DE2361230B2 - Ceramic dielectric - Google Patents

Description

The invention relates to a ceramic dielectric with a predominant proportion of barium and Strontium titanates and an addition of bismuth oxide.

Ceramic dielectrics are used, for example, in devices and / or circuits where high alternating voltages occur: for example in breakers, brackets, bushings, for absorption the traveling wave voltage in transmission systems as a voltage divider in pulse voltage measuring Devices. Ceramic dielectrics are also used at high DC voltages, for example, in voltage-multiplying rectifiers for television receivers or oscilloscopes.

For all of these applications, the ceramic dielectrics should have a high, low dielectric constant dielectric loss, little variation in dielectric characteristics with applied voltage and have a high breakdown resistance.

The previously known ceramic dielectrics used in the above-mentioned devices or circuits are mainly composed of barium titanate and small amounts of others Materials, e.g. B. from titanates and stannates.

So is from the German, Auslegeschrift 1124109 a ceramic dielectric of the type mentioned is known, the various metal oxides up to can be admixed in an amount of 10%. The materials created in this way are already used in this prior publication referred to as too coarsely crystalline. Dense sintering is not possible. The resulting electrical characteristics are therefore inadequate.

ίο From the USA patent specification 24 69 584 is a dielectric known with the main components barium titanate, strontium titanate and calcium titanate. To the Improvement of the dielectric constant, the dissipation factor and the sintering temperature becomes manganese oxide added. The structure of the mass, however, remains coarse-grained with the disadvantages described above Follow.

Finally, from US Pat. No. 33 52 697, a dielectric based on strontium titanate is known to which the expensive bismuth oxide must be added in relatively large quantities. Only a relatively small dielectric constant is achieved here.
The object of the present invention is to use a ceramic dielectric of the type mentioned at the outset to show a composition which - in particular by controlling the granularity - at the same time high dielectric constant, low dielectric loss, high breakdown ^{strength, favorable electrostrictive behavior and low variation in the dielectric} Characteristic data guaranteed with the applied voltage.

This object is achieved by the invention described in claim 1. Advantageous further training and exemplary embodiments are shown in the subclaims.

The present invention will now be further elucidated with reference to the following description and the drawing explained; it shows

F i g. 1 the changes in the dielectric loss factor tan δ (in percent) of ceramic dielectrics both according to the state of the art and according to the present invention when the applied AC voltage gradient changes (in V'mm),

F i g. 2 shows the changes in the characteristic ratio .IcZc ₁ (in percent) of ceramic dielectrics both according to the prior art and according to the present invention with variation of the applied alternating voltage gradient (in V / mm).

example 1

A predetermined amount of strontium carbonate 5S (SrCO ₃ ) and a predetermined amount of titanium dioxide (TiO ₂ ) are mixed and ^{pre-sintered at 115O 0} C for 2 hours. Then the presintered mixture is ground into powder. whereby strontium titanate (SrTiO ₃ ) is obtained. SrTiO ₃ . TiO ₂ . Bi ₂ O ₃ <io and BaO (can be _{exchanged for BaCO 3} ) are then mixed with the weight ratios (percent) as indicated in columns 1 and 2 of Table I. After binding agents have been added, the mixture obtained is pressed and shaped into disks with a diameter of 16.5 mm and a thickness of 1.0 mm under a pressure of 2000 kg / cm ^2. Then the shaped bodies are sintered for 2 hours between 1100 and 1300 ⁰ C, whereby sintered ceramic

get mixed body. Then the opposite Sides of the resulting ceramic body painted with silver electrode paste. After painting with silver electrode paste vxd the ceramic body is heated in air to about 800 "C. On this In this way, the painted silver electrode material is plated onto the surfaces of the ceramic body.

Column 1 of Table I shows, in percent by weight, various ratios of the materials SrTiO ₃ , Bi ₁ O ₃ , TiO ₂ and BaTiO ₃ in eighteen samples which were produced by the same method mentioned above. Column 2 of Table I shows the compositions (in percent by weight) of the ceramic dielectrics of the respective samples expressed in oxides (these oxides are SrO, Bi ₂ O ₃ , TiO ₂ and BaO). Columns 3, 4, 5 and 6 of Table I show the various electrical. Characteristic values of the corresponding samples. The dielectric constant ε with an alternating voltage of 5 volts and one kHz, the dielectric loss factor tano in percent with an alternating voltage of 5 volts and one kHz, the change ratios of _{the characteristics AcJc 1} in percent and AcJc ₂ in percent with an effective alternating voltage of 0, 5 kV / mm and the change ratios of _{the characteristic data AcJc 1} in percent at a direct voltage of 1.5 kV / mm for the corresponding samples are shown in columns 3, 4, 5 and 6, respectively. The change ratios of the characteristics Λ eic, and JcC ₂ in Table I are defined as follows.

Ice,

_ fjbe ^ 5 YJLkHzJ - Mbei O.SkVmm. 50Hz or 1.5 kV mm DC voltage)

y (at 5 V. 1 kHz) 100.

_ tan δ ( at 5 V.] _k_Hz) _-_ tan δ (at 0.5 kV mm. 50 Hz. or 1.5 kV mm DC voltage) ^U ' ^Cl - ~ "tan δ (at V. 1 kHz)

It should be noted in Table 1 that Samples 1 and 15 are outside the present invention and samples 19, 20 and 21 are examples of prior art Technology are. These samples were included in Table I for comparison.

ρ i g. 1 shows the change in the dielectric loss factor tan δ (in percent) of the ceramic dielectric of the sample 8 according to the present invention; the changes in the dielectric loss factor tan <5 (in percent) of samples 1 and 15, which are outside the present invention, and the changes in the dielectric loss factor tan δ (in percent) of samples 19, 20 and 21, which are the prior art correspond. In Fig. 1, the changes in the dielectric loss factor δ as a function of the applied effective alternating voltage per millimeter at 50 Hz is Darge.

F i g. 2 shows the change in the change ratio J C ₁ C _{1 of} the characteristic data (in percent) of all of the above-mentioned ceramic dielectrics from FIG. 1 in the same way as in FIG. 1. The change ratio .IcZc _{1 of} the characteristics in FIG. 2 is defined as follows:

_ t (at 5 V. 1 kHz) - * ■ (with an applied alternating voltage gradient, 5 0 Hz ) Ice ·, = rtbeTs " \. 1 kHz)

As can be seen from Table I and FIGS. 1 and 2, the ceramic dielectrics according to the present invention have a high dielectric constant and low dielectric loss and also have almost no changes in dielectric constant and dielectric loss when the applied AC or DC voltage is varied. That means, the dielectric constant. <Is between 1000 and 4700, the dielectric loss factor tan-i »is between 0.1 and 1.3% and the change ratio of _{the characteristics AcZc 1} , as explained above, is between 0.8 and 19% for AC voltage and between -17 and -1.2% for DC voltage. In a preferred exemplary embodiment of the present invention, the composition of a ceramic dielectric consists of: 10 to 40 percent by weight SrO; 2.5 to 18.5 percent by weight Bi ₂ O ₃ ; 35 to 41 weight percent TiO ₂ . and 2.5 to 53 weight percent BaO.

Example 2

In the present invention, a ceramic dielectric is obtained when the materials as shown in column 1 of Table I, the ceramic dielectric can be sintered. It is well known that a dense and uniform ceramic dielectric is obtained when one of the fabrics which the ceramic dielectric is composed of. add a small amount of a mineralizer and then sinter the fabrics and the mineralizer. It is also well known that the mineralizer prevents that the ceramic dielectric is reduced by the air during the sintering process. the various electrical characteristics of the ceramic dielectric, as shown in columns 3, 4 and 5 and 6 of Table I shown, however, should not be sacrificed when using the ceramic dielectric is made dense and even. In this example 2 is to the sample 2, which in dei

Table I and consists of 39.3 weight percent SrO, 17.4 weight percent Bi ₂ O ₃ , 40.5 weight percent TiO _2, and 2.8 weight percent BaO, with a little mineralizer added. Three types of fabric are selected for the mineralizer. This sine manganese carbonate (MnCO ₃ ). Clay and dilanthan trioxide (La ₂ O ₃ ). As can be seen from column 2 of Table I. As examples, the six samples 22, 23, 24, 25, 26 and 27 are produced, with samples 22 and 23 containing 0.2 and 0.5 percent by weight of MnCO _{3, respectively}

Hold f> o, samples 24 and 25 contain 0.2 and 0.5 percent by weight of clay and samples 26 and 2 'contain 0.2 and 0.5 percent by weight of La ₂ O _3, respectively. Column in Table II shows the composition of the ceramic mix dielectric of the corresponding samples 2:

to 27. Expressed in oxides, those with the composition of sample 2. as in column 2 of table shown matches. Columns 3, 4, 5 and 6 of Table II give the electrical characteristics

are the same as the corresponding columns in Table I. Sample 2 is inserted in Table II, the differences between the electrical characteristics of sample 2 with mineralizer and sample 2 without making mineralizers clear.

As can be seen from Table II, the electrical characteristics of Samples 22-27 with the mineralizer are as good as Sample 2. However, if more than 0.5 percent by weight of mineralizer is added to the ceramic dielectric materials, the electrical characteristics become extraordinary poor and therefore less than 0.5% by weight of the mineralizer should be added. In an experiment conducted in relation to the present invention, less than 0.3 weight percent mineralizers should be added to obtain proper electrical characteristics; greater than 0.1 percent by weight mineralizers can make the sintered ceramic dielectric dense and uniform. Accordingly, between 0.1 and 0.3 weight percent mineralizers should be added to the materials shown in columns 1 and 2 of Table I in practice. It should be noted that the same advantage, that the ceramic dielectric is made dense and uniform by the addition of a mineralizer, is obtained not only using Sample 2 but also using Samples 3-18 in Table I. It should be recognized that the mineralizers are not limited to those shown in column 2 of Table II. The mineralizer MnCO ₃ can be replaced by other compounds including, for example, MnO. In this case, of course, the weight percent of these compounds including MnO to be added is different from that of MnCO ₃ shown in column 2 of Table II. However, the weight percent of these compounds including MnO, as mentioned above, should be below 0.5 weight percent. The sintered ceramic dielectric can also be made dense and uniform by adding to the materials shown in column 1 of Table I at least one of the following mineralizers: oxides of manganese, chromium, tantalum, and niobium; Compounds of elements of the iron group such as iron or cobalt and compounds of rare earths such as lanthanum or cerium.

Example 3

The main object of the present invention can also be achieved by using the divalent metals, they are Ba and Sr, and the tetravalent metal, that is Ti, is replaced by other bivalent and tetravalent metals, respectively Metals are replaced.

For sample 8 shown in Table I and off

Table I.

20.6 percent by weight SrO: 9.1 percent by weight Bi ₂ O ₃ ; 37.4 percent by weight TiO ₂ and 32.9 percent by weight BaO, the bivalent metal oxide BaO is replaced by another bivalent metal oxide (PbO) and the tetravalent metal oxide TiO ₂ by another tetravalent metal oxide (ZrO ₂ ). However, the various electrical characteristics as shown in columns 3, 4, 5 and 6 should not be impaired by this replacement. As

ίο can be seen from Table 111, the four samples 28, 29, 30 and 31 were prepared as examples. Samples 28 and 29 replaced 10 and 20 percent by weight, respectively, of the BaO of Sample 8 with PbO. In samples 30 and 31, 10 and 20 percent by weight, respectively, of the TiO ₂ of sample 8 were replaced by ZrO ₂ . This exchange is shown in columns 1 and 2 of Table III. Column 1 of Table II! shows the composition of the ceramic material of the corresponding samples (28 to 31) in terms of oxides. The compositions of SrO and Bi ₂ O ₃ are the same as in column 2 of Table I for sample 8. Columns 3, 4, 5 and 6 of Table III give the electrical characteristics and are the same as in the corresponding columns of Table I. Sample 8 is included in Table III to clarify the differences between the electrical characteristics of Sample 8 and Sample 8 affected by the exchange.

As can be seen from columns 3 to 6 of Table III, the electrical characteristics of sample 8 do not deteriorate if a substance of sample 8 is partially replaced by other substances that are chemically similar to the original substances of sample 8. Generally speaking, the divalent metals such as Sr or Ba. those shown in columns 1 and 2 of Table I; can be replaced by other divalent metals such as Ca. Zn, Mg, Cd or Pb. The tetravalent metal (such as Ti) shown in columns 1 and 2 of Table I can also be used. be replaced by another tetravalent metal such as Sn, Hf or Zr. When the divalent metal is replaced by another divalent metal, part of the Sr and or part of the Ba can be replaced by Ca, Zn, Mg, Cd or Pb. In this case, less than 30 percent by weight of SrO or BaO should be replaced by a compound containing Ca, Zn, Mg or Cd, and less than 50 percent by weight of the SrO or BaO should be replaced by Pb, while less than 30 percent _{by weight of TiO 2 should be} replaced by a connection should be replaced, the Sn. Contains Hf or Zr.

In the above-mentioned embodiments, SrO and BaO are used in the form of carbonates. However, other forms can also be used, for example the hydrochloride of SrO and BaO be used.

Sample no. 1 Bi ₂ O ₃ TiO ₂ BaTiO ₃ -> Bi; O, TiO ₂ BaO Fabric lanyard (Weight (Weight (Weight Oxide content (Weight (Weight (Weight SrTiO ₃ percent) percent) percent) SrO percent) percent) percent) (Weight 18.2 9.1 - (Weight 18.2 40.8 . percent) 17.4 8.7 4.3 percent) 17.4 40.5 18th *1 72.7 41.0 1 69.6 39.3

Samples marked with an asterisk are not included in the present invention

jrtsctzung above no.

Substance content of SrTiO ₃

(Weight percent)

Bi ₂ O ₃

(Weight percent)

TiO ₂

(Weight percent)

BaTiOj

(Weight percent)

3 4 5 6 7 8 9 10 11 12 13 14 * 15 16 17 18 19

66.4

61.5

50.9

50.9

43.6

36.4

36.4

29.1

19.4

18.2

18.2

18.2

14.5

45

30th

30th

9.1

15.4

12.7

16.7

10.9 9.1 3.7 7.3 4.8 4.5 5.1 4.0 3.7 2.5 5.0 10

20.1

7.7 6.4 2.4 5.5 4.5 9.9 3.6 2.4 2.3 1.7 2.8 1.8 2.5 15.0 10

4.4
15.4
30th
30th
40
50

50

60

73.4

75

75

75

80

50

Oxide content of SrO

(Weight percent)

37.5 34.7 28.7 28.7 24.6 20.6 20.6 16.4 11.0 10.3 10.3 10.3 8.2 25.4 16.9 16.9

BaTiO ₃ 64.5
BaTiO ₃ 88.0
BaTiO ₃ 94.1

Bi ₂ O ₃

(Weight percent)

TiO ₂

(Weight percent)

BaO

(Weight percent)

at 5 V AC and 1 kHz

tan Λ%

at 5 V alternation

tension

and 1 kHz at 0.5 V, mm AC and 50 Hz

Ice,

at 1.5 kV mm DC voltage

Samples marked with an asterisk will fall

, not under the present invention

Table II

ίο

Sample I.

Oxide content
SrO

Bi ₂ O,

TiO,

BaO

Mineralizer share

MnCO., Cla

La, O_,

ι tan Λ% at 0.5 kV mm at at 5V at 5V AC voltage 1.5 kV Alternating Alternating and 50 Hz mm sel- sel- Same span span Iff, lc C ₂ span tion tion tion and and I kHz 1 kHz C Ci

(We (We (We (We (We (We (Weight (weight- weight- weight- weight weight percent) percent) percent) percent) percent) percent) percent)

2 39.5 I. 17.0 Bi ₂ O, 40.5 37.4 3.0 - PbO - - lOe- 1780 1110 0.1 + 0.1 0.1 5 -1.7 6th 22nd 39.5 17.0 40.5 37.4 3.0 0.2 - - wichis- 1750 1142 0.1 + 1.2 0.12 - 2.2 23 39.5 17.0 40.5 37.4 3.0 0.5 - I percent) - 1740 1109 0.2 + 1.4 0.12 at 0.5 kV mm -2.3 at 24 39.5 17.0 40.5 33.66 3.0 - 0.2 - 3.74 1680 1090 0.1 + 1.2 0.1 AC voltage -2.5 1.5 kV mm 25th 39.5 17.0 40.5 29.92 3.0 - 0.5 - 7.48 1650 922 0.1 + 1.2 0.1 and 50 Hz -2.7 Same 26th 39.5 17.0 (Ge 40.5 3.0 - (Ge - 0.2 For this purpose 2 blalt drawings 1050 0.1 + 1.0 0.1 -2.1 tension 27 39.5 17.0 weight 40.5 3.0 - weight - 0.5 988 0.07 +1.0 0.6 -2.1 Table III ) percent I c C ₁ I c C ₂ Ifc, Rehearse 2 - 3 4th No. 3.29 (%) (%) 1%) Oxide content Oxide content 6.58 » tan Λ ⁰ X - at 5V at 5V SrO TiO, BaO - ZrO, change Change + 1.8 0.1 -3.0 span span + 1.4 0.1 -3.1 tion tion + 2.0 0.2 -2.5 and and + 1.7 0.3 -2.7 1 kHz 1 kHz + 1.5 0.3 -2.4 (Ge (Ge (Ge weight weight weight percent percent) percent percent 8th 20.6 9.1 32.9 0.1 28 20.6 9.1 29.61 0.15 29 20.6 9.1 26.32 0.15 30th 20.6 9.1 32.9 0.15 31 20.6 9.1 32.9 0.15

Claims (6)

Patent claims: 1. Ceramic dielectric with a predominant proportion of barium and strontium titanates and an addition of bismuth oxide, characterized in that the proportion by weight of SrTiO _{3 is} about 18 to 70%, that of BaTiO ₃ about 4 to 75% and that of Bi ₂ O ₃ 2.5 to 17.4% and the dielectric still has 1.7 to about 20 percent by weight TiO ₂ , the weight ratio between TiO ₂ and Bi ₂ O _{3 being} between about 1 and 18. 2. Ceramic dielectric according to claim 1, characterized in that it is in a small amount Contains at least one of the substances: clay, manganese oxide, chromium oxide, niobium oxide, tantalum oxide, iron oxide. Cobalt oxide and rare earth oxides such as lanthanum or cerium. 3. Ceramic dielectric according to claim 1, characterized in that less than 30 percent by weight of the total amount of strontium and barium titanates is replaced by at least one of the titanates CaTiO ₃ , ZnTiO ₃ , MgTiO ₃ and CdTiO ₃ . 4. Ceramic dielectric according to claim 1, characterized in that less than 50 percent by weight of the total amount of strontium and barium titanates is replaced by PbTiO ₃ . 5. Ceramic dielectric according to claim 1, characterized in that less than 30 percent by weight of the total amount of TiO ₂ , SrTiO ₃ and BaTiO ₃ is replaced by at least one of the oxides ZrO ₂ , SnO ₂ and HfO ₂ . 6. Ceramic dielectric according to claim 2, characterized in that the small amount is between 0.2 and 0.5 percent by weight.