Method for growing bismuth-doped rare-earth iron garnet crystal by edge-defined film-fed-top-seed method and application

Abstract

The present application relates to a kind of methods and applications of growing bismuth-doped rare-earth iron garnet BRIG crystal by guided mode pulling-top seed crystal method.For solving the problems of large internal stress, many defects, difficult to prepare thick film of single crystal in the current liquid phase epitaxy method of growing BRIG crystal;And the problems of long growth cycle, difficult to obtain seed crystal in top seed crystal method, the present application combines the fast growth of guided mode pulling crystal and the high-quality single crystal growth of top seed crystal method, and invents guided mode pulling-top seed crystal method to realize the fast growth of high-quality BRIG single crystal.First, the large-size doped rare-earth iron garnet crystal with high lattice matching and similar composition is quickly grown by guided mode pulling method, which is cut into centimeter-level seed crystal, and high-quality BRIG bulk single crystal is quickly grown by TSSG method.The crystal grown by this method has the advantages of small internal stress, less cracking, good uniformity, fast crystal growth, etc., and has obvious advantages in high-performance magneto-optical isolator.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of magneto-optical crystals, and particularly relates to a preparation method and application of a bismuth-doped rare earth iron garnet (BRIG) bulk crystal grown by an edge-defined film-fed-top-seed growth (EFG-TSSG) method. BACKGROUND

[0002] Non-reciprocal magneto-optical devices play a key role in the fields of optical fiber communication, Internet, integrated circuits, smart grid, etc. With the development of magneto-optical devices towards miniaturization, integration and high power, higher and higher requirements are put forward for the core element of magneto-optical devices, i.e. Faraday rotator materials, which promotes the development of Faraday rotator materials towards high transmittance, strong magneto-optical effect and low temperature coefficient. In the face of broad market demand, bismuth ion-doped rare earth iron garnet crystals (BRIG) have become the best choice for Faraday rotator materials because of their high transmittance and large specific Faraday rotation angle in the near-infrared band. However, the current growth method of commercial BRIG single crystal thin films is mainly liquid phase epitaxy (LPE) method, which requires the use of very expensive substrates, and the single crystal thin film is grown in a non-equilibrium state, so there are relatively many defects in the crystal. The thickness of the epitaxial single crystal is thin, and it is difficult to grow single crystal thin films with a thickness greater than 1 mm. Secondly, the solubilizing agent used in the LPE method mostly contains lead oxide. Lead oxide is easy to corrode the crucible, and its toxicity will harm the human body and the environment.

[0003] The top seed growth (TSSG) method has simple equipment, simple and controllable growth process and low cost, and can grow bulk single crystals with small stress, uniform ion distribution and high crystalline quality in an equilibrium state. However, there are problems such as long growth period and difficulty in obtaining high-adaptation seeds when growing high-quality single crystals using this method. Although high-adaptation seeds can also be grown by the TSSG method, there are problems such as long growth period and high cost. Terbium gallium garnet (TGG) crystals and gadolinium gallium garnet (GGG) crystals are also often used as seeds for growing BRIG crystals. However, the lattice constant of TGG and GGG is relatively small, which makes the lattice mismatch degree between the seed and the BRIG crystal too large, thereby leading to large internal stress, internal cracking and many envelope defects in the grown BRIG crystal. Moreover, using TGG and GGG as seeds also makes it more likely to cause Ga 3+The ions enter the grown crystal, and affect the magnetism and magneto-optical properties of the crystal. Compared with TGG and GGG crystals, the doped rare earth iron garnet crystal grown by the edge-defined film-fed growth method can obtain a lattice constant and a thermal expansion coefficient closer to those of the BRIG crystal by selecting appropriate doping ions and doping concentrations, and using the crystal as a seed crystal can greatly improve the internal quality of the grown BRIG crystal. Moreover, the growth period of the TSSG method can be greatly shortened by using a centimeter-level or larger seed crystal. However, since the doped rare earth iron garnet is a compound that cannot be melted by the traditional pulling method, a large-size single crystal cannot be quickly grown by the traditional pulling method. The method for growing terbium aluminum garnet by the edge-defined film-fed growth method (ZL201010154255.5) invented by the first inventor is optimized, the process parameters such as the melt composition, the edge-defined film-fed mold, the temperature field, and the growth rate are adjusted, and after multiple rounds of experiments, a doped rare earth iron garnet single crystal with a size of more than a centimeter and a high lattice matching degree with the BRIG crystal is successfully grown. Then, the grown crystal is cut to be used as a seed crystal, and a high-quality BRIG single crystal is grown by the TSSG method. During the growth process, the larger the size of the seed crystal, the shorter the growth period of the BRIG single crystal, and the lower the cost.

[0004] The present application does not have the problems of expensive epitaxial substrate, lead pollution, non-equilibrium growth, and difficulty in growing thick single crystal film in the LPE method, and has the advantages of shorter growth period and lower cost compared with the TSSG method, and thus has obvious advantages in single crystal quality and cost. SUMMARY

[0005] The present application relates to a preparation method and application of a bismuth-doped rare earth iron garnet (BRIG) crystal grown by an edge-defined film-fed growth-top seed crystal (EFG-TSSG) method. The BRIG crystal has high transmittance in the near-infrared band and strong magneto-optical effect, and is widely used in magneto-optical isolators, circulators and other devices, and is a key material for optical communication, laser radar, interstellar communication, big data center, etc. To solve the problems of large internal stress, many defects, difficulty in preparing thick single crystal film, long growth period, and difficulty in obtaining a seed crystal in the current liquid phase epitaxy (LPE) method for growing a BRIG crystal, the present application combines the crystal grown by the edge-defined film-fed growth (EFG) method and the high-quality single crystal grown by the top seed crystal (TSSG) method, and invents an edge-defined film-fed growth-top seed crystal (EFG-TSSG) method to realize the rapid growth of a high-quality BRIG single crystal. First, the EFG method is used to quickly grow a large-size doped rare earth iron garnet crystal with a high lattice matching degree and a composition close to that of the BRIG crystal, the crystal is cut into a seed crystal with a size of more than a centimeter, and the TSSG method is used to quickly grow a high-quality BRIG bulk single crystal. The BRIG crystal grown by the method has the advantages of small internal stress, less cracking, and good uniformity, and has obvious advantages in high-performance magneto-optical devices.

[0006] To achieve the above-mentioned application purposes, the present application adopts the following technical solutions:

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

[0008] 2. A method for preparing a seed crystal of A x Re 3-x Fe 5-y B y O 12 (0≤x≤0.8, 0.5

[0009] (1) Preparation of raw materials: taking oxides corresponding to the molecular formula of the seed crystal as raw materials, accurately weighing corresponding high-purity raw materials in a certain proportion, grinding and pressing into a tablet, then pre-sintering at 800℃ for 10h, then sintering at 1100℃ for 10h, taking out and grinding and pressing into a tablet, then second sintering at 1100℃ for 10h to obtain polycrystalline raw materials;

[0010] (2) Crystal growth: single crystal growth is carried out by EFG method, the polycrystalline raw materials are transferred into an iridium crucible equipped with an iridium guide mold for crystal growth, the crucible is heated to be melted, the growth temperature is 1500-1700℃, N2 or Ar gas and other inert gases are used as protective atmosphere to prevent oxidation of the iridium crucible and the mold, the axial temperature gradient at the solid-liquid growth interface is 10-30℃ / cm, the crystal rotation speed and the pulling speed are controlled to be 0.1-10rpm and 0.1-2.0mm / h respectively;

[0011] (3) Crystal annealing: after the crystal growth in step (2) is completed, the crystal is lifted to separate from the upper surface of the melt of the guide mold, in order to avoid cracking caused by thermal stress, the furnace is slowly cooled to room temperature at a cooling rate of 15-120℃ / h to obtain the crystal.

[0012] (4) The grown doped rare earth iron garnet single crystal is oriented and cut to be used as a seed crystal for growing BRIG by a top-seed crystal method.

[0013] 3. A BRIG bulk magneto-optical crystal grown by a TSSG method, 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 of lanthanide ions, and C is one or more of Ga 3+ , Sc 3+ ions. The BRIG crystal belongs to a cubic system, and the space group is The cell constant is

[0014] 4. A preparation method of the BRIG bulk crystal, comprising the following specific steps:

[0015] (1) Preparation of raw materials: accurately weigh the required high-purity oxide raw materials in a molecular formula according to a certain proportion, grind the raw materials uniformly in an agate mortar, and then transfer the raw materials to a platinum crucible, and place the platinum crucible in a high-temperature molten salt furnace;

[0016] (2) Crystal growth: BRIG crystal growth is performed by a TSSG method, and a doped rare earth iron garnet single crystal with high lattice matching grown by an EFG method is used as a seed crystal. The high-temperature molten salt furnace is raised to 1200-1400 DEG C and kept constant 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 of the seed crystal grown by the EFG method is accurately determined, and after the saturation point of the melt is determined, the crystal growth is performed at a cooling rate of 0.05-0.5 DEG C / h, and the rotation speed is 10-100 rpm;

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

[0018] As a preferred technical scheme, the TSSG method adopts a lead-free Bi2O3-Fe2O3-B2O3 cosolvent system, which avoids the influence of the traditional lead-containing cosolvent on the optical performance 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 practically applied in magneto-optical isolators, magneto-optical circulators, magneto-optical modulators and the like after being oriented, cut, polished and coated.

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

[0021] (1) The present application combines the edge defined film-fed growth (EFG) method and the top seeded solution growth (TSSG) method, and invents the edge defined film-fed growth-top seeded solution growth (EFG-TSSG) method, so as to realize the rapid growth of high-quality BRIG single crystal. In the method, the EFG method is used to grow the doped rare earth iron garnet single crystal with a centimeter size, by adjusting the type and concentration of the doped ions, so as to reduce the lattice mismatching degree between the seed crystal grown by the EFG method and the BRIG bulk crystal grown by the TSSG method, effectively solve the problems of easy cracking, large thermal stress and high thermal expansion coefficient of the crystal, and greatly improve the quality of the crystal.

[0022] (2) Compared with the LPE method, the present application does not need to use expensive substrates, expensive growth equipment and complex growth control process, and can greatly reduce the growth cost of the BRIG crystal.

[0023] (3) Compared with the commercial LPE method, the present application grows the BRIG single crystal in a near equilibrium state, so that the grown crystal has small stress, uniform ion distribution and high crystallization quality. In addition, the bulk crystal grown by the present application has a thickness of tens of times of the LPE method, and through further process optimization, a single crystal with a larger size can be grown, which is very beneficial to the manufacture of high-isolation high-sensitivity magneto-optical devices.

[0024] (4) The commercial BRIG material uses a lead-containing cosolvent, so that the light loss of the single crystal thin film is increased and the transmittance is reduced. In the process of growing the crystal by the TSSG method, the present application explores a lead-free Bi2O3-Fe2O3-B2O3 cosolvent system, 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 DRAWINGS

[0025] Figure 1 The BRIG crystal photos grown by the EFG-TSSG method in Example 1, Example 2 and Example 3.

[0026] Figure 2 The X-ray diffraction spectra (XRD) of the doped rare earth iron garnet crystal grown by the EFG method and the BRIG crystal powder grown by the TSSG in Example 1, Example 2 and Example 3, and the cubic phase Tb3Fe5O12 crystal with a space group of . 12 Standard card.

[0027] Figure 3 The transmittance spectrum of the BRIG crystal grown by the EFG-TSSG method in Example 1, Example 2 and Example 3 in the range of 800-3000 nm;

[0028] Figure 4The magnetothermal weight curve of the BRIG crystal grown by the EFG-TSSG method for Example 1, Example 2 and Example 3.

[0029] Figure 5 The curve of the specific Faraday rotation angle at 1550 nm of the BRIG crystal grown by the EFG-TSSG method for Example 1, Example 2 and Example 3 as a function of the applied magnetic field. DETAILED DESCRIPTION

[0030] In order to make the content of the present application more convenient to understand, the technical solutions of the present application are further described below in combination with the embodiments of specific examples, but the present application is not limited to the examples given here.

[0031] Example 1

[0032] A method for preparing a centimeter-sized bulk magneto-optical crystal of a doped rare earth iron garnet crystal Tb 3.0 Fe 3.6 Ga 1.4 O 12 , and then using it as a seed crystal to grow Bi 0.8 Tb 2.2 Fe 4.9 Ga 0.1 O 12 The specific steps are as follows:

[0033] (1) Preparation of raw materials by EFG method: After calculation 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%, accurately weigh the high-purity raw materials of Tb4O7, Fe2O3 and Ga2O3, grind them uniformly, press them into a sheet, pre-sinter them at 800℃ for 10h, then sinter them at 1100℃ for 10h, grind them after taking them out, press them into a sheet, and obtain polycrystalline raw materials after secondary sintering at 1100℃ for 10h;

[0034] (2) Crystal growth by EFG method: transfer the polycrystalline raw materials to an iridium crucible equipped with an iridium guide mold for crystal growth, heat the crucible to melt it, the growth temperature is 1500℃, and N2 is used as the protective atmosphere. A TGG with a size of 0.5cm×0.5cm×2cm is used as a seed crystal, the axial temperature gradient at the solid-liquid growth interface is 10℃ / cm, and the rotation speed and pulling speed of the crystal are controlled at 5rpm and 0.5mm / h, respectively;

[0035] (3) EFG method crystal annealing: after the end of step (2) crystal growth, the crystal is lifted to separate from the upper surface of the mold melt. In order to avoid cracking caused by thermal stress, the furnace is slowly annealed to room temperature in steps at a cooling rate of 15-120℃ / h. A gallium-doped terbium iron garnet seed crystal is obtained;

[0036] (4) The X-ray powder diffraction spectrum of the test crystal is characterized, and the diffraction peak is consistent with the Tb3Fe5O 12 standard spectrum (PDF # 85-0545), without impurity peaks, indicating that the crystal is a single garnet phase (see Figure 2 ). The composition of the crystal is determined by ICP-OES, and the molecular formula of the seed crystal is Tb 3.0 Fe 3.6 Ga 1.4 O 12 . The crystal cell parameters obtained by refinement are: The crystal is processed and cut into a size of 0.5 cm x 0.5 cm x 1 cm for the following TSSG method seed crystal used for growth;

[0037] (5) TSSG method raw material preparation: Bi2O3, Tb4O7, Fe2O3, B2O3 high-purity raw materials are accurately weighed according to the molar percentage Re2O3: Fe2O3: Bi2O3: B2O3 = 5.0: 41.0: 53.0: 1.0, mixed in a agate mortar, and then transferred to a platinum crucible. The platinum crucible is placed 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 constant for 2 days to ensure that the raw materials are fully melted. Then, the temperature is reduced to the saturation point at a rate of 20℃ / h. The Tb 3.0 Fe 3.6 Ga 1.4 O 12 seed crystal is extended 1mm below the liquid surface for crystal growth, and the cooling rate is 0.1-0.5℃ / h, and the rotation speed is 20-50rpm;

[0039] (7) TSSG method crystal annealing: after the crystal growth is completed, the crystal is pulled out to 1cm above the melt, and the temperature is gradually reduced to room temperature at a rate of 5-50℃ / h. The crystal is soaked in dilute hydrochloric acid for a while to remove the surface of the crystal. The final BRIG crystal is obtained;

[0040] (8) As shown in (a) of Figure 1 , the BRIG grown by the TSSG method is a single crystal with a size of 10x10x7mm 3 . The XRD powder diffraction spectrum of the grown BRIG crystal is shown in Figure 2 . As can be seen, the main diffraction peak of the crystal is consistent with the Tb3Fe5O12 The standard card (PDF#85-0545) is consistent with no impurity peak, which is a single garnet crystal phase. The composition of the crystal is determined by ICP-OES, and the molecular formula of the BRIG bulk crystal is Bi 0.8 Tb 2.2 Fe 4.9 Ga 0.1 O 12 The cell parameters of the crystal obtained by refinement are as follows: The lattice mismatch degree between the gallium-doped terbium iron garnet seed crystal grown by the EFG method and the BRIG bulk crystal grown by the TSSG method is only 4 ‰. Figure 3 is the transmittance curve of the BRIG crystal at 800-3000 nm, and the transmittance at 1310 nm and 1550 nm is 70.9% and 70.5%, respectively, which basically reaches the theoretical transmittance of the crystal. Figure 4 is the magnetothermal weight curve of the BRIG crystal, and the maximum slope in the figure corresponds to the Curie temperature of the crystal, which is 286℃. Figure 5 is the variation curve of the specific Faraday rotation angle of the BRIG crystal at 1550 nm with the applied magnetic field, and the crystal can reach saturation at an applied magnetic field of 80 mT, and the specific Faraday rotation angle is -555 deg / cm.

[0041] Case 2

[0042] A method for growing a rare earth iron garnet crystal Gd3Sc 1.3 Fe 3.2 Ga 0.5 O 12 , and then using it as a seed crystal to grow Bi 1.2 Gd 0.1 Tb 1.7 Sc 0.1 Fe 4.9 O 12 A method for preparing a centimeter-level bulk magneto-optical crystal, the specific steps are as follows:

[0043] (1) EFG method raw material preparation: after calculating the molar percentage of Gd / (Gd+Sc+Fe+Ga) as 21%, the molar percentage of Sc / (Gd+Sc+Fe+Ga) as 5.6%, the molar percentage of Fe / (Gd+Sc+Fe+Ga) as 71.8%, and the molar percentage of Ga / (Gd+Sc+Fe+Ga) as 1.6%, accurately weigh the Gd2O3, Fe2O3, Sc2O3, and Ga2O3 high-purity raw materials, grind and press into a sheet, then pre-sinter at 800℃ for 10h, then sinter at 1100℃ for 10h, then grind and press into a sheet after taking out, and then sinter at 1100℃ for 10h 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. The crucible is heated to melt, the growth temperature is 1600℃, and N2 atmosphere is used as the protective gas. GGG with a size of 0.5 cm x 0.5 cm x 2 cm is used as a seed crystal, the axial temperature gradient at the solid-liquid growth interface is 20℃ / cm, and the rotation speed and pulling speed are controlled at 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 away from 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 15-120℃ / h in the furnace to obtain a scandium-gallium double-doped gadolinium-iron garnet seed crystal;

[0046] (4) The crystal is tested by X-ray powder diffraction to characterize its phase, and the diffraction peaks are all consistent with the Tb3Fe5O 12 standard spectrum (PDF #85-0545), without impurity peaks, indicating that the crystal is a single garnet crystal phase (see Figure 1 ). The composition of the crystal is determined by ICP-OES, and the molecular formula of the crystal is Gd3Sc 1.3 Fe 3.2 Ga 0.5 O 12 , and the crystal cell parameters obtained by refinement are: The crystal is processed and cut into a size of 1 cm x 1 cm x 2 cm for use as a seed crystal for the following TSSG method growth;

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

[0048] (6) TSSG method crystal growth: the high-temperature molten salt furnace is raised to 1300℃ and kept constant 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. The Gd3Sc 1.3 Fe 3.2 Ga 0.5 O 12 seed crystal is inserted into the liquid surface by 1 mm for crystal growth, the cooling rate is 0.1-0.5℃ / h, and the rotation speed is 20-50 rpm;

[0049] (7) TSSG method crystal annealing: after the crystal growth is completed, the crystal is pulled to 1 cm above the melt, gradually reduced to room temperature at a cooling rate of 5-50 °C / h, and soaked in dilute hydrochloric acid for a while to remove the surface of the crystal. The final BRIG crystal is obtained;

[0050] (8) As shown in (b) of Figure 1 , the BRIG grown by TSSG method is a single crystal with a size of 30x30x18 mm 3 . The XRD powder diffraction spectrum of the grown BRIG crystal is tested, as shown in Figure 2 . The main diffraction peak of the crystal is consistent with the Tb3Fe5O 12 standard card (PDF # 85-0545), and there is no impurity peak, which is a single garnet crystal phase. The composition of the crystal is determined by ICP-OES, and the molecular formula of the BRIG bulk crystal is Bi 1.2 Gd 0.1 Tb 1.7 Sc 0.1 Fe 4.9 O 12 . The cell parameters of the crystal are refined as follows: The lattice mismatch degree between the scandium-gallium double-doped gadolinium iron garnet seed crystal grown by the EFG method and the BRIG bulk crystal grown by the TSSG method is only 3 ‰. Figure 3 is the transmittance curve of the BRIG crystal in the range of 800-3000 nm, and the transmittance at 1310 nm and 1550 nm is 70.7% and 71%, respectively, reaching the theoretical transmittance of the crystal. Figure 4 is the magnetothermal weight curve of the BRIG crystal, and the maximum slope in the figure corresponds to the Curie temperature of the crystal, which is 301 °C. Figure 5 is the change curve of the specific Faraday rotation angle of the BRIG crystal at 1550 nm with the magnetic field, and the specific Faraday rotation angle is-1314 deg / cm when the external magnetic field is 120 mT.

[0051] Case 3

[0052] A method for growing a rare earth iron garnet crystal Ca 0.1 Mg 0.1 Tb 2.8 Fe 4.1 Ga 0.9 O 12 by EFG method, and then using it as a seed crystal to grow Bi 1.0 Tb 2.0 Fe 4.9 Ga 0.1 O 12 centimeter level bulk magneto-optical crystal by TSSG method, the specific steps are as follows:

[0053] (1) EFG method raw material preparation: according to the molar percentage of Tb / (Tb+Fe+Ga+Ca+Mg) is 18%, the molar percentage of Fe / (Tb+Fe+Ga+Ca+Mg) is 77.4%, the molar percentage of Ga / (Tb+Fe+Ga+Ca+Mg) is 3.4%, the molar percentage of Ca / (Tb+Fe+Ga+Ca+Mg) is 0.6%, the molar percentage of Mg / (Tb+Fe+Ga+Ca+Mg) is 0.6%, after calculation, accurately weigh the high-purity raw materials of MgO, CaCO3, Tb4O7, Fe2O3, Ga2O3, grind uniformly, press into a sheet, pre-sinter at 800°C for 10h, then sinter at 1100°C for 10h, after taking out, grind and press into a sheet, sinter at 1100°C for 10h to obtain polycrystalline raw material;

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

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

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

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

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

[0059] (7) TSSG method crystal annealing: after the crystal growth was completed, the crystal was pulled out of the melt to 1 cm above the melt, and the temperature was gradually reduced to room temperature at a rate of 5°C / h-50°C / h, and the crystal was immersed in dilute hydrochloric acid for a short time to remove the crystal surface. The auxiliary solvent, and finally the BRIG crystal was obtained;

[0060] (8) As shown in (c) of Figure 1 , the BRIG grown by the TSSG method is a single crystal with a size of 28x28x18mm 3 . The XRD powder diffraction spectrum of the grown BRIG crystal was tested, as shown in Figure 2 . The main diffraction peak of the crystal is consistent with the Tb3Fe5O 12 standard card (PDF # 85-0545), and there is no impurity peak, which is 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 Bi 1.0 Tb 2.0 Fe 4.9 Ga 0.1 O 12 . The cell parameters of the crystal obtained by refinement are: The lattice mismatch degree between the calcium-magnesium double-doped terbium gallium iron garnet seed crystal grown by the EFG method and the BRIG bulk crystal grown by the TSSG method is only 2 ‰. Figure 3 is the transmittance curve of the BRIG crystal in the range of 800-3000 nm, and the transmittance at 1310 nm and 1550 nm is 68.3% and 69.2%, respectively. Figure 4 is the magnetocaloric weight curve of the BRIG crystal, and the maximum slope in the figure corresponds to the Curie temperature of the crystal, which is 303°C. Figure 5For the curve of the specific Faraday rotation angle of the BRIG crystal at 1550 nm versus the magnetic field, the crystal can reach saturation at an applied magnetic field of 100 mT, and the specific Faraday rotation angle thereof is -911 deg / cm.

[0061] The above merely describes preferred embodiments of the present application, and any proportional optimization made according to the present application should be within the scope of the present application.

Claims

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

2. The method of claim 1, wherein, Doped rare earth iron garnet A x Re 3-x Fe 5-y B y O 12 A method of preparing a seed crystal comprising the steps of: (1) Preparation of raw materials: 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 proportion. After being ground uniformly and pressed into a sheet, it is pre-sintered at 800 DEG C for 10 hours, and then sintered at 1100 DEG C for 10 hours. After being taken out, it is ground and pressed into a sheet and sintered at 1100 DEG C for 10 hours to obtain a polycrystalline raw material; (2) Crystal growth: single crystal growth is carried out by using a guide mode pulling method, and 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 DEG C, N2 or Ar inert gas is used as the protective atmosphere to prevent oxidation of the iridium crucible and the mold, the axial temperature gradient at the solid-liquid growth interface is 10-30 DEG C / cm, and the rotation speed and pulling speed are controlled to be 0.1-10 rpm and 0.1-2.0 mm / h, respectively; (3) Crystal annealing: after the crystal growth in step (2) is completed, the crystal is lifted to separate from the upper surface of the guide mold melt. In order to avoid cracking caused by thermal stress, the furnace is slowly cooled to room temperature at a cooling rate of 15-120 DEG C / h to obtain the crystal.

3. The method of claim 1, wherein, Bi-doped rare earth iron garnet Bi x Re 3-x Fe 5-y C y O 12 A method for producing a bulk crystal of the formula Bi3Fe5O12-xCrx, 0 < x < 2, 0 < y < 3, comprising the following steps: (1) Preparation of raw materials: the high-purity oxide raw materials required in the molecular formula are accurately weighed according to a certain proportion, and the raw materials are ground uniformly in an agate mortar and then transferred to a platinum-gold crucible. The platinum-gold crucible is placed in the center of a high-temperature molten salt furnace; (2) Crystal growth: BRIG crystal growth is carried out by using a top seed crystal method, and a high-lattice-adaptation doped rare earth iron garnet single crystal grown by a guide mode pulling method is used as a seed crystal. The high-temperature molten salt furnace is raised to 1200-1400 DEG C and kept constant for 2 days to ensure that the raw material is fully melted. The saturation point of the melt is tested by using a doped rare earth iron garnet. After the saturation point of the melt is determined, the crystal growth is carried out at a cooling rate of 0.05-0.5 DEG C / h, and the rotation speed is 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 DEG C / h-50 DEG C / h to obtain the BRIG crystal.

4. The production method according to claim 3, characterized by, When the top seed crystal method is used to grow the crystal, a lead-free Bi2O3-Fe2O3-B2O3 fluxing agent system is used.

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

Images