DE1471445C - Electrical resistance on the basis of perovskite material and method for its manufacture - Google Patents

Description

I 471 445

The invention relates to an electrical resistor with positive temperature coefficient of resistance value in a certain, from which Curie temperature dependent temperature interval and / or with a small dependence of the resistance value from an applied voltage above the Curie temperature .. The resistor consists of sintered grains of the order of 0.1 to 2 μπι one by doping substances (Me), such as B. antimony (Sb), lanthanum (La) or niobium (Nb), made semiconducting ferroelectric ceramic substance based on perovskite material of the general formula

(Me ¹¹ Me) (Me ^ Me) O ₃ -

In this formula, Me ¹¹ primarily denotes divalent metals, such as, in particular, alkaline earth metals. Me ^IV is primarily to be understood as meaning tetravalent metals, such as, in particular, titanium, zirconium or tin. Instead of a Me ⁿ Me ^IV combination, however, monovalent metals also come together with perovskite-forming pentavalent metals, such as. B. niobium (Nb) or tantalum (Ta), for the production of the base material with suitable variation of the doping substances into consideration. .

That consisting of a structure of grains sintered together of the size indicated above Perovskite material has on the grain surfaces or in the intermediate layers between the Grains (both are to be referred to as grain boundaries in the following) one of the composition inside the grains on different composition of the constituents.

Barium titanate is, under certain conditions, a preferred perovskite material with those specified above Properties. The following considerations should therefore take the example of barium titanate be explained without thereby the invention only on barium titanate. to restrict.

This barium titanate (BaTiO ₃ ), known as ferroelectric, can be converted into the semiconducting state by suitable doping according to the principle of controlled valence (e.g. by incorporating antimony oxide Sb ₂ O ₃ ). In a limited temperature range of 50 to 100 ° C, starting at the Curie temperature (approx. 115 ° C), there is a steep increase in the contradiction, which up to now has been a maximum of four powers of ten with the known materials.

The diagram according to F i g..l gives a clear representation of this property. The specific resistance ρ and the dielectric constant ε of the doped barium titanate ceramic are plotted as a function of the temperature at field strengths of around 10 V / cm and 3 k V / cm, respectively. The previous investigations showed that the cause of the anomalous increase in resistance above the Curie temperature is localized in the grain boundaries (cf.

Magazines "Solid State Electronics", 3, pp. 51 to 58 [1061], and Journal of Americ. Cerium. Soc. «[1963], Pp. 48 to 54). At the grain boundaries, there are acceptor surface terms in which the electrons can trespass. As a result, space charge zones are formed at the core boundaries. The ones in the ribbon model The resulting banding within these space charge zones is determined by the dielectric constant as well as spontaneous polarization

ίο controlled. This results in a strong temperature dependency the junction resistance. The maximum of the band rearrangement and thus the increase in resistance is reached when the. Surface terms are raised to the Fermi level. The height the resistance maximum is essentially determined by the activation energy of the surface terms definitely. Since it is a junction resistor, it is mainly in the area of maximum Banding up a strong voltage dependence, the size of which is macroscopically determined by the number of grain boundaries connected in series is determined.

It is now known that the resistance-temperature characteristics of such semiconducting barium titanate ceramics, depending on the starting material and manufacturing conditions, show considerable differences in the steepness and magnitude of the increase in resistance, although four powers of ten between the resistance values before and after the increase are not in the case of the magnitude of the increase in resistance be crossed, be exceeded, be passed. It was assumed that the reason for the differences in steepness and height of the increase in resistance is partly to be found in differences in the surface terms, which up to now have been regarded as the most difficult factor in the overall system to control. It has already been shown that a reduction (removal of oxygen from the grid) reduces the increase in resistance or completely destroys the surface barrier layers. The assumption has even been made that the oxygen balance is the decisive factor for the formation of the surface barrier layers, but tests which have led to the present invention show that even at the same oxygen partial pressure, sintered samples of the same gross composition show considerable differences in the course of the increase in resistance. In the diagram according to FIG. 2 this is explained using individual examples, the table being used to explain the individual curves. This table shows the individual TiO ₂ materials (I to V) and barium carbonate (VI) with their impurities. Materials I to V were each converted with barium carbonate VI to form BaTiO ₃ , which was doped with 0.12 mol percent antimony oxide Sb ₂ O ₃ and sintered at 1360 ° C. for an hour. In the case of the individual resistance-temperature characteristics, only the TiO ₂ starting materials are different.

Impurities (percent by weight Al Si Mg Fe [Spectral analysis] Approx Sb As Sn Pb material Cu -ίο- » > io- » -ίο- » -ίο- » P. -ίο- » -ίο- ² <io- » -ίο- » -ίο- ³ I. Anatase -to- ² -10- » -10 ⁿ -ίο- » <io- » -lO-i -10- » <io- » <io- » <io- ³ -ίο- » II. Anatase <io- ^a -ίο- » > io- » - ίο- » <io- » -lO-i -ίο- » <io- » <io- » <io- » -ίο- » III. Anatase -K) ² -ίο- » <10 ~ » > io- » -ίο- » -'ό- ¹ -ίο- » <io- » <io- » <io- » <10-3 IV. Rutile <1 () " ² -IO ⁴ -ίο- · -ίο- ³ - 10- » <1O- ' -10- » - - - - V. Anatase (pure) --- - ΙΟ "» -lO-i -ίο- » -ίο- » - ~ io- « - - - - VI. BaCO ₃ -ίο- » -

It can be seen and proven in extensive studies that the resistance-temperature characteristic such PTC thermistors with otherwise the same. Manufacturing conditions strongly with the raw materials used vary. Both different impurities can be used for this This material as well as different crystallization states are decisive, as can be seen from the table and the diagram of FIG. 2 results.

In general it can be seen from this compilation, that the PTC thermistor effect is reduced as the degree of purity increases.

In the case of using pure anatase (V), the sudden increase in resistance is up to one small anomaly disappeared. It is interesting in this context that the values given in the table Impurities occur in concentrations as they are for the theoretically calculated surface term density required are.

But now there are impurities in the starting material, especially in the case of large-scale production Products, largely withdrawn from arbitrary influence. It was the object of the invention to provide means by which, on the one hand, the control of the increase in resistance due to contamination is avoided and on the other hand the maximum increase in resistance through the targeted choice of the surface terms can be increased beyond four powers of ten.

The electrical resistance body of the type described at the outset is characterized ^{according to the invention in that the sintered resistance body contains a Me n} O excess between 0.1 to 3 mol percent over the ^{proportion corresponding to the stoichiometry of the Me n} Me ^IV O ₃ that is present on the grain surfaces or in the intermediate layers between the grains (grain boundaries) the proportion of doping substance (Me) is at least one order of magnitude greater than the proportion of doping substance (Me) inside the grains and that, based on the total proportion of metals in the anion ( Me ^IV ), the total proportion of doping substance (Me) is 0.01 to 0.3 mol percent.

The doping substances mentioned at the beginning are used. named materials (Sb, La, Nb) in question. The known perovskite-forming tetravalent or pentavalent metals, in particular titanium, zirconium or tin, can be used individually or in a mixture as metals of the anion, while the alkaline earth metals calcium, strontium, barium, individually or in a mixture, can be used as metals in the cation part be able; but also monovalent metals, such as. B. Alkali metals, which form perovskites ^{with pentavalent metals as Me 1T} , come into question ^{as Me 11.}

A preferred cold-conducting perovskite material is barium titanate, preferably soft with antimony al «doping substance (Me) is doped. According to the invention, the antimony concentration lies in the interior of the grains between 0.01 and 0.3 mole percent, preferably between 0.08 and 0.15 mole percent, so that there is good conductivity there. On the other hand, lies on the grain surfaces or in the intermediate grain layers according to the invention the antimony concentration between 0.3 and 5 mol percent, preferably between 0.5 and 3 mole percent. According to the teaching of the invention, this occurs when the sintered Resistance body has a BaO excess between 0.1 and 3 mol percent over that corresponding to the stoichiometry Contains proportion of BaO and the total proportion of doping substance in the specified Limits. The well-known ceramic PTC thermistors made of ferroelectric material with a perovskite structure show a maximum increase in resistance in the range of the Curie temperature of about four powers of ten. As a rule, the stoichiometry is used of the perovskite lattice corresponding material used ', for example pure barium titanate or Barium titanate, in which barium and / or titanium through

• corresponding other two-valued or four-valued Ions are replaced (cf. W. Heywang in »Solid

State Electronics "[1961], Vol. 3, pp. 51 to 58;

G. Goodman, Journal of the American Ceram.

Soc. "[1963], Vol. 46, No. 1, pp. 48 to 54; H. A. Sauer and J. R. Fisher in Journal of the American Ceram. Soc. "[1960], Vol. 43, No. 6 ,. Pp. 297 to 301).

• These known works assume that for

20. Achieving conductivity the doping substance, such as lanthanum, samarium, and antimony other dopants foreign to the perovskite lattice take the place of the divalent perovskite former im Grids are built in, so that usually one

there is a slight excess of titanium over the barium, which corresponds to the proportion of the doping substance.

Attempts have also already been made to increase the incorporation of the doping substance at divalent lattice sites by increasing the titanium excess to values of up to 6 mol percent. For clarity, such a material would correspond approximately to the formula BaO · 1.06 TiO ₂ and contain the respectively intended amount of doping substance (cf. PK Ga 11 anger et al in "Journ. Of the Americ. Cer. Soc." [ 1963], Vol. 46, No. 8, pp. 359 to 365; British Patent 714,965).

The aforementioned British patent also mentions a test specimen which is composed of 50.12 BaO and 49.88 TiO ₂ and contains 0.6 atomic percent Bi as doping substance and thus an excess of BaO compared to the proportion corresponding to the stoichiometry 0.48 mol percent, but the increase in resistance achieved with this example is only 2.8% per ° C in a range from 125 to 180 ° C, that is, there is a resistance increase of just under a power of ten. This slight increase in resistance is due to the fact that the proportion of doping substance is too high. An advantageous effect of the excess of barium oxide can therefore not be inferred from the British patent, especially since this patent describes it as advantageous to work with an excess of titanium oxide of up to 20 mol percent, preferably 2 to 6 mol percent.

Compositions according to the teaching of the invention result in a completely new type of PTC thermistor (hereinafter referred to as PTC thermistor of the second type for short) with a curve character of the increase in resistance which differs widely from the usual and which is even more pronounced when using rutile than with anatase. The relationships will again be explained using antimony-doped barium titanate as an example.
In the diagram according to FIG. 3, the dashed curve shows the increase in resistance of a normal cold conductor (PTC thermistor of the first type), while curves I, IV and V (designated according to the TiO ₂ starting materials in the aforementioned table) show the course

. '■ ■ ⁵ ''■. ■■■ ⁶

the increase in resistance of PTC thermistors of the second type the structural design of the invention

represent. Body.

The most important advantageous features and characteristics of the present invention thus teaches that Shafts of the PTC type of the second type are in the dopant, z. B. Antimony, which follows the Curie compiled: 5 point of barium titanate after lower temperatures _ ■, "'■. '. , ",., Shifts, must be enriched at the grain boundaries.

1. Compared to the PTC thermistors of the first type (cons- .. _The s occurs through the above-mentioned Bsmsssungsslandsstieg up to four powers of ten) j of _the individual components of the doped perovskite resistance increase in PTC thermistors of the second type _materials . especially in the case of a barium oxide doped with a total of up to seven powers of ten are _{10 021} mol percent antimony oxide.

2. The ■ voltage dependence of the resistance _{titanate could be seen by comparison with} investigations above the Curie temperature. _{On homogeneous} material (extrapolation of the curve a diagram according to Fig. 4 results, with Ka conductors _{in the diagram according to Fig} . ₆ ) an antimony concentration of a type (curve Λ) compared with calÜeitern _{tration of about 3> 5} mol percent at the grain boundaries of the first type (curve 5) Much less than this' _{can be demonstrated} .

reduced so-called "Vasistoreffekt" can _g in _{the diagram by F} j. _{6 shows in curve a the}

Framework of the previous theory with the Fein-Curie point shift as a function of the graininess of the samples can be explained. Antimony concentration in a homogeneous material,

3. The specific resistance at room temperature probably that of the formula.
with the same doping is in part substantially _2o

higher than with PTC thermistors of the first type (diagram. Ba (Ti ₁ - ^ Sb ₁ Z) O ₃

according to Fig. 3). With higher doping it is _{equivalent. You can see from the curve that already}

possible the specific resistance at low antimony concentrations in the room

temperature, if desired, considerably ER- _{stafke Versd} / _eb ^{S S} _{ung the} Curie point to lower low. , .- ,. 25 cause temperatures. Mainly with values around

4. The beginning of the increase in resistance shifts the _{percentage of} antimony, based on the total, to lower temperatures; the shift ^ ^ _{γ arises a} larium titanate material is - in part _{> from the} starting material (anatase or _with a Curie point around 6O ⁰ C.

Rutile) dependent. Curve f shows the conductivity of with antimony

Here the question arises whether this new cold-doped barium titanate, depending on the type of conductor, has the same mechanism of action as the amount of dopant. For values of previously known PTC thermistors is decisive, ie whether 0.4 mol percent antimony oxide is practically none of the previous theories are applicable. Because the conductivity longer present, that is, in this Concentrating this insertion of the resistance increase at tratiönsbereich antimony causes no conductivity, the Curie temperature of the base material (ie at 35 but insulated barium titanate incorporated into the perovskite lattice at about 115 ⁰ C) to be expected; which becomes. Below 0.3 mol% of antimony, the ringing antimony additions can show the Curie temperature curve b that antimony has not shifted appreciably in this order of magnitude. ■■ doping, ie effecting conductivity, in the grid

In order to increase the displacement of the resistance, is incorporated.

To clarify lower temperatures, the 4 ° If an enrichment of the doping substance takes place at the Curie temperature in the doped samples at the grain boundaries, this is of course determined directly. For this purpose, the concentration of doping equivalent circuit diagram in FIG. 5 The parallel capacitance C $ substance is smaller than measured with a corresponding homogensm for the junction resistance R _s; R _v represents ■ material. This occurs in the above (diagram according to here the volume resistance of the test specimen. 45 Fig. 3) discussed increase of the specific curve A in the diagram according to FIG. 5 shows the volume level as expressed.
Course of the increase in resistance in a PTC thermistor Here the question arises as to how this

of the second type, while curve B shows this course for enrichment of the doping substance on the grains of a PTC thermistor of the first type. Curve C represents limits that can come.

the course of the capacity as a function of the 50 According to further considerations and experiments that Temperature. Have led to the present invention, must be a

One recognizes from the diagram according to FIG. 5, such inhomogeneous distribution of the doping substance that the parallel capacitance has a somewhat flattened Curie in the structure, in particular of the antimony in barium tip at the temperature (curve C), in the case of the titanate, strongly depend on the pretreatment. This begins the rise in resistance. This is true in 55 throws a new light on the influence of the un-harmony with the previous experience about the cleaning and the structure on the resistance-resistance increase, but remains inexplicable as long as the increase and the voltage dependence,
one only the gross composition of the ceramic The invention is thus based on the knowledge,

considered. An interpretation is possible if, as already mentioned, one considers Perov's treatment the barrier layer theory to explain the resisting material before sintering here a decisive increase relates. The influence will have to be exercised as a parallel capacity. ■

namely at the used measuring frequency (1 kHz) While namely dsr η conductivity delivering input

only measured the capacity of the barrier layers. The construction of the dopant at Kationenpatzsn er resistance increase in turn, it is also followed by, the insulating incorporation of the doping dielectric constant determined in the barrier layer. 65 substance at the grain boundaries on anion lattice ■ In the case of the PTC thermistors of the second type, bursting has therefore occurred in the area. The control of this installation is of the barrier layers in the grain boundaries the Curie rule according to the above-mentioned measurement rule, Temperature of the material shifted. This preferably corresponds to an excess of the cation

7 8

make belonging to divalent metals causes temperatures as the barium titanate sinters. You over-

then the doping substance is forced, with the exception therefore here sintering - analogous to

like the stoichiometry, BaO · 2 TiO _{2 is} found on anion lattice sites in wet-milled samples

to be built in. It must therefore be ensured that the grain surfaces accordingly. The-

in the conversion reaction from the starting oxides, 5-like samples generally sinter finely crystalline,

or from these oxides forming substances, such as. B. which turns out to be a further advantage of the PTC thermistor second

Carbonates or hydroxides, always with regard to the type, the low one shown in the diagram according to FIG. 4

required final gross composition in relation to the resistance of an applied

terten body results in an excess of the bivalent voltage. ·

perovskite-forming metals over the tetravalent io Structurally, the two KaIt-

perovskite-forming metals is present. conductor types, for example based on BaTiO ₃ , in the following

The method for producing electrical the way: Samples with a deficit of BaO resistors according to the invention is thus inventive have a titanium-rich intermediate layer, whereby the according to characterized in that the starting dopant material almost completely on Ba sites · for the formation the perovskite material 15 is incorporated; Samples with an excess of BaO (Me ¹¹ O or Me ¹¹ CO ₃ and Me ^IV 0 ₂ ) with addition have an intermediate layer in which, in the case of the doping substance (MeO ₃ ;), barium titanate doped with antimony is found , which has enriched the antimony of the specified final composition necessary to about 3.5 mol percent [possible amounts always while maintaining the excess of composition: Ba (Ti _o , ₉₆₅ Sb ₀₁₀₃₅ ) O ₃ ].
Me ¹¹ mixed with each other and at temperatures of 20 This intermediate layer closes because of the approximately 100O ⁰ C to the reaction, that same lattice continuously to the grains, and this reaction product, if it is maintained, is with a steady decrease in the antimony concentration Me ^{Grind the 1I} excess and, at the desired rate from the grain surface into the interior, shape into th bodies, calculate sintering at around 1350 to. This results - apart from the Ver-1400 ⁰ C with a holding time of 1 to 2 hours in 25 shift of the Curie tip - a so-called »oxidizing atmosphere is subjected. The lubrication «, which both in the widening of the maintenance of the Me ⁿ surplus can z. B. as a result of the Curie maximum of the barrier layer and also in that the grinding process of the reaction product slow onset of the resistance increase before the sintering is carried out dry, or makes it noticeable. Due to the inventive Überes, a grinding liquid is used that ^{does not dissolve the Me 11} O 30 placements and the teaching given therefrom, e.g. B. a lower alcohol, especially in this model also now the finding ethanol, methanol or propanol or acetone. one that the cold resistance (resistance below it is also possible, the starting material that of the Curie temperature) and the shift of the divalent metal oxide or carbonate in a the Curie point of the crystal structure of the TiO ₂ -necessary excess and washing out 35 depending on the source material:
Add an amount that takes into account wet grinding As a result of the low reactivity of the highly reactive product and the comminution of the reaction product by burnt rutile - compared to anatase - wet grinding must be carried out in water. . when using rutile, foreign atoms are essential

In the manufacture of the well-known PTC thermistors, the first difficulty is built into the BaTiO ₈ grid. Due to the wet grinding - due to the cold resistance of cold resistors based on rutile, the water solubility of BaO is - or due to the TiO ₂ excess given above when using anatase, always with a deficiency of the antimony not built into the grain is found worked on barium oxide, which is particularly reflected in the antimony-rich intermediate phase; ent at the grain boundaries the TiO ₂ -rich phase BaO. This PTC thermistor also shows a stronger 2 TiO ₂ forms, which takes over the sintering because of its lower melting shift of the Curie point to a lower temperature point. On the other hand, there is a risk of damage (see diagrams according to Figs. 3 and 6).
Measured an Aüsführungsbeispieles the invention dry There is a presumable explanation for the ken ground or in the case of wet grinding for a greater increase in resistance as a result of the excessively increased excess of divalent metal in the material given metal oxides, so proportions of the two - turn 50. This increase in resistance cannot be understood in terms of valuable metal, especially barium, if another activation energy is removed to the point of deficiency. The excess of the surface acceptor term assumes; because the divalent metal oxides, e.g. B. on barium oxide, the maximum height of the potential mountain in the band model probably acts as a result of the endeavor to be bound mainly by the energy position of the acceptor terms that, for example in the case of barium, is determined. According to the above, a titanate occurs, part of the antimony doping substance, such a change in the activation energy of the Oberauf Ti places, occurs during the η conduction, since the other part of the doping substance is incorporated into media with different dielectric constants in both PTC thermistor types Barium places. This arises in small built-in. In addition, there were indications of quantities that would otherwise only be found at higher antimony concentrations that in the case of the rationally occurring insulating phase, the cold iciter according to the invention of the second type, presumably according to the invention, is a matter of the formula that is supplied by the antimony itself * and

¹ in such a way that in the insulating intermediate

J (SbJz) O ₃ layer for the formation of electron traps,

65 which take on the role of the surface terms. In

is composed. the insulating antimony-rich phase is due to

From other investigations, the considerations that led to the invention could be determined that this antimony-rich phase is likely to have traps of this type at lower levels,

Certainly caused by a transition

Sb ⁵¹ "+ 2e -> Sb ³⁾ \

The antimony thus acts here as an acceptor, while in low concentrations - built into Ba ²⁺ -PI etching - it acts as a donor. Accordingly, in the case of the PTC thermistor type according to the invention, no disappearance of the increase in resistance with increasing purity of the starting material was found (cf. diagram according to FIG. 3).

F i g. 1 shows a PTC resistor according to the invention, consisting of the perovskite material body I, the metal coverings applied to this body in a manner known per se without a barrier layer and 3 and the external power supply lines 4 and 5.

F i g. 2 shows a section from the perovskite material body 1 shows the grain structure in very high magnification, with about the inside of the grains 6 composition

prevails, while at the grain boundaries 7 presumably the composition. · - ■

Me "[(L -y) Me ^ Me] O ₃
is present. ·. ".""\..

For the production of a barium titanate PTC material the following examples are given:

a) 1.1OMol barium carbonate (BaCO ₃ ) is mixed with 1 mol of titanium dioxide TiO ₂ (rutile or anatase) and 0.24 to 0.48 g of antimony oxide (Sb ₂ O ₃ ) and ground in a ball mill for 18 hours in 0.551 distilled water . Because of the relatively low solubility of barium carbonate in water, this wet grinding does not result in any loss of barium which is decisive for the properties of the end product. After the grinding, the ground material is dried and at temperatures from 1000 to HOO ⁰ C for a period of

React> 2 hours, so that the perovskite material is formed (barium titanate doped with antimony). After the reaction, the cooled product is dry-ground or ground in a grinding liquid that does not dissolve the BaO, for example in ethanol or acetone, for a period of 18 hours. After drying, the finely divided material is mixed with organic binders known per se and pressed into the desired body shapes, for example into disks. The Fertigsinterung is carried out at 1360-1440 ⁰ C for a period of 1 to 2 hours in an oxidizing atmosphere.

b) In the event that the grinding of the reaction product of the conversion reaction takes place in water

'■■. 1.3 moles of barium carbonate (BaCO ₃ ) are mixed with 1 mole of titanium dioxide TiO ₂ (rutile or anatase) and 0.24 to 0.48 g of antimony oxide (Sb ₂ O ₃ ) and immersed in 0.61 of distilled water for a period of time γόη ground in a ball mill for 18 hours. Drying and conversion to the perovskite material take place as indicated in example a). The second grinding is carried out in a ball mill with 0.5 l of distilled water for a period of 18 hours. The material dried after this grinding process is. as described in example a), treated further.

The sintered PTC thermistor bodies produced according to examples a) or b) are known per se Way then contacted with metal coatings without a barrier layer.

Claims (6)

Patent claims: 1. Electrical resistance with positive temperature coefficient the resistance value and / ίο or less dependence on the resistance value from an applied voltage consisting of sintered grains of the order of magnitude from 0.1 to 2 μΐη one by doping substances (Me) semiconducting ferroelectric ceramic material based on perovskite material the general formula (Me «Me) · (Mei ^v Me) 0 ₃ , ao in which the composition of the constituents on the grain surfaces or in the intermediate layers between . Grains (grain boundaries) deviate from the composition inside the grains, characterized in that the 'sintered resistor body contains a Me ^ir O excess between 0.1 to 3 mol percent over the ^{proportion corresponding to the stoichiometry of the MeHMei v} 0 ₃ , so that the proportion of doping substances (Me) at the grain boundaries is at least about an order of magnitude greater than the proportion of doping substance (Me) in the interior of the grains and that, based on the total proportion of metals in the anion (Me ^IV ), the total proportion of doping substance (Me) is 0.01 to 0.3 mol percent. 2. Resistor according to claim 1, characterized in that the perovskite material is barium titanate (BaTiO ₃ ) which, doped with antimony (Sb) as a dopant (Me), has an antimony concentration between 0.01 and 0.3 mol percent inside the grains, preferably between 0.08 and 0.15 mol percent, and in which an antimony concentration between 0.3 and 5 mol percent, preferably between 0.5 and 3 mol percent, is present at the grain boundaries. 3. A process for the production of electrical resistors according to claim 1 or 2, characterized in that the starting materials for the formation of the perovskite material with the addition of the doping substance in amounts necessary to achieve the specified final composition, always while maintaining the excess of Me ¹¹ O, mixed with each other and ^{brought to reaction at temperatures of about 1000 0} C, that this reaction product when upright conservation of the milled Me and ⁿ -Überschusses, formed into the desired articles, which is subjected to sintering at about 1350-1400 ⁰ C with a holding time of about 1 to 2 hours in an oxidizing atmosphere. 4. The method according to claim 3, characterized in that the maintenance of the Me ^u excess takes place by dry grinding of the reaction product before sintering. 5. The method according to claim 3, characterized shows that the Me ¹¹ excess is maintained by grinding the reaction product in a grinding liquid that does not dissolve ^{the Me n O before sintering.} ■ ' ^: ■. · ■■■■' ■ "■■■ Ίι'- · - '.'^.;'"' 6. The method according to claim 3, characterized in that the divalent metal oxide or carbonate is added to the starting materials in an ^{amount which takes into account the excess and the washing out of Me 11} O during wet milling and the comminution of the reaction products is carried out by wet milling. . 1 sheet of drawings