Method for manufacturing negative thermal expansion material, method for manufacturing reaction precursor of negative thermal expansion material, and reaction precursor of negative thermal expansion material

Abstract

This method for producing a negative thermal expansion material comprises: a step for dissolving, in a neutral or acidic solution, a bismuth salt, a nickel salt, a salt of a metal M capable of forming a trivalent ion, and optionally a rare-earth element salt or an antimony salt, to form a metal salt solution; a step for mixing the metal salt solution with a hypohalite salt and an alkaline compound and causing a metal salt to precipitate, to form a reaction precursor; and a step for pressurizing and heating the reaction precursor, to form a negative thermal expansion material containing a compound wherein, in BiNiO3, a portion of Bi is substituted by the rare-earth element or Sb and / or a portion of Ni is substituted by the metal capable of forming a trivalent ion.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a material having negative thermal expansion, a method for producing a reaction precursor of a negative thermal expansion material, a reaction precursor of a negative thermal expansion material, and a negative thermal expansion material. [Background technology]

[0002] In recent years, with the development of nanotechnology in LSI manufacturing and other areas, misalignment due to thermal expansion of components has become a problem. To address this issue, progress is being made in the development of zero-expansion materials, which are resins that contain materials that shrink when heated, i.e., materials with negative thermal expansion.

[0003] Conventionally, negative thermal expansion materials known include those in which Bi has been partially substituted with rare earth elements or Sb, or Ni has been partially substituted with Al, Fe, or the like in BiNiO3 having a perovskite structure (see, for example, Patent Documents 1 and 2). These negative thermal expansion materials exhibit a larger negative thermal expansion than existing materials, and have a negative thermal expansion coefficient that matches the thermal expansion coefficient of many resins (for example, several tens to 100 ppm / °C). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6143197 [Patent Document 2] Patent No. 6555473 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventionally, the above-mentioned negative thermal expansion material has been synthesized by dissolving a metal-oxide raw material in nitric acid, evaporating the obtained aqueous solution to dryness to obtain a reaction precursor, and reacting this reaction precursor with an oxidizing agent under high-pressure and high-temperature conditions of 6 GPa and 1000 °C. During the synthesis, nitric acid fumes are generated, and their toxicity becomes a problem. In addition, since KClO4 is added as an oxidizing agent, the load on the high-pressure synthesis apparatus is large. Further, due to the addition of KClO4, the yield of the obtained negative thermal expansion material decreases, and a step of washing away the residual KCl after the reaction is required.

[0006] The present invention has been made in view of such circumstances, and one of its objects is to provide a technique for producing a negative thermal expansion material with a small load on the apparatus, safely, and in a high yield.

Means for Solving the Problems

[0007] One aspect of the present invention is a method for producing a negative thermal expansion material. The production method includes a step of dissolving a bismuth salt, a nickel salt, a salt of a metal M that can become a trivalent ion, and optionally a rare earth element salt or an antimony salt in a neutral or acidic solution to form a metal salt solution, a step of mixing the metal salt solution with a hypohalite compound and an alkaline compound to precipitate a metal salt and form a reaction precursor, a step of subjecting the reaction precursor to pressure heating to form a negative thermal expansion material containing a compound represented by the following formula (1), and includes. Bi

[0008] , , 1-y , y , 1-x , , x , , , A x Ni 1-y M y O3 ···(1) [In formula (1), A is a rare earth element or antimony, and M is a metal that can become a trivalent ion. When x = 0, y satisfies 0.02 ≦ y ≦ 0.50. When A is a rare earth element and 0 < x ≦ 0.20, y satisfies 0.02 ≦ y ≦ 0.50. When A is antimony and 0 < x ≦ 0.20, y satisfies 0 ≦ y ≦ 0.50.]

[0008] Another aspect of the present invention is a method for producing a reaction precursor of a negative thermal expansion material having negative thermal expansion. The production method includes a step of dissolving a bismuth salt, a nickel salt, a salt of a metal M capable of becoming a trivalent ion, and optionally a rare earth element salt or an antimony salt in a neutral or acidic solution to form a metal salt solution, a step of mixing the metal salt solution with a hypohalite and an alkaline compound to precipitate a metal salt and form a reaction precursor,

[0009] Still another aspect of the present invention is a reaction precursor of a negative thermal expansion material. The reaction precursor is formed by dissolving a bismuth salt, a nickel salt, a salt of a metal M capable of becoming a trivalent ion, and optionally a rare earth element salt or an antimony salt in a neutral or acidic solution to form a metal salt solution, and mixing the metal salt solution with a hypohalite and an alkaline compound to precipitate a metal salt.

[0010] Still another aspect of the present invention is a negative thermal expansion material having negative thermal expansion. The negative thermal expansion material is formed by dissolving a bismuth salt, a nickel salt, a salt of a metal M capable of becoming a trivalent ion, and optionally a rare earth element salt or an antimony salt in a neutral or acidic solution to form a metal salt solution, mixing the metal salt solution with a hypohalite and an alkaline compound to precipitate a metal salt and form a reaction precursor, and subjecting the reaction precursor to pressure heating, and contains a compound represented by the following formula (1). Bi 1-x A x Ni 1-y M y O3···(1) [In formula (1), A is a rare earth element or antimony, and M is a metal capable of becoming a trivalent ion. When x = 0, y satisfies 0.02 ≦ y ≦ 0.50. When A is a rare earth element and 0 < x ≦ 0.20, y satisfies 0.02 ≦ y ≦ 0.50. When A is antimony and 0 < x ≦ 0.20, y satisfies 0 ≦ y ≦ 0.50.] [Advantages of the Invention]

[0011] According to the present invention, a negative thermal expansion material can be produced with less load on the device, more safely, and at a high yield.

Brief Description of the Drawings

[0012] [Figure 1] It is a graph showing the temperature dependence of the average volume of the negative thermal expansion materials according to Examples 1, 2, and 3. [Figure 2] It is a graph showing the temperature dependence of the average volume of the negative thermal expansion material according to Example 4. [Figure 3] It is a diagram showing the results of thermogravimetric analysis of the reaction precursor of BiNi0.85Fe0.15O3 obtained in Example 1. [[ID=一十六]]

Modes for Carrying Out the Invention

[0013] The negative thermal expansion material produced by the method for producing a negative thermal expansion material according to the embodiment is a compound in which part of Ni is substituted with metal M and part of Bi is substituted with a rare earth element or Sb (antimony) in the mother substance BiNiO3. This negative thermal expansion material is produced by pressurizing and heating the reaction precursor described below without using an oxidizing agent. Specifically, the negative thermal expansion material obtained by the production method of the present embodiment has negative thermal expansion and contains a compound represented by the following formula (1). Bi 1-x A x Ni 1-y M y O3···(1) [In formula (1), A is a rare earth element or antimony, and M is a metal that can become a trivalent ion. When x = 0, y satisfies 0.02 ≦ y ≦ 0.50. When A is a rare earth element and 0 < x ≦ 0.20, y satisfies 0.02 ≦ y ≦ 0.50. When A is antimony and 0 < x ≦ 0.20, y satisfies 0 ≦ y ≦ 0.50.]

[0014] The negative thermal expansion material according to this embodiment exhibits a negative thermal expansion of -30 ppm / °C or more in a predetermined temperature range, for example, 0°C to 50°C. In the above formula (1), M is a metal that can become a trivalent ion, and preferably a metal in which trivalence is more stable than other valences. Preferably, M is one or more elements selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ga, Nb, Ru, Rh, and In. More preferably, M is one or more elements selected from the group consisting of Al, Fe, Cr, and Ga.

[0015] Furthermore, in the above formula (1), when A is a rare earth element, negative thermal expansion can be reliably exhibited by setting y to 0.02 or more. Furthermore, whether A is a rare earth element or antimony, by setting y to 0.50 or less, the temperature range exhibiting negative thermal expansion can be made a practical range for realizing a zero-expansion material.

[0016] BiNiO3, the parent material of the compound represented by the above formula (1), is Bi 3+ 0.5 Bi 5+ 0.5 Ni 2+ It is a perovskite oxide with a characteristic valence state of O3. In the perovskite structure, Ni-O bonds form the framework of the structure, and Bi fills the gaps. By substituting a portion of Ni with a metal M, which has a stable trivalent state, the valence state of the perovskite oxide becomes unstable. As a result, when the temperature is increased, Bi 3+ (Ni,M) 3+ It transitions to the O3 valence state. 2+ From Ni 3+ When Ni-O contracts due to the valence change to , the overall volume contracts. Furthermore, the large-volume low-temperature phase and the small-volume high-temperature phase gradually transition from one to the other, changing their fractions. This allows for a gradual volume reduction over a wide temperature range. In other words, negative thermal expansion is achieved by the negative thermal expansion material obtained by the manufacturing method according to this embodiment.

[0017] The perovskite-type compound contained in the negative thermal expansion material of this embodiment may have a portion of Bi substituted with a rare earth element or Sb. Even when a portion of Bi is substituted with a rare earth element or Sb, volume contraction due to temperature increase can occur. In other words, negative thermal expansion is achieved by the negative thermal expansion material of this embodiment. Here, rare earth elements refer to a total of 17 elements: Sc, Y, and lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu).

[0018] In addition, Sb is a stable element in the trivalent and pentavalent states. Therefore, by substituting a portion of Bi with Sb, charge transfer can occur not only between Ni-Bi but also between Ni-Sb-Bi. This allows for a more gradual change in the valence of Ni. In other words, the charge transfer between the A and B sites of perovskite oxides can be made gradual. Therefore, in addition to the volume reduction due to the transition from the low-temperature phase to the high-temperature phase (first-order transition), a volume reduction in each phase (second-order transition) can occur. This second-order transition can then suppress temperature hysteresis.

[0019] In the above formula (1), when A = Sb, x is preferably 0.075 or more. By setting x to 0.075 or more, that is, by setting the ratio of Sb to 7.5% or more, the temperature hysteresis of the negative thermal expansion material can be more reliably suppressed. Furthermore, when A is antimony, 0≦y≦0.02 may be acceptable.

[0020] Furthermore, by dispersing this negative thermal expansion material in a resin material such as an engineering plastic or a metal material, and offsetting the positive thermal expansion of the resin material or metal material with the negative thermal expansion of the negative thermal expansion material, a zero thermal expansion material can be obtained.

[0021] (Method for manufacturing negative thermal expansion material) The method for producing a negative thermal expansion material according to the present embodiment includes the steps of forming a metal salt solution, forming a reaction precursor, and forming a negative thermal expansion material. Each step will be described below.

[0022] (Metal salt solution formation process) In this step, a bismuth salt, a nickel salt, a salt of a metal M that can become a trivalent ion, and optionally a rare earth element salt or an antimony salt are dissolved in a neutral or acidic solution. That is, when synthesizing a final product, a perovskite oxide in which part of Bi is substituted with a rare earth element or Sb, the rare earth element salt or antimony salt is dissolved in a neutral or acidic solution together with other raw materials.

[0023] Examples of the salt of each constituent metal include nitrates, acetates, halides, etc. From the viewpoint of solubility and reactivity in a solution, the salt of the constituent metal is preferably a nitrate.

[0024] The neutral or acidic solution is not particularly limited as long as it can dissolve the salts of each constituent metal. Examples of such solutions include pure water, dilute nitric acid, hydrochloric acid, sulfuric acid, etc. Dilute nitric acid is preferred from the viewpoint of reactivity with and solubility of the salts of the constituent metals. In the coprecipitation process with an alkaline compound, a low concentration of the acidic solution is preferable. Here, dilute nitric acid refers to a solution with a concentration of approximately 20% or less. In addition to an aqueous solution, the solution may also be a mixed solution of water and an organic solvent such as alcohol.

[0025] (Reaction precursor formation process) In this process, the metal salt solution obtained in the previous step is mixed with a hypohalite and an alkaline compound to precipitate the metal salt and form a reaction precursor. This results in a composite oxide in which each constituent metal is uniformly dispersed. In this process, the hypohalite functions as an oxidizing agent. Therefore, the metal in the metal salt is oxidized simultaneously with the precipitation of the metal salt. By using a hypohalite as an oxidizing agent in this way, it is not necessary to react the reaction precursor with an oxidizing agent such as KClO4. This improves the yield of the negative thermal expansion material and eliminates the need for a post-synthesis cleaning process.

[0026] The alkaline compound is not particularly limited as long as it can neutralize the acidity of the metal salt solution, and examples of the alkaline compound include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide.

[0027] The hypohalite is not particularly limited as long as it oxidizes the metal ions contained in the metal salt solution, and examples thereof include sodium hypochlorite, sodium hypobromite, potassium hypochlorite, potassium hypobromite, and calcium hypobromite.

[0028] The reaction precursor formed by precipitation of the metal salt may be washed and dried. Examples of solvents used for washing the reaction precursor include water. The method for washing the reaction precursor is not particularly limited as long as it can remove the chemicals used up to the previous stage. For example, the reaction precursor can be washed by centrifuging and stirring multiple times using a centrifuge and a vortex shaker. The washed reaction precursor can be dried by heating, vacuum drying, or the like. For example, the reaction precursor can be dried at 60 to 200°C for 6 to 24 hours. The temperature condition is preferably 80 to 150°C, more preferably 80 to 100°C. The drying time is preferably 8 to 16 hours, more preferably 12 to 14 hours.

[0029] (Process for forming negative thermal expansion material) In this step, the reaction precursor is pressurized and heated. This forms the compound represented by formula (1), allowing a negative thermal expansion material containing this compound to be obtained. Those skilled in the art can appropriately select the pressure and temperature conditions under which a negative thermal expansion material containing the compound represented by formula (1) can be obtained. For example, the pressure condition is preferably 3 GPa or higher, more preferably 4 GPa or higher but lower than 8 GPa. Furthermore, for example, the temperature condition is preferably 600°C or higher, more preferably 700°C or higher but 1100°C or lower, and more preferably 800°C or higher but 1000°C or lower. The reaction precursor can be heated and pressurized using, for example, a known high-pressure synthesis apparatus. The type of apparatus is not particularly limited as long as it can achieve the desired pressure and temperature conditions.

[0030] In the method according to the embodiment, salts of bismuth, nickel, metal M, and rare earth elements or antimony, which are the constituent metals of the perovskite oxide (the final product), are used as raw materials. These raw materials are dissolved in a neutral or acidic solution to obtain a metal salt solution. The metal salt solution is then mixed with an alkaline compound to form a reaction precursor by coprecipitation. This eliminates the generation of nitric acid fumes compared to conventional methods using nitric acid. Furthermore, in the method according to the embodiment, when forming the reaction precursor, the metal salt solution is mixed with a hypohalite and an alkaline compound. This eliminates the need to add an oxidizer when forming a negative thermal expansion material from the reaction precursor, thereby reducing the load on the high-pressure synthesis equipment and improving yield. This can promote the industrialization of negative thermal expansion materials.

[0031] (Method for producing a reaction precursor of a negative thermal expansion material) The method for producing a reaction precursor of a negative thermal expansion material according to the embodiment includes a step of forming a metal salt solution and a step of forming a reaction precursor. The details of each step are the same as the step of forming a metal salt solution and the step of forming a reaction precursor in the method for producing a negative thermal expansion material according to the embodiment described above. The reaction precursor formed by this production method contains sufficient oxygen. Therefore, a negative thermal expansion material can be produced from the reaction precursor without using an oxidizing agent.

[0032] (Reaction precursor of negative thermal expansion material) The reactive precursor of the negative thermal expansion material according to the embodiment is prepared by dissolving a bismuth salt, a nickel salt, a salt of a metal M capable of forming a trivalent ion, and optionally a rare earth element salt or an antimony salt in a neutral or acidic solution to form a metal salt solution, and then mixing the metal salt solution with a hypohalite salt and an alkaline compound to precipitate the metal salt. The reactive precursor contains sufficient oxygen. Therefore, by using this reactive precursor, a negative thermal expansion material can be produced without using an oxidizing agent. [Example]

[0033] Examples of the present invention will be described below, but these examples are merely illustrative examples for suitably explaining the present invention and do not limit the present invention in any way.

[0034] Example 1 A green solution was obtained by dissolving 4 mmol of Bi(NO3)3·5H2O, 3.4 mmol of Ni(NO3)2·6H2O, and 0.6 mmol of Fe(NO3)3·9H2O in dilute nitric acid (a mixture of 10 mL of water and 1 mL of 60% nitric acid). This green solution was then dissolved in a mixture of 15 mL of aqueous sodium hydroxide (10 M concentration) and 10 mL of aqueous sodium hypochlorite (10% available chlorine concentration). The resulting gel was washed three times with water using a centrifuge (3700-6000 G). The gel was then dried at 80°C for 8-12 hours. This process yielded a reactive precursor.

[0035] The resulting reaction precursor (0.2 g) was sealed in a gold capsule or a sodium chloride sleeve. The capsule was treated for 30 minutes under conditions of 4 GPa and 800 °C using a cubic anvil-type high-pressure synthesis apparatus. As a result, BiNi 0.85 Fe 0.15 A negative thermal expansion material containing a perovskite-type compound represented by O3 was obtained.

[0036] Example 2 A green solution was obtained by dissolving 4 mmol of Bi(NO3)3·5H2O, 3.6 mmol of Ni(NO3)2·6H2O, and 0.4 mmol of Fe(NO3)3·9H2O in dilute nitric acid (a mixture of 10 mL of water and 1 mL of 60% nitric acid). This green solution was then dissolved in a mixture of 15 mL of aqueous sodium hydroxide (10 M concentration) and 10 mL of aqueous sodium hypochlorite (10% available chlorine concentration). The resulting gel was washed three times with water using a centrifuge (3700-6000 G). The gel was then dried at 80°C for 8-12 hours. This process yielded a reactive precursor.

[0037] The resulting reaction precursor (0.2 g) was sealed in a gold capsule or a sodium chloride sleeve. The capsule or sleeve was treated for 30 minutes under conditions of 4 GPa and 800 °C using a cubic anvil-type high-pressure synthesis apparatus. As a result, BiNi 0.90 Fe 0.10 A negative thermal expansion material containing a perovskite-type compound represented by O3 was obtained.

[0038] Example 3 A green solution was obtained by dissolving 4 mmol of Bi(NO3)3·5H2O, 3.8 mmol of Ni(NO3)2·6H2O, and 0.2 mmol of Fe(NO3)3·9H2O in dilute nitric acid (a mixture of 10 mL of water and 1 mL of 60% nitric acid). This green solution was then dissolved in a mixture of 15 mL of aqueous sodium hydroxide (10 M concentration) and 10 mL of aqueous sodium hypochlorite (10% available chlorine concentration). The resulting gel was washed three times with water using a centrifuge (3700-6000 G). The gel was then dried at 80°C for 8-12 hours. This process yielded a reactive precursor.

[0039] The resulting reaction precursor (0.2 g) was sealed in a gold capsule or a sodium chloride sleeve. The capsule or sleeve was treated for 30 minutes under conditions of 4 GPa and 800 °C using a cubic anvil-type high-pressure synthesis apparatus. As a result, BiNi 0.95 Fe 0.05 A negative thermal expansion material containing a perovskite-type compound represented by O3 was obtained.

[0040] For the negative thermal expansion materials of Examples 1, 2, and 3, the lattice constant and the phase fractions of the low-temperature and high-temperature phases were estimated while changing the temperature using a powder X-ray diffractometer (Bruker D8 ADVANCE), and the average volume per unit cell was calculated. Figure 1 shows the temperature dependence of the average volume of the negative thermal expansion materials of the examples.

[0041] As shown in FIG. 1, the negative thermal expansion material of the example is BiNi 0.85 Fe 0.15 It was confirmed that negative thermal expansion occurs, similar to the thermal expansion properties of O3.

[0042] Example 4 A green solution was obtained by dissolving 3.6 mmol of Bi(NO3)3·5H2O, 0.4 mmol of Sb, and 4.0 mmol of Ni(NO3)2·6H2O in 9 mL of 60% nitric acid. This green solution was then dissolved in a mixture of 15 mL of aqueous sodium hydroxide (10 M concentration) and 18 mL of aqueous sodium hypochlorite (10% available chlorine concentration). The resulting gel was washed three times with water using a centrifuge (3700-6000 G). The gel was then dried at 100°C for 8-12 hours. This process yielded a reactive precursor.

[0043] The resulting reaction precursor (0.2 g) was sealed in a gold capsule or a sodium chloride sleeve. The capsule or sleeve was treated for 30 minutes under conditions of 6 GPa and 1100 °C using a cubic anvil-type high-pressure synthesis apparatus. As a result, Bi 0.90 Sb 0.10 A negative thermal expansion material containing a perovskite-type compound represented by NiO3 was obtained.

[0044] For the negative thermal expansion material of Example 4, the lattice constant and the phase fractions of the low-temperature and high-temperature phases were estimated while changing the temperature using a powder X-ray diffractometer (D8 ADVANCE manufactured by Bruker), and the average volume per unit cell was calculated. Figure 2 shows the temperature dependence of the average volume of the negative thermal expansion material according to the example.

[0045] Example 5 BiNi obtained in Example 1 0.85 Fe 0.15 Thermogravimetric analysis of the O3 reaction precursor was performed. The results are shown in Figure 3. In addition to the desorption of water up to 300°C, a weight loss of 3.6% was observed at approximately 600°C to 700°C, which corresponds to the desorption of oxygen. The composition after heating was Bi 3+ , Ni 2+ , Fe 3+ BiNi 0.85 Fe 0.15 O 2.575 in Therefore, the composition of the reaction precursor before heating was BiNi 0.85 Fe 0.15 O 3.30 It is thought that this was the case.

[0046] Thermogravimetric analysis was carried out on the reaction precursor prepared according to the method described in Patent Document 1. The outline of the method described in Patent Document 1 is to dissolve the raw materials in nitric acid, heat, evaporate to dryness, and then heat in air at 720°C. As a result of the analysis, no weight loss was observed at approximately 600°C to 700°C. Therefore, the composition of this reaction precursor was Bi Ni 0.85 Fe 0.15 O 2.575 A comparison of the thermogravimetric analysis results of these reaction precursors reveals that the reaction precursor according to the present embodiment contains sufficient oxygen, and a negative thermal expansion material can be obtained by high-temperature, high-pressure treatment without mixing an oxidizing agent.

[0047] Although the present invention has been described above with reference to the above-mentioned embodiments, the present invention is not limited to the above-mentioned embodiments, and appropriate combinations or substitutions of the configurations of the embodiments are also included in the present invention. Furthermore, it is possible to appropriately rearrange the combinations and order of steps in the embodiments based on the knowledge of a person skilled in the art, and to make modifications to the embodiments such as various design changes, and such modified embodiments are also included in the scope of the present disclosure. [Industrial Applicability]

[0048] The present invention can be used to produce materials with negative thermal expansion.

Claims

1. A method for producing a negative thermal expansion material having negative thermal expansion, comprising: dissolving a bismuth salt, a nickel salt, a salt of a metal M, which may be a trivalent ion, and optionally a rare earth salt or an antimony salt in a neutral or acidic solution to form a metal salt solution; mixing the metal salt solution with a hypohalite and an alkaline compound to precipitate the metal salt and form a reaction precursor; a step of pressurizing and heating the reaction precursor to form a negative thermal expansion material containing a compound represented by the following formula (1); A method for producing a negative thermal expansion material, comprising: Bi １－ｘ A ｘ Ni １－ｙ M ｙ O ３ ・・・(1) [In formula (1), A is a rare earth element or antimony, and M is a metal that can become a trivalent ion. When x = 0, y satisfies 0.02≦y≦0.

50. When A is a rare earth element and 0<x≦0.20, y satisfies 0.02≦y≦0.

50. When A is antimony and 0<x≦0.20, y satisfies 0≦y≦0.50.]

2. 2. The method for producing a negative thermal expansion material according to claim 1, wherein A is one or more elements selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, and Sb, and M is one or more elements selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ga, Nb, Ru, Rh, and In.

3. 3. The method for producing a negative thermal expansion material according to claim 1, wherein the metal salt is precipitated and the metal of the metal salt is oxidized at the same time.

4. A method for producing a reaction precursor of a negative thermal expansion material having negative thermal expansion, comprising: dissolving a bismuth salt, a nickel salt, a salt of a metal M, which may be a trivalent ion, and optionally a rare earth salt or an antimony salt in a neutral or acidic solution to form a metal salt solution; and mixing the metal salt solution with a hypohalite and an alkaline compound to precipitate the metal salt, thereby forming a reaction precursor.

5. A reaction precursor of a negative thermal expansion material is formed by dissolving a bismuth salt, a nickel salt, a salt of a metal M that can become a trivalent ion, and optionally a rare earth element salt or an antimony salt in a neutral or acidic solution to form a metal salt solution, and mixing the metal salt solution with a hypohalite and an alkaline compound to precipitate the metal salt, wherein the reaction precursor contains a compound represented by the following formula (2): Bi 1-x A x Ni 1-y M y O δ (2) [In formula (2), A is a rare earth element or antimony, and M is a metal that can become a trivalent ion. When x = 0, y satisfies 0.02≦y≦0.

50. When A is a rare earth element and 0<x≦0.20, y satisfies 0.02≦y≦0.

50. When A is antimony and 0<x≦0.20, y satisfies 0≦y≦0.

50. δ satisfies δ≧3.]

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