, the relative dielectric constant becomes low. Particularly, from the viewpoint of the relative dielectric constant of the dielectric ceramic, 1.6 to 4.0 mol parts is preferable.

Further, the rare earth element is converted to RE ₂ O ₃ (R
E is a rare earth element) containing 0.4 mole part (excluding 0) because the sinterability is deteriorated at 0 mole part, and the relative permittivity becomes small at more than 0.4 mole part, This is because sinterability deteriorates. Particularly, from the viewpoint of the relative permittivity of the dielectric ceramic, 0.25 to 0.4 mol part is preferable. Examples of rare earth elements include Sc, Y, La, Ce, Pr, Nd, Pm, and S.
m, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb
Among them, Y, La, Ce, Nd, Sm,
Dy, Ho, Er, and Tb are desirable, and Tb is more desirable.

Further, in order to stabilize characteristics having a relative dielectric constant of 2000 or more, an alkaline earth metal may be contained.
The limit is 4.0 mol parts in terms of alkaline earth metal oxide. If it exceeds 4.0 mole parts, -55 to 150 ° C
In this case, the minimum value of the rate of change in capacitance becomes a change exceeding -15%, which is not preferable. In particular, from the viewpoint of the relative dielectric constant and temperature characteristics of the dielectric ceramic, 1.2 to 2.8 mol parts is preferable.
Examples of the alkaline earth metal include Be, Mg, Oa, Ba,
There is Sr.

In the multilayer ceramic capacitor according to the present invention in which the dielectric ceramic layers 1 and the internal electrode layers 2 are alternately stacked, an alloy containing Ag is used as the internal electrode layer 2, and Ag is used as the internal electrode layer 6.
The internal electrode layer 2 containing 0% or more can be used. In this case, the electrode formation state is good, and the conduction resistance can be further reduced. When the internal electrode layer 2 having a composition containing 60% or more of Ag and the dielectric ceramic layer 1 are simultaneously fired, the firing temperature of the multilayer ceramic capacitor is 115 ° C. or less, particularly 1000 to 1150 ° C.

The dielectric ceramic layer 1 of the multilayer ceramic capacitor of the present invention is composed of, for example, main crystal grains made of BaTiO ₃ and a grain boundary phase formed between the main crystal grains. , Si, Zn and, if desired, a glass phase composed of an alkaline earth metal, and crystal grains composed of Bi ₂ Ti ₂ O ₇ .

In order to precipitate Bi titanate in the grain boundary phase as described above, Bi ₂ O ₃ powder, TiO 2
₂ powder to form Bi ₂ Ti ₂ O ₇ crystals.
It becomes possible by adding i ₂ Ti ₂ O ₇ powder to BaTiO ₃ and firing it. By adding Bi as Bi ₂ Ti ₂ O ₇ crystal powder, in X-ray diffraction measurement,
Bi ₂ Ti ₂ O ₇ peak appears, and Bi ₂ O _2
A dielectric porcelain without the peak ₃ can be produced.

The dielectric porcelain is, specifically, BaTiO ₃
The above-mentioned Bi ₂ Ti ₂ O ₇ powder, ZnO powder, rare earth element oxide powder, SiO ₂ powder, Nb ₂ O ₅ powder if desired, and alkaline earth metal oxide powder if desired are added to the powder, and the doctor blade is used. After forming by a method, a sheet on a film is formed, and a conductive film to be the internal electrode layer 2 is formed on the upper surface of the sheet by printing a conductive paste by screen printing, and then a conductive film to be the internal electrode layer 2 is formed. The laminated sheets are laminated, thermocompressed, pressed, cut, and debindered.
Baking for about 0.5 to 2 hours, baking of the terminal electrode 3,
Plating is performed to obtain a multilayer ceramic capacitor.

In addition, the multilayer ceramic capacitor of the present invention contains unavoidable impurities in the raw materials such as Fe and Al, or the ball components of the pulverized ball, such as ZrO ₂ , which are mixed in the manufacturing process. There are cases. Also,
The multilayer ceramic capacitor of the present invention may contain Mn. In addition, dielectric porcelain has an average crystal grain size of 0.3 to
1.0 μm.

In the multilayer ceramic capacitor configured as described above, since the dielectric ceramic layer 1 exists as crystal particles made of a complex oxide containing Bi and Ti having a high dielectric constant and a high Curie temperature, The relative dielectric constant of the dielectric ceramic can be as high as 2000 or more, and the temperature characteristics can be improved.

[0046]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, Bi ₂ O ₃ , TiO
₂ were weighed, pure water was added as a medium to the raw material powder, and the mixture was mixed for 24 hours in a ball mill using ZrO ₂ balls. The mixture was dried, and then the dried product was heated at 900 ° C. Was baked in the air for 1 hour. Compounds of Ba and Ti, Nb, Tb, Si, Zn
And the like were weighed so as to have a ratio shown in Table 1, and mixed with a dispersant and a dispersion medium in a ball mill for 24 hours to prepare a raw material slurry. An organic binder and a plasticizer were added to this slurry, and after sufficient stirring, a film-like sheet was formed by a doctor blade method. An Ag-Pd paste (Ag 70% by weight, Pd 30% by weight) prepared for a conductor film to be an internal electrode layer was printed on this film-like sheet by screen printing, a dummy layer was added and laminated, and thermocompression bonding was followed by cutting. This is heated in the air at a temperature of 300 ° C. for 2 hours to remove the binder.
Fired for hours. After barrel polishing, a silver paste adjusted for a terminal electrode is applied to the end face, baked at 700 ° C. in the air, plated, and has a porcelain dimension of 3.2 mm × 1.6 mm as a terminal electrode, effective electrode area. 2.2mm ×
A multilayer ceramic capacitor having a thickness of 1.1 mm and a dielectric ceramic layer thickness of 25 μm × 10 layers was formed.

Next, the capacitance of these evaluation samples was measured at a frequency of 1.0 kHz and an input signal level of 1.0 Vrms using an LCR meter 4284A. The dielectric loss was calculated from the capacitance.

Further, based on the capacitance at 25 ° C., the minimum value of the capacitance change rate in the range of −55 to 150 ° C. was examined. In the above-described composition of the dielectric ceramic, the capacitance change rate at 150 ° C. has the minimum value, so the capacitance change rate at 150 ° C. is shown.

The porcelain without the internal electrode layer was crushed into a powder in a mortar and subjected to X-ray diffraction measurement to confirm what kind of crystal Bi was present. Table 1 shows the results.

[0050]

[Table 1]

In the table, regarding the Bi crystal phase,
“A” generates a Bi ₂ Ti ₂ O ₇ crystal phase containing Ti, “B” and a Bi ₂ Ti ₂ O ₇ crystal phase are not generated, and a Bi ₂ O ₃ crystal phase is not generated. .

According to Table 1, the dielectric ceramic of the multilayer ceramic capacitor of the present invention can be fired at a low temperature of 1150 ° C. or less, can achieve a relative dielectric constant εr of 2000 or more, and satisfies the above composition formula. The sample has a relative dielectric constant of 2050 or more, a dielectric loss at a measurement frequency of 1 kHz of 3.0% or less, and EIA standard X8R (−55 ° C. to + 150 ° C. based on the capacitance at + 25 ° C.)
± 1 temperature change rate of capacitance over a wide temperature range
(Within 5%).

On the other hand, in the multilayer ceramic capacitor of the conventional composition in which Bi was added as Bi ₂ O ₃ powder (sample No. 39), only Bi ₂ O ₃ crystals were precipitated as Bi crystals, and the relative dielectric constant was low. 1720, dielectric loss is 2.4
2%, which is the sample No. of the present invention. It can be seen that the characteristics are lower than that of No. 5. FIG. The capacitance change rate of the capacitance of No. 5 is described.

[0054]

As described above, the dielectric ceramic of the multilayer ceramic capacitor of the present invention can be fired at a temperature of 1150 ° C. or less and can be fired simultaneously with the internal electrode layer containing Ag as a main component. , 2000 or more, and the temperature characteristics can be improved. In particular, when the composition formula of the present invention is satisfied, the X8R characteristics can be satisfied. Can provide a simple capacitor.

[Brief description of the drawings]

FIG. 1 is a perspective view of a multilayer ceramic capacitor according to the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 5 is a graph showing a capacity change rate of No. 5;

[Explanation of symbols]

 1 ··· dielectric ceramic layer 2 ··· internal electrode layer 3 ··· terminal electrode 4 ··· capacitor body

 ──────────────────────────────────────────────────の Continued on the front page F-term (reference) 4G031 AA06 AA07 AA11 AA14 AA26 AA30 AA35 AA39 BA09 CA03 5E001 AB03 AC03 AC10 AD03 AE00 AE02 AE03 AE04 AF00 AF06 AH01 AH05 AH09 AJ01 AJ02 5G303 CB01 AB06 AB01 CB03 CB21 CB22 CB30 CB35 CB38 CB40 CB41 CB43

Claims (1)

[Claims] 1. A multilayer ceramic capacitor comprising a dielectric ceramic layer containing BaTiO ₃ as a main component and an internal electrode layer made of Ag-Pd, wherein said dielectric ceramic layer comprises Ba, Ti and Bi as metal elements. And the composition formula based on the molar ratio of these metal element oxides is (100-a) BaTiO ₃ .aBi ₂ Ti ₂
When expressed as O ₇ , Nb is 0.7 to 1.0 as Nb ₂ O _{5 in} terms of Nb ₂ O ₅ with respect to a main component in which a satisfies 2.5 ≦ a ≦ 6.0 and 100 mol parts of the main component. 9 mol parts, Zn is 0.8 to 0.8 in terms of ZnO
1.9 mole parts, rare earth element is 0.4 mole parts or less (excluding 0) in terms of RE ₂ O ₃ (RE is a rare earth element), Si
Characterized in that it contains 0.4 to 8.3 mol parts in terms of SiO ₂ .