Preparation method of cesium lithium molybdate crystal

Abstract

The invention discloses a preparation method of a lithium molybdate cesium crystal. The chemical formula of the cesium lithium molybdate crystal is CsLiMoO4, the cesium lithium molybdate crystal is in a cubic system and # imgabs0 # point group at room temperature, and the cell parameter of the cesium lithium molybdate crystal is as follows: # imgabs1 # alpha = beta = gamma = 90 degrees. The cesium lithium molybdate crystal can be used for manufacturing important electro-optical devices such as electro-optical modulators, electro-optical switches, electric control light beam deflectors, phase delayers and electro-optical compensators. According to the method for preparing the lithium cesium molybdate through the fluxing agent method, the crystal growth temperature is effectively reduced, the grown crystals are good in quality, few in crystal defect and good in component uniformity, and preparation of large-size and high-quality single crystals can be achieved. In addition, fluxing agent method crystal growth equipment is simple, and industrial popularization is facilitated.

Description

Technical Field

[0001] The present invention belongs to the field of functional materials, and particularly relates to a preparation method of cesium lithium molybdate crystal. Background Art

[0002] Electro-optic crystals are the core key materials in important electro-optic devices such as electro-optic modulators, electro-optic switches, electrically controlled beam deflectors, phase retarders, and electro-optic compensators, and are widely used in frontier technology fields such as fiber optic gyroscopes, lidar, and quantum communication. Cesium lithium molybdate is a newly discovered electro-optic crystal in recent years and has important application value. In 2011, Aleksandrov et al. grew cesium lithium molybdate crystals by the Bridgeman method and studied their phase transition properties. In 2020, Ye Ning, Xu Feng et al. grew cesium lithium molybdate crystals by the Czochralski method and completed the measurement of the electro-optic coefficient of the crystals. Cesium lithium molybdate crystals have good electro-optic effects and nonlinear optical effects, and their electro-optic coefficient is 10.71 pm / V. In 2023, Matskevich et al. grew cesium lithium molybdate crystals by the low-temperature gradient Czochralski method and found that there is no phase transition in cesium lithium molybdate crystals in the range of 320 - 1000K, indicating that cesium lithium molybdate has application value in a relatively wide temperature range.

[0003] However, the above preparation methods all require the melt temperature to be higher than the melting point of cesium lithium molybdate crystals, which requires very high temperature control accuracy for the crystal growth equipment, the equipment is expensive, and there is volatilization of raw materials such as molybdenum oxide during the growth process, affecting the size and quality of the prepared crystals. The flux method is a method for artificially preparing single crystals from a melt with the help of a flux. This method can effectively reduce the crystal growth temperature, reduce the volatilization loss of materials at high temperatures, promote the uniform growth of crystals, reduce crystal defects, improve crystal quality, and achieve the preparation of large-size single crystals. By adjusting the composition of the flux and the growth conditions, the growth of crystals can be precisely controlled. Due to the small temperature gradient during the growth process, the crystals grown by the flux method have less stress and cracks. These advantages of the flux method make it a very important technology in the field of crystal growth. In addition, the flux growth equipment is simple, which is conducive to industrial promotion. Therefore, the inventor has developed a technology for preparing cesium lithium molybdate crystals by the flux method.

[0004] The technical difficulty of the flux method lies in finding a suitable flux system, including the type and proportion of the flux, etc. A good flux system should have the following properties: 1. It should have a strong enough dissolution ability for the crystal material; 2. In as wide a temperature range as possible, the desired crystal is the only stable phase; 3. It should have as small a viscosity as possible; 4. It should have as low a melting point and as high a boiling point as possible; 5. It should have very small volatility, corrosiveness, and toxicity. Through long-term exploration, the present invention has developed a self-flux system suitable for the growth of cesium lithium molybdate crystals. Summary of the Invention

[0005] Cesium lithium molybdate crystal is a new type of electro-optic crystal, characterized in that the chemical formula of the crystal is CsLiMoO4, and the cesium lithium molybdate crystal is in a cubic crystal system at room temperature, F point group, and its unit cell parameters are: α = β = γ = 90°.

[0006] According to an embodiment of the present invention, the cesium lithium molybdate crystal has an X-ray crystal diffraction pattern substantially as Figure 1 shown and / or a crystal structure diagram as Figure 2 shown.

[0007] According to an embodiment of the present invention, the cesium lithium molybdate crystal is a colorless transparent crystal.

[0008] The present invention provides a method for preparing the cesium lithium molybdate crystal, the method comprising: weighing a cesium compound, a lithium compound, a molybdenum compound and a flux according to the stoichiometric ratio of CsLiMoO4 and mixing them, and preparing the cesium lithium molybdate crystal by using the high-temperature molten salt method or the top-seeded method.

[0009] According to an embodiment of the present invention, the method for preparing the cesium lithium molybdate crystal (high-temperature molten salt method) comprises the following steps:

[0010] Weighing a cesium compound, a lithium compound and a molybdenum compound according to the stoichiometric ratio of cesium lithium molybdate, mixing them with a flux, and obtaining the cesium lithium molybdate crystal after heating, melting, heat preservation and cooling in a molten salt furnace.

[0011] According to an embodiment of the present invention, the method for preparing the cesium lithium molybdate crystal (top-seeded method) comprises the following steps:

[0012] Weighing a cesium compound, a lithium compound and a molybdenum compound according to the stoichiometric ratio of cesium lithium molybdate, mixing them with a flux, and obtaining the cesium lithium molybdate crystal after heating, melting, heat preservation, introducing a seed crystal, cooling and annealing in a molten salt furnace.

[0013] According to an embodiment of the present invention, the molar ratio of the raw materials of the cesium lithium molybdate stoichiometric ratio to the flux is (1-20):(0-10), for example, the molar ratio is (1.5-3):(2-6), and exemplarily 1:3. Among them, the cesium lithium molybdate stoichiometric ratio means Cs:Li:Mo:O = 1:1:1:4.

[0014] According to an embodiment of the present invention, the flux is a mixture of a molybdenum-containing compound and a cesium-containing compound, wherein the molar ratio of the molybdenum-containing compound to the cesium-containing compound is (0 to 10):(0 to 10), for example, the molar ratio is (2 to 6):(2 to 6), and exemplarily it is 1:1.

[0015] According to an embodiment of the present invention, the cesium-containing compound is at least one of Cs2CO3, Cs2O, CsCl, and CsOH.

[0016] According to an embodiment of the present invention, the lithium-containing compound is at least one of Li2CO3, Li2O, LiCl, and LiOH.

[0017] According to an embodiment of the present invention, the molybdenum-containing compound is MoO3.

[0018] According to an embodiment of the present invention, the temperature increase is to raise the temperature to 450 to 1000 °C, for example, 650 to 750 °C. Further, the rate of temperature increase is 10 to 300 °C / hour, for example, 30 to 60 °C / hour, and preferably 40 to 50 °C / hour.

[0019] According to an embodiment of the present invention, the heat preservation time is 0.5 to 5 days, such as 1 to 3 days.

[0020] According to an embodiment of the present invention, the temperature decrease is to lower the temperature to 15 to 100 °C, such as 20 to 25 °C. Further, the rate of temperature decrease is 0.1 to 100 °C / day, for example, 0.1 to 2 °C / day, such as 10 to 20 °C / day.

[0021] According to an embodiment of the present invention, the annealing rate is 5 to 40 °C / hour, for example, 10 to 40 °C / hour, such as 15 to 30 °C / hour.

[0022] The present invention also provides a cesium lithium molybdate material doped with ions, in which the doped ions are doped at the positions of any one, two or more of the lithium ions, cesium ions, oxygen ions and molybdenum ions in the cesium lithium molybdate crystal.

[0023] According to an embodiment of the present invention, based on the total molar mass of the ions to be doped and the doped ions being 100 mol.%, the molar mass percentage content of the doped ions is greater than 0 and less than 100 mol.%; for example, it is 0.5 - 50 mol.%, 1 - 25 mol.%, and exemplarily it is 2.4 mol.%.

[0024] According to the technical solution of the present invention, the doped ions include ions of at least one of the following elements: Na, Rb, Mg, Ca, Sr, Ba, Al, Sc, Y, Ta, Nb, Ti, Cr, Hf, Ta, W, Zr, Mn, Fe, Tc, Ru, V, P, Si, S, Cl, F, for example, Li, Na, Mg, Ca, Sr, Ba or W.

[0025] The present invention also provides a method for preparing the ion-doped cesium lithium molybdate material, and the method includes: using the cesium lithium molybdate crystal as a parent compound, and obtaining the ion-doped cesium lithium molybdate material by means of ion doping, component regulation, etc.

[0026] The present invention also provides an ion-doped cesium lithium molybdate material, and the ion-doped cesium lithium molybdate material includes ceramics, crystals, and thin film materials.

[0027] In this application, the "room temperature" refers to a temperature between 15 - 40 °C, for example, between 20 - 35 °C, and preferably 25 °C.

[0028] The beneficial effects of the present invention include:

[0029] The method for preparing cesium lithium molybdate crystals by the flux method provided by the present invention, compared with the existing methods for preparing cesium lithium molybdate crystals such as the Czochralski method, effectively reduces the crystal growth temperature by 50 - 150 °C. The grown crystals have good quality, few crystal defects, and good compositional homogeneity, and can realize the preparation of large-size and high-quality single crystals. Secondly, the flux method crystal growth equipment is simple, which is conducive to industrial promotion. Thirdly, the preparation of cesium lithium molybdate crystals by the flux method helps to obtain the ion-doped cesium lithium molybdate material by means of ion doping, component regulation, etc., and improves the performance of the cesium lithium molybdate material. Description of the Drawings

[0030] Figure 1 is the XRD spectrum and crystal photograph of the CsLiMoO4 crystal prepared in Example 2 of the present invention.

[0031] Figure 2 is the structural diagram of the CsLiMoO4 crystals prepared in Example 1 and Example 2 of the present invention.

[0032] Figure 3 is the transmission spectrum of the CsLiMoO4 crystal prepared in Example 3 of the present invention. Detailed Embodiments

[0033] The technical solution of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to illustrate and explain the present invention exemplarily, and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0034] Unless otherwise specified, the raw materials and reagents used in the following embodiments are all commercially available products, or can be prepared by known methods.

[0035] Example 1

[0036] The CsLiMoO4 crystal was grown by the high-temperature molten salt method.

[0037] The initial reaction raw materials Li2O, Cs2O, and MoO3 were weighed in a molar ratio of 1:1:3, that is, the ratio of CsLiMoO4 to the flux MoO3 was 1:2. The initial raw materials were mixed and ground evenly and loaded into a platinum crucible, and the platinum crucible was placed in a crystal growth furnace. The temperature was raised to 750 °C for material melting, and held at 750 °C for 30 h, then cooled at a rate of 1 °C per day until the crystal grew to more than 2 cm, and then cooled and annealed at 20 °C / h, and then the crystal was taken out to obtain the CsLiMoO4 crystal. Its structure and properties were determined by powder X-ray diffraction testing and analysis.

[0038] Example 2

[0039] The CsLiMoO4 crystal was grown by the top-seeded method.

[0040] The initial reaction raw materials Li2O, Cs2O, and MoO3 were weighed in a molar ratio of 1:2:4, that is, the ratio of CsLiMoO4 to the fluxes Cs2O and MoO3 was 1:1:3. The initial raw materials were mixed and ground evenly and loaded into a platinum crucible, and the platinum crucible was placed in a crystal growth furnace. The temperature was raised to 750 °C for material melting, and held at 750 °C for 30 h, then cooled to a temperature 5 - 10 °C above the saturation point temperature of 620 °C. The crystal prepared in Example 1 was processed and suspended on a platinum wire as a seed crystal and placed in the center of the liquid surface. After 30 minutes, it was cooled to the saturation point temperature and cooled at a rate of 1 °C / day. After the growth was completed, the crystal was lifted out of the liquid surface and cooled and annealed at 20 °C / h to obtain the CsLiMoO4 crystal. Its structure and properties were determined by powder X-ray diffraction testing and analysis. Compared with the previously reported crystal preparation methods, the crystal growth temperature in this example was reduced by about 100 °C.

[0041] Figure 1 This is the XRD pattern and crystal photograph of the CsLiMoO4 crystal prepared in this example, indicating that the CsLiMoO4 crystal was successfully prepared. The CsLiMoO4 crystal prepared in this example is a colorless transparent crystal.

[0042] Example 3

[0043] Growing Na-doped CsLiMoO4 antiferroelectric crystals by the top-seeded method

[0044] Weigh the initial reaction raw materials Li2O, Na2O, Cs2O and MoO3 in a molar ratio of 1:0.024:1:3. Mix the initial raw materials evenly by grinding and load them into a platinum crucible. Then place the platinum crucible into a crystal growth furnace. Heat up to 750 °C for material melting, and keep it at a constant temperature of 750 °C for 30 h. Then cool down to 5 - 10 °C above the saturation point temperature of 625 °C. Place the seed crystal suspended on a platinum wire into the center of the liquid surface. After 30 minutes, cool down to the saturation point temperature and cool at a rate of 1 °C per day. When the growth is completed, lift the crystal out of the liquid surface and anneal it by cooling at a rate of 20 °C / h, thus obtaining a CsLiMoO4 crystal doped with 2.4 mol.% of sodium. Determine its structure and properties through powder X-ray diffraction testing and analysis. Figure 3 This is the transmission spectrum of the Na-doped CsLiMoO4 crystal prepared in this example. When 2.4% of Na element is doped, the crystal still maintains a high transmittance.

[0045] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing lithium cesium molybdate crystals, characterized in that: The chemical formula of the lithium cesium molybdate crystal is CsLiMoO4. The lithium cesium molybdate crystal is in a cubic system at room temperature. Point group, its unit cell parameters are: α=β=γ=90°; Preferably, the lithium cesium molybdate crystal has an X-ray crystal diffraction pattern substantially as shown in FIG. 1 or a crystal structure diagram as shown in FIG. 2 ; The method comprises: weighing a lithium-containing compound, a cesium-containing compound, a molybdenum-containing compound and a flux according to a stoichiometric ratio of CsLiMoO4, mixing them, and preparing the lithium cesium molybdate crystal by a high-temperature molten salt method or a top seeding method; Preferably, the high temperature molten salt method for preparing lithium cesium molybdate crystals comprises the following steps: A lithium-containing compound, a cesium-containing compound, and a molybdenum-containing compound are weighed according to the stoichiometric ratio of CsLiMoO4, mixed with a flux, and heated, melted, kept warm, and cooled in a molten salt furnace to obtain the lithium cesium molybdate crystal; Preferably, the top seeding method for preparing lithium cesium molybdate crystals comprises the following steps: The lithium-containing compound, the cesium-containing compound and the molybdenum-containing compound are weighed according to the stoichiometric ratio of CsLiMoO4, mixed with a flux, and heated, melted, kept warm, introduced with seed crystals, cooled, and annealed in a molten salt furnace to obtain the lithium cesium molybdate crystal.

2. The preparation method according to claim 1, characterized in that The molar ratio of the CsLiMoO4 stoichiometric raw material to the flux is (1-8):(0-10).

3. The preparation method according to claim 1 or 2, characterized in that The flux is a mixture of a cesium-containing compound and a molybdenum-containing compound, wherein the molar ratio of the cesium-containing compound to the molybdenum-containing compound is (0-10):(0-10).

4. The preparation method according to claim 1 or 2, characterized in that The lithium-containing compound is at least one of Li2CO3, Li2O, LiCl, and LiOH.

5. The preparation method according to claim 1 or 2, characterized in that The cesium-containing compound is at least one of Cs2CO3, Cs2O, CsCl, and CsOH.

6. The preparation method according to claim 1 or 2, characterized in that Preferably, the molybdenum-containing compound is MoO3; Preferably, the heating is to raise the temperature to 550-1000°C, and the heating rate is 10-300°C / hour; Preferably, the insulation time is 0.5 to 5 days; Preferably, the cooling is to reduce the temperature to 15-100°C, and the cooling rate is 0.1-100°C / day; Preferably, the annealing rate is 5-40° C. / hour.

7. An ion-doped lithium cesium molybdate material, characterized in that: In the material, the doping ions are doped in the positions of any one, two or more ions of lithium ions, cesium ions, oxygen ions and molybdenum ions in the lithium cesium molybdate crystal; Based on the total molar mass of the doped ions and the doping ions being 100 mol%, the molar mass percentage of the doping ions is greater than 0 and less than 100 mol%. Preferably, the doping ions include at least one of the ions of the following elements: Na, Rb, Mg, Ca, Sr, Ba, Al, Sc, Y, Ta, Nb, Ti, Cr, Hf, Ta, W, Zr, Mn, Fe, Tc, Ru, V, P, Si, S, Cl, F.

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