JPH05129667A - Thermoelectric semiconductor element and manufacture thereof - Google Patents

Abstract

PURPOSE:To realize a new thermoelectric semiconductor element having the superior performance and stable characteristics by firing a mixture of composite oxide powders and reducing material powders in a non-oxidizing atmosphere, or by firing the mixture which is further mixed with specific fluoride powders in a non-oxidizing atmosphere. CONSTITUTION:Composite oxide powders containing strontium and titanium as principal components and reducing material powders are mixed together, and then fired in a non-oxidizing atmosphere. A pair of electrodes are formed on a resulting oxide ceramic semiconductor. Moreover, composite oxide powders containing strontium and titanium as principal components, reducing material powders, and metal fluoride powders are mixed together, and then fired in a non-oxidizing atmosphere. A pair of electrodes are formed on a resulting oxide ceramic semiconductor. Accordingly, there are obtained characteristics which are substantially equivalent to those of existing Bi-Te-based materials, and hence a thermoelectric semiconductor element having a stable performance can be realized by conventional ceramic processes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoelectric semiconductor device and a method for manufacturing the same, and more particularly to a device using an oxide ceramic semiconductor.

[0002]

2. Description of the Related Art In recent years, there have been great demands for electronic components for electronic cooling utilizing the Peltier effect due to restrictions on the use of CFCs due to global environmental problems and demands for small cooling devices such as local cooling and dehumidification of electronic devices.

Among these, as an electronic component for electronic cooling used near room temperature, one using a Bi-Te type single crystal or polycrystalline solidified body as a thermoelectric semiconductor material is known.

The performance of a thermoelectric semiconductor element for electronic cooling has a large figure of merit Z represented by Z = s × s × σ / k, where the Seebeck coefficient is s, the electrical conductivity is σ, and the thermal conductivity is k. The greater the amount of absorbed heat per power consumption during cooling and the greater the temperature difference from the heat radiating side. Various semiconductor materials are Bi-T
Although it has been studied for the purpose of replacing the e-system, what has been characteristically exceeded has not been reported so far.

[0005]

The thermoelectric semiconductor element is composed of n
The p-type element and the p-type element are electrically connected in series and used. In the Bi-Te based element, Se is added to the n-type conductive element portion for adjusting the characteristics. In these devices, Se, which is added as an additive in particular, is highly toxic, and the Bi-Te-based composition itself, which is the main component, is expensive, which limits the range of use of the device.

In view of the above problems, it is an object of the present invention to provide a new thermoelectric semiconductor element which is inexpensive, excellent in performance, and stable in characteristics, and a manufacturing method thereof.

[0007]

[Means for Solving the Problems] A structure in which reducing substance phases which are not continuous to each other are scattered in a composite oxide containing strontium and titanium as main components, or a specific fluoride phase is a reducing substance phase. With a thermoelectric semiconductor element using an oxide ceramic semiconductor having a configuration included with
The conventional problems have been overcome.

Further, regarding this manufacturing method, a process of mixing the composite oxide powder and the reducing substance powder and firing them in a non-oxidizing atmosphere, or further mixing a specific fluoride powder and firing them in a non-oxidizing atmosphere is carried out. To take.

[0009]

Since the thermoelectric semiconductor element of the present invention is composed of a complex oxide containing strontium and titanium as main components and a reducing substance, it does not contain a toxic component caused by selenium, which has been a serious problem. It is possible to provide a thermoelectric semiconductor element which has a performance as high as that of the conventional Bi-Te and is very inexpensive. Further, the method for producing a thermoelectric semiconductor element of the present invention, a composite oxide containing strontium and titanium as main components is fired in a non-oxidizing atmosphere together with a reducing substance added as a powder in advance. Can be easily made into an oxygen-deficient state, and a thermoelectric semiconductor element having stable performance can be manufactured, and at the same time, can be manufactured very easily.

[0010]

EXAMPLES The composite oxide of the present invention has a perovskite phase structure containing strontium and titanium as main components.
Strontium-based phases include barium, calcium, potassium, sodium, lithium, cesium,
Rubidium, scandium, yttrium, or a lanthanide element may be contained. Titanium-based phases include zirconium, hafnium, tin, niobium, tantalum, tungsten, molybdenum, manganese,
It may contain iron, cobalt, nickel, copper, zinc, indium, magnesium, antimony, or the like.

The reducing substance of the present invention is a metal such as titanium (Ti), zirconium (Zr), tantalum (Ta) or niobium (Nb), such as TiC or Zr.
Metal carbide such as C, NbC, TaC, or TiN, Z
Examples thereof include metal nitrides such as rN, NbN or TaN. As these reducing substances, metals and metal carbides are preferable.

The thermoelectric semiconductor element of the present invention may contain a metal fluoride phase in addition to the reducing substance phase described above. Examples of metal fluorides include fluorides of lithium, calcium, barium and strontium. When the metal fluoride phase is contained in this manner, the metal fluoride phase is selectively present in the vicinity of the triangular points of the grain boundaries of the oxide particles, and the sintered density of the thermoelectric semiconductor element of the present invention is improved and the electrical conductivity is improved. It is preferable because the degree can be obtained.

The thermoelectric semiconductor element of the present invention comprises a composite oxide powder containing strontium and titanium as main components, and a reducing substance powder mixed together and fired in a non-oxidizing atmosphere to form an oxide ceramic semiconductor. It is possible to manufacture by providing the electrodes. It goes without saying that the above-mentioned metal fluoride powder may be mixed and fired in the same non-oxidizing atmosphere in the oxide ceramic manufacturing process.

When firing in a non-oxidizing atmosphere, the reducing substance powder can reduce the insulating complex oxide powder containing strontium and titanium as the main components to an oxygen-deficient state. The oxide ceramic semiconductor can be easily formed. Since the characteristics of the oxide ceramic semiconductor thus manufactured can be easily stabilized, the performance as an element can be stabilized when used in a thermoelectric semiconductor element. The non-oxidizing atmosphere referred to in the present invention means, for example, a so-called rare gas atmosphere such as argon, neon, or helium,
Inert gas atmosphere such as carbon dioxide or nitrogen,
An atmosphere of a reducing gas such as hydrogen or methane can be used. Of these non-oxidizing atmospheres, an argon gas atmosphere is preferable because it is easy to handle and obtain. A usual method can be applied to the step of providing the electrode of the thermoelectric semiconductor element of the present invention, and a normal material such as copper can be applied to the electrode itself.

The raw material powder of the oxide ceramic semiconductor used in the thermoelectric semiconductor element of the present invention has a fine particle size, for example, 200 mesh, because the sintered body becomes dense and the figure of merit Z becomes large. preferable. It is desirable that the oxide ceramic semiconductor contains a metal fluoride because the sintered density is improved and the figure of merit is increased. Further, when the raw material powder of the oxide ceramic semiconductor is sufficiently mixed with, for example, a stirring and crushing machine, the insulating complex oxide powder and the reducing powder are adjacent to each other, and the reducing substance effectively acts, which is preferable.

Examples of the present invention will be described below. (Example 1) As the oxide semiconductor ceramic raw material, a strontium (Sr) to titanium (Ti) ratio of 0.9
A thermoelectric semiconductor element was prepared using the composite oxide of No. 8.

The oxide semiconductor ceramics were prepared by using SrCO ₃ and TiO ₂ as starting materials, weighing them to a predetermined ratio, mixing them with pure water using a zirconia boulder as a mixing medium in a ball mill, and then drying.

The dried powder was put into an alumina crucible and calcined in an electric furnace in air at 1100 ° C. for 12 hours to obtain a powder having a perovskite single phase by powder X-ray analysis.

The calcined powder thus obtained was again wet-milled with pure water using a zirconia cobblestone as a mixed medium in a ball mill to obtain a powder having an average particle size of 0.8 μm and dried.

Predetermined amounts of metallic titanium, metallic zirconium, metallic tantalum and metallic niobium powder were added to this composite oxide powder, and dry mixed using a stirring and crushing machine. However, the metal powder used had a purity of about 99% and a particle size of 200 mesh pass.

5 wt% of water was added to the mixed powder thus obtained, and then granulated, 2.5 g of the powder was added to a mold having a length of 30 mm and a width of 10 mm, and pressed at 700 kg / cm ² to obtain a green compact. did.

The green compact was put in a porcelain pod and placed in a tubular furnace, and was fired at 1500 ° C. for 2 hours while flowing an argon gas.

Gold electrodes were vapor-deposited on both ends of the fired body, lead wires were taken out from the gold electrodes, both ends were sandwiched by different heating plates to make a temperature difference, and the Seebeck coefficient S was obtained from the temperatures at both ends and the thermoelectromotive force. ..

Further, two electrodes were formed in the middle of the fired body where the thermoelectromotive force was measured, and a direct current of 10 m was applied to the sample by the 4-terminal method.
A was flown, and the electrical conductivity σ of the sample was obtained from the initial potential difference.

The lead wire of the sample for which electrical conductivity was obtained in this way was removed, one end was nickel-plated, soldered to a copper hot plate, placed in a vacuum container of about 10 ^-2 Pa, and the hot plate temperature was measured by the Angstrom method. Was periodically changed to determine the temperature change at both ends of the sample, and the specific heat was determined from the DSC measurement separately performed, and thereby the thermal conductivity k was determined.

The figure of merit Z was obtained from the Seebeck coefficient S, electrical conductivity σ and thermal conductivity k obtained by these measurements.

After the measurement, the sample was polished into thin pieces and the phases were observed by an optical microscope. It was confirmed that metallic phases having a particle size of about 200 μm were not continuous with each other and were scattered in the sample.

As a comparative example, a sample was prepared by firing the calcined powder prepared above in the same shape and in the same process without adding the metal powder, and the sample was heated in nitrogen gas containing 5% hydrogen for 150 times.
The sample was reduced at 0 ° C. for a predetermined time, and the sponge titanium agglomerate was placed at a windward position with respect to the sample in the tubular furnace, and the argon gas passed through the sponge titanium agglomerate in a high temperature
A sample reduced at 00 ° C. for a predetermined time was prepared.

Table 1 shows the type of metal, Seebeck coefficient S, electrical conductivity σ, thermal conductivity k, and figure of merit Z.

[0030]

[Table 1]

As shown in Table 1, in the thermoelectric semiconductor element made of oxide ceramic, the oxide ceramic is made of an oxide semiconductor containing a complex oxide of strontium and titanium as a main component, and metal phases which are not continuous with each other are contained in the oxide semiconductor. A large figure of merit for a thermoelectric semiconductor device characterized in that this phase is a metallic phase containing as a main component at least one component selected from the group consisting of titanium, zirconium, tantalum, and niobium. On the other hand, in the case of containing no metal phase, the Seebeck coefficient increases, but the progress of reduction is slow, so the electrical conductivity is small and therefore the figure of merit does not increase. Further, the time required for the reduction may be long, which leads to an increase in manufacturing cost.

Example 2 A thermoelectric semiconductor element was prepared by using a composite oxide of Sr _0.69 Ba _0.3 TiO _2.99 as an oxide semiconductor ceramic raw material.

The oxide semiconductor ceramics were prepared by using SrCO ₃ , BaCO ₃ and TiO ₂ as starting materials, weighing them to a predetermined ratio, mixing them with pure water using a zirconia boulder as a mixing medium in a ball mill, and then drying.

The dried powder was put in an alumina crucible and calcined for 2 hours at 1150 ° C. in air using an electric furnace, and powder perovskite single phase powder was obtained by powder X-ray analysis.

The calcined powder was again wet-milled with pure water using a zirconia cobblestone as a mixed medium in a ball mill to obtain a powder having an average particle size of 0.8 μm, and dried.

A predetermined amount of Ti is added to this composite oxide powder.
C, ZrC, TaC and NbC powders were added and dry mixed using a stirrer. The metal carbide powder used had a purity of about 99% and a particle size of 50 μm.

The mixed powder was granulated after adding 5 wt% of water, 2.0 g of the powder was added to a mold having a length of 30 mm and a width of 10 mm, and pressed at 700 kg / cm ² to obtain a green compact. The green compact thus obtained is put into a porcelain pod and inserted into a tubular furnace.
Firing was performed at 1450 ° C. for 2 hours while flowing an argon gas.

Evaluation of the fired body was performed in the same manner as in Example 1. Samples after measurement are X-ray micro analyzer and SEM
By observing the phases by observation, the particle size in the sample is 30 μm.
It was confirmed that some carbide phases were not continuous with each other and were scattered.

In addition, as a comparative example, a sample obtained by firing in the same process in the same shape without adding the metal carbide powder to the calcined powder produced above was prepared in a nitrogen gas containing 5% hydrogen at 1500 ° C. A sample that has been reduced for a certain period of time and a sample that has been reduced for a certain period of time at 1500 ° C in argon gas that has passed through the sponge titanium aggregate in a high temperature state by arranging the titanium sponge aggregate at the windward position with respect to the sample of the tubular furnace did.

Table 2 shows the type of metal, Seebeck coefficient S, electrical conductivity σ, thermal conductivity k, and figure of merit Z.

[0041]

[Table 2]

As shown in Table 2, in the thermoelectric semiconductor device made of oxide ceramic, the oxide ceramic is made of an oxide semiconductor containing a composite oxide of strontium and titanium as a main component, and the metal carbide phases are not continuous with each other. The thermoelectric semiconductor element is characterized in that this phase is a metal carbide phase containing at least one component selected from the group consisting of titanium, zirconium, tantalum, and niobium as a main component. In contrast to the figure of merit, those not containing a metal carbide phase have a large Seebeck coefficient, but the progress of reduction is slow, so the electrical conductivity is small, and therefore the figure of merit does not increase. Further, the time required for the reduction may be long, which leads to an increase in manufacturing cost.

Example 3 A thermoelectric semiconductor element was prepared by using a composite oxide of Sr _0.9 Ca _0.1 TiO ₃ as the oxide semiconductor ceramic raw material.

The oxide semiconductor ceramics were prepared by using SrCO ₃ , CaCO ₃ and TiO ₂ as starting materials, weighing them to a predetermined ratio, mixing them with pure water using a zirconia boulder as a mixing medium in a ball mill, and then drying.

The dried powder was put in an alumina crucible and calcined in an electric furnace in air at 1200 ° C. for 2 hours to obtain a perovskite single phase powder by powder X-ray analysis.

The calcined powder was again wet-milled with pure water using a zirconia cobblestone as a mixing medium in a ball mill to obtain a powder having an average particle size of 0.8 μm, which was then dried.

With respect to this composite oxide powder, 0.2 wt% of Ti or TiC powder and a predetermined amount of LiF, CaF ₂ ,
SrF ₂ and BaF ₂ were added, and dry mixing was performed using a stirring and crushing machine. This metal powder has a purity of about 99% and a particle size of 300.
μm, metal carbide powder has a purity of about 99% Particle size 1
The thing of about 20 micrometers was used.

The mixed powder was granulated after adding 5 wt% of water, 2.0 g of the powder was added to a mold having a length of 30 mm and a width of 10 mm, and pressed at 700 kg / cm ² to obtain a green compact. The green compact thus obtained is put into a porcelain pod and inserted into a tubular furnace.
Firing was performed at 1300 ° C. for 2 hours while flowing an argon gas.

Evaluation of the fired body was performed in the same manner as in Example 1. Samples after measurement are X-ray micro analyzer and SEM
By observing the phase, the particle size of 150μ in the sample
A metal phase of about m or a carbide phase having a particle size of about 50 μm was not continuous with each other and was scattered, and a fluoride phase was confirmed near the triangular points of the oxide particles.

In addition, as a comparative example, a sample was prepared by firing the calcination powder prepared above in the same process in the same shape without adding any metal powder or fluoride powder, and in a nitrogen gas containing 5% hydrogen. And a sponge titanium agglomerate was placed at a windward position with respect to the sample of the tubular furnace and the sample was reduced at 1500 ° C. for a predetermined time in argon gas passing through the sponge titanium agglomerate in a high temperature state. A sample was prepared.

Table 3 shows the type of metal or carbide, the type of fluoride, the Seebeck coefficient S, the electrical conductivity σ, the thermal conductivity k, and the figure of merit Z.

[0052]

[Table 3]

As shown in Table 3, in the thermoelectric semiconductor element made of oxide ceramic, the oxide ceramic is made of an oxide semiconductor containing a complex oxide of strontium and titanium as a main component, and the metal phase which is not continuous with each other or A thermoelectric semiconductor device having a large performance in which metal carbide phases are scattered and at least one metal fluoride phase selected from the group consisting of lithium, calcium, barium, and strontium is present. Indicates the index.

In particular, those containing a fluoride phase as in the examples tend to have a high sintering density and a high thermal conductivity instead of a high electrical conductivity, but the figure of merit itself is hardly changed.

The sample of the thermoelectric semiconductor element of the present invention is
Since the sintering temperature can be selected low, the sample can be easily manufactured and the characteristics can be stably obtained.

On the other hand, a sample containing neither a metal phase or a metal carbide phase nor a fluoride phase has a large Seebeck coefficient, but since the progress of reduction is slow, the electric conductivity is small and therefore the figure of merit does not become large. Further, the time required for the reduction may be long, which leads to an increase in manufacturing cost.

(Example 4) A composite oxide of Sr _0.94 La _0.04 TiO ₃ was used as a raw material material for an oxide semiconductor ceramic to prepare a thermoelectric semiconductor element.

The oxide semiconductor ceramics were prepared by using SrCO ₃ , La ₂ O ₃ and TiO ₂ as starting materials, weighing them to a predetermined ratio, mixing them with pure water using a zirconia boulder as a mixing medium in a ball mill, and then drying.

The dried powder was put into an alumina crucible and calcined for 2 hours at 1300 ° C. in the air using an electric furnace, and powder perovskite single phase powder was obtained by powder X-ray analysis.

The calcined powder was again wet-milled with pure water using a zirconia cobblestone as a mixed medium in a ball mill to obtain a powder having an average particle size of 0.4 μm and dried.

0.2 wt% Ti or Zr powder with respect to this composite oxide powder, and 0.2 wt% for some.
% LiF and BaF ₂ were added, and dry mixing was performed using a stirrer. This metal powder has a purity of about 99% and a particle size of 30.
The metal carbide powder having a purity of about 99% and the particle diameter of about 120 μm was used.

The mixed powder was granulated after adding 5 wt% of water, 2.0 g of the powder was added to a mold having a length of 30 mm and a width of 10 mm, and pressed at 700 kg / cm ² to obtain a green compact. The green compact thus obtained is put into a porcelain sheath and inserted into a tubular furnace. Fluoride-containing material is 1300 ° C., fluoride-free material is 150
Firing was performed at 0 ° C. for 2 hours while flowing an argon gas or a nitrogen gas.

Evaluation of the fired body was performed in the same manner as in Example 1. Samples after measurement are X-ray micro analyzer and SEM
By observing the phases by observation and firing in argon, the metallic phases with a particle size of about 150 μm are scattered in the sample and are not continuous with each other. A fluoride phase was confirmed near the point. On the other hand, in the one fired in nitrogen, a metal phase was partly scattered, and titanium nitride and zirconium nitride phases were partly observed.

Table 4 shows the type of metal or carbide, the type of fluoride, the Seebeck coefficient S, the electric conductivity σ, the thermal conductivity k, and the figure of merit Z.

[0065]

[Table 4]

As described above, in the method of manufacturing a thermoelectric semiconductor device made of an oxide ceramic, if the non-oxidizing atmosphere at the time of firing is nitrogen, the metal phase in the device is apt to change to a nitride phase, and it is scattered in the ceramic. Since the nitride phase has a lower reducing power than the metal phase, the Seebeck coefficient of the thermoelectric semiconductor device manufactured in this way is large, but the electric conductivity is small, so that the figure of merit is slightly lowered.

On the other hand, the sample fired in argon exhibits more excellent characteristics without nitriding of the metal phase, which is more preferable for obtaining more excellent characteristics.

[0068]

INDUSTRIAL APPLICABILITY The present invention is a thermoelectric semiconductor using an oxide ceramic semiconductor which is composed of a composite oxide containing strontium and titanium as main components, and in which a reducing substance phase which is not continuous with each other is scattered. Since it is an element, it has characteristics that are almost comparable to those of conventional Bi-Te-based materials, has no toxicity problem as a material, can be easily manufactured using conventional ceramic processes, and the raw materials themselves are inexpensive. It is advantageous industrially because it has the advantage of cost reduction.

Claims (7)

[Claims] 1. A thermoelectric semiconductor comprising an oxide ceramic semiconductor which is composed of a composite oxide containing strontium and titanium as main components, and in which a reducing substance phase which is not continuous with each other is scattered in the composite oxide. element. 2. A composite oxide comprising strontium and titanium as main components, in which reducing material phases which are not continuous with each other are scattered in the composite oxide, and further selected from the group consisting of lithium, calcium, barium and strontium. A thermoelectric semiconductor device comprising an oxide ceramic semiconductor in which at least one selected metal fluoride phase is present. 3. The reducing substance phase is titanium, zirconium,
At least one selected from the group consisting of tantalum and niobium
The thermoelectric semiconductor element according to claim 1, wherein the thermoelectric semiconductor element is a metal phase containing at least one kind of component as a main component. 4. The reducing substance phase is TiC, ZrC, Nb.
The thermoelectric semiconductor device according to claim 1, which is a metal carbide phase containing at least one component selected from the group consisting of C and TaC as a main component. 5. An oxide ceramic semiconductor obtained by mixing a composite oxide powder containing strontium and titanium as main components with a reducing substance powder and firing the mixture in a non-oxidizing atmosphere.
A method of manufacturing a thermoelectric semiconductor device, comprising providing a pair of electrodes. 6. An oxide ceramic semiconductor obtained by mixing a composite oxide powder containing strontium and titanium as main components, a reducing substance powder, and a metal fluoride powder, and firing the mixture in a non-oxidizing atmosphere. A method of manufacturing a thermoelectric semiconductor element, comprising the step of: providing a pair of electrodes. 7. The method of manufacturing a thermoelectric semiconductor element according to claim 5, wherein the non-oxidizing atmosphere is an argon atmosphere.