JP2006256889A - Nonstoichiometric metal oxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stable method for manufacturing a nonstoichiometric metal oxide by solving such a problem that a stable production method of a nonstoichiometric metal oxide is not established and quantitative properties of the nonstoichiometric metal oxide as a semiconductor are unknown although it is known that a nonstoichiometric metal oxide of a oxygen excess type exhibits properties as a p-type semiconductor and a nonstoichiometric metal oxide of a oxygen deficiency type exhibits properties as a n-type semiconductor, and to provide a new industrial application of the nonstoichiometric metal oxide manufactured by the method. <P>SOLUTION: A p-type semiconductor of the oxygen excess type and an n-type semiconductor of the oxygen deficiency type, being each a nonstoichiometric metal oxide, can be stably manufactured by a combustion synthesis method. A thermoelectric power generating material having excellent cost performance and heat resistance is obtained by constituting a module by using the oxygen deficiency type metal oxide as an n-type element of the thermoelectric power generating material and the oxygen excess type metal oxide as a p-type element of the thermoelectric power generating material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an oxygen-rich nonstoichiometric metal oxide produced by combustion synthesis, and industrial utilization of the oxygen-deficient nonstoichiometric metal oxide and the nonstoichiometric metal oxide.

It has already been theoretically proved that oxygen-rich nonstoichiometric metal oxides exhibit p-type semiconductors and oxygen-deficient nonstoichiometric metal oxides exhibit n-type semiconductor characteristics.

In particular, oxygen-rich nonstoichiometric metal oxides exhibit excellent p-type semiconductor characteristics, and are used as thermistors by utilizing the temperature dependence of electrical resistance.

It is well known that oxygen sensors using the characteristic that the electrical resistance of non-stoichiometric titanium oxide changes in proportion to the degree of oxygen non-stoichiometry.

According to a recent report, a thermoelectric power generation module comprising a thermoelectric power generation element in which an oxygen-rich non-stoichiometric metal is p-type and an oxygen-deficient non-stoichiometric metal oxide is n-type has an unprecedented superior power generation. It has also been reported to have a function.

  Non-stoichiometric metal oxides are not only expected to be used more widely as semiconductors due to their characteristics, but may also be able to provide harmless and safe semiconductors for the human body by specifying the metal selected from transition metals. .

Thus, the use of non-stoichiometric metal oxides for semiconductor applications has just begun, but it can be said that a vast future can be expected.
Japanese Patent Application No. 2004-111957 Junji Kosuge “Science of non-stoichiometric compounds” Baifukan (1985) Yasutoshi Saito et al. “Non-stoichiometry and electrical conductivity of metal oxides” Uchida Otsukuru (1992)

The composition of the non-stoichiometric compound is generally determined by the pressure and temperature of the atoms and molecules in which it deviates (composition) from the stoichiometric ratio of the compound. Various production methods have been tried depending on the target non-stoichiometric compound.

1) Method for adjusting partial pressure of gas such as oxygen 2) Pyrolysis method for oxide 3) Hydrogen reduction method for oxide etc. is adopted according to the purpose, but there is no established mass production method at present .

  As for the non-stoichiometric metal oxide proposed in this patent, a stable production method has not been established.

Therefore, a stable and efficient production method for non-stoichiometric metal oxides and a production method that can withstand industrial mass production are proposed, and a new industrial application of non-stoichiometric metal oxides is proposed using the production method.

Various raw materials obtained from thermodynamic reaction formulas are precisely weighed and sealed in a high pressure resistant container, and the reaction is started by external ignition, and the target compound can be synthesized by controlling the reaction temperature and pressure. The “combustion synthesis method” is optimal as a means for synthesizing non-stoichiometric metal oxides.

Table 1 shows the currently known nonstoichiometric metal oxide compounds. These are also called nonstoichiometic compounds. However, these efficient manufacturing methods are not known, and the characteristics of each of the semiconductors are not known.

An example in which TiO _1.1 and TiO _1.2 are synthesized by a combustion synthesis method will be described below.

1) TiO _1.1 was synthesized based on the following reaction formula.
Ti + 0.275 NaClO ₄ = TiO _1.1
+ 0.275 NaCl

2) TiO _1.2 was synthesized based on the following reaction formula.
Ti + 0.3 NaClO ₄ = TiO _1.2 + 0.3 NaCl

The non-stoichiometric coefficient of each non-stoichiometric titanium oxide obtained was determined by identification by an X-ray diffraction method and identification from a precise identification diagram of the density and oxygen content of titanium oxide determined in advance.

  It has been confirmed that other non-stoichiometric metal oxides can be synthesized in the same manner as the above reaction formula, and all non-stoichiometric metal oxides can be synthesized by combustion synthesis.

In addition, with regard to TiO _1.1 and TiO _1.2 , the composition of components, reaction pressure and reaction temperature were controlled to be the same, and N = 10 was repeatedly synthesized. Yes.

From the above, confirmation was obtained that industrial mass production of nonstoichiometric metal compounds was possible with a large-scale combustion synthesizer. The detailed design specifications for the large combustion synthesizer will be proposed in subsequent patents.

The various p-type semiconductor and n-type semiconductor characteristics of various non-stoichiometric metal oxides stably produced for combustion synthesis were measured.

As a result, it is clear that it can be applied to materials demanded in the industry such as high-efficiency thermoelectric power generation material 2) thermistor material for wide temperature range 3) low-temperature activation catalyst 4) various high-performance gas sensor materials, etc. It was.

The reason why the non-stoichiometric metal oxide can be applied to such an industrial application is that the non-stoichiometric metal oxide can be stably synthesized by combustion synthesis.

According to the present invention, the social effects of being able to mass-produce n-type and p-type semiconductors at low cost are immense. Various semiconductors produced inefficiently by the conventional MCVD method, single crystal method, and reaction sintering method will be produced by this method.

Specifically, since the thermoelectric generator, which is one of the present invention, is excellent in cost performance, mass production is possible, not only can the exhaust heat energy of a reciprocating engine automobile be converted into electric energy, but also fuel efficiency. As efficiency can be improved, not only is it effective for pollution control, but it can also contribute to resource savings in fossil fuels and can contribute to the reduction of GHG specified in the Kyoto Protocol.

The target nonstoichiometric metal oxide is synthesized by combustion synthesis. The synthesized non-stoichiometric metal oxide is preferably obtained in a powder state.

Subsequently, the powder is sintered. In order to improve the properties as a sintered body, the powder particle diameter is preferably 1 μm or less. Since the characteristic value is better as the sintered density is higher, it is included in this patent to which PECS (Plus Electric Current Sintering), Hotpressing, and HIP methods are applied.

A typical application proposed in this patent is a module for thermoelectric power generation. The module has the structure shown in FIG. An n-type thermoelectric element 3 composed of a sintered body of a non-stoichiometric compound of a metal oxide in which the non-stoichiometric metal compound exhibits n-type semiconductor properties and the p-type element 4 having the above-described configuration are connected via the good conductor 2 (FIG. Connect in series as in 3). A plate-like insulating plate 1 made of an insulator is bonded to a good conductor, and lead wires are arranged on the p-type element and the n-type element at both ends.

Since the thermoelectric element proposed by the present invention has a high heat-resistant temperature, solid-liquid diffusion diffusion bonding using an amorphous foil and a high-frequency induction heating method is suitable for bonding the element and the substrate.

The insulator 1 surface of the module configured in this way is held on the high temperature side (T1) and the low temperature side (T2) under a temperature difference ΔT to function as a thermoelectric generator.

Thermoelectric power generation characteristics Dimensionless figure of merit (ZT) was obtained using sintered bodies obtained from TiO _1.1 and TiO _1.2 as examples of oxygen-rich non-stoichiometric metal oxides produced by combustion synthesis. . In addition, the dimensionless figure of merit was also measured for the same non-stoichiometric metal oxide synthesized by the thermobalance method.

The results are shown in (Table 2).

First, it is clearly recognized from (Table 2) that the oxygen-excess type nonstoichiometric titanium oxide has heat resistance superior to any of the conventional high-temperature type thermoelectric power generation materials.

  In particular, the dimensionless figure of merit of the oxygen-excess non-stoichiometric metal oxide produced by combustion synthesis proposed by the present invention is 1.64 at 1100K and shows a threatening value.

The temperature dependence of electrical conductivity as a p-type semiconductor of TiO _1.1 sintered body of oxygen-rich non-stoichiometric metal oxide combusted and synthesized is shown in the temperature dependence of electrical conductivity (FIG. 2).

  Excellent linearity from 300K to 800K. Conventionally, various p-type semiconductors have been adopted as thermistors, but the region where the relationship between electrical conductivity and temperature shows linearity is at most 200 ° C., and is biased toward the low temperature region. The present invention proposes a new thermistor that can be applied in an unprecedented wide temperature range.

The function as an oxidizing catalyst was shown in the function as a low temperature active catalyst (FIG. 3). Compared with Pt currently used, a catalyst function is recognized from extremely low temperature.

  The p-type and n-type non-stoichiometric metal oxide semiconductors can be produced stably and reliably by the combustion synthesis method. A new stone will be invested in conventional semiconductor manufacturing. The semiconductor proposed in this patent has high heat resistance and can be expected to develop new applications that have never existed before.

Module arrangement of thermoelectric element powder sintered material. The figure which shows the temperature dependence of the electrical conductivity of TiO _1.1 proposed by the present invention. The figure which shows the catalytic function of TiO _1.1 proposed by the present invention.

Explanation of symbols

1. Insulating ceramic plate 2. 2. Copper electrode n-type thermoelectric element 4. 4. p-type thermoelectric element 5. decomposition diagram of TiO _1.1 Pt decomposition diagram

Claims (6)

An oxygen-rich nonstoichiometric metal oxide and an oxygen-deficient nonstoichiometric metal oxide produced by a combustion synthesis method. The basic composition is a p-type semiconductor element for thermoelectric power generation elements composed of an oxygen-rich non-stoichiometric metal oxide produced by combustion synthesis as a basic component and an oxygen-deficient non-stoichiometric metal oxide produced similarly by combustion synthesis. A thermoelectric power generator configured for thermoelectric power generation using the n-type semiconductor element for thermoelectric power generation elements configured. In claim 2, the p-type element for thermoelectric power generation is any one of oxygen-excess type metal oxides based on TiO, VO, MnO, FeO, CoO, NiO, ZrO ₂ and UO ₂ . _{3. The} thermoelectric generator according to claim ₂ , wherein the n-type element is any one of oxygen-deficient metal oxides based on TiO ₂ , TiO, VO, ZrO ₂ and UO ₂ .   The thermoelectric power generation element according to claim 2, wherein the thermoelectric power generation element according to claim 2 is a sintered body from a fine powder of non-stoichiometric metal oxide according to claim 2.   A thermistor capable of measuring a wide range of temperature, using oxygen-rich nonstoichiometric metal oxides produced by combustion synthesis. Low-temperature active catalyst composed of non-stoichiometric metal oxide produced by combustion synthesis method.

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