Method for growing bismuth-doped rare earth iron garnet crystal by guided-mode pulling-top seed crystal method and application of bismuth-doped rare earth iron garnet crystal

Abstract

The invention relates to a method for growing a bismuth-doped rare earth iron garnet BRIG crystal by adopting a guided-mode pulling-top seed crystal method and application of the bismuth-doped rare earth iron garnet BRIG crystal. The invention aims to solve the problems of large internal stress, many defects and difficulty in preparation of a single-crystal thick film in BRIG crystal growth by a liquid phase epitaxy method at present; in order to solve the problems of long growth cycle, difficult seed crystal acquisition and the like of a top seed crystal method in the prior art, the invention combines the rapid growth of crystals by a guided mode pulling method and the high-quality single crystal growth by the top seed crystal method, and the guided mode pulling-top seed crystal method is invented to realize the rapid growth of the high-quality BRIG single crystal. The method comprises the following steps: firstly, rapidly growing a large-size rare-earth-doped iron garnet crystal which is high in BRIG crystal lattice adaptation degree and relatively close to BRIG in components by adopting a guided-mode pulling method, cutting the large-size rare-earth-doped iron garnet crystal into seed crystals of more than centimeter level, and rapidly growing a high-quality BRIG blocky single crystal by adopting a TSSG method. The crystal grown by the method has the advantages of small internal stress, less cracking, good uniformity, fast crystal growth and the like, and has obvious advantages in high-performance magneto-optical isolators.

Description

Technical Field

[0001] The invention belongs to the technical field of magneto-optical crystals, and in particular relates to a preparation method and application of bismuth-doped rare earth iron garnet (BRIG) block crystals grown by a guided mode pulling-top seed crystal (EFG-TSSG) method. Background Art

[0002] Non-reciprocal magneto-optical devices play a key role in the fields of optical fiber communication, Internet, integrated circuits, smart grids, etc. As magneto-optical devices develop towards miniaturization, integration, and high power, higher and higher requirements are put forward for the core components of magneto-optical devices - Faraday rotator materials, which promotes the development of Faraday rotator materials towards high transmittance, strong magneto-optical effect, and low temperature coefficient. Faced with the vast market demand, rare earth iron garnet crystals doped with bismuth ions (BRIG) have become the only choice for Faraday rotator materials because of their high transmittance and large specific Faraday rotation angle in the near-mid-infrared band. However, the current commercial BRIG single crystal film growth method is mainly liquid phase epitaxy (LPE), which requires the use of very expensive substrates, and the single crystal film grows in a non-equilibrium state, with relatively more internal defects in the crystal; the thickness of the epitaxial single crystal is thin, and it is difficult to grow a single crystal film greater than 1 mm. Secondly, the co-solvents used in the LPE method mostly contain lead oxide. Lead oxide is easy to corrode the crucible, and its toxicity will cause harm to the human body and the environment.

[0003] The top seeding (TSSG) method has simple equipment, simple and controllable growth process, and low cost. It can grow bulk single crystals with low stress, uniform ion distribution, and high crystal quality in equilibrium. However, there are problems such as long growth cycle and difficulty in obtaining high-fit seed crystals when growing high-quality single crystals using this method. Although the TSSG method can also be used to grow high-fit seed crystals, there are problems such as long growth cycle and high cost. Terbium gallium garnet (TGG) crystals and gadolinium gallium garnet (GGG) crystals are also often used as seed crystals for growing BRIG crystals. However, the lattice constants of TGG and GGG are relatively small, which makes the lattice mismatch between the seed crystal and the BRIG crystal too large, resulting in large internal stress, internal cracking, and many envelope defects in the grown BRIG crystals. Moreover, TGG and GGG as seed crystals are more likely to cause Ga in the seed crystals. 3+Ions enter the grown crystal, affecting the magnetic and magneto-optical properties of the crystal. Compared with TGG and GGG crystals, the doped rare earth iron garnet crystals grown rapidly using the guided mode pulling method can obtain lattice constants and thermal expansion coefficients that are closer to BRIG crystals by selecting appropriate doping ions and doping concentrations, and using them as seed crystals can greatly improve the internal quality of the grown BRIG crystals. Moreover, the use of such seed crystals above the centimeter level can also greatly shorten the growth cycle of the TSSG method. However, since the doped rare earth iron garnet is a compound of non-isotropic melting, it is impossible to use the traditional pulling method to quickly grow large-sized single crystals. The present invention optimizes the method for growing terbium aluminum garnet by the guided mode pulling method (ZL201010154255.5) invented by the first inventor before, and by adjusting the process parameters such as melt composition, guided mode mold, temperature field, and growth rate, after multiple rounds of experiments, a doped rare earth iron garnet single crystal with a high degree of adaptability to the BRIG lattice is successfully grown and obtained above the centimeter level. The grown crystal is then cut and used as a seed crystal, and high-quality BRIG single crystals are grown using the TSSG method. During the growth process, the larger the seed crystal size, the shorter the growth cycle of the BRIG single crystal and the lower the cost.

[0004] The present invention does not have the problems of expensive epitaxial substrate, lead pollution, non-equilibrium growth, difficulty in growing thick single crystal films, etc. existing in the LPE method. Compared with the TSSG method, the present invention has the advantages of shorter growth cycle and lower cost, and thus has obvious advantages in terms of single crystal quality and cost. Summary of the invention

[0005] The present invention relates to a preparation method and application of bismuth-doped rare earth iron garnet (BRIG) crystals grown by guided mode pulling-top seed crystal (EFG-TSSG) method. BRIG crystals have the advantages of high transmittance and strong magneto-optical effect in the near-mid-infrared band and are widely used in devices such as magneto-optical isolators and circulators. They are key materials for optical communications, laser radars, interstellar communications, and big data centers. In order to solve the problems of large internal stress, many defects, and difficulty in preparing thick single crystal films in the current liquid phase epitaxy (LPE) method for growing BRIG crystals, as well as long growth cycles and difficulty in obtaining seed crystals by the top seed crystal (TSSG) method, the present invention combines the crystals of the guided mode pulling (EFG) method with the high-quality single crystals of the TSSG method, and invents the guided mode pulling-top seed crystal (EFG-TSSG) method to achieve rapid growth of high-quality BRIG single crystals. The invention first uses the EFG method to quickly grow large-sized rare earth iron garnet crystals with high lattice compatibility and similar composition to the BRIG, cuts them into seed crystals of centimeters or above, and uses the TSSG method to quickly grow high-quality BRIG block single crystals. The BRIG crystals grown by this method have the advantages of low internal stress, less cracking, and good uniformity, which have obvious advantages in high-performance magneto-optical devices.

[0006] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme:

[0007] 1. A method for rapidly growing a rare earth iron garnet single crystal by an EFG method, wherein the chemical formula of the rare earth iron garnet is A x Re 3-x Fe 5-y B y O 12 (0≤x≤0.8, 0.5<y≤3), A is Ca 2+ Mg 2+ One or more ions, B is Ga 3 + Sc 3+ ions, Re is one or more lanthanide rare earth ions. The crystal belongs to the cubic system, space group The unit cell constant is As a preferred technical solution, the doping concentration and ion type of the A or B ions are controlled according to the unit cell constant of the BRIG crystal grown by the TSSG method.

[0008] 2. A method for growing A using the EFG method x Re 3-x Fe 5-y B y O 12 The method for preparing a seed crystal (0≤x≤0.8, 0.5<y≤3) comprises the following steps:

[0009] (1) Raw material preparation: The oxide corresponding to the molecular formula of the seed crystal is used as the raw material, and the corresponding high-purity raw material is accurately weighed according to a certain ratio, and the raw material is ground and uniformly pressed into a sheet, and then pre-sintered at 800°C for 10 hours, and then sintered at 1100°C for 10 hours. After taking out, the sheet is ground and pressed, and then secondary sintered at 1100°C for 10 hours to obtain a polycrystalline raw material;

[0010] (2) Crystal growth: The EFG method is used for single crystal growth. The polycrystalline raw material is transferred to an iridium crucible equipped with an iridium guide mold for crystal growth. The crucible is heated to melt. The growth temperature is 1500-1700°C. Inert gases such as N2 or Ar are used as protective atmosphere to prevent oxidation of the iridium crucible and mold. The axial temperature gradient at the solid-liquid growth interface is 10-30°C / cm. The crystal rotation speed and pulling speed are controlled to be 0.1-10 rpm and 0.1-2.0 mm / h respectively.

[0011] (3) Crystal annealing: After the crystal growth in step (2) is completed, the crystal is lifted out of the melt on the upper surface of the guide mold. To avoid cracking caused by thermal stress, the temperature is slowly cooled to room temperature at a cooling rate of 15 to 120°C / h in a furnace to obtain a crystal.

[0012] (4) The grown rare earth iron garnet single crystal can be used as the seed crystal for growing BRIG by the top seed crystal method after orientation and cutting.

[0013] 3. A BRIG bulk magneto-optical crystal grown by TSSG method, wherein the chemical formula of the crystal is Bi x Re 3-x Fe 5- y C y O 12 (0<x≤2, 0≤y≤3), Re is one or more lanthanide rare earth ions, C is Ga 3+ Sc 3+ One or more ions. BRIG crystal belongs to the cubic system, and the space group is The unit cell constant is

[0014] 4. The method for preparing the BRIG bulk crystal comprises the following specific steps:

[0015] (1) Raw material preparation: accurately weigh the high-purity oxide raw materials required in the molecular formula according to a certain ratio, grind the raw materials evenly in an agate mortar, transfer them to a platinum crucible, and place the platinum crucible in a high-temperature molten salt furnace;

[0016] (2) Crystal growth: BRIG crystals are grown using the TSSG method, and the high lattice-matched rare earth iron garnet single crystals grown by the EFG method are used as seed crystals. The high-temperature molten salt furnace is raised to 1200-1400°C and kept at a constant temperature for 2 days to ensure that the raw materials are fully melted, and then the saturation point of the melt is tested. The saturation point is accurately determined using the seed crystals grown by the EFG method. After the melt saturation point is determined, crystal growth is carried out at a cooling rate of 0.05-0.5°C / h and a rotation speed of 10-100rpm;

[0017] (3) Crystal annealing: After the crystal growth is completed, the crystal is lifted to 1 to 2 cm above the liquid surface and gradually cooled to room temperature at a cooling rate of 5°C / h to 50°C / h to obtain a BRIG crystal.

[0018] As a preferred technical solution, the TSSG method uses a lead-free Bi2O3-Fe2O3-B2O3 solvent system as the solvent, which avoids the influence of traditional lead-containing solvents on the optical properties of the crystal and the harm to the crucible and the environment.

[0019] The prepared BRIG bulk magneto-optical crystal can be expected to be used in magneto-optical isolators, magneto-optical circulators, magneto-optical modulators and other devices after orientation, cutting, polishing and coating.

[0020] The significant advantages of the present invention are:

[0021] (1) The present invention combines the guided-mode pulling (EFG) method with the top seed crystal (TSSG) method to invent the guided-mode pulling-top seed crystal (EFG-TSSG) method, which achieves the rapid growth of high-quality BRIG single crystals. Among them, by adjusting the type and concentration of doping ions, the EFG method is used to grow centimeter-level single crystals of doped rare earth iron garnet to reduce the lattice mismatch between the seed crystal grown by the EFG method and the BRIG bulk crystal structure grown by the TSSG method, effectively solving the problems of easy cracking of the crystal, large thermal stress, and high thermal expansion coefficient, and the crystal quality is greatly improved.

[0022] (2) Compared with the LPE method, the present invention does not require expensive substrates, expensive growth equipment, and complex growth control processes, and can significantly reduce the cost of BRIG crystal growth.

[0023] (3) Compared with the commercial LPE method, the present invention grows BRIG single crystals in a near-equilibrium state, so the grown crystals have low stress, uniform ion distribution, and high crystal quality. In addition, the thickness of the bulk crystals grown by the present invention is more than ten times that of the LPE method. Through further process optimization, larger single crystals can be grown, which is very beneficial in the manufacture of high-isolation and high-sensitivity magneto-optical devices.

[0024] (4) The commercial BRIG material uses a lead-containing solvent, which increases the optical loss of the single crystal film and reduces the transmittance. The present invention explores a lead-free Bi2O3-Fe2O3-B2O3 solvent system in the TSSG method of growing crystals, which greatly reduces the corrosion of the crucible, avoids the harm of lead oxide to the human body and the environment, and the influence of lead ions on the optical properties of the crystal. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 These are photos of BRIG crystals grown using the EFG-TSSG method in Examples 1, 2 and 3.

[0026] Figure 2 The X-ray diffraction spectra (XRD) and space groups of the rare earth iron garnet crystals grown by the EFG method and the BRIG crystal powder grown by TSSG in Example 1, Example 2 and Example 3 are Cubic phase Tb3Fe5O 12 Standard cards.

[0027] Figure 3 The transmission spectra of BRIG crystals grown by EFG-TSSG method in Example 1, Example 2 and Example 3 at 800-3000 nm;

[0028] Figure 4Magnetic thermogravimetric curves of BRIG crystals grown by EFG-TSSG method in Example 1, Example 2 and Example 3.

[0029] Figure 5 The curves of the Faraday rotation angle of the BRIG crystal grown by the EFG-TSSG method at 1550nm as a function of the external magnetic field are shown in Examples 1, 2 and 3. DETAILED DESCRIPTION

[0030] In order to make the contents of the present invention easier to understand, the technical solution of the present invention is further described below in conjunction with the implementation methods of specific examples, but the present invention is not limited to the examples given here.

[0031] Implementation Case 1

[0032] A method for growing rare earth iron garnet crystal doped with Tb by EFG 3.0 Fe 3.6 Ga 1.4 O 12 , and then use it as a seed crystal to grow Bi using the TSSG method 0.8 Tb 2.2 Fe 4.9 Ga 0.1 O 12 The preparation method of centimeter-scale block magneto-optical crystals has the following specific steps:

[0033] (1) EFG method raw material preparation: according to the molar percentage of Tb / (Tb+Fe+Ga) of 20%, the molar percentage of Ga / (Tb+Fe+Ga) of 6.4%, and the molar percentage of Fe / (Tb+Fe+Ga) of 73.6%, high-purity raw materials of Tb4O7, Fe2O3, and Ga2O3 are accurately weighed, ground and uniformly pressed into tablets, pre-sintered at 800°C for 10 hours, and then sintered at 1100°C for 10 hours. After taking out, grind and press the tablets, and then re-sinter at 1100°C for 10 hours to obtain polycrystalline raw materials;

[0034] (2) EFG method crystal growth: The polycrystalline raw material is transferred to an iridium crucible equipped with an iridium guide mold for crystal growth. The crucible is heated to melt. The growth temperature is 1500°C and N2 is used as the protective atmosphere. TGG with a size of 0.5 cm long × 0.5 cm wide × 2 cm high is used as the seed crystal. The axial temperature gradient at the solid-liquid growth interface is 10°C / cm. The crystal rotation speed and pulling speed are controlled to be 5 rpm and 0.5 mm / h respectively.

[0035] (3) EFG method crystal annealing: After the crystal growth in step (2) is completed, the crystal is lifted out of the melt on the upper surface of the guide mold. To avoid cracking caused by thermal stress, the crystal is slowly annealed in a furnace at a cooling rate of 15 to 120°C / h to room temperature to obtain a gallium-doped terbium iron garnet seed crystal;

[0036] (4) The X-ray powder diffraction spectrum of the test crystal characterizes its physical phase, and its diffraction peak is similar to that of Tb3Fe5O 12 The standard spectrum (PDF#85-0545) is in good agreement with the standard spectrum (PDF#85-0545), with no impurity peaks, indicating that the crystal is a single garnet phase (see Figure 2 ). The composition of the crystal was determined by ICP-OES, and the molecular formula of the seed crystal was determined to be Tb 3.0 Fe 3.6 Ga 1.4 O 12 The unit cell parameters of the crystal obtained by refinement are: The crystal was processed and cut into the size of 0.5 cm long × 0.5 cm wide × 1 cm high, which was used as the seed crystal for the following TSSG method growth;

[0037] (5) TSSG method raw material preparation: accurately weigh Bi2O3, Tb4O7, Fe2O3, and B2O3 high-purity raw materials according to the molar percentage of Re2O3:Fe2O3:Bi2O3:B2O3=5.0:41.0:53.0:1.0, mix them thoroughly in an agate mortar, and then transfer them to a platinum crucible, and place the platinum crucible in a high-temperature molten salt furnace;

[0038] (6) TSSG method crystal growth: The high temperature molten salt furnace is raised to 1200℃ and kept at this temperature for 2 days to ensure that the raw materials are fully melted, and then the temperature is lowered to the saturation point at a rate of 20℃ / h to grow Tb 3.0 Fe 3.6 Ga 1.4 O 12 The seed crystal is inserted 1mm below the liquid surface for crystal growth, the cooling rate is 0.1-0.5℃ / h, and the rotation speed is 20-50rpm;

[0039] (7) TSSG crystal annealing: After the crystal growth is completed, pull the crystal to 1 cm above the melt, gradually cool it to room temperature at a cooling rate of 5°C / h to 50°C / h, and soak it in dilute hydrochloric acid for a while to remove the co-solvent on the crystal surface, and finally obtain BRIG crystal;

[0040] (8) Figure 1 As shown in (a), the BRIG grown by the TSSG method is a centimeter-scale single crystal with a size of 10×10×7mm. 3 The XRD powder diffraction spectrum of the grown BRIG crystals was tested, such as Figure 2 As shown. It can be seen that the main diffraction peaks of the crystal are similar to those of Tb3Fe5O12 The standard card (PDF#85-0545) is consistent with the standard card (PDF#85-0545), with no impurity peaks, and a single garnet crystal phase. The composition of the crystal was determined by ICP-OES, and the molecular formula of the BRIG bulk crystal was determined to be Bi 0.8 Tb 2.2 Fe 4.9 Ga 0.1 O 12 The unit cell parameters of the crystal obtained by refinement are: The lattice mismatch between the Ga-doped Tb-iron garnet seed crystals grown by the EFG method and the BRIG bulk crystals grown by the TSSG method is only 4‰. Figure 3 This is the transmittance curve of the BRIG crystal at 800-3000nm. The transmittance at 1310nm and 1550nm is 70.9% and 70.5% respectively, which basically reaches the theoretical transmittance of the crystal. Figure 4 This is the magnetic thermogravimetric curve of BRIG crystal. The Curie temperature of the crystal corresponding to the maximum slope in the figure is 286℃. Figure 5 This is the curve of the specific Faraday rotation angle of the BRIG crystal at 1550nm as a function of the external magnetic field. The crystal can reach saturation when the external magnetic field is 80mT, and its specific Faraday rotation angle is -555deg / cm.

[0041] Implementation Case 2

[0042] A method for growing rare earth iron garnet crystal Gd3Sc by EFG method 1.3 Fe 3.2 Ga 0.5 O 12 , and then use it as a seed crystal to grow Bi using the TSSG method 1.2 G 0.1 Tb 1.7 Sc 0.1 Fe 4.9 O 12 The preparation method of centimeter-scale block magneto-optical crystals has the following specific steps:

[0043] (1) EFG method raw material preparation: according to the molar percentage of Gd / (Gd+Sc+Fe+Ga) of 21%, the molar percentage of Sc / (Gd+Sc+Fe+Ga) of 5.6%, the molar percentage of Fe / (Gd+Sc+Fe+Ga) of 71.8%, and the molar percentage of Ga / (Gd+Sc+Fe+Ga) of 1.6%, high-purity raw materials of Gd2O3, Fe2O3, Sc2O3, and Ga2O3 are accurately weighed, ground and uniformly pressed into tablets, pre-sintered at 800°C for 10 hours, and then sintered at 1100°C for 10 hours. After taking out, grind and press the tablets, and then re-sinter at 1100°C for 10 hours to obtain polycrystalline raw materials;

[0044] (2) EFG method crystal growth: high-purity polycrystalline raw materials are transferred to an iridium crucible equipped with an iridium guide mold for crystal growth, and the crucible is heated to melt. The growth temperature is 1600°C, and N2 atmosphere is used as the protective gas. GGG with a size of 0.5 cm long × 0.5 cm wide × 2 cm high is used as the seed crystal. The axial temperature gradient at the solid-liquid growth interface is 20°C / cm. The crystal rotation speed and pulling speed are controlled to be 10 rpm and 1.0 mm / h respectively;

[0045] (3) EFG method crystal annealing: After the crystal growth in step (2) is completed, the crystal is lifted out of the melt on the upper surface of the guide mold. To avoid cracking caused by thermal stress, the crystal is slowly annealed to room temperature at a cooling rate of 15 to 120°C / h in a furnace to obtain a scandium gallium doped gadolinium iron garnet seed crystal;

[0046] (4) The X-ray powder diffraction spectrum of the test crystal characterizes its physical phase, and its diffraction peaks are consistent with Tb3Fe5O 12 The standard spectrum (PDF#85-0545) is in good agreement with the standard spectrum (PDF#85-0545), with no impurity peaks, indicating that the crystal is a single garnet phase (see Figure 1 ). The composition of the crystal was determined by ICP-OES, and the molecular formula of the crystal was determined to be Gd3Sc 1.3 Fe 3.2 Ga 0.5 O 12 , the unit cell parameters of the crystal obtained by refinement are: The crystal was processed and cut into the size of 1 cm long × 1 cm wide × 2 cm high, which was used as the seed crystal for the following TSSG growth method;

[0047] (5) TSSG method raw material preparation: according to the molar percentage of Re2O3:Fe2O3:Bi2O3:B2O3=3.8:41.0:54.2:1.0, Bi2O3, Tb4O7, Fe2O3, B2O3 high-purity raw materials are fully mixed in an agate mortar and then transferred to a platinum crucible, and the platinum crucible is placed in a high-temperature molten salt furnace;

[0048] (6) TSSG method crystal growth: The high temperature molten salt furnace was raised to 1300℃ and kept at this temperature for 2 days to ensure that the raw materials were fully melted, and then the temperature was lowered to the saturation point at a rate of 20℃ / h to grow Gd3Sc 1.3 Fe 3.2 Ga 0.5 O 12 The seed crystal is inserted 1mm below the liquid surface for crystal growth, the cooling rate is 0.1-0.5℃ / h, and the rotation speed is 20-50rpm;

[0049] (7) TSSG crystal annealing: After the crystal growth is completed, pull the crystal to 1 cm above the melt, gradually cool it to room temperature at a cooling rate of 5°C / h to 50°C / h, and soak it in dilute hydrochloric acid for a while to remove the co-solvent on the crystal surface, and finally obtain BRIG crystal;

[0050] (8) Figure 1 As shown in (b), the BRIG grown by the TSSG method is a centimeter-scale single crystal with a size of 30×30×18mm 3 The XRD powder diffraction spectrum of the grown BRIG crystals was tested, such as Figure 2 The main diffraction peaks of the crystal are similar to those of Tb3Fe5O 12 The standard card (PDF#85-0545) is consistent with the standard card (PDF#85-0545), with no impurity peaks, and a single garnet crystal phase. The composition of the crystal was determined by ICP-OES, and the molecular formula of the BRIG bulk crystal was determined to be Bi 1.2 G 0.1 Tb 1.7 Sc 0.1 Fe 4.9 O 12 The unit cell parameters of the crystal obtained by refinement are: The lattice mismatch between the scandium gallium doped gadolinium iron garnet seed crystals grown by the EFG method and the BRIG bulk crystals grown by the TSSG method is only 3‰. Figure 3 This is the transmittance curve of the BRIG crystal at 800-3000nm. The transmittance at 1310nm and 1550nm is 70.7% and 71% respectively, reaching the theoretical transmittance of the crystal. Figure 4 This is the magnetic thermogravimetric curve of BRIG crystal. The Curie temperature of the crystal corresponding to the maximum slope in the figure is 301℃. Figure 5 Figure 3 is the curve of the specific Faraday rotation angle of the BRIG crystal at 1550nm versus magnetic field. The crystal can reach saturation when the external magnetic field is 120mT, and its specific Faraday rotation angle is -1314deg / cm.

[0051] Implementation Case 3

[0052] A method for growing rare earth iron garnet crystal Ca doped with EFG 0.1 Mg 0.1 Tb 2.8 Fe 4.1 Ga 0.9 O 12 , and then use it as a seed crystal to grow Bi using the TSSG method 1.0 Tb 2.0 Fe 4.9 Ga 0.1 O 12 The preparation method of centimeter-scale block magneto-optical crystals has the following specific steps:

[0053] (1) Preparation of raw materials by EFG method: according to the molar percentage of Tb / (Tb+Fe+Ga+Ca+Mg) of 18%, the molar percentage of Fe / (Tb+Fe+Ga+Ca+Mg) of 77.4%, the molar percentage of Ga / (Tb+Fe+Ga+Ca+Mg) of 3.4%, the molar percentage of Ca / (Tb+Fe+Ga+Ca+Mg) of 0.6%, and the molar percentage of Mg / (Tb+Fe+Ga+Ca+Mg) of 0.6%, high-purity raw materials of MgO, CaCO3, Tb4O7, Fe2O3, and Ga2O3 are accurately weighed, ground and uniformly pressed into tablets, pre-sintered at 800°C for 10h, and then sintered at 1100°C for 10h. After taking out, ground and pressed into tablets, and then secondary sintered at 1100°C for 10h to obtain polycrystalline raw materials;

[0054] (2) EFG method crystal growth: high-purity polycrystalline raw materials are transferred to an iridium crucible equipped with an iridium guide mold for crystal growth, and the crucible is heated to melt. The growth temperature is 1600°C, and N2 atmosphere is used as the protective gas. TGG with a size of 0.5 cm long × 0.5 cm wide × 2 cm high is used as a seed crystal. The axial temperature gradient at the solid-liquid growth interface is 20°C / cm. The crystal rotation speed and pulling speed are controlled to be 10 rpm and 0.5 mm / h respectively;

[0055] (3) EFG method crystal annealing: After the crystal growth in step (2) is completed, the crystal is lifted out of the melt on the upper surface of the guide mold. To avoid cracking caused by thermal stress, the crystal is slowly annealed to room temperature at a cooling rate of 15 to 120°C / h in a furnace to obtain a calcium-magnesium dual-doped terbium-gallium-iron-garnet seed crystal;

[0056] (4) The X-ray powder diffraction spectrum of the test crystal characterizes its physical phase, and its diffraction peaks are consistent with Tb3Fe5O 12 The standard spectrum (PDF#85-0545) is in good agreement with the standard spectrum (PDF#85-0545), with no impurity peaks, indicating that the crystal is a single garnet phase (see Figure 1 ). The composition of the crystal was determined by ICP-OES, and the molecular formula of the crystal was determined to be Ca 0.1 Mg 0.1 Tb 2.8 Fe 4.1 Ga 0.9 O 12 , the unit cell parameters of the crystal obtained by refinement are: The crystal was processed and cut into the size of 1 cm long × 1 cm wide × 1.5 cm high, which was used as the seed crystal for the following TSSG growth method;

[0057] (5) TSSG method raw material preparation: according to the molar percentage of Re2O3:Fe2O3:Bi2O3:B2O3=4.3:41.0:53.7:1.0, Bi2O3, Tb4O7, Fe2O3, and B2O3 high-purity raw materials are fully mixed in an agate mortar and then transferred to a platinum crucible, and the platinum crucible is placed in a high-temperature molten salt furnace;

[0058] (6) TSSG method crystal growth: The high temperature molten salt furnace was raised to 1250℃ and kept at this temperature for 2 days to ensure that the raw materials were fully melted, and then the temperature was lowered to the saturation point at a rate of 20℃ / h. 0.1 Mg 0.1 Tb 2.8 Fe 4.1 Ga 0.9 O 12 The seed crystal is inserted 1mm below the liquid surface for crystal growth, the cooling rate is 0.1-0.5℃ / h, and the rotation speed is 20-50rpm;

[0059] (7) TSSG crystal annealing: After the crystal growth is completed, pull the crystal to 1 cm above the melt, gradually cool it to room temperature at a cooling rate of 5°C / h to 50°C / h, and soak it in dilute hydrochloric acid for a while to remove the co-solvent on the crystal surface, and finally obtain BRIG crystal;

[0060] (8) Figure 1 As shown in (c), the BRIG grown by the TSSG method is a centimeter-scale single crystal with a size of 28×28×18mm 3 The XRD powder diffraction spectrum of the grown BRIG crystals was tested, such as Figure 2 The main diffraction peaks of the crystal are similar to those of Tb3Fe5O 12 The standard card (PDF#85-0545) is consistent with the standard card (PDF#85-0545), with no impurity peaks, and a single garnet crystal phase. The composition of the crystal was determined by ICP-OES, and the molecular formula of the BRIG bulk crystal was determined to be Bi 1.0 Tb 2.0 Fe 4.9 Ga 0.1 O 12 The unit cell parameters of the crystal obtained by refinement are: The lattice mismatch between the CaMg doped TbGaI garnet seed crystals grown by the EFG method and the BRIG bulk crystals grown by the TSSG method is only 2‰. Figure 3 It is the transmittance curve of BRIG crystal in 800-3000nm, and its transmittance at 1310nm and 1550nm is 68.3% and 69.2% respectively. Figure 4 This is the magnetic thermogravimetric curve of BRIG crystal. The Curie temperature of the crystal corresponding to the maximum slope in the figure is 303℃. Figure 5Figure 3 is the curve of the specific Faraday rotation angle of the BRIG crystal at 1550nm versus magnetic field. The crystal can reach saturation when the external magnetic field is 100mT, and its specific Faraday rotation angle is -911deg / cm.

[0061] The above description is only a preferred embodiment of the present invention. Any optimization of the proportions in a patent application based on the present invention should fall within the scope of the present invention.

Claims

1. A method for growing bismuth-doped rare earth iron garnet crystals using a guided mold pulling-top seeding method, characterized in that: First, a guided-mode Czochralski method is used to rapidly grow a doped rare earth iron garnet single crystal with a high lattice compatibility and a similar composition to the bismuth-doped rare earth iron garnet BRIG, which is cut into a seed crystal, and then a top seed crystal method is used to rapidly grow a high-quality BRIG bulk single crystal; wherein the chemical formula of the doped rare earth iron garnet is A x Re 3-x Fe 5-y B y O 12 (0≤x≤0.8, 0.5<y≤3), A is Ca 2+ Mg 2+ One or more ions, B is Ga 3+ Sc 3+ ions, Re is one or more lanthanide rare earth ions; the rare earth doped iron garnet crystal belongs to the cubic system, space group , the unit cell constant is 12.40~12.60Å; the chemical formula of the BRIG bulk crystal is Bi x Re 3-x Fe 5-y C y O 12 (0<x≤2, 0≤y≤3), Re is one or more lanthanide rare earth ions, C is Ga 3+ Sc 3+ One or more of the ions, BRIG crystal belongs to the cubic system, the space group is , the unit cell constant is 12.40~12.60Å.

2. The method according to claim 1, characterized in that Doped rare earth iron garnet A x Re 3-x Fe 5-y B y O 12 (0≤x≤0.8, 0.5<y≤3) A method for preparing a seed crystal comprises the following steps: (1) Raw material preparation: The oxide corresponding to the molecular formula of the seed crystal is used as the raw material, and the corresponding high-purity raw material is accurately weighed according to a certain ratio, and the raw material is ground and uniformly pressed into a sheet, and then pre-sintered at 800°C for 10 hours, and then sintered at 1100°C for 10 hours. After taking out, the sheet is ground and pressed, and then secondary sintered at 1100°C for 10 hours to obtain a polycrystalline raw material; (2) Crystal growth: The single crystal is grown by the guided mold pulling method. The polycrystalline raw material is transferred to an iridium crucible equipped with an iridium guided mold for crystal growth. The crucible is heated to melt. The growth temperature is 1500-1700°C. N2 or Ar inert gas is used as a protective atmosphere to prevent oxidation of the iridium crucible and mold. The axial temperature gradient at the solid-liquid growth interface is 10-30°C / cm. The crystal rotation speed and pulling speed are controlled to be 0.1-10rpm and 0.1-2.0mm / h respectively. (3) Crystal annealing: After the crystal growth in step (2) is completed, the crystal is lifted out of the melt on the upper surface of the guide mold. To avoid cracking caused by thermal stress, the temperature is slowly cooled to room temperature at a cooling rate of 15-120°C / h in a furnace to obtain a crystal.

3. The method according to claim 1, characterized in that Bismuth-doped rare earth iron garnet x Re 3-x Fe 5-y C y O 12 A method for preparing a (0<x≤2, 0≤y≤3) bulk crystal comprises the following steps: (1) Raw material preparation: accurately weigh the high-purity oxide raw materials required in the molecular formula according to a certain ratio, grind the raw materials evenly in an agate mortar, and then transfer them to a platinum crucible, and place the platinum crucible in the center of a high-temperature molten salt furnace; (2) Crystal growth: BRIG crystal growth was performed using the top seeding method. A single crystal of doped rare earth iron garnet with high lattice adaptability grown by the guided mold pulling method was used as the seed crystal. The high-temperature molten salt furnace was heated to 1200-1400°C and kept at a constant temperature for 2 days to ensure that the raw materials were fully melted. The saturation point of the melt was tested with doped rare earth iron garnet. After the melt saturation point was determined, crystal growth was performed at a cooling rate of 0.05-0.5°C / h and a rotation speed of 10-100 rpm. (3) Crystal annealing: After the crystal growth is completed, the crystal is lifted to 1-2 cm above the liquid surface and gradually cooled to room temperature at a cooling rate of 5°C / h-50°C / h to obtain a BRIG crystal.

4. The preparation method according to claim 3, characterized in that: When the top seeding method is used to grow crystals, a lead-free Bi2O3-Fe2O3-B2O3 solvent system is used.

5. Use of the bismuth-doped rare earth iron garnet magneto-optical crystal obtained by the method according to any one of claims 1 to 4 in a magneto-optical isolator.

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