Laminate and manufacturing method thereof

Abstract

To provide a method for producing a laminate that can form, by a simple process, a laminate having a metal oxide layer composed of Magneli phase titanium oxide on a surface layer, and a laminate formed by the production method.SOLUTION: A laminate 100 has a metal layer 10, a metal oxide layer 20 provided on a surface layer of a metal layer 10 and composed of Magneli phase titanium oxide, the Magneli phase titanium oxide represented by the formula TinO2n-1(n≥3).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laminate and a method for producing the same. [Background technology]

[0002] Titanium dioxide is a material known as a photocatalyst. While titanium dioxide can absorb high-energy ultraviolet light, it has a low light absorption efficiency in the visible light region. Therefore, there is a demand for photocatalysts that can absorb light in the visible light region.

[0003] Magneli phase oxides are known as photocatalysts that absorb light in the visible light region. Examples of such Magneli phase oxides include Ti n O 2n-1 Magneli phase titanium oxides are known.

[0004] Patent Documents 1 and 2 disclose Ti n O 2n-1 Specifically, Patent Document 1 describes a method for producing TiO2 nanoparticles of about 10 nm to 30 nm with a hydrogen reducing agent such as CaH2, LiH, NaH, MgH2, LiAlH4, or NaBH4, which are mixed and pressurized under an inert gas atmosphere to produce a pellet-shaped sample, which is then reduced by heating at a low temperature of about 350°C for several days while being crushed along the way, to produce a composition such as particulate Ti2O3. Patent Document 2 describes a method for producing TiO2 nanoparticles of about 10 nm to 30 nm with a hydrogen reducing agent such as CaH2, LiH, NaH, MgH2, LiAlH4, or NaBH4, which are mixed and pressurized under an inert gas atmosphere to produce a pellet-shaped sample, which is then reduced by being heated at a low temperature of about 350°C for several days while being crushed along the way. α Ti β O γ Ti is present on part of the crystal surface of titanium oxide represented by n O 2n-1 It is described that titanium oxide crystals having the following structure are formed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-214348 [Patent Document 2] International Publication No. 2016 / 159323 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the manufacturing methods of Patent Documents 1 and 2 require complex processes to form Magneli phase oxides, and there is no disclosure of a layered body made of Magneli phase oxides or a manufacturing method thereof.Furthermore, no laminate having a layered body made of Magneli phase oxides in the surface layer portion is known.

[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a method for producing a laminate, which can obtain a laminate having a metal oxide layer composed of a Magneli phase oxide through a simple process, and a laminate obtained by the production method. [Means for solving the problem]

[0008] As a result of extensive research, the inventors have found that when the surface of a metal substrate is oxidized in the atmosphere and then heat-treated in an environment controlled to reduce the oxygen partial pressure, metal ions diffuse outward, changing the composition and thickness of the metal oxide layer formed on the surface. This makes it possible to thin the metal oxide layer composed of Magneli phase oxide and control the composition of the thin-layered Magneli phase oxide through a simple process, and as a result, it is possible to form a laminate having a Magneli phase metal oxide layer on the surface, and it is also possible to easily form a Magneli phase metal oxide layer on a treated object with a complex shape.

[0009] That is, the gist and configuration of the present invention are as follows.

[0010] (1) A laminate according to a first aspect of the present invention comprises a metal layer and a metal oxide layer formed on a surface layer portion of the metal layer and made of Magneli phase titanium oxide, the Magneli phase titanium oxide having a composition formula of Ti n O 2n-1(n≧3).

[0011] (2) In the laminate according to the above aspect, the metal oxide layer made of the Magneli phase titanium oxide may have an average thickness of 2 μm or more.

[0012] (3) In the laminate according to the above aspect, the metal oxide layer has two regions with different compositions in the stacking direction, and the more distant the region from the metal layer is from the other region, the higher the composition ratio of the titanium element in the Magneli-phase titanium oxide is. Low That's fine.

[0013] (4) Either of the two regions may be made of Ti4O7.

[0014] (5) In the laminate according to the above aspect, voids may be present between the metal layer and the metal oxide layer made of Magneli phase titanium oxide.

[0015] (6) A method for producing a laminate according to a second aspect of the present invention is a method for producing a laminate according to the first aspect, comprising a first step of preheating a titanium substrate in the atmosphere, and a second step of heat-treating the preheated titanium substrate under a low oxygen partial pressure.

[0016] (7) In the method for producing a laminate according to the above aspect, in the first step, a titanium substrate is preheated at 650°C to 750°C, and in the second step, the preheated titanium substrate is heated to a temperature of 750°C to 950°C and an oxygen partial pressure of 1.0 × 10 -7 Heat treatment may be performed at or below 1000 kJ / cm. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a laminate having a metal oxide layer made of a Magneli phase oxide. [Brief explanation of the drawings]

[0018] [Figure 1]1 is a schematic cross-sectional view showing a cross section of a laminate according to an embodiment of the present invention. [Figure 2] 1 shows the results of thin-film GI-XRD measurement of the sample of Example 1, which is a laminate according to the present embodiment. [Figure 3] 1 is a TEM image showing a cross section of a sample of Example 1, which is a laminate according to the present embodiment. [Figure 4] This is an example of an electron diffraction image of Ti5O9 crystal grains. [Figure 5] FIG. 2 is a cross-sectional view schematically showing a modified example of the laminate of FIG. [Figure 6] FIG. 2 is a cross-sectional view schematically showing another modified example of the laminate of FIG. [Figure 7] FIG. 2 is a cross-sectional view schematically showing another modified example of the laminate of FIG. [Figure 8] FIG. 4 is a diagram schematically illustrating an example of a second step in the method for producing a laminate according to the present embodiment. [Figure 9] 1 shows the results of thin film GI-XRD measurement of the laminate of Example 2. [Figure 10] 1 shows the results of thin film GI-XRD measurement of the laminates of Examples 3 to 5. [Figure 11] 1 shows the results of XRD measurement of the laminates of Comparative Examples 1 to 3. [Figure 12] 1 shows the results of XRD measurement of the laminates of Comparative Examples 4 to 6. [Figure 13] 10 shows the results of XRD measurement of the laminate of Comparative Example 7. [Figure 14] 1 shows the results of thin film GI-XRD measurement of the laminates of Comparative Examples 8 and 9. [Figure 15] 10 shows the results of thin film GI-XRD measurement of the laminate of Comparative Example 10. [Figure 16] 10 shows the results of XRD measurement of the laminate of Comparative Example 11. [Figure 17] 1 is a TEM image showing a cross section of a sample of Example 1. [Figure 18] 1 is a TEM image showing a cross section of a sample of Example 2. [Figure 19] 1 is a TEM image showing a cross section of a sample of Comparative Example 1. [Figure 20]1 is a TEM image showing a cross section of a sample of Comparative Example 2. [Figure 21] 1A and 1B are an enlarged view of the vicinity of region Rd of the sample of Example 1 and an electron beam diffraction image of region Rd. [Figure 22] 1A and 1B are an enlarged view of the vicinity of region R1 of the sample of Comparative Example 1 and an electron beam diffraction image of region R1. [Figure 23] 1 shows an HAADF-STEM image of region Rb of the sample of Example 1 and an image obtained by Fourier transform of the image. [Figure 24] 1A and 1B are diagrams showing the contrast intensity of XY lines in an HAADF-STEM image of the sample of Example 1 and the atomic arrangement of region Ra. [Figure 25] FIG. 1 is a diagram showing the reflectance of Example 1, Comparative Examples 1 and 2, and rutile-type white TiO 2 powder. [Figure 26] FIG. 10 is a diagram showing the thermogravimetric curve of Comparative Example 12. [Figure 27] FIG. 10 is a photograph showing the appearance of the sample in state c in Comparative Example 12 and a diagram showing the results of XRD measurement. DETAILED DESCRIPTION OF THE INVENTION

[0019] An example of an embodiment of the present invention will be described in detail below with reference to the drawings. Note that the drawings used in the following description may show characteristic parts enlarged for the sake of convenience in order to make the features of the present invention easier to understand. Therefore, the dimensional ratios of each component may differ from the actual ones.

[0020] [Laminate] 1 is a schematic cross-sectional view showing a cross section of a laminate 100 according to this embodiment. The laminate 100 has a metal layer 10 and a metal oxide layer 20 made of Magneli-phase titanium oxide and provided on the surface of the metal layer 10.

[0021] (metal layer) The metal layer 10 is a layer containing, for example, titanium element as a main component.

[0022] (metal oxide layer) The metal oxide layer 20 is provided above the metal layer 10, for example, on the surface of the metal layer 10. The metal oxide layer 20 in this embodiment is not limited to a configuration in which it is in direct contact with the metal layer 10, but also includes a configuration in which it is separated from the metal layer 10, for example, a configuration in which it is provided on the metal layer 10 via one or more other layers. Note that "above" does not necessarily coincide with the direction along the direction of gravity.

[0023] The metal oxide layer 20 is a layer made of Magneli phase titanium oxide. Magneli phase titanium oxide has the composition formula Ti n O 2n-1 (n≧3). Examples of such compositions include Ti3O5, Ti4O7, Ti5O9, and Ti6O 11 , Ti7O 13 etc. are included.

[0024] Magneli phase titanium oxide is a rutile-type metal dioxide in which oxygen vacancies are periodically introduced. Magneli phase titanium oxide with n 3≦n≦9 has periodic planar defects on the (121) plane, while Magneli phase titanium oxide with n≧10 has periodic planar defects on the (132) plane.

[0025] The metal oxide layer 20 contains, for example, two or more compounds having different composition ratios. Note that all of the compounds contained in the metal oxide layer 20 are composed of Magneli phase titanium oxide.

[0026] FIG. 1 shows an example in which the metal oxide layer 20 contains two or more compounds having different compositions. The metal oxide layer 20 has, for example, a first region 21, a second region 22, and a third region, in this order from the metal layer 10 side. The first region 21 is the region closest to the metal layer 10 and is in direct contact with the metal layer 10. The second region 22 is located farther from the metal layer 10 than the first region 21 and is disposed on the opposite side of the first region 21 from the metal layer 10. The third region 23 is located farther from the metal layer 10 than the second region 22 and is disposed on the opposite side of the second region 22 from the first region 21. In this embodiment, the third region 23 constitutes the outermost layer exposed on the surface.

[0027] The first region 21, the second region 22, and the third region 23 are each, for example, a region of a compound having the same composition and are regions composed of crystal grains of the respective compounds. The Magneli phase titanium oxides constituting the first region 21, the second region 22, and the third region 23 have, for example, different compositions. Furthermore, crystal grain boundaries exist between the first region 21, the second region 22, and the third region 23.

[0028] Of the three regions of the metal oxide layer 20, the more distant the region from the metal layer 10, the higher the composition ratio of the titanium element in the Magneli phase titanium oxide. low 1, the Magneli-phase titanium oxide contained in the first region 21 has the highest titanium element composition ratio, and the Magneli-phase titanium oxide contained in the third region 23 has the lowest titanium element composition ratio. An example of such a configuration is one in which the first region 21 is composed of the composition formula Ti3O5, the second region 22 is composed of the composition formula Ti4O7, and the third region 23 is composed of the composition formula Ti5O9.

[0029] Each of the first region 21, the second region, and the third region 23 does not necessarily have to be made of a single compound having a single composition ratio, but may be a mixed crystal of two compounds having different composition ratios. Examples of such a mixed crystal include a case where the third region 23 is made of a mixed crystal of Ti4O7 and Ti5O9, and a case where the second region 22 is a (1-20) twin crystal of Ti4O7.

[0030] The fact that the metal oxide layer 20 is composed of Magneli-phase titanium oxide can be confirmed by X-ray diffraction (XRD). FIG. 2 shows an example of the results of X-ray diffraction measurement of the metal oxide layer 20 of the laminate 100 according to this embodiment, showing the results of thin-film GI-XRD measurement. As shown in FIG. 2, in the XRD profile of the metal oxide layer 20, only peaks due to Magneli-phase titanium oxide are detected, and peaks due to other titanium oxides such as TiO are not detected. Note that the X-ray penetration depth in XRD is preferably adjusted according to the thickness of the metal oxide layer 20.

[0031] The composition of the Magneli phase titanium oxide constituting the metal oxide layer 20 can be measured using a transmission electron microscope (TEM). To identify the composition of the Magneli phase titanium oxide, first, a TEM image showing a cross section of the laminate 100 is observed to identify the crystal grains. Next, an electron beam diffraction image of the crystal grains is obtained. Based on this electron beam diffraction image, the composition of the Magneli phase titanium oxide constituting each crystal grain can be identified.

[0032] 3 is an example of a TEM image of the laminate 100 according to this embodiment. In this TEM image, it can be confirmed that the regions Ra, Rb, and Rc of the metal oxide layer 20 are mixed crystals of TiO, TiO, TiO, and TiO, respectively, using an electron beam analysis image described below.

[0033] Specifically, for example, the composition formula Ti n O 2n-1 The composition of Magneli phase titanium oxide represented by (3≦n≦9) corresponds to the (000) and (121) rutile TiO2 planes through which transmitted waves are transmitted in the electron diffraction pattern. R-TiO2 It can be identified by the number of atoms (spots) between them. n O 2n-1The titanium atomic columns of the Magneli phase titanium oxide, represented by (3≦n≦9), are arranged in n-cycles. Therefore, the transmitted wave penetrates the (000) spot and the (121) spot, which corresponds to the rutile AO2 surface. R-TiO2 If the number of spots located on the line segment connecting the spots is (N-1), the composition of the Magneli phase titanium oxide that constitutes the region is Ti N O 2N-1 For example, if there are three spots, the Magneli phase titanium oxide constituting the region can be identified as Ti4O7, and if there are four spots, it can be identified as Ti5O9. These spots can be identified as, for example, a (000) spot and a (121) spot. R-TiO2 Divide the line segment connecting the spots into equal parts.

[0034] Figure 4 shows the composition formula Ti n O 2n-1 An example of an electron diffraction image for identifying the composition of Magneli phase titanium oxide represented by (3≦n≦9) is shown below. In the electron diffraction image shown in Figure 4, there are spots of (000) where the transmitted wave is transmitted and (121) which corresponds to the rutile TiO2 plane. R-TiO2 The number of spots located on the line segment connecting the two spots is four, and the line segment connecting the two spots is divided into five equal parts. Therefore, the crystal grains whose electron beam diffraction pattern is shown in Figure 4 can be identified as Ti5O9.

[0035] Similarly, the composition formula Ti n O 2n-1 The composition of Magneli phase titanium oxides represented by (10≦n) can be identified by the number of atoms (spots) between (000) and (132) in the electron diffraction pattern. n O 2n-1 The titanium atomic columns of the Magneli-phase titanium oxide, expressed as (10≦n), are arranged in a period of n. Therefore, if the number of spots located on the line segment connecting the (000) spot and the (132) spot through which the transmitted wave passes is (N-1), the composition of the Magneli-phase titanium oxide constituting the region is Ti N O 2N-1These spots can be identified as, for example, equally dividing the line segment connecting the (000) spot and the (132) spot.

[0036] In addition, once the electron diffraction pattern is indexed by the above method, the (000) spots and (121) R-TiO2 Even if (N-1) spots are not confirmed between the (000) spots or between the (132) spots and the (000) spots, the composition of the crystal grains can be identified based on the spacing and angle between the spots. n O 2n-1 If the orientation is correct, the (000) spot and the (121) spot will appear depending on the grain composition. R-TiO2 It is confirmed that (N-1) spots are located between the (000) spot and the (132) spot, or between the (000) spot and the (132) spot.

[0037] The Magneli phase titanium oxide constituting the metal oxide layer 20 preferably has crystal grains with a crystallite size of, for example, 100 nm to 1.0 μm, and more preferably is composed of crystal grains with a crystallite size of 100 nm to 1.0 μm.

[0038] For example, voids V are formed between the metal layer 10 and the metal oxide layer 20 (FIG. 3). The size of the voids V in the stacking direction is, for example, about several tens to several hundreds of nanometers, and they are distributed in the in-plane direction, for example, along the interface between the metal layer 10 and the metal oxide layer 20. For example, the voids V are approximately cylindrical voids of several tens to several hundreds of nanometers in size that are connected to each other in the in-plane direction of the interface within a range of several hundreds of nanometers from the interface between the metal layer 10 and the metal oxide layer 20 in the stacking direction toward the surface layer portion.

[0039] From the viewpoint of improving electrical conductivity, the metal oxide layer 20 according to this embodiment preferably has an average thickness of, for example, 200 nm or more, more preferably 500 nm or more, and even more preferably 1 μm or more. The metal oxide layer 20 may also have an average thickness of, for example, 2 μm or less. The average thickness of the metal oxide layer 20 can be calculated by measuring the distance in the stacking direction from the surface of the outermost layer of the laminate to the voids in a TEM image at 10 points in the in-plane direction of the laminate and averaging the measured values.

[0040] From the viewpoint of improving conductivity, the third region 23 preferably has an average thickness of 200 nm or more, more preferably 500 nm or more, and even more preferably 1 μm or more. The third region 23 may have an average thickness of 2 μm or less. The average thickness of the third region 23 can be calculated by measuring the distance in the stacking direction from the boundary between the second region 22 and the third region 23 of the laminate to the boundary between the third region 23 and the void in a TEM image at 10 points in the in-plane direction of the laminate and calculating the average.

[0041] The metal oxide layer according to this embodiment is TiO 2、 Furthermore, compared to a mixture of TiO2 and Magneli phase titanium oxide, the metal oxide layer according to this embodiment has high conductivity in the in-plane direction and in the stacking direction. Furthermore, since the metal oxide layer according to this embodiment has high light absorption efficiency in the visible light region and near-infrared light region, it is expected to be used as a photocatalyst in the visible light and near-infrared light region.

[0042] 1 illustrates a configuration in which the first region 21, the second region 22, and the third region 23 are layered one on top of the other, but the laminate according to this embodiment is not limited to this example. For example, while the surface of each layer is flat in FIG. 1, it may be curved or uneven. Furthermore, the thickness of each layer may not be uniform, and may include thin and thick portions.

[0043] Although Figure 1 shows a Magneli phase with three regions, the number of regions may be any number greater than or equal to one, and the metal oxide layer may consist of a single region with a specific composition ratio, or may include four or more regions.

[0044] Figures 5 to 7 are cross-sectional views schematically showing modifications of the laminate 100 of Figure 1. In the laminates 101, 102, and 103 of Figures 5 to 7, the same components as those in the laminate 100 are denoted by the same reference numerals, and the description thereof will be omitted.

[0045] 5, the metal oxide layer 20 of the laminate 101 is composed of a first region 21 and a second region 22. The first region 21 is composed of, for example, a composition formula of Ti3O5, and the second region 22 is composed of, for example, a composition formula of Ti4O7. The second region 22 of the laminate 101 constitutes the outermost layer. 6, the metal oxide layer 20 of the laminate 102 is composed of a second region 22 and a third region 23. The second region 22 is composed of, for example, a composition formula of Ti4O7, and the third region 23 is composed of, for example, a composition formula of Ti5O9. The third region 23 of the laminate 102 constitutes the outermost layer. 7, the metal oxide layer 20 of the laminate 103 is composed of a second region 22. That is, in the laminate 103, the entire metal oxide layer 20 is composed of a single Magneli-phase titanium oxide consisting of a single compound having a specific composition ratio. The second region 22 in the laminate 103 constitutes the outermost layer.

[0046] In this way, the metal oxide layer of the laminate according to this embodiment may be composed of two regions having different compositions in the stacking direction, or may be composed of one region. In this case, the more distant the region from the metal layer 10, the higher the composition ratio of the titanium element in the Magneli-phase titanium oxide. low It is preferable that either of the two regions is made of Ti4O7, which has relatively excellent electrical properties, particularly electrical conductivity, among the Magneli-phase titanium oxides (see FIGS. 5 and 6). The Magneli-phase titanium oxide contained in each region may contain the same Magneli-phase titanium oxide as the Magneli-phase titanium oxide contained in the corresponding region in FIG. 1.

[0047] The thickness of each of the first region 21, the second region 22, and the third region 23 can be selected arbitrarily. For example, in FIG. 5, the thickness of the second region 22 is greater than the thickness of the first region 21, but the thickness of the second region 22 may be smaller than the thickness of the first region 21. Also, in FIG. 6, the thickness of the second region 22 is greater than the thickness of the third region 23, but the thickness of the second region 22 may be smaller than the thickness of the third region 23.

[0048] Of the Magneli-phase titanium oxides contained in each region, the Magneli-phase titanium oxide represented by the composition formula Ti4O7 has the highest electrical conductivity. Therefore, from the viewpoint of increasing the electrical conductivity of the metal oxide layer 20, it is preferable that the thickest region among the first region 21, the second region 22, and the third region 23 be composed of the composition formula Ti4O7. For example, it is preferable that the second region 22 be thickest among the first region 21, the second region 22, and the third region 23, and that the second region 22 be composed of the Magneli-phase titanium oxide represented by the composition formula Ti4O7.

[0049] [Method of manufacturing laminate] The method for producing a laminate according to this embodiment is a method for producing a metal oxide layer according to the above embodiment, and includes a first step of preheating a titanium substrate and a second step of heat-treating the preheated metal substrate under a low oxygen partial pressure.

[0050] (1st step) In the first step, the metal substrate can be preheated in the atmosphere using a known heating furnace such as an electric furnace, etc. In the first step, the surface of the metal substrate can be converted to titanium dioxide.

[0051] A commercially available substrate may be used. The thickness of the substrate is, for example, 3 μm or more, preferably 5 μm or more. When the substrate has a thickness equal to or greater than a predetermined value, it is possible to secure a sufficient amount of titanium ions and titanium elements that diffuse outward, making it easier to control the formation of Magneli phase titanium oxide. The substrate may contain titanium elements as a main component, but it is preferable to use a substrate consisting only of titanium elements. The substrate may also contain a third element other than titanium elements. The substrate may have a flat shape, or may have a complex shape including curved or bent portions.

[0052] The heat treatment temperature in the first step is, for example, 600°C to 800°C, preferably 650°C to 750°C. By controlling the heat treatment temperature in the first step within this range and performing the second step described below, it is possible to produce a laminate including a metal oxide layer according to the above embodiment. Titanium element undergoes a rapid oxidation reaction at approximately 800°C. Therefore, if the heat treatment temperature in the first step is excessively high, the oxidation reaction of titanium element on the surface may proceed excessively, and even when the second step described below is performed, a metal oxide layer composed of Magneli phase titanium oxide may not be obtained, or the surface may peel off.

[0053] The heat treatment time for the first step is, for example, 30 minutes to 5 hours, and preferably 30 minutes to 3 hours. Here, the heat treatment time refers to the time for which the above-mentioned heat treatment temperature is maintained after it is reached. The heat treatment time may be shortened when the heat treatment temperature is high, and may be lengthened when the heat treatment temperature is low. By controlling the heat treatment time within the above range, it is possible to prevent cracks and fractures from occurring.

[0054] (2nd process) In the second step, the preheated metal substrate is heat-treated under a low oxygen partial pressure. In the second step, the heat treatment can be performed using, for example, a known electric furnace, and the same heating furnace as in the first step or a different heating furnace from the first step can be used.

[0055] "Under a low oxygen partial pressure" means that the heat treatment is performed in a gas having an oxygen partial pressure sufficiently lower than that of air. The gas may be, for example, air or oxygen gas. The gas may be composed of oxygen alone or may contain oxygen and an inert gas such as N2 or Ar. However, the gas is preferably composed of oxygen alone or oxygen and an inert gas.

[0056] The oxygen partial pressure during the second step is, for example, 1.0 × 10 -7 atm~1.0×10 -15 atm, preferably 1.0 × 10 -7 atm~1.0×10 -10 It is an ATM.

[0057] The oxygen partial pressure can be controlled by a known method, for example, by supplying air and an inert gas into the heating furnace and adjusting the amount of air and / or inert gas supplied based on the measured oxygen partial pressure in the heating furnace using an oxygen partial pressure controller.

[0058] The heat treatment temperature in the second step is, for example, 750°C to 950°C, preferably 780°C to 930°C, and more preferably 870°C to 930°C, when a preheated titanium substrate is heat treated.

[0059] The heat treatment temperature in the second step is the maximum temperature in the second step, and it is preferable that the temperature is not maintained at the heat treatment temperature. For example, in the second step, heating is performed at a predetermined temperature increase rate until the maximum temperature is reached, and after the maximum temperature is reached, preferably immediately after the maximum temperature is reached, the heat is removed at a predetermined temperature decrease rate. The temperature increase rate in the second step is, for example, 10°C / min, and the temperature decrease rate is, for example, 3°C / min to 5°C / min.

[0060] In the heat treatment of the second step, after the maximum temperature is reached, the maximum temperature may be maintained for a certain period of time, for example, within 15 hours, and preferably within 10 hours.

[0061] Figure 8 is a diagram showing an example of the change in composition inside the sample during the second step. After the first step, the surface of the metal substrate becomes a rutile dioxide. By performing the second step, titanium elements and titanium ions from the titanium substrate diffuse outward, forming Magneli phase titanium oxide from the inside of the sample. When the second step is completed, the metal oxide layer is composed of Magneli phase titanium oxide.

[0062] By controlling the oxygen partial pressure range and heat treatment temperature in the second step within the above ranges, it is possible to control the rate at which oxygen penetrates from the outside and the rate at which the outward-diffusing titanium element and its ions react with the oxygen taken inside, thereby forming a metal oxide layer composed of Magneli phase titanium oxide.

[0063] By carrying out the second step, it is possible to control the rate at which titanium ions and titanium elements in the titanium substrate outwardly diffuse, the rate at which oxygen penetrates into the metal oxide layer from the outside, and the rate at which the oxygen penetrated from the outside progresses inwardly, thereby forming a metal oxide layer composed of Magneli phase titanium oxide on the metal layer. Note that, because oxygen is being taken in from the outside and the outward diffusion of titanium elements in the metal layer continues during the second step, the thickness of the metal oxide layer after the second step is thicker than the thickness of the metal oxide layer immediately after the first step.

[0064] Furthermore, by adjusting the heat treatment temperature and time in the first step, and the oxygen partial pressure, heat treatment temperature and time in the second step, it is possible to adjust the thickness of the metal oxide layer composed of Magneli phase titanium oxide and the composition of Magneli phase titanium oxide in the formed metal oxide layer.

[0065] The method for producing a laminate according to this embodiment allows for the safe and easy production of a laminate containing Magneli-phase titanium oxide. The method for producing a metal oxide according to this embodiment allows for the production of a desired laminate containing Magneli-phase titanium oxide by controlling heat treatment conditions such as temperature and oxygen partial pressure. For example, the thickness and chemical composition ratio of the metal oxide layer can be precisely controlled.

[0066] The laminate manufacturing method according to this embodiment can be implemented using substrates with complex shapes, and flexible oxide semiconductors of any shape can also be produced. The metal oxide layer may be peeled off from the laminate manufactured by the laminate manufacturing method according to this embodiment and used independently. When using the metal oxide layer independently, it can be peeled off from the metal substrate of the laminate by, for example, peeling it off with tweezers or by dissolving only the metal substrate using a concentrated acid solution such as aqua regia. It is also possible to form a laminate composed solely of the Magneli phase, or a layered material composed solely of the Magneli phase (Magneli phase sheet), by using a thin metal substrate of 3 μm or less as a starting material.

[0067] 5 to 7 are manufactured by the same method as the manufacturing method of the laminate according to the above embodiment. In this case, by carrying out the second step under an appropriate oxygen partial pressure, a metal oxide layer consisting of two regions or a metal oxide layer consisting of one region can be formed. [Example]

[0068] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0069] [Example 1] First, a titanium substrate having a thickness of 5 μm was prepared. The titanium substrate used in Example 1 was composed of 99.9 mass % titanium and the remaining 0.1 mass % elements other than titanium.

[0070] Next, in the first step, the titanium substrate was placed in an electric furnace and preheated in an air atmosphere to prepare an intermediate sample. The temperature increase rate for preheating the titanium substrate was approximately 10°C / min, the heat treatment temperature was 700°C, and the heat treatment time was 3 hours. After the heat treatment, the substrate was cooled in the furnace (cooling at a rate of approximately 5°C / min).

[0071] Next, in the second step, the intermediate sample was placed in an electric furnace and heat-treated in a gas with an oxygen partial pressure sufficiently lower than that of air. In addition to oxygen gas, argon gas was used as a process gas. The heat treatment was performed at a heat treatment temperature of 900°C, for a heat treatment time of 0 minutes, and with an oxygen partial pressure of 1.0 x 10 -10 The heat treatment was carried out at a pressure of 10 ...

[0072] [Example 2] The oxygen partial pressure in the second step is 1.0 x 10 -7 A sample was prepared in the same manner as in Example 1, except that the pressure was changed to atm.

[0073] [Example 3] The samples were prepared in the same manner as in Example 1, except that the maximum temperature in the second step was changed to 800°C and the maximum temperature was maintained for 10 hours. That is, the heating rate and furnace cooling rate during the heat treatment were the same as in Example 1.

[0074] [Example 4] A sample was prepared in the same manner as in Example 1, except that the heat treatment temperature in the second step was changed to 800° C. and the maximum temperature was maintained for 5 hours.

[0075] [Example 5] A sample was prepared in the same manner as in Example 1, except that the heat treatment temperature in the second step was changed to 800°C.

[0076] [Comparative Example 1] A sample was prepared in the same manner as in Example 1, except that the second step was not carried out.

[0077] Comparative Example 2 The oxygen partial pressure in the second step is 1.0 x 10 -5 A sample was prepared in the same manner as in Example 1, except that the pressure was changed to atm.

[0078] Comparative Example 3 A sample was prepared in the same manner as in Example 1, except that the second step was carried out in an atmospheric pressure atmosphere.

[0079] Comparative Example 4 The heat treatment temperature in the second step was changed to 1000°C, and the oxygen partial pressure was changed to 1.0×10 -20 A sample was prepared in the same manner as in Example 1, except that the pressure was changed to atm.

[0080] Comparative Example 5 A sample was prepared in the same manner as in Example 1, except that the maximum temperature in the second step was changed to 1000°C.

[0081] Comparative Example 6 The maximum temperature in the second process was changed to 1000°C, and the oxygen partial pressure was increased to 1.0×10 -5 A sample was prepared in the same manner as in Example 1, except that the pressure was changed to atm.

[0082] Comparative Example 7 The oxygen partial pressure in the second step is 1.0 x 10 -5 A sample was prepared in the same manner as in Example 1, except that the pressure was changed to 1000 kJ / cm 2 atm and the maximum temperature was maintained for 5 hours.

[0083] [Comparative Example 8] The maximum temperature in the second step was changed to 800°C, and the maximum temperature was maintained for 10 hours. The oxygen partial pressure was also increased to 1.0×10 -5 The pressure was changed to atm, and a sample was prepared in the same manner as in Example 1.

[0084] Comparative Example 9 The maximum temperature in the second step was changed to 800°C, and the oxygen partial pressure was increased to 1.0×10 -5 A sample was prepared in the same manner as in Example 1, except that the pressure was changed to atm.

[0085] [Comparative Example 10] The maximum temperature in the second step was changed to 900°C, and the oxygen partial pressure was increased to 1.0×10 -5A sample was prepared in the same manner as in Example 1, except that the pressure was changed to atm.

[0086] [Comparative Example 11] The oxygen partial pressure in the second step is 1.0 x 10 -5 A sample was prepared in the same manner as in Example 1, except that the pressure was changed to 1000 kJ / cm 2 atm and the maximum temperature was maintained for 3 hours.

[0087] The sample preparation conditions after the first step in Examples 1 to 5 and Comparative Examples 1 to 11 are summarized in Table 1. In Table 1, conditions under which a heat treatment was performed after a step corresponding to the first step are indicated by ◯, and conditions under which a heat treatment was not performed after a step corresponding to the first step are indicated by ×.

[0088] [Table 1]

[0089] (Sample evaluation) The samples prepared in Examples 1 to 5 and Comparative Examples 1 to 11 were measured and analyzed by the following methods.

[0090] (XRD measurement, thin film GI-XRD measurement) First, an arbitrary cross section of the sample was cut out, and XRD and thin-film GI-XRD measurements were performed. XRD measurements were performed using a fully automated multipurpose X-ray diffractometer (Rigaku Corporation, model Utima IV) under the following conditions: CuKα source, 40 kV tube voltage, 40 mA tube current, and an incidence angle of 20° to 80°. Thin-film GI-XRD measurements were performed using a fully automated multipurpose X-ray diffractometer (Rigaku Corporation, model SmartLab) under the following conditions: CuKα source, 45 kV tube voltage, 200 mA tube current, and an incidence angle of 20° to 60°. Figure 9 shows the results of thin-film GI-XRD measurements performed on the sample of Example 2. Figure 10 shows the results of thin-film GI-XRD measurements performed on the samples of Examples 3 to 5. Figure 11 shows the results of XRD measurements performed on the samples of Comparative Examples 1 to 3. Fig. 12 shows the results of XRD measurement on the samples of Comparative Examples 4 to 6. Fig. 13 shows the results of XRD measurement on the sample of Comparative Example 7. Fig. 14 shows the results of thin-film GI-XRD measurement on the samples of Comparative Examples 8 and 9. Fig. 15 shows the results of thin-film GI-XRD measurement on the sample of Comparative Example 10. Fig. 16 shows the results of XRD measurement on the sample of Comparative Example 11. Note that "I" in Figs. 12 to 16 indicates that the first step is the same heat treatment step as the first step in Example 1.

[0091] 2, 9, and 10, it was confirmed that the laminates of Examples 1 to 5 had a metal oxide layer made of Magneli-phase titanium oxide in the surface layer portion. Of these, it was confirmed that the main phase in the surface portion of Examples 1, 2, and 4 was Ti4O7, which has the highest electrical conductivity among Magneli-phase titanium oxides.

[0092] On the other hand, it was confirmed that the laminates of Comparative Examples 1 to 11 did not have a metal oxide layer made of Magneli-phase titanium oxide in the surface layer portion.

[0093] When only the first step was carried out without carrying out the second step as in Comparative Example 1, it was confirmed that a metal oxide layer made of rutile-type TiO2 was formed on the surface layer portion.

[0094] When the oxygen partial pressure in the heat treatment of the second step is high, as in Comparative Example 2, Magneli phase titanium oxide is formed inside the laminate and near the interface with the metal layer, but rutile-type TiO2 is formed in the surface layer, and a metal oxide layer consisting of Magneli phase titanium oxide is not formed.

[0095] When the heat treatment was also carried out under atmospheric pressure in the step following the first step as in Comparative Example 3, no Magneli phase titanium oxide was formed.

[0096] When the heat treatment in the second step was carried out at a high temperature as in Comparative Examples 4 to 6, excess oxygen was taken in, and Ti2O3, TiO, etc. were formed in the surface layer portion.

[0097] When the oxygen partial pressure was high in the second step as in Comparative Examples 7, 10, and 11, excessive oxygen was taken in, resulting in the formation of rutile-type TiO2.

[0098] When the oxygen partial pressure was high in the second step as in Comparative Examples 8 and 9, the surface was excessively oxidized even if the heat treatment temperature was low, and Magneli phase titanium oxide could not be obtained.

[0099] When the oxygen partial pressure was high and the heat treatment temperature in the second step was high, as in Comparative Examples 10 and 11, Magneli phase titanium oxide was formed, but rutile-type TiO2 was also contained, and a metal oxide layer consisting of Magneli phase titanium oxide was not formed in the surface layer. In Comparative Examples 10 and 11, the heat treatment temperature was higher than in Comparative Examples 8 and 9, which promoted the outward diffusion of titanium elements and their ions in the metal layer, resulting in the formation of Magneli phase oxide. On the other hand, the high oxygen partial pressure caused excessive oxygen to be taken in from the outside, resulting in the surface layer becoming rutile-type TiO2, and a laminate with a surface layer consisting of Magneli phase oxide was not obtained.

[0100] (Cross-section observation) Next, the cross section of the sample of Example 1 was observed using a TEM. TEM images showing cross sections of the sample of Example 1 at different positions are shown in Figures 3 and 17. Observation of the TEM images in Figures 3 and 17 confirmed that the sample of Example 1 had a void V in a direction intersecting the stacking direction, two layers sandwiching the void V, and the surface layer of the two layers had multiple crystal grains ranging from several hundred nanometers to approximately 1.0 μm. Thin-film GI-XRD measurement confirmed that the surface layer of the sample was a metal oxide layer composed of Magneli-phase titanium oxide. Next, the distance in the stacking direction from the surface of the outermost layer of the metal oxide layer to the void was measured at 10 locations in the in-plane direction of the stack in the TEM image, and the average value was calculated to determine the average thickness of the metal oxide layer. The average thickness of the metal oxide layer was 3.2 μm.

[0101] As in Example 1, the cross section of the sample of Example 2 was observed by TEM. A TEM image showing the cross section of the sample of Example 2 is shown in FIG. 18. Observation of the TEM image in FIG. 18 confirmed that the sample of Example 2 had a void V in a direction intersecting the stacking direction, had two layers sandwiching the void V, and that the surface layer of the two layers was composed of crystal grains ranging from several hundred nm to approximately 1.0 μm. Thin-film GI-XRD measurement confirmed that the surface layer of the sample was a metal oxide layer composed of Magneli-phase titanium oxide. The average thickness of the metal oxide layer was 2.9 μm.

[0102] As in Example 1, the cross section of the sample of Comparative Example 1 was observed by TEM. Figure 19 shows a TEM image showing the cross section of the sample of Comparative Example 1. From the TEM image in Figure 19, it was confirmed that the sample of Comparative Example 1 has a void V in a direction intersecting the stacking direction, has two layers sandwiching the void V, and that the surface layer of the two layers is composed of crystal grains of several hundred nanometers. XRD measurement confirmed that the layer provided on the metal layer of the sample is composed of TiO2.

[0103] As in Example 1, the cross section of the sample of Comparative Example 2 was observed by TEM. Fig. 20 shows a TEM image showing the cross section of the sample of Comparative Example 2. From the TEM image in Fig. 20, it was confirmed that the sample of Comparative Example 2 has a void V in a direction intersecting the stacking direction, has two layers sandwiching the void V, and that the surface layer of the two layers is composed of crystal grains of several hundred nm to approximately 1.0 µm. XRD measurement confirmed that the layer provided on the metal layer of the sample is composed of rutile-type TiO2 and Magneli-phase titanium oxide.

[0104] (electron diffraction) First, electron beam diffraction was performed on the sample of Example 1. The electron beam diffraction was performed on the region R in FIG. a , R b and R c and region R in Figure 17 d The experiment was carried out on grains of 1000 μm.

[0105] area R c In the electron diffraction pattern of the sample, the transmitted wave is transmitted through the (000) and (121) planes, which correspond to the rutile TiO2 planes. R-TiO2 The number of spots included between these two points is 3 and 4, and the line segment connecting these two points is divided into 4 and 5 equal parts, respectively. c It was confirmed that the Magneli phase titanium oxide located in the region is a mixed crystal of Ti4O7 and Ti5O9. area R b In the electron diffraction pattern of the (000) and (121) TiO2 planes, R-TiO2 The number of spots included between these points is three, and the line segment connecting the two points is divided into four equal parts. Also, the electron diffraction image is mirror symmetric with respect to the line connecting the (000) and (120) spots. Therefore, the region R b The Magneli phase titanium oxide located at was confirmed to be a (1-20) twin of Ti4O7. area R a In the electron diffraction pattern of the sample, the transmitted wave is transmitted through the (000) and (121) planes, which correspond to the rutile TiO2 planes. R-TiO2The number of spots included between and is two, and the line segment connecting the two points is divided into three equal parts. a The Magneli phase titanium oxide located at was identified as Ti3O5.

[0106] In Example 1, the region R in FIG. d An enlarged view and electron diffraction image of the area R are shown in Figure 21. d From the electron diffraction pattern, the transmitted wave is transmitted through the (000) and (121) planes corresponding to the rutile TiO2 planes. R-TiO2 It was confirmed that there was a superlattice reflection between the (000) and (121) planes, which correspond to the rutile TiO2 planes. R-TiO2 The number of spots included between and is three, and the line segment connecting the two spots is divided into four equal parts. d The Magneli phase titanium oxide located in the region was confirmed to be Ti4O7. Therefore, it was confirmed that planar defects exist periodically in the metal oxide layer.

[0107] Next, electron beam diffraction was performed on the sample of Example 2. The electron beam diffraction was performed in the region R in FIG. e and R f The grain size was measured in the region R. e In the electron diffraction pattern of (000) and (121) R-TiO2 The number of spots included between and is 5, and the line segment connecting the two spots is divided into 6 equal parts. e is TiO 11 It was confirmed that the area R f In the electron diffraction pattern of (000) and (121) R-TiO2 The number of spots included between and is three, and the line segment connecting the two spots is divided into four equal parts. f was confirmed to be Ti4O7.

[0108] Next, electron beam diffraction was performed on the sample of Comparative Example 1. An enlarged view and an electron beam diffraction image of the vicinity of region R1 in Figure 19 are shown in Figure 22. From the electron beam diffraction image of region R1, it was confirmed that the crystal grains in region R1 were composed of rutile-type TiO2.

[0109] Next, electron beam diffraction was performed on the sample of Comparative Example 2. Electron beam diffraction was performed on regions R2, R3, and R4 in FIG. 20. From the electron beam diffraction image of region R2, it was found that the crystal grains in region R2 were composed of TiO2 (101) Rutile It was confirmed that the region R is composed of twin crystals. 3、 In the electron diffraction image of R4, the transmitted wave passes through the (000) and (121) planes corresponding to the rutile TiO2 planes. R-TiO2 The number of spots included between and is three, and the line segment connecting the two spots is divided into four equal parts. 3、 R4 was confirmed to be a (1-20) twin crystal of Ti4O7. Furthermore, the electron beam diffraction results for Comparative Example 2 confirmed that Magneli phase titanium oxide is formed by outward diffusion of titanium element or ions when the second step is performed under a low oxygen partial pressure on a laminate structure having titanium dioxide on the surface, as shown in Figure 8. In a laminate in which TiO2 remains as in Comparative Example 2, a laminate having a metal oxide layer made of Magneli phase titanium oxide provided on the surface layer of a metal layer cannot be obtained.

[0110] (HAADF-STEM observation) Region R of the sample of Example 1 B The atomic arrangement of the cross section was confirmed using a high-angle annular dark-field scanning transmission microscope (HAADF-STEM) (instrument name: Cs-correced Titan3 microscope, manufactured by Fisher Scientific International Inc.). Figure 23 shows an image (left) observed using HAADF-STEM and an enlarged image of the area framed in the left image, which has been further Fourier filtered using Digital Micrograph software manufactured by Gatan. As a result of observation using HAADF-STEM, the atomic arrangement of the region R BThe electron beam was identified as Ti4O7. Fourier filtering was performed at an accelerating voltage of 300 kV, an electron beam diameter of approximately 0.08 nm, and a convergence angle of 17.8 mrad.

[0111] Figure 24 shows the contrast intensity along the XY axis of the HAADF-STEM image in Figure 23 and a schematic diagram of the atomic arrangement calculated based on the contrast intensity. The bright spots in the HAADF-STEM image were confirmed to be Ti atomic columns based on their contrast intensity (Z = 22). The contrast intensity of spots with lower contrast intensity than the Ti atomic columns was (Z = 8), where Z indicates the atomic number. In this crystal grain, the Ti atomic columns are arranged in a periodic pattern of four, which is consistent with the atomic arrangement of Ti4O7 reported in a previous study (Y. Le Page, M. Marezio, Journal Solid State Chemistry, Volume 53, (1984) pp. 13-21). The low-brightness spots around the Ti atomic columns in Figure 23 are presumably due to O atomic columns.

[0112] (light absorption efficiency) Next, the reflectance was measured to determine the light absorption efficiency of the samples of Example 1, Comparative Example 1, and Comparative Example 2, and the rutile-type white TiO powder. The reflectance was measured in the range of 300 nm to 1500 nm using an ultraviolet-visible-near-infrared spectrophotometer (device name: UV-3600, manufactured by Shimadzu Corporation).

[0113] FIG. 25 shows the reflectance (%) versus wavelength for the samples of Example 1, Comparative Example 1, and Comparative Example 2, and the rutile-type white TiO powder. The sample of Example 1 exhibited low reflectance not only in the ultraviolet light region but also in the visible light region and near-infrared light region. Specifically, the sample of Example 1 exhibited a reflectance of 25% or less in the range of approximately 400 nm to approximately 1800 nm. Furthermore, the sample of Example 1 exhibited a lower reflectance than Comparative Example 1 in the range of approximately 300 nm to approximately 1800 nm, and a lower reflectance than Comparative Example 2 in the range of approximately 350 nm to approximately 1250 nm. In particular, the sample of Example 1 exhibited a lower reflectance than both Comparative Examples 1 and 2 in the visible light region, which is the range of approximately 360 nm to approximately 830 nm. Therefore, it was found that the sample of Example 1 exhibited excellent light absorption efficiency in the visible light region and near-infrared light region.

[0114] (resistance measurement) Next, using a DC stabilized power supply (model number AD-8735D, manufactured by A&D Corporation), the four-terminal method was used to measure the resistance values ​​in the plane direction and thickness direction of the constituent phases of the samples of Example 1, Comparative Example 1, and Comparative Example 2. When measuring the resistance value in the thickness direction, the metal oxide layer was not peeled off from the metal layer of the sample, and measurements were taken on the front and back of the sample.

[0115] [Table 2]

[0116] As shown in Table 2, the resistance value in the plane direction and the resistance value in the thickness direction of the constituent phase (rutile-type TiO2) of Comparative Example 1 were within the measurement limit (3 × 10 4 Ω) or more. 2、 The resistance value in the plane direction of the TiO and TiO was 0.56 Ω, and the resistance value in the thickness direction was 1.93 Ω. On the other hand, the resistance value in the plane direction of the constituent phases of Example 1 (Magneli phase titanium oxides (TiO and TiO)) was 0.17 Ω, and the resistance value in the thickness direction was 0.04 Ω. Compared with the resistance values ​​of Comparative Examples 1 and 2, it was found that the resistance values ​​in both the plane direction and the thickness direction were lower, and in particular the resistance value in the thickness direction was significantly lower.

[0117] [Comparative Example 12] A 1 cm x 1 cm x 5 μm titanium substrate was heated in air at a constant heating rate and subjected to thermogravimetry (TG). Thermogravimetry was performed using a thermogravimetric differential calorimeter (NETCH, model STA2500) at a heating rate of 10°C / min. Figure 26 shows the thermogravimetric curve (TG curve) of the sample of Comparative Example 12. The TG curve of the sample of Comparative Example 12 confirmed that, in the temperature range of approximately 600°C or higher, oxidation of the metal substrate progressed as the temperature increased, and that the gradient of weight change with temperature increased significantly at temperatures of 700°C, 800°C, and 900°C.

[0118] Figure 27 shows photographs of the sample in states a (room temperature), b (700°C), and c (1000°C) in Figure 26, as well as the XRD measurement results for state c. As can be seen from the photographs, the surface of the sample in state c has peeled off. The XRD measurement results also confirm that the surface of the sample in state c is rutile-type TiO2. Figure 27 shows that the surface peels off if the temperature in the first step is not controlled within a specified range. [Industrial Applicability]

[0119] The laminate having a metal oxide layer made of Magneli-phase titanium oxide according to the above embodiment can effectively utilize the visible light range and can accommodate complex shapes and arbitrary dimensions. Therefore, the laminate according to the above embodiment is expected to be used as a photocatalytic electrode or an optical sensor. The metal oxide layer of the laminate according to the above embodiment has high electrical conductivity and can have high oxidation resistance, so it is expected to be used as a fuel cell. [Explanation of symbols]

[0120] 10: metal layer, 20: metal oxide layer, 100, 101, 102, 103: laminate, V: void

Claims

1. a metal layer; and a metal oxide layer formed on a surface portion of the metal layer and composed of Magneli phase titanium oxide, The Magneli phase titanium oxide has the composition formula Ti ｎ O ２ｎ－１ (n≧3), the metal oxide layer has two or three regions having different compositions in the stacking direction; A laminate, wherein the value of n in the composition formula of one of the two or three regions is larger as the region is more distant from the metal layer.

2. 2. The laminate according to claim 1, wherein the metal oxide layer made of the Magneli phase titanium oxide has an average thickness of 2 μm or more.

3. the metal oxide layer has two regions having different compositions in a stacking direction, 3. The laminate according to claim 1, wherein the region away from the metal layer has a larger value of n in the composition formula than the region on the metal layer side.

4. Any of the two or three regions is Ti ４ O ７ The laminate of claim 1 , comprising:

5. 5. The laminate according to claim 1, wherein a void is present between the metal oxide layer made of Magneli phase titanium oxide and the metal layer.

6. A method for producing the laminate according to any one of claims 1 to 5, A first step of preheating a titanium substrate in the atmosphere at a temperature lower than that of a second step to be performed later; a second step of heat-treating the preheated titanium substrate under a low oxygen partial pressure of 1.0×10 −7 atm or less at a temperature higher than that of the first step.

7. In the first step, the titanium substrate is preheated at 650°C to 750°C, In the second step, the preheated titanium substrate is heated to a temperature of 750°C to 950°C and an oxygen partial pressure of 1.0 x 10 －７ The method for producing a laminate according to claim 6, wherein the heat treatment is carried out at a temperature equal to or lower than atm.

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