A trivalent chromium-doped yttrium aluminum garnet powder and its preparation method

Abstract

This invention discloses a trivalent chromium-doped yttrium aluminum garnet powder and its preparation method. The chemical formula of the powder is (Y 1‑ y Ca y )3(Al 1‑x‑z Cr x Mg z )5O 12 Furthermore, 0.001≤x≤0.02, 0.0001≤y≤0.005, and 0.0001≤z≤0.003; This invention uses yttrium nitrate and aluminum nitrate as main materials, and chromium nitrate, magnesium acetate, and calcium acetate as dopants. The precursor is prepared by adding it dropwise to ammonium bicarbonate bottom solution via reverse co-precipitation. The target powder is obtained by drying and calcination. This invention constructs a nitrate-acetate composite system and utilizes the in-situ thermal decomposition gas generation effect of acetate to suppress grain necking, reconstructing hard agglomerates into soft agglomerates. At the same time, it achieves atomic-level in-situ doping of Mg and Ca in the YAG lattice. The resulting powder has both high dispersibility and high sintering activity, and is suitable for preparing Cr:YAG transparent ceramics with high linear transmittance.

Description

Technical Field

[0001] This invention belongs to the field of ceramic powder preparation technology, and relates to a trivalent chromium-doped yttrium aluminum garnet powder and its preparation method. Background Technology

[0002] Yttrium aluminum garnet (YAG) transparent ceramics are high-performance laser matrix materials. Their core properties, such as optical uniformity and laser emission efficiency, are highly positively correlated with the sintering activity of the initial powder used in preparation. Furthermore, the dispersion and agglomeration state of the powder directly determine the subsequent forming quality and densification degree of the ceramic green body. Currently, chemical co-precipitation is the mainstream method for preparing YAG nanopowders. In existing technical solutions (such as CN104445341A), pure nitrate systems (i.e., yttrium nitrate, aluminum nitrate, chromium nitrate, etc.) are typically used as the metal ion source.

[0003] However, the traditional chemical coprecipitation method for pure nitrate systems has significant process defects: during the initial stages of drying and calcination of the nitrate-based precursor, the nitrate decomposition process is accompanied by melting characteristics, and strong capillary contraction forces are generated between particles. Under these dual effects, nanoparticles are prone to dense packing and severe grain necking, ultimately forming dense "hard agglomerates." These hard agglomerates are chemically bonded with extremely strong binding forces, making it difficult for subsequent conventional mechanical ball milling and other dispersion processes to completely break them down to a monodisperse state. When such powders are used for sintering Cr:YAG transparent ceramics, the unbroken hard agglomerates easily become pore nuclei during the sintering process, resulting in a large number of micropores and defects remaining at the grain boundaries. These defects become strong light scattering centers, which not only significantly reduce the linear transmittance of the ceramic but also cause non-radiative loss of laser energy, significantly degrading the laser performance and lifespan of Cr:YAG ceramics.

[0004] Therefore, how to precisely control the chemical composition and anionic system of the precursor solution to suppress the formation and growth of hard agglomerates during calcination at the microscopic mechanism level, and prepare loose YAG-based powder with uniform particle size, good dispersibility and high sintering activity, has become a key technical problem that urgently needs to be solved in the field of high-quality Cr:YAG transparent ceramics preparation. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention aims to provide a trivalent chromium-doped yttrium aluminum garnet powder and its preparation method. The chemical formula of the trivalent chromium-doped yttrium aluminum garnet powder is (Y... 1-y Ca y )3(Al 1-x-z Cr x Mg z )5O 12Where x, y, and z represent the molar ratios of each element, 0.001≤x≤0.02, 0.0001≤y≤0.005, and 0.0001≤z≤0.003. This invention uses yttrium nitrate and aluminum nitrate as main materials, and chromium nitrate, magnesium acetate, and calcium acetate as dopants. A precursor is prepared by dropwise addition of these materials to an ammonium bicarbonate solution via a reverse addition co-precipitation method. The precursor is then dried and calcined to obtain the target powder. This invention constructs a "nitrate-acetate" composite system, utilizing the in-situ thermal decomposition of acetate to counteract capillary contraction, thus reconstructing hard agglomerates into loose, soft agglomerates. Simultaneously, atomic-level in-situ doping of Mg and Ca is achieved through liquid-phase molecular-level mixing. The resulting powder has a pure-phase YAG structure, with Cr... 3+ With well-occupied lattice sites and an average particle size of approximately 100 nm, it combines high dispersibility, high purity, and high sintering activity. Free from impurities such as sulfur and sodium, it effectively solves the problems of severe agglomeration and low sintering activity inherent in traditional powders, paving the way for the preparation of Cr with high linear transmittance. 4+ YAG laser-transparent ceramics offer high-quality raw materials, have strong process controllability, and are easy to industrialize.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A trivalent chromium-doped yttrium aluminum garnet powder, with the general chemical formula (Y 1-y Ca y )3(Al 1-x-z Cr x Mg z )5O 12 Where x, y, and z represent the atomic molar substitution amount of each dopant ion in the corresponding lattice site, 0.001≤x≤0.02, 0.0001≤y≤0.005, 0.0001≤z≤0.003, and the molar amount of each metal ion satisfies the stoichiometric ratio of garnet, i.e., [n(Y 3+ )+n(Ca 2+ )]:[n(Al 3+ )+n(Cr 3+ )+n(Mg 2+ )]=3:5.

[0007] As a limitation of the present invention, the trivalent chromium-doped yttrium aluminum garnet powder is a loose and porous soft aggregate with an average particle size of about 100 nm.

[0008] This invention also provides a method for preparing trivalent chromium-doped yttrium aluminum garnet powder, characterized by the following steps being performed sequentially: S1. Disperse yttrium nitrate, aluminum nitrate, magnesium acetate, calcium acetate, and chromium nitrate separately in deionized water to prepare solutions; S2. Add magnesium acetate solution, calcium acetate solution and chromium nitrate solution together to a mixture of yttrium nitrate solution and aluminum nitrate solution to obtain mixed solution A; S3. Under stirring, slowly add mixed solution A dropwise to ammonium bicarbonate aqueous solution. After titration, continue stirring for 1-2 hours before aging. S4. The aged precipitate is filtered, washed and dried to obtain a loose precursor containing acetate. S5. The precursor is placed in a high-temperature furnace for calcination to obtain trivalent chromium-doped yttrium aluminum garnet powder.

[0009] As a limitation of the preparation method of the present invention, in step S2, the concentration of the yttrium nitrate solution is 96.2-96.7 mg / mL, and the concentration of the aluminum nitrate solution is 102.8-105.1 mg / mL.

[0010] As another limitation of the preparation method of the present invention, in step S2, the concentrations of the magnesium acetate solution, calcium acetate solution and chromium nitrate solution are all 5-20 mg / mL.

[0011] In this invention, the concentrations of magnesium acetate solution, calcium acetate solution, and chromium nitrate solution affect the local supersaturation and nucleation kinetics of the reaction system. If the concentration is less than 5 mg / mL, the solution volume is too large, and the local supersaturation is extremely low, resulting in incomplete precipitation or slow nucleation and a wider grain size distribution. If the concentration is greater than 20 mg / mL, the local concentration is too high, the nucleation rate is too fast and uncontrollable, resulting in severe component segregation of metal cations and hard agglomeration between powders.

[0012] As a third limitation of the preparation method of the present invention, in step S3, the initial pH value of the ammonium bicarbonate aqueous solution is 8.0-9.0, and the pH value of the ammonium bicarbonate aqueous solution must be strictly controlled to be stable at 7.0-7.5 throughout the entire process of adding mixed solution A and at the titration endpoint.

[0013] During the dropwise addition of mixed solution A to the ammonium bicarbonate aqueous solution, the pH value of the ammonium bicarbonate aqueous solution should be stably controlled between 7.0 and 7.5. This is because within this pH range, it can ensure that Y... 3+ Al 3+ and doped ions (Cr) 3+ Mg 2+ Ca 2+ At the same time, it achieves co-precipitation by reaching the solubility product of precipitation, effectively preventing stepwise precipitation due to different pH values ​​of various ion precipitation, and fundamentally eliminating component segregation and the formation of impurity phases.

[0014] As a fourth limitation of the preparation method of the present invention, in step S3, the dropping rate of the mixed solution A is 2-5 mL / min.

[0015] As a fifth limitation of the preparation method of the present invention, in step S3, the aging temperature is 25-50 ℃ and the time is 10-24 h.

[0016] As a sixth limitation of the preparation method of the present invention, in step S4, the drying temperature is 60-100 ℃ and the time is 12-24 h.

[0017] As a seventh limitation of the preparation method of the present invention, in step S5, the calcination process is carried out according to the following procedure: (a) In the first heating stage, the temperature is increased from room temperature to 300-500 ℃ at a heating rate of 1-3 ℃ / min, and held for 1-3 hours; (b) In the second heating stage, the temperature is increased from 300-500℃ to 1100-1300℃ at a heating rate of 3-5℃ / min, and held for 2-4 hours; (c) Cooling stage: The furnace is cooled to room temperature.

[0018] The calcination process of this invention affects the precursor decomposition path, crystal transformation law, and final agglomeration morphology of the powder. In the first heating stage, at a heating rate of 1-3 °C / min, when the temperature is increased from room temperature to 300-500 °C, acetate and carbonate will preferentially undergo in-situ thermal decomposition, releasing gases such as CO2 and H2O. Holding at this time for 1-3 hours is to ensure the complete decomposition of organic groups such as acetate ions, and to utilize the gas expansion effect generated by their decomposition to fully counteract capillary contraction force and prevent the formation of hard agglomerates. In the second heating stage, at a heating rate of 3-5 °C / min, when the temperature is increased from 300-500 °C to 1100-1300 °C, the amorphous precursor will undergo a complete transformation and crystallization into the pure phase YAG crystal form. If the temperature is less than 1100 °C in this stage, the acetate in the precursor will not decompose completely, and the gas expansion effect will be insufficient. If the temperature is greater than 1300 °C, the amorphous precursor will undergo a complete transformation and crystallization into the pure phase YAG crystal form. At temperatures above ℃, the residual powder will prematurely undergo initial sintering and necking, losing its soft agglomeration properties. Holding at this temperature for 2-4 hours is to ensure the precursor is completely transformed into a highly crystalline pure phase YAG, promoting the growth of Cr. 3+ Mg 2+ Ca 2+ The doped ions are fully and uniformly dissolved into specific sites in the crystal lattice, while the grain development is controlled to prevent abnormal grain growth, loss of high sintering activity, and reformation of hard agglomerates due to excessively long holding time.

[0019] The above-described technical solution of this invention, as a whole, involves interconnected and mutually influential steps that collectively determine the morphological characteristics and properties of the product. This invention constructs a "nitrate-acetate" mixed system, utilizing the molecular-level uniform dispersion and high-temperature decomposition characteristics of acetate in the liquid phase to allow trace amounts of Mg to be contained. 2+ Ca 2+ During calcination, the garnet powder is generated in situ and dissolved in the crystal lattice, achieving maximum charge compensation and inhibiting grain growth with a low addition amount. Simultaneously, by utilizing the difference in thermal decomposition characteristics between acetate and nitrate in the precursor, in the early stage of calcination, the carbon dioxide and water vapor generated by the preferential decomposition of acetate form an in-situ thermal decomposition gas generation effect, generating a significant volume expansion force to counteract the capillary contraction force during nitrate decomposition. This physically blocks the direct contact and necking between adjacent grains, transforming the dense hard agglomerates into loose porous soft agglomerates, thereby obtaining garnet powder with a smaller particle size. This powder can be used to prepare Cr:YAG transparent ceramics.

[0020] The above technical solution has the following advantages or beneficial effects: 1. This invention abandons the traditional solid-phase / physical mixing method of adding oxides (e.g., magnesium oxide or calcium oxide). Instead, it uses magnesium acetate and calcium acetate as Mg and Ca sources, utilizing the molecular-level dispersion characteristics of acetate in the liquid phase, combined with the in-situ decomposition phase formation mechanism during calcination, to achieve trace amounts of Mg. 2+ Ca 2+ Uniform solid solution in YAG lattice allows for full utilization of the dual effects of charge compensation and grain growth inhibition with low addition amount, solving the industry problems of dopant segregation and poor modification effect; 2. The Cr:YAG powder prepared by this invention has a fine and uniform particle size and soft agglomeration characteristics, which gives it excellent sintering activity and lays the foundation for subsequent ceramic sintering densification. At the same time, all anions in the system volatilize in gaseous form after calcination, which avoids the introduction of impurities from the source. 3. The preparation method of this invention is simple, the process is easy to control, and it is suitable for large-scale industrial production.

[0021] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0022] Figure 1 The XRD patterns are of the precursor obtained in step S4 of Embodiment 1 of the present invention and the final trivalent chromium-doped yttrium aluminum garnet powder. Figure 2 This is a scanning electron microscope image of trivalent chromium-doped yttrium aluminum garnet powder prepared in Example 1 of the present invention; Figure 3The fluorescence spectra of trivalent chromium-doped yttrium aluminum garnet powders prepared in Examples 2 and 3 of this invention are shown. Detailed Implementation

[0023] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0024] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified. Example 1

[0025] This embodiment prepares a trivalent chromium-doped yttrium aluminum garnet powder, the chemical formula of which is: (Y 1-y Ca y )3(Al 1-x-z Cr x Mg z )5O 12 (x=0.01, y=0.002, z=0.0015) The preparation process and steps of this powder are as follows: S1. Weigh 19.303 g of yttrium nitrate, 31.210 g of aluminum nitrate, 0.500 g of magnesium acetate, 0.500 g of calcium acetate, and 0.500 g of chromium nitrate, and disperse them separately in deionized water to prepare solutions. The concentration of the yttrium nitrate solution is 96.5 mg / mL, the concentration of the aluminum nitrate solution is 104.0 mg / mL, and the concentrations of the magnesium acetate solution, calcium acetate solution, and chromium nitrate solution are all 10 mg / mL. S2. Take 3.37 mL of magnesium acetate solution, 1.60 mL of calcium acetate solution and 1.41 mL of chromium nitrate solution and add them together to the mixture formed by 200 mL of yttrium nitrate solution and 300 mL of aluminum nitrate solution to obtain mixed solution A; S3. Prepare an ammonium bicarbonate aqueous solution with a pH of 8.2. Under stirring, slowly add mixed solution A to the ammonium bicarbonate aqueous solution at a dropping rate of 3 mL / min. Throughout the entire process of adding mixed solution A and at the titration endpoint, the pH of the ammonium bicarbonate aqueous solution must be strictly controlled to 7.3. After the reaction is completed, continue stirring for 1 h and then let it stand at 50 ℃ for 12 h to age. S4. The aged precipitate was filtered and washed, and dried at 60 °C for 24 h to obtain a loose precursor containing acetate. S5. The precursor is placed in a high-temperature furnace. First, the temperature is increased from room temperature to 300 ℃ at a heating rate of 1 ℃ / min and held for 3 h. Then, the temperature is increased from 300 ℃ to 1100 ℃ at a heating rate of 5 ℃ / min and held for 4 h. Subsequently, the furnace is cooled to room temperature to obtain trivalent chromium-doped yttrium aluminum garnet powder.

[0026] like Figure 1 The figure shows the XRD patterns of the precursor obtained in step S4 of Embodiment 1 of the present invention and the final trivalent chromium-doped yttrium aluminum garnet powder. As can be seen from the figure, the positions of all diffraction peaks (shown by the red curve) are completely consistent with the standard card of cubic YAG (shown by the green vertical line), and the peaks are sharp and the baseline is flat, proving that the No. 1 powder is entirely YAG phase and there are no other intermediate phases or impurities.

[0027] like Figure 2 The image shows a scanning electron microscope (SEM) image of the trivalent chromium-doped yttrium aluminum garnet powder prepared in Example 1 of this invention. As can be seen from the image, the powder exhibits a loose and porous soft agglomerate morphology, with weak bonding between nanocrystals and a relatively uniform distribution. No dense hard agglomerates commonly seen in traditional processes are observed, and the average particle size is approximately 100 nm. Example 2

[0028] This embodiment prepares a trivalent chromium-doped yttrium aluminum garnet powder, the chemical formula of which is: (Y 1-y Ca y )3(Al 1-x-z Cr x Mg z )5O 12 (x=0.001, y=0.0001, z=0.0001) The preparation process and steps of this powder are as follows: S1. Weigh 19.340 g of yttrium nitrate, 31.536 g of aluminum nitrate, 0.250 g of magnesium acetate, 0.250 g of calcium acetate, and 0.250 g of chromium nitrate, and disperse them separately in deionized water to prepare solutions. The concentration of the yttrium nitrate solution is 96.7 mg / mL, the concentration of the aluminum nitrate solution is 105.1 mg / mL, and the concentrations of the magnesium acetate solution, calcium acetate solution, and chromium nitrate solution are all 5 mg / mL. S2. Take 0.36 mL of magnesium acetate solution, 0.18 mL of calcium acetate solution and 6.74 mL of chromium nitrate solution and add them together to the mixture formed by 200 mL of yttrium nitrate solution and 300 mL of aluminum nitrate solution to obtain mixed solution A; S3. Prepare an ammonium bicarbonate aqueous solution with a pH of 8.0. Under stirring, slowly add mixed solution A to the ammonium bicarbonate aqueous solution at a dropping rate of 2 mL / min. Throughout the entire process of adding mixed solution A and at the titration endpoint, the pH of the ammonium bicarbonate aqueous solution must be strictly controlled to 7.0. After the titration is completed, continue stirring for 2 h and let it stand at 40 ℃ for 10 h. S4. The aged precipitate was filtered and washed, and dried at 100 °C for 12 h to obtain a loose precursor containing acetate. S5. The precursor is placed in a high-temperature furnace. First, the temperature is increased from room temperature to 400 ℃ at a heating rate of 2 ℃ / min and held for 2 h. Then, the temperature is increased from 400 ℃ to 1200 ℃ at a heating rate of 4 ℃ / min and held for 3 h. Subsequently, the furnace is cooled to room temperature to obtain trivalent chromium-doped yttrium aluminum garnet powder. Example 3

[0029] This embodiment prepares a trivalent chromium-doped yttrium aluminum garnet powder, the chemical formula of which is: (Y 1-y Ca y )3(Al 1-x-z Cr x Mg z )5O 12 (x=0.02, y=0.005, z=0.003) The preparation process and steps of this powder are as follows: S1. Weigh 19.245 g of yttrium nitrate, 30.847 g of aluminum nitrate, 1.000 g of magnesium acetate, 1.000 g of calcium acetate, and 1.000 g of chromium nitrate, and disperse them separately in deionized water to prepare solutions. The concentration of the yttrium nitrate solution is 96.2 mg / mL, the concentration of the aluminum nitrate solution is 102.8 mg / mL, and the concentrations of the magnesium acetate solution, calcium acetate solution, and chromium nitrate solution are all 20 mg / mL. S2. Take 2.71 mL of magnesium acetate solution, 2.22 mL of calcium acetate solution and 33.68 mL of chromium nitrate solution and add them together to the mixture formed by 200 mL of yttrium nitrate solution and 300 mL of aluminum nitrate solution to obtain mixed solution A; S3. Prepare an ammonium bicarbonate aqueous solution with a pH of 9.0. Under stirring, slowly add mixed solution A to the ammonium bicarbonate aqueous solution at a dropping rate of 5 mL / min. Throughout the entire process of adding mixed solution A and at the titration endpoint, the pH of the ammonium bicarbonate aqueous solution must be strictly controlled to 7.5. After the titration is completed, continue stirring for 1.5 h and let it stand at 25 ℃ for 24 h to age. S4. The aged precipitate was filtered and washed, and dried at 90 °C for 18 h to obtain a loose precursor containing acetate. S5. The precursor is placed in a high-temperature furnace. First, the temperature is increased from room temperature to 500 ℃ at a heating rate of 3 ℃ / min and held for 1 h. Then, the temperature is increased from 500 ℃ to 1300 ℃ at a heating rate of 3 ℃ / min and held for 2 h. Subsequently, the furnace is cooled to room temperature to obtain trivalent chromium-doped yttrium aluminum garnet powder.

[0030] like Figure 3 The figures show the fluorescence spectra of trivalent chromium-doped yttrium aluminum garnet powders prepared in Examples 2 and 3 of this invention. As can be seen from the figures, the clear and sharp R-line emission peaks confirm the presence of Cr in the powders of Examples 2 and 3. 3+ It has successfully entered the octahedral sites of the YAG lattice and has good crystallinity.

[0031] Comparative Example To investigate the influence of different raw materials used in the preparation process of this invention on the performance of the product, the following comparative experiments were conducted. Different yttrium aluminum garnet powders were prepared according to the following comparative examples: Comparative Example 1 This comparative example prepares a yttrium aluminum garnet powder. The preparation process is similar to that of Example 1, except that magnesium acetate solution, calcium acetate solution, and chromium nitrate solution are not added in step S2.

[0032] Because this comparative example lacks magnesium, calcium, and chromium doping, it lacks the synergistic regulation of the "nitrate-acetate" mixed system, making it impossible to achieve in-situ lattice solid solution and charge compensation of magnesium and calcium ions. This makes it difficult to effectively suppress lattice defects and abnormal grain growth, easily leading to lattice distortion and insufficient sintering activity. At the same time, it lacks the in-situ gas generation effect brought about by the difference in thermal decomposition between acetate and nitrate, making it unable to resist capillary contraction force and block grain necking in the early stage of calcination. This makes it difficult to transform dense hard agglomerates into loose porous soft agglomerates, resulting in larger particle size, more severe agglomeration, and poorer dispersibility and sintering uniformity. Furthermore, it does not introduce chromium ion luminescent centers and does not possess the characteristic luminescent properties of Cr:YAG, failing to meet the functional application requirements of transparent ceramics and other applications. Both the material properties and application scenarios are significantly limited.

[0033] Comparative Example 2 This comparative example prepares a yttrium aluminum garnet powder. The preparation process is similar to that of Example 1, except that in step S2, magnesium acetate solution and calcium acetate solution are not added, and a trace amount of ammonium sulfate [(NH4)2SO4] is added and dissolved in the ammonium bicarbonate aqueous solution in step S3 as an anti-agglomeration additive during the precipitation process.

[0034] Because of the high thermal stability of sulfate, this method inevitably leads to trace amounts of sulfur remaining inside the powder. These residual trace amounts of sulfur will form a large number of micropore defects and color centers at the grain boundaries, causing light scattering and harming the optical transmittance of transparent ceramics.

[0035] Comparative Example 3 This comparative example prepares a yttrium aluminum garnet powder. The preparation process is similar to that of Example 1, except that in step S2, magnesium acetate solution and calcium acetate solution are not added, and sodium dodecylbenzenesulfonate (SDBS) with a mass fraction of 0.5 wt% is added and dissolved in the ammonium bicarbonate aqueous solution in step S3 as a surfactant in the precipitation process.

[0036] Due to sodium ions (Na) in SDBS + During subsequent calcination, these substances are extremely difficult to completely volatilize and will inevitably dissolve into the YAG lattice, becoming harmful impurities. Simultaneously, large amounts of glucose and long-chain SDBS easily lead to carbon residue during microwave and calcination processes, affecting the high transmittance of transparent ceramics.

[0037] Comparative Example 4 This comparative example prepares a yttrium aluminum garnet powder. The preparation process is similar to that in Example 1, except that magnesium acetate solution and calcium acetate solution are not added. Instead, magnesium acetate solution and calcium acetate solution are replaced with equimolar amounts of magnesium oxide and calcium oxide. The specific steps are as follows: S1. Weigh 19.303 g of yttrium nitrate, 31.210 g of aluminum nitrate and 0.500 g of chromium nitrate and disperse them separately in deionized water to prepare solutions, wherein: the concentration of the yttrium nitrate solution is 96.5 mg / mL, the concentration of the aluminum nitrate solution is 104.0 mg / mL and the concentration of the chromium nitrate solution is 10 mg / mL; S2. Transfer 1.41 mL of chromium nitrate solution to the mixture formed by 200 mL of yttrium nitrate solution and 300 mL of aluminum nitrate solution to obtain mixed solution A; S3. Prepare an ammonium bicarbonate aqueous solution with a pH of 8.2. Under stirring, slowly add mixed solution A to the ammonium bicarbonate aqueous solution at a dropping rate of 3 mL / min. Throughout the entire process of adding mixed solution A and at the titration endpoint, the pH of the ammonium bicarbonate aqueous solution must be strictly controlled to 7.3. After the reaction is completed, continue stirring for 1 h and then let it stand at 50 ℃ for 12 h to age. S4. The aged precipitate was filtered and washed, and dried at 60 °C for 24 h to obtain precursor powder without Mg and Ca doping. S5. The precursor is placed in a high-temperature furnace. First, the temperature is increased from room temperature to 300 ℃ at a heating rate of 1 ℃ / min and held for 3 h. Then, the temperature is increased from 300 ℃ to 1100 ℃ at a heating rate of 5 ℃ / min and held for 4 h. After that, it is cooled to room temperature with the furnace to obtain yttrium aluminum garnet powder precursor. S6. The yttrium aluminum garnet powder precursor was mechanically ball-milled with 0.14 g of magnesium oxide and 0.18 g of calcium oxide to obtain yttrium aluminum garnet powder.

[0038] Mechanical ball milling, being a solid-phase physical mixture, cannot achieve atomic-level uniform contact with the Y-Al-Cr precursor, leading to severe compositional segregation of Mg and Ca elements at the microscale. Furthermore, because MgO and CaO are physically mixed, they cannot fully function as charge compensators during subsequent sintering, failing to achieve the desired Cr content. 4+ Conversion rate.

[0039] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A trivalent chromium-doped yttrium aluminum garnet powder, characterized in that, The general chemical expression formula is (Y 1-y Ca y )3(Al 1-x- z Cr x Mg z )5O 12 Where x, y, and z represent the atomic molar substitution amount of each dopant ion in the corresponding lattice site, 0.001≤x≤0.02, 0.0001≤y≤0.005, 0.0001≤z≤0.003, and the molar amount of each metal ion satisfies the stoichiometric ratio of garnet, i.e., [n(Y 3+ )+n(Ca 2+ )]:[n(Al 3+ )+n(Cr 3+ )+n(Mg 2+ )]=3:

5.

2. The trivalent chromium-doped yttrium aluminum garnet powder according to claim 1, characterized in that, The trivalent chromium-doped yttrium aluminum garnet powder is a loose and porous soft aggregate with an average particle size of about 100 nm.

3. A method for preparing trivalent chromium-doped yttrium aluminum garnet powder according to claim 1 or 2, characterized in that, Follow these steps in sequence: S1. Disperse yttrium nitrate, aluminum nitrate, magnesium acetate, calcium acetate, and chromium nitrate separately in deionized water to prepare solutions; S2. Add magnesium acetate solution, calcium acetate solution and chromium nitrate solution together to a mixture of yttrium nitrate solution and aluminum nitrate solution to obtain mixed solution A; S3. Under stirring, slowly add mixed solution A dropwise to ammonium bicarbonate aqueous solution. After titration, continue stirring for 1-2 hours before aging. S4. The aged precipitate is filtered, washed and dried to obtain a loose precursor containing acetate. S5. The precursor is placed in a high-temperature furnace for calcination to obtain trivalent chromium-doped yttrium aluminum garnet powder.

4. The method for preparing trivalent chromium-doped yttrium aluminum garnet powder according to claim 3, characterized in that, In step S2, the concentration of the yttrium nitrate solution is 96.2-96.7 mg / mL, and the concentration of the aluminum nitrate solution is 102.8-105.1 mg / mL.

5. The method for preparing trivalent chromium-doped yttrium aluminum garnet powder according to claim 3, characterized in that, In step S2, the concentrations of the magnesium acetate solution, calcium acetate solution, and chromium nitrate solution are all 5-20 mg / mL.

6. The method for preparing trivalent chromium-doped yttrium aluminum garnet powder according to claim 3, characterized in that, In step S3, the initial pH value of the ammonium bicarbonate aqueous solution is 8.0-9.

0. Throughout the entire process of adding mixed solution A and at the titration endpoint, the pH value of the ammonium bicarbonate aqueous solution must be strictly controlled to be stable at 7.0-7.

5.

7. The method for preparing trivalent chromium-doped yttrium aluminum garnet powder according to claim 3, characterized in that, In step S3, the dropping rate of the mixed solution A is 2-5 mL / min.

8. The method for preparing trivalent chromium-doped yttrium aluminum garnet powder according to claim 3, characterized in that, In step S3, the aging temperature is 25-50 ℃ and the time is 10-24 h.

9. The method for preparing trivalent chromium-doped yttrium aluminum garnet powder according to claim 3, characterized in that, In step S4, the drying temperature is 60-100 ℃ and the time is 12-24 h.

10. The method for preparing trivalent chromium-doped yttrium aluminum garnet powder according to claim 3, characterized in that, In step S5, the calcination process is carried out according to the following procedure: (a) In the first heating stage, the temperature is increased from room temperature to 300-500 ℃ at a heating rate of 1-3 ℃ / min, and held for 1-3 h; (b) In the second heating stage, the temperature is increased from 300-500 ℃ to 1100-1300 ℃ at a heating rate of 3-5 ℃ / min, and held for 2-4 h; (c) Cooling stage: The furnace is cooled to room temperature.

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