Preparation method of yttrium ferrite single crystal

Abstract

The invention provides a preparation method of a yttrium ferrite single crystal, which comprises the following steps: mixing Y2O3 and Fe2O3 according to a molar ratio of 1: (1.05-1.08), then mixing with a composite fluxing agent LiCl-KCl-B2O3 to form a mixed raw material, with the molar ratio of LiCl, KCl and B2O3 in the composite fluxing agent being (6-9): (6-9): (2-3); putting the mixed raw material into a platinum crucible, and heating the inside of the platinum crucible to 1050-1100 DEG C; the temperature inside the platinum crucible is kept for at least 24 h, and it is ensured that Y2O3 and Fe2O3 completely react to form homogeneous melt; cooling the inside of the platinum crucible to 860-900 DEG C, and inserting a seed crystal into the platinum crucible; continuously cooling the inside of the platinum crucible, and rotating and lifting the seed crystal; the temperature in the platinum crucible is reduced to 750-800 DEG C, and crystal growth is finished; lifting the crystal away from the liquid level, and cooling and annealing to obtain the yttrium ferrite single crystal. According to the invention, the dimension bottleneck is broken through, the component volatilization is inhibited, the crystallization quality is improved, and environmental protection and no pollution are realized.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of functional crystal material preparation, and in particular to a preparation method of a yttrium ferrite single crystal. BACKGROUND

[0002] YFeO3 is a room-temperature multiferroic material, has a high Curie temperature, excellent magneto-optical effect and spin wave transmission characteristics, and is mainly applied to core elements of optical isolators, magneto-optical modulators, spin electronic devices and multiferroic memories. Traditional processes are difficult to prepare a YFeO3 single crystal with a large size and high optical uniformity, thereby restricting the application of the YFeO3 single crystal in 5G communication and integrated photon chips. Compared with a garnet-type magneto-optical crystal, i.e. a yttrium iron garnet (YIG) crystal, the YFeO3 crystal belongs to a high-temperature phase of a Fe2O3-Y2O3 system, and the crystallization behavior is uncontrollable, and impurities are easily generated. At present, the preparation methods of the YFeO3 crystal include a hydrothermal method, a pulling method, a flux method, an optical floating zone method and a crucible lowering method. The above methods have the following shortcomings:

[0003] 1. The hydrothermal method: the method needs to use a high-pressure hydrothermal kettle, the crystal crystallization temperature is low, directional growth can be achieved, the growth temperature is 400 DEG C, but the crystal size is less than or equal to 5 mm, the crystal size is small, the quality is poor, and the growth cycle is long.

[0004] 2. The pulling method: due to the special physical and chemical properties of the YFeO3 high-temperature melt, it is very difficult to grow the crystal by the pulling method, and the crystal needs to be grown near the melting point (about 1725 DEG C), but the YFeO3 high temperature is easy to decompose into Y3Fe5O 12 and Fe2O3, which leads to cracking and composition segregation of the crystal, and generates impurities, and the maximum size is only 5 mm.

[0005] 3. The flux method: a lead-containing system (such as PbO-PbF2) can grow a millimeter-level single crystal (size <5 mm), but the toxic lead pollutes the environment, and the flux inclusion leads to an increase of more than 20% in optical loss (such as patent CN108315754A); a lead-free system (such as Na2CO3-NaCl) system, which is easy to produce Fe3O4, Y3Fe5O 12 , PbFe 12 O 19 impurities, the prepared crystal has poor quality, is easy to crack, and the size is less than or equal to 3 mm; a lead-free system (such as KCl-NaCl) system, the growth temperature is 1000 DEG C, but the crystal size is only 0.5 mm, and Fe 3+ volatilization leads to a deviation of the composition from the stoichiometric ratio (such as patent CN112342598A).

[0006] 4. Optical floating zone method: this method has the advantages of no crucible, no pollution, fast growth speed, etc., but the process is complex, the polycrystalline rod raw material needs to be synthesized, the crystal size prepared is ≤5mm, the growth temperature is >1500℃, and the preparation process is easy to produce Y3Fe5O12 12 , Y2O3 impurities, and the quality of the crystal cannot be controlled.

[0007] 5. Crucible lowering method: this method is complex, the raw material needs to be pre-fired to synthesize polycrystalline material, the crystal ingot prepared is polycrystalline, the crystal size is φ15mm, the growth temperature is >1710℃, and high-quality single crystal material cannot be obtained. The addition of flux can greatly reduce the growth temperature and help control the number of spontaneous nucleation, but it is easy to get flaky crystals.

[0008] In summary, the prior art has four core problems:

[0009] (1) Size limitation: the maximum single crystal size of the existing method is ≤5mm, which cannot meet the device processing requirements.

[0010] (2) Toxic pollution: lead and fluorine fluxes cause environmental hazards.

[0011] (3) Optical performance degradation: inclusions and cracks cause the Faraday rotation angle to decay.

[0012] (4) Unstable crystal quality: Fe 3+ High-temperature volatilization, difficult to control composition. SUMMARY

[0013] The present application aims to provide a preparation method of yttrium ferrite single crystal, in order to break through the size bottleneck, inhibit the volatilization of components, improve the crystal quality, and realize environmental protection and pollution-free.

[0014] To this end, the technical scheme adopted by the present application is as follows: a preparation method of yttrium ferrite single crystal, comprising the following steps:

[0015] S1, mix Y2O3 and Fe2O3 with a molar ratio of 1:(1.05-1.08) to obtain a preliminary mixed material, and then mix a composite flux LiCl-KCl-B2O3 to form a mixed raw material, wherein the molar ratio of the preliminary mixed material to the composite flux in the mixed raw material is 1:(20-40), and the molar ratio of LiCl, KCl and B2O3 in the composite flux is (6-9):(6-9):(2-3);

[0016] S2, put the mixed raw material into a platinum crucible, and then heat the inside of the platinum crucible to 1050-1100℃;

[0017] S3, the inside of the platinum crucible is kept for at least 24h to ensure that Y2O3 and Fe2O3 completely react to form a homogeneous melt;

[0018] S4, the platinum crucible is internally cooled to 860-900℃, and a seed crystal is inserted into the platinum crucible;

[0019] S5, the platinum crucible is continuously cooled, the seed crystal is rotated and pulled out;

[0020] S6, the platinum crucible is internally cooled to 750-800℃, and the crystal growth is completed;

[0021] S7, the crystal is pulled out of the liquid surface and annealed, thereby obtaining a yttrium ferrite single crystal.

[0022] As a preferred embodiment of the above, in step S3, the internal temperature of the platinum crucible is maintained for 24-26h.

[0023] Further preferably, in step S5, the cooling rate of the platinum crucible is 0.6-0.8℃ / h.

[0024] Further preferably, in step S5, the rotation rate of the seed crystal is 20-25rpm.

[0025] Further preferably, in step S5, the pulling rate of the seed crystal is 0.007-0.01mm / h.

[0026] Further preferably, in step S7, the cooling rate of the annealing is 3-7℃ / h.

[0027] The beneficial effects of the present application are as follows:

[0028] 1. The crystal size of the YFeO3 single crystal prepared by the present application can reach 8mm×8mm×2mm, which exceeds the maximum single crystal size of 5mm in the prior art and breaks through the size bottleneck.

[0029] 2. The present application uses a fluxing agent (KCl-LiCl-B2O3) free of lead and fluorine, avoids toxic pollution caused by heavy metal impurities, and realizes environmental protection and pollution-free.

[0030] 3. B2O3 network stabilizes Fe 3+ ions, reduces the Fe 3+ volatility, ensures stoichiometric ratio control, suppresses component volatility, and improves the crystallization quality.

[0031] 4、The crystal growth temperature of the application is 1050-1100℃, which reduces the growth temperature, reduces the thermal stress crack, realizes the preparation of single crystal without inclusion and high optical uniformity, thereby increasing the Faraday rotation angle and optical performance, and further improving the crystallization quality. The application can reduce energy consumption by reducing the growth temperature, and the composite flux can be recycled more than 3 times, improving the utilization rate of raw materials and reducing the cost.

[0032] 5、The saturation magnetization of the YFeO3 single crystal prepared by the application can reach 1.42 emu / g, the residual magnetization can reach 0.98 emu / g, and the coercive field can reach 4100 Oe, and the crystal magnetism is excellent. The YFeO3 crystal prepared by the application is a pure phase and does not contain any impurity phase. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is the physical map of the YFeO3 single crystal prepared by the application.

[0034] Figure 2 is the powder diffraction data graph of the YFeO3 single crystal prepared by the application.

[0035] Figure 3 is the magnetic hysteresis loop graph of the YFeO3 single crystal prepared by the application. DETAILED DESCRIPTION

[0036] The application will be further described below in combination with the drawings and examples.

[0037] Example 1:

[0038] A preparation method of yttrium ferrite single crystal, comprising the following steps:

[0039] S1, Y2O3 and Fe2O3 with a molar ratio of 1:1.05 are mixed, and then a composite flux LiCl-KCl-B2O3 is mixed, so as to form a mixed raw material, the molar ratio of the preliminary mixed material and the composite flux in the mixed raw material is 1:20, and the molar ratio of LiCl, KCl and B2O3 in the composite flux is 6:6:2.

[0040] S2, the mixed raw material is put into a platinum gold crucible, and then the inside of the platinum gold crucible is heated to 1100℃.

[0041] S3, the inside of the platinum gold crucible is kept warm for 26h, so as to ensure that Y2O3 and Fe2O3 completely react to form a homogeneous melt.

[0042] S4, the inside of the platinum gold crucible is cooled to 900℃, and a seed crystal is inserted into the platinum gold crucible.

[0043] S5, the inside of the platinum gold crucible continues to cool, the seed crystal is rotated and pulled.

[0044] In step S5, the cooling rate inside the platinum crucible is 0.8℃ / h, the rotation rate of the seed crystal is 25rpm, and the pulling rate of the seed crystal is 0.01mm / h.

[0045] S6, the temperature inside the platinum crucible is lowered to 800℃, and the crystal growth is completed.

[0046] S7, the crystal is pulled out of the liquid surface and subjected to cooling annealing, thereby obtaining a yttrium ferrite single crystal.

[0047] In step S7, the cooling rate of the cooling annealing is 7℃ / h.

[0048] Example 2:

[0049] A method for preparing a yttrium ferrite single crystal comprises the following steps:

[0050] S1, Y2O3 and Fe2O3 with a molar ratio of 1:1.06 are mixed, and a composite flux LiCl-KCl-B2O3 is mixed, thereby forming a mixed raw material, the molar ratio of the preliminary mixed material and the composite flux in the mixed raw material is 1:30, and the molar ratio of LiCl, KCl and B2O3 in the composite flux is 7:7:2.4.

[0051] S2, the mixed raw material is placed in a platinum crucible, and the temperature inside the platinum crucible is raised to 1070℃.

[0052] S3, the temperature inside the platinum crucible is kept for 25h to ensure that Y2O3 and Fe2O3 completely react to form a homogeneous melt.

[0053] S4, the temperature inside the platinum crucible is lowered to 880℃, and a seed crystal is inserted into the platinum crucible.

[0054] S5, the temperature inside the platinum crucible is continuously lowered, and the seed crystal is rotated and pulled.

[0055] In step S5, the cooling rate inside the platinum crucible is 0.7℃ / h, the rotation rate of the seed crystal is 22rpm, and the pulling rate of the seed crystal is 0.008mm / h.

[0056] S6, the temperature inside the platinum crucible is lowered to 770℃, and the crystal growth is completed.

[0057] S7, the crystal is pulled out of the liquid surface and subjected to cooling annealing, thereby obtaining a yttrium ferrite single crystal.

[0058] In step S7, the cooling rate of the cooling annealing is 5℃ / h.

[0059] Example 3:

[0060] A method for preparing a yttrium ferrite single crystal comprises the following steps:

[0061] S1, Y2O3 and Fe2O3 with a molar ratio of 1:1.08 are mixed, and a composite flux LiCl-KCl-B2O3 is mixed, so as to form a mixed raw material, the molar ratio of the preliminary mixed material and the composite flux in the mixed raw material is 1:40, and the molar ratio of LiCl, KCl and B2O3 in the composite flux is 9:9:3.

[0062] S2, the mixed raw material is put into a platinum gold crucible, and the inside of the platinum gold crucible is heated to 1050°C.

[0063] S3, the inside of the platinum gold crucible is kept for 24 hours to ensure that Y2O3 and Fe2O3 completely react to form a homogeneous melt.

[0064] S4, the inside of the platinum gold crucible is cooled to 860°C, and a seed crystal is inserted into the platinum gold crucible.

[0065] S5, the inside of the platinum gold crucible continues to cool, the seed crystal is rotated and pulled.

[0066] In step S5, the cooling rate of the inside of the platinum gold crucible is 0.6°C / h, the rotation rate of the seed crystal is 20 rpm, and the pulling rate of the seed crystal is 0.007 mm / h.

[0067] S6, the inside of the platinum gold crucible is cooled to 750°C, and the crystal growth is completed.

[0068] S7, the crystal is pulled away from the liquid surface and annealed to obtain a yttrium ferrite single crystal.

[0069] In step S7, the cooling rate of the annealing is 3°C / h.

[0070] Synergistic effect of molten salt components: LiCl-KCl in the composite flux LiCl-KCl-B2O3 forms a eutectic mixture, Li + effectively reduces the viscosity of the melt, accelerates the diffusion of Y 3+ and Fe 3+ B2O3 forms a [BO3] 3- viscoelastic network at 750-900°C, which can wrap Fe 3+ and effectively suppresses the volatilization of Fe 3+ Excess 5-8% Fe2O3 can compensate for the high-temperature volatilization of Fe 3+ .

[0071] Interface stability control: ultra-slow cooling (0.6-0.8°C / h) stabilizes the crystal growth rate at 0.5 mm / h, matching the anisotropic growth ability of the (001) surface of YFeO3 crystal.

[0072] Defect suppression mechanism: B2O3 is adsorbed on the step edge, blocking the dislocation extension and reducing the formation of inclusions.

[0073] The growth process parameters of the YFeO3 crystal prepared by the application are shown in the following table:

[0074] Table 1 Growth process parameters of the crystal

[0075]

[0076] Figure 1 A physical map of the YFeO3 single crystal prepared by the application is shown, Figure 2 A powder diffraction data map of the YFeO3 single crystal prepared by the application is shown, Figure 3 A magnetic hysteresis loop map of the YFeO3 single crystal prepared by the application is shown.

[0077] The advantage of the YFeO3 single crystal prepared by the application is that the technology is an efficient and environmentally friendly preparation technology, which breaks through the technical bottleneck of YFeO3 single crystal preparation through the innovation of LiCl-KCl-B2O3 composite flux, and provides a material basis for core components such as optical isolators, magneto-optical modulators, spin electronic devices and multiferroic memories, while significantly reducing energy consumption and cost.

[0078] Although the embodiments of the application have been shown and described, those skilled in the art can understand that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and purposes of the application, and the scope of the application is defined by the claims and their equivalents.

Claims

1. A method for preparing yttrium ferrite single crystal, characterized in that: The following steps are involved: S1. Y2O3 and Fe2O3 in a molar ratio of 1:(1.05-1.08) are mixed to obtain a preliminary mixture, and then a composite flux LiCl-KCl-B2O3 is mixed to form a mixed raw material, wherein the molar ratio of the preliminary mixture to the composite flux in the mixed raw material is 1:(20-40), and the molar ratio of LiCl, KCl, and B2O3 in the composite flux is (6-9):(6-9):(2-3); S2, placing the mixed raw materials into a platinum crucible, and then heating the interior of the platinum crucible to 1050-1100° C.; S3, the platinum crucible is kept warm for at least 24 hours to ensure that Y2O3 and Fe2O3 react completely to form a homogeneous melt; S4, the temperature inside the platinum crucible is lowered to 860-900° C., and a seed crystal is inserted into the platinum crucible; S5, the temperature inside the platinum crucible continues to decrease, and the seed crystal is rotated and pulled; S6, the temperature inside the platinum crucible is lowered to 750-800° C., and the crystal growth is completed; S7. Lift the crystal from the liquid surface and perform annealing by cooling to obtain an yttrium ferrite single crystal.

2. The method for preparing a yttrium ferrite single crystal according to claim 1, wherein: In step S3, the platinum crucible is kept warm for 24-26 hours.

3. The method for preparing a yttrium ferrite single crystal according to claim 1, wherein: In step S5, the cooling rate inside the platinum crucible is 0.6-0.8°C / h.

4. The method for preparing a yttrium ferrite single crystal according to claim 1, wherein: In step S5, the rotation rate of the seed crystal is 20-25 rpm.

5. The method for preparing a yttrium ferrite single crystal according to claim 1, wherein: In step S5, the pulling rate of the seed crystal is 0.007-0.01 mm / h.

6. The method for preparing a yttrium ferrite single crystal according to claim 1, wherein: In step S7, the cooling rate of the cooling annealing is 3-7°C / h.

Images