METHOD FOR PRODUCING Y2Ti2O5S2

Abstract

To provide a method for safely producing large amounts of Y2Ti2O5S2 without using toxic hydrogen sulfide gas.SOLUTION: A method for producing Y2Ti2O5S2 comprising accommodating sulfur, Y2O3, TiO2, Y2S3 and at least one flux selected from halides of alkali metals in a lower part of a reaction vessel having an opening at an upper end, then holding the opening of the reaction vessel upward, closing the opening of the reaction vessel, heating the lower part of the reaction vessel without heating an upper part of the reaction vessel to vaporize sulfur and react the sulfur with Y2O3, TiO2, and Y2S3 to obtain Y2Ti2O5S2, liquefying the vaporized sulfur at the upper part of the reaction vessel to cause the liquefied sulfur to descend, and repeating vaporization of the liquefied sulfur again at the heated lower part of the reaction vessel, while reacting the vaporized sulfur with Y2O3, TiO2, and Y2S3 to obtain Y2Ti2O5S2.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing Y2Ti2O5S2 used as a photocatalyst.

Background Art

[0002] In recent years, from the viewpoints of suppressing global warming and eliminating dependence on depleting fossil resources, technologies related to hydrogen production by photocatalysts that can generate hydrogen from water using only solar energy have attracted attention, and the social demand for them has been increasing.

[0003] The water decomposition reaction by photocatalysts has been widely studied for a long time. For example, the water decomposition reaction on photocatalyst particles in an acidic aqueous solution is estimated as follows. H2O + 2h + →1 / 2O2 + 2H + 2H + + 2e - →H2

[0004] As photocatalyst materials, those obtained by doping TiO2 with transition metals such as Cr and V have been proposed in the past. In recent years, Y2Ti2O5S2 has been found as a photocatalyst having excellent photocatalytic activity.

[0005] As methods for producing Y2Ti2O5S2, a vacuum sealed tube method and a hydrogen sulfide method have already been applied (Patent Documents 1 to 4). The vacuum sealed tube method is a method in which powders of Y2O3, TiO2, and Y2S3 are weighed so as to form Y2Ti2O5S2 in a stoichiometric ratio, and further, sulfur (S) is added. Then, these mixtures are put into a quartz tube and vacuum sealed, and the mixtures are heated at a temperature of about 750 °C for about 96 hours to obtain a compound of Y2Ti2O5S2. In addition, the hydrogen sulfide method involves placing a mixture of Y2O3, TiO2, and Y2S3 powder, which serves as the raw material, in the central part of a quartz tube in a stoichiometric ratio to form Y2Ti2O5S2, flowing hydrogen sulfide gas, and heating it at around 1100°C for about 3 hours to obtain Y2Ti2O5S2. In this method, since synthesis is carried out while flowing hydrogen sulfide gas, the remaining oxygen becomes water (H2O), and there is an advantage in that the influence of oxygen during synthesis can be reduced. In addition, when synthesizing Y2Ti2O5S2 by the above method, it is sometimes synthesized by mixing a halide that serves as a flux with the raw material mixture and then using the above method.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the vacuum sealed tube method, since the quartz tube must be vacuum sealed, a large amount of synthesis cannot be carried out at once, and there is a risk of rupture due to an increase in internal pressure. In addition, in the hydrogen sulfide method, although large-scale synthesis is possible, since toxic hydrogen sulfide gas is used, there are problems with its safety. On the other hand, in the synthesis of compounds using sulfur as a raw material, a method using sulfur vapor has also been proposed (Patent Document 5), but there are no reported examples of synthesizing Y2Ti2O5S2. The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for safely producing a large amount of Y2Ti2O5S2 without using toxic hydrogen sulfide gas.

Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the present inventors placed at least one flux selected from sulfur, Y2O3, TiO2, Y2S3, and a halide of an alkali metal in the lower part of a reaction vessel having an opening at the upper end. After that, the opening of the reaction vessel is held upward, the opening of the reaction vessel is closed, and the lower part of the reaction vessel is heated without heating the upper part of the reaction vessel, thereby vaporizing sulfur and reacting it with Y2O3, TiO2, and Y2S3 to obtain Y2Ti2O5S2. At the same time, the vaporized sulfur is liquefied and dropped at the upper part of the reaction vessel, and the liquefied sulfur is repeatedly vaporized again at the heated lower part of the reaction vessel. By reacting the vaporized sulfur with Y2O3, TiO2, and Y2S3 to obtain Y2Ti2O5S2, it was found that a large amount of Y2Ti2O5S2 can be safely produced without using toxic hydrogen sulfide gas, and the present invention was thus completed.

[0009] That is, the present invention is 1. After placing at least one flux selected from sulfur, Y2O3, TiO2, Y2S3, and a halide of an alkali metal in the lower part of a reaction vessel having an opening at the upper end, the opening of the reaction vessel is held upward, the opening of the reaction vessel is closed, and the lower part of the reaction vessel is heated without heating the upper part of the reaction vessel, thereby vaporizing sulfur and reacting it with Y2O3, TiO2, and Y2S3 to obtain Y2Ti2O5S2, and a method for producing Y2Ti2O5S2 including a step of reacting vaporized sulfur with Y2O3, TiO2, and Y2S3 to obtain Y2Ti2O5S2 while repeatedly liquefying and dropping the vaporized sulfur at the upper part of the reaction vessel and vaporizing the liquefied sulfur again at the heated lower part of the reaction vessel. 2. By heating the lower part of the reaction vessel and maintaining the upper part of the reaction vessel at a temperature below the boiling point of sulfur, the vaporized sulfur is cooled and liquefied at the upper part of the reaction vessel, and the liquefied sulfur naturally descends to the lower part of the reaction vessel, the production method according to claim 1, 3. The production method according to claim 1 or 2, wherein the heating temperature is 600 to 1100 °C, 4. After sulfur is contained in the lower part of the reaction vessel, Y2O3, TiO2, Y2S3 and a flux are mixed and put into a raw material storage container, and this raw material storage container is housed in the reaction vessel to carry out the reaction according to any one of claims 1 to 3, 5. The production method according to any one of claims 1 to 4, wherein the flux is at least one selected from NaCl, NaBr, NaI, KCl, KBr, KI, CsCl, CsBr and CsI is provided.

Advantages of the Invention

[0010] According to the present invention, without using hydrogen sulfide gas, a large amount of Y2Ti2O5S2 can be synthesized more simply and safely at one time and in a shorter time than before.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0012] The manufacturing method of the present invention involves the following steps: after accommodating at least one flux selected from sulfur, Y2O3, TiO2, Y2S3, and halides of alkali metals in the lower part of a reaction vessel having an opening at the upper end, holding the opening of the reaction vessel upward, closing the opening of the reaction vessel, and heating the lower part of the reaction vessel while not heating the upper part of the reaction vessel. By doing so, sulfur is vaporized and reacted with Y2O3, TiO2, and Y2S3 to obtain Y2Ti2O5S2. At the same time, the vaporized sulfur is liquefied and dropped at the upper part of the reaction vessel, and the liquefied sulfur is vaporized again at the heated lower part of the reaction vessel. While repeating this process, the vaporized sulfur is reacted with Y2O3, TiO2, and Y2S3 to obtain Y2Ti2O5S2.

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic diagram of a reaction apparatus 10 used in an embodiment of the manufacturing method of the present invention. (A) shows the state before heating, and (B) shows the state during the heating reaction.

[0014] In this embodiment, first, as shown in FIG. 1(A), sulfur 12, Y2O3, TiO2, Y2S3 (hereinafter, these may be collectively referred to as synthetic raw materials other than sulfur in some cases) 13, and a flux 14 are placed in the lower part of the reaction vessel 11.

[0015] [Sulfur] The form of sulfur used in the present invention is not particularly limited, and examples include powder form, lump form, etc. Any of crystalline, amorphous, etc. can be used, but from the perspective of reactivity, powder is preferred. The amount of sulfur used in the present invention is not particularly limited either. However, the ratio of Y2O3 to sulfur (Y2O3 / S) is preferably 10 / 1 to 1 / 1000, more preferably 1 / 1 to 1 / 100, and even more preferably 1 / 30 to 1 / 100 in terms of molar ratio. If the amount of sulfur is too large, it may take time to recover the reactants. If it is too small, the sulfidation reaction may not proceed.

[0016] [Y2O3, TiO2, Y2S3] The forms of Y2O3, TiO2, and Y2S3 are not particularly limited, and examples include powder form, massive form, etc. From the perspective of reactivity, powder is preferred. The usage amounts of Y2O3, TiO2, and Y2S3 are not particularly limited either, but the ratio of these is preferably 1 / 1 / 1 to 1 / 10 / 5, more preferably 1 / 1 / 1 to 1 / 8 / 3 in terms of molar ratio for Y2O3 / TiO2 / Y2S3.

[0017] [Flux] In the present invention, in order to obtain Y2Ti2O5S2 alone or to increase its amount, it is necessary to add a flux substance together with the raw materials Y2O3, TiO2, and Y2S3. The flux is not particularly limited, and those commonly used in the synthesis of Y2Ti2O5S2 can be used. For example, alkali metal halides and the like can be mentioned. Specific examples thereof include NaCl, NaBr, NaI, KCl, KBr, KI, RbCl, RbBr, RbI, CsF, CsCl, CsBr, CsI, etc. Among these, NaCl, NaBr, NaI, KCl, KBr, KI, CsCl, CsBr, CsI are preferred. These can be used alone or in combination of two or more.

[0018] The form of the flux is not particularly limited, and examples include powder form, massive form, etc. From the perspective of reactivity, powder is preferred. The addition amount of the flux is not particularly limited, but preferably 1 to 300% by mass, more preferably 1 to 200% by mass, still more preferably 3 to 150% by mass, and particularly preferably 5 to 150% by mass of the total amount of the raw materials Y2O3, TiO2, and Y2S3. If it exceeds 300% by mass, Y2Ti2O7 may be the main component as the product. If it is less than 1% by mass, the raw materials may not completely dissolve in the flux during the reaction heating, resulting in unreacted raw materials.

[0019] Sulfur, Y2O3, TiO2, Y2S3, and the flux can all be mixed and then placed in a reaction vessel. The mixing method is not particularly limited and may be carried out by a method usually used for the synthesis of Y2Ti2O5S2. However, in order to avoid the generation of impurities such as oxide phases during the synthesis reaction, the mixing is preferably carried out in an inert gas atmosphere such as nitrogen or argon. In addition, these raw materials may be separately contained in a reaction vessel. For example, only sulfur may be contained first, and then a mixture of Y2O3, TiO2, Y2S3 and a flux may be contained. In this case, since sulfur and the product do not mix, the product can be easily recovered, and sulfur can be reused, which is preferable.

[0020] [Reaction vessel] As the reaction vessel, for example, as shown in FIGS. 1(A) and 1(B), a vessel having an opening at the upper end and formed in a bottomed cylindrical shape can be used. In the present invention, when carrying out the reaction, for example, the lower part of the reaction vessel is placed inside a heating device such as a heat treatment furnace, and the reaction vessel is installed so that the upper part of the reaction vessel is placed outside the heating device. While maintaining the temperature below the boiling point of sulfur without heating the upper part of the reaction vessel, by heating the lower part of the reaction vessel, sulfur in the lower part of the reaction vessel is heated and vaporized, and the vaporized sulfur is naturally cooled and liquefied on the wall surface of the upper part of the reaction vessel or the like. The liquefied sulfur naturally descends from the upper part to the lower part of the reaction vessel along the side wall of the reaction vessel, for example, and is heated in the lower part of the reaction vessel and vaporized again. During heating, in a state where the vaporization and liquefaction of sulfur are repeated, in order to react the vaporized sulfur with Y2O3, TiO2, and Y2S3, the overall size of the reaction vessel is not particularly limited, but it preferably has a height sufficient for the vaporized sulfur to be cooled and liquefied at the upper part of the reaction vessel. The height of the reaction vessel depends on the type of heating device and heating conditions, but for example, 10 to 500 mm is preferable, 15 to 300 mm is more preferable, and 100 to 300 mm is even more preferable.

[0021] In addition, if the diameter (inner diameter) of the reaction vessel is too small, the liquefied sulfur will not easily descend from the upper part to the lower part of the reaction vessel due to capillary action or the like. Therefore, the diameter is preferably, for example, 5 to 500 mm, more preferably 10 to 200 mm, and even more preferably 10 to 100 mm.

[0022] The material of the reaction vessel is not particularly limited, but those having heat resistance and not reacting with sulfur are preferred. Examples include glass such as quartz, borosilicate glass, crystallized glass, and soda-lime glass, and ceramics such as alumina. Among them, quartz is more preferred.

[0023] In this embodiment, a bottomed cylindrical reaction vessel is used. However, the shape of the reaction vessel may have an opening through which the synthesis raw materials can be put in and taken out and can accommodate the synthesis raw materials inside, and as long as the sulfur vaporized at the lower part of the vessel can liquefy at the upper part of the vessel and descend to the lower part. In addition to the bottomed cylindrical shape, for example, a bottomed elliptical cylinder shape, a bottomed square tube shape, a bottomed cylindrical shape with an open upper end and a spherical part at the lower end (round bottom flask shape), a bottomed cylindrical shape with an open upper end and a conical part at the lower end (Erlenmeyer flask shape), a bottomed conical shape with an open upper end, a bottomed square pyramid shape with an open upper end, etc. can also be used. However, from the viewpoint that the liquefied sulfur at the upper part of the vessel easily descends to the lower part, those having a cylindrical or tubular shape are preferred, and the shape of the cross-section perpendicular to the length direction of the cylindrical or tubular part is preferably circular or elliptical.

[0024] In addition, the upper part of the reaction vessel is arranged outside the heating device and is maintained at a temperature below the boiling point of sulfur during the reaction if it is not heated at room temperature (25°C). However, in order to liquefy the vaporized sulfur as quickly as possible, cooling means such as cooling fins may be provided on a part of the upper part of the reaction vessel or the like.

[0025] Next, hold the opening of the reaction vessel 11 upward. For example, as shown in FIGS. 1(A) and (B), place the lower part of the reaction vessel 11 inside the heating device 15 and arrange the upper part of the reaction vessel 11 outside the heating device 15. Close the opening with the stopper 16, supply power to the heating device 15 from a power supply source (not shown), and heat the lower part of the reaction vessel 11 without heating the upper part of the reaction vessel 11. Even if the opening of the reaction vessel is closed and sealed, since sulfur liquefies and the internal pressure does not rise too much, the risk of rupture is lower than in the case of a vacuum. Note that the upper end opening of the reaction vessel may be open without being closed.

[0026] [Heating Conditions] The heating temperature is not particularly limited, but preferably 600 to 1100 °C, more preferably 700 to 1100 °C, even more preferably exceeding 700 °C and not exceeding 1100 °C, and still more preferably 750 to 1000 °C. If it exceeds 1100 °C, the fluxing agent may evaporate and Y2Ti2O7 may be generated. If it is less than 600 °C, the synthesis reaction may not occur. The heating time is also not particularly limited. Although it depends on the total amount of the synthesis raw materials, preferably 5 minutes to 96 hours, more preferably 5 minutes to 10 hours, and still more preferably 5 minutes to 2 hours. If it exceeds 96 hours, since the synthesis reaction has ended, unnecessary heating may be performed. If it is less than 5 minutes, the synthesis reaction may not be completed. The heating device is also not particularly limited and can be appropriately selected and used from conventionally used heat treatment furnaces, etc., according to the reaction vessel.

[0027] By heating the lower part of the reaction vessel 11 in this way, as shown in FIG. 1(B), sulfur vaporizes, and by reacting the vaporized sulfur 17 with the synthesis raw materials 13 other than sulfur, Y2Ti2O5S2 can be obtained. In addition, the vaporized sulfur 17 is not disposed outside the heating device 15 and is not heated, and naturally cools and liquefies on the upper wall surface or the like of the reaction vessel 11 that is maintained at a temperature below the boiling point of sulfur. The liquefied sulfur 18 descends from the upper part to the lower part of the reaction vessel 11, for example, along the side wall of the reaction vessel 11. The sulfur that has liquefied and descended to the lower part of the reaction vessel 11 vaporizes again at the heated lower part of the reaction vessel 11, and the vaporized sulfur reacts with the synthesis raw material 13 other than sulfur. This vaporization and liquefaction are repeated during the heating reaction. Furthermore, the vaporized sulfur also reacts with oxygen in the reaction vessel, thereby suppressing compositional fluctuations due to oxidation during the synthesis reaction.

[0028] In the above embodiment, sulfur, Y2O3, TiO2, Y2S3, and flux are directly placed in the reaction vessel, but the production method of the present invention is not limited to this, and for example, the production methods shown in FIGS. 2(A) and (B) may also be used.

[0029] FIG. 2 shows a schematic diagram of a reaction apparatus 20 used in another embodiment of the present invention, where (A) shows the state before heating and (B) shows the state during the heating reaction. In this method, a synthesis raw material other than sulfur is placed in the raw material storage container 23 for the reaction. By placing the synthesis raw material other than sulfur in the raw material storage container, it is possible to prevent the low-temperature liquefied sulfur from mixing with the synthesis raw material other than sulfur, so that a decrease in the reaction temperature can be suppressed. Here, first, as shown in FIG. 2(A), sulfur 22 is placed in the lower part of the reaction vessel 21. Next, Y2O3, TiO2, Y2S3, and flux, which are synthesis raw materials other than sulfur, are mixed. The mixing method is the same as above. Subsequently, the obtained mixture is placed in the raw material storage container 23, and a lid 24 with low airtightness is placed thereon as necessary, and it is stored on the sulfur 22 placed in the lower part of the reaction vessel 21. The reaction vessel 21 can be the same as the above, but preferably has a size that can accommodate the raw material storage container. Next, hold the opening of the reaction vessel upward. For example, as shown in FIGS. 2(A) and (B), place the lower part of the reaction vessel 21 inside the heating device 25 and place the upper part of the reaction vessel 21 outside the heating device 25. When closing the opening, close the opening with a stopper 26, supply power to the heating device 25 from a power supply source (not shown), and heat the lower part of the reaction vessel 21 without heating the upper part of the reaction vessel 21. The heating method and conditions are the same as above.

[0030] [Raw material storage container] The shape and size of the raw material storage container and the lid are not particularly limited as long as they can be accommodated in the reaction vessel. The material of the raw material storage container is not particularly limited either, but similar to the reaction vessel, those having heat resistance and not reacting with sulfur are preferred. For example, ceramics such as alumina are preferred. After the reaction is completed, it is preferable to perform the synthesis using a raw material storage container from the viewpoints of easy recovery of the obtained Y2Ti2O5S2 and easy separation from the obtained Y2Ti2O5S2 in the case of unreacted sulfur. As the raw material storage container, for example, a ceramic crucible or the like can be used. In this embodiment, a lid is placed on the raw material storage container as needed, but the lid may or may not be present. By using a lid, the volatilization of the flux can be suppressed. However, when using a lid, it is preferable to use a structure with low airtightness so that the reaction is not inhibited.

[0031] By heating the lower part of the reaction vessel 21 as described above, as shown in FIG. 2(B), sulfur vaporizes, and the vaporized sulfur 27 reacts with Y2O3, TiO2, and Y2S3 (not shown) in the raw material storage container 23 to obtain Y2Ti2O5S2. In addition, the vaporized sulfur 27 cools and liquefies on the wall surface of the upper part of the reaction vessel 21 that is disposed outside the heating device 25 and not heated. The liquefied sulfur 28 descends from the upper part to the lower part of the reaction vessel 21, for example, along the side wall of the reaction vessel 21. The sulfur that has liquefied and descended to the lower part of the reaction vessel 21 vaporizes again at the heated lower part of the reaction vessel 21, and the vaporized sulfur reacts with Y2O3, TiO2, and Y2S3 (not shown) in the raw material storage container 23.

[0032] In the present invention, during the synthesis of Y2Ti2O5S2, the phenomenon of vaporization → liquefaction occurs continuously. That is, since sulfur is refluxed in the reaction vessel, sulfur can be reused. In addition, in the present invention, it has been found that the time required for synthesis can also be shortened. Although the reason is unknown, it can be presumed that, compared with the conventional method, sulfur at a high concentration always reacts with the synthesis raw materials Y2O3, TiO2, and Y2S3. Furthermore, in the present invention, no steps such as pretreatment are required, and Y2Ti2O5S2 can be directly synthesized from the raw material powder, and the reaction can be easily carried out.

[0033] In addition, in the above embodiments, when the reaction vessel is installed in the heating device, the opening of the reaction vessel is always held upward. However, as the method for holding the reaction vessel, as long as the opening of the reaction vessel can be held upward and sulfur can be refluxed in the reaction vessel, it is not particularly limited. The reaction vessel may be held such that the vertical direction of the reaction vessel is perpendicular (vertical) to the installation surface, or may be inclined. Also, Y2Ti2O5S2 can be obtained in the same manner whether the upper end opening of the reaction vessel is in an open state or a closed state. When the upper end opening of the reaction vessel is in an open state, it is preferable to heat while flowing an inert gas such as nitrogen or argon. However, from the point of not letting the vaporized sulfur escape, it is preferable to keep the opening of the reaction vessel closed and sealed (completely sealed).

Examples

[0034] Hereinafter, the present invention will be specifically described by showing examples and comparative examples, but the present invention is not limited to the following examples.

[0035] In the following examples, X-ray diffraction (XRD) measurements were performed under the following conditions. <XRD Measurement> Manufacturer: BRUKER Device: D8 ADVANCE Measurement Conditions: · Radiation source: Cu-Kα · Measurement range: 10 to 70° · Measurement step: 1° · Scanning speed: 10° / min · Analysis software: DIFFRAC.SUITE

[0036] [Example 1] Weighed 75 mg of Y2O3 powder, 160 mg of TiO2 powder, 183 mg of Y2S3 powder, and 0.6 g of sulfur powder, put them into a mortar. Further, as a flux, 0.5 g of CsBr powder was put into the mortar, and then stirred in a nitrogen atmosphere for 30 minutes to mix the powders. Next, using the reaction apparatus 10 shown in Fig. 1(A), the mixed powders were transferred to the bottom of a quartz tube 11 (inner diameter Φ10 mm × height 250 mm). The upper opening of the quartz tube 11 was covered with a rubber stopper 16, the lower part of the quartz tube 11 was inserted into the heat treatment furnace 15 and set vertically, and power was supplied to the heat treatment furnace 15 from a power supply source (not shown), and the lower part of the quartz tube 11 was heated at 850 °C for 1 hour as shown in Fig. 1(B).

[0037] By heating, sulfur vaporized, and the vaporized sulfur was cooled and liquefied on the wall surface of the upper part of the quartz tube. The liquefied sulfur flowed down to the lower part of the quartz tube along the side wall of the quartz tube, or dropped as droplets from the upper part of the quartz tube and descended to the lower part of the quartz tube, and was heated in the lower part of the quartz tube and vaporized again. It was visually confirmed that this was continuously repeated during heating and sulfur refluxed in the quartz tube. After the heating was completed, the quartz tube 11 was cooled, the powder inside was taken out, the flux was washed away with water, the product was recovered by filtration, and as a result of performing XRD measurement, Y2Ti2O5S2 was observed, and no other compounds were observed.

[0038] [Example 2] Weighed 1.1 g of Y2O3 powder, 2.3 g of TiO2 powder, and 2.7 g of Y2S3 powder, put them into a mortar. Further, as a flux, 9 g of CsBr powder was put into the mortar, and then stirred in a nitrogen atmosphere for 30 minutes to mix the powders. Next, the mixed powders were transferred to an alumina crucible (shape: B type, inner diameter Φ36 mm × height 31 mm, capacity 15 mL). Using the reaction apparatus 20 shown in Fig. 2(A), after putting 10 g of sulfur powder 22 at the bottom of a quartz tube 21 (inner diameter Φ46 mm × height 250 mm), an alumina crucible 23 containing the mixed powder was covered with a lid 24 in an unsealed state and placed in the quartz tube 21. The upper end opening of the quartz tube 21 was plugged with a rubber stopper 26, and the lower part of the quartz tube 21 was inserted into a heat treatment furnace 25 and set vertically. As shown in Fig. 2(B), power was supplied to the heat treatment furnace 25 from a power supply source (not shown), and the lower part of the quartz tube 21 was heated at 850 °C for 0.5 hours.

[0039] Upon heating, sulfur vaporized, and the vaporized sulfur was cooled and liquefied on the wall surface of the upper part of the quartz tube. The liquefied sulfur flowed down to the lower part of the quartz tube along the side wall of the quartz tube or dropped as droplets from the upper part of the quartz tube and descended to the lower part of the quartz tube, where it was heated and vaporized again. During heating, this was continuously repeated, and it was visually confirmed that sulfur refluxed in the quartz tube. After the heating was completed, the quartz tube 21 was cooled, the powder in the crucible 23 was taken out, the flux was washed away with water, and the product was recovered by filtration. As a result of performing XRD measurement, Y2Ti2O5S2 was observed, and no other compounds were observed. The XRD measurement results are shown in Fig. 3.

[0040] [Comparative Example 1] Similar to Example 2, powders of Y2O3, TiO2, Y2S3, and flux were mixed and transferred to an alumina crucible. Using the reaction apparatus 30 shown in Fig. 4, 10 g of sulfur powder 32 was spread at the bottom of a quartz tube 31. An alumina crucible 33 containing the mixed powder was covered with a lid 34 in an unsealed state and placed on top of the sulfur powder 32. The bottom of the quartz tube 31 was inserted into a heat treatment furnace 35, and after evacuating the inside of the quartz tube 31, the opening was closed with a rubber stopper 36. While keeping the longitudinal direction of this quartz tube 31 horizontal, power was supplied to the heat treatment furnace 35 from a power supply source (not shown), and the bottom of the quartz tube 31 was heated at 850 °C for 1 hour by the heat treatment furnace 35.

[0041] Upon heating, sulfur vaporized, and liquefaction of the vaporized sulfur was observed near the opening of the quartz tube, but sulfur reflux was not confirmed. After the heating was completed, the quartz tube 31 was cooled, and the powder in the crucible was taken out. As a result of performing XRD measurement, hardly any Y2Ti2O5S2 was observed, and mainly Y2Ti2O7 was observed.

[0042] [Comparative Example 2] The reaction was carried out in the same manner as in Example 2 except that sulfur was not added and heating was performed at 850 °C for 1 hour. After the heating was completed, the quartz tube was cooled, and the powder in the crucible was taken out. As a result of performing XRD measurement, hardly any Y2Ti2O5S2 was observed, and mainly Y2Ti2O7 was observed.

Explanation of Signs

[0043] 10, 20, 30 Reaction apparatus 11, 21, 31 Reaction vessel (quartz tube) 12, 22, 32 Sulfur powder 13 Synthesis raw material 14 Flux 15, 25, 35 Heating device (heat treatment furnace) 16, 26, 36 Rubber stopper 17, 27 Vaporized sulfur 18, 28 Liquefied sulfur 23, 33 Raw material storage container (crucible) 24, 34 Lid of crucible

Claims

1. After accommodating at least one flux selected from sulfur, YO, TiO, YS, and a halide of an alkali metal in the lower part of a reaction vessel having an opening at the upper end, holding the opening of the reaction vessel upward, closing the opening of the reaction vessel, and heating the lower part of the reaction vessel without heating the upper part of the reaction vessel, sulfur is vaporized to react with YO, TiO, and YS to obtain YTiO, and 2 O 3 TiO 2 Y 2 S 3 while repeating the steps of liquefying and dropping the vaporized sulfur at the upper part of the reaction vessel and re-vaporizing the liquefied sulfur at the lower part of the heated reaction vessel, reacting the vaporized sulfur with YO, TiO, and YS to obtain YTiO, a method for producing YTiO. 2 O 3 TiO 2 Y 2 S 3 Y 2 Ti 2 O 5 S 2 obtain, and while repeating the steps of liquefying and dropping the vaporized sulfur at the upper part of the reaction vessel and re-vaporizing the liquefied sulfur at the lower part of the heated reaction vessel, reacting the vaporized sulfur with YO, TiO, and YS to obtain YTiO, a method for producing YTiO. 2 O 3 TiO 2 Y 2 S 3 Y 2 Ti 2 O 5 S 2 Y 2 Ti 2 O 5 S 2 manufacturing method.

2. The manufacturing method according to claim 1, wherein the lower part of the reaction vessel is heated and the upper part of the reaction vessel is maintained at a temperature below the boiling point of sulfur, so that the vaporized sulfur is cooled and liquefied at the upper part of the reaction vessel, and the liquefied sulfur naturally drops to the lower part of the reaction vessel.

3. The manufacturing method according to claim 1, wherein the heating temperature is 600 to 1100 °C.

4. After accommodating sulfur in the lower part of the reaction vessel, YO, TiO, YS, 2 O 3 TiO 2 Y 2 S 3And mix with a flux, put it into a raw material storage container, and accommodate this raw material storage container in a reaction container to carry out the reaction according to the manufacturing method described in claim 1.

5. The manufacturing method according to claim 1, wherein the flux is at least one selected from NaCl, NaBr, NaI, KCl, KBr, KI, CsCl, CsBr, and CsI.

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