A ce cr 2 si 2 c single crystal and a method for growing the same

Abstract

The application provides a CeCr2Si2C single crystal and a growth method thereof, and belongs to the technical field of crystal growth. The growth method comprises the following steps: S1. In a protective atmosphere, raw materials are loaded into a graphite crucible to obtain a graphite crucible assembly; the raw materials comprise Ce, Cr and Si; S2. The graphite crucible assembly is subjected to heat treatment and cooling treatment to obtain a CeCr2Si2C single crystal. The growth method of the CeCr2Si2C single crystal provided by the application is simple in operation, short in period, and can obtain a high-quality CeCr2Si2C single crystal in a sheet shape.

Description

Technical Field

[0001] This invention belongs to the field of crystal growth technology, and specifically relates to a CeCr2Si2C single crystal and its growth method. Background Technology

[0002] Among Ce-based compounds, CeCr2Si2, with its strong electronic correlation, has attracted widespread attention. However, its structural instability limits the study of its potential properties, especially its magnetic behavior. Currently, the CeCr2Si2 structure is mainly stabilized by introducing carbon atoms to form quaternary CeCr2Si2C. However, research on CeCr2Si2C is mainly based on powder samples, which cannot reveal its intrinsic magnetic behavior. Therefore, there is an urgent need to provide a single-crystal growth method to obtain high-quality CeCr2Si2C single crystals. Summary of the Invention

[0003] To address one or more technical problems existing in the prior art, the present invention provides a CeCr2Si2C single crystal and its growth method. The growth method of CeCr2Si2C single crystal provided by the present invention has a simple process and a short cycle, and can obtain high-quality CeCr2Si2C single crystals in sheet form.

[0004] The present invention provides a method for growing CeCr2Si2C single crystals in a first aspect, the method comprising the following steps:

[0005] S1. Under a protective atmosphere, the raw material is loaded into a graphite crucible to obtain a graphite crucible assembly; the raw material contains Ce, Cr and Si;

[0006] S2. The graphite crucible assembly is subjected to heat treatment and cooling treatment to obtain the CeCr2Si2C single crystal.

[0007] Preferably, the molar ratio of Ce, Cr and Si in the raw material is 1:(5-17):(5-17).

[0008] Preferably, the molar ratio of Cr to Si in the raw material is 1:1.

[0009] Preferably, Ce, Cr, and Si are added in the raw materials in the form of elements or alloys.

[0010] Preferably, the graphite crucible has a purity of 99.999%.

[0011] Preferably, the heat treatment is performed under vacuum conditions, raising the temperature to a preset temperature and holding it at that temperature for 24–30 hours.

[0012] The preset temperature is not lower than the eutectic temperature of SiCr in the raw material.

[0013] Preferably, the vacuum degree of the heat treatment process is 10. -4 ~10 -3 Pa;

[0014] The heating rate of the heat treatment process is 5–10 °C / min.

[0015] Preferably, the preset temperature is 1700–1800°C.

[0016] Preferably, the cooling process involves first reducing the temperature to 900°C at a cooling rate of 1–5°C / h, and then reducing it to room temperature at a cooling rate of 50–100°C / h.

[0017] In a second aspect, the present invention provides a CeCr2Si2C single crystal, which is prepared by the growth method described in the first aspect.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects:

[0019] This invention uses excess Cr and Si as fluxes and a graphite crucible as a carbon source. The raw material containing Ce, Cr and Si is placed in the graphite crucible and subjected to heat treatment and cooling treatment to obtain high-quality sheet-like CeCr2Si2C single crystals. Compared with the Czochralski method, the growth method of CeCr2Si2C single crystals in this invention is simpler to operate and has a shorter growth cycle. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a physical image of the CeCr2Si2C single crystal provided by this invention;

[0022] Figure 2 This is a crystal structure diagram of CeCr2Si2C single crystal provided by the present invention;

[0023] Figure 3 This is the XRD diffraction pattern of the CeCr2Si2C single crystal provided in Example 1 of this invention;

[0024] Figure 4 This is the XRD diffraction pattern of the powder obtained by grinding the CeCr2Si2C single crystal provided in Example 1 of the present invention;

[0025] Figure 5These are the zero-field cold (ZFC) magnetic susceptibility curves of the μ0H / / ab plane and the μ0H⊥ab plane obtained by CeCr2Si2C single crystal at a temperature of 300K to 2K and a magnetic field of μ0H = 1T, provided in Example 1 of this invention.

[0026] Figure 6 The zero-field-cooled (ZFC) magnetic susceptibility curves of the CeCr2Si2C single crystal provided in Example 1 of this invention are obtained by fitting the μ0H / / ab plane and the μ0H⊥ab plane using the Curie-Weiss law. -1 ~T curve;

[0027] Figure 7 This is the M-μOH curve of the μOH / / ab plane of CeCr2Si2C single crystal provided in Example 1 of the present invention;

[0028] Figure 8 This is the M-μOH curve of the CeCr2Si2C single crystal μOH⊥ab plane provided in Embodiment 1 of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] The present invention provides a method for growing CeCr2Si2C single crystals in a first aspect, the method comprising the following steps:

[0031] S1. Under a protective atmosphere, the raw material is loaded into a graphite crucible to obtain a graphite crucible assembly; the raw material contains Ce, Cr and Si;

[0032] S2. The graphite crucible assembly is subjected to heat treatment and cooling treatment to obtain the CeCr2Si2C single crystal.

[0033] It should be noted that the protective atmosphere in this invention can be a protective gas such as argon.

[0034] Current research on CeCr2Si2C is based on powder crystal samples, but its magnetic behavior remains controversial. For example, the small spontaneous magnetization caused by Cr sublattice below 30K and the Pauli paramagnetic behavior related to the intermediate valence state of Ce cannot be well obtained. Therefore, this invention provides a method for growing CeCr2Si2C single crystals, which can obtain high-quality CeCr2Si2C single crystals, so as to better study the magnetic behavior of CeCr2Si2C.

[0035] This invention uses excess Cr and Si as fluxes and a graphite crucible as a carbon source. The raw material containing Ce, Cr and Si is placed in the graphite crucible and subjected to heat treatment and cooling treatment to obtain high-quality sheet-like CeCr2Si2C single crystals. Compared with the Czochralski method, the growth method of CeCr2Si2C single crystals in this invention is simpler to operate and has a shorter growth cycle.

[0036] According to some preferred embodiments, the molar ratio of Ce, Cr and Si in the raw materials is 1:(5-17):(5-17) (for example, it can be 1:5:5, 1:6:6, 1:7:7, 1:8:8, 1:9:9, 1:10:10, 1:11:11, 1:12:12, 1:13:13, 1:14:14, 1:15:15, 1:16:16 or 1:17:17).

[0037] Based on a Ce, Cr, and Si molar ratio of 1:2:2, this invention introduces additional Cr and Si as fluxes to lower the eutectic temperature of Ce, Cr, and Si, allowing Ce, Cr, and Si to fully melt at a lower temperature, resulting in a uniform liquid phase that provides an environment for single crystal formation and growth. Within the above range, the size of the single crystal can be controlled by adjusting the flux content. Too much or too little Cr and Si is detrimental to single crystal nucleation and growth, making it impossible to obtain high-quality single crystal samples.

[0038] According to some preferred embodiments, the molar ratio of Cr to Si in the raw materials is 1:1; when the molar ratio of excess Cr to Si is 1:1, the eutectic temperature of the Ce, Cr and Si mixture can be ensured to be lower, resulting in a low eutectic mixture of Ce, Cr and Si, which can effectively reduce energy consumption during the heat treatment process.

[0039] According to some preferred embodiments, Ce, Cr, and Si are added in the raw materials in the form of elements or alloys; in this invention, Ce, Cr, and Si can be added in the form of elements or alloys, as long as the molar ratio of each atom meets the above range.

[0040] The purity of the graphite crucible is 99.999%; the C in the CeCr2Si2C single crystal comes from the graphite crucible, therefore, the present invention selects a high-purity (99.999%) graphite crucible.

[0041] According to some preferred embodiments, the heat treatment is performed under vacuum conditions, raising the temperature to a preset temperature and holding it at that temperature for 24 to 30 hours (e.g., 24 hours, 25 hours, 26 hours, 27 hours, 28 hours, 29 hours, or 30 hours).

[0042] The preset temperature is not lower than the eutectic temperature of SiCr in the raw material.

[0043] According to some preferred embodiments, the preset temperature is 1700-1800℃ (for example, it can be 1700℃, 1710℃, 1720℃, 1730℃, 1740℃, 1750℃, 1760℃, 1770℃, 1780℃, 1790℃ or 1800℃).

[0044] This invention uses heat treatment to melt Ce, Cr, and Si into a uniform liquid phase, providing a liquid environment for the subsequent formation and growth of single crystals. The heat treatment temperature is controlled above the eutectic temperature of SiCr, preferably within the range mentioned above, to ensure sufficient melting of Ce, Cr, and Si to obtain a uniform liquid phase. Excessive temperature increases energy consumption; insufficient temperature prevents Ce, Cr, and Si from forming a uniform liquid phase quickly, hindering the formation and growth of CeCr2Si2C single crystals.

[0045] According to some preferred embodiments, the vacuum degree of the heat treatment process is 10. -4 ~10 -3 Pa;

[0046] The heating rate of the heat treatment process is 5 to 10 °C / min (for example, it can be 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min or 10 °C / min).

[0047] According to some preferred embodiments, the cooling process involves first reducing the temperature to 900°C at a cooling rate of 1–5°C / h (e.g., 1°C / h, 2°C / h, 3°C / h, 4°C / h, or 5°C / h), and then reducing the temperature to room temperature at a cooling rate of 50–100°C / h (e.g., 50°C / h, 60°C / h, 70°C / h, 80°C / h, 90°C / h, or 100°C / h).

[0048] The cooling process of this invention includes two stages. The first stage involves cooling to 900°C at a rate of 1–5°C / h (e.g., 1°C / h, 2°C / h, 3°C / h, 4°C / h, or 5°C / h). This stage is mainly for single crystal formation and growth. If the cooling rate is too high, it will be detrimental to the formation and growth of single crystals. The second stage involves cooling to room temperature at a rate of 50–100°C / h (e.g., 50°C / h, 60°C / h, 70°C / h, 80°C / h, 90°C / h, or 100°C / h). This stage is mainly for rapidly cooling the high-temperature furnace without damaging it.

[0049] In some specific embodiments, Ce blocks (approximately 2cm × 2cm), Cr particles (1-3mm in diameter), and silicon blocks (approximately 3cm × 3cm to 10cm × 10cm) are placed in a graphite crucible (the graphite crucible has a purity of 99.999%, and the crucible lid can be either an open ring lid or a closed ring lid) at a molar ratio of 1:(5-17):(5-17) to obtain a graphite crucible assembly. Then, the graphite crucible assembly is stably installed into a graphite heating cylinder in a high-temperature furnace. The heating cylinder is located at the center of the high-temperature furnace and is coaxial with the heating coil. The furnace is then filled with insulating graphite felt around the furnace and topped with the furnace lid and door. The furnace is then kept in a sealed vacuum environment, and the temperature is increased to 1700–1800°C at a rate of 5–10°C / min, and held for 24–30 hours to allow the Ce blocks, Cr particles, and silicon blocks to completely liquidate and mix uniformly. Finally, the temperature is lowered to 900°C at a rate of 1–5°C / h, and then to room temperature at a rate of 50–100°C / h to complete the crystal growth process. Once the furnace temperature has cooled to room temperature, the graphite crucible is removed, and the sheet-like CeCr2Si2C crystals can be peeled off. It should be noted that to prevent further oxidation of Ce, the oxide layer on the surface of the Ce rods is removed in an Ar-filled glove box, and the Ce rods are cut into blocks to reduce the contact area between the Ce blocks and oxygen during the transfer of the graphite crucible assembly, thus preventing Ce oxidation. If the Ce blocks are too small, their surface is easily oxidized, which is detrimental to single crystal growth.

[0050] In a second aspect, the present invention provides a CeCr2Si2C single crystal, which is prepared by the growth method described in the first aspect.

[0051] The CeCr2Si2C single crystal of this invention is a large, plate-like single crystal (maximum size up to 8mm × 13mm), with a tetragonal structure, space group P4 / mmm (No. 123), and lattice constant: It is ferromagnetic, with a ferromagnetic transition temperature of about 12.4K and a melting point of over 1800℃.

[0052] To more clearly illustrate the technical solution and advantages of the present invention, the present invention will be further described below in conjunction with embodiments.

[0053] The materials and reagents used in this invention can be purchased directly from the market or synthesized in-house, and there are no restrictions on the specific models.

[0054] Example 1

[0055] (1) In a glove box filled with Ar gas, Ce blocks (2cm×2cm), Cr particles (3mm in diameter), and silicon blocks (8cm×8cm) with the surface oxide layer removed were weighed according to the molar ratio of Ce:Cr:Si = 1:12:12. Then they were placed into a graphite crucible and the crucible lid was put on to obtain a graphite crucible assembly.

[0056] (2) Carefully place the graphite crucible assembly into the graphite heating cylinder in the high-temperature furnace. Fill the area around and top of the heating cylinder with insulating graphite felt, then cover the furnace with the lid and door; maintain a sealed vacuum environment inside the furnace at a pressure of approximately 10. -3 Pa, and heat to 1700℃ at a heating rate of 5℃ / min, and hold for 30h to completely turn the raw material into a liquid phase and mix it evenly; then slowly cool to 900℃ at a cooling rate of 2℃ / h, and finally cool to room temperature at a cooling rate of 50℃ / h. Remove the graphite crucible to obtain CeCr2Si2C single crystals with an average size of about 4mm×5mm and a maximum size of 8mm×13mm in sheet form.

[0057] Depend on Figure 1-2 It can be seen that Example 1 yields CeCr2Si2C single crystals with an average size of approximately 4mm × 5mm and a maximum size of 8mm × 13mm in sheet form, exhibiting a tetragonal structure, space group P4 / mmm (No. 123), and a lattice constant of: Depend on Figure 3 It can be seen that the XRD pattern of the CeCr2Si2C single crystal obtained in Example 1 only shows the (00l) peak (l is an integer), indicating that the CeCr2Si2C single crystal is grown along the ab plane (the ab plane is from a crystallographic perspective); from Figure 4 It can be seen that all diffraction peaks in the XRD diffraction pattern of the CeCr2Si2C single crystal after grinding in Example 1 correspond to the peaks on the standard card, indicating that the CeCr2Si2C single crystal has high purity; it should be noted that, Figure 4 In the diagram, "observed" represents the actual measured curve, "Calculated" represents the theoretically calculated curve, "Diffeence" represents the difference between the actual and theoretical values ​​(i.e., slight deviations in peak position due to various reasons), and the short vertical bar represents the peak of CeCr2Si2C. Figure 5-6It can be seen that CeCr2Si2C single crystals exhibit ferromagnetism at low temperatures. The Curie-Weiss law is used to fit the χ² value. -1 The T curve yielded a ferromagnetic transition temperature of 12.4 K. Figure 7-8 This study further revealed the behavior of CeCr2Si2C single crystal undergoing a ferromagnetic transition at low temperatures, which is consistent with the results of magnetic susceptibility curve measurements.

[0058] Example 2

[0059] (1) In a glove box filled with Ar gas, Ce blocks, Cr particles and silicon blocks with the surface oxide layer removed are weighed according to the molar ratio of Ce:Cr:Si=1:7:7, and then put into a graphite crucible and cover the crucible to obtain a graphite crucible assembly.

[0060] (2) Carefully place the graphite crucible assembly into the graphite heating cylinder in the high-temperature furnace. Fill the area around and top of the heating cylinder with insulating graphite felt, then cover the furnace with the lid and door; maintain a sealed vacuum environment inside the furnace at a pressure of approximately 10. -4 Pa, and heat to 1700℃ at a heating rate of 5℃ / min, and hold for 30h to completely turn the raw material into a liquid phase and mix it evenly; then slowly cool to 900℃ at a cooling rate of 3℃ / h, and finally cool to room temperature at a cooling rate of 50℃ / h. Remove the graphite crucible to obtain CeCr2Si2C single crystal in sheet shape with a size of about 3mm×4mm.

[0061] Example 3

[0062] (1) In a glove box filled with Ar gas, Ce blocks, Cr particles and silicon blocks with the surface oxide layer removed are weighed according to the molar ratio of Ce:Cr:Si=1:5:5, and then put into a graphite crucible and cover the crucible to obtain a graphite crucible assembly.

[0063] (2) Carefully place the graphite crucible assembly into the graphite heating cylinder in the high-temperature furnace. Fill the area around and top of the heating cylinder with insulating graphite felt, then cover the furnace with the lid and door; maintain a sealed vacuum environment inside the furnace at a pressure of approximately 10. -3 Pa, and heat to 1700℃ at a heating rate of 5℃ / min, and hold at that temperature for 28h to completely turn the raw material into a liquid phase and mix it evenly; then slowly cool to 900℃ at a cooling rate of 5℃ / h, and finally cool to room temperature at a cooling rate of 50℃ / h. Remove the graphite crucible to obtain CeCr2Si2C single crystals with a size of about 2mm×3mm.

[0064] Example 4

[0065] (1) In a glove box filled with Ar gas, Ce blocks, Cr particles and silicon blocks with the surface oxide layer removed are weighed according to the molar ratio of Ce:Cr:Si=1:17:17, and then put into a graphite crucible and cover the crucible to obtain a graphite crucible assembly.

[0066] (2) Carefully place the graphite crucible assembly into the graphite heating cylinder in the high-temperature furnace. Fill the area around and top of the heating cylinder with insulating graphite felt, then cover the furnace with the lid and door; maintain a sealed vacuum environment inside the furnace at a pressure of approximately 10. -3 Pa, and heat to 1700℃ at a heating rate of 5℃ / min, and hold for 24h to completely turn the raw material into a liquid phase and mix it evenly; then slowly cool to 900℃ at a cooling rate of 1℃ / h, and finally cool to room temperature at a cooling rate of 50℃ / h. Remove the graphite crucible to obtain CeCr2Si2C single crystal in sheet shape with a size of about 3mm×4mm.

[0067] Example 5

[0068] (1) In a glove box filled with Ar gas, Ce powder, Cr powder and silicon powder with the surface oxide layer removed are weighed according to the molar ratio of Ce:Cr:Si=1:12:12, and then put into a graphite crucible and cover the crucible to obtain a graphite crucible assembly.

[0069] (2) Carefully place the graphite crucible assembly into the graphite heating cylinder in the high-temperature furnace. Fill the area around and top of the heating cylinder with insulating graphite felt, then cover the furnace with the lid and door; maintain a sealed vacuum environment inside the furnace at a pressure of approximately 10. -3 Pa, and heat to 1700℃ at a heating rate of 5℃ / min, and hold for 30h to completely turn the raw material into a liquid phase and mix it evenly; then slowly cool to 900℃ at a cooling rate of 2℃ / h, and finally cool to room temperature at a cooling rate of 50℃ / h. Remove the graphite crucible to obtain a CeCr2Si2C single crystal with a size of about 1mm×1mm.

[0070] Comparative Example 1

[0071] Comparative Example 1 is basically the same as Example 1, except that in step (1), the molar ratio of Ce:Cr:Si is 1:2:2.

[0072] Comparative Example 1, due to insufficient amounts of Cr and Si, ultimately yielded a CeCr2Si2C polycrystalline sample.

[0073] Comparative Example 2

[0074] Comparative Example 2 is basically the same as Example 1, except that in step (1), the molar ratio of Ce:Cr:Si is 1:20:20.

[0075] In Comparative Example 2, due to excessive flux, it was not conducive to single crystal nucleation and growth, and a single crystal sample could not be obtained.

[0076] Comparative Example 3

[0077] Comparative Example 3 is basically the same as Example 1, except that in step (2), the furnace is controlled to be a sealed vacuum environment with a pressure of approximately 10. -3 Pa, and heat to 1500℃ at a heating rate of 5℃ / min, and hold at that temperature for 30h to completely turn the raw material into a liquid phase and mix it evenly; then slowly cool to 900℃ at a cooling rate of 2℃ / h, and finally cool to room temperature at a cooling rate of 50℃ / h.

[0078] In Comparative Example 3, the heat treatment temperature was only slightly higher than the melting points of Si and Cr. At this temperature, the surfaces of Cr and Si in the raw materials began to slowly become molten, and it took a long time to completely form a homogeneous liquid state. The results showed that this temperature was not conducive to the growth of CeCr2Si2C single crystals.

[0079] Comparative Example 4

[0080] Comparative Example 4 is basically the same as Example 1, except that in step (2), the furnace is controlled to be a sealed vacuum environment with a pressure of approximately 10. -3 Pa, and heat to 1700℃ at a heating rate of 5℃ / min, and hold at that temperature for 30h to completely turn the raw material into a liquid phase and mix it evenly; then slowly cool to 900℃ at a cooling rate of 15℃ / h, and finally cool to room temperature at a cooling rate of 50℃ / h.

[0081] Comparative Example 4 shows that the excessively rapid cooling rate is not conducive to the formation and growth of single crystals.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for growing CeCr2Si2C single crystals, characterized in that, The growth method includes the following steps: S1. Under a protective atmosphere, the raw material is loaded into a graphite crucible to obtain a graphite crucible assembly; the raw material contains Ce, Cr and Si; the molar ratio of Ce, Cr and Si in the raw material is 1:(5~17):(5~17); the molar ratio of Cr and Si in the raw material is 1:1; S2. The graphite crucible assembly is subjected to heat treatment and cooling treatment to obtain the CeCr2Si2C single crystal; the heat treatment is carried out under vacuum conditions, the temperature is raised to a preset temperature and held for 24~30h; the preset temperature is 1700~1800℃; The cooling process involves first reducing the temperature to 900℃ at a rate of 1~5℃ / h, and then reducing it to room temperature at a rate of 50~100℃ / h.

2. The growth method according to claim 1, characterized in that, Ce, Cr, and Si are added in the raw materials in the form of elements or alloys.

3. The growth method according to claim 1, characterized in that, The purity of the graphite crucible is 99.999%.

4. The growth method according to claim 1, characterized in that, The vacuum degree of the heat treatment process is 10. -4 ~10 - 3 Pa; The heating rate of the heat treatment process is 5~10℃ / min.

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