A preparation method of a potassium tantaloniobate crystal with a three-dimensional periodic polarization structure

Abstract

This invention belongs to the field of nonlinear optical crystal material preparation, and particularly relates to a method for preparing potassium tantalate niobate crystals with a three-dimensional periodic polarization structure. The method includes uniformly mixing raw materials in a mixer, pressing them into blocks using a press, and sintering them in a muffle furnace to obtain polycrystalline potassium tantalate niobate. The polycrystalline potassium tantalate niobate is grown using a top-seeded solution method, with the seed crystal placed at a position r / 2 to r / 3 away from the center of the melt temperature field. The seed crystal pulling speed v changes periodically with time t to complete crystal growth. The resulting crystal is then subjected to thermal annealing to prepare a potassium tantalate niobate crystal with a three-dimensional periodic polarization structure. This invention directly achieves the preparation of periodically polarized crystals by controlling the crystal growth process parameters, relying on the spontaneous polarization of the crystal. It does not require external high voltage or complex photolithography electrodes. Furthermore, the addition of the thermal annealing process further improves the integrity and uniformity of the periodically polarized flipped ferroelectric domains.

Description

Technical Field

[0001] This invention belongs to the field of nonlinear optical crystal material preparation, and particularly relates to a method for preparing potassium tantalate niobate crystal with a three-dimensional periodic polarization structure. Background Technology

[0002] Periodic polarization of nonlinear crystal materials is a technique used to obtain quasi-phase matching in nonlinear interactions, which can realize nonlinear optical frequency conversion and has the advantages of high efficiency, design freedom, small size and low cost.

[0003] Currently, the commonly used nonlinear crystal materials suitable for achieving periodic polarization mainly include lithium niobate (LN), lithium tantalate (LT), and potassium titanium oxyphosphate (KTP). They are usually prepared by electric field polarization, but electric field polarization can usually only achieve one-dimensional or two-dimensional periodic polarization.

[0004] How to prepare crystals with three-dimensional periodic polarization has always been a research challenge and hot topic in this field. Summary of the Invention

[0005] This invention addresses the aforementioned technical difficulties in the preparation of three-dimensional periodic polarized crystals by proposing a method for preparing potassium tantalate niobate crystals with a three-dimensional periodic polarization structure. The three-dimensional periodic polarization structure, as a more complex spatial periodic polarization structure, can further expand the possible applications of this crystal in the field of nonlinear optics.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing potassium tantalate niobate crystals with a three-dimensional periodic polarization structure is characterized by mixing raw materials uniformly on a mixer, pressing them into blocks using a press, and sintering them in a muffle furnace to obtain potassium tantalate niobate polycrystalline material. The potassium tantalate niobate polycrystalline material is grown using the top seed crystal solution method.

[0008] In this process, the seed crystal is placed at a position r / 2 to r / 3 away from the center of the melt temperature field. The seed crystal pulling speed v changes periodically with time t to complete crystal growth. Then, the obtained crystal is subjected to thermal annealing to prepare a potassium tantalate niobate crystal with a three-dimensional periodic polarization structure.

[0009] Preferably, the raw material molar ratio of the potassium tantalate niobate crystal is: K2CO3:(Ta2O5+Nb2O5)=(1.0~1.2):1; Ta2O5:Nb2O5=(1-x):x, where 0.6≤x≤0.75.

[0010] Preferably, the potassium tantalate niobate crystal is made of Li + Mn 2+ Co-doping, Li in the raw material+ Doping amount is (5-10)at%, Mn 2+ The doping amount is (1-2)at%.

[0011] Preferably, the seed crystal pulling speed v varies periodically with time t, expressed as v = Asin(Bt) + C, where v is in mm / s, t is in s, and A, B, and C are constants with values ​​ranging from 0.5 × 10⁻⁶ to 10⁻⁶. -4 ≤A≤1.5×10 -4 , 2≤B≤2.5, 0.2×10 -4 ≤C≤0.8×10 -4 .

[0012] Preferably, the annealing temperature of the heat annealing treatment is 350-450℃, the heating rate is 30-50℃ / h, and the holding time is 10-15h; after the holding time is completed, the temperature is reduced to room temperature at a cooling rate of 30-50℃ / h.

[0013] Preferably, when preparing the potassium tantalate niobate polycrystalline material, the raw material needs to be pre-sintered in a muffle furnace at a temperature of 850-900℃ for 5-8 hours.

[0014] Preferably, the seed crystal rotation speed during the constant diameter stage of the top seed crystal solution growth process is 20-25 rpm, which can avoid the occurrence of growth defects such as hollow cores.

[0015] Compared with the prior art, the advantages and positive effects of the present invention are as follows: It provides a method for preparing potassium tantalate niobate crystals with a three-dimensional periodic polarization structure. Compared with the external electric field polarization method that is currently widely used in the preparation of periodically polarized lithium niobate crystals, the present invention can directly achieve the preparation of periodically polarized crystals by controlling the crystal growth process parameters and relying on the spontaneous polarization of the crystal. It does not require external high voltage or complex photolithography electrodes. Moreover, the addition of thermal annealing technology further improves the integrity and uniformity of the periodically polarized flipped ferroelectric domains.

[0016] Furthermore, traditional electric field polarization techniques can typically only prepare one-dimensional and two-dimensional periodically polarized crystal structures. This invention combines eccentric growth techniques with periodic variable-speed Czochralski growth techniques, enabling the crystal to simultaneously generate periodic compositional fringes along the axial and radial directions. This allows the crystal to spontaneously form a three-dimensional periodically polarized structure, solving the problem of preparing three-dimensional periodically polarized crystals and expanding the application space of potassium tantalate niobate crystals. Compared with existing femtosecond laser three-dimensional direct writing and femtosecond laser-induced polarization reversal techniques, this technology has the advantages of being simple, efficient, and low-cost. Attached Figure Description

[0017] Figure 1This is a schematic diagram showing the positional relationship between the seed crystal and the center of the melt temperature field when potassium tantalate niobate polycrystalline material is grown in the top seed crystal solution method in an embodiment of the present invention.

[0018] Figure 2 This is a graph showing the change in lifting speed versus time in Examples 1-3 of the present invention;

[0019] Figure 3 The potassium tantalate niobate crystal prepared in Example 1 of the present invention was observed to have a three-dimensional periodic polarization structure along three different directions (a, b, and c) using a polarizing microscope.

[0020] Figure 4 The lattice diffraction images of the potassium tantalate niobate crystal prepared in Example 1 of the present invention were obtained by laser incident along three different directions a, b, and c of the crystal.

[0021] Figure 5 A polarized light micrograph of a two-dimensional periodic polarized structure prepared for Comparative Example 1;

[0022] Figure 6 A polarized light micrograph of a two-dimensional periodic polarized structure prepared for Comparative Example 2;

[0023] Among them, 1. Platinum crucible; 2. Seed crystal. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] K2CO3, Ta2O5 and Nb2O5 with a purity of 4N were selected as raw materials and prepared into powder according to a molar ratio of 1.2:0.37:0.63. 5 at% Li2CO3 and 1 at% MnO were added and mixed evenly on a mixer for 12 hours. The mixture was then pressed into blocks using a press and placed in a bowl-shaped platinum crucible. The blocks were sintered in a muffle furnace at 850℃ for 8 hours to obtain potassium tantalate niobate polycrystalline material.

[0027] Then, crystal growth is performed using the top seed solution method, with the crystal growth apparatus as follows: Figure 1As shown, the heating method is medium-frequency induction heating. The seed crystal is located at a position r / 2 away from the center of the temperature field to generate periodic component stripes in the radial direction of the crystal. During the material preparation stage, after the melt has completely melted, the temperature needs to be increased by 100-150℃ to ensure that the melt components are fully mixed and homogeneous. Then, the temperature is slowly lowered to slightly above the melting point, and the oriented seed crystal is slowly lowered into the melt. The seed crystal rod speed is set to 10 rpm. After the surface of the seed crystal has slightly melted, the temperature is slowly lowered and the seed crystal is thinned at a pulling speed of 2 mm / h, with a necking length of 2 mm. Then, the system temperature is further reduced, and the pulling speed is controlled to 0.1 mm / h to form the shoulder of the crystal. After the crystal diameter reaches 15 mm, the temperature is appropriately increased by 3-5℃ to enter the constant diameter growth stage. During this stage, the seed crystal rotation speed is set to 20 rpm to avoid growth defects such as hollow cores. The pulling speed is programmed to change periodically with time, i.e., v = 0.5 × 10⁻⁶. -4 sin(2t) + 0.2 × 10 -4 The lifting speed change curve is as follows Figure 2 It is used to produce periodic composition stripes in the axial direction of the crystal.

[0028] Once the crystal length reached 30 mm, the melt temperature was increased to 50°C above the melting point, and the crystal was rapidly pulled out of the liquid surface. It was then cooled to room temperature at a rate of 30°C / h to complete the crystal growth. To improve the integrity and uniformity of the domain structure, the crystal was thermally annealed in a muffle furnace after growth. The heating rate was 30°C / h, the annealing temperature was 350°C, and the holding time was 10 h. It was then cooled to room temperature at a rate of 30°C / h to obtain potassium tantalate niobate crystals with a three-dimensional periodic polarization structure.

[0029] Figure 3 These are three-dimensional periodic polarization structure images of the potassium tantalate niobate crystal prepared in Example 1, observed along three different directions (a, b, and c) using a polarizing microscope. Figure 4 The lattice diffraction images obtained by incident laser light along three different directions (a, b, and c) on the potassium tantalate niobate crystal prepared in this embodiment demonstrate the formation of a three-dimensional periodic polarization structure inside the crystal.

[0030] Example 2

[0031] K2CO3, Ta2O5 and Nb2O5 raw materials with a purity of 4N were selected and prepared into powder according to a molar ratio of 1:0.25:0.75. 10 at% Li2CO3 and 2 at% MnO were also added. After being mixed evenly on a mixer for 20 hours, the mixture was pressed into blocks using a press and placed in a platinum crucible. The blocks were then sintered in a muffle furnace at 900℃ for 5 hours to obtain potassium tantalate niobate polycrystalline material.

[0032] Then, crystal growth is performed using the top-seeded solution method, with medium-frequency induction heating. The seed crystal is positioned r / 3 away from the center of the temperature field to induce periodic component striations in the radial direction. During the melting stage, the temperature is increased by 100–150°C after the melt has completely melted to ensure thorough and uniform mixing of the melt components. The temperature is then slowly lowered to slightly above the melting point, and the oriented seed crystal is slowly lowered into the melt. The seed crystal rod speed is set to 5 rpm. After the seed crystal surface has slightly melted, the temperature is slowly lowered, and the seed crystal is thinned at a pulling speed of 3 mm / h, with a necking length of 1 mm. The system temperature is then further reduced, and the pulling speed is controlled to 0.2 mm / h to develop the shoulder of the crystal. Once the crystal diameter reaches 20 mm, the temperature is appropriately increased by 5–10°C, transitioning to the constant-diameter growth stage. In this stage, the seed crystal rotation speed is set to 25 rpm, and the pulling speed is programmed to vary periodically over time, i.e., v = 1.5 × 10⁻⁶. -4 sin(2.5t) + 0.8 × 10 -4 The lifting speed change curve is as follows Figure 2 It is used to produce periodic composition stripes in the axial direction of the crystal.

[0033] Once the crystal length reaches 25 mm, the melt temperature is increased to 40°C above the melting point, and the crystal is rapidly pulled out of the liquid surface. It is then cooled to room temperature at a rate of 20°C / h to complete the crystal growth. To improve the integrity and uniformity of the domain structure, the crystal is further annealed in a muffle furnace after growth. The annealing temperature is 450°C, with a heating rate of 50°C / h and a holding time of 15 h. It is then cooled to room temperature at a rate of 50°C / h, finally yielding potassium tantalate niobate crystals with a three-dimensional periodic polarization structure.

[0034] Example 3

[0035] K2CO3, Ta2O5 and Nb2O5 raw materials with a purity of 4N were selected and prepared into powder according to a molar ratio of 1.1:0.4:0.6. 6 at% Li2CO3 and 1.5 at% MnO were also doped into the powder. After being mixed evenly on a mixer for 18 hours, the powder was pressed into blocks using a press and placed in a platinum crucible. The blocks were then sintered in a muffle furnace at 880℃ for 6 hours to obtain potassium tantalate niobate polycrystalline material.

[0036] Then, crystal growth is performed using the top-seeded solution method, with medium-frequency induction heating. The seed crystal is positioned r / 3 away from the center of the temperature field to induce periodic component striations in the crystal radially. During the melting stage, after the melt has completely melted, the temperature is increased by 100–150°C to ensure thorough and uniform mixing of the melt components. The temperature is then slowly lowered to slightly above the melting point, and the oriented seed crystal is slowly lowered into the melt. The seed crystal rod speed is set to 8 rpm. After the seed crystal surface has slightly melted, the temperature is slowly lowered, and the seed crystal is thinned at a pulling speed of 3 mm / h, with a necking length of 2 mm. The system temperature is then further reduced, and the pulling speed is controlled to 0.1 mm / h to develop the shoulder of the crystal. Once the crystal diameter reaches 25 mm, the temperature is appropriately increased by 5–10°C, transitioning to the constant-diameter growth stage. In this stage, the seed crystal rotation speed is set to 22 rpm to avoid growth defects such as hollow cores. The pulling speed is programmed to change periodically with time, i.e., v = 10. -4 sin(2.2t) + 0.5 × 10 -4 The change curve is as follows Figure 2 It is used to produce periodic composition stripes in the axial direction of the crystal.

[0037] Once the crystal length reaches 15 mm, the melt temperature is increased to 60°C above the melting point, and the crystal is rapidly pulled out of the liquid surface. It is then cooled to room temperature at a rate of 40°C / h to complete the crystal growth. To improve the integrity and uniformity of the domain structure, the crystal is subjected to thermal annealing in a muffle furnace after growth. The heating rate is 40°C / h, the annealing temperature is 400°C, and the holding time is 12 hours. The crystal is then cooled to room temperature at a rate of 40°C / h, finally yielding a potassium tantalate niobate crystal with a three-dimensional periodic polarization structure.

[0038] Example 4

[0039] K2CO3, Ta2O5 and Nb2O5 raw materials with a purity of 4N were selected and prepared into powder according to a molar ratio of 1.05:0.3:0.7. 7 at% Li2CO3 and 1.2 at% MnO were also added. After mixing for 15 hours in a mixer, the mixture was pressed into blocks using a press and placed in a platinum crucible. The blocks were then sintered in a muffle furnace at 860℃ for 7 hours to obtain potassium tantalate niobate polycrystalline material.

[0040] Then, crystal growth is performed using the top-seeded solution method, with medium-frequency induction heating. The seed crystal is positioned r / 2 away from the center of the temperature field to induce periodic component striations in the radial direction. During the melting stage, the temperature is increased by 100–150°C after the melt has completely melted to ensure thorough and uniform mixing of the melt components. The temperature is then slowly lowered to slightly above the melting point, and the oriented seed crystal is slowly lowered into the melt. The seed crystal rod speed is set to 7 rpm. After the seed crystal surface has slightly melted, the temperature is slowly lowered, and the seed crystal is thinned at a pulling speed of 2 mm / h, with a necking length of 1 mm. The system temperature is then further reduced, and the pulling speed is controlled to 0.1 mm / h to develop the shoulder of the crystal. Once the crystal diameter reaches 18 mm, the temperature is appropriately increased by 5–10°C, transitioning to the constant-diameter growth stage. In this stage, the seed crystal rotation speed is set to 21 rpm to avoid growth defects such as hollow cores. The pulling speed is programmed to change periodically over time, i.e., v = 0.8 × 10⁻⁶. -4 sin(2.1t) + 0.3 × 10 -4 It is used to produce periodic composition stripes in the axial direction of the crystal.

[0041] Once the crystal length reaches 20 mm, the melt temperature is increased to 55°C above the melting point. The crystal is then rapidly pulled out of the liquid surface and cooled to room temperature at a rate of 35°C / h to complete the crystal growth. To improve the integrity and uniformity of the domain structure, the crystal is further annealed in a muffle furnace after growth. The heating and cooling rate is 35°C / h, the annealing temperature is 420°C, and the holding time is 11 h. The crystal is then cooled to room temperature at a rate of 50°C / h, finally yielding potassium tantalate niobate crystals with a three-dimensional periodic polarization structure.

[0042] Example 5

[0043] K2CO3, Ta2O5 and Nb2O5 raw materials with a purity of 4N were selected and prepared into powder according to a molar ratio of 1.05:0.6:0.4. 9 at% Li2CO3 and 1.8 at% MnO were also added. After mixing for 18 hours in a mixer, the mixture was pressed into blocks using a press, placed in a platinum crucible, and sintered in a muffle furnace at 890℃ for 5.5 hours to obtain potassium tantalate niobate polycrystalline material.

[0044] Then, crystal growth is performed using the top-seeded solution method, with medium-frequency induction heating. The seed crystal is positioned r / 3 away from the center of the temperature field to induce periodic component striations in the radial direction. During the melting stage, the temperature is increased by 100–150°C after the melt has completely melted to ensure thorough and uniform mixing of the melt components. The temperature is then slowly lowered to slightly above the melting point, and the oriented seed crystal is slowly lowered into the melt. The seed crystal rod speed is set to 9 rpm. After the seed crystal surface has slightly melted, the temperature is slowly lowered, and the seed crystal is thinned at a pulling speed of 2 mm / h, with a necking length of 2 mm. The system temperature is then further reduced, and the pulling speed is controlled to 0.2 mm / h to develop the shoulder of the crystal. Once the crystal diameter reaches 22 mm, the temperature is appropriately increased by 5–10°C, transitioning to the constant-diameter growth stage. In this stage, the seed crystal rotation speed is set to 24 rpm to avoid growth defects such as hollow cores. The pulling speed is programmed to change periodically over time, i.e., v = 1.2 × 10⁻⁶. -4 sin(2.4t) + 0.6 × 10 -4 It is used to produce periodic composition stripes in the axial direction of the crystal.

[0045] Once the crystal length reaches 25 mm, the melt temperature is increased to 55°C above the melting point. The crystal is then rapidly pulled out of the liquid surface and cooled to room temperature at a rate of 35°C / h to complete the crystal growth. To improve the integrity and uniformity of the domain structure, the crystal is further annealed in a muffle furnace after growth. The heating and cooling rate is 45°C / h, the annealing temperature is 380°C, and the holding time is 14 h. The crystal is then cooled to room temperature at a rate of 45°C / h, finally yielding potassium tantalate niobate crystals with a three-dimensional periodic polarization structure.

[0046] Comparative Example 1

[0047] Unlike Example 1, the crystal pulling speed v during the constant diameter growth stage was kept constant at 0.5 mm / h. All other steps and parameters were identical to those in Example 1, resulting in a potassium tantalate niobate crystal with a two-dimensional periodic polarization structure. The internal polarization structure of the crystal, observed using a polarizing microscope, is as follows: Figure 5 As shown.

[0048] Comparative Example 2

[0049] Unlike Example 1, the seed crystal position is changed to the temperature field center. All other steps and parameters are exactly the same as in Example 1, and a potassium tantalate niobate crystal with a two-dimensional periodic polarization structure can be obtained. The internal polarization structure of the crystal observed using a polarizing microscope is as follows: Figure 6 As shown.

Claims

1. A method for preparing potassium tantalate niobate crystals with a three-dimensional periodic polarization structure, characterized in that, The raw materials are mixed evenly on a mixer, pressed into blocks by a press, and sintered in a muffle furnace to obtain potassium tantalate niobate polycrystalline material. The potassium tantalate niobate polycrystalline material is grown using the top seed crystal solution method. In this process, the seed crystal is placed at a position r / 2 to r / 3 away from the center of the melt temperature field. The seed crystal pulling speed v changes periodically with time t to complete crystal growth. Then, the obtained crystal is subjected to thermal annealing to prepare a potassium tantalate niobate crystal with a three-dimensional periodic polarization structure. The seed crystal pulling speed v is expressed as v = Asin(Bt) + C, where v is in mm / s, t is in s, and A, B, and C are constants with values ​​ranging from 0.5 × 10⁻⁶ to 0.5 × 10⁻⁶. -4 ≤A≤1.5×10 -4 , 2≤B≤2.5, 0.2×10 -4 ≤C≤0.8×10 -4 .

2. The method of producing a potassium tantaloniobate crystal having a three-dimensional periodic polarization structure according to claim 1, characterized by, The raw material molar ratio of the potassium tantalate niobate crystal is: K2CO3:(Ta2O5+Nb2O5)=(1.0~1.2):1; Ta2O5:Nb2O5=(1-x):x, where 0.6≤x≤0.

75.

3. The method of producing a potassium tantaloniobate crystal having a three-dimensional periodic polarization structure according to claim 2, characterized by, Potassium tantalate niobate crystals are made of Li + Mn 2+ Co-doping, Li in the raw material + The doping amount is (5-10) at%, Mn 2+ The doping amount is (1-2) at%.

4. The method of producing a potassium tantaloniobate crystal having a three-dimensional periodic polarization structure according to claim 3, characterized by, The annealing temperature for the heat annealing treatment is 350-450℃, the heating rate is 30-50℃ / h, and the holding time is 10-15h; after the holding time is completed, the temperature is reduced to room temperature at a cooling rate of 30-50℃ / h.

5. The method for preparing potassium tantalate niobate crystal with a three-dimensional periodic polarization structure according to claim 4, characterized in that, When preparing the potassium tantalate niobate polycrystalline material, the raw material needs to be pre-sintered in a muffle furnace at a temperature of 850-900°C for 5-8 hours.

6. The method of producing a potassium tantaloniobate crystal having a three-dimensional periodic polarization structure according to claim 4, characterized by, The seed crystal rotation speed during the constant diameter stage of the top seed crystal solution growth process is 20-25 rpm.

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