A method for preparing GeI2 single crystal by vapor transport method

Abstract

The present invention discloses a method for preparing GeI2 single crystals by a vapor transport method. Germanium oxide, hypophosphorous acid, hydroiodic acid, and cesium iodide are used as raw materials for the powder synthesis of CsGeI3. CsGeI3 powder is placed at the bottom of a quartz tube. After the quartz tube is purged with argon, it is evacuated and then sealed. The quartz tube is heated and held using a Bridgman furnace, and then cooled at a gradient to obtain GeI2 single crystals in the cold zone of the quartz tube. The remaining material at the bottom of the quartz tube is cesium iodide, and this part of cesium iodide can be reused for the synthesis of CsGeI3 powder. The present invention provides a method for preparing high-quality GeI2 single crystals by vapor transport with a simple process, easy industrial production, high repeatability, high yield, high single crystal quality, and low cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of two-dimensional material single crystals, and specifically relates to a method for preparing GeI2 single crystals. Background Art

[0002] Two-dimensional materials have attracted extensive attention due to the absence of dangling bonds and their special physical and chemical properties. In particular, the successful exfoliation of graphene in 2004 was one of the milestones in scientific research. Graphene has excellent chemical and physical properties, but most of these two-dimensional materials exhibit narrow bandgaps, which hinder their practical applications in ultraviolet optoelectronic devices. Although the hydrogenation and fluorination treatments of graphene can open the bandgap, this chemical treatment is difficult to achieve in experiments.

[0003] Germanium iodide (GeI2) was first synthesized by E. Urgiles et al. It is a crystal with a hexagonal layered structure and the space group P-3m1. Its indirect bandgap is 2.35 eV, which can collect visible light and ultraviolet light. In addition, hydrogenated GeI2 becomes a ferromagnetic half-metal, opening up a new way for spintronics. Moreover, GeI2 is also a raw material for the production of Ge. Currently, the process for producing GeI2 is to react germanium tetraiodide with hypophosphorous acid and hydroiodic acid in solution, and there will be more impurities in the reaction process, the quality of the prepared single crystals is not high, the preparation process is long, and the yield is low. The method for preparing GeI2 in the laboratory is to react germanium and iodine at 200 - 400 °C, but there will be impurities such as GeI4 in the product, and the yield is not high, and the cost is high, making it difficult to produce on a large scale. Summary of the Invention

[0004] In order to solve the problems of the prior art, the purpose of the present invention is to overcome the deficiencies of the existing technology and provide a method for preparing GeI2 single crystals by the vapor transport method. The method provided by the present invention is simple to operate, has a high repetition rate and a high yield, and the single crystals can be used in fields such as ultraviolet photodetection.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A method for preparing GeI2 single crystals by the vapor transport method, using CsGeI3 perovskite powder as the raw material; placing the CsGeI3 perovskite powder at the bottom of a quartz tube, cleaning the quartz tube with nitrogen at least three times and then evacuating to a pressure of not less than 10 Pa, and sealing the quartz tube; then heating, insulating, and slowly lifting and cooling the quartz tube using a heating furnace, and hexagonal plate-shaped yellow transparent GeI2 single crystals can be obtained in the cold zone at the top inside the quartz tube.

[0007] Preferably, germanium oxide (GeO2), hydroiodic acid (HI), hypophosphorous acid (H3PO4), and cesium iodide (CsI) are used as the raw materials, and CsGeI3 is prepared by a chemical synthesis method, and CsGeI3 perovskite powder is prepared.

[0008] Preferably, the method for preparing CsGeI3 by chemical synthesis is as follows:

[0009] Add germanium oxide to aqueous hypophosphorous acid solution and aqueous hydrogen iodide solution, then pour the mixed solution into a beaker. After sealing the beaker, stir at a temperature not lower than 80 °C for at least 12 hours to carry out the reaction; after the reaction is complete, filter the solution with a 0.22 μm filter; add cesium iodide powder to the filtered clear liquid, and immediately obtain CsGeI3 perovskite. Collect the solid matter, and then dry it using a drying dish or in a nitrogen atmosphere to obtain CsGeI3 perovskite powder for standby.

[0010] Preferably, the molar ratio of germanium oxide, hydroiodic acid, hypophosphorous acid, and cesium iodide is 1:5:5:1.

[0011] Preferably, the temperature set by the heating furnace is 430 - 450 °C, and the heat preservation time is 24 - 48 hours.

[0012] Preferably, the heating rate-up time is at least 1 hour.

[0013] Preferably, control the temperature of the upper cold zone inside the quartz tube not to be higher than 240 °C.

[0014] Preferably, the heating furnace used is a Bridgman furnace or a vertical furnace of the same type.

[0015] Preferably, the length of the quartz tube used is 10 - 15 cm, the diameter is 1.0 - 1.5 cm, and the wall thickness is not less than 0.3 mm; the mass range of CsGeI3 added is 1 - 3 g.

[0016] Compared with the prior art, the present invention has the following obvious prominent substantial features and remarkable advantages:

[0017] 1. The method of the present invention has a simple process flow, is easy to industrialize, has a high repetition rate, a high yield, a high single crystal quality, and low costs;

[0018] 2. The method of the present invention uses germanium oxide (GeO2), hydroiodic acid (HI), hypophosphorous acid (H3PO4), and cesium iodide (CsI) as raw materials to prepare CsGeI3 perovskite powder, with fewer impurities and being easy to prepare. Description of the Drawings

[0019] Figure 1 is the XRD pattern of the GeI2 single crystal prepared by the method of the preferred embodiment of the present invention.

[0020] Figure 2 is the physical photo of the GeI2 single crystal prepared by the method of the preferred embodiment of the present invention.

[0021] Figure 3It is a product diagram of GeI2 single crystal prepared by the method of the preferred embodiment of the present invention and a quartz tube device diagram.

[0022] Figure 4 It is a Raman spectrogram of GeI2 single crystal prepared by the method of the preferred embodiment of the present invention. Detailed implementation manners

[0023] The above scheme will be further described below in conjunction with specific implementation examples. The preferred embodiments of the present invention are described in detail as follows:

[0024] Example 1:

[0025] In this embodiment, a method for preparing GeI2 single crystal by vapor transport method is as follows:

[0026] (1) Add germanium oxide GeO2 (104 mg, 1 mmol) into 1 mL of hypophosphorous acid aqueous solution and 1.5 mL of hydroiodic acid aqueous solution, then pour the mixed solution into a beaker. After sealing the beaker, stir at 80 °C for 12 hours for reaction; wherein, the molar ratio of germanium oxide, hydroiodic acid, and hypophosphorous acid is 1:5:5;

[0027] (2) After complete reaction, filter the solution with a 0.22 μm filter; add cesium iodide powder (260 mg, 1 mmol) to the filtered clear liquid, and immediately obtain CsGeI3 perovskite. Collect the solid matter, and then dry it using a drying dish or in a nitrogen atmosphere to obtain CsGeI3 perovskite powder for standby;

[0028] (3) Wash the CsGeI3 perovskite powder with ethanol, and then transfer it to a nitrogen environment for drying;

[0029] (4) Place the CsGeI3 perovskite powder obtained in step (3) at the bottom of a quartz tube. The length of the quartz tube is 10 - 15 cm, the tube diameter is 1.0 - 1.5 cm, and the wall thickness is 0.3 mm; then wash the quartz tube three times with nitrogen and evacuate it to a pressure below 10 Pa, and seal the quartz tube;

[0030] (5) Then place the quartz tube in step (3) on a Bridgman furnace, heat it to 450 °C, with a heating time of 1 hour, keep it warm for 24 hours, and then naturally cool it to room temperature, so as to obtain hexagonal plate-like yellow transparent GeI2 single crystal in the cold area at the top inside the quartz tube.

[0031] Experimental test analysis:

[0032] The hexagonal plate-like yellow transparent GeI2 single crystal prepared in this embodiment is as Figure 2 , Figure 3 shown. Its XRD and Raman of GeI2 single crystal are respectively shown in Figure 1 and Figure 4 respectively. FromFigure 1 It can be seen that the single crystal grown by the method of the present invention has a high quality, strong crystallinity, and almost no common impurities such as GeI4 and I. And it can be seen that the growth of the single crystal is preferentially along the 001 plane; Figure 4 It is known that the characteristic Raman peak positions of GeI2 are at 80, 120, and 175 cm -1 . The method of this embodiment can prepare high-quality GeI2 single crystals by vapor transport, with a simple process, easy industrial production, high repeatability, high yield, high single crystal quality, and low cost.

[0033] Example 2:

[0034] This embodiment is basically the same as Example 1, with the special feature that:

[0035] In this embodiment, a method for preparing GeI2 single crystals by vapor transport method is as follows:

[0036] (1) Add germanium oxide GeO2 (104 mg, 1 mmol) to 1 mL of hypophosphorous acid aqueous solution and 1.5 mL of hydroiodic acid aqueous solution, then pour the mixed solution into a beaker, seal the beaker, and stir at 80 °C for 12 hours for reaction; among them, the molar ratio of germanium oxide, hydroiodic acid, and hypophosphorous acid is 1:5:5;

[0037] (2) After the reaction is complete, filter the solution with a 0.22 μm filter; add cesium iodide powder (260 mg, 1 mmol) to the filtered clear liquid, and immediately obtain CsGeI3 perovskite. Collect the solid matter, and then dry it using a drying dish or in a nitrogen atmosphere to obtain CsGeI3 perovskite powder for standby;

[0038] (3) Wash the CsGeI3 perovskite powder with ethanol, and then transfer it to a nitrogen environment for drying;

[0039] (4) Place the CsGeI3 perovskite powder obtained in step (3) at the bottom of a quartz tube. The length of the quartz tube is 10 - 15 cm, the diameter is 1.0 - 1.5 cm, and the wall thickness is 0.3 mm; then use nitrogen to wash the quartz tube three times and evacuate it to a pressure below 10 Pa, and seal the quartz tube;

[0040] (5) Then place the quartz tube in step (3) on a Bridgman furnace, heat it to 430 °C, with a heating time of 1 hour, keep it warm for 48 hours, and then cool it naturally to room temperature, so as to obtain hexagonal flake-shaped yellow transparent GeI2 single crystals in the cold area at the top inside the quartz tube.

[0041] The method of this embodiment can prepare high-quality GeI2 single crystals by vapor transport, with a simple process, easy industrial production, high repeatability, high yield, high single crystal quality, and low cost.

[0042] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made according to the purpose of the invention of the present invention. Any changes, modifications, substitutions, combinations or simplifications made based on the spirit and principle of the technical solution of the present invention shall be equivalent replacement methods. As long as they meet the invention purpose of the present invention and do not deviate from the technical principle and inventive concept of the present invention, they all fall within the protection scope of the present invention.

Claims

1. A method for preparing GeI2 single crystals by vapor transport method, characterized in that: Using CsGeI3 perovskite powder as raw material; placing the CsGeI3 perovskite powder at the bottom of a quartz tube, cleaning the quartz tube with nitrogen at least three times and then evacuating it to a pressure of no more than 10 Pa; then heating, insulating, and slowly lifting and cooling the quartz tube using a heating furnace, and hexagonal plate-shaped yellow transparent GeI2 single crystals can be obtained in the cold zone at the top inside the quartz tube; the heating temperature set by the heating furnace is 430 - 450 °C, and the temperature in the upper cold zone inside the quartz tube is controlled not to be higher than 240 °C.

2. The method for preparing GeI2 single crystal by vapor transport method according to claim 1, characterized in that: Using germanium oxide (GeO2), hydroiodic acid (HI), phosphorous acid (H3PO4), and cesium iodide (CsI) as raw materials, CsGeI3 is prepared by a chemical synthesis method, and CsGeI3 perovskite powder is prepared.

3. The method for preparing GeI2 single crystal by vapor transport method according to claim 2, characterized in that, The method for preparing CsGeI3 by the chemical synthesis method is as follows: Adding germanium oxide to an aqueous solution of phosphorous acid and an aqueous solution of hydrogen iodide, then pouring the mixed solution into a beaker, sealing the beaker, and stirring at no less than 80 °C for at least 12 hours for reaction; after complete reaction, filtering the solution with a 0.22 μm filter; adding cesium iodide powder to the filtered clear liquid, and CsGeI3 perovskite can be immediately obtained. Collect the solid matter, and then dry it using a drying dish or in a nitrogen atmosphere to obtain CsGeI3 perovskite powder for standby.

4. The method for preparing GeI2 single crystal by vapor transport method according to claim 2, characterized in that: The molar ratio of germanium oxide, hydroiodic acid, phosphorous acid, and cesium iodide is 1:5:5:

1.

5. The method for preparing GeI2 single crystal by vapor transport method according to claim 1, characterized in that: The insulation time set by the heating furnace is 24 - 48 hours.

6. The method for preparing GeI2 single crystal by vapor transport method according to claim 1, characterized in that: The heating rate-up time is at least 1 hour.

7. The method for preparing GeI2 single crystal by vapor transport method according to claim 1, characterized in that: The heating furnace used is a Bridgman furnace or a vertical furnace of the same type.

8. The method for preparing GeI2 single crystal by vapor transport method according to claim 1, characterized in that: The quartz tube used has a length of 10 - 15 cm, an inner diameter of 1.0 - 1.5 cm, and a wall thickness of no less than 0.3 mm; the mass range of CsGeI3 added is 1 - 3 g.

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