阅读说明：本技术 一种多坩埚梯度冷凝晶体生长装置及其用于生长大尺寸溴化镧单晶的方法 (Multi-crucible gradient condensation crystal growth device and method for growing large-size lanthanum bromide single crystal by using same ) 是由 牛晓冉 刘涛 于 2019-10-21 设计创作，主要内容包括：一种多坩埚梯度冷凝晶体生长装置及其用于生长大尺寸溴化镧单晶的方法,它涉及生长溴化镧单晶的装置及方法。它是要解决现有的溴化镧单晶的生长方法的单晶质量差、易开裂的技术问题。该装置包括双层壳体、保温盖、内衬陶瓷管、两组外加热线圈、两组内加热线圈、多个控温热电偶、多个坩埚托、多个石英坩埚；其中内衬陶瓷管设置在圆柱形双层壳体的轴线上；多个坩埚托均布并固定在双层壳体与内衬陶瓷管之间的环形区域内；两组外加热线圈设置在双层壳体内；两组内加热线圈设置在内衬陶瓷管上。本方法：将溴化镧籽晶封装在石英坩埚中,再放到坩埚托上,采用全静态的原位梯度冷凝降温生长和退火,得到无开裂的大尺寸溴化镧单晶,可用于晶体生长领域。(A multi-crucible gradient condensation crystal growth device and a method for growing large-size lanthanum bromide single crystals relate to a device and a method for growing lanthanum bromide single crystals. The method aims to solve the technical problems of poor single crystal quality and easy cracking of the existing lanthanum bromide single crystal growth method. The device comprises a double-layer shell, a heat preservation cover, a lining ceramic tube, two groups of outer heating coils, two groups of inner heating coils, a plurality of temperature control thermocouples, a plurality of crucible holders and a plurality of quartz crucibles; wherein the lining ceramic tube is arranged on the axis of the cylindrical double-layer shell; a plurality of crucible supports are uniformly distributed and fixed in an annular area between the double-layer shell and the lining ceramic tube; the two groups of external heating coils are arranged in the double-layer shell; two groups of inner heating coils are arranged on the inner lining ceramic tube. The method comprises the following steps: and packaging lanthanum bromide seed crystals in a quartz crucible, placing the quartz crucible on a crucible holder, and adopting full-static in-situ gradient condensation cooling growth and annealing to obtain a large-size lanthanum bromide single crystal without cracking, wherein the large-size lanthanum bromide single crystal can be used in the field of crystal growth.)

1. A multi-crucible gradient condensation crystal growth device is characterized by comprising a cylindrical double-layer shell (1), a heat-insulating cover (2), a lining ceramic tube (3), two groups of outer heating coils (4), two groups of inner heating coils (5), a plurality of temperature control thermocouples (6), a plurality of crucible holders (7) and a plurality of quartz crucibles (8);

wherein the lining ceramic tube (3) is arranged on the axis of the cylindrical double-layer shell (1); a plurality of crucible supports (7) are uniformly distributed and fixed in an annular area between the double-layer shell (1) and the lining ceramic tube (3);

the two groups of external heating coils (4) are respectively arranged at the upper part and the lower part in the double-layer shell (1); the double-layer shell (1) is provided with a heat-insulating layer;

the two groups of inner heating coils (5) are respectively arranged at the upper part and the lower part in the inner lining ceramic tube (3);

a plurality of temperature control thermocouples (6) are arranged from top to bottom along the inner wall of the double-layer shell (1).

2. A multi-crucible gradient condensed crystal growth apparatus as claimed in claim 1, wherein the quartz crucible (8) is composed of an upper cylindrical tube (8-1), a lower inverted cone (8-2) and a bottom cylindrical tube (8-3).

3. A multi-crucible gradient condensed crystal growth apparatus as claimed in claim 2, wherein the vertex angle α of the inverted cone (8-2) of the lower portion of the quartz crucible (8) is 30 to 120 °.

4. A multi-crucible gradient condensed crystal growth apparatus as defined in claim 2, wherein the vertex angle α of the inverted cone of the lower inverted cone (8-2) is 60 °.

5. A multi-crucible gradient condensation crystal growth apparatus as claimed in claim 1, 2, 3 or 4, wherein the bottom cylinder (8-3) is 40 to 50mm high and 2 to 6mm in diameter.

6. A multi-crucible gradient condensation crystal growth apparatus as claimed in claim 1, 2, 3 or 4, characterized in that the inner diameter of the upper cylindrical barrel (8-1) of the quartz crucible (8) is 2.54 to 7.62 cm.

7. The multi-crucible gradient condensation crystal growth device according to claim 1, 2, 3 or 4, characterized in that the number of the crucible supports (7) is 4-10.

8. A multi-crucible gradient condensation crystal growth apparatus as claimed in claim 1, 2, 3 or 4, wherein the number of temperature control thermocouples (6) is 3 to 6.

9. A method for growing a large-size lanthanum bromide single crystal by using the multi-crucible gradient condensation crystal growth device as claimed in claim 1, which is characterized by comprising the following steps:

firstly, putting cylindrical lanthanum bromide seed crystals with the axial direction of [001] crystal orientation into a bottom cylindrical barrel (8-3) of a quartz crucible (8);

secondly, filling with N₂In a circulating glove box, lanthanum bromide with the purity of more than 99.99 percent and cerium bromide with the purity of more than 99.99 percent are weighed, put into an agate mortar for grinding and mixing uniformly, then put into a quartz crucible (8) filled with seed crystals, and the upper end of the quartz crucible is sealed by a sealing film; wherein the amount of the cerium bromide substance accounts for 3-10% of the sum of the amounts of the lanthanum bromide and the cerium bromide substance;

thirdly, taking the quartz crucible (8) out of the glove box, connecting the quartz crucible to a vacuum pump, and vacuumizing the vacuum pump to 10 DEG^-3～10^-5Pa, then melting and sealing the upper port of the quartz crucible (8) by using oxyhydrogen flame;

fourthly, the packaged quartz crucible (8) is arranged on a crucible support (7) in the crystal growth device, and the height of the crucible support (7) is adjusted, so that the 1/2 position in the height direction of the seed crystal corresponds to the position corresponding to the radial temperature of 780-782 ℃ when the growth device reaches the target temperature; then, the crystal growth device is heated to a target temperature, namely the temperature of a high-temperature area is heated to 800-850 ℃, the temperature of a low-temperature area is heated to 680-740 ℃, and the temperature distribution of a gradient area is 5-15 ℃/cm; after the raw materials and the seed crystals of 1/2 are melted, preserving the heat for 24 hours; then, starting temperature gradient condensation to grow single crystals, namely integrally cooling the high-temperature area, the gradient area and the low-temperature area at a cooling rate of 0.13-0.5 ℃/h;

fifthly, after the temperature of the high-temperature area is reduced by 80-85 ℃, the temperature is integrally reduced at the speed of 2-3 ℃/h until the temperature of the high-temperature area reaches 700-705 ℃, the high-temperature area is subjected to constant-temperature thermal annealing at the temperature of 700-705 ℃ for 200-210 h, then the temperature is integrally reduced to the room temperature at the speed of 5-10 ℃/h, and the crystal is taken out.

10. The method for growing a large-sized lanthanum bromide single crystal using the multi-crucible gradient condensation crystal growth apparatus according to claim 9, wherein the amount of the cerium bromide substance in the second step is 5% of the sum of the amounts of the lanthanum bromide and cerium bromide substances.

Technical Field

The invention relates to a device and a method for growing large-size lanthanum bromide single crystals.

Background

The scintillation crystal can convert the kinetic energy of high-energy particles into light energy under the impact of the high-energy particles to produce light. The scintillation crystal is combined with a photomultiplier, can be used for detecting X rays, gamma rays, neutrons and other high-energy particles, and has important application in the aspects of space physics, nuclear medicine, high-energy physics, safety detection, nuclear anti-terrorism, nuclear power station environment monitoring, industrial flaw detection, nuclear prospecting and the like.

The Netherlands Delft university of science and technology discovered in Ce in 2001³⁺Lanthanum bromide (LaBr) obtained from doped halide crystals₃Ce) crystals exhibit excellent scintillation properties: high light output (not less than 40000Photons/MeV), fast attenuation time (not more than 40ns), high energy resolution (not more than 5% @662keV), uniform nonlinear response and the like, and is particularly suitable for detecting gamma rays in a low-intensity mixed field when lanthanum bromide crystals are at lower Ce³⁺The inorganic scintillation crystal has good scintillation performance under concentration, has higher density and better energy response linearity, and is the inorganic scintillation crystal with the best energy resolution discovered so far. The radiation detector made by taking the lanthanum bromide crystal as a medium has important application in the aspects of gamma ray detection, nuclear medicine imaging (PET, SPECT), space science research and the like.

The lanthanum bromide crystal is easy to generate problems of deliquescence, cracking, component segregation and the like, for example, the thermal expansion coefficient of lanthanum bromide along the a axis is 5-6 times of that along the c axis, so that the lanthanum bromide is easy to crack or break along a (100) dissociation surface in the crystal growth and subsequent mechanical cutting and polishing processes, and the growth of a complete large-size single crystal is difficult.

At present, the method for growing lanthanum bromide single crystal reported at home and abroad is mainly a Bridgman method (also called a Bridgman method), and the basic principle of the method is a growth method for directional crystallization by forming a certain temperature gradient through relative movement between a crucible and a solid-liquid growth interface and providing a driving force for a melt. The growth of lanthanum bromide crystals by the Bridgman method has several disadvantages as follows: 1) the action of the moving device can cause the micro vibration of the crucible, thereby generating defects and stress to influence the quality of the single crystal; 2) the single-layer thermal field of the traditional multi-crucible crystal growth furnace cannot realize uniform temperature field distribution environment, and is not beneficial to forming a nearly flat solid-liquid growth interface; 3) in the process of crystal growth, along with the descending of the crucible, the part of the crucible in the low-temperature area is increased, so that the crystallized single crystal ingot is positioned in an uneven temperature field, generates larger internal stress and is easy to crack.

Disclosure of Invention

The invention aims to solve the technical problems of poor single crystal quality and easy cracking of the existing lanthanum bromide single crystal growth method, and provides a multi-crucible gradient condensation crystal growth device and a method for growing large-size lanthanum bromide single crystals by using the same.

The multi-crucible gradient condensation crystal growth device comprises a cylindrical double-layer shell, a heat preservation cover, a lining ceramic tube, two groups of outer heating coils, two groups of inner heating coils, a plurality of temperature control thermocouples, a plurality of crucible holders and a plurality of quartz crucibles;

wherein the lining ceramic tube is arranged on the axis of the cylindrical double-layer shell; a plurality of crucible supports are uniformly distributed and fixed in an annular area between the double-layer shell and the lining ceramic tube;

the two groups of external heating coils are respectively arranged at the upper part and the lower part in the double-layer shell; the double-layer shell is provided with a heat-insulating layer;

the two groups of internal heating coils are respectively arranged at the upper part and the lower part in the internal ceramic lining pipe;

a plurality of temperature control thermocouples are arranged from top to bottom along the inner wall of the double-layer shell.

The crystal growth device divides a furnace chamber into a high-temperature area, a gradient area and a low-temperature area from top to bottom through an upper group of outer heating coils, a lower group of outer heating coils and an upper group of inner heating coils. The temperature of the high temperature zone is controlled to be 800-850 ℃, the temperature of the low temperature zone is controlled to be 680-740 ℃, and the temperature distribution of the gradient zone is 5-15 ℃/cm. The inner heating coil arranged on the lining ceramic tube 3 in the hearth is used for additionally arranging a compensation temperature field for the furnace chamber, the double-layer temperature field of the inner heating coil and the outer heating coil is adopted to obtain uniform and approximately flat annular transverse temperature field distribution, and the thermal field provides an approximately flat solid-liquid growth interface for 4-10 lanthanum bromide single crystal growths of 1-3 inches.

The method for growing the large-size lanthanum bromide single crystal by using the device comprises the following steps:

firstly, putting cylindrical lanthanum bromide seed crystals with the axial direction of [001] crystal orientation into a cylindrical barrel at the bottom of a quartz crucible;

secondly, filling with N₂In a circulating glove box, lanthanum bromide with the purity of more than 99.99 percent and cerium bromide with the purity of more than 99.99 percent are weighed, put in an agate mortar for grinding and mixing uniformly, then put in a quartz crucible filled with seed crystals, and the upper end of the quartz crucible is sealed by a sealing film; wherein the amount of the cerium bromide accounts for 3% -10% of the sum of the amounts of the lanthanum bromide and the cerium bromide;

thirdly, taking the quartz crucible out of the glove box, connecting the quartz crucible to a vacuum pump, and vacuumizing to 10 DEG^-3～10^-5Pa, then melting and sealing the upper port of the quartz crucible by using oxyhydrogen flame;

fourthly, the packaged quartz crucible is loaded on a crucible support in the crystal growth device, and the height of the crucible support is adjusted, so that the 1/2 position in the height direction of the seed crystal corresponds to the position corresponding to the radial temperature of 780-782 ℃ when the growth device reaches the target temperature; then, the crystal growth device is heated to a target temperature, namely the temperature of a high-temperature area is heated to 800-850 ℃, the temperature of a low-temperature area is heated to 680-740 ℃, and the temperature distribution of a gradient area is 5-15 ℃/cm; after the raw materials and the seed crystals of 1/2 are melted, preserving the heat for 24 hours; then, starting temperature gradient condensation to grow single crystals, namely integrally cooling the high-temperature area, the gradient area and the low-temperature area at a cooling rate of 0.13-0.5 ℃/h;

fifthly, after the temperature of the high-temperature area is reduced by 80-85 ℃, the temperature is integrally reduced at the speed of 2-3 ℃/h until the temperature of the high-temperature area reaches 700-705 ℃, the high-temperature area is subjected to constant-temperature thermal annealing at the temperature of 700-705 ℃ for 200-210 h, then the temperature is integrally reduced to the room temperature at the speed of 5-10 ℃/h, and the crystal is taken out.

The multi-crucible gradient condensation crystal growth device is utilized to grow lanthanum bromide single crystals, the furnace body adopts double heating layers, a compensation thermal field is added in the center of the furnace body, so that a plurality of crucibles are simultaneously positioned in an even and nearly flat transverse thermal field, and the small temperature gradient of the transverse thermal field ensures a nearly flat solid-liquid growth interface, thereby being beneficial to reducing the internal stress on a (100) dissociation surface and effectively relieving the cracking problem of large-size crystals during growth;

and a fully-static in-situ gradient condensation cooling growth and annealing method is adopted, so that the vibration interference of growth is reduced, the crystallized single crystal ingot is always in a high-temperature area with uniform temperature field distribution, the temperature field distribution of the high-temperature area is kept uniform, the whole temperature field is reduced at a constant speed for crystallization, and the large-size lanthanum bromide single crystal without cracking is obtained.

The growth device can be placed into a plurality of crucibles at one time, and the production cost of the crystal is greatly reduced. Can be used in the field of crystal growth.

Drawings

FIG. 1 is a schematic structural diagram of a multi-crucible gradient condensation crystal growth apparatus according to the present invention;

FIG. 2 is a top view of the multi-crucible gradient condensing crystal growing apparatus of the present invention;

FIG. 3 is a schematic structural view of the quartz crucible 8;

FIG. 4 is a temperature field distribution diagram of the multi-crucible gradient condensed crystal growth apparatus in example 1;

in the figure: 1 is a cylindrical double-layer shell, 2 is a heat-insulating cover, 3 is a lining ceramic tube, 4 is an external heating coil, 5 is an internal heating coil, 6 is a temperature-control thermocouple, 7 is a crucible support, and 8 is a quartz crucible; 9 is a liquid phase, 10 is a solid-liquid interface, and 11 is a crystal;

8-1 in the quartz crucible 8 is an upper cylindrical barrel, 8-2 is a lower inverted cone, and 8-3 is a bottom cylindrical barrel;

FIG. 5 is a photograph of a lanthanum bromide single crystal obtained in example 1;

FIG. 6 is a photograph of a lanthanum bromide single crystal obtained in example 2;

FIG. 7 is a photograph of a lanthanum bromide single crystal obtained in example 1.

Detailed Description