EP0810611A1 - High temperature thermistor containing rare earth metals - Google Patents

High temperature thermistor containing rare earth metals Download PDF

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EP0810611A1
EP0810611A1 EP97201494A EP97201494A EP0810611A1 EP 0810611 A1 EP0810611 A1 EP 0810611A1 EP 97201494 A EP97201494 A EP 97201494A EP 97201494 A EP97201494 A EP 97201494A EP 0810611 A1 EP0810611 A1 EP 0810611A1
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mixed crystal
temperature
rare earth
thermistor
semiconductor ceramic
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EP0810611B1 (en
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Wilhelm-Albert Dr. Groen
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Philips Intellectual Property and Standards GmbH
Koninklijke Philips NV
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Philips Patentverwaltung GmbH
Koninklijke Philips Electronics NV
Philips Electronics NV
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
    • H01C7/02—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having positive temperature coefficient
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
    • H01C7/04—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having negative temperature coefficient
    • H01C7/042—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having negative temperature coefficient mainly consisting of inorganic non-metallic substances
    • H01C7/043—Oxides or oxidic compounds

Definitions

  • the present invention relates to a high-temperature thermistor with a semiconductor ceramic made of a mixed crystal oxide of rare earth oxides, in particular a thermistor that can be used over the entire temperature range from room temperature to 1100 ° C.
  • Thermistors for high temperatures have become increasingly important in recent years due to new areas of application in immissions protection. They are used, for example, as a temperature sensor for industrial exhaust gas temperature measurements or for temperature control and overtemperature protection for catalytic exhaust gas combustion in cars.
  • the typical application temperatures in cars are between 600 ° C and 1100 ° C, only at these elevated temperatures does the catalytic exhaust gas combustion work optimally.
  • Thermistors made of oxidic semiconductor ceramics offer the advantage over thermocouples in this temperature range that they have a much larger output signal, so that a simpler circuit technology is sufficient for signal processing.
  • Thermistors are also called NTC resistors because their resistance has a negative temperature coefficient (NTC).
  • thermistors are based on oxidic semiconductor ceramics, which are based on oxidic compounds of the transition metals of the spinel or perovskite type.
  • Multi-phase systems are often used, in which the base material is modified by additional components.
  • Today's NTC components consist almost exclusively of mixed crystals with a spinel structure, which are composed of 2 to 4 cations from the group Mn, Ni, Co, Fe, Cu and Ti.
  • the nominal resistance R 25 and the B constant relevant for temperature sensitivity are set to variable values by appropriate reaction control during manufacture, so that the production of a certain range of thermistors is possible with a given offset.
  • NTC thermistors The production spread of NTC thermistors is quite critical because the contamination content in the sintered material is difficult to control.
  • the ceramic compounds and their crystal structures that form during manufacture can change over time, especially at high temperatures. At high temperatures, there can also be a slow reaction with the oxygen in the atmosphere, which causes a permanent change in the resistance value and the temperature characteristic.
  • mixed crystal oxides of the spinel or perovskite type can only be used up to about 500 ° C. At higher temperatures, their long-term stability is too low and their specific resistance is too low for many areas of application.
  • a thermistor is suitable as a temperature sensor for temperatures up to 1100 ° C. It is characterized by its particular stability at very high operating temperatures above 1000 ° C. It is therefore particularly suitable as a sensor in the hot area of catalytic exhaust gas cleaning or for temperature control for engine control.
  • the mixed crystal oxide has a cubic crystal structure of the CM 2 O 3 type.
  • Thermistors with a semiconductor ceramic made of such mixed crystal oxides are characterized by a special high temperature stability.
  • the mixed crystal oxide contains, as further dopants, an element from the group of neodymium, europium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.
  • a semiconductor ceramic which is characterized in that the mixed crystal oxide has a cubic crystal structure of the CM 2 O 3 type is particularly preferred.
  • the semiconductor ceramic with a mixed crystal oxide of the rare earth metals according to the invention contains binary, ternary, quaternary, etc. generally multiple mixed crystal oxides, the essential component of which is terbium and at least one further rare earth metal oxide from the group yttrium, samarium, gadolinium.
  • the mixed crystal oxide can also contain neodymium, europium, dyspprosium, holmium, erbium, thulium, ytterbium or lutetium as further dopants.
  • the semiconductor ceramic Due to the terbium content in the structure, the semiconductor ceramic contains movable electrons, which make a significant contribution to the conductivity of the semiconductor ceramic.
  • the composition of the mixed crystal oxide is preferably chosen so that a cubic CM 2 O 3 type crystal structure is obtained.
  • the prerequisite for this is that the average ionic radius of the cations is based on that of RD Shannon, Acta Cryst. A32 (1976) 751 values are less than 1.06 angstroms.
  • These semiconductor ceramics are monomorphic, ie they do not change their crystal structure at higher temperatures.
  • the mixed crystal oxides according to the invention which crystallize in the CM 2 O 3 type have an outstandingly improved stability at very high temperatures, because in the mixed crystal oxides according to the invention with cations according to the definition given, the crystal structure does not change at higher temperatures.
  • the semiconductor ceramics are manufactured according to the usual ceramic manufacturing methods.
  • the binary oxides of the rare earth metals mentioned or, for example, their oxalates, carbonates, hydroxides or the like are used as starting compounds. used.
  • the starting mixtures are weighed, then mixed dry or wet and ground. This is preferably followed by a calcination process at 1000 ° C. for better chemical homogenization and for better compaction.
  • the shaping process for the green body follows by pressing, film drawing, screen printing or the like.
  • the shaped green bodies go through a binder burnout and are then sintered at 1250 ° C to 1400 ° C.
  • the sintering process is not very susceptible to faults and is not dependent on the gas atmosphere or the cooling curve.
  • connection electrodes preferably made of platinum
  • platinum paste can also be applied and baked using the screen printing process.
  • Other methods are also possible, such as application using vacuum evaporation technology.
  • the resistance and its temperature dependency were determined in the temperature range from 200 ° C to 1100 ° C.
  • the thermal resistance of the thermistors was also measured at high temperatures.
  • Mixed crystal oxides are produced which contain Y 2 O 3 and 3, 10 and 30 at% terbium.
  • the starting compounds Y 2 O 3 and Tb 4 O 7 are mixed in the appropriate mixing ratio and ground with zircon grinding balls for 16 hours.
  • This premixed powder is granulated with a conventional binder preparation. Tablets with a diameter of 6 mm and a thickness of 1 mm are pressed from the granules. These tablets are sintered in the air for six hours at 1350 ° C.
  • X-ray diffraction pictures show that the semiconductor ceramic thus obtained from mixed crystal oxides is a single-phase material with a CM 2 O 3 structure.
  • the average ionic radius of the mixed crystal oxides is 1.016 ⁇ , 1.018 ⁇ and 1.023 ⁇ , respectively.
  • the relative density of the mixed crystal oxides is greater than 94% of the theoretical density.
  • Quaternary mixed crystal oxides of yttrium oxide, samarium oxide and terbium oxide with the composition Y 0.5 Sm 0.9 Tb 0.6 O 3 and Y 0.5 Sm 0.5 Tb 1.0 O 3 are produced by the same method as in Example 1.
  • X-ray diffraction images show that the material is single-phase and crystallizes in the CM 2 O 3 type.
  • the average ionic radius of the mixed crystal oxides is 1.056 ⁇ and 1.046 ⁇ , respectively.
  • the relative density is greater than 95% of the theoretical density.
  • a ternary mixed crystal oxide with the composition Gd 1.4 Tb 0.6 O 3 is produced by the same method as in Example 1.
  • X-ray diffraction images show that the material is single-phase and crystallizes in the CM 2 O 3 type.
  • the average ion radius of the mixed crystal oxide is 1.054 ⁇ .
  • the density is greater than 95% of the theoretical density.
  • tablets made from the semiconductor ceramic according to the invention are coated with platinum paste on both sides for contacting.
  • the specific resistance is measured while the temperature is varied.
  • the reciprocal temperature is plotted against the logarithm of the specific conductivity ⁇ .
  • You get according to the Arrhenius curve, the slope of which gives the coefficient of thermal resistance B according to the formula B (lnR 1 -lnR 2nd ) / (1 / T 1 - 1 / T 2nd ) calculated.
  • Thermistors are required to have a linear relationship between temperature and electrical output.
  • the semiconductor ceramic can be used as a thermistor.
  • Yttrium-terbium mixed crystal oxides with a terbium content of more than 10 at% have particularly favorable properties. They can be used up to temperatures of 1100 ° C.
  • Fig. 2 shows the Arrhenius curve for Y 0.5 Sm 0.9 Tb 0.6 O 3 (lower curve) and Y 0.5 Sm 0.5 Tb 1.0 O 3 (upper curve). Due to the lower resistance and the non-linearity of the Arrhenius curves above 600 ° C, mixed crystal oxides can be used as a sensor at temperatures from 20 ° C to 600 ° C.
  • the temperature-resistance characteristic must be reliably reproducible even at high temperatures. Especially for applications in motor vehicle construction, the deviations in the temperature ⁇ T at 600 ° C to 1000 ° C should not exceed +/- 2%, i.e. 20 ° C at 1000 ° C.
  • Two identical thermistors are selected for each of these measurements.
  • One thermistor is heated to 1000 ° C for 100 h. Then the resistance-temperature characteristics of both thermistors are measured. If the resistance as a function of temperature is plotted for both thermistors, two parallel curves are obtained which are shifted by ⁇ t against each other. The result of the measurements is shown in Table 4.5. The results show that mixed crystal oxides based on yttrium oxide showed the best results. No aging effect was observed in 70% at% Y 2 O 3 with 30 at% terbium oxide. Tab.

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Ceramic Engineering (AREA)
  • Thermistors And Varistors (AREA)
  • Compositions Of Oxide Ceramics (AREA)

Abstract

A semiconductor ceramic, consisting of a rare earth metal oxide solid solution of composition (I), is new. (YaGdbSmcTbd)2O3 (I), in which a = 0 to 0.995, b = 0 to 0.995, c = 0 to 0.995, d = 0.01 to 0.995 and a = greater than 0, when b = 0, or b = greater than 0, when a = 0. Preferably, the oxide solid solution has a cubic crystalline structure of C-M2O3 type and may contain further doping elements selected from Nd, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu. Also claimed is a thermistor with a semiconductor ceramic of the above composition (I).

Description

Die vorliegende Erfindung betrifft einen Hochtemperatur-Thermistor mit einer Halbleiterkeramik aus einem Mischkristalloxid der Seltenerdmetalloxide, insbesondere einen Thermistor, der über den gesamten Temperaturbereich von Raumtemperatur bis 1100°C eingesetzt werden kann.The present invention relates to a high-temperature thermistor with a semiconductor ceramic made of a mixed crystal oxide of rare earth oxides, in particular a thermistor that can be used over the entire temperature range from room temperature to 1100 ° C.

Thermistoren für hohe Temperaturen haben in den letzten Jahren durch neue Anwendungsgebiete im Immisionsschutz an Bedeutung gewonnen. Sie werden beispielsweise als Temperatursensor für industrielle Abgastemperaturmessungen oder zur Temperatursteuerung und Übertemperatursicherung für die katalytische Abgasverbrennung in Autos verwendet. Die typischen Anwendungstemperaturen in Autos liegen zwischen 600°C und 1100°C, erst bei diesen erhöhten Temperaturen arbeitet die katalytische Abgasverbrennung optimal. Thermistoren aus oxidischer Halbleiterkeramik bieten gegenüber Thermoelementen in diesem Temperaturbereich den Vorteil, daß sie ein wesentlich größeres Ausgangssignal haben, so daß zur Signalverarbeitung eine einfachere Schaltungstechnik ausreicht.Thermistors for high temperatures have become increasingly important in recent years due to new areas of application in immissions protection. They are used, for example, as a temperature sensor for industrial exhaust gas temperature measurements or for temperature control and overtemperature protection for catalytic exhaust gas combustion in cars. The typical application temperatures in cars are between 600 ° C and 1100 ° C, only at these elevated temperatures does the catalytic exhaust gas combustion work optimally. Thermistors made of oxidic semiconductor ceramics offer the advantage over thermocouples in this temperature range that they have a much larger output signal, so that a simpler circuit technology is sufficient for signal processing.

Thermistoren werden auch als NTC-Widerstände bezeichnet, weil ihr Widerstand einen negativen Temperaturkoeffizienten (NTC) aufweist. Der spezifische elektrische Widerstand der NTC-Widerstände nimmt mit erhöhter Temperatur annähernd exponentiell ab gemäß der Gleichung ρ = ρ 0 exp B ( 1/T - 1/T o )

Figure imgb0001
, wobei ρ und ρ0 die jeweiligen spezifischen Widerstände bei den absoluten Temperaturen T und T0 sind, B ein thermische Konstante und T die Temperatur in Kelvin ist. Für einen Thermistoren ist es besonders günstig, wenn die Widerstands- Temperatur- Kennlinie möglichst steil ist. Diese Steilheit wird durch die Konstante B bestimmt.Thermistors are also called NTC resistors because their resistance has a negative temperature coefficient (NTC). The specific electrical resistance of the NTC resistors decreases approximately exponentially with increased temperature according to the equation ρ = ρ 0 exp B (1 / T - 1 / T O )
Figure imgb0001
 , where ρ and ρ 0 are the respective resistivities at the absolute temperatures T and T 0 , B is a thermal constant and T is the temperature in Kelvin. It is particularly favorable for a thermistor if the resistance-temperature characteristic is as steep as possible. This slope is determined by the constant B.

Bekannte technische Lösungen für Thermistoren gehen von oxidischen Halbleiterkeramiken aus, die auf oxidischen Verbindungen der Übergangsmetallen vom Spinell- oder Perowskit-Typ basieren. Vielfach gelangen Mehrphasensysteme zur Anwendung, bei denen das Basismaterial durch weitere Komponenten modifiziert wird. Heutige NTC-Bauelemente bestehen fast ausschließlich aus Mischkristallen mit Spinellstruktur, die sich aus 2 bis 4 Kationen der Gruppe Mn, Ni, Co, Fe, Cu und Ti zusammensetzen. Für solche mehrphasigen Systeme wird der Nennwiderstand R25 und die für die Temperaturempfindlichkeit maßgebliche B-Konstante durch eine entsprechende Reaktionsführung bei der Herstellung auf variable Werte eingestellt, so daß bei einem gegebenen Versatz die Produktion eines bestimmten Sortiments von Thermistoren möglich ist. Diese Verfahrensweise schließt im allgemeinen eine beträchtliche Streubreite der Daten der Einzelexemplare und von Charge zu Charge ein, da die den Thermistor kennzeichnenden elektrischen Parameter je nach dem erreichten Strukturgefüge der Keramik verschiedene Werte einnehmen. Ein hinreichend eng toleriertes Sortiment von langzeitstabilen Thermistoren verlangt daher verschiedene Formen thermischer und elektrischer Nachbehandlung sowie Sortieren und Vereinzeln als gesonderte Arbeitsschritte.Known technical solutions for thermistors are based on oxidic semiconductor ceramics, which are based on oxidic compounds of the transition metals of the spinel or perovskite type. Multi-phase systems are often used, in which the base material is modified by additional components. Today's NTC components consist almost exclusively of mixed crystals with a spinel structure, which are composed of 2 to 4 cations from the group Mn, Ni, Co, Fe, Cu and Ti. For such multiphase systems, the nominal resistance R 25 and the B constant relevant for temperature sensitivity are set to variable values by appropriate reaction control during manufacture, so that the production of a certain range of thermistors is possible with a given offset. This procedure generally involves a considerable spread of the data of the individual specimens and from batch to batch, since the electrical parameters characterizing the thermistor take on different values depending on the structural structure of the ceramic that has been achieved. A sufficiently narrowly tolerated range of long-term stable thermistors therefore requires various forms of thermal and electrical aftertreatment as well as sorting and separating as separate work steps.

Die Fertigungsstreuung von NTC-Thermistoren ist durchaus kritisch, weil der Kontaminationsgehalt im Sinterwerkstoff schwer kontrollierbar ist. Außerdem können sich die bei der Herstellung bildenden keramischen Verbindungen und deren Kristallstrukturen mit der Zeit verändern, besonders bei hohen Temperaturen. Bei hohen Temperaturen kann auch eine langsame Reaktion mit dem Sauerstoff in der Atmosphäre stattfinden, die eine permanente Änderung des Widerstandswertes und der Temperaturcharakteristik verursacht.The production spread of NTC thermistors is quite critical because the contamination content in the sintered material is difficult to control. In addition, the ceramic compounds and their crystal structures that form during manufacture can change over time, especially at high temperatures. At high temperatures, there can also be a slow reaction with the oxygen in the atmosphere, which causes a permanent change in the resistance value and the temperature characteristic.

Daher sind Mischkristalloxide vom Spinell- oder Perowskittyp nur bis etwa 500°C einsatzfähig. Bei höheren Temperaturen ist ihre Langzeitstabilität zu gering und außerdem ihr spezifischer Widerstand für viele Anwendungsgebiete zu klein.Therefore, mixed crystal oxides of the spinel or perovskite type can only be used up to about 500 ° C. At higher temperatures, their long-term stability is too low and their specific resistance is too low for many areas of application.

Aus A.J. Moulson und J.M. Herbert, "Electroceramics", Chapman and Hall, London, S.141 (1990) ist es bereits bekannt, für Thermistoren für sehr hohe Temperaturen Mischungen von Seltenerdmetalloxiden, d.h. eine Mischung aus 70 cat. % Sm und 30 cat% Tb zu verwenden. Diese Mischung kann bis zu Temperaturen von 1000°C eingesetzt werden, weil sie keine Tendenz zeigt, mit dem Sauerstoff der Atmosphäre zu reagieren.From A.J. Moulson and J.M. Herbert, "Electroceramics", Chapman and Hall, London, p.141 (1990) already discloses mixtures of rare earth metal oxides, e.g. a mixture of 70 cat. % Sm and 30 cat% Tb to use. This mixture can be used up to temperatures of 1000 ° C because it shows no tendency to react with the oxygen in the atmosphere.

Bei sehr hohen Temperaturen oberhalb 1000°C treten jedoch auch bei diesem Hochtemperaturthermistormaterial Instabilitäten im Widerstandswert auf.At very high temperatures above 1000 ° C, however, instabilities in the resistance value also occur with this high-temperature thermistor material.

Es ist daher die Aufgabe der vorliegenden Erfindung, einen Hochtemperaturthermistor zu schaffen, der enge Toleranzen aufweist und auch bei sehr hohen Temperaturen langzeitstabil ist.It is therefore the object of the present invention to provide a high-temperature thermistor which has narrow tolerances and is long-term stable even at very high temperatures.

Erfindungsgemäß wird die Aufgabe gelöst, indem man einen Thermistor mit einer Halbleiterkeramik aus einem Mischkristalloxid der Seltenerdmetalle der Zusammensetzung [YaGdbSmcTbd]2O3 mit 0 ≤ a ≤ 0,995; 0 ≤ b ≤ 0,995; 0 ≤ c ≤ 0,995; 0,01 ≤ d ≤ 0,995 und a > 0, wenn b = 0 oder b > 0, wenn a = 0 zur Verfügung stellt. Ein derartiger Thermistor ist als Temperatursensor für Temperaturen bis 1100°C geeignet. Er zeichnet sich durch eine besondere Stabilität bei sehr hohen Betriebstemperaturen oberhalb von 1000°C aus. Er eignet sich daher besonders als Sensor im Heißbereich der katalytischen Abgasreinigung oder zur Temperaturregelung für die Motorsteuerung.According to the invention, the object is achieved by using a thermistor with a semiconductor ceramic made from a mixed crystal oxide of rare earth metals of the composition [Y a Gd b Sm c Tb d ] 2 O 3 with 0 ≤ a ≤ 0.995; 0 ≤ b ≤ 0.995; 0 ≤ c ≤ 0.995; 0.01 ≤ d ≤ 0.995 and a> 0 if b = 0 or b> 0 if a = 0 is available. Such a thermistor is suitable as a temperature sensor for temperatures up to 1100 ° C. It is characterized by its particular stability at very high operating temperatures above 1000 ° C. It is therefore particularly suitable as a sensor in the hot area of catalytic exhaust gas cleaning or for temperature control for engine control.

Im Rahmen der vorliegenden Erfindung ist es besonders bevorzugt, daß das Mischkristalloxid eine kubische Kristallstruktur vom C-M2O3 -Typ hat. Thermistoren mit einer Halbleiterkeramik aus derartigen Mischkristalloxiden zeichnen sich durch eine besondere Hochtemperaturstabilität aus.In the context of the present invention, it is particularly preferred that the mixed crystal oxide has a cubic crystal structure of the CM 2 O 3 type. Thermistors with a semiconductor ceramic made of such mixed crystal oxides are characterized by a special high temperature stability.

Es kann auch bevorzugt sein, daß das Mischkristalloxid als weitere Dotierungen ein Element aus der Gruppe Neodym,Europium, Gadolinium, Dysprosium, Holmium, Erbium, Thulium, Ytterbium und Lutetium enthält.It can also be preferred that the mixed crystal oxide contains, as further dopants, an element from the group of neodymium, europium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.

Es ist bevorzugt, daß 0,5 ≤ a ≤ 0,99; b = 0, c = 0 und 0,01 ≤ d ≤ 0,5 ist.
Es ist weiterhin bevorzugt, daß 0,65 ≤ a ≤ 0,75, b = 0, c = 0, 0,25 ≤ d ≤ 0,35 ist.
Es ist besonders bevorzugt, daß a = 0 und 0,1 ≤ b ≤ 0,7, c = 0 und 0,3 ≤ d ≤ 0,9 ist.
Es ist auch bevorzugt, daß 0 ≤ a ≤ 0,30, b = 0 und 0,2 ≤ c ≤ 0,5 und 0,2 ≤ d ≤ 0,6 ist.It is preferred that 0.5 ≤ a ≤ 0.99; b = 0, c = 0 and 0.01 ≤ d ≤ 0.5.
It is further preferred that 0.65 a a 0,7 0.75, b = 0, c = 0, 0.25 d d 0,3 0.35.
It is particularly preferred that a = 0 and 0.1 ≤ b ≤ 0.7, c = 0 and 0.3 ≤ d ≤ 0.9.
It is also preferred that 0 ≤ a ≤ 0.30, b = 0 and 0.2 ≤ c ≤ 0.5 and 0.2 ≤ d ≤ 0.6.

Die Erfindung betrifft weiterhin eine Halbleiterkeramik aus einem Mischkristalloxid der Zusammensetzung [YaGdbSmcTbd]2O3 mit 0 ≤ a ≤ 0,995; 0 ≤ b ≤ 0,995; 0 ≤ c ≤ 0,995; 0,01 ≤ d ≤ 0,995 und a > 0, wenn b = 0 oder b > 0, wenn a = 0.
Besonders bevorzugt ist eine Halbleiterkeramik, die dadurch gekennzeichnet ist, daß das Mischkristalloxid eine kubische Kristallstruktur vom C-M2O3 -Typ hat.The invention further relates to a semiconductor ceramic made of a mixed crystal oxide of the composition [Y a Gd b Sm c Tb d ] 2 O 3 with 0 ≤ a ≤ 0.995; 0 ≤ b ≤ 0.995; 0 ≤ c ≤ 0.995; 0.01 ≤ d ≤ 0.995 and a> 0 if b = 0 or b> 0 if a = 0.
A semiconductor ceramic which is characterized in that the mixed crystal oxide has a cubic crystal structure of the CM 2 O 3 type is particularly preferred.

Nachfolgend wird die Erfindung anhand von Beispielen und drei Figuren weiter erläutert.

  • Fig. 1: Arrhenius-Kurve für Halbleiterkeramik aus Yttrium-Terbium-Oxid-Mischkristallen
  • Fig. 2: Arrhenius-Kurve für Halbleiterkeramik aus Yttrium-Samarium-Terbium-Oxid-Mischkristallen
  • Fig. 3: Arrhenius-Kurve für Halbleiterkeramik aus Gadolinium-Terbium-Oxid-Mischkristallen im Vergleich mit Arrhenius-Kurven gemäß Fig. 1 und 2.
The invention is explained in more detail below with the aid of examples and three figures.
  • Fig. 1: Arrhenius curve for semiconductor ceramics made of yttrium-terbium-oxide mixed crystals
  • Fig. 2: Arrhenius curve for semiconductor ceramics made of yttrium-samarium-terbium-oxide mixed crystals
  • 3: Arrhenius curve for semiconductor ceramics made of gadolinium-terbium oxide mixed crystals in comparison with Arrhenius curves according to FIGS. 1 and 2.

Die Halbleiterkeramik mit einem Mischkristalloxid der Seltenerdmetalle gemäß der Erfindung enthält binäre, ternäre, quaternäre usw. allgemein multiple Mischkristalloxide, deren wesentlicher Bestandteil Terbium und mindestens ein weiteres Seltenerdmetalloxid aus der Gruppe Yttrium, Samarium, Gadolinium ist. Als weitere Dotierungen kann das Mischkristalloxid noch Neodym, Europium, Dyspprosium, Holmium, Erbium, Thulium, Ytterbium oder Lutetium enthalten.The semiconductor ceramic with a mixed crystal oxide of the rare earth metals according to the invention contains binary, ternary, quaternary, etc. generally multiple mixed crystal oxides, the essential component of which is terbium and at least one further rare earth metal oxide from the group yttrium, samarium, gadolinium. The mixed crystal oxide can also contain neodymium, europium, dyspprosium, holmium, erbium, thulium, ytterbium or lutetium as further dopants.

Durch den Terbiumanteil in der Struktur enthält die Halbleiterkeramik bewegliche Elektronen, die den wesentlichen Beitrag zu der Leitfähigkeit der Halbleiterkeramik leisten.Due to the terbium content in the structure, the semiconductor ceramic contains movable electrons, which make a significant contribution to the conductivity of the semiconductor ceramic.

Die Zusammensetzung des Mischkristalloxides wird bevorzugt so gewählt, daß man eine Kristallstruktur vom kubischen C-M2O3 -Typ erhält. Voraussetzung hierfür ist es, daß der mittlere Ionerradius der Kationen nach den von R.D. Shannon, Acta Cryst. A32(1976) 751 angegebenen Werten Kleiner als 1.06 Angström ist. Diese Halbleiterkeramiken sind monomorph, d.h. sie verändern ihre Kristallstruktur bei höheren Temperaturen nicht.The composition of the mixed crystal oxide is preferably chosen so that a cubic CM 2 O 3 type crystal structure is obtained. The prerequisite for this is that the average ionic radius of the cations is based on that of RD Shannon, Acta Cryst. A32 (1976) 751 values are less than 1.06 angstroms. These semiconductor ceramics are monomorphic, ie they do not change their crystal structure at higher temperatures.

Mischkristalloxide der Seltenerdmetalle mit einem größeren mittleren Ionenradius, wie reines Terbiumsesquioxid, kristallisieren in dem weniger symmetrischen A-M2O3-Typ oder B-M2O3-Typ. Sie sind polymorph, bei mittleren und hohen Temperaturen wandelt sich ihre Kristallstruktur in den C-M2O3-Typ um (vgl. A.F. Wells, Structural Inorganic Chemistry 4th. Edition, Clarendon Press, Oxford, S.450ff.(1975). Terbiumsesquioxid selbst wandelt sich bei etwa 1000°C in diese kubische C-M2O3-Struktur um. Überraschenderweise wurde gefunden, daß die im C-M2O3-Typ kristallisierenden, erfindungsgemäßen Mischkristalloxide eine hervorragend verbesserte Stabilität bei sehr hohen Temperaturen haben, weil in den erfindungsgemäßen Mischkristalloxiden mit Kationen gemäß der angegebenen Definition sich die Kristallstruktur nicht bei höheren Temperaturen verändert.Mixed crystal oxides of rare earth metals with a larger average ion radius, such as pure terbium sesquioxide, crystallize in the less symmetrical AM 2 O 3 type or BM 2 O 3 type. They are polymorphic, at medium and high temperatures their crystal structure changes to the CM 2 O 3 type (see AF Wells, Structural Inorganic Chemistry 4th Edition, Clarendon Press, Oxford, pp. 450 ff. (1975). Terbium sesquioxide itself converts to this cubic CM 2 O 3 structure at about 1000 ° C. Surprisingly, it was found that the mixed crystal oxides according to the invention which crystallize in the CM 2 O 3 type have an outstandingly improved stability at very high temperatures, because in the mixed crystal oxides according to the invention with cations according to the definition given, the crystal structure does not change at higher temperatures.

Die Herstellung der Halbleiterkeramik erfolgt nach den üblichen keramischen Fertigungsmethoden. Als Ausgangsverbindungen werden die binären Oxide der genannten Seltenerdmetalle oder auch beispielsweise deren Oxalate, Carbonate, Hydroxide o.ä. verwendet. Die Ausgangsmischungen werden abgewogen, dann trocken oder naß gemischt und gemahlen. Daran schließt sich vorzugsweise zur besseren chemischen Homogenisierung und zur besseren Verdichtung ein Kalzinierungsprozeß bei 1000°C an. Nach einem weiteren Mahlvorgang folgt der Formgebungsprozeß zum grünen Körper durch Pressen, Folienziehen, Siebdrucken o.ä. Die geformten grünen Körper durchlaufen einen Binderausbrand und werden anschließend bei 1250°C bis 1400°C gesintert. Der Sinterprozeß ist wenig anfällig für Störungen und weder von der Gasatmosphäre oder der Abkühlkurve abhängig.The semiconductor ceramics are manufactured according to the usual ceramic manufacturing methods. The binary oxides of the rare earth metals mentioned or, for example, their oxalates, carbonates, hydroxides or the like are used as starting compounds. used. The starting mixtures are weighed, then mixed dry or wet and ground. This is preferably followed by a calcination process at 1000 ° C. for better chemical homogenization and for better compaction. After a further grinding process, the shaping process for the green body follows by pressing, film drawing, screen printing or the like. The shaped green bodies go through a binder burnout and are then sintered at 1250 ° C to 1400 ° C. The sintering process is not very susceptible to faults and is not dependent on the gas atmosphere or the cooling curve.

Die Anschlußelektroden, vorzugsweise aus Platin, können als Drahtelektroden während des Sinterns eingebrannt werden. Es kann aber auch Platinpaste im Siebdruckverfahren aufgebracht und eingebrannt werden. Möglich sind auch andere Verfahren, wie das Aufbringen in Vakuum-Aufdampftechnik.The connection electrodes, preferably made of platinum, can be burned in as wire electrodes during the sintering. However, platinum paste can also be applied and baked using the screen printing process. Other methods are also possible, such as application using vacuum evaporation technology.

Zur Prüfung der Thermistoren wurden der Widerstand und dessen Temperaturabhängigkeit im Temperaturbereich von 200°C bis 1100°C bestimmt. Weiterhin wurde die Thermobeständigkeit der Thermistoren bei hohen Temperaturen gemessen.To test the thermistors, the resistance and its temperature dependency were determined in the temperature range from 200 ° C to 1100 ° C. The thermal resistance of the thermistors was also measured at high temperatures.

BEISPIEL 1EXAMPLE 1

Es werden Mischkristalloxide hergestellt, die Y2O3 und jeweils 3, 10 und 30 at% Terbium enthalten. Die Ausgangsverbindungen Y2O3 und Tb4O7 werden im entsprechenden Mischungsverhältnis gemischt und 16 Stunden mit Zirkon-Mahlkugeln gemahlen. Dies vorgemischte Pulver wird mit einer konventionellen Bindemittelzubereitung granuliert. Aus dem Granulat werden Tabletten mit einem Durchmesser von 6 mm und einer Dicke von 1 mm gepreßt. Diese Tabletten werden sechs Stunden bei 1350°C an der Luft gesintert. Röntgenbeugungsaufnahmen zeigen, daß die so erhaltene Halbleiterkeramik aus Mischkristalloxiden ein einphasiges Material mit C-M2O3 - Struktur ist. Der mittlere Ionenradius der Mischkristalloxide beträgt jeweils 1,016 Å, 1,018Å und 1,023 Å. Die relative Dichte der Mischkristalloxide ist größer als 94 % der theoretischen Dichte.Mixed crystal oxides are produced which contain Y 2 O 3 and 3, 10 and 30 at% terbium. The starting compounds Y 2 O 3 and Tb 4 O 7 are mixed in the appropriate mixing ratio and ground with zircon grinding balls for 16 hours. This premixed powder is granulated with a conventional binder preparation. Tablets with a diameter of 6 mm and a thickness of 1 mm are pressed from the granules. These tablets are sintered in the air for six hours at 1350 ° C. X-ray diffraction pictures show that the semiconductor ceramic thus obtained from mixed crystal oxides is a single-phase material with a CM 2 O 3 structure. The average ionic radius of the mixed crystal oxides is 1.016 Å, 1.018 Å and 1.023 Å, respectively. The relative density of the mixed crystal oxides is greater than 94% of the theoretical density.

BEISPIEL 2EXAMPLE 2

Es werden quaternäre Mischkristalloxide von Yttriumoxid, Samariumoxid und Terbiumoxid der Zusammensetzung Y0.5Sm0.9Tb0.6O3 und Y0.5Sm0.5Tb1.0O3 nach dem gleichen Verfahren wie in Beispiel 1 hergestellt. Röntgenbeugungsaufnahmen zeigen, daß das Material einphasig ist und im C-M2O3 - Typ kristallisiert. Der mittlere Ionenradius der Mischkristalloxide beträgt jeweils 1,056 Å und 1,046 Å. Die relative Dichte ist größer als 95% der theoretischen Dichte.Quaternary mixed crystal oxides of yttrium oxide, samarium oxide and terbium oxide with the composition Y 0.5 Sm 0.9 Tb 0.6 O 3 and Y 0.5 Sm 0.5 Tb 1.0 O 3 are produced by the same method as in Example 1. X-ray diffraction images show that the material is single-phase and crystallizes in the CM 2 O 3 type. The average ionic radius of the mixed crystal oxides is 1.056 Å and 1.046 Å, respectively. The relative density is greater than 95% of the theoretical density.

BEISPIEL 3EXAMPLE 3

Es wird ein ternäres Mischkristalloxid der Zusammensetzung Gd1.4Tb0.6O3 nach dem gleichen Verfahren wie in Beispiel 1 hergestellt. Röntgenbeugungsaufnahmen zeigen, daß das Material einphasig ist und im C-M2O3 - Typ kristallisiert. Der mittlere Ionenradius des Mischkristalloxides beträgt 1,054 Å. Die Dichte ist größer als 95% der theoretischen Dichte.A ternary mixed crystal oxide with the composition Gd 1.4 Tb 0.6 O 3 is produced by the same method as in Example 1. X-ray diffraction images show that the material is single-phase and crystallizes in the CM 2 O 3 type. The average ion radius of the mixed crystal oxide is 1.054 Å. The density is greater than 95% of the theoretical density.

TESTERGEBNISSSETEST RESULTS Temperatur-WiderstandscharakteristikaTemperature resistance characteristics

Zur Testung der erfindungsgemäßen Thermistoren werden deren Temperatur-Widerstandscharakteristiken gemessen.To test the thermistors according to the invention, their temperature-resistance characteristics are measured.

Dazu werden Tabletten aus der erfindungsgemäßen Halbleiterkeramik zur Kontaktierung auf beiden Seiten mit Platinpaste beschichtet. Es wird der spezifische Widerstand gemessen, während die Temperatur variiert wird. Man trägt die reziproke Temperatur gegen den Logarithmus der spezifischen Leitfähigkeit σ auf. Man erhält so die Arrhenius-Kurve, aus deren Steigung sich der Koeffizient des Wärmewiderstandes B nach der Formel B= (lnR 1 -lnR 2 )/(1/T 1 - 1/T 2 )

Figure imgb0002
berechnet. Für Thermistoren wird gefordert, daß zwischen Temperatur und elektrischer Ausgangsgröße ein linearer Zusammenhang besteht. Für den Temperaturbereich, in dem die Arrhenius-Kurve linear oder angenähert linear ist, kann die Halbleiterkeramik als Theremistor verwendet werden.For this purpose, tablets made from the semiconductor ceramic according to the invention are coated with platinum paste on both sides for contacting. The specific resistance is measured while the temperature is varied. The reciprocal temperature is plotted against the logarithm of the specific conductivity σ. You get according to the Arrhenius curve, the slope of which gives the coefficient of thermal resistance B according to the formula B = (lnR 1 -lnR 2nd ) / (1 / T 1 - 1 / T 2nd )
Figure imgb0002
 calculated. Thermistors are required to have a linear relationship between temperature and electrical output. For the temperature range in which the Arrhenius curve is linear or approximately linear, the semiconductor ceramic can be used as a thermistor.

Fig. 1 zeigt die Arrheniuskurven für drei Yttrium-Terbium-Mischkristalloxide. Die drei Kurven verlaufen im ganzenTemperaturbereich von etwa 200°C bis 1100°C angenähert linear. In diesem Temperaturbereich können die Halbleiterkeramiken als Thermistoren verwendet werden. Besonders günstige Eigenschaften haben Yttrium-Terbium-Mischkristalloxide mit einem Terbium-Gehalt von mehr als 10 at%. Sie können bis zu Temperaturen von 1100°C eingesetzt werden.1 shows the Arrhenius curves for three yttrium-terbium mixed crystal oxides. The three curves are approximately linear over the entire temperature range from approximately 200 ° C to 1100 ° C. In this temperature range, the semiconductor ceramics can be used as thermistors. Yttrium-terbium mixed crystal oxides with a terbium content of more than 10 at% have particularly favorable properties. They can be used up to temperatures of 1100 ° C.

Fig.2 zeigt die Arrhenius-Kurve für Y0.5Sm0.9Tb0.6O3 (untere Kurve) und Y0.5Sm0.5Tb1.0O3 (obere Kurve). Wegen des niedrigeren Widerstandes und der Nichtlinearität der Arrhenius-Kurven oberhalb von 600°C können dies Mischkristalloxide bei Temperaturen von 20°C bis 600°C als Sensor eingesetzt werden.Fig. 2 shows the Arrhenius curve for Y 0.5 Sm 0.9 Tb 0.6 O 3 (lower curve) and Y 0.5 Sm 0.5 Tb 1.0 O 3 (upper curve). Due to the lower resistance and the non-linearity of the Arrhenius curves above 600 ° C, mixed crystal oxides can be used as a sensor at temperatures from 20 ° C to 600 ° C.

Fig.3 zeigt die Arrheniuskurven für Gd1.4Tb0.6O3 zusammen mit den Arrheniuskurven aus Fig. 1 und Fig. 2 zum Vergleich. Auch diese Material kann von Temperaturen von 200°C bis 1100°C eingesetzt werden.3 shows the Arrhenius curves for Gd 1.4 Tb 0.6 O 3 together with the Arrhenius curves from FIGS. 1 and 2 for comparison. This material can also be used at temperatures from 200 ° C to 1100 ° C.

In Tab. 1 sind die Werte für die spezifischen elektrischen Leitfähigkeiten und für die thermischen Konstanten B der Mischkristalloxide aus Ausführungsbeispiel 1 bis 3 zusammengestellt. Tab. 1 Spezifische elektrische Leitfähigkeiten und B-Konstanten Composition log σ (300 °C) (Ω-1.cm-1) log σ (600 °C) (Ω-1.cm-1) log σ (900 °C) (Ω-1.cm-1) B300/600 (K) B600/900 (K) 97%Y2O3:3%Tb -9.333 -7.386 - 7472 - 90%Y2O3:10%Tb -7.225 -5.445 -4.483 6831 7570 70%Y2O3:30%Tb -5.310 -3.553 -2.487 6743 6252 70%Gd2O3:30%Tb -5.082 -3.215 -2.487 7165 5729 45%Sm2O3:30%Tb: 25%Y -3.771 -2.262 - 5791 - 25%Sm2O3:50%Tb: 25%Y -2.587 -1.430 - 4440 - 1 shows the values for the specific electrical conductivities and for the thermal constants B of the mixed crystal oxides from exemplary embodiments 1 to 3. Tab. 1 Specific electrical conductivities and B constants Composition log σ (300 ° C) (Ω -1 .cm -1 ) log σ (600 ° C) (Ω -1 .cm -1 ) log σ (900 ° C) (Ω -1 .cm -1 ) B 300/600 (K) B 600/900 (K) 97% Y 2 O 3 : 3% Tb -9,333 -7,386 - 7472 - 90% Y 2 O 3 : 10% Tb -7,225 -5,445 -4,483 6831 7570 70% Y 2 O 3 : 30% Tb -5,310 -3,553 -2,487 6743 6252 70% Gd 2 O 3 : 30% Tb -5,082 -3,215 -2,487 7165 5729 45% Sm 2 O 3 : 30% Tb: 25% Y -3,771 -2,262 - 5791 - 25% Sm 2 O 3 : 50% Tb: 25% Y -2,587 -1,430 - 4440 -

AlterungAging

Die Temperatur-Widerstands-charakteristik muß auch bei hohenTemperaturen zuverlässig reproduzierbar sein. Insbesondere für Anwendungen im Kraftfahrzeugbau soll die Abweichungen in der Temperatur Δ T bei 600°C bis 1000°C +/- 2%, i.e 20°C bei 1000°C nicht übersteigen.The temperature-resistance characteristic must be reliably reproducible even at high temperatures. Especially for applications in motor vehicle construction, the deviations in the temperature Δ T at 600 ° C to 1000 ° C should not exceed +/- 2%, i.e. 20 ° C at 1000 ° C.

Für diese Messungen werden jeweils zwei gleiche Thermistoren ausgesucht. Jeweils ein Thermistor wird 100 h auf 1000°C erhitzt. Danach werden die WiderstandsTemperatur-Charakeristiken von beiden Thermistoren gemessen. Wenn der Widerstand als Funktion der Temperatur für beide Thermistoeren aufgetragen wird, erhält man zwei parallele Kurven, die um Δt gegeneinander verschoben sind. Das Ergebnis der Messungen ist in Tabelle 4.5 dagestellt. Die Ergebnisse zeigen, daß Mischkristalloxide auf der Basis von Yttriumoxid die besten Ergebnisse zeigten. Bei 70%at%Y2O3 mit 30 at% Terbiumoxid wurde keinerlei Alterungseffekt beobachtet. Tab. 2 Hochtemperaturzuverlässigkeit Composition ΔT (°C) 70%Sm2O3:30%Tb 13 65%Sm2O3:30%Tb:5%Nd 10 90%Y2O3:10%Tb 4 70%Y2O3:30%Tb 0 Two identical thermistors are selected for each of these measurements. One thermistor is heated to 1000 ° C for 100 h. Then the resistance-temperature characteristics of both thermistors are measured. If the resistance as a function of temperature is plotted for both thermistors, two parallel curves are obtained which are shifted by Δt against each other. The result of the measurements is shown in Table 4.5. The results show that mixed crystal oxides based on yttrium oxide showed the best results. No aging effect was observed in 70% at% Y 2 O 3 with 30 at% terbium oxide. Tab. 2 High temperature reliability Composition ΔT (° C) 70% Sm 2 O 3 : 30% Tb 13 65% Sm 2 O 3 : 30% Tb: 5% Nd 10th 90% Y 2 O 3 : 10% Tb 4th 70% Y 2 O 3 : 30% Tb 0

Claims (10)

Thermistor mit einer Halbleiterkeramik aus einem Mischkristalloxid der Seltenerdmetalle der Zusammensetzung

        [YaGdbSmcTbd]2O3

mit 0 ≤ a ≤ 0,995 0 ≤ b ≤ 0,995 0 ≤ c ≤ 0,995 0,01 ≤ d ≤ 0,995 und a > 0, wenn b = 0 oder b > 0, wenn a = 0. Thermistor with a semiconductor ceramic made of a mixed crystal oxide of the rare earth elements of the composition

[Y a Gd b Sm c Tb d ] 2 O 3

With 0 ≤ a ≤ 0.995 0 ≤ b ≤ 0.995 0 ≤ c ≤ 0.995 0.01 ≤ d ≤ 0.995 and a> 0 if b = 0 or b> 0 if a = 0. Thermistor gemäß Anspruch 1,
dadurch gekennzeichnet,
daß das Mischkristalloxid eine kubische Kristallstruktur vom C-M2O3 -Typ hat.Thermistor according to claim 1,
characterized by
that the mixed crystal oxide has a cubic crystal structure of the CM 2 O 3 type. Thermistor gemäß Anspruch 2,
dadurch gekennzeichnet,
daß das Mischkristalloxid als weitere Dotierungen ein Element aus der Gruppe Neodym,Europium, Gadolinium, Dysprosium, Holmium, Erbium, Thulium, Ytterbium und Lutetium enthält.Thermistor according to claim 2,
characterized by
that the mixed crystal oxide contains as further doping an element from the group neodymium, europium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. Thermistor gemäß Anspruch 1,
dadurch gekennzeichnet, daß 0,5 ≤ a ≤ 0,99 b = 0 c = 0 0,01 ≤ d ≤ 0,5 ist. Thermistor according to claim 1,
characterized in that 0.5 ≤ a ≤ 0.99 b = 0 c = 0 0.01 ≤ d ≤ 0.5. Thermistor gemäß Anspruch 1,
dadurch gekennzeichnet,
daß 0,65 ≤ a ≤ 0,75 b = 0 c = 0 0,25 ≤ d ≤ 0,35 Thermistor according to claim 1,
characterized by
that 0.65 ≤ a ≤ 0.75 b = 0 c = 0 0.25 ≤ d ≤ 0.35 Thermistor gemäß Anspruch 1,
dadurch gekennzeichnet,
daß a = 0 0,1 ≤ b ≤ 0,7 c = 0 0,3 ≤ d ≤ 0,9 Thermistor according to claim 1,
characterized by
that a = 0 0.1 ≤ b ≤ 0.7 c = 0 0.3 ≤ d ≤ 0.9 Thermistor gemäß Anspruch 1,
dadurch gekennzeichnet,
daß 0 ≤ a ≤ 0,30 b = 0 0,3 ≤ c ≤ 0,5 0,2 ≤ d ≤ 0,60 Thermistor according to claim 1,
characterized by
that 0 ≤ a ≤ 0.30 b = 0 0.3 ≤ c ≤ 0.5 0.2 ≤ d ≤ 0.60 Halbleiterkeramik aus einem Mischkristalloxid der Zusammensetzung

        [YaGdbSmcTbd]2O3

mit 0 ≤ a ≤ 0,995 0 ≤ b ≤ 0,995 0 ≤ c ≤ 0,995 0,01 ≤ d ≤ 0,995 und a > 0, wenn b = 0 oder b > 0, wenn a = 0. Semiconductor ceramic from a mixed crystal oxide of the composition

[Y a Gd b Sm c Tb d ] 2 O 3

With 0 ≤ a ≤ 0.995 0 ≤ b ≤ 0.995 0 ≤ c ≤ 0.995 0.01 ≤ d ≤ 0.995 and a> 0 if b = 0 or b> 0 if a = 0. Halbleiterkeramik gemäß Anspruch 8,
dadurch gekennzeichnet,
daß das Mischkristalloxid eine kubische Kristallstruktur vom C-M2O3 -Typ hat.Semiconductor ceramic according to claim 8,
characterized by
that the mixed crystal oxide has a cubic crystal structure of the CM 2 O 3 type. Halbleiterkeramik gemäß Anspruch 9,
dadurch gekennzeichnet,
daß das Mischkristalloxid als weitere Dotierungen ein Element aus der Gruppe Neodym,Europium, Gadolinium, Dysprosium, Holmium, Erbium, Thulium, Ytterbium und Lutetium enthält.Semiconductor ceramic according to claim 9,
characterized by
that the mixed crystal oxide contains as further doping an element from the group neodymium, europium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.
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