CN108203844A - Tantalic acid magnesium serial crystal and preparation method thereof - Google Patents

Abstract

The invention discloses a kind of tantalic acid magnesium serial crystals, i.e. MgO Ta₂O₅Pseudo binary system, respectively Mg₄Ta₂O₉、Mg₃Ta₂O₈And MgTa₂O₆.The method for preparing tantalic acid magnesium serial crystal is additionally provided, using excessive MgO or Mg (OH)₂Component compensates, and passes through the high-purity MgTa of solid state reaction kinetics₂O₆And Mg₄Ta₂O₉Powder, and the rodlike MgTa of Centimeter Level is grown using micro- glass tube down-drawing₂O₆And Mg₄Ta₂O₉Monocrystal；With Mg₄Ta₂O₉And MgTa₂O₆Make melting starting material, using spontaneous nucleation technology, in MgTa₂O₆The rodlike Mg of Centimeter Level is grown on ceramic seed crystal stick₃Ta₂O₈Monocrystal.It is of the invention to use micro- glass tube down-drawing, the high-temperature gradient of growth near interface is efficiently used, realizes quick, high uniformity crystallization, post-heater is efficiently used and avoids the excessive caused problem of Cracking of thermal stress.

Description

Magnesium tantalate series crystals and preparation method thereof

technical field

The invention belongs to the field of chemical industry, and relates to a microwave dielectric material, specifically magnesium tantalate series crystals and a preparation method thereof.

Background technique

With the rapid development of microwave communication, modern mobile phones and electronic communication, microwave dielectric materials, which play an important role in communication systems, have attracted great attention from scientific researchers and technology industry manufacturers. Mg ₄ Ta ₂ O ₉ , Mg ₃ Ta ₂ O ₈ , MgTa ₂ O ₆ and their doped materials have excellent microwave dielectric properties and luminescent properties, and have been widely studied in the form of ceramics and powders. In order to deeply explore the intrinsic properties of MgO-Ta ₂ O ₅ system materials such as microwave dielectric and optics and their changes with composition, structure and crystal orientation, the preparation of its crystal materials is imminent.

The Mg ₄ Ta ₂ O ₉ crystal material belongs to the hexagonal system, has an ilmenite structure, the space group is P3c1(165), and the lattice constants are a=0.51611nm, c=1.40435nm, V=0.32396nm ³ . During the period when Mg ₄ Ta ₂ O ₉ is heated to its melting point of 1825°C, although no phase transition occurs, because MgO is volatile at high temperature, Mg ₄ Ta ₂ O ₉ will be slightly decomposed into MgTa ₂ O ₆ , which is not conducive to pure phase powder Synthesis of high crystal quality crystals, continuous growth of crystals and equal stoichiometric component requirements, so the present invention uses MgO or Mg(OH) ₂ component compensation to synthesize high-purity Mg ₄ Ta ₂ O ₉ powder and crystals.

Mg ₃ Ta ₂ O ₈ is an orthorhombic crystal system, which belongs to the Cmcm(63) space group. The unit cell parameters are a=1.0238nm, b=1.1456nm and c=1.0065nm. The MgO-Ta ₂ O ₅ phase diagram shows that its It only exists stably at 1475～1675℃, above or below this temperature range, it decomposes into Mg ₄ Ta ₂ O ₉ and MgTa ₂ O ₆ . Even if the pure-phase powder or crystal is prepared, more or less decomposition products will be produced during the process of heating, melting or cooling. Therefore, no single-phase pure-phase Mg ₃ Ta ₂ O ₈ has been reported so far. The invention utilizes the high temperature gradient of the micro-pulling down method, the MgO compensation of the initial powder material and the spontaneous nucleation method to prepare the pure phase Mg ₃ Ta ₂ O ₈ crystal.

MgTa ₂ O ₆ is a tantalate with a three-rutile structure. It is a tetragonal crystal system and belongs to the P42/mnm space group. The lattice constant and In the process of synthesizing MgTa ₂ O ₆ powder and growing MgTa ₂ O ₆ crystal, MgO volatilizes at high temperature, resulting in Ta ₂ O ₅ impurity phase, so MgO component compensation is required to obtain equal stoichiometric ratio and high crystallinity Quality MgTa ₂ O ₆ crystals.

The micro-pull-down method is a single crystal growth technology that can realize the preparation of high-quality single crystal optical fibers. It has many advantages such as control and the ability to grow crystals with high segregation coefficients, and has great development value in the exploration of new materials and the optimization of single crystal performance.

Contents of the invention

Aiming at the above-mentioned technical problems in the prior art, the present invention provides magnesium tantalate series crystals and a preparation method thereof. The magnesium tantalate series crystals and the preparation method thereof will solve the problems of preparing magnesium tantalate crystals in the prior art. Technical issues with poor quality and performance.

The invention provides a magnesium tantalate crystal, the molecular formula of which is Mg ₄ Ta ₂ O ₉ , the crystal is a hexagonal crystal system, the space group it belongs to is P-3c1(165), and the unit cell parameters are a=0.51625(10)nm, c=1.4062(4)nm, the density is 6.171g/cm ³ , and the refined structure constant is 0.0356.

The present invention also provides a magnesium tantalate crystal whose molecular formula is Mg ₃ Ta ₂ O ₈ , belongs to the orthorhombic crystal system, belongs to the space group Cmcm(63), and has a lattice constant of a=0.38087(12)nm, b =1.0034(2)nm, c=1.0206(3)nm, the density is 5.965g/cm ³ , and the refined structure constant is 0.0207.

The present invention also provides a magnesium tantalate crystal, whose molecular formula is MgTa ₂ O ₆ , belongs to the tetragonal crystal system, belongs to the space group P42/mnm(136), and has a lattice constant of a=0.46821(3)nm, c= 0.91382(7)nm, the crystal density is 8.03265g/cm ³ , and the refinement parameter RAII is 0.026.

The present invention also provides a method for preparing the above-mentioned Mg ₄ Ta ₂ O ₉ crystal, comprising the following steps:

1) According to the molar ratio of 5.2:1 or 5.6:1, weigh the pure phase Mg(OH) ₂ and Ta ₂ O ₅ , grind and mix, sieve, ball mill, press into cylindrical tablets, and pre-fire at 1300°C or 1350°C 16h, the heating and cooling rate is 100°C/h; or according to the molar ratio of 4.04:1, weigh the pure phase MgO and Ta ₂ O ₅ raw materials, grind and mix, sieve, ball mill, press into cylindrical pieces, and pre-fire at 1400°C 2h, the heating and cooling rate is 1400°C/h, and the pure phase Mg ₄ Ta ₂ O ₉ ceramic cylinder is obtained, which is ground to powder;

2) Weigh Mg ₄ Ta ₂ O ₉ and Mg(OH) ₂ or MgO powder at a molar ratio of 10:1, mix them by ball milling, put them into an Ir crucible, and use Mg ₄ Ta ₂ O ₉ single crystal rods to make Seed crystal, evacuated for 12 hours, put in protective atmosphere Ar, adjust the flow rate of the incoming and outgoing gas to 20mL/min, make the air pressure stable at 1.5atm, set the micro-pulling speed to 0.05mm/min to grow, after the growth is completed, cool down for 3h After that, a colorless and transparent single crystal Mg ₄ Ta ₂ O ₉ was obtained. The present invention also provides the method for the above-mentioned _MgTa2O6 crystal, comprising _the following steps:

1) According to the molar ratio of 4:1, weigh the pure phase Mg(OH) ₂ and Ta ₂ O ₅ , grind and mix them evenly, sieve, ball mill, press into cylindrical pieces, pre-calcine at 1300°C for 16h, 100°C/h cool down;

2) Put the synthetic ceramic cylinder into a crucible such as Ir, use MgTa ₂ O ₆ polycrystalline rod as the seed crystal, vacuumize for 12 hours, and then inject Ar gas, the pressure is stable at 1.5atm, the flow rate is controlled at 20mL/min, set The pull-down speed is 0.2mm/min, spontaneous nucleation, adjust the power to perform multiple necking and shoulder expansion processes, optimize the crystal quality, set the cooling time to 10h, cool to room temperature, and grow to the end, and obtain a light yellow transparent single crystal Mg ₃ Ta ₂ O ₈ .

The present invention also provides the method for the above-mentioned _MgTa2O6 crystal, comprising _the following steps:

1) According to the molar ratio of 1.15:1, weigh the pure phase Mg(OH) ₂ and Ta ₂ O ₅ , grind and mix them evenly, sieve, ball mill, press them into cylindrical pieces, pre-calcine at 1400°C for 8h, 100°C/h cool down;

2) Weigh MgTa ₂ O ₆ and Mg(OH) ₂ powders at a molar ratio of 10:1, ball mill and mix them evenly, put them into an Ir crucible, use Y ₃ Al ₅ O ₁₂ single crystal rods as seed crystals, and vacuumize 12h, enter the protective atmosphere Ar, adjust the flow rate of the incoming and outgoing gases to 20mL/min, make the air pressure stable at 1.5atm, set the micro-pulling down speed to 0.2mm/min for growth, after the crystal growth is completed, take it out after cooling down for 8h, and in the After annealing at 1000°C in air for 12 hours, it becomes light yellow and transparent, and a transparent single crystal Mg ₄ Ta ₂ O ₉ is obtained.

3) The present invention uses MgO or Mg(OH) ₂ component compensation, synthesizes high-purity MgTa ₂ O ₆ and Mg ₄ Ta ₂ O ₉ powders through solid-state reaction, and grows centimeter-scale rod-shaped MgTa ₂ by micro-pulling down method O ₆ and Mg ₄ Ta ₂ O ₉ single crystals, the sizes are Φ(2～3)mm×60mm and Φ(1.2～1.6)mm×97mm respectively; Mg ₄ Ta ₂ O ₉ and MgTa ₂ O ₆ are used as melting initiation Using spontaneous nucleation technology, centimeter-scale rod-shaped Mg ₃ Ta ₂ O ₈ single crystals are grown on MgTa ₂ O ₆ ceramic seed rods, with a size of Φ1.2mm×19mm. The grown crystals have high crystallization integrity and are transparent without macroscopic Defects fully satisfy the characterization and testing of various intrinsic properties of crystals.

Compared with the prior art, the technical progress of the present invention is remarkable. The present invention uses excess MgO or Mg(OH)2 for component compensation, thereby effectively suppressing the volatilization of MgO, the decomposition of compounds and the formation of impurity phases during the preparation of pure-phase powders, ceramics and crystals, and obtaining equistoichiometric ratios Three types of crystals. The micro-pull-down method used in the present invention has a high temperature gradient near the solid-liquid interface. Compared with other crystal growth methods, it is easier to grow the MgO-Ta ₂ O ₅ system crystal material that is easy to decompose and phase transition. A rear heater is installed near the solid-liquid interface, thereby effectively solving the problem of easy cracking of the MgO-Ta ₂ O ₅ system crystal material.

Description of drawings:

Fig. 1 is the structural representation of the micro-drawn crystal growth furnace of the radio frequency induction heating type that micro-drawn crystal growth adopts;

Figure 2(a) is the XRD pattern of Mg ₄ Ta ₂ O ₉ powder synthesized from 5.2Mg(OH) ₂ :Ta ₂ O ₅ raw materials;

Figure 2(b) is the XRD pattern _{of Mg 4 Ta 2 O 9 powder synthesized from} raw materials with a ratio of 5.6Mg(OH) ₂ : _Ta 2 O 5;

Figure 2(c) is the XRD pattern of Mg ₄ Ta ₂ O ₉ powder synthesized from 4.04MgO:Ta ₂ O ₅ ratio raw materials;

Figure 3 is a Mg _{4 Ta 2 O 9} rod-shaped single crystal grown with an excess of 10% Mg(OH) 2 Mg ₄ Ta ₂ O ₉ powder;

Fig. 4 Mg ₄ Ta ₂ O ₉ rod-shaped single crystal with a diameter of 1.6mm grown with an excess of 10% MgO Mg ₄ Ta ₂ O ₉ powder;

Figure 5 is a 2 mm diameter Mg ₄ Ta ₂ O ₉ rod-shaped single crystal grown with an excess of 10% MgO Mg ₄ Ta ₂ O ₉ powder;

Figure 6(a) XRD pattern of _{Mg 4} Ta ₂ O ₉ rod-shaped single crystal powder grown with Mg ₄ Ta ₂ O ₉ powder with excess 10% Mg(OH) 2;

Figure 6(b) XRD pattern of Mg ₄ Ta ₂ O ₉ rod-shaped single crystal powder with a diameter of 1.6mm grown by Mg ₄ Ta ₂ O ₉ powder with an excess of 10% MgO;

Figure 6(c) XRD pattern of 2 mm diameter Mg ₄ Ta ₂ O ₉ rod-shaped single crystal powder grown with Mg ₄ Ta ₂ O ₉ powder with excess 10% MgO;

Figure 7(a) is the powder XRD spectrum of ceramics synthesized from raw materials with a ratio of 4Mg(OH) ₂ :Ta ₂ O ₅ ;

Figure 7(b) is the powder XRD pattern of Mg ₃ Ta ₂ O ₈ crystals grown by the micro pull-down method;

Fig. 8 is the Mg ₃ Ta ₂ O ₈ crystal grown by the micro pull-down method;

Figure 9 is a structural diagram of Mg ₃ Ta ₂ O ₈ crystal;

Fig. 10(a) powder XRD pattern of MgTa ₂ O ₆ ceramics synthesized from raw materials with a ratio of 1.15Mg(OH) ₂ : Ta ₂ O ₅ ;

Fig. 10(b) powder XRD pattern of MgTa ₂ O ₆ crystals grown by micro pull-down method;

Fig. 11 is MgTa ₂ O ₆ crystals grown by micro-pulling method by adding 1% Mg(OH) ₂ in MgTa ₂ O ₆ powder;

Fig. 12 is a structure diagram of MgTa ₂ O ₆ crystal.

Detailed ways

The MgO-Ta ₂ O ₅ micro-pulled crystal growth is a radio-frequency induction heating micro-pulled crystal growth furnace produced by the French Cyberstar company. As shown in Figure 1, the front end of the Ir crucible 1 used is conical, with a size of Φ16mm×10mm. The size of the nozzle is Φ3mm×3mm, the diameter of the through hole of the nozzle is 1mm, the rear end is cylindrical, the size is Φ16mm×30mm, a meniscus 13 is formed during the falling process of the melting material 12, and the Ir rear heater 2 is placed at the bottom of the crucible, and the size is Φ16mm×15mm, used to adjust the temperature field distribution near the solid-liquid interface at the nozzle, to a certain extent anneal the crystal 11 grown on the lower rod 15 and prevent cracking. Two ring column adiabatic supports 3 and 14 made of Al ₂ O ₃ with different inner and outer diameters are placed under the rear heater 2 to further adjust the temperature field distribution in the growth area of the crystal 11 and provide a suitable temperature gradient for crystallization. A transparent quartz glass tube 4 is placed under the heat insulating support 14 to adjust the vertical position of the crucible 1 on the radio frequency heating coil 5 and to display the macroscopic state of the growth of the crystal 11 . The inner layer insulation wall 6, the outer layer insulation wall 7 and the outer layer insulation cover 8 are placed outside the crucible 1 to optimize the temperature field distribution. Add glass protective cover 9 and top protective cover 10 on the outside again, prevent that growth raw material 12 leaks and pollute the radio frequency heating coil 5 outside protective cover, also prevent outside uncontrollable impurity from polluting the growing environment in glass cover.

The present invention is further described below by embodiment, but does not limit the present invention.

Example 1 Growth of Mg ₄ Ta ₂ O ₉ crystals by micro pull-down method

(1) Synthesis of high-purity Mg ₄ Ta ₂ O ₉ powder by solid state reaction

1) Synthesis of pure phase Mg ₄ Ta ₂ O ₉ powder with 5.2Mg(OH) ₂ :1Ta ₂ O ₅

According to the molar ratio of 5.2:1, take a total of 5 g of raw materials of Mg(OH) ₂ and Ta ₂ O ₅ with a purity of 99.999% and 99.99%, put them into a mortar, grind and mix them evenly, and sieve them through a 220-mesh sieve. Put it into a ball mill jar filled with _ZrO2 balls, and mill it on a ball mill for 1h. Under the action of 350MPa pressure, a cylindrical sheet with a size of Φ13mm×5mm was prepared, put into a muffle furnace for pre-firing at 1300°C for 16h, and the heating and cooling rate was 100°C/h. The phase purity of the obtained ceramic cylinders was characterized by powder XRD (Fig. 2(a)).

2) Synthesis of pure phase Mg ₄ Ta ₂ O ₉ powder with 5.6Mg(OH) ₂ :1Ta ₂ O ₅

The ratio of raw materials was raised to 5.6:1, while the pre-firing temperature was raised to 1350°C, and other conditions remained unchanged. The phase purity of the obtained ceramic cylinder was characterized by powder XRD (Fig. 2(b)).

3) 4.04MgO:1Ta ₂ O ₅ to synthesize pure phase Mg ₄ Ta ₂ O ₉ powder

According to the molar ratio of 4.04:1, take a total of 5 g of MgO and Ta ₂ O ₅ with a purity of 99.9995% and 99.99% respectively, put them into a mortar, grind and mix them evenly, pass through a 220-mesh sieve, and put them into a ZrO ₂ balls in a ball mill jar, milled on a ball mill for 1 h. Under the action of 350MPa pressure, a cylindrical sheet with a size of Φ13mm×5mm was prepared, put into a muffle furnace for pre-firing at 1400°C for 2h, and the heating and cooling rate was 1400°C/h. The phase purity of the obtained ceramic cylinders was characterized by powder XRD (Fig. 2(c)).

(2) Growth of Mg ₄ Ta ₂ O ₉ single crystal rods by micro-pull method

1) Mg ₄ Ta ₂ O ₉ +0.1Mg(OH) ₂ Micro pull-down method to grow fiber crystal

The pure-phase Mg ₄ Ta ₂ O ₉ powder synthesized from Mg(OH) ₂ and Ta ₂ O ₅ and Mg(OH) ₂ powder are ball-milled at a molar ratio of 10:1, and a total of 5g is put into the In the Ir crucible shown in 1, the Mg ₄ Ta ₂ O ₉ single crystal rod _optimized for spontaneous nucleation in the early stage was used as _the seed crystal. crystal rod. Adjust various components such as the crucible and the axis of the seed crystal to be on the vertical line, and make the upper surface of the seed crystal close to the lower surface of the crucible nozzle. Seal the spherical growth chamber, evacuate it for 12 hours, pass in the protective atmosphere Ar, adjust the flow rate of the incoming and outgoing gas to 20mL/min, and stabilize the air pressure at 1.5atm. After the atmosphere flow and pressure are stable for 1 hour, set the heating rate for 1 hour to raise the temperature to 35% of the rated power, and keep it warm for 1 hour. After the melt flows out from the through hole of the crucible nozzle, and slowly expands and spreads to form a meniscus, move the seed crystal up to dock with it , keep warm for 1h, and wait for no change in the solid-liquid interface, set the micro-pulling speed to 0.05mm/min for growth, and fine-tune it in the range of 35-36% of the rated power according to the change of the growth interface. After the crystal growth was completed, it was taken out after cooling down for 3 hours, and a colorless and transparent single crystal with a size of Φ1.2 mm×97 mm was obtained as shown in FIG. 3 .

2) Mg ₄ Ta ₂ O ₉ +0.1MgO micro pull-down method to grow Mg ₄ Ta ₂ O ₉ crystals

The pure-phase Mg ₄ Ta ₂ O ₉ powder synthesized from MgO and Ta ₂ O ₅ and MgO powder were ball milled and mixed at a molar ratio of 10:1, and put into an Ir crucible for growth. The growth power was the rated power of the equipment 36% of , the growth rate is 0.05mm/min, and the grown crystal size is Φ1.6mm×76mm. As shown in Figure 4, the powder XRD characterization of the crystal shows that it is a pure phase, as shown in Figure 6(b) . Using the same powder under the conditions of rated power of 37.5% and growth rate of 0.05mm/min, the size of the growth is Φ2.0mm×16mm, and the crystal is more transparent, as shown in Figure 5, and the powder XRD spectrum is shown in Figure 6(c ), indicating that it is a pure phase.

(3) Crystal characterization of Mg ₄ Ta ₂ O ₉

As shown in Figure 6(a), (b) and (c), Mg ₄ Ta ₂ O ₉ rod-shaped single crystals grown with Mg ₄ Ta ₂ O ₉ powder with an excess of 10% Mg(OH) ₂ or MgO, respectively Powder XRD patterns show that the grown crystals are pure phase Mg ₄ Ta ₂ O ₉ .

Single crystal X-ray diffraction data analysis, Mg ₄ Ta ₂ O ₉ crystal is hexagonal, the space group is P-3c1(165), and the unit cell parameters are a=0.51625(10)nm, c=1.4062(4)nm , the density is 6.171g/cm ³ , and the refined structure constant is 0.0356, which proves that its crystal quality is good.

Example 2 Growth of Mg ₃ Ta ₂ O ₈ crystals by micro pull-down method

Mix the high-purity powder raw materials Mg(OH) ₂ (99.999%) and Ta ₂ O ₅ (99.99%) in a molar ratio of 4:1, put a total of 5g into a mortar, grind and mix, pass through a 220-mesh sieve, and put it into the put _ZrO2 balls into a ball mill tank, mill on a ball mill for 1 hour, grind the ball milled material again in a mortar, sieve through 220 mesh, press 350MPa into cylindrical pieces with a size of Φ13mm×5mm, put them into In the high-temperature muffle furnace, set the pre-firing temperature to 1300°C, hold the temperature for 16 hours, and heat up and down at a rate of 100°C/h. The phase purity of the obtained ceramic cylinder was characterized by powder XRD, and its spectral features are shown in Figure 7(a). It is found that there is no Mg ₃ Ta ₂ O ₈ phase, but a mixed phase of 0.62Mg ₄ Ta ₂ O ₉ +0.38MgTa ₂ O ₆ . According to the phase diagram analysis, its composition is roughly in the vicinity of the composition of Mg ₃ Ta ₂ O ₈ .

Put the synthetic ceramic cylinder into the Ir crucible as shown in Figure 1, use the MgTa ₂ O ₆ polycrystalline rod as the seed crystal, move the seed rod up to the top of the seed crystal and roughly align it with the conical bottom nozzle of the Ir crucible, everything Adjust properly, close the growth chamber, make it in a sealed state, vacuumize for 12 hours, and then introduce Ar gas. By controlling the flow rate of the atmosphere inlet and outlet, the pressure is stabilized at 1.5atm, and the flow rate of the gas in the chamber is controlled at 20mL/ min, after the atmosphere flow rate and pressure are stable for 1 hour, set the heating time for 1 hour, raise it to 25% of the rated power, keep it warm for a period of time, when the melt flows out from the nozzle through hole, a crescent-shaped infiltrating droplet is formed, and keep at this power for 1 hour, After the shape is stable, slowly move the seed crystal up and connect it, keep the connection state for 1 hour, and slowly adjust the growth power so that the width of the melting zone is preferably smaller than the diameter of the crucible nozzle and larger than the diameter of the micropore. After everything is ready, set the pull-down speed of the seed rod to 0.2mm/h. By adjusting the power, the process of necking and expanding shoulders is performed multiple times to speed up the rate of spontaneous nucleation and crystallization growth. When it is seen that the grown crystal is more transparent and brighter than the previous crystal, keep the growth parameters unchanged. Continue isodiametric growth until no solution flows out from the nozzle of the crucible. Set the cooling time to 10 h, and slowly cool down to room temperature, and the growth is over. As shown in Figure 8, after about 20 cm long spontaneous nucleation process to optimize the crystal quality, light yellow transparent Mg ₃ Ta ₂ O ₈ crystals with no macroscopic defects and a size of Φ1.2mm×19mm were produced by spontaneous nucleation. grow out. The optimized growth power is 29.5% of the maximum power of the instrument, and the growth speed is 0.2mm/min.

Any part of the single crystal was cut and ground into powder, and the XRD pattern test was performed, as shown in Figure 7(b), which was characterized as a pure Mg ₃ Ta ₂ O ₈ phase.

Single crystal X-ray diffraction data analysis shows that the Mg ₃ Ta ₂ O ₈ crystal belongs to the orthorhombic crystal system, the space group is Cmcm(63), and the lattice constants are a=0.38087(12)nm, b=1.0034(2)nm , c=1.0206(3)nm, the density is 5.965g/cm ³ , and the refined structure constant is 0.0207, which proves that its crystal quality is good. The test structure diagram is shown in Figure 9 .

Example 3 Growth of MgTa ₂ O ₆ crystals by micro pull-down method

The raw materials Mg(OH) ₂ (Noah chemical, 99.999%) and Ta ₂ O ₅ (Aldrich, 99.99%) were weighed at a molar ratio of 1.15:1, mixed in a 5g mortar, sieved at 220 mesh, and ball milled for 1 hour. At 350MPa, a cylindrical sheet of Φ13mm×5mm was prepared, put into a muffle furnace for pre-calcination at 1400°C for 8h, and the temperature was raised and lowered at 100°C/h. Powder XRD, as shown in Figure 10(a), shows that the obtained ceramic sheet is pure phase MgTa ₂ O ₆ . Mix the synthesized pure-phase _MgTa2O6 powder and Mg(OH) ₂ powder with a molar ratio of 100:1 by ball milling, and dry-press a total of 5 g into _a column with a diameter of 13 mm, and put it into an Ir crucible as shown in Figure 1 In this method, Y ₃ Al ₅ O ₁₂ (abbreviated as YAG) single crystal rod is used as the seed crystal, the upper end of the seed crystal is cut flat and polished, kept clean and dry, and fixed on the hollow Al ₂ O ₃ seed rod. Adjust various components such as the crucible and the axis of the seed crystal to be on the vertical line, and make the upper surface of the seed crystal close to the lower surface of the crucible nozzle. Seal the spherical growth chamber, evacuate it for 12 hours, pass in the protective atmosphere Ar, adjust the flow rate of the incoming and outgoing gas to 20mL/min, and stabilize the air pressure at 1.5atm. After the atmosphere flow rate and pressure are stable for 1 hour, set the heating rate for 1 hour to raise the temperature to 29.6% of the rated power, keep it warm for 1 hour, wait for the melt to flow out from the through hole of the crucible nozzle, and slowly expand and spread to form a meniscus, and move the seed crystal up to connect with it , keep warm for 1h, and wait for no change in the solid-liquid interface, set the micro-pulling speed to 0.2mm/min for growth, and fine-tune it in the range of 29.6-34% of the rated power according to the change of the growth interface. After the crystal growth was completed, it was taken out after cooling down for 8 hours. As shown in Figure 11, the obtained crystal was black in color and bright in color, with a diameter of 2-3 mm and a length of 60 mm, without macroscopic defects. The black is because the growth atmosphere is a reducing atmosphere Ar gas, and it will become light yellow and transparent after annealing at 1000°C for 12 hours in air.

A part of the single crystal was randomly cut and ground into powder, and tested by XRD pattern, which was characterized as pure phase MgTa ₂ O ₆ , as shown in Figure 10(b).

Single crystal X-ray diffraction data analysis shows that the MgTa ₂ O ₆ crystal belongs to the tetragonal system, the space group is P42/mnm(136), and the lattice constants are a=0.46821(3)nm, c=0.91382(7)nm , the crystal density is 8.03265g/cm ³ , and the refinement parameter RAII is 0.026, which proves that the crystal quality is good. The test structure diagram is shown in Figure 12. The grown crystals are cut, oriented, and processed for various performance tests.

The above content is only a basic description of the concept of the present invention, and any equivalent transformation made according to the technical solution of the present invention shall fall within the scope of protection of the present invention.

Claims (6)

1. a kind of tantalic acid magnesium crystal, it is characterised in that：Its molecular formula is Mg₄Ta₂O₉, belong to hexagonal crystal system, affiliated space group is P- 3c1 (165), cell parameter are a=0.51625 (10) nm, c=1.4062 (4) nm, density 6.171g/cm³, refined structure Constant is 0.0356.

2. a kind of tantalic acid magnesium crystal, it is characterised in that：Its molecular formula is Mg₃Ta₂O₈, belong to rhombic system, affiliated space group is Cmcm (63), lattice constant is a=0.38087 (12) nm, b=1.0034 (2) nm, c=1.0206 (3) nm, density 5.965g/ cm³, refined structure constant is 0.0207.

3. a kind of tantalic acid magnesium crystal, it is characterised in that：Its molecular formula is MgTa₂O₆, belong to tetragonal crystal system, affiliated space group is P42/ Mnm (136), lattice constant are a=0.46821 (3) nm, c=0.91382 (7) nm, crystalline density 8.03265g/cm³, essence It is 0.026 to repair parameter RAII.

4. a kind of as claimed in claim 1 prepare Mg₄Ta₂O₉The method of crystal, it is characterised in that include the following steps：

1) according to 5.2:1 or 5.6:1 molar ratio weighs pure phase Mg (OH)₂And Ta₂O₅, it is ground, is sieved, ball milling, compacting Into slice of cylinder, 1300 DEG C or 1350 DEG C of pre-burning 16h, temperature rate is 100 DEG C/h；Or according to 4.04:1 molar ratio claims Take pure phase MgO and Ta₂O₅Raw material is ground, and sieving, ball milling is pressed into slice of cylinder, 1400 DEG C of pre-burning 2h, and temperature rate is 1400℃/h；

2) by Mg₄Ta₂O₉With Mg (OH)₂Or MgO powders are with 10:1 molar ratio weighing, ball milling mixing, are put into Ir crucibles, with Mg₄Ta₂O₉Monocrystal rod does seed crystal, vacuumizes 12h, is passed through protective atmosphere Ar, adjusts into and out of gas flow to 20mL/min, makes it Stable gas pressure is grown for 0.05mm/min in 1.5atm, the micro- drop-down speed of setting, after growth, after 3h cools down, is obtained A kind of tantalic acid magnesium crystal described in claims 1.

5. the method for a kind of tantalic acid magnesium crystal described in claims 2, it is characterised in that include the following steps：

1) according to 4:1 molar ratio weighs pure phase Mg (OH)₂And Ta₂O₅, it being ground, is sieved, ball milling is pressed into slice of cylinder, 1300 DEG C of pre-burning 16h, 100 DEG C/h heating and cooling；

2) synthesis ceramic cylinder piece is put into as in Ir crucibles, with MgTa₂O₆Polycrystalline rod does seed crystal, vacuumizes 12h, then be passed through Ar Gas, pressure stabilization are 0.2mm/min in 20mL/min, setting drop-down speed in 1.5atm, flow control, and spontaneous nucleation is adjusted Power carries out multiple necking down and expands shoulder process, optimizes crystalline quality, and setting temperature fall time is 10h, but to room temperature, so far grown junction Beam obtains a kind of tantalic acid magnesium crystal described in claims 2.

6. the method for a kind of tantalic acid magnesium crystal described in claims 3, it is characterised in that include the following steps：

1) according to 1.15:1 molar ratio weighs pure phase Mg (OH)₂And Ta₂O₅, it is ground, sieving, ball milling are pressed into cylinder Piece, 1400 DEG C of pre-burning 8h, 100 DEG C/h heating and cooling；

2)MgTa₂O₆With Mg (OH)₂Powder is with 10:1 molar ratio weighing, ball milling mixing, are put into Ir crucibles, with Y₃Al₅O₁₂It is single Crystal bar does seed crystal, vacuumizes 12h, is passed through protective atmosphere Ar, adjusts into and out of gas flow to 20mL/min, makes its stable gas pressure In 1.5atm, micro- drop-down speed is set to be grown for 0.2mm/min, after crystal growth, taken out after 8h coolings, in air In 1000 DEG C annealing 12h after become pale yellow transparent, obtain a kind of tantalic acid magnesium crystal described in claims 3.