Preparation method of rare earth replacement yttrium iron garnet crystal
Technical Field
The invention relates to the technical field of crystal growth, in particular to a preparation method of a rare earth replacement yttrium iron garnet crystal.
Background
The improvement of the performance of the optical fiber transmission system promotes the arrival of the 5G information high-speed era. The magneto-optical material is used as one of key materials for optical fiber communication, has unique magneto-optical effect and optical nonreciprocity from visible to near infrared bands, has the characteristics of high transmittance, low absorption, large Verdet constant and the like in the near infrared band, has an excellent core position in magnetic theory and technical research, is popular in the field of magneto-optical devices such as an optical isolator, optical fiber communication and the like, and is widely applied to various devices in the magneto-optical field.
Wherein yttrium iron garnet (Y)3Fe5O12YIG) crystal is an important magneto-optical material and has a typical garnet crystal structure and the theoretical density of 5.171g/cm3The ferrimagnetic ferrite material with excellent performance belongs to a cubic crystal system, and the body-centered cubic lattice is relatively complex and presents a semitransparent state under visible light and a fully transparent state under near-infrared radiation. Due to Y3+Is a non-magnetic ion, and contains only Fe as a magnetic ion3+From the magnetic point of view, YIG magnetism is relatively simple, and becomes the basis for researching other rare earth substituted yttrium iron garnet with magnetism.
Researches show that the rare earth ions can improve the performance of the YIG material and have greater application prospect in the field of optical fiber communication, such as Ce3+The introduction of (b) can greatly improve the Faraday rotation magneto-optical effect of the material, and Tb: YIG has a negative Faraday temperature wavelength coefficient and Sc3+Doping can change the magnetic anisotropy of YIG, La3+Doping can change the saturation field strength of YIG. Therefore, the preparation of the magneto-optical material with good magneto-optical performance, temperature and wavelength characteristics and small saturation magnetic field can be realized through ion doping.
Since the melting point of YIG is 1550 ℃, the raw material Y2O3Has a melting point of 2425℃,Fe2O3The melting point of (a) is 1539 ℃, and the compound is a non-uniform molten compound, and a peritectic reaction and a eutectic reaction can occur in the growth process to generate YFeO3、Fe3O4And the like. The methods commonly used to prepare crystals, such as the czochralski method, are not suitable for such non-uniformly molten materials; the YIG single crystal obtained by a flux method, a pulling method, a zone melting method and the like is generally small in size and is difficult to meet the application of large-size devices. Rare earth doped garnets are therefore currently present mainly in the form of thin films, which limits their use. Therefore, a new method for preparing a high quality garnet single crystal is urgently sought.
Disclosure of Invention
In view of the above, the present invention provides a method for preparing a rare earth-substituted yttrium iron garnet crystal, which solves the bottleneck encountered in the existing method for preparing a rare earth-doped yttrium iron garnet crystal, and overcomes the shortcomings of the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of rare earth replaced yttrium iron garnet crystals comprises the following steps:
(1) according to the crystal formula Y(3-x)RexFe5O12Wherein x = 0-1.3, and Y with the purity of more than or equal to 99.99% is respectively weighed according to the molar ratio2O3、Re2O3And Fe2O3Putting the weighed raw materials into an agate mortar, and fully grinding the raw materials to be uniform to obtain a mixed powder raw material; pressing the mixed powder raw materials into blocks, and performing solid phase reaction at the temperature of 1000-1300 ℃ for 10-20h to obtain a polycrystalline block;
(2) crushing and grinding the polycrystalline material block obtained in the step (1), and adding Bi2O3The composite fluxing agent is placed in an agate mortar for fully grinding until the mixture is uniform, and a mixed material is obtained;
(3) placing seed crystals at the tail of a platinum crucible, filling the mixed material obtained in the step (2) into the crucible, and sealing;
(4) heating the crystal growth furnace to 1000-1400 ℃, then placing the sealed crucible in the crystal growth furnace, enabling the mixed material part in the crucible to be located in the high-temperature region of the hearth of the crystal growth furnace by changing the relative position of the crucible and the heating coil, and preserving heat for 10-20 hours at 1000-1400 ℃ to melt the mixed material and the top of the seed crystal to obtain a high-temperature solution;
(5) gradually moving the high-temperature solution obtained in the step (4) to a low-temperature area at a moving speed of 0.05-1 mm/h by changing the relative position of the crucible and the heating coil until the high-temperature solution is completely crystallized, and stopping moving to obtain crystals;
(6) continuously changing the relative position of the crucible and the heating coil, carrying out in-situ annealing on the crystal obtained in the step (5) in the crystal growth furnace for 10 hours at the annealing temperature of 500-900 ℃ to eliminate thermal stress, then cooling the crystal growth furnace to room temperature at the speed of 20-40 ℃/h, and naturally cooling the crystal to room temperature to obtain a rare earth substituted yttrium iron garnet crystal ingot;
(7) and (4) mechanically stripping the rare earth replaced yttrium iron garnet crystal ingot obtained in the step (6) or putting the crystal ingot into nitric acid solution for cleaning, and removing impurities wrapped outside the crystal ingot to obtain the rare earth replaced yttrium iron garnet crystal.
Aiming at the technical scheme, the crystal growth temperature is effectively reduced by adding the fluxing agent, the requirement on equipment is reduced, and convenient conditions are provided for crystal growth; the growth of the crystal can be promoted by changing the relative position of the crucible and the heating coil to give a driving force in the vertical direction to the crystal; the quality of the crystal can be ensured by controlling the moving speed of the crucible, and high-quality single crystals can be grown; the annealing temperature and the cooling rate can avoid the occurrence of crystal cracking and cracks. In addition, the addition of the seed crystal can be selectively added or not added according to specific situations.
Preferably, said Bi2O3The composite fluxing agent is Bi2O3+B2O3The composite fluxing agent is mainly added in an amount of 50-70% of the total mass of the mixed materials. The temperature for crystal growth is effectively reduced, and the internal components of the crystal are ensured to be uniform.
Preferably, the orientation of the seed crystal is <111>, <110>, <100> or <001>, and the cross-sectional shape of the seed crystal is circular, rectangular or square.
Preferably, the thickness of the platinum crucible is 0.1-0.5 mm.
Preferably, the crucible sealed in step (4) is loaded into an alumina ceramic tube and the periphery thereof is filled with alumina powder. The filling can play a role in heat preservation, so that the crystal has certain temperature buffering, the crystal growth failure caused by too large instantaneous temperature difference is avoided, and the quality of the crystal can be improved.
Preferably, the mass of the rare earth substituted yttrium iron garnet crystal obtained in the step (7) is 40-50% of the total mass of the mixed material. The obtained crystal has high conversion rate, reduces resource waste and reduces cost.
Preferably, the nitric acid solution in the step (7) is prepared by using concentrated nitric acid with the concentration of 69 percent according to the volume ratio of HNO3:H2O is 1: 2.5. Effectively remove impurities on the surface of the crystal without damaging the crystal.
The invention has the beneficial effects that:
the melting point of the material is effectively reduced by adding the fluxing agent, a driving force is provided for crystal growth in the vertical direction by a vertical moving method, the growth and the growth of the crystal are promoted, the growth difficulty and the energy consumption cost are reduced, the limitation of the existing rare earth replacement yttrium iron garnet crystal preparation method on the crystal growth is overcome, the block rare earth replacement yttrium iron garnet crystal is prepared, and the crystal is smooth and free of cracking and can be used as a magneto-optical material; the use requirement of a magneto-optical device which needs a block magneto-optical crystal material is met, and the development of industrialization is promoted.
Drawings
FIG. 1 is a schematic view of a crystal growth furnace.
In the figure: 1 furnace body, 2 lifting fixing devices, 3 heating coils and 4 crucibles.
Detailed Description
The present invention will be further described with reference to the following examples.
Example 1
A preparation method of an ytterbium-substituted yttrium iron garnet crystal comprises the following steps:
(1) according to the crystal formula Y(3-x)YbxFe5O12Wherein x =0.45, and Y with purity not less than 99.99% is respectively weighed according to molar ratio2O3、Yb2O3And Fe2O3Mixing and stirring the weighed raw materials for 30-50min to obtain a mixed powder raw material; pressing the mixed powder raw materials into blocks, and placing the blocks at the temperature of 1100 ℃ for solid-phase reaction for 12 hours to obtain polycrystalline blocks;
(2) crushing and grinding the polycrystalline material block obtained in the step (1), adding a fluxing agent, and placing the mixture into an agate mortar for fully grinding until the mixture is uniform, so as to obtain a mixed material; the fluxing agent is Bi2O3+B2O3The purity of the raw material of the composite fluxing agent is 99.999 percent, and the raw material accounts for 58 percent of the total mass of the mixed material;
(3) selecting seed crystals, wherein the orientation of the seed crystals is <111>, and the cross section of each seed crystal is circular; then placing the selected seed crystal at the tail of a platinum crucible, and filling the mixed material obtained in the step (2) into the crucible for sealing; and (3) filling the sealed crucible into an alumina ceramic tube and filling the periphery of the alumina ceramic tube with alumina powder.
(4) Heating the crystal growth furnace to 1250 ℃, then placing an alumina ceramic tube provided with a crucible into the crystal growth furnace, adjusting the vertical position of the alumina ceramic tube to enable the mixed material part in the crucible to be positioned in the high-temperature region of the hearth of the crystal growth furnace, and preserving heat at 1250 ℃ for 15 hours to enable the mixed material and the top of the seed crystal to be melted to obtain a high-temperature solution;
(5) gradually moving the high-temperature solution obtained in the step (4) to a low-temperature region at the moving speed of 0.12mm/h by adjusting the relative position of the crucible and the heating coil until the high-temperature solution is completely crystallized, and stopping moving to obtain crystals;
(6) continuously changing the relative position of the crucible and the heating coil, carrying out in-situ annealing on the crystal obtained in the step (5) in the crystal growth furnace for 10 hours at the annealing temperature of 800 ℃ to eliminate thermal stress, then cooling the crystal growth furnace to room temperature at the speed of 30 ℃/h, and naturally cooling the crystal to room temperature to obtain a rare earth substituted yttrium iron garnet crystal ingot;
(7) mechanically stripping the rare earth replaced yttrium iron garnet crystal ingot obtained in the step (6) or cleaning the crystal ingot in a nitric acid solution, wherein the nitric acid solution is prepared by concentrated nitric acid with the concentration of 69 percent according to the volume ratio of HNO3:H2O is 1: 2.5 configured to remove the impurities wrapped outside thereof to obtain a rare earth-substituted yttrium iron garnet crystal, wherein the mass of the rare earth-substituted yttrium iron garnet crystal is 46% of the weight of the mixed material, the rare earth-substituted yttrium iron garnet crystal is ∅ 40mm, the height of the rare earth-substituted yttrium iron garnet crystal is 20mm, and the volume of the rare earth-substituted yttrium iron garnet crystal obtained after stripping is 14 x 8 x 6 mm.
Example 2
A preparation method of an yttrium iron garnet crystal comprises the following steps:
(1) according to the crystal formula Y3Fe5O12Respectively weighing Y with the purity of more than or equal to 99.99 percent according to the molar ratio2O3And Fe2O3Putting the weighed raw materials into an agate mortar, and fully grinding the raw materials to be uniform to obtain a mixed powder raw material; pressing the mixed powder raw materials into blocks, and placing the blocks at 1150 ℃ for solid-phase reaction for 20 hours to obtain polycrystalline blocks;
(2) crushing and grinding the polycrystalline material block obtained in the step (1), and adding a fluxing agent for grinding for 40-60min to obtain a mixed material; the fluxing agent is Bi2O3+B2O3The purity of the raw material of the composite fluxing agent is 99.999 percent, and the raw material accounts for 64 percent of the total mass of the mixed material;
(3) putting the mixed material obtained in the step (2) into the crucible, and sealing; and (3) filling the sealed crucible into an alumina ceramic tube and filling the periphery of the alumina ceramic tube with alumina powder.
(4) Heating a crystal growth furnace to 1280 ℃, then placing an alumina ceramic tube provided with a crucible into the crystal growth furnace, adjusting the vertical position of the alumina ceramic tube to ensure that the mixed material part in the crucible is positioned in the high-temperature region of the hearth of the crystal growth furnace, and preserving heat at 1280 ℃ for 20 hours to melt the mixed material and the top of the seed crystal to obtain a high-temperature solution;
(5) gradually moving the high-temperature solution obtained in the step (4) to a low-temperature region by changing the relative position of the crucible and a heating coil, wherein the moving speed is 0.15mm/h until the high-temperature solution is completely crystallized, and stopping moving to obtain crystals;
(6) continuously changing the relative position of the crucible and the heating coil, carrying out in-situ annealing on the crystal obtained in the step (5) in the crystal growth furnace for 10 hours at the annealing temperature of 900 ℃ to eliminate thermal stress, then cooling the crystal growth furnace to room temperature at the speed of 20 ℃/h, and naturally cooling the crystal to room temperature to obtain a rare earth substituted yttrium iron garnet crystal ingot;
(7) mechanically stripping the rare earth replaced yttrium iron garnet crystal ingot obtained in the step (6) or cleaning the crystal ingot in a nitric acid solution, wherein the nitric acid solution is prepared by concentrated nitric acid with the concentration of 69 percent according to the volume ratio of HNO3:H2O is 1: 2.5, removing impurities wrapped outside the rare earth-substituted yttrium iron garnet crystal to obtain the rare earth-substituted yttrium iron garnet crystal, wherein the mass of the rare earth-substituted yttrium iron garnet crystal is 49% of the weight of the mixed material, and the volume of the rare earth-substituted yttrium iron garnet crystal is 10 multiplied by 9 multiplied by 8 mm.
Example 3
A preparation method of a terbium-replaced yttrium iron garnet crystal comprises the following steps:
(1) according to the crystal formula Y(3-x)TbxFe5O12Wherein x =1.25, and Y with purity not less than 99.99% is respectively weighed according to molar ratio2O3、Tb2O3And Fe2O3Putting the weighed raw materials into an agate mortar, and fully grinding the raw materials to be uniform for 30-50min to obtain a mixed powder raw material; pressing the mixed powder raw materials into blocks, and placing the blocks at the temperature of 1300 ℃ for solid-phase reaction for 10 hours to obtain polycrystalline blocks;
(2)crushing and grinding the polycrystalline material block obtained in the step (1), adding a fluxing agent, and placing the mixture into an agate mortar for fully grinding until the mixture is uniform, so as to obtain a mixed material; the fluxing agent is Bi2O3+B2O3The purity of the raw material of the composite fluxing agent is 99.999 percent, and the raw material accounts for 50 percent of the total mass of the mixed material;
(3) putting the mixed material obtained in the step (2) into the crucible, and sealing; and (3) filling the sealed crucible into an alumina ceramic tube and filling the periphery of the alumina ceramic tube with alumina powder.
(4) Heating a crystal growth furnace to 1400 ℃, then placing an alumina ceramic tube provided with a crucible in the crystal growth furnace, adjusting the vertical position of the alumina ceramic tube to enable the mixed material part in the crucible to be positioned in the high-temperature region of the hearth of the crystal growth furnace, and preserving heat at 1400 ℃ for 10 hours to melt the mixed material and the top of the seed crystal to obtain a high-temperature solution;
(5) gradually moving the high-temperature solution obtained in the step (4) to a low-temperature region at a moving speed of 1mm/h by changing the relative position of the crucible and the heating coil until the high-temperature solution is completely crystallized, and stopping moving to obtain crystals;
(6) continuously changing the relative position of the crucible and the heating coil, carrying out in-situ annealing on the crystal obtained in the step (5) in the crystal growth furnace for 10 hours at the annealing temperature of 500 ℃ to eliminate thermal stress, then cooling the crystal growth furnace to room temperature at the speed of 40 ℃/h, and naturally cooling the crystal to room temperature to obtain a rare earth substituted yttrium iron garnet crystal ingot;
(7) mechanically stripping the rare earth replaced yttrium iron garnet crystal ingot obtained in the step (6) or cleaning the crystal ingot in a nitric acid solution, wherein the nitric acid solution is prepared by concentrated nitric acid with the concentration of 69 percent according to the volume ratio of HNO3:H2O is 1: 2.5 configured to remove impurities wrapped outside thereof to obtain a rare earth-substituted yttrium iron garnet crystal, wherein the mass of the rare earth-substituted yttrium iron garnet crystal is 40% of the weight of the mixed material, the rare earth-substituted yttrium iron garnet crystal is ∅ 40mm, the height of the rare earth-substituted yttrium iron garnet crystal is 22mm, and the volume of the rare earth-substituted yttrium iron garnet crystal is 13 × 11 × 8mm after stripping.
The crystal grown by the method is smooth and has no cracking phenomenon, and can be used as a magneto-optical material.
The crystal growth furnace for preparing the crystals by adopting the method comprises a furnace body 1, an adjustable lifting fixing device 2 is arranged at the bottom of the furnace body 1, a heating coil 3 is arranged on the inner wall of the furnace body 1, and a high-temperature area and a low-temperature area are formed in the furnace body 1 according to different densities of the heating coil 3. The lifting fixing device 2 is arranged conventionally, can be composed of a supporting seat and a motor, and the motor drives the supporting seat to move up and down. The crucible is fixed on the supporting seat during the growth of the crystal, and the crucible 4 is driven by the motor to move up and down in the furnace body, so that the growth of the crystal is completed.
The crystal growth furnace can also be designed to adjust the temperature interval of the crucible by moving the heating coil or the furnace body.
Finally, the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting, and other modifications or equivalent substitutions made by the technical solutions of the present invention by those of ordinary skill in the art should be covered within the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solutions of the present invention.