Refractory oxide monocrystals growing method

FIELD: processes for high-temperature crystallization from melts, possibly growing of super-large mono-crystals of refractory oxides.

SUBSTANCE: method for growing refractory oxide mono-crystals by directional horizontal crystallization comprises steps of creating in vacuum chamber by means of heating devices temperature field; melting in created field initial crystallized material placed in container being open upwards reservoir in the form narrowed at one side parallelepiped shaped boat; forming crystal from oriented mono-crystalline seed arranged in narrowed part of container and made of material corresponding to grown crystal due to moving container with melt charge in gradient temperature field. At growing process, crystallization speed is controlled in axial, radial and vertical directions by regulating relations of heat flux values of heating devices irradiation, namely heat flux of radiant energy incident to melt heel surface and conductive heat flux passing through lateral walls and bottom of container. Desired temperature gradients of temperature field along interface of melt material phases and grown crystal - crystallization front are provided due to setting difference between temperature of phase interface and equilibrium melting temperature equal to 15 - 25°C. Inclination angle of crystallization front relative to plane of container bottom at forming vertical temperature gradient is set in range 55 -90°. Width of seed is selected in range 3 - 5 mm; enlargement angle of mono-crystal is set in range 100 - 140°; values of enlargement arms of mono-crystal are selected up to 300 mm. Invention provides increased useful surface area (rectangular portion) of grown crystals by 30 - 45% and flat crystallization front in zones of lateral corrugations of container.

EFFECT: minimized possibility of occurring stresses, complete elimination of block formation in grown crystal.

5 cl, 1 tbl, 2 dwg

 

The invention relates to a technology for high-temperature crystallization of the dielectric material from the melt and can be used to obtain large single crystals.

There is a method of growing single crystals of sapphire using the kyropoulos method, comprising the melt by means of a heating device placed in the original container kristallicheskogo material and the formation of the single crystal from the seed crystal directly in the melt by the smooth decrease of the temperature (see, for example, Husbandcare. "High-temperature crystallization from the melt", "Fizmatlit", M, 2004, s).

The known method provides the possibility of obtaining large single crystals, however, it is characterized by impermanence speed growing and in order to avoid the formation in the grown single crystal of various inclusions, when using this method of growing a single crystal is required notoriously low (for sapphire of about 2 mm/h) growth rate (see ibid.).

The closest analogue prototype is a method of growing single-crystal plates of complex refractory oxides horizontal directional solidification, comprising melting in a crucible having the form of a boat, the original mixture, seeding and subsequent cultivation of the front tree Olney part of the single crystal plate by moving the crucible with the molten mixture through a thermal gradient field with a speed of 8 to 20 mm/h, and the cultivation of the rectangular part is carried out by movement of the crucible through thermal field gradient at the rate of 1-2 mm/h (see, for example, patent of Ukraine No. 21982 priority from 26.04.95, IPC: SW 11/00, 29/20).

This method solves the problem of growing single-crystal plates of complex refractory oxides, without cracks and internal stresses that lead to cracking of these plates when they are cut, however, using the area of the front triangular part of the grown crystal (square boules) is comparable with the area of the rectangular part of the crystal, and, in addition, required when growing a rectangular part of the crystal moving speed of the crucible through thermal field gradient, as already mentioned, is obviously low, which leads to the excessive length of the growing process.

The objective of the invention is to develop a method of growing single crystal, minimizing razresevanja nasal area single crystals, for example of refractory oxide single crystals, in order to grow a single crystal from the optimal crystallization rate and simultaneously guaranteeing a flat crystallization front in the region of the side folds of the container without changing temperature regimes.

The essence of the invention is that the method of growing single crystals of refractory oxides horizontal directional solidification, including creating in a vacuum chamber by means of a heating device temperature field, melting in the source kristallicheskogo material placed in the container, made in the form of an open top vessel having a shape tapering from one side of the parallelepiped - shaped boats, and the formation of a crystal from installed in the intended part of the container oriented monocrystalline seed crystal grown from the corresponding crystal material by moving the container with the molten mixture in a gradient temperature field, when growing crystal control the crystallization rate in the axial, radial and vertical directions by controlling the ratio of heat flux values of the radiation heating devices, namely, falling on the surface mirrors melt heat flux of radiant energy, and conductive heat flow passing through the side walls and the bottom of the container, and in these areas form the required temperature gradients in the fields on the phase boundary of the molten material and the formed crystal solidification front by setting the difference between the temperature at the surface of separation of the phases and the equilibrium melting temperature equal to 15-25°With the angle of the crystallization front with what Locosto the bottom of the container while forming a vertical gradient set equal 55-90° width of the seed is chosen equal to 3-5 mm, the angle of razresevanja single crystal set in the range of 100-140°and the amount of shoulder razresevanja choose to 300 mm

The speed of movement of the container with crystallisatum substance depending on the geometric dimensions of the grown crystal set in the range of 3-8 mm/h

In addition, the heat fluxes of radiation heating units, namely, the heat flux incident on the mirror surface of the melt, and conductive heat flow passing through the side walls and the bottom of the container, specify separately due to separate control of the heating device, when the corresponding execution of their elements, one of which is a located above the melt surface is a flat heater, and the other is made in the form of an inverted U-shaped form and is placed under the container and with its sides.

This heating device is made of carbon material, and the number and configuration of these devices is selected taking into account the possibility of formation of symmetrical thermal field in which the growth front of the crystal coincides with isothermal surface, and the heat transfer in the radiative-conductive heat transfer ensures the continuity of the passage of heat flow through unit area of the surface the displacement of an interface of the molten material and the growing crystal in accordance with the expression:

λs∂T1/∂n=λ1∂T2/∂n VρsΔH,

where λsand λ1- thermal conductivity, respectively, of the crystal and the melt; ∂T1/∂n and ∂T2/∂n - temperature gradients, respectively, in the crystal and the melt; V is the velocity of crystal growth; ρsthe density of the crystal; ΔH - heat of phase transformation.

In addition, the growing crystal is carried out in an inert gas, for example argon, and this inert gas is introduced into the atmosphere chamber at a pressure of (1-5)10-4mm Hg and heating the mixture up to 1200-1500°C, crystallization was carried out in a flow of inert gas with a speed of 10-50 l/h

The technical result of the proposed invention is the provision of opportunity to increase the usable square (rectangular portion) of the grown crystals by 30-45%and get flat crystallization front in the areas of the lateral folds of the container, thereby eliminating the possibility of occurrence in the grown crystal, mechanical stress, microcracks, blocks and counter crystallization, and by creating appropriate temperature regimes in the zone annealing practical exceptions occur in aligawesa crystal thermoelastic deformations.

Figure 1 presents a diagram of the device is La growing refractory single crystals by the method of horizontal directional crystallization (STC), figure 2 shows a General view of the container for kristallicheskogo material.

The proposed method of growing single crystals by the method of detection can be implemented using a crystallization device comprising a vacuum chamber 1 (Fig 1)designed to ensure the environmental conditions melting kristallicheskogo material and subsequent growing crystals and comes in a sealed housing (see, for example, Husbandcare "high-Temperature crystallization from the melt", "Fizmatlit", M, 2004, s, RES), in which is mounted a heating unit 2, designed to create a thermal field by means of a heating device 3 (this example uses one heating device) and system (not shown) heat shields (not shown)made of pregrevica brands UTM and UKM (classification research Institute of graphite) and creating a corridor (not shown)surrounding the container 4, made (2) in the form of an open top vessel having a shape tapering from one side of the parallelepiped - shaped boats, for example from a sheet (thickness of 0.3-0.7 mm) of molybdenum, and is designed to accommodate the original kristallicheskogo material (not shown) (charge) and the melt 5 in the mixture and for forming the container of crystal 6, and the angle razresevanja α chosen equal 100-40° and the amount of shoulder razresevanja (A) of this angle is chosen equal to 300 mm

In addition, crystallization device has an actuator 7 to move the container 4 through thermal unit 2, and a vacuum pump 8, block 9 of the inert gas system 10 visual control and block 11 control output coupled with the control input of the transformer 12, the outputs connected to corresponding inputs is made of two parts (figure 2) of the heating device 3, one of which is a located above the melt surface is a flat heating element 13, and the other part in the form of the heating element 14 of the inverted U-shaped form is placed under the container 4 and with its sides.

This heating device is made of carbon material, and the number of these devices and their configuration is chosen taking into account the possibility of formation of symmetrical thermal field in which the growth front of the crystal coincides with isothermal surface, and the heat transfer in the radiative-conductive heat transfer provides the boundary conditions of the process of crystallization of continuity of heat flow through unit area of a surface section of the crystal-melt") meet the Stefan condition:

λs∂T1/∂n=λ1∂T2/∂ n-VρsΔH,

where λsand λ1- thermal conductivity, respectively, of the crystal and the melt; ∂T1/∂n and ∂T2/∂n - temperature gradients, respectively, in the crystal and the melt;

V is the velocity of crystal growth (the velocity of the boundary crystal-melt"); ρsthe density of the crystal; ΔH - heat of the phase change (latent heat of crystallization released on the boundary crystal-melt") (see, for example, Husbandcare. "High-temperature crystallization from the melt", "Fizmatlit", M, 2004, p.98).

To create an effective thermal field in the whole volume of thermal node 2 from a special carbon-graphite materials brands UTM and UKM, with low values (respectively 0.3 and 0.6 W/m2glad at 2000° (C) thermal conductivity, made lining (not shown), providing education typical thermal zones, namely zone of the melt and the temperature range of the plastic deformation of the crystal (for example, sapphire 1700-1800° (C)with decreasing temperature below 1700°passing in the area of thermoelastic deformations, which allows the entire process to maintain optimum such affecting the quality of grown crystals characteristics of the temperature field, as symmetry, Lin is inost and inertia. Thus the symmetry of the temperature field provides a constant shape of the crystallization front in the axial and perpendicular to the crystal directions, linearity provides morphological stability of front-line growth, and we have increased more than two times) the inertia delivers greater isothermal stability of the temperature field from possible fluctuations in the amount of thermal unit 2 caused by different reasons, such as instability in the power system or natural temperature fluctuations due to the convective flow in the melt, etc.

In the example device, the actuator 7 to move made in the form of the corresponding traction mechanism (see, for example, Husbandcare. "High-temperature crystallization from the melt", "Fizmatlit", M, 2004, s, RES)operating through a reduction gear 15, providing the desired speed of travel of the container 4 through thermal unit 2, the vacuum pump 8 is intended to create in a vacuum chamber 1 of the required underpressure in the form of the corresponding device (see, for example, Husbandcare. "High-temperature crystallization from the melt", "Fizmatlit", M, 2004, s, RES), the system 10 visual inspection made in the form of sapphire Windows, designed for online monitoring of process crystal is ment, the control block 11 is designed to control the operating modes of the transformer 12 and stabilization asked modes current, voltage and power and is designed as a stabilizer (see, for example, Utica and Klenk. "Semiconductor circuit", Moscow, Mir, 1982, SS-267).

Unit 9 inert gas is made in a container, for example a cylinder with an inert gas such as argon, which is connected with the set in the camera body 1 by fitting (not shown), and valve (not shown) of the cylinder is connected with the pressure gauge 16, designed to control the pressure of the inert gas fed into the chamber 1.

The transformer 12 is in the form of a corresponding device brand TSS-160/0,UM, the gear 15 is in the form of a block continuously variable transmission connected to the stepper motor brand of DSHI-200-3-1 (see, for example. Product catalogue. "Reducers and motor-reducers", Scientific-technological center "Reducer", St.-Petersburg, 2002, p.72).

When working with the device in the intended part of the container 4 pre-set oriented monocrystalline seed 17 (2), made in the form, for example, the plate thickness (width) δ=3-5 mm, and length l=30-50 mm from the corresponding grown crystal 6 material, such as sapphire, and fill the container 4 crystallisatum substance (not shown) in the form, in the example, powder or crystalline battle, after which the container is placed in a thermal unit 2 of the vacuum chamber 1, where using a vacuum pump 8 gain depression order (1-5) 10-4mm Hg and using the control block 11 through the transformer 12 serves current to the heating device 3, the heating elements which generate a corresponding temperature field. After reaching the desired temperature and heating the mixture up to 1200-1500°With the help of block 9 of the inert gas in the atmosphere chamber is injected inert gas, for example argon, and while observing through the window system 10 visual inspection continue heating until the melt 5 (2) in the container 4 and establish fixed boundaries (not shown) of an interface.

After seeding by moving the container 4 with the molten mixture in the temperature field, thermal unit 2, the flow of inert gas with a speed of 10-50 l/h produce crystallization (cultivation) of the corresponding crystal. While using the system 10 visual inspection to determine compliance of the implemented mode of cultivation required and adjust with unit 11 controls the amount of heat fluxes of radiation elements of the heater 3, and it is incident on the mirror surface - melt heat flux of radiant energy, and conductive heat flow were asego through the side walls and the bottom of the container, by changing the value supplied through the transformer 12 to the heating device 3 DC, control the rate of crystallization in the axial, radial and vertical directions, and in these areas, by controlling the superheat of the melt ΔT set the required temperature gradients in the fields on the phase boundary of the molten material and the formed crystal (solidification front), as well as the angle from the crystal solidification front between the melt 5 and the crystal 6 with the plane of the bottom (not shown) of the container.

When required for normal (negrinho and neodenticula) crystal growth temperature gradients in the fields on the phase boundary of the molten material and kristallicheskogo substances at the crystallization front is chosen equal to 5,0-10°S/cm and are provided by separate power control top (flat) and lower (N-shaped) heaters (respectively 13 and 14), in which the optimal difference (ΔT) between the temperature on the surface of the section of the crystal-melt" and the equilibrium melting temperature equal to, as mentioned above, 15-25°create so that the speed of crystal growth during the whole process would be constant and matches the speed of the transport container 4 that is selected in the range of 3-8 mm/CV depending on the geometric dimensions of the grown crystal. The angle of the crystallization front with the plane of the bottom of the container from the side of the crystal is equal 55-90°and the vertical gradient set by establishing the ratio of the electric capacity of the upper and lower elements (respectively 13 and 14) of the heating device 3, in which the electric power of the upper heater element 13 3 exceeds the relevant characteristics of the lower member 14 of the heater 3 7 -20%.

Consequently set separately and heat fluxes of radiation elements 13 and 14 of the heating device 3, namely, the heat flux incident on a surface (mirror) of the melt 5, and conductive heat flow passing through the side walls and the bottom of the container 4, and the evaluation of thermal regimes of crystallization is carried out by measuring the temperature inside the chamber 1 using a tungsten-rhenium thermocouples (not shown) (see, for example, Husbandcare. "High-temperature crystallization from the melt", "Fizmatlit", M, 2004, p.114).

Here it should be noted that, if the classic case of supply and heat removal is determined only by molecular thermal conductivity of the material, and the temperature gradient in the solid phase is always greater than in the liquid, and eye-catching on the front of crystallization heat is dissipated via solid phase, the crystallization of the dielectric materials,in particular synthetic sapphire, related to highly transparent materials, the temperature gradient in the solid phase is always less than in the liquid, since most of the heat flow away from the solidification front due to radiation and molecular conductivity to transfer heat flow recedes to the background.

The phase boundary during crystallization of sapphire can be considered as an ideal contact (in the sense of heat transfer) highly transparent crystal with almost opaque melt (at a temperature of 2100°With the absorption of radiant energy growing crystalline phase is equal to 0.5 cm-1and melt - 25 cm-1and therefore in the region of the phase transition should be observed jump in the internal flow portable due to radiation of heat. While the magnitude of the temperature gradients are determined not so much by the values of the molecular conductivity of the phases as the difference in absorption coefficients and refractive indices.

Calculations showed that with the decrease of the coefficient of molecular conductivity of the liquid phase of sapphire 5 times the temperature gradients in the melt and the crystal in the region of the phase transition is practically unchanged, while changing only 2 times the absorption coefficient of the liquid phase leads to a sharp change in the attitude of the temperature hail the clients in the liquid and solid phases, moreover, the temperature gradient in the crystal 4-5 times more than in the melt, which confirms the importance of the impact on the behavior of the temperature field on the phase boundary of the optical properties of boundary surfaces of the crystal-melt" and especially the border from the crystalline phase. The above was taken into account when developing technological modes of cultivation of sapphire and other highly transparent dielectrics.

It should also be noted that according to the criterion of Neuhaus (see, for example, Cthwiut. "Methods of growing crystals", Tr., Ed. "Nedra, Leningrad, 1968, p.148) in comparative proximity to the conditions of equilibrium for the linear velocity (VLin) increase in fair dependency:

VLin=dm/dt˜(T0-TX),

where TX- the surface temperature of the section "crystal-melt"; T0the melting temperature; m is the number zakristallizuetsya substances; t - time.

Practically this means that the surface temperature of the crystallization front of the TXmust be below the equilibrium melting temperature T0at some value ΔT=(T0-TX), is proportional to the speed of crystallization.

It is known (see, for example, Husbandcare. "High-temperature crystallization from the melt", "Fizmatlit", M., 2004, p.114)that feature HDSM is what I nonlinearity of the temperature distribution along the thickness of the growing crystal, since the heat flow in the upper part of the crystal differ significantly from the heat flows in the lower part. Therefore, for the formation and management of growth form, you must also create the optimal vertical temperature gradient for crystals of sapphire, for example, such that the slope of the crystallization front was 55-90° with the bottom of the container 4 from the side of the crystal, because the increase of this angle and its reduction (concave front growth) leads to the capture of a growing crystal of various inclusions (impurities, bubbles of the gas phase, resulting thermodissociation substance mixture in the melt) and, ultimately, to the deterioration of the optical quality of the grown crystal. The possibility of compliance with conditions create the desired vertical temperature gradient is also provided through separate control of the heating of the upper and lower parts of the heating device 3. So for sapphire crystals grown in this way, the optimal vertical gradient is obtained when excess electric power of the upper element on the electrical power of the lower element by 7-20%.

Application in the design of thermal unit carbon-graphite materials eliminates the nonlinearity of the temperature field in the temperature region below 1700#x000B0; With that, without resorting to additional annealing of the crystal after the process of its cultivation, to minimize the magnitude and even avoid formation in the growing crystal thermoelastic stresses. This indicates that the resulting temperature field at T<1700°at any point of the crystal in the direction of growth and perpendicular to it, tends to zero the value of the second derivative of the temperature d2T/dn2[as it is known (see, for example, Cthwiut. "Methods of growing crystals", Tr., Ed. "Nedra, Leningrad, 1968, s), responsible for the emergence of thermoelastic deformations in the crystal].

The possibility of obtaining single crystals of the proposed method is confirmed in table examples.

The size of the crystalConditions
The name crystalcultivationThe atmosphere crystallizationThe crystal defects
Angle razresevanja, °The length from the mouth, *) mmWidth (below the shoulders), *) mmHeight, mmThe crystallization temperature, °**) Axial gradient °C/cmThe unwinding speed, mm/h
Al2O3100>380toto21005Inert-Anionic
(sapphire)14052050--5the restorerand
23008nyecation
10 mm Hgvacancies
up to 1014-15
cm-3
Y3Al5O12100>380tobefore 20007Inert and recovery, 10 mm HgAnyoneee cationically to 1014-15cm-3
(yttrium-14052050--3
aluminum220010
pomegranate)
*) The final size of the crystals are determined by the particular design of thermal node.
**) In terms of control of each heating element on an individual algorithm with 10%excess power to the upper heating element.

1. A method of growing single crystals of refractory oxides horizontal directional solidification, including the creation of a vacuum chamber by means of a heating device temperature field, melting in the source kristallicheskogo material placed in the container, made in the form of an open top vessel having a shape tapering from one article the Rhone parallelepiped - the shape of the boat, and the formation of a crystal from installed in the intended part of the container oriented monocrystalline seed crystal grown from the corresponding crystal material by moving the container with the molten mixture in a temperature gradient field, wherein when growing the crystal control the crystallization rate in the axial, radial and vertical directions by controlling the ratio of heat flux values of the radiation heating devices, namely, falling on the mirror surface of the melt heat flux of radiant energy and conductive heat flow passing through the side walls and the bottom of the container, and in these areas form the required temperature gradients in the fields on the phase boundary of the molten material, and the growing crystal solidification front, by setting the difference between the temperature at the surface of separation of the phases and the equilibrium melting temperature equal to 15-25°With the angle of the crystallization front with the plane of the bottom of the container during formation of the vertical temperature gradient is set equal 55-90°, the width of the seed is chosen equal to 3-5 mm, the angle of razresevanja single crystal set in the range of 100-140°and the amount of shoulder razresevanja choose to 300 mm

2. The method according to claim 1, Otley is audica fact, that speed of movement of the container with crystallisatum substance depending on the geometric dimensions of the grown crystal set in the range of 3-8 mm/h

3. The method according to claim 1, characterized in that the heat fluxes radiation heating units, namely, the heat flux incident on the mirror surface of the melt, and conductive heat flow passing through the side walls and the bottom of the container, specify separately due to separate control of the heating device, when the corresponding execution of their elements, one of which is a located above the melt surface is a flat heater, and the other is made in the form of an inverted U-shaped form and is placed under the container and with its sides.

4. The method according to any of claim 1 or 3, characterized in that a heating device made of a carbon material, and the number and configuration of these devices is selected taking into account the possibility of formation of symmetrical thermal field in which the growth front of the crystal coincides with isothermal surface, and the heat transfer in the radiative-conductive heat transfer ensures the continuity of the passage of heat flow through unit area of the interface of the molten material and the growing crystal in accordance with expression is the group

λs∂T1/∂n=λ1∂T2/∂n VρsΔH,

where λsand λ1- thermal conductivity, respectively, of the crystal and the melt; ∂T1/∂n and ∂T2/∂n - temperature gradients, respectively, in the crystal and the melt; V is the velocity of crystal growth; ρsthe density of the crystal; ΔH - heat of phase transformation.

5. The method according to claim 1, characterized in that the growing crystal is carried out in an inert gas, for example argon, and this inert gas is introduced into the atmosphere chamber at a pressure of (1-5)·10-4mm Hg and heating the mixture up to 1200-1500°C, crystallization was carried out in a flow of inert gas with a speed of 10-50 l/h



 

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The invention relates to the cultivation of artificial crystals (ZnO, SiO2Caso3, Al2ABOUT3)

FIELD: inorganic chemistry and crystallography.

SUBSTANCE: the invention is pertaining to the field of inorganic chemistry and crystallography, in particular, to a method and a device for growing of large-size refractory monocrystals. The method provides for seed melting in a fixed container by heating of a feed stock and its weld penetration with subsequent crystallization and cooling-down. The seed melting of a monocrystal is conducted by a contact of a seeding agent with a melt and connection with it due to a capillary tension with a diameter in the place of the contact about 20-50 microns, At that the seeding agent is placed outside of the container at a distant of 3-5 mm away from the container spout, and the crystallization is conducted at variation of a gradient of temperatures within the limits of T = 15-20°ะก along the whole length of the container. The device for growing of refractory monocrystals contains a chamber of growing composed of two parts: the upper part - with a thermal unit containing a heater made in the form of a cylinder turned upside down and a system of the multilayered shields iterating the form of the heater, and the fittings for fixation of the seeding agent; and the lower part, on which a container with the feed stock mounted rigidly fixed on a support composed out of the multilayered shields. The support is made with a capability of lifting and a tight coupling with the upper part of the chamber after the container enters a thermal assembly. The invention allows to grow monocrystals of the special large dimensions and weights and at that to improve significantly their optical characteristics.

EFFECT: the invention allows to grow monocrystals of especially big dimensions and weights and to improve significantly their optical characteristics.

2 cl, 3 dwg

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