Inorganic compound crystal as well as preparation method and application thereof

Abstract

The invention discloses an inorganic compound crystal as well as a preparation method and application thereof, and belongs to the field of crystal materials. The chemical formula of the inorganic compound crystal is Na2 [B4IO9] (IO3). The powder frequency doubling intensity of the inorganic compound crystal under 1064nm laser irradiation is 7.8 times that of KH2PO4 (KDP), phase matching can be realized, and the inorganic compound crystal has a relatively high laser damage threshold; the inorganic compound crystal has high transmittance in the spectral range of 243 nm to 2500 nm, and the ultraviolet absorption cutoff wavelength is about 243 nm; and the Na2 [B4IO9] (IO3) can be well permeated in the range of 0.24 to 7.33 microns. The inorganic compound crystal can be stabilized to 435 DEG C, and has excellent thermal stability.

Description

Technical Field

[0001] The present application relates to an inorganic compound crystal, a preparation method and an application thereof, belonging to the field of crystal materials. Background Art

[0002] Nonlinear optical crystals can broaden the application range of laser wavelengths and obtain coherent light sources in special bands through sum frequency, difference frequency, frequency doubling and parametric oscillation. According to different application bands, the research on laser frequency conversion crystals mainly focuses on three main bands: deep ultraviolet and ultraviolet bands, visible to near-infrared bands, and mid- and far-infrared bands. Among them, the research on laser frequency conversion crystals in the deep ultraviolet and ultraviolet bands mainly focuses on borates.

[0003] Ideal nonlinear optical crystals meet these requirements: (1) Crystallize in an effective non-centrosymmetric space group. (2) Have a large nonlinear optical coefficient. (3) Wide light transmission range and high transmittance. (4) Have an appropriate birefringence. In fact, there are very few nonlinear optical crystals that strictly meet all the above conditions. Therefore, in the research and practical application process, it is necessary to make a comprehensive balance according to the application requirements, and improve or even overcome the performance indicators for related requirements through new technologies and new methods. Therefore, more and higher physical and chemical performance requirements are put forward for nonlinear optical materials. Summary of the Invention

[0004] According to the first aspect of the present application, an inorganic compound crystal is provided. The inorganic compound crystal exhibits a strong frequency doubling effect. Its powder second harmonic generation (SHG) intensity at the 1064 ultraviolet band is 7.8 times that of K 2 HPO 4 (KDP), and it can achieve phase matching and has a high laser damage threshold, making it a nonlinear optical material with potential application value.

[0005] An inorganic compound crystal, the chemical formula of the inorganic compound crystal is Na 2 [B 4 IO 9 (IO 3 ).

[0006] Optionally, the inorganic compound crystal has a three-dimensional crystal structure;

[0007] The three-dimensional crystal structure includes 2 {[B 4 IO 9} - ∞ Two-dimensional planar layers;

[0008] The 2 {[B4 IO 9} - ∞ The two-dimensional planar layers are stacked along the c-axis;

[0009] The 2 {[B 4 IO 9} - ∞ The two-dimensional planar layer includes [BO 4 5- groups, [BO 3 3- groups and [IO 3 - groups;

[0010] One [BO 4 5- group, three [BO 3 3- groups and one [IO 3 - group are connected through common vertices to form [B 4 IO 11 5- basic building units, and these building units continue to be connected through common edges and common vertices to form a layer;

[0011] The interconnection between Na(2) and the iodate part results in 2 {Na(2)(IO 3 ) 2} - ∞ layer.

[0012] One [BO 4 5- group, three [BO 3 3- groups and one [IO 3 - group in the inorganic compound crystal form [B 4 IO 11 5- basic building blocks (FBBs) ( Figure 1 b). Then, these FBBs are connected into 2 {[B 4 IO 9} - ∞ layer, where [IO 3 - hangs on the same side of the borate layer ( Figure 1 a). Then these borate iodates 2 {[B​​​​​​​​​​​​4 I(1)O 9} - ∞ The layers are arranged in a parallel manner with an interlayer distance of , which is beneficial for inducing a strong SHG effect and large birefringence. The borate layer also contains 18-membered rings (18-MRs) with an inner diameter of approximately , which contain Na(1) ions. In addition, the interconnection of Na(2) and the iodate moiety results in 2 {Na(2)(IO 3 ) 2} - ∞ layers ( Figure 1 d). This layered structure is beneficial for the effective superposition of the microscopic second-harmonic generation intensity, thereby generating a strong macroscopic second-harmonic generation effect.

[0013] Optionally, the inorganic compound crystal belongs to the monoclinic system with the space group Cc.

[0014] Optionally, the unit cell parameters of the inorganic compound crystal are as follows:

[0015] α = γ = 90°, β = 101.021 - 101.031°, Z = 4.

[0017] Optionally, the unit cell parameters of the inorganic compound crystal are as follows:

[0018] α = γ = 90°, β = 101.026°, Z = 4.

[0020] Specifically, the unit cell parameters of the inorganic compound crystal are as follows:

[0021] α = γ = 90°, β = 101.026°, Z = 4.

[0022] Optionally, the ultraviolet absorption cut-off wavelength of the inorganic compound crystal is 240 nm - 247 nm.

[0023] Optionally, the ultraviolet absorption cut-off wavelength of the inorganic compound crystal is 243 nm - 247 nm.

[0024] Specifically, the ultraviolet absorption cut-off wavelength of the inorganic compound crystal is 243 nm.

[0025] Optionally, the inorganic compound crystal has a weight loss of no more than 5% at 435 °C.

[0026] Optionally, the inorganic compound crystal has a weight loss of no more than 2% at 435 °C.

[0027] Optionally, the powder SHG intensity of the inorganic compound crystal under 1064 nm laser irradiation is 7.5 to 8 times that of KDP.

[0028] Specifically, the powder SHG intensity of the inorganic compound crystal under 1064 nm laser irradiation is 7.8 times that of KDP.

[0029] According to the second aspect of the present application, there is provided a method for preparing the above-mentioned inorganic compound crystal. The preparation method has a simple process and can obtain an inorganic compound crystal Na 2 [B 4 IO 9 (IO 3 ) material with high purity and high crystallinity.

[0030] The method for preparing the above-mentioned inorganic compound crystal includes the following steps:

[0031] Placing a mixture containing a sodium source, an iodine source, a boron source, and an oxygen source in a sealed container, and crystallizing to obtain the inorganic compound crystal.

[0032] Among them, the sealed container does not need to be evacuated, there needs to be air in the container, or an oxygen-containing gas or oxygen can be filled into the sealed container. In actual operation, the air in the reaction kettle is sufficient.

[0033] Optionally, the sodium source is selected from at least one of sodium iodate and sodium halide;

[0034] The iodine source is selected from at least one of sodium iodate and iodic acid;

[0035] The boric acid source is selected from at least one of boric acid and boron oxide;

[0036] The oxygen source is selected from at least one of sodium iodate and boric acid.

[0037] Optionally, the sodium halide is selected from at least one of sodium chloride, sodium bromide, and sodium iodide.

[0038] Optionally, the molar ratios of sodium element in the sodium source, iodine element in the iodine source, boron element in the boron source, and oxygen element in the oxygen source are as follows:

[0039] Na: I: B: O = 1 to 5: 1 to 3: 1 to 5: 1 to 15.

[0040] Preferably, the molar ratios of sodium element in the sodium source, iodine element in the iodine source, boron element in the boron source, and oxygen element in the oxygen source are as follows:

[0041] Na: I: B: O = 2 to 4: 1 to 2: 2 to 4: 5 to 10.

[0042] Preferably, the molar ratios of sodium element in the sodium source, iodine element in the iodine source, boron element in the boron source, and oxygen element in the oxygen source are as follows:

[0043] Na: I: B: O = 2.5 - 3.5: 1.2 - 1.5: 2.5 - 3.8: 6 - 9.

[0044] Optionally, the conditions for crystallization are as follows: the temperature is 230°C - 240°C, and the time is 72 h - 122 h.

[0045] Optionally, the crystallization temperature is independently selected from any value of 230°C, 235°C, 240°C or the range value between any two of them.

[0046] Optionally, the crystallization time is independently selected from any value of 72 h, 80 h, 100 h, 110 h, 122 h or the range value between any two of them.

[0047] Optionally, after the crystallization is completed, the system is cooled to room temperature at a cooling rate not exceeding 5°C / h, and the inorganic compound crystal is obtained after separation and drying.

[0048] Optionally, the preparation method of the above-mentioned inorganic compound crystal comprises the following steps:

[0049] (a) Crystallizing a raw material mixture containing sodium element, iodine element, boron element and oxygen element by the boric acid melting method at a crystallization temperature of 230°C - 240°C for more than 72 hours;

[0050] (b) After the crystallization is completed, the system is cooled to room temperature at a cooling rate not exceeding 5°C / h, and the inorganic compound crystal is obtained after separation and drying.

[0051] Optionally, the cooling rate in step (b) is 0.5°C / h - 5°C / h.

[0052] Optionally, the cooling rate is independently selected from any value of 0.5°C / h, 1°C / h, 2°C / h, 3°C / h, 4°C / h, 5°C / h or the range value between any two of them.

[0053] As a preferred embodiment, the preparation method of the above-mentioned inorganic compound crystal comprises the following steps:

[0054] Placing a raw material mixture containing sodium element, iodine element, boron element and oxygen element in a polytetrafluoroethylene reaction kettle and then tightening it, crystallizing at a crystallization temperature of 230°C - 240°C for more than 72 hours; after the crystallization is completed, the system is cooled to room temperature at a cooling rate not exceeding 5°C / h, and the solid sample obtained after separation and drying is the inorganic compound crystal.

[0055] The morphology of the inorganic compound crystal prepared by the boric acid melting method is a colorless massive crystal.

[0056] According to the third aspect of the present application, there is provided an application of the above-mentioned inorganic compound crystal.

[0057] The application of the above-mentioned inorganic compound crystal and / or the inorganic compound crystal obtained by the above-mentioned preparation method in a nonlinear optical crystal material and a laser frequency converter.

[0058] The inorganic compound crystal Na 2 [B 4 IO 9 (IO 3 ) outputs very strong second harmonic generation light under 1064 nm laser irradiation, and its powder SHG intensity is 7.8 times that of K 2 HPO 4 (KDP), and phase matching can be achieved.

[0059] The beneficial effects that the present application can produce include:

[0060] 1) An inorganic compound crystal provided by the present application, the powder SHG intensity of the inorganic compound crystal under 1064 nm laser irradiation is 7.8 times that of K 2 HPO 4 (KDP), and phase matching can be achieved. Therefore, Na 2 [B 4 IO 9 (IO 3 ) crystal has good potential utilization value as a nonlinear optical material; the inorganic compound crystal has a high transmittance in the spectral range of 243 nm to 2500 nm, and its ultraviolet absorption cut-off wavelength is about 243 nm; Na 2 [B 4 IO 9 (IO 3 ) can be well transmitted in the range of 0.24 - 7.33 microns. The inorganic compound crystal can be stable up to 435 °C and has excellent thermal stability.

[0061] 2) A preparation method of an inorganic compound crystal provided by the present application, the preparation method adopts the boric acid melting method to grow a colorless massive Na 2 [B 4 IO 9 (IO 3 ) crystal. The process of the method is simple, and a high-purity and high-crystallinity inorganic compound Na 2 [B 4 IO 9 (IO 3 ) crystal material can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 For the inorganic compound crystal Na 2 [B 4 IO 9 (IO 3 ) of the present application, a is the layer parallel to the ab plane in the molecule; b is the basic building unit [B 2 {[B 4 I(1)O 9} - ∞ in the molecule; c is the three-dimensional structure of the molecule; d is the layer parallel to the ab plane of {Na(2)(IO 4 I(1)O 11}. 2 {Na(2)(IO 3 ) 2} - ∞

[0063] Figure 2 Comparison between the X-ray diffraction pattern obtained by fitting the crystal structure analyzed by single crystal X-ray diffraction of Sample 1# of the present application and the X-ray diffraction pattern obtained by testing the sample ground into powder.

[0064] Figure 3 Ultraviolet-visible-near infrared diffuse reflectance spectrum of Sample 1# of the present application.

[0065] Figure 4 Thermogravimetric diagram of Sample 1# of the present application.

[0066] Figure 5 Infrared transmission spectrum of Sample 1# of the present application.

[0067] Figure 6 Second harmonic generation test result of Sample 1# of the present application, where KDP is the reference standard sample. DETAILED DESCRIPTION OF THE INVENTION

[0068] The present application will be described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0069] Unless otherwise specified, the raw materials in the embodiments of the present application are all purchased through commercial channels.

[0070] Unless otherwise specified, the test methods are all conventional methods, and the instrument settings are all the settings recommended by the manufacturer.

[0071] In the present application, "room temperature" refers to 25°C.

[0072] ​In this application, SHG refers to Second harmonic generation (second harmonic generation - i.e., frequency doubling effect).

[0073] Synthesis of the sample in Example 1

[0074] Place the raw material mixture containing sodium, iodine, boron, and oxygen elements in a polytetrafluoroethylene reaction kettle and tighten it. At a crystallization temperature of 230°C to 240°C, keep it at a constant temperature for more than 72 hours; after crystallization, cool the system to room temperature at a cooling rate not exceeding 5°C / h. The solid sample obtained after ultrasonic washing, separation, and drying is the inorganic compound crystal sample, that is, the sample of the inorganic compound crystal.

[0075] The sample numbers, types and dosages of raw materials, crystallization temperature and holding time, and cooling rate are shown in Table 1.

[0076] Table 1

[0077]

[0078] Crystal structure analysis of Example 2

[0079] Use single crystal X-ray diffraction and powder X-ray diffraction methods to analyze the structure of samples 1 # ~3 # for structure analysis.

[0080] Among them, single crystal X-ray diffraction is carried out on a SuperNova CCD type X-ray single crystal diffractometer of Agilent Company in the United States. The data collection temperature is 293K, and the diffraction light source is graphite-monochromatized Mo-Kα ray The scanning mode is ω-2θ; the data is processed by the Multi-Scan method for absorption correction. The structure analysis is completed using the SHELXTL-2016 program package; the positions of heavy atoms are determined by the direct method, and the coordinates of the remaining atoms are obtained by the difference Fourier synthesis method; using the full matrix least squares method based on F 2 to refine the coordinates of all atoms and the anisotropic thermal parameters.

[0081] Powder X-ray diffraction is carried out on a Miniflex II type X-ray powder diffractometer of Rigaku Corporation in Japan. The test conditions are a fixed target monochromatic light source Cu-Kα, wavelength The voltage and current are 30kV / 15A, the scanning range is 10 to 60°, and the scanning step is 0.02°.

[0082] Among them, the results of single crystal X-ray diffraction show that samples 1 # ~3 # The chemical formulas are all Na 2 [B4 IO 9 (IO 3 ), belonging to the monoclinic system, with the space group Cc, and the unit cell parameters are α = γ = 90°, β = 101.026°, Z = 4 (the unit cell parameters vary within 5% due to crystallinity). The inorganic compound crystal Na 2 [B 4 IO 9 (IO 3 ) has a crystal structure as shown in Figure 1 , and this inorganic compound crystal has a three-dimensional crystal structure; the three-dimensional crystal structure includes 2 {[B 4 IO 9} - ∞ two-dimensional planar layers; the 2 {[B 4 IO 9} - ∞ two-dimensional planar layers are stacked along the c-axis; the 2 {[B 4 IO 9} - ∞ two-dimensional planar layer includes [BO 4 5- groups, [BO 3 3- groups and [IO 3 - groups; one [BO 4 5- group, three [BO 3 3- groups and one [IO 3 - group are connected by sharing vertices to form [B 4 IO 11 5- basic building blocks (FBBs), and these basic building blocks continue to be connected by sharing edges and vertices to form 2 {[B 4 IO 9} - ∞ layers, where [IO 3 - hangs on the same side of the borate layer; these borate iodide 2 {[B 4 I(1)O 9} - ∞ The interlayer distance between layers is​​​​​​​​ are arranged in a parallel manner, which is beneficial to inducing a strong SHG effect and large birefringence. The borate layer also contains 18-membered rings (18-MRs) with an inner diameter of about and contains Na(1) ions. The interconnection of Na(2) and the iodate moiety results in 2 {Na(2)(IO 3 ) 2} - ∞ layers. As shown in Figure 1 a, for the layer in the molecule where 2 {[B 4 I(1)O 9} - ∞ is parallel to the ab plane, and adjacent layers are parallel to each other, which may be beneficial to generating a large SHG effect. Figure 1b shows the basic building unit [B 4 I(1)O 11 in the molecule; Figure 1c shows the three-dimensional structure of the molecule; in addition, Figure 1d is 2 {Na(2)(IO 3 ) 2} - ∞ layer parallel to the ab plane, and adjacent layers are parallel to each other. This layered structure is beneficial to the effective superposition of microscopic second-harmonic generation intensities, thus generating a strong macroscopic second-harmonic generation effect.

[0083] Taking sample 1 # as a typical representative, it belongs to the monoclinic system, the space group is Cc, and the unit cell parameters are α = γ = 90°, β = 101.026°, Z = 4. The powder X-ray diffraction results show that for samples 1 # ~3 # on the XRD pattern, the peak positions are basically the same, and the peak intensities of each sample are slightly different.

[0084] Taking sample 1 # as a typical representative, as shown in Figure 2 , according to the crystal structure analyzed by its single-crystal X-ray diffraction, the fitted X-ray diffraction pattern is consistent with the pattern obtained by X-ray diffraction testing of sample 1 # ground into powder. This indicates that the obtained samples all have high purity.

[0085] Example 3 Second-Harmonic Generation Test Experiment and Results

[0086] Taking sample 1 # as a representative, for the inorganic compound crystal Na 2 [B 4 IO 9 (IO3 )Perform frequency doubling test.

[0087] The specific steps are as follows: Use a laser with a wavelength of 1064 nm as the fundamental frequency light to irradiate the crystal powder to be tested. Detect the generated second harmonic with a photomultiplier tube, and display the harmonic intensity with an oscilloscope. Screen out crystals with different particle sizes from the crystal sample to be tested using a standard sieve. The particle sizes are 45 - 53 μm, 53 - 75 μm, 75 - 105 μm, 105 - 150 μm, 150 - 210 μm, and 210 - 300 μm respectively. Observe the change trend of the frequency doubling signal with the particle size, and judge whether phase matching can be achieved. Under the same test conditions, compare the intensity of the second harmonic generated by the sample to be tested with that of the reference crystal K 2 HPO 4 (KDP) to obtain the relative magnitude of the frequency doubling effect of the sample.

[0088] The test results show that: The powder SHG intensity of the compound Na 2 [B 4 IO 9 (IO 3 ) under 1064 nm laser irradiation is 7.8 times that of Na 2 [B 4 IO 9 (IO 3 ) and can achieve phase matching.

[0089] Example 4 Diffuse Reflection Absorption Spectrum Test

[0090] Taking Sample 1 # as an example, perform a diffuse reflection absorption spectrum test on Na 2 [B 4 IO 9 (IO 3 ) on a Perkin-Elmer Lambda-950 UV-Vis-NIR spectrophotometer in the United States. Grind the crystal sample into powder and use BaSO 4 as the reference substrate. The test results are as Figure 3 shown, indicating that the crystal of the compound Na 2 [B 4 IO 9 (IO 3 ) has a wide transmission range, has a very high transmittance in the spectral range of 243 - 2500 nm, and the ultraviolet absorption cut-off wavelength is about 243 nm.

[0091] Example 5 Thermogravimetric Analysis of the Sample

[0092] Taking Sample 1 # as an example, for Na 2[B 4 IO 9 (IO 3 ) was subjected to thermogravimetric analysis on a STA449F3 thermogravimetric analyzer of NETZSCH Company in Germany, and the results are as Figure 4 shown. It can be seen from the figure that Na 2 [B 4 IO 9 (IO 3 ) crystals can be stable up to 435 °C.

[0093] Infrared spectrum test of the sample in Example 6

[0094] Taking sample 1 # as a representative, thermogravimetric analysis was carried out on Na 2 [B 4 IO 9 (IO 3 ), and the infrared spectrum was measured using a Nicolet Magna750 Fourier transform infrared spectrometer. 1% by weight of Na 2 [B 4 IO 9 (IO 3 ) 4 powder was thoroughly mixed with dry KBr for measurement, and the measurement spectral range was 4000 to 400 wavenumbers. As Figure 5 shown, the absorption peaks at 1364 / 436 cm -1 are I-O absorption vibrations, while the absorption peaks at 1105 - 529 cm -1 and 1512 / 1460 cm -1 are B-O absorption vibrations. Combining with the ultraviolet absorption spectrum, it can be known that Na 2 [B 4 IO 9 (IO 3 ) can transmit well in the range of 0.24 - 7.33 microns.

[0095] Second harmonic generation response test of the sample in Example 7

[0096] The second harmonic generation response was measured using a 1064 nm Q-switched laser by the Kurtz and Perry method. Taking microcrystalline K 2 HPO 4 with the same particle size range as a reference, Na 2 [B 4 IO 9 (IO 3) The crystals were separately screened into 6 groups with particle sizes of 45 - 53 μm, 53 - 75 μm, 75 - 105 μm, 105 - 150 μm, 150 - 210 μm, and 210 - 300 μm. Then they were placed in a narrow light-transmitting box and detected under the pulsed infrared beam of a Q-switched Nd:YAG laser. As Figure 6 shown, Na 2 [B 4 IO 9 (IO 3 ) microcrystals have a powder second harmonic generation intensity of K 2 HPO 4 (KDP) 7.8 times that of, and can achieve phase matching.

[0097] As described above, these are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed with preferred embodiments as above, it is not intended to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, making some changes or modifications using the disclosed technical content is equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. An inorganic compound crystal, characterized in that: The chemical formula of the inorganic compound crystal is Na2[B4IO9](IO3).

2. The inorganic compound crystal according to claim 1, characterized in that: The inorganic compound crystal is a three-dimensional crystal structure; The three-dimensional crystal structure includes 2 {[B4IO9]} - ∞ Two-dimensional plane layer; Said 2 {[B4IO9]} - ∞ The two-dimensional planar layers are stacked along the c-axis; Said 2 {[B4IO9]} - ∞ Two-dimensional plane layers include [BO4] 5- Group, [BO3] 3- Group and [IO3] - Group; The one [BO4] 5- Group, three [BO3] 3- group and a [IO3] - The groups are connected by common vertices to form [B4IO 11 ] 5- Basic building blocks, which are connected to form layers through common edges and common vertices; The interconnection of the Na(2) and iodate moieties leads to 2 {Na(2)(IO3)2} - ∞ layer.

3. The inorganic compound crystal according to claim 1, characterized in that: The inorganic compound crystal belongs to the monoclinic system and has a space group of Cc; Preferably, the unit cell parameters of the inorganic compound crystal are as follows: α=γ=90°, β=101.021~101.031°, Z=4.

4. The inorganic compound crystal according to claim 1, characterized in that: The ultraviolet absorption cutoff wavelength of the inorganic compound crystal is 240nm to 247nm; Preferably, the inorganic compound crystals lose no more than 5% of their weight at 435°C; Preferably, the powder SHG intensity of the inorganic compound crystal under 1064 nm laser irradiation is 7.5 to 8 times that of KDP.

5. The method for preparing an inorganic compound crystal according to any one of claims 1 to 4, characterized in that: The following steps are involved: A mixture containing a sodium source, an iodine source, a boron source and an oxygen source is placed in a sealed container and crystallized to obtain the inorganic compound crystal.

6. The preparation method according to claim 5, characterized in that: The sodium source is selected from at least one of sodium iodate and sodium halide; The iodine source is selected from at least one of sodium iodate and iodic acid; The boric acid source is selected from at least one of boric acid and boron oxide; The oxygen source is selected from at least one of sodium iodate and boric acid; Preferably, the sodium halide is selected from at least one of sodium chloride, sodium bromide and sodium iodide.

7. The preparation method according to claim 5, characterized in that: The molar ratio of the sodium element in the sodium source, the iodine element in the iodine source, the boron element in the boron source, and the oxygen element in the oxygen source is as follows: Na:I:B:O=1~5:1~3:1~5:1~15; Preferably, the molar ratio of the sodium element in the sodium source, the iodine element in the iodine source, the boron element in the boron source, and the oxygen element in the oxygen source is as follows: Na:I:B:O=2~4:1~2:2~4:5~10; Preferably, the molar ratio of the sodium element in the sodium source, the iodine element in the iodine source, the boron element in the boron source, and the oxygen element in the oxygen source is as follows: Na: I: B: O = 2.5~3.5: 1.2~1.5: 2.5~3.8: 6~9.

8. The preparation method according to claim 5, characterized in that: The crystallization conditions are as follows: temperature is 230° C. to 240° C., and time is 72 h to 122 h.

9. The preparation method according to claim 5, characterized in that: After the crystallization is completed, the system is cooled to room temperature at a cooling rate not exceeding 5° C. / h, and the inorganic compound crystals are obtained after separation and drying.

10. Use of the inorganic compound crystal according to any one of claims 1 to 4 and / or the inorganic compound crystal obtained by the preparation method according to any one of claims 5 to 9 in nonlinear optical crystal materials and laser frequency converters.

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