JPH05218511A - Thermoelectric semiconductor element - Google Patents

Abstract

PURPOSE:To acquire a thermoelectric semiconductor element which is safe and inexpensive as a material and has stable characteristics by realizing a specified composition which consists of at least strontium oxide and titanium oxide or of strontium oxide, barium oxide and titanium oxide. CONSTITUTION:SrCO3 and TiO2 are used as a starting material of an oxide semiconductor ceramic. After weighed for specified ratio, it is mixed with pure water using zirconia ball as a mixture medium and dried. Dried powder is put in an alumina crucible and calcinated for 12 hours at 1100 deg.C in air using an electrical furnace. The calcined powder is wet-ground again together with pure water using zirconia ball as a mixture medium, formed to powder of average grain diameter of 0.8mm and dried at 300 deg.C. Calcinated powder is formed after water of 5wt.% is added and formed to green compact by adding powder of 2.5g to a 30mm-long and 10mm-wide die and by pressing at 700kg/cm<2>. The green compact is put in a porcelain sheath, inserted into a tubular furnace and fired by changing a firing time while making hydrogen- argon gas flow.

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 more particularly to a device using an oxide 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 thermoelectric semiconductor element is used by electrically connecting an n-type element and a p-type element in series, but in the Bi-Te-based element, Se is added to the n-type conductive element portion to adjust the characteristics.

[0004]

However, in these devices, Se, which is added as an additive, is highly toxic, and the Bi-Te-based composition itself as the main component is expensive, so that the range of use of the device is limited. It had been. Further, generally, the performance of a thermoelectric semiconductor element for electronic cooling is represented by a performance index Z = s × s × σ / k, where s is the Seebeck coefficient, σ is the electrical conductivity, and k is the thermal conductivity. , Z has a larger amount of absorbed heat per power consumption during cooling and a larger temperature difference from the heat radiating side, and various semiconductor materials are Bi-Te.
Although it has been investigated for the purpose of replacing the system, no more than this characteristic has been reported so far.

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

[0006]

In order to achieve the above object, in the first thermoelectric semiconductor device of the present invention, the oxide semiconductor comprises a complex oxide containing at least strontium oxide and titanium oxide as constituent components. , Where the molar ratio of Ti to Sr in the composite oxide composition is a.
When the value is in the range of 005 ≦ a ≦ 1.120 and the amount of oxygen deficiency with respect to the weight after the element oxide semiconductor is completely oxidized at high temperature in oxygen is represented by b,
It is characterized in that it is within the range of 0.06 ≦ b ≦ 0.55.

Next, in the second thermoelectric semiconductor element of the present invention, the oxide semiconductor is composed of a strontium oxide, a composite oxide containing at least barium oxide and titanium oxide, and has a composite oxide composition. When the molar ratio of Sr to the total number of moles of Sr and Ba is c and the molar ratio of Ti to the total number of moles of Sr and Ba is d, 0.4
Value in the range of 5 ≦ c <1.00 and 1.005 ≦ d ≦ 1.120, and the amount of oxygen deficiency with respect to the weight after the element oxide semiconductor is completely oxidized at high temperature in weight% Is defined as e, the range is 0.06 ≦ e ≦ 0.55.

[0008]

According to the first and second aspects of the present invention, at least strontium oxide and titanium oxide,
Or strontium oxide, because it has a specific composition with barium oxide and titanium oxide as constituent components, it does not contain elements with strong toxicity, is highly safe, is inexpensive, and has performance as a thermoelectric semiconductor device. It is possible to provide an industrially useful thermoelectric semiconductor device which is excellent in characteristics and stable.

[0009]

EXAMPLES The present invention will be described in more detail below with reference to examples. Example 1 A thermoelectric semiconductor element was prepared using a composite oxide of strontium and titanium in a predetermined ratio as the oxide semiconductor ceramic material. The oxide semiconductor ceramic is Sr as a starting material.
After CO ₃ and TiO ₂ were weighed to a predetermined ratio, they were mixed with pure water using a zirconia boulder as a mixing medium in a ball mill and dried. The dried powder was put in an alumina crucible and calcined in air at 1100 ° C. for 12 hours using an electric furnace.

The calcined powder was subjected to Sr by powder X-ray analysis.
A perovskite phase of TiO ₃ is observed as a main phase, and Sr ₂ TiO ₄ and Sr ₃ Ti ₂ O ₇ are contained in some compositions.
Phase and TiO ₂ phase are observed. No residual SrCO ₃ phase was confirmed.

The calcined powder was again wet-milled with pure water in a ball mill using zirconia cobblestone as a mixed medium to obtain a powder having an average particle size of 0.8 μm, and dried at 300 ° C. The calcined powder is granulated after adding 5 wt% of water, length 30 mm width 1
Add 2.5g powder to 0mm mold, 700kg / c
It was pressed at m ² to obtain a green compact.

The green compact is placed in a porcelain sheath so as to be embedded in titanium sponge particles, inserted into a tubular furnace, and fired at 1500 ° C. for 2 to 24 hours while changing the firing time while flowing a 20% hydrogen-argon gas. did.

Gold electrodes were vapor-deposited on both ends of the fired body, lead wires were taken out from the ends, and both ends were sandwiched by different heating plates to give a temperature difference, and the Seebeck coefficient S was obtained from the temperature at both ends and the thermoelectromotive force. The fired body, whose thermoelectromotive force was measured, had 2
An electrode at a point was formed, a direct current of 10 mA was applied to the sample by the 4-terminal method, and the electrical conductivity σ of the sample was determined from the initial potential difference.

The temperature average at both ends of the evaluated Seebeck coefficient and the sample temperature at the time of measuring the electric conductivity were set to 35 ° C. Furthermore, the lead wire of the sample 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 periodically changed by the Angstrom method to make both ends of the sample. The specific heat was obtained from the DSC measurement performed separately from the temperature change, and the thermal conductivity k was obtained.

The figure of merit Z was obtained from the Seebeck coefficient S, electric conductivity σ and thermal conductivity k obtained by these measurements. The amount of oxygen deficiency in the sample is 1500 after crushing only the ceramic part of the sample after measurement to a particle size of about 100 μm.
The weight change was determined by heating in oxygen at 0 ° C, and the weight change was determined from the weight change during the heating time when the weight increase stopped.

In all the samples, when the total treatment time in 1500 ° C. oxygen reached 72 hours, the weight increase stopped and the reoxidation was completely completed. The molar ratio of Sr and Ti in the sample was measured by a fluorescent X-ray analysis method.

It was confirmed that the molar ratios of Sr and Ti in all the samples did not change between the compounding composition and the samples after firing, and that the effects of diffusion and evaporation of Ti from titanium sponge can be ignored. In Table 1, the molar ratio a of Ti to Sr, the oxygen deficiency b, the Seebeck coefficient S, the electrical conductivity σ, the thermal conductivity k,
A performance index Z is shown.

[0018]

[Table 1]

As is clear from Table 1, when the molar ratio of Ti to Sr in the composite oxide composition is a, it is 1.0.
When the value is in the range of 05 ≦ a ≦ 1.120, and the value of oxygen deficiency with respect to the weight after the element oxide semiconductor is completely oxidized in oxygen at high temperature is expressed as% by weight, b is 0.
The thermoelectric semiconductor element in the range of 06 ≦ b ≦ 0.55 is
While a large figure of merit is shown, a value of a less than 1.005 has poor sinterability and thus a low electric conductivity and a small figure of merit, and a value of more than 1.120 has a Seebeck coefficient. It becomes smaller and the figure of merit does not increase.

When the oxygen deficiency is less than 0.06 wt%, the electric conductivity becomes small and the figure of merit does not become large.
If it is more than 0.55 wt%, the Seebeck coefficient is lowered and the figure of merit is not increased. Further, the thermoelectric semiconductor element within the scope of the present invention has substantially the same performance as Bi-Te, is inexpensive and has high safety. This is because it does not contain a highly toxic element.

Example 2 A thermoelectric semiconductor element was prepared by using a complex oxide of strontium, barium and titanium in a predetermined ratio as the oxide semiconductor ceramic 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 is put in an alumina crucible and heated in air at 1100 ° C for 12 hours using an electric furnace.
I calcined for an hour. The calcined powder was again wet-milled with pure water in a ball mill using zirconia cobblestone as a mixed medium to obtain a powder having an average particle size of 0.8 μm, and dried at 300 ° C.

The calcined powder was granulated after adding 5 wt% of water, 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. The green compact was put in a porcelain sheath so as to be embedded in titanium sponge particles, inserted into a tubular furnace, and fired at 1500 ° C. for 2 to 24 hours while changing the firing time while flowing a 20% hydrogen-argon gas.

Gold electrodes were vapor-deposited on both ends of the fired body, lead wires were taken out from the both ends, 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. In the fired body whose thermoelectromotive force was measured, two electrodes were further formed in the middle portion, a direct current of 10 mA was applied to the sample by the 4-terminal method, and the electrical conductivity σ of the sample was determined from the initial potential difference.

The temperature average at both ends of the evaluated Seebeck coefficient and the sample temperature at the time of measuring the electric conductivity are the same as those in the example.
℃ was examined. Furthermore, for the sample, remove the lead wire, apply nickel plating to one end, solder to a copper hot plate, and apply 10 ^-2 P
Put in a vacuum container of about a, and periodically change the temperature of the hot plate by the Angstrom method to determine the temperature change at both ends of the sample. Determine the specific heat from the DSC measurement separately performed.
With this, the thermal conductivity k was obtained. The figure of merit Z was obtained from the Seebeck coefficient S, electric conductivity σ, and thermal conductivity k obtained by these measurements.

The amount of oxygen deficiency in the sample was determined by the same method as in Example 1.

[0027]

[Table 2]

Table 2 shows S relative to the total number of moles of Sr and Ba.
The molar ratio c of r, the molar ratio d of Ti to the total number of moles of Sr and Ba, and the oxygen deficiency e, and the Seebeck coefficient S at 35 ° C., the electrical conductivity σ, the thermal conductivity k, and the figure of merit Z are shown. ..

As is clear from Table 2, a composite oxide composed of strontium oxide, barium oxide and titanium oxide is used. In the composite oxide composition, the molar ratio of Sr to the total number of moles of Sr and Ba is c, When the molar ratio of titanium to the total number of moles of Sr and Ba is d, 0.45
Value in the range of ≦ c <1.00 and 1.005 ≦ d ≦ 1.120, and the amount of oxygen deficiency relative to the weight after the element oxide semiconductor is completely oxidized in oxygen at high temperature, expressed as a weight percentage. Where e is a thermoelectric semiconductor element having a large figure of merit in the range of 0.06 ≦ e ≦ 0.55, a value of c smaller than 0.45 has a low electric conductivity and a low performance. The index also does not increase.

If the value of d is less than 1.005, the sinterability is poor, so the electrical conductivity is small and the figure of merit is also small.
If the value of is larger than 1.120, the Seebeck coefficient becomes small and the figure of merit does not become large.

When the oxygen deficiency amount e is less than 0.06 wt%, the electrical conductivity is small and the figure of merit does not increase. When it is more than 0.55 wt%, the Seebeck coefficient is low and the figure of merit is large. I won't.

Thermoelectric semiconductor elements within the scope of the present invention include Bi
It is possible to provide a new thermoelectric semiconductor element which has substantially the same performance as that of -Te, is inexpensive, does not contain an element having strong toxicity, is highly safe, and is industrially useful. It is particularly useful for electronic components for electronic cooling.

[0033]

As described above, according to the first and second aspects of the present invention, at least strontium oxide and titanium oxide, or strontium oxide, barium oxide and titanium oxide are used as constituent components. Since it has a specific composition, it does not contain a highly toxic element, is highly safe, is also inexpensive, and has excellent performance as a thermoelectric semiconductor element, which is characteristically stable and industrially useful. be able to.

Further, the thermoelectric semiconductor device of the present invention has characteristics almost comparable to those of the conventional Bi-Te-based material, has no toxicity as a material, and can be easily manufactured by using the conventional ceramic process. Since the raw material itself is inexpensive, it has advantages such as comprehensive cost reduction, and is industrially useful.

Claims (2)

[Claims] 1. A thermoelectric semiconductor device using an oxide semiconductor, wherein the oxide semiconductor is a composite oxide containing strontium oxide and titanium oxide as at least constituents, and the molar ratio of Ti to Sr in the composite oxide composition. Where a is in the range of 1.005 ≦ a ≦ 1.120, and the oxygen deficiency amount with respect to the weight after the element oxide semiconductor is completely oxidized at high temperature in oxygen is expressed as a weight percentage. A thermoelectric semiconductor element having a range of 0.06 ≦ b ≦ 0.55 when b. 2. A thermoelectric semiconductor device using an oxide semiconductor, wherein the oxide semiconductor is composed of strontium oxide, a composite oxide containing at least barium oxide and titanium oxide, and Sr in the composite oxide composition is Sr. And B
The molar ratio of Sr to the total number of moles of a is c, Sr and Ba
When the molar ratio of Ti to the total number of moles of is d,
0.45 ≦ c <1.00 and 1.005 ≦ d ≦ 1.12
In the range of 0, and when the value of oxygen deficiency with respect to the weight after the element oxide semiconductor is completely oxidized at high temperature in oxygen is expressed as weight%, e is 0.06 ≦ e ≦ 0.55. A thermoelectric semiconductor device characterized by being within the range.