Composite crucible for growing single crystals

Abstract

Disclosed herein is a composite crucible comprising a wall; and a base; where the base contacts the wall to create an internal volume that is used to produce a melt for a crystalline boule; where the wall comprises a binder and an electrically conducting filler; and wherein the wall has a greater electrical conductivity at an inner surface when compared with the electrical conductivity at the outer surface.

Description

COMPOSITE CRUCIBLE FOR GROWING SINGLE CRYSTALSBACKGROUND

[0001] This disclosure is related to a composite crucible for growing single crystals. In particular, this disclosure is related to a composite crucible for growing single crystals that can be used as scintillators.

[0002] Scintillation crystals such as rare earth-activated rare earth oxyorthosilicates with or without co-dopants, such as, for example, lutetium based oxyorthosilicates (e g., LSO, LYSO, LGSO, activated by cerium and co-doped with cerium and divalent ions such as calcium and / or magnesium) and garnets such as cerium activated GAGG co-doped with cerium and divalent ions such as calcium and / or magnesium, are generally grown from a melt located in a crucible. These crucibles with the melt contained therein are heated by resistance or RF induction in a furnace. The selection of the crucible material composition is dependent on its compatibility with the melt composition, the temperature range required for the melt and its growth atmosphere to limit the evaporation and oxidation of the crucible material.

[0003] During the manufacturing of the single crystal the crucible may undergo oxidation (depending on the growth atmosphere) and evaporation resulting in material losses from the crucible (e.g., example evaporative loss of iridium in an oxygen containing growth atmosphere). Small amount of oxygen presence in the growth atmosphere during the growth process is usually a requirement to prevent the melt from undergoing decomposition. Oxygen presence as a constituent of raw materials used in the growth process contribute to corrosive effect and losses of metals.

[0004] The evaporative metal losses of iridium crucibles are expensive (because of the cost of these metals), thus making the process of manufacturing the crystals an expensive one. In addition, the crucibles periodically have to be replaced and refabricated due to deformation. Deformation of the crucibles is a result of differences in the coefficients of thermal expansion of the oxide crystal material and that of the iridium metal, along with softening and creep of the alloy at elevated temperatures accompanied by grain boundary growth. All of these factors collectively limit the lifetime of the crucible.

[0005] It is therefore desirable to use crucibles that are initially less expensive and that do not undergo such large material losses and / or deformation during a crystal growth manufacturing process. This will reduce the overall costs of manufacturing single crystals.SUMMARY

[0006] Disclosed herein is a composite crucible comprising a wall; and a base; where the base contacts the wall to create an internal volume that is used to produce a melt for a crystalline boule; where the wall comprises a binder and an electrically conducting filler; and wherein the wall has a greater electrical conductivity at an inner surface when compared with the electrical conductivity at the outer surface.

[0007] Disclosed herein too is a method of manufacturing a composite crucible, the method comprising blending a binder with a carbonaceous material to create an electrically conductive mixture; hot pressurizing the electrically conductive mixture in a mold in a first hot pressing step; forming a green body that has a shape of the composite crucible; sintering the green body at a high temperature greater than 1500°C; densifying the green body to a value of more than 95% of the theoretical density; and conducting a second hot pressing step to cause the densified green body to reach approximately 100% of the theoretically achievable density.

[0008] Disclosed herein is a furnace for manufacturing a crystalline boule, the furnace comprising a furnace that includes a furnace wall; a composite crucible disposed on a first bed of grog within the furnace; where the first bed of grog has a porosity of 1 to 80 volume percent, based on a total volume of the first grog; and where the grog comprises free flowing particles of zirconia, alumina or a combination thereof; an induction coil disposed inside the furnace wall and outside the crucible; and a refractory lining being disposed in an annulus between the furnace wall and the crucible; where the crucible comprises a wall; and a base; where the base contacts the wall to create an internal volume that is used to produce a melt for a crystalline boule; where the wall comprises a binder and an electrically conducting filler; and wherein the wall has a greater electrical conductivity at an inner surface when compared with the electrical conductivity at the outer surface.BRIEF DESCRIPTION OF THE FIGURES

[0009] FIG. 1 depicts a composite crucible that contain a thin inner layer of a noble metal or any other type of material resistant to high temperature, while the remainder of the crucible is manufactured from a less expensive material that has a good susceptibility to the RF field;

[0010] FIG. 2 depicts a section ABCD from the FIG. 1 .

[0011] FIG. 3 depicts a device that contain the furnace in which lies the composite crucible that contains the crystalline boule.DETAILED DESCRIPTION

[0012] Disclosed herein is a composite crucible that may be used for manufacturing single crystals. The composite crucible is used to melt raw materials disposed in it that are then drawn from the crucible to produce a crystalline boule. A crystal boule is a single-crystal ingot produced by using a seed crystal to create a larger crystal, or ingot. This seed crystal is dipped into the molten raw material and slowly extracted. The melt grows on the seed crystal in a crystalline fashion. As the seed is extracted, the melt solidifies and eventually a large, cylindrical crystal boule is produced.

[0013] The composite crucible comprises a thin inner coating of a metal or a high temperature metal oxide disposed on an inner surface of an electrically conducting low- cost ceramic or metal composite vessel. This thin coating is a protective layer and protects the ceramic or metal composite vessel from the oxidative effect of the growth atmosphere as well as the effect of the melt itself. The composite crucible comprises an inner surface that is electrically conducting and / or has a good susceptibility to the RF field. The outer surface of the composite crucible comprises a material that is stable at the temperature of the melt contained in the crucible.

[0014] The inner coating of metal is preferably a noble metal or alloy of metals. The presence of the thin inner coating of noble metal or alternatively, the complete replacement of the noble metal by a high temperature metal oxide reduces the initial cost of the crucible. In addition, because the inner layer is of a lesser thickness compared with the walls of conventional crucibles, evaporative and oxidative losses of the noble metal are reduced (when compared with conventional crucibles). This leads to a furtherreduction in the manufacturing costs of single crystals. Use of any metal oxide as an external coating is even more preferable.

[0015] FIG. 1 depicts a composite crucible 100 (hereinafter crucible 100) that comprises a wall 200 and a base 300 that contact each other to form a space 400 that can hold as well as heat a molten material for manufacturing a crystalline boule.

[0016] The crystalline boules manufactured in the composite crucible 100 may be single crystal boules, with dopant activators to form a scintillating material, that may also contain co-dopants to enhance the scintillator performance characteristics and / or improve mechanical / physical properties. In an embodiment, the crystal boules may comprise high temperature materials that are not oxides crystals or oxide scintillators. Examples of such scintillators are, but are not limited to: lutetium oxy-orthosilicates (LSO’s), lutetium yttrium oxy-orthosilicates (LYSO’s), gadolinium oxy-orthosilicates (GSO’s), gadolinium aluminum gallium garnets (GAGG’s), gadolinium-gallium- aluminum garnet (GGAG’s), gadolinium-yttrium-gallium-aluminum garnet (GYGAG’s), gadolinium-lutetium-gallium-aluminum garnet (GLuGAG’ s), gadolinium-scandium- gallium garnet (GSGG’s), gadolinium -yttrium-aluminum garnet (GY AG’s), gadolinium- scandium-aluminum garnet (GSAG’s), gadolinium-gallium garnet (GGG’s) or gadolinium-yttrium-scandium-aluminum garnet (GYSAG’s). The crystal can be a single crystal or a polycrystalline solid.

[0017] With reference now to FIGS. 1 and 2, the wall 200 (and the base 300) of the crucible 100 comprise a non-metallic or metallic electrically conducting inner surface 202 and an outer surface 204 that has a different composition from the inner surface 202. The wall 200 and the base 300 are collectively referred to herein as the wall 200. Disposed on the inner surface 202 is a coating 102 that comprises a metal or a metal oxide. The metal used in coating 102 preferably comprises a thin layer of a noble metal deposited via electroforming, physical vapor deposition, sputtering, or any other methods. The metal used in the coating 102 has a coefficient of thermal expansion that is proximate to the coefficient of thermal expansion to that of the wall 200.

[0018] The composite crucible has an inner diameter dj, which may range from 5 centimeters (2 inches) to 45 centimeters ( 18 inches). The inner surface 202 of the wall has an optional inner rim 302 with a larger diameter d4 than the inner diameter d.r of the crucible. The optional rim 302 serves as a seat for a lid (not shown) that may be placedon the crucible during the manufacturing of the crystalline boule. If the rim 302 is not present, then the lid may be placed directly on surface 102. The lid has a hole (not shown) through which a pull rod with a seed crystal may be introduced to contact the melt present in the composite crucible.

[0019] The composite crucible also has an optional lip 304 at its upper surface that has a diameter ds that is greater than diameter d4. The lip 304 is a radial protrusion of the uppermost surface of the crucible that extends beyond the outer surface 204 of the crucible wall 200. It is located at the upper surface of the crucible and facilitates lifting and lowering the crucible into a furnace (now shown).

[0020] FIG. 2 depicts an enlarged section ABCD from the FIG. 1. With reference now again to the FIGs. 1 and 2, the wall 200 has a carbonaceous-rich region 104 (closer to the inner surface 202) and a carbonaceous-poor region 106 (closer to the outer surface 204). The carbonaceous-rich region contains a greater amount of the carbonaceous (electrically conducting) material relative to the amount of binder at the inner surface 202, while at the outer surface 204 there is a greater amount of binder relative to the amount of carbonaceous material.

[0021] As a result of the inner surface 202 being rich in the carbonaceous material, the inner surface is electrically conducting while the outer surface 204 may be electrically conducting (if the binder is a metal) or may be electrically insulating (if the binder is an electrically insulating ceramic).

[0022] Examples of noble metals that may be used in the metal coating 102 include gold, silver, platinum, rhenium, palladium, iridium, ruthenium, rhodium, osmium, or a combination thereof. A preferred noble metal for the metal coating 102 is iridium or an alloy of iridium and rhenium. Any combination of these metals may be used to provide better adhesion between the metal coating 102 and the wall 200.

[0023] In lieu of metals, a variety of high temperature oxides or a combinations of high temperature oxides may be used as the inner coating. Examples of high temperature oxides that may be used in the coating 102 include silicon dioxide, aluminum oxide, titanium dioxide, zirconium dioxide, indium tin oxide, antimony tin oxide, or the like, or a combination thereof. Rare earth metal oxides (e g., cerium oxide) having melting points greater than 2400°C may also be used in the coating 102. The high temperatureoxides need not be electrically conducting. The carbonaceous materials provide the electrical conductivity for RF coupling.

[0024] The coating 102 may have a thickness of sub -micrometers to a few millimeters. In an embodiment, the coating 102 may have a thickness of 10 micrometers to 5 millimeters, preferably 20 micrometers to 3 millimeters, and more preferably 30 micrometers to 2 millimeters. The metal coating may penetrate into pores present on the inner surface 202 of the wall 200. The coating 102 may adhere to the wall 200 via chemical bonding or mechanical interlocking and has a coefficient of thermal expansion that is proximate to the coefficient of thermal expansion of the wall 200. This proximity of the two thermal expansion coefficients prevents delamination of the coating from the wall.

[0025] In an embodiment, the wall 200 has a non-metallic electrically conducting inner surface 202 that comprises a carbonaceous material mixed with a binder. In another embodiment, the wall 200 has a non-metallic electrically conducting inner surface 202 that comprises an indium tin oxide or antimony tin oxide mixed with the binder.

[0026] The binder used in the wall 200 may be a metal or a ceramic. It may be electrically conducting or electrically insulating. In an embodiment, the binder is preferably a ceramic. In another embodiment, the binder may be a low cost but high temperature metal alloy. Alloys of molybdenum and tungsten may be used as a binder. The binder is preferably a ceramic. Suitable ceramics include metal oxides, metal carbides, metal nitrides, metal borides, metal silicides, metal oxycarbides, metal oxynitrides, metal boronitrides, metal carbonitrides, metal borocarbides, or the like, or a combination thereof. Examples of ceramics that may be used as the binder or outer coating include silicon dioxide, aluminum oxide, titanium dioxide, zirconium dioxide, indium tin oxide, antimony tin oxide, cerium oxide, cadmium-oxide, titanium nitride, silicon nitride, aluminum nitride, titanium carbide, silicon carbide, titanium niobium carbide, stoichiometric silicon boride compounds (SiBn, where n = 14, 15, 40, and so on) (e.g., silicon triboride, SiBs, silicon tetraboride, SiB4, silicon hexaboride, SiBg, or the like), or the like, or a combination thereof. A preferred ceramic is a metal oxide. A preferred metal oxide is alumina, YSZ, or a combination thereof. Ceramics used as thermal barrier coatings in turbines may be used as binders.

[0027] The outer surface of the crucible 204 can also be protected by the same type of protective metal coating (as coating 102) as well as by other ceramic materials bonded to the vessel material by a high temperature cement.

[0028] The carbonaceous material used to form the wall 200 comprises graphene, graphite, graphite oxide, carbon black, carbon nanotubes, vapor grown carbon fibers (VGCF), conductive metal oxides, or a combination thereof.

[0029] Graphene is an allotrope of carbon consisting of a single layer of atoms arranged in a hexagonal lattice nanostructure. Graphene that is added to the crucible may be in the form of individual graphene sheets or in the form of a plurality of loosely connected graphene sheets.

[0030] Graphite particles may also be used in the crucible. Graphite is a natural manifestation of pure carbon with a hexagonal crystal structure that is arranged in several parallel levels, called graphene layers. In short, graphite particles comprise a plurality of graphene sheets that are arranged to be parallel to each other. This anisotropic structure gives the graphite special properties, such as electrical conductivity or a particular strength along the individual layers. It is extremely heat-resistant with a sublimation point of over 3,800°C, thermally highly conductive and chemically inert.

[0031] Graphite oxide (GO), sometimes called graphene oxide, graphitic oxide or graphitic acid, is a compound of carbon, oxygen, and hydrogen in variable ratios, obtained by treating graphite with strong oxidizers and acids for resolving of extra metals. Graphene oxide sheets exist in the form of strong paper-like materials, membranes, thin fdms, and composite materials and can be used in the electrically conducting slurry that is used to prepare the crucible.

[0032] Carbon black having a high surface area is preferred for use in the crucible. Carbon black (subtypes are acetylene black, channel black, furnace black, lamp black and thermal black) is a material produced by the incomplete combustion of coal. Carbon black is a form of paracrystalline carbon that has a high surface-area-to-volume ratio, albeit lower than that of activated carbon. Carbon black having a surface area of 50 to 1000 m2 / gm may be used in the slurry that is used to form the crucible.

[0033] Carbon nanotubes include single wall carbon nanotubes (SWNTs), double wall carbon nanotubes (DWNTs), multiwall carbon nanotubes (MWNTs), or a combination thereof and have diameters of 2 to 100 nanometers, preferably 10 to 50nanometers. They have lengths of 20 to 10,000 nanometers, preferably 200 to 5000 nanometers. Aspect ratios greater than 10, preferably greater than 50 and more preferably greater than 100 are desirable. These nanotubes could be incorporated in the ceramic structure enabling its electric conductivity and susceptivity to RF field.

[0034] A preferred carbonaceous material is graphite. The graphite may be artificial or synthetic graphite. Graphite flakes may be mixed with the binder to produce the walls and base of the crucible.

[0035] FIG. 2 depicts the wall 200 having a thickness t with a thin metal layer 102 having a thickness di disposed on the wall 200. As the distance dz from the inner surface 202 (of the region 104) is increased the amount of carbonaceous material decreases till it reaches a minimum amount at the outer surface 204 (of the region 106). The amount of carbonaceous material is present in a maximum amount at the inner surface 104 and is present in a minimum amount at the outer surface 106. The amount of binder is conversely present in a maximum amount at the outer surface 106 and is present in a minimum amount at the inner surface 104. In other words, the amount of carbonaceous material is inversely related to the amount of binder in the wall.

[0036] While both the inner surface 202 and the outer surface 204 of the wall 200 is electrically conducting, the electrical conductivity of the inner surface is greater than that of the outer surface 204. A gradient in electrical conductivity exists from the inner surface 202 to the outer surface 204. This increased electrical conductivity at the inner surface 202 is due to a larger amount of carbonaceous material (when ratioed by weight to the binder) at the inner surface 202. The reduced electrical conductivity at the outer surface 204 is due to a smaller amount of carbonaceous material (when ratioed by weight to the binder) as compared with the amount of carbonaceous material (when ratioed by weight to the binder) at the inner surface 202.

[0037] At the inner surface 202 (in the carbonaceous-rich region 104), the carbonaceous material may be present in an amount of 50 to 98 wt%, based on the total weight of the wall at its inner surface 202. The binder may be present in an amount of 2 to 50 wt%, based on the total weight of the wall at the inner surface 202.

[0038] At the outer surface 204 (in the carbonaceous-poor region 106), the carbonaceous material may be present in an amount of 2 to 50 wt%, based on the totalweight of the wall at its outer surface 204. The binder may be present in an amount of 50 to 98 wt%, based on the total weight of the wall at the outer surface 204.

[0039] In an embodiment, there may be a gradient in the weight ratio of the carbonaceous material to the binder from the inner surface to the outer surface. The presence of a gradient reduces thermal shock when the crucible is heated or cooled. The gradient may be a linear gradient, a curvilinear gradient, a step gradient, or the like.

[0040] In an embodiment, the wall 200 may be electrically conducting but may have a uniform electrical conductivity from the inner surface 202 to the outer surface 204. In other words, there is no gradient in electrical conductivity (or in the amount of the electrically conducting filler) from the inner surface 202 to the outer surface 204. In this embodiment, the amount of the electrically conducting filler is uniformly distributed through the thickness of the wall 200.

[0041] In yet another embodiment, the wall 200 may be electrically conducting but may have the highest electrical conductivity at the outer surface 204 with the lowest electrical conductivity at the inner surface 202. In other words, the concentration of the electrically conductive filler is greatest at the outer surface 204 and lowest at the inner surface 202.

[0042] In an embodiment, the wall 200 and base 300 are porous. The amount of porosity is 5 to 30 volume percent based on the total volume of the wall or the total volume of the base. The porosity is optional. Having porous walls permits the noble metal (from the coating 102) to penetrate the region 104 of the wall 200 (and to undergo mechanical interlocking with it) thereby minimizing thermal shock.

[0043] The coating 102 may be deposited via chemical vapor deposition, physical vapor deposition, sputtering, plasma enhanced chemical vapor deposition, or a combination thereof. When the coating 102 is reduced in thickness due to usage of the crucible, the noble metal may be replenished by CVD.

[0044] In an embodiment, the crucible 100 can be manufactured layer-by-layer. Each layer is manufactured by preparing a slurry containing the binder, the carbonaceous material and a suitable solvent. The slurry for the inner most layer (proximate to surface 202) will have the largest amount of carbonaceous material and the smallest amount of binder, while the layer closest to the surface 204 has the largest amount of binder and the smallest amount of carbonaceous material.

[0045] A plurality of slurries may therefore be manufactured, where each slurry has a different electrical conductivity. The respective slurries may be prepared by intimately mixing the solvent, the binder and the carbonaceous material in a mixer such as a Waring blender, Henschel mixer, roll mills, or the like to manufacture the slurry. The composite crucible may have hot / cold zones fabricated internally during manufacturing processes to control thermal gradients.

[0046] The slurry with the largest amount of carbonaceous material may then be deposited in a mold and dried till the solvent is evaporated to prepare a first green fractional crucible. The wall thickness of this first green fractional crucible (manufactured in the mold) is a fraction of the total wall thickness. A second layer of slurry may then be applied to the outer surface of the first green fractional crucible. The second layer of slurry has a lower electrical conductivity than the electrical conductivity of first green fractional crucible. The second layer of slurry is then dried to form a second green fractional crucible. In this way, several layers of slurry may be added to the original first green fractional crucible (and subjected to solvent removal) till a crucible with the desired thickness is achieved. It is to be noted that the crucible may be built from the innermost layer outwards or from the outermost layer inwards.

[0047] If the crucible is built from the innermost layer outwards, then each successive layer has a lower electrical conductivity if the layers are successively applied to the outer surface of the crucible. If the crucible is built from the outermost layer inwards, then each successive layer is applied to an inner surface of the crucible and each successive inner layer will have a higher electrical conductivity than the preceding layer. It is to be noted that there does not need to be a gradient in electrical conductivity across the thickness of the crucible, or alternatively, the gradient in electrical conductivity can be reversed, with the highest at the outer surface and the lowest electrical conductivity at the inner surface.

[0048] The final green fractional crucible may then be sintered at a temperature and pressure to produce the composite crucible. The composite crucible may be coated with a layer of a noble metal to form coating 102 on an inner surface of the crucible.

[0049] The coating 102 may be formed via anodizing, electroplating, thermal spraying, hot-dip galvanizing, vapor deposition, or a combination thereof.

[0050] The composite crucible may be placed in a furnace like a conventional iridium crucible to produce a crystalline boule.

[0051] In another embodiment, the crucible may be manufactured using powders of raw materials (used to manufacture the binder) as well as the carbonaceous materials. The powders of the binder and the carbonaceous material are mixed together to form an electrically conductive mixture. The electrically conductive mixture is disposed in a mold and hot pressed to produce a green body (e g., a first hot pressing step). In an embodiment, the hot pressing may include isostatic pressing. The hot pressing on the powders is conducted to form the powders into a green body that has the shape of the crucible.

[0052] The green body is then sintered at a high temperature greater than 1500°C, preferably greater than 1800°C, and more preferably greater than 2000°C leading the powders to densify to more than 95% of the theoretical density. A second hot pressing step can cause the densified green body to further density to bring the density of the ceramic to approximately 100% of the theoretically achievable value. A layer of a noble metal may then be disposed on a surface of the composite crucible.

[0053] There coating 102 of the noble metal is then disposed on a surface of the composite crucible using methods such as anodizing, electroplating, thermal spraying, hot-dip galvanizing, vapor deposition, or a combination thereof.

[0054] In an embodiment, the composite crucible may be disposed in a furnace and used to manufacture a crystalline boule. FIG. 3 depicts device 1000 that uses the composite crucible to produce a crystalline boule. The device 1000 comprises a furnace 1020 that contains cooling tubes 1030 disposed in its walls. Alternatively, the cooling coils may be located outside the walls of the furnace. Fluid flowing through the cooling tubes 1030 can be used to extract heat from the furnace. The furnace 1020 is mounted on a base surface 1040 and has a furnace cover 1060 disposed on an end opposite the base surface 1040. The base surface 1040 may contain channels that can be used to locate induction coils (not shown), coils for carrying a cooling fluid (not shown) or components that can facilitate mechanical movement (not shown). Disposed in the furnace is a growth chamber 1080 in which is disposed the composite crucible 1 100.

[0055] Disposed upon the base surface 1040 is a base frame 1050 upon which is located the growth chamber 1080. A conduit 1350 that functions as an inlet for a firstgrowth gas stream is disposed in the base surface 1040 and the base frame 1050. The growth atmosphere (formed by the first growth gas stream) is crystal composition dependent. The growth atmosphere may be a reducing atmosphere when using hydrogen gas, slightly reducing when using nitrogen gas, oxidizing when using air, CO2, nitrogen mixed with air or oxygen, or any noble gas mixed with air or O2. In an embodiment, the furnace may be completely sealed from the outside atmosphere (this is not depicted in the FIG. 3) to fully control the gas mixture. In FIG. 3, the opening for the pull rod 1140 that produces the crystal boule is usually open to the environment. When the atmosphere is completely controlled, this opening will be closed by a sleeve enclosure (not shown) that isolates the pull rod and the melt in the crucible from the outside air.

[0056] The growth chamber 1080 protrudes through an opening in the furnace cover 1060. The furnace cover 1060 may contain internal cooling coils (not shown) through which a cooling fluid is discharged. The composite crucible 1100 contains a melt 1120 that is obtained from melting raw materials. A pull rod 1140 having a seed crystal 1160 disposed at its lower end is dipped into the melt 1120 and then slowly moved away from the melt (moved vertically) while undergoing rotary motion. The rotary motion either clockwise or counterclockwise is used to control the interface shape of the boule while it is in the melt. The translation motion is used to control the pull rate of the boule by extracting the boule from the melt under a controlled translation rate. The translational motion refers to the linear movement of the pull rod (or boule) either upward or downward, which controls the rate at which the boule is extracted from the melt. This means that the pull rod moves vertically in a straight line to pull the crystal boule 1180 out of the melt at a controlled speed. In an embodiment (not shown), the crucible can be rotated clockwise and counterclockwise in the same direction as the pull rod or in an opposite direction. The rotary speed may be the same or different from that of the pull rod.

[0057] A crystal boule is a single-crystal ingot produced by using a seed crystal to create a larger crystal, or ingot. This seed crystal is dipped into the molten raw material and slowly extracted. The melt grows on the seed crystal in a crystalline fashion. As the seed is extracted, the melt solidifies and eventually a large, cylindrical crystal boule is produced.

[0058] The growth chamber 1080 contains an outer tube 1070, an inner tube 1090, a growth chamber bottom plate 1280 and a growth chamber outer top plate 1290. The outer tube 1070 and inner tube 1090 are disposed between the growth chamber bottom plate 1280 and the growth chamber outer top plate 1290. The growth chamber outer top plate 1290 may be disposed on a growth chamber inner top plate 1320. The growth chamber inner top plate 1320 contacts the upper portion of the outer tube 1070. The outer tube 1070 is typically manufactured from quartz, while the inner tube 1090 is typically manufactured from zirconia. A first O-ring seal (not shown) may be disposed between the outer tube 1070 and the growth chamber bottom plate 1280. A second O- ring (not shown) is disposed between the outer tube 1070 and the growth chamber inner top plate 1320. Disposed between the growth chamber bottom plate 1280 and the composite crucible 1100 is a first layer of beads 1270 (also referred to herein as grog). In an embodiment, the first layer of beads 1270 contacts the bottom of the composite crucible 1100. The first layer of beads 1270 may have the same composition or a different composition as a second layer of beads 1260 that are typically located between the growth chamber bottom plate 1280 and the bottom of the composite crucible 1100. In an embodiment, the two layers of beads 1270 and 1260 may be the same or different. In other words, the two layers of beads 1260 and 1270 may be merged into a single layer. They may have the same composition or a different composition. Alternatively, the sizes of the beads in the two layers may be different from one another. The beads used in the layers 1270 and 1260 comprise zirconia and / or alumina.

[0059] Disposed beneath the growth chamber bottom plate 1280 and the base surface 1040 of the furnace is a porous frit 1300 that comprises granules or briquettes of a heat resistant material. The porous frit 1300 can also permit an inert gas to pass through it.

[0060] The upper plate 1290 contain two inlet ports 1340 (that contact two eyepieces 1200) through which a second growth gas stream may be introduced to surround the crystal boule and the melt in the composite crucible 1100. The second growth gas stream may be the same as the first growth gas stream (which is described above). The eyepieces 1200 may contain lenses (not shown) through which the activity in the growth chamber 1080 may be viewed.

[0061] Disposed between the furnace 1020 and the growth chamber 1080 are induction coils 1240. The induction coils 1240 (also referred to as radio-frequency (RF) coils) are used to heat the composite crucible 1100 and its contents and to produce the melt from which the crystal boule is manufactured. The growth chamber 1080 can be moved vertically (up and down) or kept stationary with respect to the induction coils 1240. It is to be noted in the FIG. 3 that the growth chamber bottom plate 1280 and the growth chamber upper plate 1290 may also contain cooling coils (not shown) through which a cooling fluid is transported.

[0062] While the invention has been described with reference to some embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A composite crucible comprising: a wall; and a base; where the base contacts the wall to create an internal volume that is used to produce a melt for a crystalline boule; where the wall comprises a binder and an electrically conducting filler; and wherein the wall has a greater electrical conductivity at an inner surface when compared with the electrical conductivity at the outer surface, a uniform electrical conductivity across an entire thickness of the wall, or a lesser electrical conductivity at an inner surface when compared with the electrical conductivity at the outer surface.

2. The composite crucible of Claim 1, where the base comprises a binder and an electrically conducting filler; and wherein the wall has a greater electrical conductivity at an inner surface when compared with the electrical conductivity at the outer surface.

3. The composite crucible of Claim 1, further comprising a metal, a metal alloy or metal oxide coating on the inner surface of the wall and at an inner surface of the base.

4. The composite crucible of Claim 3, where the metal is a noble metal.

5. The composite crucible of Claim 4, where the noble metal comprises iridium.

6. The composite crucible of Claim 4, where the metal or metal oxide coating has a thickness of 10 micrometers to 5 millimeters.

7. The composite crucible of Claim 4, where the metal oxide is silicon dioxide, aluminum oxide, titanium oxide, zirconium oxide, indium tin oxide, antimony tin oxide, cerium oxide, cadmium-oxide, titanium nitride, silicon nitride, aluminumnitride, titanium carbide, silicon carbide, titanium niobium carbide, or a combination thereof.

8. The composite crucible of Claim 1, where the binder is electrically insulating.

9. The composite crucible of Claim 1, where the binder comprises molybdenum, tungsten, or an alloy of molybdenum and tungsten.

10. The composite crucible of Claim 1, where the wall is porous.

11. The composite crucible of Claim 1, where the electrically conducting filler is a carbonaceous filler.

12. The composite crucible of Claim 11, where the carbonaceous filler comprises carbon black, carbon nanotubes, graphene, graphite, graphite oxide, carbon fibers, or a combination thereof.

13. The composite crucible of Claim 11, where the carbonaceous filler is graphite.

14. The composite crucible of Claim 1, where the wall and base have a gradient in electrical conductivity from the inner surface to the outer surface; where the electrical conductivity at the inner surface is greater than at the outer surface.

15. The composite crucible of Claim 1, where the composite crucible can be heated via electromagnetic induction.

16. A method of manufacturing a composite crucible, the method comprising: blending a binder with a carbonaceous material to create an electrically conductive mixture; hot pressurizing the electrically conductive mixture in a mold in a first hot pressing step; forming a green body that has a shape of the composite crucible;sintering the green body at a high temperature greater than 1500°C; densifying the green body to a value of more than 95% of the theoretical density; and conducting a second hot pressing step to cause the densified green body to reach approximately 100% of the theoretically achievable density.

17. The method of Claim 16, further comprising blending the binder with the carbonaceous material and a solvent to form a slurry and subjecting the slurry to the first hot pressing step.

18. The method of Claim 16, wherein the first hot pressing step and the second hot pressing step each comprise hot isostatic pressing.

19. The method of Claim 16, further comprising coating an inner surface of the composite crucible that has achieved 100% of theoretical density with a noble metal.

20. A furnace for manufacturing a crystalline boule, the furnace comprising: a furnace that includes a furnace wall; a composite crucible disposed on a first bed of grog within the furnace; where the first bed of grog has a porosity of 1 to 80 volume percent, based on a total volume of the first grog; and where the grog comprises free flowing particles of zirconia, alumina or a combination thereof; an induction coil disposed inside the furnace wall and outside the crucible; and a refractory lining being disposed in an annulus between the furnace wall and the crucible.