Series of tellurium niobate compounds, method for preparing crystals thereof and use thereof

Abstract

The application provides a preparation method and application of a series of tellurium niobate compounds and crystals thereof, and the chemical general formula of the crystals is A2Nb2Te4O 15 , wherein A is selected from Ca, Mg, Sr or Ba. The molecular formula of the series of tellurium niobate compounds is Mg2Nb2Te4O 15 , Ca2Nb2Te4O 15 , Sr2Nb2Te4O 15 , Ba2Nb2Te4O 15 , respectively. The crystals are crystallized in an orthorhombic system, and the space group is Pma 2. The application successfully synthesizes a series of novel compounds with non-centrosymmetric structures based on a functional unit complex method. Experimental measurement shows that the crystals have high powder frequency doubling effect, are superior to a commercial benchmark material KTP, have an ultraviolet absorption cutoff edge shorter than 300 nm, an infrared cutoff edge wider than 6 mm, and moderate birefringence, and are expected to realize wide-band and high-power laser output. In the preparation method, a flux method is used to obtain single crystals with excellent optical quality.

Description

Technical Field

[0001] This invention relates to the field of nonlinear optics, specifically to a series of tellurium niobate compounds and their crystal preparation methods, as well as their applications in nonlinear optical devices. Background Technology

[0002] Mid-infrared nonlinear optical crystals are core materials for generating lasers in the 3-5 micrometer and 8-12 micrometer bands, and are widely used in communications, environmental monitoring, and national defense. Currently, commercially available infrared crystals such as AgGaS2, AgGaSe2, and ZnGeP2 possess excellent infrared transmission characteristics and high nonlinear optical coefficients, but they suffer from inherent defects such as low laser damage thresholds and severe two-photon absorption, limiting their application in high-power laser systems. Oxide materials, due to their larger band gaps, theoretically offer higher laser damage thresholds, thus showing potential in high-power output scenarios. However, traditional oxides suffer from narrow mid-infrared transmission windows and low second harmonic generation coefficients. Therefore, how to maintain the wide band gap advantage of oxides while synergistically optimizing their frequency doubling effect and mid-infrared transmission range has become a core scientific challenge in the development of novel infrared nonlinear optical materials.

[0003] Among numerous oxide systems, tellurate systems have become important research subjects for exploring novel mid-infrared nonlinear optical crystal materials due to their structural diversity and unique physicochemical properties. On the one hand, structural units such as [TeO3], [TeO4], and [TeO5] possess stereochemically active lone pairs of electrons, which can significantly increase the probability of crystallization in noncentrosymmetric space groups; at the same time, the inherent low-frequency phonon vibration characteristics of the heavy element Te help to broaden the infrared transmission range. On the other hand, introducing d-type electrons with second-order Jan Taylor distortion into the tellurate system... 0 Transition metal cations with improved electronic configurations can further enhance the second harmonic response. Furthermore, alkaline earth metal cations effectively broaden the band gap of crystals by enhancing ionicity, modulating band structure, and suppressing defect state formation. Therefore, exploring novel tellurate-based mid-infrared nonlinear optical crystals not only enriches the synthesis and structural chemistry of this system but also holds significant scientific importance for promoting the development of high-performance infrared nonlinear optical materials. Summary of the Invention

[0004] The present invention aims to provide a quaternary series of tellurium niobate compounds containing alkaline earth metal or other divalent metal cations, the general molecular formula of which is A2Nb2Te4O. 15 Where A = Mg, Ca, Ba, Sr. The molecular formulas are Mg₂Nb₂Te₄O₄. 15 Ca2Nb2Te4O 15 Sr2Nb2Te4O 15,Ba2Nb2Te4O 15 .

[0005] Another objective of this invention is to provide a molecular formula of A2Nb2Te4O 15 A series of telluride niobate mid-infrared nonlinear optical crystals (A = Mg, Ca, Ba, Sr) are described. These crystals possess a non-centrosymmetric structure, belong to the orthorhombic crystal system, and have the space group Pma2. The chemical formula of calcium niobate tellurate is Ca2Nb2Te4O. 15 The molecular weight is 1016.38 g / mol, and the unit cell parameters are: a=7.5955(6) Å, b=11.1691(6) Å, c=3.9748(3) Å, α=β=γ=90°, Z=1, and the volume is 337.20(4) Å. 3 .

[0006] Another objective of this invention is to provide a molecular formula of A2Nb2Te4O 15 A method for preparing a series of tellurium niobate mid-infrared nonlinear optical crystals (A = Mg, Ca, Sr, Ba). This method employs a flux-assisted growth process.

[0007] Another objective of this invention is to provide a molecular formula of A2Nb2Te4O 15 Applications of infrared nonlinear optical crystals in a series of tellurium niobates (A = Mg, Ca, Ba, Sr).

[0008] The present invention discloses a quaternary tellurium niobate compound containing an alkaline earth metal or other divalent metal cation, wherein the general molecular formula of the compound is A₂Nb₂Te₄O. 15 Where A = Mg, Ca, Ba, Sr. Taking calcium telluride niobate as an example, its chemical formula is Ca₂Nb₂Te₄O₂. 15 The molecular weight is 1016.38 g / mol. All of these compounds possess an asymmetric central structure and crystallize in the orthorhombic crystal system, space group Pma2.

[0009] The method for preparing a quaternary tellurium niobate compound containing an alkaline earth metal or other divalent metal cation, wherein the general molecular formula of the compound is A₂Nb₂Te₄O 15 The composition A is Mg, Ca, Ba, and Sr. The mixture is prepared using a high-temperature solid-state method. The specific steps are as follows:

[0010] A compound containing A (A = Mg, Ca, Ba, Sr), a compound containing Nb, and a compound containing Te were mixed in a molar ratio of 1.8-2.5 : 1.5-2.5 : 3.8-4.2, and thoroughly ground to ensure homogeneity. The mixture was placed in a Pt crucible and sintered in a muffle furnace. Pre-firing for 24 h was performed to remove moisture and gases from the raw materials. The temperature was then increased to 600-800 °C and sintered for at least 72 h, with repeated grinding during the process. After the reaction was complete, the mixture was cooled to room temperature to obtain A₂Nb₂Te₄O. 15 Pure phase of polycrystalline powder;

[0011] The A-containing compound (A = Mg, Ca, Ba, Sr) includes at least one of AO, A(OH)2, or an A salt; the A salt includes at least one of AF2, ACl2, and ACO3;

[0012] The niobium-containing compounds include, but are not limited to, niobium oxide and niobium chloride;

[0013] The tellurium-containing compounds include, but are not limited to, tellurium dioxide, tellurium disulfide, and tellurium tetrachloride;

[0014] It employs a high-temperature solid-state synthesis method, including but not limited to the following chemical reaction formulas, to prepare a series of quaternary tellurium niobate compounds:

[0015] 1) Nb2O5 + 2AO + 4TeO2 → A2Nb2Te4O 15

[0016] 2) Nb2O5 + 2A(OH)2 + 4TeO2 → A2Nb2Te4O 15 + 2H2O ↑

[0017] 3) Nb2O5 + 2ACO3 + 4TeO2 → A2Nb2Te4O 15 + 2CO2 ↑

[0018] 4) Nb2O5 + 2AO + 4TeCl4 + 4O2 → A2Nb2Te4O 15 + 8Cl2 ↑

[0019] 5) Nb2O5 + 2ACO3 + 4TeCl4 + 4O2 → A2Nb2Te4O 15 + 2CO2 ↑ + 8Cl2 ↑

[0020] 6) Nb2O5 + 2AF2 + 4TeO2 + O2 → A2Nb2Te4O 15 + 2F2 ↑

[0021] 7) Nb2O5 + 2ACl2 + 4TeCl4 + 5O2 → A2Nb2Te4O 15 + 10Cl2 ↑

[0022] 8) Nb2O5 + 2ACl2 + 4TeO2 + O2 → A2Nb2Te4O 15 + 2Cl2 ↑

[0023] 9) Nb2O5 + 2AF2 + 4TeCl4 + 5O2 → A2Nb2Te4O 15 + 2F₂ ↑ + 8Cl₂ ↑

[0024] 10) 4NbCl5 + 4ACl2 + 8TeCl4 + 15O2 → 2A2Nb2Te4O 15 + 30Cl2 ↑

[0025] 11) 4NbCl5 + 4AO + 8TeO2 + 5O2 → 2A2Nb2Te4O 15 + 10Cl2 ↑

[0026] 12) 4NbCl5 + 4ACO3 + 8TeO2 + 5O2 → 2A2Nb2Te4O 15 + 10Cl2 ↑ + 4CO2 ↑

[0027] 13) 4NbCl5 + 4ACl2 + 8TeO2 + 7O2 → 2A2Nb2Te4O 15 + 14Cl2 ↑

[0028] 14) 4NbCl5 + 4AF2 + 8TeO2 + 7O2 → 2A2Nb2Te4O 15 + 10Cl2 ↑ + 4F2 ↑

[0029] 15) 4NbCl5 + 4AO+ 8TeCl4 + 13O2 → 2A2Nb2Te4O 15 + 26Cl2 ↑

[0030] This invention provides a molecular formula of A2Nb2Te4O 15 The preparation method of the series of tellurium niobates adopts the flux method for growth, and the specific operation is carried out according to the following steps:

[0031] a. Mix the pure phase of polycrystalline tellurium niobate compound powder with flux evenly, heat to 700-900 ℃ at a heating rate of 10-100 ℃ / h, hold at this temperature for at least 24 h, and slowly cool the mixed solution to 300-500 ℃, wherein the molar ratio of the pure phase of polycrystalline tellurium niobate compound powder to flux is 1:0-40;

[0032] Alternatively, the mixture containing compound A, compound Nb, compound Te, and flux can be heated to 700-900 ℃ at a heating rate of 10-100 ℃ / h, held at that temperature for at least 24 h, and then cooled to 300-500 ℃. The molar ratio of compound A, compound Nb, compound Te, and flux is 1.5-2.5 : 1.8-2.2 : 3.5-4.5 : 0-40.

[0033] Fluxes include alkali metal salts, namely alkali metal borates, alkali metal carbonates, alkali metal phosphates, alkali metal nitrates, alkali metal fluoroborates, alkali metal sulfates, alkali metal oxalates, alkali metal halides, alkali metal metaborates or alkali metal oxides, alkali metal hydroxides, and one or more of boric acid, phosphoric acid, tellurium oxide, boron oxide, lanthanum fluoride, lanthanum nitrate, lanthanum oxide, scandium fluoride, scandium nitrate, scandium oxide, lead oxide, bismuth oxide, lead fluoride, molybdenum oxide, and tungsten oxide. Preferably, the fluxes mainly include TeO2, MoO3, WO3, Li2CO3, and LiF, and composite fluxes mainly include one or more of TeO2-MoO3, TeO2-WO3, TeO2-Li2CO3, or TeO2-Li2CO3-LiF.

[0034] b. Preparation of tellurium niobate compound seed crystals: The mixed solution obtained in step a is slowly cooled to room temperature at a cooling rate of 0.1-10 ℃ / h to obtain tellurium niobate compound seed crystals by spontaneous crystallization;

[0035] c. Place the Pt crucible containing the mixed solution obtained in step a into a molten salt furnace. Fix the seed crystal obtained in step b onto the seed crystal rod using platinum wire, and place the seed crystal above the solution surface. First, preheat the seed crystal for 30-40 min. When the temperature is 5-15 ℃ above the saturation point, slowly immerse the seed crystal below the solution surface and hold it at that temperature for 5-20 min to remove impurities from the seed crystal surface. Then, reduce the temperature to the saturation point temperature at a cooling rate of 0.2-1 ℃ / min.

[0036] d. The crystal is then slowly cooled at a rate of 1-5 °C / h, with the seed crystal rod rotating at 3-60 rpm. Once the crystal reaches the desired size, it is lifted to a position 1-2 cm above the liquid surface. The temperature is then reduced to room temperature at a rate of 10-50 °C / h. Finally, the furnace is opened, and the crystal is removed to obtain the tellurium niobate nonlinear optical crystal A2Nb2Te4O. 15 ;

[0037] The molar ratio of TeO2 to MoO3 in the flux TeO2-MoO3 system is 1-10 : 1-10; the molar ratio of TeO2 to WO3 in the TeO2-WO3 system is 1-10 : 1-10; the molar ratio of TeO2 to Li2CO3 in the TeO2-Li2CO3 system is 1-10 : 1-20; and the molar ratio of TeO2 to Li2CO3 to LiF in the TeO2-Li2CO3-LiF system is 1-5 : 1-6 : 1-6.

[0038] The above-mentioned tellurium niobate crystal A2Nb2Te4O 15 The product has high purity, the crystals are easy to grow and are transparent without inclusions. It has advantages such as fast growth rate, low cost, and easy to obtain large-sized crystals. The obtained crystals have a relatively wide light transmission band, high hardness, good mechanical properties, are not easy to break or deliquesce, and are easy to process and store.

[0039] Tellurium niobate crystals A2Nb2Te4O obtained by the method described in this invention 15 It possesses a strong second harmonic generation effect, a large band gap, high electro-optic coefficient and piezoelectric coefficient, a wide transmission range and moderate birefringence. It can be used as a nonlinear optical crystal in the preparation of multi-band frequency doubling devices or optical elements, and can be used to manufacture second harmonic generators, up-down frequency converters, optical parametric oscillators, etc., and has potential application value. Attached Figure Description

[0040] Figure 1 The preferred compound in this invention is Ca2Nb2Te4O. 15 Powder XRD patterns;

[0041] Figure 2 The preferred compound in this invention is Ca2Nb2Te4O. 15 Crystal structure diagram;

[0042] Figure 3 The present invention is A2Nb2Te4O 15 A schematic diagram illustrating the working principle of a nonlinear optical device fabricated from a crystal, where 1 represents the light source, 2 represents the incident laser beam, and 3 represents A₂Nb₂Te₄O₂. 15 4 is the crystal, 5 is the laser beam produced, and 6 is the filter. Detailed Implementation

[0043] To better illustrate the present invention, the following description is provided in conjunction with embodiments. However, the scope of protection of the present invention is not limited to the scope described in the embodiments.

[0044] Example 1:

[0045] A2Nb2Te4O 15 The pure-phase synthesis follows the reaction equation: Nb₂O₅ + 2AO + 4TeO₂ → A₂Nb₂Te₄O 15

[0046] Analytical-grade AO, Nb₂O₅, and TeO₂ raw materials were weighed, ground, and mixed evenly in a molar ratio of 2:1:4. The mixture was then transferred to a 70 mm × 70 mm Pt crucible and placed in a muffle furnace. The temperature was raised to 300 °C and held for 24 h for pre-calcination to remove moisture and gases from the raw materials. Subsequently, the temperature was increased to 750 °C and calcined for at least 72 h. Finally, heating was stopped, and the sample was allowed to cool to room temperature with the furnace to prepare a polycrystalline powder, namely A₂Nb₂Te₄O₂. 15 Pure phase. The sample powder X-ray diffraction pattern is obtained using powder X-ray diffraction testing. This invention uses Ca2Nb2Te4O... 15 For example, its powder XRD pattern is shown in the attached figure. Figure 1 As shown, Ca2Nb2Te4O 15 The crystal structure diagram is attached. Figure 2 As shown;

[0047] The prepared tellurium niobate compound A2Nb2Te4O 15 Pure-phase polycrystalline powder and flux TeO2 were mixed at a molar ratio of 1:5 and thoroughly ground. The mixture was then placed in a 70 mm × 70 mm Pt crucible. The mixture was heated to approximately 700 °C at a heating rate of 50-80 °C / h to melt the raw materials and flux. The temperature was then maintained for 10-12 h to ensure a uniform concentration of the high-temperature solution within the Pt crucible. Simultaneously, a platinum wire was slowly lowered below the solution surface, followed by cooling to induce spontaneous crystallization. The chemical formula of this crystal is A₂Nb₂Te₄O₂. 15 ;

[0048] The solution was slowly cooled at a rate of 1-5 °C / h to obtain tellurium niobate crystals;

[0049] A2Nb2Te4O obtained by spontaneous crystallization 15Small crystals are used as seed crystals to grow tellurium niobate crystals using Top Seed Granules (TSSG) technology. The seed crystal is fixed to a seed rod using platinum wire. First, the seed crystal is preheated by placing it 1-2 cm above the solution surface. Then, at a temperature 5-15 °C above the saturation point, the seed crystal is slowly lowered into the solution and held for 30-40 minutes to remove surface impurities. Subsequently, the temperature is lowered to the saturation point.

[0050] Then, cool the crystal at a rate of 0.5-3 ℃ / day, with the seed crystal rod rotating at 5-60 rpm. After growth, lift the crystal to a point 1-2 cm above the liquid surface and cool it to room temperature at a rate of 10-50 ℃ / h. Then remove the crystal to obtain A2Nb2Te4O. 15 Crystal.

[0051] Example 2:

[0052] A2Nb2Te4O 15 The pure-phase synthesis follows the reaction equation: Nb₂O₅ + 2AF₂ + 4TeO₂ + O₂ → A₂Nb₂Te₄O 15 + 2F2 ↑

[0053] The prepared tellurium niobate compound A2Nb2Te4O 15 Polycrystalline powder (pure phase) was mixed with flux TeO2-MoO3 at a molar ratio of 1:3 and ground until homogeneous. The molar ratio of flux TeO2 to MoO3 was 1:2. The mixed sample was placed in a 70 mm × 70 mm Pt crucible, and the mixture was heated to 650-750 °C at a heating rate of 50-80 °C / h. After the mixture melted, it was held at this temperature for 10-12 h to ensure uniform concentration of the high-temperature solution in the Pt crucible. A platinum wire was then lowered below the surface of the solution, and the temperature was slowly lowered to induce spontaneous crystallization.

[0054] The solution was slowly cooled at a cooling rate of 1-5 °C / h to obtain tellurium niobate crystals;

[0055] A2Nb2Te4O obtained by spontaneous crystallization 15 The grain is used as a seed crystal for crystal growth. The seed crystal is fixed on the seed crystal rod using platinum wire. The seed crystal is first placed 1-2 cm above the liquid surface for preheating treatment. Then, at a temperature 5-15 ℃ above the saturation point, the seed crystal is slowly immersed below the liquid surface and held for 30-40 min to remove surface impurities. Afterward, the temperature is lowered to the saturation point temperature.

[0056] The crystal is then cooled at a rate of 0.5-3 °C / day, with the crystal rotation speed at 25-30 rpm and automatic forward and reverse rotation. After crystal growth is complete, the crystal is raised to 1-2 cm above the liquid surface, and the temperature is lowered to room temperature at a rate of 10-50 °C / h to obtain A₂Nb₂Te₄O. 15 Crystal.

[0057] Example 3:

[0058] A2Nb2Te4O 15 The pure-phase synthesis follows the reaction equation: 2A(OH)₂ + Nb₂O₅ + 4TeO₂ → A₂Nb₂Te₄O 15 + 2H2O ↑

[0059] The prepared compound tellurium niobate A2Nb2Te4O 15 Pure-phase polycrystalline powder and flux TeO2-Li2CO3 were mixed and ground uniformly in a molar ratio of 1:3, with a molar ratio of TeO2 to Li2CO3 of 2:1. The ground raw material mixture was placed in a 70 mm × 70 mm Pt crucible, and heated to 650-750 ℃ ​​at a heating rate of 50-80 ℃ / h. After the growth material and flux were completely melted, the temperature was maintained for 10-15 h to ensure uniform concentration of the high-temperature solution in the Pt crucible. Platinum wire was immersed below the surface of the solution, and then the temperature was slowly lowered to allow spontaneous crystallization.

[0060] The solution was slowly cooled at a cooling rate of 1-5 °C / h to obtain tellurium niobate crystals;

[0061] A2Nb2Te4O obtained by spontaneous crystallization 15 Small crystal grains are used as seed crystals for crystal growth. The seed crystal is fixed to the seed crystal rod using platinum wire. The seed crystal is first placed 1-2 cm above the liquid surface for preheating treatment. Then, at a temperature 5-15 ℃ above the saturation point, the seed crystal is slowly immersed below the liquid surface and held for 30-40 min to remove surface impurities. The temperature is then lowered to the saturation point temperature.

[0062] The liquid is then cooled at a rate of 0.5-3 °C / day, with the crystal rotation speed at 25-30 rpm and automatic forward and reverse rotation. After crystal growth is complete, the crystal is raised to 1-2 cm above the liquid surface, and the temperature is lowered to room temperature at a rate of 10-50 °C / h to obtain A₂Nb₂Te₄O. 15 Crystal.

[0063] Example 4:

[0064] A2Nb2Te4O 15The pure-phase synthesis follows the reaction equation: 2ACl₂ + Nb₂O₅ + 4TeO₂ + O₂ → A₂Nb₂Te₄O 15 + 2Cl2 ↑

[0065] The prepared compound tellurium niobate A2Nb2Te4O 15 Pure-phase polycrystalline powder was mixed with flux TeO2-Li2CO3-LiF in a molar ratio of 1:2 and ground until homogeneous, with the molar ratio of TeO2, Li2CO3, and LiF being 2:1:1. The ground raw material mixture was placed in a 70 mm × 70 mm Pt crucible, and the mixture was heated to 650-750 °C at a heating rate of 50-80 °C / h. After the crystal growth raw material and flux were completely melted, the temperature was maintained for 10-15 h to ensure uniform concentration of the high-temperature solution in the Pt crucible. Platinum wire was immersed below the surface of the solution, and then the temperature was slowly lowered to allow spontaneous crystallization.

[0066] The solution was slowly cooled at a cooling rate of 1-5 °C / h to obtain tellurium niobate crystals;

[0067] A2Nb2Te4O obtained by spontaneous crystallization 15 Small crystal grains are used as seed crystals for crystal growth. The seed crystal is fixed on the seed crystal rod using platinum wire. The seed crystal is first placed 1-2 cm above the liquid surface for preheating treatment. Then, at a temperature 5-15 ℃ above the saturation point, the seed crystal is slowly immersed below the liquid surface and held for 30-40 min to remove surface impurities. The temperature is then lowered to the saturation point temperature.

[0068] The liquid is then cooled at a rate of 0.5-3 °C / day, with the crystal rotation speed at 25-30 rpm and automatic forward and reverse rotation. After crystal growth is complete, the crystal is raised to 1-2 cm above the liquid surface, and the temperature is lowered to room temperature at a rate of 10-50 °C / h to obtain A₂Nb₂Te₄O. 15 Crystal.

[0069] Example 5:

[0070] A2Nb2Te4O 15 The pure-phase synthesis follows the reaction equation: Nb₂O₅ + 2ACO₃ + 4TeO₂ → A₂Nb₂Te₄O 15 +2CO2 ↑

[0071] The prepared compound tellurium niobate A2Nb2Te4O 15Pure-phase polycrystalline powder and flux TeO2 were mixed at a molar ratio of 1:5 and ground uniformly. The ground raw material mixture was placed in a 70 mm × 70 mm Pt crucible, and the mixture was heated to 650-750 ℃ ​​at a heating rate of 50-80 ℃ / h. After the crystal growth raw material and flux were completely melted, the temperature was maintained for 10-15 h to ensure uniform concentration of the high-temperature solution in the Pt crucible. Platinum wire was immersed below the surface of the solution, and then the temperature was slowly lowered to allow spontaneous crystallization.

[0072] The solution was slowly cooled at a cooling rate of 1-5 °C / h to obtain tellurium niobate crystals;

[0073] A2Nb2Te4O obtained by spontaneous crystallization 15 Small crystal grains are used as seed crystals for crystal growth. The seed crystal is fixed on the seed crystal rod using platinum wire. The seed crystal is first placed 1-2 cm above the liquid surface for preheating treatment. Then, at a temperature 5-15 ℃ above the saturation point, the seed crystal is slowly immersed below the liquid surface and held for 30-40 min to remove surface impurities. The temperature is then lowered to the saturation point temperature.

[0074] The liquid is then cooled at a rate of 0.5-3 °C / day, with the crystal rotation speed at 25-30 rpm and automatic forward and reverse rotation. After crystal growth is complete, the crystal is raised to 1-2 cm above the liquid surface, and the temperature is lowered to room temperature at a rate of 10-50 °C / h to obtain A₂Nb₂Te₄O. 15 Crystal.

[0075] Example 6:

[0076] A2Nb2Te4O 15 The pure-phase synthesis follows the reaction equation: Nb₂O₅ + 2ACl₂ + 4TeCl₄ + 5O₂ → A₂Nb₂Te₄O 15 + 10Cl2 ↑

[0077] The prepared compound tellurium niobate A2Nb2Te4O 15 Pure-phase polycrystalline powder and flux TeO2-MoO3 were mixed and ground uniformly at a molar ratio of 1:3, wherein the molar ratio of flux TeO2 to MoO3 was 1:2. The ground raw material mixture was placed in a 70 mm × 70 mm Pt crucible, and the mixture was heated to 650-750 °C at a heating rate of 50-80 °C / h. After the crystal growth raw material and flux were completely melted, the temperature was maintained for 10-15 h to ensure uniform concentration of the high-temperature solution in the Pt crucible. Platinum wire was immersed below the surface of the solution, and then the temperature was slowly lowered to allow spontaneous crystallization.

[0078] The solution was slowly cooled at a cooling rate of 1-5 °C / h to obtain tellurium niobate crystals;

[0079] A2Nb2Te4O obtained by spontaneous crystallization 15 Small crystal grains are used as seed crystals for crystal growth. The seed crystal is fixed on the seed crystal rod using platinum wire. The seed crystal is first placed 1-2 cm above the liquid surface for preheating treatment. Then, at a temperature 5-15 ℃ above the saturation point, the seed crystal is slowly immersed below the liquid surface and held for 30-40 min to remove surface impurities. The temperature is then lowered to the saturation point temperature.

[0080] The liquid is then cooled at a rate of 0.5-3 °C / day, with the crystal rotation speed at 25-30 rpm and automatic forward and reverse rotation. After crystal growth is complete, the crystal is raised to 1-2 cm above the liquid surface, and the temperature is lowered to room temperature at a rate of 10-50 °C / h to obtain A₂Nb₂Te₄O. 15 Crystal.

[0081] Example 7:

[0082] A2Nb2Te4O 15 The pure-phase synthesis follows the reaction equation: Nb₂O₅ + 2AF₂ + 4TeCl₄ + 5O₂ → A₂Nb₂Te₄O 15 + 2F₂ ↑ + 8Cl₂ ↑

[0083] The prepared compound tellurium niobate A2Nb2Te4O 15 Pure-phase polycrystalline powder and flux TeO2-Li2CO3-LiF were mixed and ground uniformly at a molar ratio of 1:2. The ground raw material mixture was placed in a 70 mm × 70 mm Pt crucible, and the mixture was heated to 650-750 ℃ ​​at a heating rate of 50-80 ℃ / h. After the crystal growth raw material and flux were completely melted, the temperature was kept constant for 10-15 h to ensure uniform concentration of the high-temperature solution in the Pt crucible. Platinum wire was immersed below the surface of the solution, and then the temperature was slowly lowered to allow spontaneous crystallization.

[0084] The solution was slowly cooled at a cooling rate of 1-5 °C / h to obtain tellurium niobate crystals;

[0085] A2Nb2Te4O obtained by spontaneous crystallization 15 Small crystal grains are used as seed crystals for crystal growth. The seed crystal is fixed on the seed crystal rod using platinum wire. The seed crystal is first placed 1-2 cm above the liquid surface for preheating treatment. Then, at a temperature 5-15 ℃ above the saturation point, the seed crystal is slowly immersed below the liquid surface and held for 30-40 min to remove surface impurities. The temperature is then lowered to the saturation point temperature.

[0086] The liquid is then cooled at a rate of 0.5-3 °C / day, with the crystal rotation speed at 25-30 rpm and automatic forward and reverse rotation. After crystal growth is complete, the crystal is raised to 1-2 cm above the liquid surface, and the temperature is lowered to room temperature at a rate of 10-50 °C / h to obtain A₂Nb₂Te₄O. 15 Crystal.

[0087] Example 8:

[0088] A2Nb2Te4O 15 The pure-phase synthesis follows the reaction equation: Nb₂O₅ + 2ACO₃ + 4TeCl₄ + 4O₂ → A₂Nb₂Te₄O 15 + 2CO2 ↑ + 8Cl2 ↑

[0089] The prepared compound tellurium niobate A2Nb2Te4O 15 Pure-phase polycrystalline powder and flux Li₂CO₃ were mixed and ground uniformly at a molar ratio of 1:3. The ground raw material mixture was placed in a 70 mm × 70 mm Pt crucible, and the mixture was heated to 650-750 °C at a heating rate of 50-80 °C / h. After the crystal growth raw material and flux were completely melted, the temperature was maintained for 10-15 h to ensure uniform concentration of the high-temperature solution in the Pt crucible. Platinum wire was immersed below the surface of the solution, and then the temperature was slowly lowered to allow spontaneous crystallization.

[0090] The solution was slowly cooled at a cooling rate of 1-5 °C / h to obtain tellurium niobate crystals;

[0091] A2Nb2Te4O obtained by spontaneous crystallization 15 Small crystal grains are used as seed crystals for crystal growth. The seed crystal is fixed on the seed crystal rod using platinum wire. The seed crystal is first placed 1-2 cm above the liquid surface for preheating treatment. Then, at a temperature 5-15 ℃ above the saturation point, the seed crystal is slowly immersed below the liquid surface and held for 30-40 min to remove surface impurities. The temperature is then lowered to the saturation point temperature.

[0092] The liquid is then cooled at a rate of 0.5-3 °C / day, with the crystal rotation speed at 25-30 rpm and automatic forward and reverse rotation. After crystal growth is complete, the crystal is raised to 1-2 cm above the liquid surface, and the temperature is lowered to room temperature at a rate of 10-50 °C / h to obtain A₂Nb₂Te₄O. 15 Crystal.

[0093] Example 9:

[0094] A2Nb2Te4O 15The pure-phase synthesis follows the reaction equation: 4NbCl5 + 4ACl2 + 8TeO2 + 7O2 → 2A2Nb2Te4O 15 + 14Cl2 ↑

[0095] The prepared compound tellurium niobate A2Nb2Te4O 15 Pure-phase polycrystalline powder and flux TeO2 were mixed at a molar ratio of 1:5 and ground uniformly. The ground raw material mixture was placed in a 70 mm × 70 mm Pt crucible, and the mixture was heated to 650-750 ℃ ​​at a heating rate of 50-80 ℃ / h. After the crystal growth raw material and flux were completely melted, the temperature was kept constant for 10-15 h to ensure uniform concentration of the high-temperature solution in the Pt crucible. Platinum wire was immersed below the surface of the solution, and then the temperature was slowly lowered to allow spontaneous crystallization.

[0096] The solution was slowly cooled at a cooling rate of 1-5 °C / h to obtain tellurium niobate crystals;

[0097] A2Nb2Te4O obtained by spontaneous crystallization 15 Small crystal grains are used as seed crystals for crystal growth. The seed crystal is fixed on the seed crystal rod using platinum wire. The seed crystal is first placed 1-2 cm above the liquid surface for preheating treatment. Then, at a temperature 5-15 ℃ above the saturation point, the seed crystal is slowly immersed below the liquid surface and held for 30-40 min to remove surface impurities. The temperature is then lowered to the saturation point temperature.

[0098] The liquid is then cooled at a rate of 0.5-3 °C / day, with the crystal rotation speed at 25-30 rpm and automatic forward and reverse rotation. After crystal growth is complete, the crystal is raised to 1-2 cm above the liquid surface, and the temperature is lowered to room temperature at a rate of 10-50 °C / h to obtain A₂Nb₂Te₄O. 15 Crystal.

[0099] Example 10:

[0100] The A2Nb2Te4O obtained in Examples 1-9 15 A single-crystal device is fabricated along the phase-matching direction and placed in the adjacent... Figure 3 In the optical path shown, at room temperature, a Q-switched Nd:YAG laser is used as the light source, with an incident wavelength of 1064 nm. An infrared beam 2 with a wavelength of 1064 nm emitted from the Q-switched Nd:YAG laser 1 is incident on the tellurate crystal A2Nb2Te4O. 15 The emitted beam 4 contains infrared light with a wavelength of 1064 nm and green light with a wavelength of 532 nm. After being filtered by filter 5, a green laser with a wavelength of 532 nm is obtained.

[0101] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A series of tellurium niobate compounds, characterized in that, Its general chemical formula is A2Nb2Te4O 15 Where A = Mg, Ca, Sr, Ba; the molecular formulas are Mg₂Nb₂Te₄O₄, respectively. 15 Ca2Nb2Te4O 15 Sr2Nb2Te4O 15 ,Ba2Nb2Te4O 15 .

2. The method for preparing the series of tellurium niobate compounds according to claim 1, characterized in that, The solid-state reaction method is used for preparation, including the following steps: A compound containing A, a compound containing Nb, and a compound containing Te are mixed evenly, ground, and then placed in a muffle furnace for pre-calcination to remove moisture and gases from the raw materials. After cooling to room temperature, the mixture is removed, ground again, and then calcined in a muffle furnace to obtain the tellurium niobate compound A₂Nb₂Te₄O. 15 Pure-phase polycrystalline powder; wherein the molar ratio of element A in the A-containing compound, element Nb in the Nb-containing compound, and element Te in the Te-containing compound is 1.8-2.5 : 1.5-2.5 : 3.8-4.2, and A = Mg, Ca, Sr, Ba.

3. The method for preparing the series of tellurium niobate compounds according to claim 2, characterized in that: The A-containing compound includes at least one of AO, A(OH)2, or an A salt; the A salt includes at least one of AF2, ACl2, and ACO3. The Nb-containing compound includes at least one of Nb₂O₅ and NbCl₅; The Te-containing compound includes at least one of TeO2, TeS2, and TeCl4.

4. Tellurium niobate crystal A₂Nb₂Te₄O 15 Its characteristics are, This crystal has a non-centrosymmetric structure, belongs to the orthorhombic crystal system, space group Pma2, and A = Mg, Ca, Sr, Ba, among which Ca2Nb2Te4O 15 The unit cell parameters are: a = 7.5955(6) Å, b = 11.1691(6) Å, c = 3.9748(3) Å, α = β = γ = 90°, Z = 1, and the volume is 337.20(4) Å. 3 .

5. The tellurium niobate crystal A2Nb2Te4O as described in claim 4 15 The preparation method of the [method] is characterized by, Growth was achieved using a fluxing method.

6. The method according to claim 5, characterized in that, The specific operation is carried out according to the following steps: a. The pure-phase polycrystalline powder of tellurium niobate compound obtained in claim 2, or a mixture of the pure-phase polycrystalline powder of tellurium niobate compound obtained in claim 2 and a flux, is heated to melt to obtain an unsaturated molten mixture, and then cooled or grown at a constant temperature to prepare tellurium niobate crystals A2Nb2Te4O. 15 Seed crystals; or directly heating a mixture containing A, Nb, and Te compounds, or a mixture containing A, Nb, and Te compounds and a flux, to melt to obtain an unsaturated mixed melt, then cooling or growing at an isothermal temperature to prepare tellurate crystals A₂Nb₂Te₄O. 15 Seed crystals; where A = Mg, Ca, Sr, Ba; b. Place the crucible containing the mixed melt obtained in step a into a crystal growth furnace, fix the seed crystal on the seed crystal rod, and lower the seed crystal to the surface of the mixed melt or into the mixed melt for remelting until it reaches the saturation temperature; then grow at a lower or constant temperature to prepare tellurium niobate crystal A2Nb2Te4O. 15 .

7. The method according to claim 6, characterized in that, The molar ratio of the pure-phase polycrystalline powder of tellurium niobate compound to the flux is 1:0-40; or the molar ratio of the A-containing compound, Nb-containing compound, Te-containing compound to the flux is 1.8-2.5 : 1.5-2.5 : 3.8-4.2 : 0-40; the flux includes alkali metal salts, namely alkali metal borates, alkali metal carbonates, alkali metal phosphates, alkali metal nitrates, alkali metal fluoroborates, alkali metal sulfates, alkali metal oxalates, alkali metal halides, alkali metal metaborates and alkali metal oxides, alkali metal hydroxides, as well as at least one or more of boric acid, phosphoric acid, tellurium oxide, boron oxide, lanthanum fluoride, lanthanum nitrate, lanthanum oxide, scandium fluoride, scandium nitrate, scandium oxide, lead oxide, bismuth oxide, lead fluoride, molybdenum oxide, and tungsten oxide.

8. The tellurium niobate crystal A2Nb2Te4O as described in claim 4 15 Its uses, characterized in that, Used as an optical frequency conversion crystal, it is used to prepare multi-band frequency doubling devices or optical elements, second harmonic generators, up- and down-frequency converters, and optical parametric oscillators.

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