Preparation method and use of niobium oxide target material

Abstract

The present invention provides a preparation method and use of a niobium oxide target material, the preparation method comprising the following steps: (1) mixing niobium pentoxide powder and a polyvinyl alcohol binder, and spraying and granulating the mixture; (2) cold pressing the mixture to obtain a green body; (3) subjecting the green body to oxygen-depleted pressureless sintering in a hydrogen atmosphere, and then machining the green body to obtain a niobium oxide target material. The preparation method of the present invention is simple to operate, and the niobium oxide green body is subjected to oxygen-depleted pressureless sintering under specific conditions in a hydrogen atmosphere to obtain a molybdenum-tantalum oxide sputtering target material with high density and excellent electrical conductivity, which is suitable for large-scale promotion and application.

Description

Technical Field

[0001] The present invention relates to the technical field of target material preparation, and in particular to a preparation method and application of a niobium oxide target material. Background Art

[0002] Niobium pentoxide target is an important material for preparing anti-reflection and anti-reflection glass and anti-shadow touch screen glass. Anti-reflection and anti-reflection glass is made by coating niobium pentoxide anti-reflection film on the glass surface using sputtering coating technology, which can effectively reduce the reflection of the glass itself, increase the transmittance of the glass, and make the original color through the glass brighter and more realistic. Anti-shadow touch screen glass is made by coating a layer of anti-reflection and anti-reflection film between the ITO film and the glass. While meeting the conductivity of ITO, it can obtain better visual brightness by reducing the influence of ambient light. In addition, the high transmittance of the anti-reflection and anti-reflection film can be used to reduce the visual contrast between the ITO area and the non-ITO area, making the ITO lines of the capacitive screen lighter and improving the visual effect. Due to these significant advantages, niobium pentoxide targets are widely used in solar cells, liquid crystal displays, ion displays, mobile phone touch screens, optical glass and other fields.

[0003] At present, the preparation methods of niobium oxide targets mainly include hot pressing sintering, hot isostatic pressing sintering, etc.

[0004] CN106747439A discloses a niobium oxide target and a preparation method thereof. Niobium pentoxide powder and niobium powder are pre-treated by high-temperature calcination to obtain a powder with a high specific surface area, and then a densified niobium oxide target is prepared by hot pressing and sintering.

[0005] CN103572236A discloses a high-performance niobium oxide target and a preparation method thereof. Niobium pentoxide powder and activator carbon powder are uniformly mixed, a reducing agent is added and mixed to obtain a mixture, and then a densified niobium oxide target is prepared by hot pressing and sintering.

[0006] CN105734506A discloses a method for preparing a hot isostatically pressed niobium oxide target, wherein niobium pentoxide powder is pre-treated by cold isostatic crushing and then packed into a package, degassed and deoxidized, and then hot isostatically pressed and sintered to prepare a densified niobium oxide target.

[0007] CN104973864A discloses a method for preparing a niobium oxide planar target and a niobium oxide planar target, wherein niobium oxide powder and metal niobium powder are mixed and finely ground for nano-processing, thereby improving the conductivity of the target. A densified niobium oxide target is prepared by adding a binder for granulation and then cold forming, and finally sintering in an argon or nitrogen atmosphere.

[0008] CN102659405A discloses a method for preparing a high-density niobium oxide sputtering target. After deoxygenating niobium oxide powder in a hydrogen atmosphere, the powder is compacted by cold isostatic pressing and then crushed. The niobium oxide powder is densified and finally hot-pressed and sintered to prepare a densified niobium oxide target.

[0009] However, the density and conductivity of the niobium pentoxide target obtained by the above method need to be further improved. Summary of the invention

[0010] In order to solve the above technical problems, the present invention provides a method for preparing a niobium oxide target and its use. By adding a binder to niobium pentoxide powder and performing oxygen-depleted pressureless sintering, a molybdenum-tantalum oxide sputtering target with high density and excellent conductive properties is prepared, which has a wide range of applications.

[0011] To achieve this object, the present invention adopts the following technical solutions:

[0012] In a first aspect, the present invention provides a method for preparing a niobium oxide target, the preparation method comprising the following steps:

[0013] (1) mixing niobium pentoxide powder and polyvinyl alcohol binder, and obtaining a mixture by spray granulation;

[0014] (2) The mixed material is subjected to cold pressing to obtain a green body;

[0015] (3) The green body is subjected to oxygen-depleted pressureless sintering in a hydrogen atmosphere and then machined to obtain a niobium oxide target.

[0016] The preparation method of the niobium oxide target material of the present invention comprises the following steps: mixing niobium pentoxide powder and a binder, performing spray granulation treatment, enhancing the strength between particles, preparing a green body with a regular shape and high density by cold pressing treatment, and performing oxygen-depleted pressureless sintering in a hydrogen atmosphere, thereby improving the activity, electrical conductivity and density of the green body, reducing the production process, improving the production efficiency, and preparing a molybdenum-tantalum oxide sputtering target material with excellent electrical conductivity.

[0017] Preferably, the mass fraction of the polyvinyl alcohol binder in the mixture of step (1) is 0.2-1%, for example, it can be 0.2%, 0.3%, 0.5%, 0.6%, 0.8%, 0.9% or 1%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] The preferred mass fraction of the polyvinyl alcohol binder in the present invention is 0.2-1%, which increases the strength of the ceramic powder and makes the ceramic powder easier to shape.

[0019] Preferably, the spray granulation in step (1) is carried out in a spray granulator.

[0020] Preferably, the atomizer speed of the spray granulator is 10000-20000 rpm, for example, it can be 10000 rpm, 12000 rpm, 14000 rpm, 16000 rpm, 17000 rpm, 19000 rpm or 20000 rpm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] Preferably, the peristaltic pump speed of the spray granulator is 50 to 200 rpm, for example, it can be 50 rpm, 80 rpm, 100 rpm, 120 rpm, 150 rpm, 180 rpm or 200 rpm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] Preferably, the air inlet temperature of the spray granulator is 250-400°C, for example, it can be 250°C, 260°C, 280°C, 300°C, 330°C, 350°C or 400°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] Preferably, the air outlet temperature of the spray granulator is 80-200°C, for example, it can be 80°C, 90°C, 100°C, 120°C, 130°C, 150°C or 200°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] Preferably, the mixed material is placed in a steel mold before the cold pressing treatment in step (2).

[0025] Preferably, the cold pressing treatment in step (2) is carried out in an oil press.

[0026] Preferably, the pressure of the cold pressing treatment in step (2) is 20 to 40 MPa, for example, it can be 20 MPa, 22 MPa, 25 MPa, 28 MPa, 30 MPa, 35 MPa or 40 MPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] Preferably, the holding time of the cold pressing treatment is 2 to 5 minutes, for example, it can be 2 minutes, 2.3 minutes, 2.5 minutes, 2.8 minutes, 3 minutes, 3.5 minutes or 5 minutes, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] Preferably, the oxygen-depleted pressureless sintering in step (3) is carried out in a pressureless sintering furnace.

[0029] Preferably, in the oxygen-depleted pressureless sintering process of step (3), vacuum is first evacuated, and then hydrogen is introduced to start heating, and the heating rate is controlled to be 2 to 5°C / min, for example, it can be 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 3.8°C / min, 4°C / min or 5°C / min, etc., but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the flow rate of hydrogen is 300-600 sccm, for example, 300 sccm, 350 sccm, 400 sccm, 450 sccm, 500 sccm, 550 sccm or 600 sccm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] Preferably, the hydrogen passing time is 60 to 120 min, for example, 60 min, 65 min, 70 min, 75 min, 80 min, 90 min, 100 min or 120 min, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] The present invention preferably has a hydrogen flow rate of 300 to 600 sccm and a hydrogen passing time of 60 to 120 minutes, and the niobium oxide target material finally prepared has excellent electrical conductivity. When the hydrogen flow rate is small or the hydrogen passing time is short, it will lead to incomplete reduction and poor conductivity; when the hydrogen flow rate is large or the hydrogen passing time is long, it will cause a waste of hydrogen and increase the preparation cost of the niobium oxide target material.

[0033] Preferably, the temperature of the oxygen-depleted pressureless sintering in step (3) is 400-800°C, for example, it can be 400°C, 450°C, 500°C, 600°C, 650°C, 700°C or 800°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] The preferred temperature of the oxygen-depleted pressureless sintering in the present invention is 400-800° C., which has the advantages of more complete reduction and sintering.

[0035] Preferably, the holding time of the oxygen-depleted pressureless sintering is 60 to 120 min, for example, it can be 60 min, 70 min, 80 min, 90 min, 95 min, 100 min or 120 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] The preferred holding time of the oxygen-depleted pressureless sintering in the present invention is 60 to 120 minutes, which has the advantages of more complete reduction and sintering.

[0037] Preferably, after the oxygen-depleted pressureless sintering in step (3), the introduction of hydrogen is stopped, and the pressure is evacuated to ≤50Pa, for example, it can be 50Pa, 48Pa, 45Pa, 40Pa, 35Pa, 30Pa or 20Pa, etc., but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable; the protective gas is continued to heat to 1200℃~1350℃, for example, it can be 1200℃, 1250℃, 1280℃, 1290℃, 1300℃, 1320℃ or 1350℃, etc., but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable; the heat preservation is carried out for 8~15h, for example, it can be 8h, 9h, 10h, 11h, 12h, 13h or 15h, etc., but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0038] The present invention preferably stops introducing hydrogen after oxygen-depleted pressureless sintering, and continues to raise the temperature to 1200° C. to 1350° C. after vacuuming and introduces protective gas for 8 to 15 hours, which can significantly improve the compactness of the niobium oxide target.

[0039] Preferably, the protective gas comprises nitrogen and / or argon.

[0040] In the present invention, after the green body is subjected to oxygen-depleted pressureless sintering in a hydrogen atmosphere, the machining steps include wire cutting and grinding.

[0041] As a preferred technical solution of the present invention, the preparation method comprises the following steps:

[0042] (1) mixing niobium pentoxide powder and polyvinyl alcohol binder, and obtaining a mixture by spray granulation; wherein the mass fraction of the polyvinyl alcohol binder in the mixture is 0.2 to 1%;

[0043] The spray granulation is carried out in a spray granulator; the atomizer speed of the spray granulator is 10000-20000 rpm; the peristaltic pump speed of the spray granulator is 50-200 rpm; the air inlet temperature of the spray granulator is 250-400°C; the air outlet temperature of the spray granulator is 80-200°C;

[0044] (2) The mixed material is placed in a steel mold and subjected to cold pressing treatment in an oil press at a pressure of 20 to 40 MPa and a holding time of 2 to 5 minutes to obtain a green body;

[0045] (3) placing the green body into a pressureless sintering furnace, first evacuating the vacuum, then passing hydrogen at a flow rate of 300 to 600 sccm for 60 to 120 min, starting to heat up, controlling the heating rate to 2 to 5° C. / min, and performing oxygen-depleted pressureless sintering at a temperature of 400 to 800° C. and a holding time of 60 to 120 min; after the oxygen-depleted pressureless sintering, stop passing hydrogen, evacuate to ≤50 Pa, continue to heat up to 1200° C. to 1350° C. with protective gas, and keep the temperature for 8 to 15 h; and obtain a niobium oxide target by machining.

[0046] In a second aspect, the present invention provides a use of a niobium oxide target material obtained by the preparation method of the niobium oxide target material as described in the first aspect, wherein the niobium oxide target material is applied in the field of solar cells, displays, mobile phone touch screens or optical glass.

[0047] Compared with the prior art, the present invention has at least the following beneficial effects:

[0048] The preparation method of the niobium oxide target provided by the present invention is simple to operate. A polyvinyl alcohol binder is mixed into niobium pentoxide powder, spray granulation is performed to enhance the strength between particles, and then a cold pressing treatment is performed to obtain a green body with a regular shape and a high density. The green body is placed in a hydrogen atmosphere for oxygen-depleted pressureless sintering to prepare a molybdenum-tantalum oxide sputtering target with a high density and excellent conductive performance, which has a wide range of applications. DETAILED DESCRIPTION

[0049] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0050] The present invention is further described in detail below. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0051] Example 1

[0052] This embodiment provides a method for preparing a niobium oxide target, the preparation method comprising the following steps:

[0053] (1) mixing niobium pentoxide powder and polyvinyl alcohol binder, and obtaining a mixture by spray granulation; wherein the mass fraction of the polyvinyl alcohol binder in the mixture is 0.5%;

[0054] The spray granulation is carried out in a spray granulator; the atomizer speed of the spray granulator is 13000 rpm; the peristaltic pump speed of the spray granulator is 100 rpm; the air inlet temperature of the spray granulator is 300°C; the air outlet temperature of the spray granulator is 100°C;

[0055] (2) The mixed material is placed in a steel mold and subjected to cold pressing treatment in an oil press at a pressure of 30 MPa and a holding time of 3 min to obtain a green body;

[0056] (3) placing the green body into a pressureless sintering furnace, first evacuating the vacuum, then passing hydrogen with a flow rate of 500 sccm for 80 minutes, starting to heat up, controlling the heating rate to 3°C / min, and performing oxygen-depleted pressureless sintering at a temperature of 500°C and a holding time of 70 minutes; after the oxygen-depleted pressureless sintering, stopping the introduction of hydrogen, evacuating the vacuum to 30 Pa, passing nitrogen and continuing to heat to 1300°C, and holding for 10 hours; and machining to obtain a niobium oxide target.

[0057] Example 2

[0058] This embodiment provides a method for preparing a niobium oxide target, the preparation method comprising the following steps:

[0059] (1) mixing niobium pentoxide powder and polyvinyl alcohol binder, and obtaining a mixture by spray granulation; wherein the mass fraction of the polyvinyl alcohol binder in the mixture is 0.2%;

[0060] The spray granulation is carried out in a spray granulator; the atomizer speed of the spray granulator is 20000 rpm; the peristaltic pump speed of the spray granulator is 200 rpm; the air inlet temperature of the spray granulator is 400°C; the air outlet temperature of the spray granulator is 200°C;

[0061] (2) The mixed material is placed in a steel mold and subjected to cold pressing treatment in an oil press at a pressure of 20 MPa and a holding time of 2 min to obtain a green body;

[0062] (3) placing the green body into a pressureless sintering furnace, first evacuating the vacuum, then passing hydrogen with a flow rate of 600 sccm for 120 minutes, starting to heat up, controlling the heating rate to 5°C / min, and performing oxygen-depleted pressureless sintering at a temperature of 800°C and a holding time of 60 minutes; after the oxygen-depleted pressureless sintering, stopping the introduction of hydrogen, evacuating the vacuum to 40 Pa, passing nitrogen and continuing to heat up to 1200°C, and holding the temperature for 15 hours; and machining to obtain a niobium oxide target.

[0063] Example 3

[0064] This embodiment provides a method for preparing a niobium oxide target, the preparation method comprising the following steps:

[0065] (1) mixing niobium pentoxide powder and polyvinyl alcohol binder, and obtaining a mixture by spray granulation; wherein the mass fraction of the polyvinyl alcohol binder in the mixture is 0.8%;

[0066] The spray granulation is carried out in a spray granulator; the atomizer speed of the spray granulator is 17000 rpm; the peristaltic pump speed of the spray granulator is 58 rpm; the air inlet temperature of the spray granulator is 270°C; the air outlet temperature of the spray granulator is 130°C;

[0067] (2) The mixed material is placed in a steel mold and subjected to cold pressing treatment in a hydraulic press at a pressure of 36 MPa and a holding time of 2.5 min to obtain a green body;

[0068] (3) The green body is placed in a pressureless sintering furnace, and vacuum is first applied, and then hydrogen with a flow rate of 450 sccm is passed for 70 minutes, and the temperature is started to be increased, and the heating rate is controlled to be 3.3°C / min, and oxygen-depleted pressureless sintering is performed at a temperature of 550°C and a holding time of 88 minutes; after the oxygen-depleted pressureless sintering, the hydrogen is stopped from being introduced, the vacuum is applied to 42 Pa, and the temperature is continued to be increased to 1275°C by argon, and the temperature is kept for 11 hours; and the niobium oxide target is obtained by machining.

[0069] Example 4

[0070] This embodiment provides a method for preparing a niobium oxide target, the preparation method comprising the following steps:

[0071] (1) mixing niobium pentoxide powder and polyvinyl alcohol binder, and obtaining a mixture by spray granulation; wherein the mass fraction of the polyvinyl alcohol binder in the mixture is 1%;

[0072] The spray granulation is carried out in a spray granulator; the atomizer speed of the spray granulator is 10000 rpm; the peristaltic pump speed of the spray granulator is 50 rpm; the air inlet temperature of the spray granulator is 250°C; the air outlet temperature of the spray granulator is 80°C;

[0073] (2) The mixed material is placed in a steel mold and subjected to cold pressing treatment in an oil press at a pressure of 40 MPa and a holding time of 5 min to obtain a green body;

[0074] (3) The green body is placed in a pressureless sintering furnace, and vacuum is first applied, and then hydrogen with a flow rate of 300 sccm is passed for 60 minutes, and the temperature is started to be increased, and the heating rate is controlled to be 2°C / min, and oxygen-depleted pressureless sintering is performed at a temperature of 400°C and a holding time of 120 minutes; after the oxygen-depleted pressureless sintering, the hydrogen is stopped from being introduced, the vacuum is applied to 50 Pa, and the temperature is continued to be increased to 1350°C by argon, and the temperature is kept for 8 hours; after machining, a niobium oxide target is obtained.

[0075] Example 5

[0076] This embodiment provides a method for preparing a niobium oxide target. The preparation method is the same as that of Embodiment 1 except that the flow rate of hydrogen in the oxygen-depleted pressureless sintering in step (3) is 200 sccm and the time of passing hydrogen is 50 min.

[0077] Example 6

[0078] This embodiment provides a method for preparing a niobium oxide target. The preparation method is the same as that of Embodiment 1 except that the temperature of the oxygen-depleted pressureless sintering in step (3) is 350° C.

[0079] Example 7

[0080] This embodiment provides a method for preparing a niobium oxide target. The preparation method is the same as that of Embodiment 1 except that in step (3), after the oxygen-depleted pressureless sintering, nitrogen is introduced and the temperature is continuously raised to 1300° C. and kept at this temperature for 7 hours.

[0081] Comparative Example 1

[0082] This comparative example provides a method for preparing a niobium oxide target. The preparation method is the same as that of Example 1 except that step (3) is to perform pressureless sintering in an oxygen atmosphere.

[0083] The density of the niobium oxide targets obtained in the above examples and comparative examples was determined using the measured density / theoretical density × 100% method;

[0084] The resistivity of the niobium oxide targets obtained in the above embodiments and comparative examples was measured using a four-probe tester. The results are shown in Table 1.

[0085] Table 1

[0086] Density(%) Resistivity (Ω·cm) Example 1 99.5％ <![CDATA[2.5×10 -3 ]]> Example 2 99.1％ <![CDATA[2.9×10 -3 ]]> Example 3 99.2％ <![CDATA[2.8×10 -3 ]]> Example 4 99.6％ <![CDATA[2.7×10 -3 ]]> Example 5 99.2％ <![CDATA[9.3×10 -3 ]]> Example 6 99.2％ <![CDATA[12.1×10 -3 ]]> Example 7 97.5％ <![CDATA[9.8×10 -3 ]]> Comparative Example 1 99.2％ <![CDATA[23.5×10 -3 ]]>

[0087] From Table 1 we can see that:

[0088] (1) It can be seen from Examples 1 to 4 that the method for preparing the niobium oxide target provided by the present invention is simple to operate and can prepare a niobium oxide target with a density of more than 99% and excellent conductivity;

[0089] (2) Combining Example 1 and Example 5, it can be seen that in Example 5, the flow rate of hydrogen in the oxygen-depleted pressureless sintering is small and the hydrogen flow time is short, resulting in a decrease in the conductivity of the niobium oxide target material finally prepared;

[0090] (3) Combining Example 1 and Example 6, it can be seen that the temperature of oxygen-depleted pressureless sintering in Example 6 is relatively low, resulting in a decrease in the electrical conductivity of the niobium oxide target material finally prepared;

[0091] (4) Combining Example 1 and Example 7, it can be seen that in Example 7, after the oxygen-depleted pressureless sintering, the temperature is continuously raised to 1300° C. with nitrogen, and the holding time is short, resulting in a decrease in the density of the niobium oxide target material finally prepared;

[0092] (5) It can be seen from the combination of Example 1 and Comparative Example 1 that the pressureless sintering in oxygen atmosphere in Comparative Example 1 leads to a decrease in the conductive performance.

[0093] In summary, by adopting the preparation method of niobium oxide target provided by the present invention, polyvinyl alcohol binder is mixed into niobium pentoxide powder, spray granulation is carried out, and then cold pressing treatment and oxygen-depleted pressureless sintering under specific conditions are carried out in sequence to prepare molybdenum-tantalum oxide sputtering target with high density and excellent conductive performance, which has a wide range of applications.

[0094] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a niobium oxide target with excellent conductive properties, characterized in that: The preparation method comprises the following steps: (1) mixing niobium pentoxide powder and polyvinyl alcohol binder, and obtaining a mixture by spray granulation; (2) The mixed material is subjected to cold pressing to obtain a green body; (3) subjecting the green body to oxygen-depleted pressureless sintering in a hydrogen atmosphere and then machining to obtain a niobium oxide target; During the oxygen-depleted pressureless sintering process, vacuum is first drawn, and then hydrogen is introduced to start heating, and the heating rate is controlled to be 2-5°C / min; the flow rate of hydrogen is 300-600sccm; and the time of hydrogen introduction is 60-120min; The temperature of the oxygen-depleted pressureless sintering is 400-800° C.; the holding time of the oxygen-depleted pressureless sintering is 60-120 min; After the oxygen-depleted pressureless sintering, the hydrogen is stopped, the vacuum is evacuated to ≤50Pa, the protective gas is passed and the temperature is continued to rise to 1200°C to 1350°C, and the temperature is kept for 8 to 15 hours; The atomizer speed of the spray granulator is 10000-20000 rpm; The peristaltic pump speed of the spray granulator is 50 to 200 rpm; The air inlet temperature of the spray granulator is 250-400°C; The outlet air temperature of the spray granulator is 80-200°C.

2. The preparation method according to claim 1, characterized in that: The mass fraction of the polyvinyl alcohol binder in the mixture of step (1) is 0.2-1%.

3. The preparation method according to claim 1, characterized in that: The spray granulation in step (1) is carried out in a spray granulator.

4. The preparation method according to claim 1, characterized in that: Before the cold pressing process in step (2), the mixed material is placed in a steel mold.

5. The preparation method according to claim 1, characterized in that: The cold pressing process is carried out in an oil press.

6. The preparation method according to claim 1, characterized in that: The pressure of the cold pressing treatment in step (2) is 20 to 40 MPa.

7. The preparation method according to claim 1, characterized in that: The holding time of the cold pressing treatment is 2 to 5 minutes.

8. The preparation method according to claim 1, characterized in that: The oxygen-depleted pressureless sintering in step (3) is carried out in a pressureless sintering furnace.

9. The preparation method according to claim 1, characterized in that: The protective gas includes nitrogen and / or argon.

10. The preparation method according to claim 1, characterized in that: The preparation method comprises the following steps: (1) mixing niobium pentoxide powder and polyvinyl alcohol binder, and obtaining a mixture by spray granulation; wherein the mass fraction of the polyvinyl alcohol binder in the mixture is 0.2 to 1%; The spray granulation is carried out in a spray granulator; the atomizer speed of the spray granulator is 10000-20000 rpm; the peristaltic pump speed of the spray granulator is 50-200 rpm; the air inlet temperature of the spray granulator is 250-400°C; the air outlet temperature of the spray granulator is 80-200°C; (2) The mixed material is placed in a steel mold and subjected to cold pressing treatment in an oil press at a pressure of 20 to 40 MPa and a holding time of 2 to 5 minutes to obtain a green body; (3) placing the green body into a pressureless sintering furnace, first evacuating the vacuum, then passing hydrogen at a flow rate of 300 to 600 sccm for 60 to 120 min, starting to heat up, controlling the heating rate to 2 to 5° C. / min, and performing oxygen-depleted pressureless sintering at a temperature of 400 to 800° C. and a holding time of 60 to 120 min; after the oxygen-depleted pressureless sintering, stop passing hydrogen, evacuate to ≤50 Pa, continue to heat up to 1200° C. to 1350° C. with protective gas, and keep the temperature for 8 to 15 h; and obtain a niobium oxide target by machining.