Negative thermal expansion materials and composites
The development of Pb-free negative thermal expansion materials using BiFeO3 derivatives with substituted ions achieves negative thermal expansion near room temperature, addressing the toxicity issue of lead-containing materials and enabling zero thermal expansion composites.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-08-28
- Publication Date
- 2026-03-13
AI Technical Summary
Existing negative thermal expansion materials contain harmful lead, necessitating the development of Pb-free alternatives.
A novel negative thermal expansion material comprising compounds represented by formulas Bi1-xA2+xFe1-xMxO3, Bi1-xA+xFe1-xM5+O3, Bi1-2xA2+2xFe1-xM5+O3, and Bi1-3xA2+3xFe1-xM6+O3, where A is Mg, Ca, or Sr, and M forms tetravalent, pentavalent, or hexavalent ions, respectively, with x ranging between specific values, and their composites with resin or metal materials.
Provides a Pb-free negative thermal expansion material with controlled phase transition temperatures, enabling negative thermal expansion near room temperature and the creation of zero thermal expansion materials by offsetting thermal expansion.
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Abstract
Description
Technical Field
[0001] The present invention relates to a negative thermal expansion material and a composite.
Background Art
[0002] Materials having the property of shrinking when heated, that is, negative thermal expansion property, have attracted attention as leading to the solution of problems caused by thermal expansion, such as positioning deviation in semiconductor manufacturing equipment and peeling at the bonding interface of different materials.
[0003] Research on negative thermal expansion in PbVO3 substitution compounds, which are perovskite-type compounds, has been underway. PbVO3 has a large tetragonal distortion due to the 6s , , , 0.1 , , x , , 4+ ,
[0005] , ,
[0004] , 0.1 , 0.8 ,
[0006] , 1-x , , , , , lone pair of electrons of Pb and the orbital order of V 2 Non-Patent Document 1 discloses that under pressure, a large volume contraction of 10.6% occurs in PbVO3. 4+ In Non-Patent Document 2, it is disclosed that PbBiVO3 in which a part of Pb in PbVO3 is substituted with Bi and V
[0004] 4+ is electron-doped shows large negative thermal expansion at normal pressure. It is also disclosed that when a part of Pb is substituted with La, negative thermal expansion can be realized in the temperature range across room temperature. 1-x x 0.8 0.1 0.1 Non-Patent Document 3 discloses that PbBiSrVO3 shows a volume contraction of 9.3% when heated from 450 K to 700 K.
[0005] 0.8 0.1 0.1 0.1 0.1 0.1
Prior Art Documents
Non-Patent Documents
[0006]
Non-Patent Document 1
[0007] However, the substances described in Non-Patent Documents 1-3 contain harmful lead. Therefore, there is a need for novel negative thermal expansion materials that do not contain lead.
[0008] This invention has been made in view of these circumstances, and one of its exemplary objectives is to provide a novel Pb-free negative thermal expansion material. [Means for solving the problem]
[0009] One aspect of the present invention is a negative thermal expansion material having negative thermal expansion properties. This negative thermal expansion material comprises a compound represented by any one of the following general formulas (1) to (4). Bi 1-x A 2+ x Fe 1-x M 4+ x O3···(1) (In the formula, A is Mg, Ca, or Sr, and M is an element that can form a tetravalent ion. x satisfies 0.10 ≤ x ≤ 0.40.) Bi 1-x A + x Fe 1-x M 5+ x O3···(2) (In the formula, A is either Na or K, and M is an element that can form a pentavalent ion. x satisfies 0.10 ≤ x ≤ 0.40.) Bi 1-2x A 2+ 2x Fe 1-x M 5+ x O3···(3) (In the formula, A is Mg, Ca, or Sr, and M is an element that can be a pentavalent ion. x satisfies 0.05 ≤ x ≤ 0.40.) Bi 1-3x A 2+ 3x Fe 1-x M 6+ x O3···(4) (In the formula, A is Mg, Ca, or Sr, and M is an element that can form a hexavalent ion. x satisfies 0.03 ≤ x ≤ 0.40.)
[0010] Another aspect of the present invention is a composite, which comprises the negative thermal expansion material and a resin material or metal material having positive thermal expansion properties.
[0011] Furthermore, any combination of the above components, as well as conversions of the expression of the present invention between methods, materials, composites, etc., are also valid embodiments of the present invention. [Effects of the Invention]
[0012] According to the present invention, a novel Pb-free negative thermal expansion material can be provided. [Brief explanation of the drawing]
[0013] [Figure 1] This figure shows the results of the X-ray diffraction pattern analysis of sample 1. [Figure 2] This figure shows the temperature dependence of the X-ray diffraction pattern of sample 2. [Figure 3] This figure shows the results of the X-ray diffraction pattern analysis of sample 2. [Figure 4] This figure shows the results of the X-ray diffraction pattern analysis of sample 3. [Figure 5] This figure shows the results of the X-ray diffraction pattern analysis of sample 4. [Figure 6]This figure shows the results of the X-ray diffraction pattern analysis of sample 5. [Figure 7] This figure shows the results of the X-ray diffraction pattern analysis of sample 6. [Figure 8] This figure shows the results of the X-ray diffraction pattern analysis of sample 7. [Figure 9] This figure shows the results of the analysis of the X-ray diffraction pattern of sample 8. [Figure 10] This figure shows the analysis results of the X-ray diffraction pattern of sample 9. [Modes for carrying out the invention]
[0014] (Negative thermal expansion material) The negative thermal expansion material according to this embodiment has negative thermal expansion properties, specifically exhibiting negative thermal expansion within a predetermined temperature range. The negative thermal expansion material includes a compound in which, in the parent material BiFeO3, a portion of Bi is substituted with Mg, Ca, or Sr, and a portion of Fe is substituted with an element that can become a tetravalent, pentavalent, or hexavalent ion. Specifically, the negative thermal expansion material includes a compound represented by any one of the following formulas (1) to (4). Bi 1-x A 2+ x Fe 1-x M 4+ x O3···(1) In equation (1), A is Mg, Ca, or Sr, and M is an element that can form a tetravalent ion. x satisfies 0.10 ≤ x ≤ 0.40. Bi 1-x A + x Fe 1-x M 5+ x O3···(2) In equation (2), A is either Na or K, and M is an element that can form a pentavalent ion. x satisfies 0.10 ≤ x ≤ 0.40. Bi 1-2x A 2+ 2x Fe 1-x M 5+ x O3···(3) In equation (3), A is Mg, Ca, or Sr, and M is an element that can be a pentavalent ion. x satisfies 0.05 ≤ x ≤ 0.40. Bi 1-3x A 2+ 3x Fe 1-x M 6+ x O3···(4) In equation (4), A is Mg, Ca, or Sr, and M is an element that can form a hexavalent ion. x satisfies 0.03 ≤ x ≤ 0.40.
[0015] BiFeO3, the parent material of any one of the compounds represented by the above formulas (1) to (4), was known to undergo a phase transition from a rhombohedral ferroelectric phase to a smaller orthorhombic paraelectric phase at temperatures above 1100 K or 6 GPa (see Mael. G., et al., CR Phys., 16, 2, 182-192 (2015)). However, its high transition temperature made it impractical as a negative thermal expansion material.
[0016] As a result of extensive research on BiFeO3, the inventors have discovered that by substituting an equal amount of Bi with Mg, Ca, or Sr, and an equal amount of Fe with elements that can become tetravalent, pentavalent, or hexavalent ions, the phase transition temperature from the rhombohedral ferroelectric phase to the orthorhombic or cubic paraelectric phase is reduced, and a negative thermal expansion function appears at temperatures close to room temperature.
[0017] In equation (1) above, when x is 0.1 or greater, the ferroelectric rhombohedral phase in the compound becomes mixed with the paraelectric orthorhombic phase or paraelectric cubic phase. As the temperature increases, the paraelectric orthorhombic or paraelectric cubic phase becomes dominant, causing the volume to shrink. From this, it can be seen that the phase transition temperature can be controlled by the substitution amount x. For example, if the substitution amount is around 15%, i.e., x is 0.15 or greater, the phase transition temperature decreases, making it possible to shrink at a temperature closer to room temperature.
[0018] Elements that can form a tetravalent ion of M include ruthenium (Ru), iridium (Ir), zirconium (Zr), tungsten (W), molybdenum (Mo), rhodium (Rh), iron (Fe), cobalt (Co), vanadium (V), chromium (Cr), manganese (Mn), and hafnium (Hf).
[0019] Elements that can form a pentavalent ion of M include niobium (Nb), rhenium (Re), molybdenum (Mo), tungsten (W), and tantalum (Ta).
[0020] Elements that can form the hexavalent ion M include chromium (Cr), molybdenum (Mo), and tungsten (W).
[0021] To obtain a material that more reliably exhibits negative thermal expansion, in formula (1), A is preferably Mg or Ca, and M is preferably Ru, Ir, Zr, W, Mo, Rh, Fe, or Co. For similar reasons, in formula (2), M is preferably Nb, Re, Mo, or W; in formula (3), A is preferably Mg or Ca, and M is preferably Nb, Re, Mo, or W; and in formula (4), A is preferably Mg or Ca, and M is preferably Mo, or W.
[0022] By dispersing the negative thermal expansion material of this embodiment in a resin material such as engineering plastic, and by selecting the material and setting the content of each component so that the thermal expansion of the resin material is offset by the negative thermal expansion of the negative thermal expansion material, a zero thermal expansion material can be obtained.
[0023] (Method for manufacturing materials with negative thermal expansion) A method for producing a negative thermal expansion material containing a compound represented by any one of the above formulas (1) to (4) will be described. Note that the method for producing a negative thermal expansion material is not limited to the following method.
[0024] First, oxides of Bi, A, Fe, and M are mixed in stoichiometric ratios, and an oxidizing agent (e.g., KClO4) is added as needed. This mixture is then sealed in a container such as a gold capsule. Subsequently, a negative thermal expansion material can be obtained by processing the mixture under predetermined pressure conditions (e.g., around 6 GPa), a predetermined heating temperature (e.g., around 1200°C), and a predetermined processing time (e.g., around 30 minutes) using a high-pressure synthesis apparatus such as a cubic anvil type.
[0025] (complex) The composite according to this embodiment includes the negative thermal expansion material and a resin material or metal material having positive thermal expansion properties. The resin material used in the composite is not particularly limited, but may be, for example, epoxy resin, phenolic resin, or polycarbonate. The metal material used in the composite is not particularly limited, but may be, for example, copper or aluminum.
[0026] The mixing ratio (volume ratio) of the negative thermal expansion material and the resin or metal material depends on the thermal expansion coefficients of the negative thermal expansion material, resin material, and metal material used, but may be, for example, 5:95 to 80:20. According to the composite according to this embodiment, the positive thermal expansion of the resin or metal material can be offset by the negative thermal expansion of the negative thermal expansion material. This makes it possible to provide a material with a small rate of dimensional change in response to temperature changes.
[0027] (Examples) The following describes embodiments of the present invention, but these embodiments are merely illustrative examples for suitably illustrating the present invention and do not limit the present invention in any way.
[0028] (Samples 1-9) The starting materials Bi2O3, MgO, CaO, Fe2O3, RuO2, IrO2, ZrO2, Nb2O5, HfO2, WO3, and MoO3 were mixed in stoichiometric composition, and the mixture was encapsulated in a gold capsule. The oxidizing agent KClO4 was added as needed. Then, the mixture was heat-treated for 30 minutes at 6 GPa and 1200 °C using a cubic anvil-type high-pressure synthesis apparatus to synthesize Samples 1 to 5. The compositions of Samples 1 to 4, 6, and 7 are represented by the above formula (1) and are as follows. The composition of Sample 5 is represented by the above formula (3) and is as follows. The compositions of Samples 8 and 9 are represented by the above formula (4) and are as follows. Sample 1: Bi 0.85 Ca 0.15 Fe 0.85 Ru 0.15 O3 (x = 0.15) Sample 2: Bi 0.90 Ca 0.10 Fe 0.90 Ir 0.10 O3 (x = 0.10) Sample 3: Bi 0.85 Ca 0.15 Fe 0.85 Ir 0.15 O3 (x = 0.15) Sample 4: Bi 0.90 Ca 0.10 Fe 0.90 Zr 0.10 O3 (x = 0.10) Sample 5: Bi 0.80 Ca 0.20 Fe 0.90 Nb 0.10 O3 (x = 0.10) Sample 6: Bi 0.80 Mg 0.20 FeO3 (x = 0.20) Sample 7: Bi 0.90 Ca 0.10 Fe 0.90 Hf 0.10 O3 (x = 0.10) Sample 8: Bi 0.85 Ca 0.15 Fe 0.95 W 0.05 O3 (x = 0.05) Sample 9: Bi 0.70 Ca 0.30 Fe 0.90Mo 0.10 O3(x=0.10)
[0029] Using the beamline at SPring-8, the temperature dependence (100K to 900K) of the X-ray diffraction (XRD) patterns of samples 1-7 and 9 was measured at λ = 0.42 Å. The temperature dependence (100K to 900K) of the XRD pattern of sample 8 was measured at λ = 1.5405 Å using a Bruker D8 Advance. Rietveld analysis was performed on the measurement results of samples 1-5 and 7-9 to determine the unit cell volume of the rhombohedral phase, the unit cell volume of the orthorhombic phase, the average unit cell volume, and the weight fraction of the orthorhombic phase in the region where the rhombohedral and orthorhombic phases coexist. The average unit cell volume was calculated as the sum of the values obtained by multiplying the unit cell volume of the rhombohedral phase and the unit cell volume of the orthorhombic phase by their respective weight fractions. The measurement results for sample 6 were also subjected to Rietveld analysis, but instead of calculating the unit cell volume of the orthorhombic phase, the weight fraction of the unit cell volume of the cubic phase was determined, and the weight fraction of the cubic phase in the region where the rhombohedral and cubic phases coexisted was calculated. Furthermore, the average unit cell volume of sample 6 was calculated as the sum of the values obtained by multiplying the unit cell volume of the rhombohedral phase and the unit cell volume of the cubic phase, respectively, by their respective weight fractions.
[0030] Figure 1 shows the analysis results for sample 1, which was substituted with 15% Ru. As shown in Figure 1, it was confirmed that sample 1 underwent a transition from the ferroelectric rhombohedral phase to the paraelectric orthorhombic phase with a volume contraction of 1.7% at 300K to 500K, which is close to room temperature.
[0031] Figure 2 shows the temperature dependence of the X-ray diffraction pattern of sample 2, which was substituted with 10% Ir. This X-ray diffraction pattern was obtained by changing the temperature in the following order: 300K (1st time) → 600K (1st time) → 900K → 600K (2nd time) → 300K (2nd time). Figure 2 shows the X-ray diffraction patterns at 300K (1st time), 600K (1st time), 900K, 600K (2nd time), and 300K (2nd time), from bottom to top. As shown in Figure 2, when the temperature is increased from 300K to 600K, the peak of the paraelectric orthorhombic phase mixes with the peak of the ferroelectric rhombohedral phase, and at 900K, the peak of the paraelectric orthorhombic phase becomes dominant. Subsequently, as the temperature is decreased from 900K to 600K and then to 300K, the peak of the paraelectric orthorhombic phase decreases. Furthermore, the X-ray diffraction pattern at 300K showed no change between the first and second measurements, indicating that the change in crystal structure is reversible between 300K and 900K.
[0032] Figure 3 shows the analysis results for sample 2 with 10% Ir substitution (x=0.10). Figure 4 shows the analysis results for sample 3 with 15% Ir substitution (x=0.15). As shown in Figure 3, in sample 2, a transition from the ferroelectric rhombohedral phase to the paraelectric orthorhombic phase was confirmed at 500K to 600K with a volume contraction of 1.1%. As shown in Figure 4, in sample 3, a transition from the ferroelectric rhombohedral phase to the paraelectric orthorhombic phase was confirmed at 300K to 400K with a volume contraction of 1.7%. From these results, it can be seen that the phase transition temperature from the ferroelectric rhombohedral phase to the paraelectric orthorhombic phase can be lowered by increasing the substitution amount x.
[0033] Figure 5 shows the analysis results for sample 4 with 10% Zr substitution. In sample 4, it was confirmed that a transition occurred from the ferroelectric rhombohedral phase to the paraelectric orthorhombic phase with a volume contraction of 1.1% between 700K and 900K.
[0034] Figure 6 shows the analysis results for sample 5 with 10% Nb substitution. In sample 5, it was confirmed that a transition occurred from the ferroelectric rhombohedral phase to the paraelectric orthorhombic phase with a volume contraction of 0.55% between 500K and 700K.
[0035] Figure 7 shows A=Mg, Fe 4+ This figure shows the analysis results for sample 6 with 20% substitution. In sample 6, it was confirmed that a transition occurred from the ferroelectric rhombohedral phase to the paraelectric cubic phase with a volume contraction of 0.40% at 850K to 900K.
[0036] Figure 8 shows the analysis results for sample 7 with 10% Hf substitution. In sample 7, it was confirmed that a transition occurred from the ferroelectric rhombohedral phase to the paraelectric orthorhombic phase with a volume contraction of 1.31% between 700K and 900K.
[0037] Figure 9 shows A=Ca, W 6+ This figure shows the analysis results for sample 8 with 5% substitution. In sample 8, it was confirmed that a transition occurred from the ferroelectric rhombohedral phase to the paraelectric orthorhombic phase with a 1.5% volume contraction between 550K and 750K.
[0038] Figure 10 shows A=Ca, Mo 6+ This figure shows the analysis results for sample 9 with 10% substitution. In sample 9, it was confirmed that a transition occurred from the ferroelectric rhombohedral phase to the paraelectric orthorhombic phase with a volume contraction of 0.4% between 350K and 450K.
[0039] The present invention has been described above based on embodiments. These embodiments are illustrative, and it will be understood by those skilled in the art that various modifications are possible in combinations of these components and processing processes, and that such modifications also fall within the scope of the present invention.
Claims
1. A negative thermal expansion material having negative thermal expansion properties, A negative thermal expansion material containing a compound represented by one of the following general formulas (1) to (4). Bi １－ｘ A ２＋ ｘ Fe １－ｘ M ４＋ ｘ O ３ ・・・(1) (In the formula, A is Mg, Ca, or Sr, and M is an element that can form a tetravalent ion. x satisfies 0.10 ≤ x ≤ 0.40.) Bi １－ｘ A ＋ ｘ Fe １－ｘ M ５＋ ｘ O ３ ・・・(2) (In the formula, A is Na or K, and M is an element that can form a pentavalent ion. x satisfies 0.10 ≤ x ≤ 0.40.) Bi １－２ｘ A ２＋ ２ｘ Fe １－ｘ M ５＋ ｘ O ３ ・・・(3) (In the formula, A is Mg, Ca, or Sr, and M is an element that can form a pentavalent ion. x satisfies 0.05 ≤ x ≤ 0.40.) Bi １－３ｘ A ２＋ ３ｘ Fe １－ｘ M ６＋ ｘ O ３ ・・・(4) (In the formula, A is Mg, Ca, or Sr, and M is an element that can form a hexavalent ion. x satisfies 0.03 ≤ x ≤ 0.40.)
2. The negative thermal expansion material according to claim 1, wherein the compound is a compound represented by formula (1), A is Mg or Ca, and M is Ru, Ir, Zr, W, Mo, Rh, Fe, or Co.
3. The negative thermal expansion material according to claim 1, wherein the compound is a compound represented by formula (2), and M is Nb, Re, Mo, or W.
4. The negative thermal expansion material according to claim 1, wherein the compound is a compound represented by formula (3), A is Mg or Ca, and M is Nb, Re, Mo or W.
5. The negative thermal expansion material according to claim 1, wherein the compound is a compound represented by formula (4), A is Mg or Ca, and M is Mo or W.
6. The negative thermal expansion material according to claim 1, wherein the compound exhibits negative thermal expansion due to a transition of its ferroelectric rhombohedral phase to a paraelectric orthorhombic phase or a paraelectric cubic phase.
7. A composite comprising a negative thermal expansion material according to any one of claims 1 to 6 and a resin material or metal material having positive thermal expansion properties.