DE1464462C - Process for the production of electrical capacitors. Eliminated from: 1244038 - Google Patents

Description

The invention relates to a method for producing electrical capacitors, in which glass strips alternately built into a stack with metal foils and an envelope made of glass are surrounded and this structure then, under pressure, to form a hermetically sealed one Body is fused.

A method for the production of capacitors is already known, in which preformed parts for the dielectric coating and for the dielectric intermediate layer (s) with the electrically conductive ones Layers put together and the parts of the envelope using heat and pressure fused to each other and to the lead wires (U.S. Patent 2,696,577). According to the invention a capacitor is now to be developed using glasses that extend through Convert heat treatment into a glass crystal mixed body and here in the most economical Functioning of a capacitor with the desired properties that are only ceramic in themselves Intermediate layers would come.

The invention is not intended to be limited to one by the use of any particular glass Capacitor of particularly small dimensions to get its layers between the metal layers with a corresponding increase in the dielectric constant and dielectric strength the necessary for this have small thickness dimensions, but also provide information on how to proceed has to get to the desired result in the fastest and most economical way reach.

This is achieved according to the invention in a method for the production of electrical capacitors, in which glass strips with metal foils are alternately built into a stack and surrounded by an envelope made of glass, and this structure is then fused under pressure to form a hermetically sealed body, in that For the glass strips and the enveloping body, a composition of oxide-based, a total amount of 30 to 90 mol percent of the constituents of at least one ferroelectric oxygen octahedral compound from the group of BaTiO ₃ , CdTiO. ,, NaNbO ₃ , KNbO ₃ , Cd _{0 5} NbO ₃ , Sr _{0 5} Nb0 ₃ , Pb _{0 5} NbO ^, Ba _0-5 NbQ ₃ , CdNbO _{3 5} , SrNbO _{3 5} , BaNbO ₃₅ , PbNbO _3-5 , CdZrO ₃ , CaZrO ₃ and PbZrO ₃ 'and from a glass-forming Oxide from the class SiO ₂ , B ₂ O ₃ and P ₂ O ₅ is used and the condenser is cooled after fusing, reheated and at a temperature between the peak temperature of the crystallization of the ferr oelectric compound and about 50 ° C below the lowest point of the first melting drop of the DTA curve of the glass for a period of at least one hour at the lowest temperature, up to at least half a minute at the higher temperature for crystallization of the ferroelectric compound and then is completely cooled.

A glass body that has good dielectric properties has become known (French Patent specification 1 177 799), in which a mixture of ferroelectric octahedral compounds and glass-forming Oxides are fused together, whereupon this material is brought into the desired shape will. The finished, molded body is cooled to a temperature which is between that and while it is still hot The peak temperature of the crystallization and the tempering temperatures is until a sufficient temperature is reached in the glass Number of crystal nuclei has formed and then heated again to a temperature at which the forming Crystals do not yet loosen again. This temperature is kept until the Viscosity of the material at this temperature due to the progressive crystal formation practically becomes infinite.

Glasses which develop a lead titanate crystal phase during the heat treatment are cited as an example of this known teaching. Such ferroelectric only at high temperature materials are unsuitable for the purposes of the invention because the lead titanate exhibits only at elevated temperatures in the range of 400 to 500 ° C ferroelectric properties and no useful ferroelectric property in the range between room temperature and operating temperatures up to about 20O ⁰ C. Mixtures of BaO, TiO ₂ , SiO ₂ and Al ₂ O ₃ are also given, the BaTiO ₃ content of which is less than 30 mol percent. The known glasses are unsuitable for the purposes of the invention.
Further advantages of the invention, including a method for producing this capacitor and novel compositions for producing this capacitor by the method mentioned, are to be explained in more detail below with reference to the drawings.

'3 ° The drawings show in,

F i g. 1 is a graph showing the relationship of the temperature in ⁰ C urjä 'the, dielectric constant K of capacitor dielectrics according to the present invention to illustrate the influence of fluorine in the composition of BaTiO ₃ , SiO ₂ and Al ₂ O ₃ ,

F i g. 2 one of the F i g. 1 similar graph to show the effect of an additional stable oxide in the compositions; the expression "stable oxide" means an oxide a metal or a metalloid which is included in the molten glass composition for the capacitor can be incorporated according to the invention and without significant losses due to decomposition and / or Volatilization remains in this glass composition,

F i g. 3 is a curve of a differential thermal analysis of a glass composition consisting essentially of BaO, TiO ₂ , SiO ₂ and Al ₂ O ₃ , the approximate temperatures of the tempering point of the glass, the formation of the ferroelectric crystal phase in the glass and the melting of this phase as the increase progresses the temperatures of the glass are shown,

F i g. 4 shows a differential thermal analysis curve according to FIG. 3 for a glass composition consisting essentially of BaO, TiO ₂ and CaO to reproduce the approximate temperatures of the tempering point, the crystal phase formation and the melting

zen of the glass,.

F i g. 5 is a differential _{thermal analysis curve of a glass composition consisting essentially of Nb 2} O ₅ , Na ₂ O, CdO and SiO ₂ , showing the approximate temperatures of the tempering point, the

Crystal phase formation and melting of the glass. F i g. Fig. 6 shows some curves showing the relationship between dielectric constant and temperature some semi-crystalline bodies,

F i g. 7 shows a section through a capacitor according to the invention.

It has been found that a ceramic body containing at least one ferroelectric crystalline phase with a high dielectric constant, which is to be referred to below in the usual way with K , a low loss factor (LT) and a high flashover voltage and higher insulation resistance than in known products together with Other desirable physical and electrical properties are obtained when a glass body of the desired size and shape with oxide constituents which combine to form one or more such ferroelectric crystalline phases is subjected to controlled crystallization by heat treatment.

The new products have, since they are made from homogeneous glasses made from liquid melts, a porosity that is practically == zero, an optimal homogeneity and a uniform distribution of the crystalline phase or phases in very small particle size, so that their specific resistance ^{reaches values of 10 u} ohm cm at temperatures up to 400 ° C. and their dielectric constants and flashover voltages are unexpectedly higher than those of the bodies which consist of the same or essentially the same oxide compositions, but are bonded and sintered by the known processes. The temperature at which these products are heat-treated has an extremely large effect on the value of K of the capacitor so manufactured and provides a convenient and practical means of controlling it.

In addition, the thermal expansion coefficients of the starting glass and the one derived from it semicrystalline product at least in some cases so similar that in proportion thin bodies, for example disks or layers, no breaking forces arise, so that one These thin bodies can heat up locally and crystallize to form different parts of the area to achieve different jKV values.

In these cases, any change in volume of the semicrystalline part during its crystallization can occur due to the comparatively low viscosity of the surrounding glass that occur for these glasses is characteristic above its softening point and allows readjustment of the volume.

As a rule, the glasses used in the invention soften without crystallization at about 10 to 50 ° C or more below the temperature at which crystallization starts. This allows merging one piece of glass with the other before it crystallizes.

It has been found that the ferroelectric compounds begin to form and crystallize before other phases at temperatures in the total range from about 700 to HOO ⁰ C and that, because of the low forming temperatures, fewer defective crystals with an oxygen deficiency are produced in the process according to the invention than in the known Sintering process, which means a further advantage for the dielectric properties of the product according to the invention. Furthermore, a further variation possibility of the compositions is possible and can be made of silver or _copper: stationary electrodes applied to the glass body and together burn with the body in the final semi-crystalline state, since in this temperature range, these metal electrodes are not adversely affected. Ferroelectric compounds can generally be divided into four classes, of which the oxygen octahedron family, which is characterized by an octahedral arrangement of the oxygen ions in the crystal lattice, contains the ceramic ferroelectrics mentioned here (Proceedings of IRE, Vol. 43, p. 1738 to 1793, especially p. 1740).

The ferroelectric oxygen octahedral compounds, which are crystallographically referred to as perovskite of the most important group, "pyrochlore" etc., as well as mixtures thereof, are particularly suitable for the purposes of the present invention. Ferroelectric perovskite compounds have the general oxide formula ABO ₃ , where A and B are ions with a large and small radius, respectively, and the total value of their valences is 6 and individually refer to either the corresponding values 3 and 3, as for example in LaGaO ₃ , or 2 and 4, as in BaTiO ₃ , or calculated to 1 and 5, as in NaNbO _3. In general, the Α-ions from the L, II. And III. Group of the periodic table and the B ions can be selected from groups II to V. Other ferroelectric oxygen octahedral compounds are, for example, CdNb ₂ O ₆ and WO ₃ . Mixed crystal formation is widespread among ferroelectrics, and a structural excess or deficiency of oxygen octahedron with respect to the can by suitable WaIiI ^ ₄ of the constituents of the solid solutions compensate.

Although the invention is generally applicable to the production of capacitors which contain ferroelectric compounds of the oxygen octahedron families and mixtures thereof, bodies with perovskite-like ferroelectric compounds, in particular BaTiO ₃ , have particularly advantageous properties, and the In the following, the invention is to be described in more detail for the sake of brevity, but not for the purpose of limitation and restriction with regard to such preferred capacitors, their compositions and the processes for their production.

As a result, the following discussion mainly relates to ferroelectric ceramic capacitors in which the ferroelectric crystalline phase is BaTiO ₃ . However, the invention in its broad scope also includes capacitors in which the crystalline phase or phases contain one or more other ferroelectric compounds of the oxygen octahedral families or solid solutions or mixtures thereof, as can be seen from the later to be discussed Compositions

knows. -

For the production of a group of ferroelectric ceramic capacitors from BaTiO _{3 , SiO 2} and Al ₂ O _{3 are} preferably incorporated into the composition in order to promote glass formation. The addition of small amounts of fluorine improves the dielectric properties of the semi-crystalline product and the melting properties of the glass. The broadest range of such oxide-based compositions has been found to be cationic. Mole percent of 30 to 45% BaO, 15 to 40% TiO _2, 7 to 26% SiO _2, 3 to 30% AlO _{1 5,} wherein the proportion of AlO _{1 5} of the proportion of SiO ₂ by no more than about four thirds of the Amount of SiO ₂ differs, and 0.5

up to 1.5% fluorine, the total amount of BaO, TiO ₂ , SiO ₂ , AlO ₁₅ and fluorine being at least 90%. The proportion of BaO O should preferably be up to 100% in excess of the 1: 1 stoichiometric equivalent of BaTiO ₃ , based on the amount of TiO ₂ present, the excess preferably being higher as the _{proportion of TiO 2 decreases.}

Cation. Mole percentages are used in the specified compositions in order to avoid inaccuracies resulting from calculating, on the assumed oxide basis, the mole percentages of compositions with an oxide containing two or more of a given cation. According to this method of determining the appropriate proportions, any given oxide formula expresses that it contains a metal atom as the cation. When individual elements in one of the compositions are in fluoride form, the cation. Mole percentage of the element still given on an oxide basis. The oxide components of such compositions make a total of 100 cations. Mole percent. Fluorine, calculated as F ₂ , is specified separately and comes in cation. Mole percent of the total amount expressed. Since the fluorine content is very small, the error resulting therefrom is negligible.

A narrow range of compositions falling within the range given above, in which the presence of fluorine is optional, contains, on an oxide basis, cation. Mole percent 30 to 40% BaO, 15 to 40% TiO ₂ , the amount of BaO being 0 to 100% in excess of the 1: 1 stoichiometric equivalent of BaTiO ₃ based on the amount of TiO ₂ present and the excess being so is higher, the lower the amount of TiO ₂ is 0.5 to 26% SiO ₂ and 7 to 25% AlO _15, wherein the amount of AlO _{1 5} no longer deviates than about four-thirds of the amount of SiO _2, and the total amount of BaO ₅ TiO ₂ , SiO ₂ and AlO _{15 is} at least 90%. '

When using one of the compositions given above, the procedure is to melt it, cool it quickly to form a glass and then heat the glass to preferably between 850 and 1150 ° C for a period of at least one hour at 850 ° C or at least V heat treated at 1150 ° C for _{2 minutes to crystallize the glass.} While a minimum heating time is essential, longer heating times are not disadvantageous, but are undesirable for economic reasons. The ferroelectric crystalline phase resulting from this heat treatment is BaTiO ₃ , the advantageous dielectric advantages of which are known.

The ranges of the constituents BaO, TiO ₂ , SiO ₂ , Al ₂ O ₃ and F given above are critical for the purposes of the present invention for the following reasons. Because the desired dielectric properties of the capacitors primarily depend on their proportions. depend on crystalline BaTiO ₃ , a significant deviation from the minimum and maximum _{limit percentages of BaO and TiO 2} given above leads to an undesirable reduction in the proportion of crystallized BaTiO ₃ and thus the dielectric constant. For optimal results, an excess of BaO up to 100% of the 1: 1 stoichiometric equivalent of the amount of TiO _{2 present is} desirable, this excess apparently leading to the formation of other titanium compounds, such as those of titanium silicates of barium, with a corresponding loss of the advantageous properties of the BaTiO ₃ prevented. This excess must be higher, the lower the amount of TiO ₂ , in order to promote the formation of BaTiO ₃ and to hinder the formation of other undesired crystal phases.

An excess of SiO ₂ or a deficiency of AlO _{1 5} above or below the specified limits further increases the tendency towards the undesired formation of silicates and the resulting lowering of the value of K, but causes too small an amount of SiO ₂ or too large a proportion of AlO ₁₅ causes spontaneous devitrification of the molten composition regardless of the rate of cooling. In order to produce a satisfactory glass, the amount of AlO _{1 5} should not be more than the amount of SiO _2. four thirds of the existing amount of SiO ₂ differ. '.

Although the presence of fluorine is optional when the amount of BaO and TiO _{2 are} near their maxima, it promotes the formation of BaTiO ₃ and suppresses the formation to a lesser extent. desirable crystalline compounds, especially when the proportions of BaO and TiO _{2 are} high, but excessive amounts of fluorine make the glass susceptible to reduction during the melting process, which results in a decrease in dielectric properties.

The fluorine is in the glass as metal fluoride, ' preferably introduced as a fluoride of a metal of the I. or II. Periodic groups, the thermally are more stable than other fluorides. The proportion changes as a result of the fluctuations in their molecular weight of fluorine as such in this composition, depending on the metal. For the sake of clarity are both in the following information. Mole percent compositions denote the percentages of fluorine and of the oxide of the corresponding metal given separately. On this basis, the maximum amount of fluorine should be do not exceed a share of around 1.5%.

To further illustrate the invention, compositions with BaTiO ₃ as ferroelectric compounds, SiO ₂ as glass-forming oxide, and AlO _1-5 within the above ranges mentioned for practicing the invention are included in Table I. Mol percent based on oxide, calculated from their mixtures, together with the time (in hours) and temperature ( ⁰ C) of the heat treatment, as well as the dielectric constant K and the loss factor (LT) in percent of the finished ceramic body, each measured at 25 ° C .

1 Table I. 3 4th 5 - 6 7th 8th 44.3
22.5 2 35.7.
28.2 37.8
32.3 33.4
19.7. 36.6
35.0 36.4
35.2 36.1
36.1 BaO 31.2
23.0 TiO ₂ ;

Table I (continued)

SiO ₂

AlO ₁ ^

CaO

Excess BaO,%
Hours .........

° C

L.T.

1 2 3 4th 5 6th 7th 9.9 15.6 21.4 16.5 14.9 21.7 13.2 17.2 16.2 23.3 17.2 13.7 23.7 13.9 0.6 0.6 0.5 1.3 0.5 0.6 0.5 1.3 1.4 1.1 2.4 1.3 1.5 1.3 3.4 97.0 35.6 26.6 17.0 69.6 4.6 2 / 2 2 3 3 2 2 1075 1000 1000 925 925 925 1000 840 240 260 820 1370 300 860 2.9 ' 1.5 2.8 3.1 A ° 3.2 3.1

16.7 9.8 0.6 1.3

2.5 915 600

Table I (continued)

ll

12th

13th

15th

BaO

SiO ₂

A1O _{1> 5}

F ₂ .

CaO

MgO.

ZnO

SrO

Excess BaO,%
Excess TiO ₂ ,%

hours

⁰ C

K

L.T

36.1 31.8 14.8 17.3

13.5

1075 800 3.6

.2. 1075 1340 3.0 36.7
32.4
14.2
15.4
0.6

1.3

13.3

1000
1370

2.9

36.8

32.5
14.2
15.6 ■
'0.6

0.9
13.3

1075
1220

3.2

36.9
32.5
14.1
15.6
0.5

0.9
13.5

1075
1320

2.5

37.9 32.0 14.3 15.8 0.7

18.4

925
1350

2.8

35.2

.37.4

16.4

9.8

1.2

1.2 /

6.3

950 500

2.2

950 1300 1.2

The compositions for the capacitors according to the present invention are melted in pans, crucibles or containers for 1 to 8 hours or more at 1400 ° C. or above to produce homogeneous melts, depending on the size of the melt. Since the viscosities of the resulting glasses are generally comparatively low - they are on the order of 1 poise above 1400 ° C - refining the melts is not a problem and the use of refining agents in the baths is therefore unnecessary. Preferably, the Schmel. zen carried out under neutral or oxidizing conditions. If necessary, barium nitrate or other nitrates can be used as the oxidizing agent. The use of reducing agents worsens the dielectric properties. _{BaCO 3} is preferably used as the source for BaO, which has the advantage that the CO ₂ evolved maintains an equilibrium with its dissociation products CO and O, as a result of which the state of oxidation of the melt is stabilized.

These compositions crystallize spontaneously, if you do not use the correct composition and the glasses from a temperature above the liquefaction status in a few seconds,

for example 2 to 10 seconds, to temperatures of about 700 ° C or below. The speed the cooling process limits the strength of the objects to a certain extent can produce from the molten state. It

has been found that the viscosity in the molten State is so low - it is on the order of 1 to 10 poise, at Ί350 to 1400 ° C - that the glasses are particularly suitable for the production of thin glass panes by rolling

suitable.

Such thin glass panes are particularly suitable for dielectric laminates of capacitors suitable, as can be seen from Fig. 7, for which the thin glass layers in a known manner

alternately layered with metal foil tapes or before layering with an electric one conductive plating can be coated. the Glass layers are then sealed together again under pressure by heating to 700 ° C,

so that they enclose the metal layers (see U.S. Patent 2,405,529). Then the glass is through the heat treatment described above is converted into the semicrystalline state.

ίο

According to Table I, the basic compositions of Examples 4 and 9 to 14, inclusive, are similar to one another and differ in principle only in their fluorine contents, composition 9 being free of fluorine and compositions 4 and 10 to 14 containing different metal fluorides. It can be seen that the introduction of fluorine into the glass results in a substantial increase in the values of the dielectric constants and a small decrease in the loss. factor leads. The change in the dielectric constant at room temperature is, however, small and not critical in the case of the particularly added metal fluoride. The curves of FIG. 1 generally show the influence of the change in the TiO ₂ content in compositions with an excess of BaO and also the influence of the presence or absence of fluorine on the dielectric constant versus temperature in capacitor dielectrics made according to the invention and having the above composition . Examples 2, 3 and 11 of Table I contain fluorine and 23.0, 28.2 and 32.4 cation, respectively. Mole percent of TiO ₂ and are represented by curves 2, 3 and 11, while Example 9 is 31.3 cation. Mol percent TiO ₂ but does not contain fluorine and is shown by curve 9. Small ² S changes during the heat treatment and / or in the SiO ₂ -Al ₂ O ₃ ratio, BaO-TiO ₂ ratio and the fluorine content have an insignificant influence on the curves. The Curie point, which is indicated by the maximum value of K at approximately 120 ^° C., can be determined for every curve 2, 3 and 11 and is in agreement with the known data for BaTiO ₃ alone. A large difference in dielectric constant and Curie point is found in curve 9 compared to curve 11 and indicates that fluorine present _{promotes the formation of BaTiO 3} during the heat treatment of the glass compositions.

The compositions 15 and 16 according to Table I contain an excess of TiO ₂ .

In the composition 14 fluorine was introduced as BaF ₂ , of which the barium is included as BaO in the total amount of BaO.

In Fig. 2 are plotted curves showing the influence on the dielectric constant versus temperature caused by the addition of stable oxides to a semicrystalline body according to Example 10 of Table I. Similar effects are produced by the same oxides when added to other Table I compositions. The amount of such oxides should be about 10 cation. Mole percent and preferably about 4 cation. Do not exceed mole percent either alone or together. In particular, curve A shows the composition according to Example 10 alone, and curves B, C, D, E and F in comparison show the same composition with the incorporation of stable oxides, as are shown, for example, in Table II. There the individual columns mean:

1. the amount of the composition 10 added corresponding glass-forming oxides in cation. Mole percent;

2. the corresponding dielectric constant K at 25 ° C; .

3. the loss factor LT at 25 ° C .;

4. the Curie point (C. E) at ⁰ C;

5. the dielectric constant K at the Curie point; '

6. the type of curve A, B, C, D, E or F according to the. Curie point;

7. the maximum amount of oxide added, if marked with "best". The dielectric constant and the loss factor are measured at a frequency of 1 MHz.

K
25 ° C Table II LT,%
250 ° C C.P. ° C K at the CP Curve type Remarks Cation, mole percent
of the admitted
Oxyds 1100
1100
1200
1700.
850
1150
2350
1500
1230
1520
1100
1140
1420
1340
1400
1250
1700
900
780 2.5
2.5
3.0
3.0
3.1
2.5
0.5
3.1
3.0
2.7
2.9
3.3
3.3 ₄
3.0 ·
2.8
2.9
2.8
2.7
. 3.4 120
120
110
. 50
120
100
15th
105
120
80
120.
120
105
90
80
110
50
90
150 1400
1400
1900
1900
1770
2050
2450
2280
2250
1720
1850
2,100
2300
1900
1600
2200
2100
1350
1500 A.
A.
A.
C.
A.
AWAY
D.
AWAY
A.
B.
A.
A.
AWAY
B.
B.
·. A.
.C '
'B
G best
1 ■
■ best
best - 1,2 ko _0i5 ..: ...
3.6 LiO _{0> 5}
2.2BeO -
1.3 MgO
2.9 CaO
1.6SrO ■ ....
2.7ZnO
1.3 CdO .......
0.8 GaO ₁ 5,
1.2 InO ₁₅
TlO 0.2 _{1 5}
i, oyo _1i5
1,2LaO ₁₅
0.9 CeO ₂
1,3ZrO ₂
1.0 GeO ₂
1.3 SnO ₂
1.4 SbO ₁₅
0.8 BiO ₁ 5

Table II continued

Cation, mole percent
of the admitted
Oxyds K
25 ° C L.7.,%
250 ° C C. P. ° C K at the CP Curve type Remarks 1,8VO ₂ , ₅
1.2 NbO _{2> 5} .....
0.4TaO ₂ , ₅ ....,
0.8CrO _li5
0.4 MoO ₃
0.2WO ₃ .......
1.0 TeO ₂
0.4UO ₂ .......
1.0 MnO _{1 5}
0.6 FeO ₁₅
0.7CoO .......
1.1NOK ........
0.7PbO
0.4CuO 800
1500
1250
820
1250
1150
950
1050
1050
1500
1600
1200
1100
1300. 2; 9
2.1
2.8
2.8
2.8
3.0
4.0
2.5
0.6
3.3
2.2
0.6
3.0
2.5 120
80
120
105
120
120.
120
105
65
80
50
0
120
100 1300
2100
1860
1900
2000
2100
1350
1600
-1200
2100
1750
1230
1950
2350 A.
B.
A.
• AR
A.
A.
A.
AWAY
E.
B.
C.
F.
. A.
AWAY best
best
best
best
best
best

In some cases the changes in the Curie point due to the variously added oxides are not more than 20 ° C and the percentage of oxide added is not critical. Some of the added oxides, such as the oxides of Ca, B, Ga, P, As, Tl, Y, Ge, In, Ce, Zr, Sb, Nb, Fe, Cd, La, Sn, Zn, Bi and PB, improve the glass former properties of the compositions and lower the temperature coefficient of dielectric constant of the other products, and one can therefore use larger amounts, i. H. It is advantageous to add up to 10% of these oxides.

The addition of oxides of In, Ce, Zr, Sb, Nb or Fe lowers the Curie point at about 8O ⁰ C, as seen from the curve B to F i g. 2 recognizes which is characteristic of compositions containing such oxides.

A generally between curves A and B , but shown in FIG. The curve not shown in Figure 2 is obtained by adding the oxides of Sr, Cd, La, Cr or Cu.

The curve C illustrates the influence of the addition of the oxides of Mg, Sn or Co, which the Curie point in the vicinity of 50 ° C.

As can be seen from curve D , the addition of ZnO produces Curie points near room temperature and also lowers the loss factor significantly.

A low loss factor is also obtained by adding oxides of Mn, as can be seen from curve E , and by adding an oxide of Ni, as can be seen from curve F.

The addition of an oxide of Bi, as shown in Table II, increases the Curie point, as can be seen from curve G.

The temperatures to which the capacitors must be heated in order to convert their dielectric to ferroelectric semicrystalline ceramic bodies vary with composition and are generally lower for the glass-forming oxide B ₂ O ₃ or mixtures of B ₂ O ₃ and SiO ₂ or P. Compositions containing ₂ O _5. The correct heat treatment temperature also changes with the desired proportion of ferroelectric crystalline phase and is higher the higher the desired amount of ferroelectric phase or phases. It is therefore impossible to specify a temperature or a temperature range which is suitable or suitable for all compositions is effective, but with the help of the well-known "differential thermal analysis or DTA method" according to "Differential ■> ■ Thermal Analysis: Theory and Practice" by WJ / Smothers, 1958, the approximate tempering and softening points and the Easily determine the heat treatment temperature for each particular glass used for the condenser. According to this procedure, the temperature of a small capsule containing a powdered sample of the glass to be heat treated is slowly increased and, by means of a thermocouple inserted into the powdered glass , whose emf is that of a similar, in an inert, in the same Wise heated powder, for example Al ₂ O ₃ thermocouple used, counteracts, together with ^ automatic temperature recording, all endothermic and exothermic reactions within the ^ 31ases at its temperature recorded on a continuous strip, the abscissa of which indicates the increasing temperature. As long as there is no reaction in the glass, the differential is zero and the curve is an essentially straight horizontal line. Once the tempering point of the glass has been reached, the beginning of a drop becomes visible in the curve, which indicates the beginning of heat absorption. The temperature at the lowest point of this drop is then the softening point of the glass. This drop occurs in the range from about 500 to about 700 ^° C. for the glasses in question. If the temperature is increased further and the endothermic reaction comes to an end, the curve returns to the horizontal, and at 50 to 150 ° C above this starting point an exothermic reaction occurs, which causes a sudden pronounced peak in the curve, Which

shows the crystallization of the ferroelectric compound as the primary crystalline phase according to X-ray diffraction measurements. The separation of the other crystallizable phases, if any, is indicated by corresponding peaks following the first peak. A drop of a few 100 ° above the temperature of the first peak occurs in the curve which represents the first melting of the crystalline phase. The useful range of heat treatment temperatures for the capacitors according to the invention is generally between the temperature of the first DTA tip or crystallization of the. ferroelectric crystalline phase and a temperature of about 50 ° C below the lowest point of the first melt drop. The time required for the heat treatment varies between one hour at · of the peak temperature of the crystallization of the ferroelectric phase until at least ¹ J ₂ minutes at about 5O ⁰ C below the lowest point of the first melting drop of the DTA curve of the corresponding lens.

F i g. 3 shows the DTA curve for composition 4 according to Table I, which is typical for compositions with BaO, TiO ₂ , SiO ₂ and Al ₂ O ₃ . It can be seen from the curve that the glass of composition 4 has a tempering point of about 670.degree. C., the ferroelectric crystalline phase crystallizes at about 820.degree. C. and the first melting point is about 1280.degree. It has been found that the wide ^ total range of the heat treatment of such '' Glasses suitable temperatures and for each of the generally described herein glasses to that of the peak temperature of, crystallization of the ferroelectric crystal phase to a temperature of about 50 ° C below the first melting point drop DTA curve of the corresponding glass extends and that the optimum temperature lies in such a range between the tip of the ferroelectric crystal phase and the apex of the first melting point drop of this curve. For composition 4 it can be seen that this temperature range extends from about 820 to about 1230.degree. C. and that the optimum for achieving a high K value is about 1050.degree. By way of illustration, the approximate values for the tempering point, the peak temperature of the ferroelectric crystalline phase and the first melting point of each of the compositions 1 to 14 according to Table I are shown in Table III in ⁰ C. ;

Although compositions with at least one ferroelectric composition, preferably BaTiO ₃ , together with at least one glass-forming oxide, preferably SiO ₂ , and an additional oxide, preferably Al ₂ O ₃ , are shown in the preferred compositions according to Table I, it has been found that compositions with at least one ferroelectric compound and at least one glass-forming oxide lead to good glasses which can be treated with heat to achieve the desired capacitors according to the invention. Such compositions are in cation, for example, in Table IV. Mol percent given together with the corresponding values for K and LT for the resulting semi-crystalline products.

In compositions 17, 18 and 20 of Table IV, the corresponding amounts of TiO _{2 are} 70.8, 30.7 and 19.5% in excess of the 1: 1 stoichiometric corresponding amount of BaO, which affects the meltability and beneficial glass-forming properties of these glasses. The compositions 19 to 24 are examples of glasses which individually contain two of the three glass-forming oxides SiO ₂ , B ₂ O ₃ and P ₂ O ₅ . The resulting increased amount of glass-forming oxide contributes to its glass-forming properties. The compositions 19, 22, 23 and 24 contain stoichiometric amounts of BaO and TiO ₂ .

The compositions of Table II individually contain the oxide components of BaTiO ₃ together with SiO ₂₅ Al ₂ O ₃ and an oxide selected from the stable oxides of a large number of elements. These glass compositions result in semi-crystalline bodies with useful and desirable dielectric properties. It was also found that a large number of. Glass compositions which, when heat treated in accordance with the present invention, provide useful semicrystalline products, can be prepared by incorporating such stable oxides into compositions comprising oxide components BaTiO ₃ and a glass-forming oxide. Examples of such compositions, which consist of oxide components of BaTiO ₃ and one of the glass-forming oxides SiO ₂ , B ₂ O ₃ and P ₂ O ₅ and the additional stable oxide, are shown in Table V in cation. Mole percent listed along with their corresponding values of K, LT . The compositions according to Table V all lead to glasses if their melts are cooled rapidly. Some of these compositions contain oechiometric amounts of BaO and TiO ₂ , undüie cation. Mol percentages are always the same in such cases. Are either BaO or TiO ₂ present in excess over the stoichiometric amount, as it results from the respective specified percentages, then the percentage of such excess can optionally by customary methods ER \ expected. Compositions in which 3as ^f glass- forming oxide B ₂ O _3, is treated for 2 hours under heat at about 850 ° C. All other compositions according to Table V are treated for 2.5 hours at about 1000 ° C.

Table III

Starting point Peak temperature First the ferroelectric Melt Glass no. ° c crystalline phase ⁰ C 690 "C , 1270 1 680 880 * 1280 ./ 2 680 860 "1280 3 670 ■ 850 1280 4th 670 • 820 1260 5 680 820 1260 6th 680 830 1280 7th 670 840 1260 8th 660 830 1270 9 670 . 800 1280 10 670 830 1270 11th 660 '- 820 1270 12th 660 800 1280 13th 660 820 1270 14th 790 '

15th

Table IV

16

17th

18th

20th

24

BaO
TiO ₂

SiO ₂

B0 _{according to 5}

Excess BaO,%. Excess TiO ₂ ,% K ....

31.5
56.3
12.2

70.8
42

34.2
44.7

21.1

30.7
47
0.8

32.2 32.2 11.9 23.7

40 8.0

34.2

40.9

. 3.8

21.1

19.5 68 1.0

40.0
33.3
13.4

13.3
20.1

36.5

36.5

8.3

18.7

31.6 31.6

18.4 18.4

115

Table V

(Continuation)

(Continuation)

33.8 33.8

15.2 17.2

63 5.0

25th 26th 27 28 29 30th 31 32 BaO
TiO ₂
SiO ₂
BO _lj5 .
PO ₂ , 5
CuO
BeO
MgO
CaO
K . 31.8
38.1
18.0
12.1
34
<1 28.4
34.0
27.8
9.8
68
5.0 30.4
30.4
31.3
'7.9
37
<1 35.2
42.2
12.7
9.9
54
<1 31.8
31.8
29.1
7.3
46
<1 35.2
. 42.2
12.7
9.9
75
<1 31.8
31.8
29.1
7.3
40
<1 33.6
28.1
29.2
Λ
420 '
2.5 LT,%

33 34 35. . 36 37. 38 39 40 BaO
TiO ₂
SiO ₂
BO _1-5
PO ₂ , 5
CaO
ZnO
SrO
CdO '.:.'
K Γ ... 32.9
26.6
31.7 '
8.8 28.1
28.1
29.2
14.6
63
1.5 33.6
28.1
29.2
9.1
79
1 31.8
31.8
29.1
7.3
540
1 30.4
30.4
31.3
7.9
32
1 32.7
32.7.
17.3
. 17.3
250
1 29.3
29.3
27.6
13.8
200
2.5 28.1 '
28.1
29 ^ 2
14.6
55 /
, 1.3 LX, %

41 42 43 44 45 46 47 48 BaO
TiO ₂
SiO ₂
ZrO ₂
ThO ₂
GeO ₂
K 26.0
31.2
16.2
26.6
32 40.0
33.3
13.4
13.3
560
1.7 31.6
31.6
18.4
18.4
126
1.7 31.5
37.8
12.2
18.5
63
ι, ί 34.2
40.8
21.1
3.9
. 74
• 0.9 32.5
38.9
20.3
8.3
106
2.5 31.5
37.8
12.2
18.5
40 34.8
34.8
20.3
- ιο, ι
66
0.9
209 632/50 LX,% .... ■

17th

Table V (continued)

49 50 51 52 . 53 54 55 56 BaO
TiO ₂
SiO ₂
BO _{1> 5}
PO _{2> 5}
SnO ₂
PbO ..........
VO ₂ , ₅
NbO ₂ , ₅
TaO _{2> 5} :
K 34.8
34.8
20.3
10.1
210
3.6 34.2
40.8
21.1
3.9
230
<1 40.0
33.2
12.6
13.2
21 31.6
31.6
18.4
18.4
43
<1 32.1
32.1
11.9
23.9
80
<1 33.8
33.8
17.2
1.5.2
52
<1 32.9
39.4
20.3
7.4
43
<1 27.6
33.1
15.1
24.2
'130
3.0 1.1,%

(Continuation)

57

58

61

63

BaO. TiO ₂ . SiO ₂ . BO _li5 . PO ₂ , ₅ SbO _li5 BiO _{1> 5} MoO ₃ . WHERE ₃ . TeO ₂ . Κ .... LT, %

31.6 31.6

18.4 18.4

24.5 24.5

25.5 25.5

105

55 1.5

250

34.2
40.8

21.1

3.9

31.5
37.8
12.2

34.8
34.8

20.3

18.5
68

. 10.1
250

(Continuation) 74. 27.0
32.6 BaO ...... TiO,. BO _{1> 5} ^? 3 36.6
36.6
21.4

31.5 37.8 12.2

18.5 26

(Continuation) BaO
TiO ₂
SiO ₂
BO _li5 ..
PO ₂ , ₅
UO ₂
MnO _{1 5}
FeO _liS
NOK
CoO
K 65 66 67 68 69 70 71 72 LT, % 39.9
39.9
13.4
6.8
68 30.9
36.1
18.7
15.3
28 28.1
28.1
29.1
14.7
33 32.0
38.4
11.6
18.0
65 34.7
34.7
20.4
10.2
42 .35.2
42.2
12.7
9.9
28 30.4
30.4
31.3
7.9
23 ■ 35.2
42.2
'12, 7
~ f
9.9
52

73 74 PO 5.4
52 • 30.1
10.3
33 ⁶⁵ CoO ⁵ K L.T.,%

F i g. 4 shows the DTA curve for composition 33 of Table V, which contains the oxide components of BaTiO ₃ and the glass-forming oxide B ₂ O ₃ . The temperatures of the corresponding drops and peaks of this curve are generally lower than the corresponding temperatures of the DTA curve of FIG. 3. From this curve it is seen that the glass composition has approximately an occasion point of about 530 ⁰ C 33, the ferroelectric crystalline phase is formed at about 660 ⁰ C and a first melting point drop at about 970 ° C is present. The total range of temperatures suitable for heat treating this glass is 660 to 920 ° C with an optimum at about 790 ⁰ C.

The compositions according to Table VI are in cation. Mole percent indicated and contain the Oxide components of a variety of ferroelectric compounds including some or more of the titanate of barium or cadmium, of the niobate of sodium or potassium or strontium

or cadmium or barium or lead, the zirconate of cadmium or barium or lead, the tantalate of sodium or cadmium, of ferrate of lead or lanthanum, of germanate of iron or des

5 oxides of tungsten, namely WO ₃ . After the heat treatment, each glass according to Table VI contains one or more such crystal phases (Hi Perm) showing a high dielectric constant. The most likely phases are given for the corresponding compositions. It will be understood, however, that while all high dielectric constant crystalline phases or solid solutions may be indicated for the semicrystalline product of each composition, no attempt has been made to all

identify here, on the other hand, show the high Dielectric constants the presence of one or more ferroelectric values given in the table Phases. In the finished semi-crystalline state, the substances generally show hysteresis effects, which are characteristic of ferroelectric substances.

.75. Table VI 76 77 78 79 42.7
28.3
7.1
21.9
1000 45.0
29.7
7.4 • 40.3
27.0
6.8
7.3
18.6
1000 41.3
27.6
6.9
6.6
17.6
925 45.8
14.9- NbO ₂ , 375 17.9
1000 520 990 / __ ' NaOn <. 2.4
NaNbO ₃
Cd _{0 5} Nb0 ₃
CdNbO _{3 5} 590 .1.6
NaNbO ₃
Cd _{0 5} Nb0 ₃
Ba ₀₅ NbO ₃
CdNbO _{3 5}
BaNbO ₃ ' ₅ 1.5
NaNbO ₃
Cd _{0 5} NbO ₃
CdTiO ₃
CdNbO ₃ s CdO ... .... 2.1
NaNbO ₃
Cd ₀ 5NbO ₃
CdNbO _{3 5} . . 13.7
18.4,
925 BaO 308 / TiO ₂ 2.6.
NaNbO ₃
KNbO ₃
Cd _{0 5} Nb0 ₃
CdNbO _{3 5} KO _n , SiO ₂ ⁰ C K LT., % Hi Perm-
crystal
phases

(Continuation)

81 82

84

NbO ₂ , ₅ ...

NaO ₀ , ' ₅ · ·.

CdO

TaO ₂ , ₅ ...

ZrO ₂

WHERE ₃

SiO ₂

BO _{1> 5}

PO ₂ , 5 ...

⁰ C

K

Hi Perm crystal
phases

42.6

28.2

7.0

3.5

18.7

1000
1138

2.2:

NaNbO ₃
NaTaO ₃
Cd ₀₅ TaO ₃

43.5

26.6

7.1

4.5 18.3

1000 520

1.5

NaNbO ₃ Cd _{0 5} NbO ₃ CdZrO ₃ 40.5

29.6

9.8

2.0.
-18.1

850
645

2.3

NaNbO ₃
Cd ₀ 5NbO ₃
WHERE ₃

29.8 -T- 33.8 7.2. - 12.7 44.5 16.5 - ■ - 31.3 --- .- "-. 18.2 775 900 90 2100, 1.1. . 120 ' NaNbO ₃ WHERE ₃

Cd _{0 5} NbO ₃

WHERE,

Table VI (continued)

22nd

86

88

89

NbO _2i5 . .
CdO

ZrO ₃ ... ·.
NaO _{0, 5} ..
BaO ....
PbO

SrO .....
FeO _li5
AlO ₁ J ...

BO _{1> 5}

SiO ₂

k

Hi Perm crystal
phases

10.5 30.0

10.3 23.8

5.2

20.2

1.1 925
161

1.0

BaZrO ₃
PbZrO ₃ CdZrO ₃

34.0

11.1 12.5 10.5

16.2

15.7 2.0 1000 148

0.1

Ba _{0 5} NbO ₃ Sr _{0 5} NbO ₃ Pb _{0 5} NbO ₃ BaNbO ₃ j SrNbO ₃ S PbNbO _3iS 45.1

22.6-11.3

21.0

1075 214 1.4

NaNbO ₃ Pbo, ₅ Nb0 ₃ PbNbO

'3.5

39.6

10.4

10.2

8.8

2.3 11.6 17.1

1000 1200

3.7

Ba _{0 s} NbO ₃ Sr ₀ ' ₅ NbO ₃ Pb ₀₅ NbO ₃ BaNbO ₃ j SrNbO ₃ j PbNbO _{3> 5}

(Continuation)

18.3

36.2 18.3

27.2.

850 182

3.0

Pb ₀ 5NbO ₃ Pb ₂ NbFeO ₆ Pb ₂ Nb ₂ O ₇ PbNb _0j5 FeO ₃

90

92

NbO _2i5

NaO ₀ , s

BaO

FeO ₁₁ S.

AlO _li5

BO _li5

SiO ₂

TiO ₂

LaO ₁₅

GeO ₂

⁰ C

K

Hi Perm crystal phases

17.4 17.4 25.8

4.0

9.6

25.8

1000 401

1.4

NaNbO ₃ BaTiO ₃ Ba _{0 5} Nb0 ₃ BaNbO ₃ 16.4 16.2 24.6

3.6 5.4 9.3 24.5

850 165 0.8

NaNbO ₃ BaTiO ₃ Ba _{0 5} NbO ₃ BaNbO ₃ s

29.3

25.9 15.0

29.8

900

1468

30th

LaFeO ₃

33.6.

13.8 13.8

34.1 4.7 850 11.500 45

LaFeO ₃ FeGeO ₆

5 shows the DTA curve for the composition 76 of Table VI, which contains the oxide components of NaNbO ₃ and Cd ₀ 15 NbO ₃ and the glass-forming oxide SiO ₂ .

The corresponding positions of the peaks and slopes of these curves roughly correspond to those of the DTA curve according to FIG. 3. From the curve it is seen that the Glaszüsammensetzung 76 has a rise point at about 600 ° C, has a first ferroelectric phase at about 690 ° C and shows a first melting drop at about 1170 ⁰ C. The total range of temperatures suitable for heat treating this glass is 690-1160 ⁰ C, with an optimum at about 905 ⁰ C. It requires a 2-hour heat treatment in order to achieve a maximum crystallization at the optimum heat treatment temperature.

It should be pointed out that the composition 90 according to Table VI contains the oxides of the ferroelectric compounds BaTiO ₃ and NaNbO ₃ in their total amount of 86.4 cation. Contains mole percent. The dielectrics for the capacitors according to the invention should preferably not contain more than 90% of the forming oxides of the ferroelectric compounds, since a small amount of a glassy phase or. Structure is desirable to that

to give semi-crystalline bodies mechanical strength. On the other hand, Composition 5 according to Table I contains a calculated total amount of only 39.4 cations. Mole percent BaTiO ₃ and has a dielectric constant K = 300. Compositions with less than about 30 cation. Mol percent of the total forming oxides of one or more ferroelectric compounds have comparatively low dielectric constants, although they still have a good insulation resistance and a comparatively high flashover voltage.

In general, the capacitors according to the invention is characterized by unusually high insulation resistance up to 10 ¹¹ ohms at 400 ⁰ C (composition 11 of Table I) and flashover voltages up to 4 ■ 10 ⁵ volts DC per centimeter, or 2 x 10 ⁵ Volts AC per centimeter (an average of one of the most common compositions in the system

20th

BaO - TiO ₂ - SiO ₂ - Al ₂ O ₃ ).

In the curves according to FIG. 6 the dielectric constant is given as a function of the temperature for semicrystalline products of a number of the compositions according to Table VI. The curves are denoted by the numerals of the respective compositions, and the temperatures at which the respective compositions are heat treated to convert them to the semicrystalline state are also indicated. It can be seen from the curves ¹ that a large number of changes in capacitance with temperature can be obtained with the aid of the various compositions.

Claims (1)

Patent claims: 1. A process for the production of electrical capacitors, in which the glass strips with metal foils are alternately built into a stack and surrounded by an envelope made of glass and this structure is then fused under pressure to form a hermetically sealed body, characterized in that for the glass strips and the Enveloping body a composition based on oxide, a total amount of 30 to 90 mol percent of the constituents of at least one ferroelectric oxygen octahedral compound from the group of BaTiO ₃ , CdTiO ₃ , NaNbO ₃ , KNbO ,, Cd ₀₁₅ NbO ₃ , Sr ₀₁₅ NbO ₃ , Pb _{0, 5} NbO _3> Ba _{0) 5} NbO ₃ , CdNbO. 3.5 ' SrNbO. 3.5 ' BaNbO 3.5 ' PbNbO _3-5 , CdZrO ₃ , CaZrO ₃ and PbZrO ₃ and a glass-forming oxide from the class SiO ₂ , B ₂ O ₃ and P ₂ O ₅ is used and the condenser is cooled after fusing, reheated and at a temperature between the peak temperature of the crystallization of the ferroelectric compound and about 50 ° C below the lowest point of the first melting point of the DTA curve of the glass for a period of at least one hour at the low temperature to at least half a minute at the higher temperature for crystallization the ferroelectric compound is held and then completely cooled. 2. The method according to claim 1, characterized in that the ferroelectric oxygen octahedron compound Perovskite, pyrochlore, and mixtures thereof can be used. 3. The method according to claim 2, characterized in that BaTiO _{3 is} used as the ferroelectric oxygen octahedral compound. 4. The method according to claim T, characterized in that a composition of, based on oxide, 30 to 90 mol percent BaTiO ₃ , SiO ₂ and at least 3 mol percent of a metal oxide from the group CuO, BeO, MgO, CdO, AlO _{1 5} ZrO ₂ , GeO ₂ , VO _{2> 5} , WO ₃ , TeO ₂ and CoO is used. 5. The method according to claim 3, characterized .gekennzeichnet that is a composition of substantially with oxide base, 30 to 90 mole percent of the components of BaTiO _3, 3 to 30 mole percent of ₁ AlO ₅ and SiO _{2 was} used. 6. The method according to claim 3, characterized in that 'that a composition of essentially, based on oxide, 30 to 90 mol percent of the constituents BaTiO ₃ , 3 to 30 mol percent AlO ₁₅ , up to 4 mol percent of an oxide of a metal from the class Na, K, Be, Mg, Ca, Sr, Zn,. Cd, Ga, In, Tl, Y, La, Ce, Zr, Ge, Sm, Sb, Bi, V, Nb, Ta, Cr, Mb, W, Te, U, Mn, Fe, Co, Ni, Pb and Cu and SiO ₂ is used. 7. The method according to claim 5, characterized in that a composition with 0.5 to 1.5 mole percent fluorine is used. ^ 8. The method according to claim 1 to 3 b / ei use of B ₂ O ₃ as a glass-forming oxide, characterized in that a composition is used which, in addition to the forming oxides of BaTiO ₃ and B ₂ O _3, at least 3 mol percent of a metal oxide Class CuO, BeO, MgO, CaO, ZnO, SrO, CdO, AlO _{1 5} , YO ₁₅ , ZrO ₂ / ThO ₂ , CeO ₂ , SnO ₂ , PbO, VO _{2 5} , TaO ₁ ' ₅ ,' SbO _{1 5} / Contains BiO ₁₁₅ , MoO ₃ , WO ₃ , TeO ₂ , MnO _{1> 5} , FeO _{1> s} , NiO and CoO. 9. The method according to claim 1 to 3 when using P ₂ O ₅ as glass-forming oxide, characterized in that a composition is used which, in addition to the components of BaTiO ₃ and P ₂ O _5, at least 3 mol percent of a metal oxide Contains grade CuO, CaO, SrO, CdO, NbO _2i5 and TaO ₂₁₅ . 10. The method according to claim 2, characterized in that a niobate from the class NkNbO ₃ , KNbOy, is used as the ferroelectric compound. '' 11. The method according to claim 2, characterized in that a Met aniobat from the class CdNb O _{3 5} , SrNbO _{3 5} , BaNb O _{3 5} and PbNb O _{3 ä is} used as the ferroelectric compound. 12. The method according to claim 2, characterized in that a zirconate from the class CdZrO ₃ , BaZrO ₃ and PbZrO _{3 is} used as the ferroelectric compound. 13. The method according to claim 1, characterized in that the ferroelectric compound is used with tungsten oxide. 14. The method according to one or more of the preceding claims, characterized in that a composition, based on oxide and in molar percent, to 30 to 45% BaO, 15 to 40% TiO ₂ , the amount of BaO to 100% in excess over the 1: 1 stoichiometric equivalent of BaTiO ₃ , based on the amount of pre- 209 632/50 handenen TiO ₂ is, 7 to 26% SiO _2, 3 to 30% AlO ₁ 5, wherein the amount of AlO _{1 5} does not deviate from the amount of SiO ₂ by more than about four-thirds of the amount of SiO ₂ and 0 , 5 to 1.50% F, the total amount of BaO, TiO ₂ , SiO ₂ , AlO ₁ j and F being at least 90%, melted, the melt into glass strips and enveloping bodies is preformed, these are fused with metal foils to form a capacitor and cooled, and the capacitor is treated by heating to temperatures between 850 and 115O ⁰ C for a period of at least half a minute at 1150 ⁰ C to crystallize the glass. For this purpose 2 sheets of drawings ■ '/ ■ - ■ ^;