EP4193008A1 - Procédé et dispositif de croissance d'un cristal de sesquioxyde de terres rares - Google Patents

Procédé et dispositif de croissance d'un cristal de sesquioxyde de terres rares

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Publication number
EP4193008A1
EP4193008A1 EP21748512.7A EP21748512A EP4193008A1 EP 4193008 A1 EP4193008 A1 EP 4193008A1 EP 21748512 A EP21748512 A EP 21748512A EP 4193008 A1 EP4193008 A1 EP 4193008A1
Authority
EP
European Patent Office
Prior art keywords
crystal
oxide
rare earth
earth sesquioxide
starting material
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP21748512.7A
Other languages
German (de)
English (en)
Inventor
Christian KRÄNKEL
Emile HAURAT
Anastasia UVAROVA
Detlef Klimm
Christo Guguschev
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Forschungsverbund Berlin FVB eV
Original Assignee
Forschungsverbund Berlin FVB eV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Forschungsverbund Berlin FVB eV filed Critical Forschungsverbund Berlin FVB eV
Publication of EP4193008A1 publication Critical patent/EP4193008A1/fr
Pending legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/16—Oxides
    • C30B29/22—Complex oxides
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
    • C30B15/10—Crucibles or containers for supporting the melt
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B35/00—Apparatus not otherwise provided for, specially adapted for the growth, production or after-treatment of single crystals or of a homogeneous polycrystalline material with defined structure
    • C30B35/002—Crucibles or containers

Definitions

  • the invention relates to a method for growing a rare earth sesquioxide crystal with a cubic crystal structure from a melt.
  • the invention further relates to a crystal growth system for growing a rare earth sesquioxide crystal having a cubic crystal structure.
  • Rare earth sesquioxide crystals have a ratio of a rare earth metal (rare earths for short) to oxygen of 1 to 1.5. Examples of rare earth sesquioxide crystals are scandium oxide (Sc 2 O 3 ), lutetium oxide (Lu 2 O 3 ), yttria (Y 2 O 3 ) and neodymium oxide (Nd 2 O 3 ).
  • DE 197 02465 A1 describes how a rhenium crucible is suitable for growing, inter alia, single crystals of scandium oxide or yttrium oxide, but also of scandium yttrium oxide and lutetium yttrium oxide from the melt using the Czochralski method.
  • a single crystal is grown from a melt by first melting a starting material in a heated crucible. A seed crystal attached to a holder is then brought into contact with the melt. Without losing contact with the melt, the seed crystal is slowly pulled in the direction perpendicular to the surface of the melt while rotating it. Due to a slight supercooling at the solid-liquid phase boundary, the solidifies Melt at the seed crystal and the monocrystal continues to grow in a controlled manner through suitable process control.
  • the invention is also based on the object of providing an improved crystal growth system for growing a rare earth sesquioxide crystal with a cubic crystal structure.
  • the invention proposes a method for growing a rare earth sesquioxide crystal with a cubic crystal structure from a melt, the rare earth sesquioxide crystal containing at least 5% yttria, preferably at least 20% yttria, and at least 5% scandium oxide , preferably at least 15% scandium oxide.
  • the method according to the invention comprises the step:
  • a starting material which has at least yttrium oxide and scandium oxide, in a crucible consisting of a material which has a melting temperature of below 3000° C., preferably below 2800° C., particularly preferably below 2500° C., in particular between 2200°C and 2500°C.
  • a melting temperature refers to the temperature at which a substance or mixture of substances begins to melt, ie at which it begins to change from its solid to its liquid aggregate state.
  • the melting temperature of a pure substance at a defined pressure is called the melting point.
  • the melting point is given at atmospheric pressure.
  • the melting temperature is also referred to as the solidus temperature.
  • the solidus temperature is the temperature at which the mixture of substances begins to melt.
  • the liquidus temperature is given for a mixture of substances. The liquidus temperature indicates the temperature at which the mixture of substances melts completely.
  • the solidus point or liquidus point of a mixture of substances describes the solidus temperature or the liquidus temperature of a mixture of substances at a defined pressure.
  • the invention includes the finding that rare earth sesquioxide crystals made of scandium oxide or yttrium oxide are not grown from iridium crucibles using conventional crystal growth methods, in particular not using the Czochralski method, due to their melting points of over 2400° C. in each case be able.
  • the melting point of iridium is 2466 °C. If the melt is above 2200°C, it will come through increasing grain growth in the iridium crucible and associated stresses leading to crack formation in the crucible and thus to leakage from the crucible.
  • the targeted heat dissipation through the growing crystal is regularly important in order to maintain the necessary temperature gradients, so that the crystal to be grown has a lower temperature than the melt and the material on the seed crystal crystallizes.
  • a temperature gradient from the melt through the crystal to the drawing rod is required.
  • Targeted temperature gradients also avoid the formation of stresses due to excessive temperature differences in the growing crystal.
  • Rare earth sesquioxide crystals of scandium oxide or yttrium oxide have therefore hitherto generally been produced using the HEM (heat exchanger method) method using rhenium crucibles and not the Czochralski method using other crucibles with lower melting temperatures , For example, iridium crucibles produced. Since the processing of rhenium into crucibles is complex and therefore expensive due to its hardness and very high melting point, rare earth sesquioxide crystals made of scandium oxide or yttrium oxide have so far only been used commercially on a small scale, although they are well suited for the production of laser materials , especially for rare-earth-doped solid-state lasers.
  • HEM heat exchanger method
  • Binary or ternary rare earth sesquioxide crystals containing at least 5% yttrium oxide, preferably at least 20% yttrium oxide, and at least 5% scandium oxide, preferably at least 15% scandium oxide, can be grown using the method according to the invention.
  • a rare earth sesquioxide crystal grown by the method may contain only scandium oxide and yttria such that the proportions of scandium oxide and yttria add up to 100%, which includes growing the binary rare earth sesquioxide crystal with dopant atoms can be endowed. Accordingly, a total proportion of 100% does not rule out the presence of doping atoms, in particular with a proportion of a few percent, for example up to 15%.
  • a substance is considered to be doping in particular if the doping atoms are essentially responsible for the laser-relevant optical properties of the material.
  • the method has the advantage that a rhenium crucible is not used to grow the rare earth sesquioxide crystal, but a crucible made of a material which has a melting temperature lower than the melting temperature of rhenium.
  • crucibles can be used in the method which have more favorable properties than rhenium crucibles, for example those made of iridium.
  • the manufacturing cost for growing a rare earth sesquioxide crystal can be remarkably reduced. This allows such rare earth sesquioxide crystals to become more interesting for commercial use. Since the rare earth sesquioxide crystal to be grown contains at least 15% scandia, the hexagonal phase of yttria can be bypassed so that the rare earth sesquioxide crystal to be grown has a cubic crystal structure. The fact that the rare earth sesquioxide crystal has a cubic crystal structure is advantageous for a large number of different applications.
  • Such applications include the use of the rare earth sesquioxide crystal with a cubic crystal structure as a host material for a laser crystal, but also as a substrate for functional crystalline layers that are to be applied lattice-matched or specifically strained on a monocrystalline substrate.
  • the invention is also based on the finding that a starting material from a mixture of substances which has at least yttrium oxide and scandium oxide can have a liquidus temperature which is below that of the individual components scandium oxide and yttrium oxide.
  • This makes it possible to use a crucible made of a material with a significantly lower melting temperature than the melting temperature of rhenium for growing the rare earth sesquioxide crystal.
  • the liquidus temperature of the starting material, which has at least scandium oxide and yttrium oxide can therefore be lowered below the melting point of the individual components scandium oxide and yttrium oxide because this mixture of substances behaves azeotropically.
  • the starting material consists, for example, of at least 5% yttrium oxide, preferably at least 20% yttrium oxide, and at least 5% scandium oxide, preferably at least 15% scandium oxide, and optionally further sesquioxides, such as in particular lutetium oxide and/or erbium oxide an azeotropic mixture series.
  • sesquioxides such as in particular lutetium oxide and/or erbium oxide an azeotropic mixture series.
  • the melting temperature of the mixture of substances can be lowered below that of the individual components.
  • an iridium crucible can be used in the process. If the rare earth sesquioxide crystal to be grown has a liquidus temperature higher than 2200°C, there is a risk of destruction of the iridium crucible due to cracking due to grain growth. In addition, at higher temperatures, due to excessive temperature gradients, there is a risk of local overheating of the crucible and thus melting of the crucible.
  • a crucible made of a material other than iridium alone should be used in the process.
  • a material preferably has a melting temperature between that of iridium and rhenium.
  • a crucible made of an alloy for example an alloy of iridium and rhenium, is conceivable.
  • the method includes the step:
  • the crystal is produced by growing from the melt.
  • the rare earth sesquioxide crystal can be grown on a seed crystal by the Czochralski method.
  • the rare earth sesquioxide crystal is grown using the Czochralski method or the HEM method.
  • Rare-earth sesquioxide crystals produced by the Czochralski method or the HEM method can be produced with high crystal quality, making them suitable for laser crystals.
  • the method according to the invention can represent a modification of an already known crystal growth method, for example the Czochralski method. Process or the HEM process.
  • a rare earth sesquioxide crystal with at least 5% yttria, preferably at least 20% yttria, and at least 5% scandium oxide, preferably at least 15% scandium oxide are grown, in which Czochralski method or the HEM method, a crucible is used which consists of a material which has a melting temperature of below 3000° C., preferably below 2800° C., particularly preferably below 2500° C., in particular between 2200° C. and 2500° C, has.
  • the method according to the invention can also be part of a modified skull melting method in which the starting material is melted in its own crucible.
  • the starting material is in powder form. In the skull melting process, only the central area of the powder is melted and the surrounding material serves as a crucible.
  • the method according to the invention can also be carried out as part of a modified “Bagdasarov” method, in which the powder is pushed through the hot zone in a boat-shaped crucible.
  • the "Bagdasarov” process is described, for example, in US Pat. No. 4,303,465.
  • HEM method is described, for example, in US Pat. No. 3,898,051.
  • the starting material comprises the substances of the rare earth sesquioxide crystal to be grown and preferably in the same proportions as are present in the rare earth sesquioxide crystal being grown. That is, when the rare earth sesquioxide crystal contains 60% yttria and 40% scandia, the starting material also contains 60% yttria and 40% scandia.
  • the starting material preferably has at least 5% yttrium oxide, preferably at least 20% yttrium oxide, and at least 5% scandium oxide, preferably at least 15% scandium oxide.
  • the starting material is preferably in powder form.
  • the starting material can be in the form of granules or pieces with a maximum diameter of up to 1.5 cm.
  • the method can include the further step:
  • the rare earth sesquioxide crystal to be grown is to be used as a substrate for a functional layer that is to be applied lattice-matched or specifically strained to the substrate, for example to be grown on the substrate, the proportions of yttrium oxide and scandium oxide can be adjusted in the starting material in order to produce the rare earth sesquioxide crystal with such a lattice constant that corresponds to the lattice constant of the material of the functional layer or has a certain difference therefrom.
  • the lattice constant of the rare earth sesquioxide crystal is specified by the lattice constant of the functional layer and the proportions of yttrium oxide and scandium oxide in the starting material are selected accordingly.
  • the lattice constant of the rare earth sesquioxide crystal to be grown can be calculated, for example, using Vergard's rule, which takes into account the lattice constants of the individual components, e.g. the lattice constants of yttrium oxide and scandium oxide and their proportions in the rare earth sesquioxide crystal to be grown.
  • the starting material and accordingly also the rare earth sesquioxide crystal to be grown contain other substances, e.g. lutetium oxide and/or erbium oxide, their proportions in the starting material can also be adjusted accordingly in order to produce the rare earth sesquioxide crystal with a predetermined lattice constant.
  • the lattice constant of the rare earth sesquioxide crystal to be grown can also be predetermined and the proportions of the substances in the starting material adjusted accordingly in that the rare earth sesquioxide crystal should have a predetermined crystal field strength, which can also be set by adjusting the lattice constant.
  • the crystal field strength can be set in such a way and the proportions of the substances in the starting material adjusted accordingly that a laser crystal can emit light with a specific wavelength or in a specific wavelength range.
  • the mixed raw material may be charged into the crucible in bulk or pressed powder, granular or lump form and melted.
  • the rare earth sesquioxide crystal is grown by the zone melting method such as optical zone melting, the starting material in powder form should be pressed and sintered beforehand to bring it into a mechanically stable form.
  • the starting material may be pressed and/or sintered prior to filling the crucible to fill the crucible with comparatively fewer reflow operations .
  • the starting material preferably has a purity of at least 4N, i.e. it contains less than 0.01% of other substances. If the rare-earth sesquioxide crystal is not to be used as a laser crystal, the starting material may contain other substances mixed in by 0.01% or more.
  • the invention proposes a crystal growth system for growing a rare earth sesquioxide crystal with a cubic crystal structure from a melt, the rare earth sesquioxide crystal containing at least 5% yttria, preferably at least 20% yttria, and at least 5% scandium oxide , preferably at least 15% scandium oxide.
  • the crystal growing system according to the invention contains:
  • crucible made of a material with a melting temperature of below 3000 °C, preferably below 2800 °C, particularly preferably below 2500 °C, in particular between 2200 °C and 2500 °C,
  • a heating element which is arranged and designed to heat the crucible at least until the starting material is completely melted.
  • Complete melting can be achieved, for example, by heating up to the liquidus temperature.
  • the above-described method according to the invention for growing a rare earth sesquioxide crystal with a cubic crystal structure from a melt can be carried out with the crystal growing system according to the invention.
  • the starting material can additionally contain lutetium oxide and the rare earth sesquioxide crystal to be grown can additionally contain, for example, up to 45% lutetium oxide.
  • Lutetium oxide has a cubic crystal structure and is also suitable as a host material for a laser crystal, for example for a rare earth-doped solid-state laser.
  • the liquidus temperature of the rare earth sesquioxide crystal can be lowered to temperatures below 2200 °C, so that growth from iridium crucibles made possible by the Czochralski method.
  • the rare earth sesquioxide crystal to be grown can, for example, have proportions of yttrium oxide, scandium oxide and lutetium oxide, so that their proportions add up to 100%, this including that the rare earth sesquioxide crystal can be doped with doping atoms.
  • the rare earth sesquioxide crystal to be grown and accordingly the starting material can also contain other substances, such as erbium oxide, in addition to yttrium oxide, scandium oxide and lutetium oxide.
  • a rare earth sesquioxide crystal containing at least 5% yttria, preferably at least 20% yttria, and at least 5% scandia, preferably at least 15% scandia, and additionally up to 45% lutetium oxide has a liquidus temperature that is regular is below 2400°C and in particular below 2200°C.
  • a rare earth sesquioxide crystal of at least yttria, scandium oxide and lutetium oxide can be grown in a crucible made of a material with a melting temperature below 3000°C, preferably below 2800°C, especially be - preferably below 2500 °C, in particular between 2200 °C and 2500 °C.
  • the rare earth sesquioxide crystal composed of at least yttrium oxide, scandium oxide and lutetium oxide has a liquidus temperature below 2200° C.
  • it can be grown from the melt in an iridium crucible, for example by the Czochralski method.
  • the rare earth crystal to be grown includes sesquioxide crystal
  • yttria between 5% and 95% yttria, preferably between 40% and 70% yttria
  • the starting material additionally having lutetium oxide if the proportion of lutetium oxide in the rare earth sesquioxide crystal is greater than 0%.
  • a rare earth sesquioxide crystal has a liquidus temperature below 2400°C, and in particular below 2200°C, and can be regularly grown in an iridium crucible.
  • the starting material may include at least ytterbium (Yb), thulium (Tm), holmium (Ho), erbium (Er) and/or neodymium (Nd), and the rare earth sesquioxide crystal to be grown may include Yb, Tm, Ho, Er and/or Nd be doped.
  • the starting material can have up to 6 at.% Yb or Tm, so that the rare earth sesquioxide crystal to be grown has up to 2 ⁇ 10 21 cm ⁇ 3 Yb or Tm atoms.
  • the starting material can also contain up to 1 at.% Ho or Nd, so that the rare earth sesquioxide crystal to be grown has up to 3 ⁇ 1 O 20 cm -3 Ho or Nd atoms.
  • the starting material can have up to 15 at.% Er, so that the rare earth sesquioxide crystal to be grown has up to 5 ⁇ 10 21 cm -3 Er atoms.
  • the liquidus temperature of the rare earth sesquioxide crystal can be lowered further. It has been shown that this effect is particularly strong when the rare earth sesquioxide crystal is doped with erbium.
  • the proportions of yttrium oxide, scandium oxide and lutetium oxide in the starting material can be selected in such a way that the material composition of the rare earth sesquioxide crystal to be grown corresponds to a composition in which (Y 0.7 Sc 0.3 ) 2 O 3 , ( Y 0.45 Sc 0.55 ) 2 O 3 and (Lu 0.25 Y 0.4 Sc 0.35 ) 2 O 3 area of the ternary phase diagram of yttrium oxide, scandium oxide and lutetium oxide.
  • Thermodynamic measurements have shown that in the compositions (Y 0.7 Sc 0.3 ) 2 O 3 , (Y 0.45 Sc 0.55 ) 2 O 3 and (Lu 0.25 Y 0 .4 Sc 0.35 ) 2 O 3 in the ternary phase diagram crystallization takes place in a cubic phase at a temperature below 2170 °C ⁇ 30 °C.
  • a binary or ternary rare earth sesquioxide crystal having a composition in this range in the ternary phase diagram can be grown with a crystal growing system using an iridium crucible. The proportions of yttrium oxide, scandium oxide and lutetium oxide add up to 100% in such crystals, which includes that the rare earth sesquioxide crystal can be doped with doping atoms.
  • the proportions of yttrium oxide, scandium oxide and Lutetium oxide in the starting material can be selected in such a way that the material composition of the rare earth sesquioxide crystal to be grown corresponds to a composition in which (Y 0.75 Sc 0.25 ) 2 O 3 , (Y 0, 3 Sc 0.7 ) 2 O 3 , (Lu 0.35 Y 0.25 Sc 0.4 ) 2 O 3 and (Lu 0.4 Y 0.4 Sc 0.2 ) 2 O 3 in the ternary phase diagram of yttrium oxide, scandium oxide and lutetium oxide.
  • the proportions of yttrium oxide, scandium oxide and lutetium oxide in the starting material can be selected in such a way that the material composition of the rare earth sesquioxide crystal to be grown corresponds to a composition that is defined by (Y 0.85 Sc 0.15 ) 2 O 3 , (Y 0.15 Sc 0.85 ) 2 O 3 , (Lu 0.5 Y 0.1 Sc 0.4 ) 2 O 3 and (Lu 0.6 Y 0.25 Sc 0.15 ) 2 O 3 spanned area in the ternary phase diagram of yttrium oxide, scandium oxide and lutetium oxide.
  • the proportions of yttrium oxide, scandium oxide and lutetium oxide in the starting material can be selected in such a way that the material composition of the rare earth sesquioxide crystal to be grown corresponds to a composition that is defined by (Y 0.95 Sc 0.05 ) 2 O 3 , (Y 0.05 Sc 0.95 ) 2 O 3 , (Lu 0.8 Sc 0.15 Y 0.05 ) 2 O 3 and (Lu 0.8 Y 0.15 Sc 0.05 ) 2 O 3 spanned area in the ternary phase diagram of yttrium oxide, scandium oxide and lutetium oxide.
  • the rare earth sesquioxide crystal may contain at least 5% yttria, preferably at least 20% yttria, and at least 5% scandia, preferably at least 15% scandia, and additionally up to 15% erbia.
  • a rare earth sesquioxide crystal can additionally contain up to 80% lutetium oxide, in particular up to 45% lutetium oxide.
  • the starting material then additionally has erbium oxide and optionally also lutetium oxide.
  • the resulting comparatively greater disorder in the crystal can lead to a comparatively greater broadening of the emission bandwidth of the crystal lead, which is advantageous for certain types of lasers.
  • thermodynamic measurements have shown that a rare earth sesquioxide crystal with the composition (Er 0.07 Y 0.43 Sc 0.5 ) 2 O 3 has a liquidus temperature below 2050 °C, in particular 2010+/-30 °C, and has a cubic crystal structure. If the proportion of erbia in the rare earth sesquioxide crystal to be grown is more than 0%, the starting material also contains erbia in addition.
  • the proportions of yttrium oxide, scandium oxide and erbium oxide in the starting material are preferably selected in such a way that the material composition of the rare earth sesquioxide crystal to be grown corresponds to a composition that is defined by (Y 0.7 Sc 0.3 ) 2 O 3 , (Y 0.45 Sc 0.55 ) 2 O 3 and (Er 0.07 Y 0.43 Sc 0.5 ) 2 O 3 spanned ternary phase diagram of yttrium oxide, scandium oxide and erbium oxide.
  • a rare earth sesquioxide crystal has only yttrium oxide, scandium oxide and erbia oxide, so that their proportions in the rare earth sesquioxide crystal add up to 100%.
  • a rare earth sesquioxide crystal having a composition represented by (Y 0.7 Sc 0.3 ) 2 O 3 , (Y 0.45 Sc 0.55 ) 2 O 3 and (Er 0.07 Y 0, 43 Sc 0.5 ) 2 O 3 spanned ternary phase diagram has a liquidus temperature below 2200 °C and a cubic crystal structure.
  • Such a rare earth sesquioxide crystal can be grown in particular in an iridium crucible, for example using the Czochralski method.
  • a rare earth sesquioxide crystal can be grown from yttria, scandia and erbia with a crystal quality suitable for use as a laser crystal.
  • the proportions of yttrium oxide and scandium oxide in the starting material of the crystal growth system are selected such that the rare earth sesquioxide crystal to be grown has a liquidus temperature which is 2200° C. or less, in particular between 2000° C. and 2200° C or between 2100°C and 2200°C.
  • the rare earth sesquioxide crystal to be grown contains other substances, e.g. erbium oxide and/or lutetium oxide, their proportions in the starting material are also selected in such a way that the rare earth sesquioxide crystal to be grown has a liquidus temperature of 2200 °C or less, in particular between 2000°C and 2200°C or between 2100°C and 2200°C.
  • the invention also includes using a crucible in a crystal growth process, the crucible being made of a material which has a melting temperature of below 3000° C., preferably below 2800° C., particularly preferably below 2500° C., in particular between 2200 °C and 2500 °C, for growing a rare earth sesquioxide crystal having a cubic crystal structure and containing at least 5% yttria, preferably at least 20% yttria, and at least 5% scandia, preferably at least 15% scandia.
  • the crystal growth method can be, for example, the Czochralski method, the HEM method, or an alternative method in which to grow a rare earth sesquioxide crystal using a crucible.
  • the crucible is preferably made of iridium.
  • the rare earth sesquioxide crystal may contain only yttria and scandium oxide or additionally up to 15% erbia and/or up to 45% lutetium oxide.
  • other rare earths can also be contained in the rare earth sesquioxide crystal and correspondingly also in the starting material. In particular, such rare earth sesquioxide crystals can be doped.
  • the invention also includes a rare earth sesquioxide crystal having a cubic crystal structure containing at least 5% yttria, preferably at least 20% yttria, and at least 5% scandia, preferably at least 15% scandia, and having the invention described above Method or one of the methods of the other embodiments was produced in such a way that it is suitable as a laser crystal for a solid-state laser.
  • Such a rare earth sesquioxide crystal with the crystal quality required for a laser crystal can have been produced, for example, using the Czochralski method or the HEM method, with a crucible being used in these methods which consists of a material which has a melting temperature of below 3000°C, preferably below 2800°C, particularly preferably below 2500°C, in particular between 2200°C and 2500°C.
  • Appropriate doping can be used to change the wavelength or the wavelength range in which the rare earth sesquioxide crystal used as the laser crystal for a solid-state laser consists of at least 5% yttrium oxide, preferably at least 20% yttrium oxide, and at least 5% scandium oxide, preferably at least 15%. Scandium oxide, emits light, can be adjusted. Doping can be up to 15% of the rare earth sesquioxide crystal. In particular, doping includes those substances that are responsible for the laser-relevant optical properties of the material.
  • the rare earth sesquioxide crystal is doped with Yb, for example, it is suitable as or for a laser crystal for a laser which emits light at 1 pm-1.1 pm.
  • Tm When the rare earth sesquioxide crystal is doped with Tm, it is suitable as or for a laser crystal for a laser emitting light at 1.8 pm - 2 pm.
  • Ho it is suitable as or for a laser crystal for a laser which emits light at 1.9 pm - 2.1 pm.
  • the rare earth sesquioxide crystal is doped with Er, it is suitable as or for a laser crystal for a laser which emits light at 1.5 pm or 2.95 pm.
  • the rare earth sesquioxide crystal is doped with Nd, it is suitable as or for a laser crystal for a laser which emits light at wavelengths between 0.9 pm and 1.6 pm. It is also possible to use the rare earth sesquioxide crystal according to the invention with at least 5% yttrium oxide, preferably at least 20% yttrium oxide, and at least 5% scandium oxide, preferably at least 15% scandium oxide, as or for a scintillator.
  • the invention also includes a substrate formed from a rare earth sesquioxide crystal having a cubic crystal structure containing at least 5% yttria, preferably at least 20% yttria, and at least 5% scandium oxide, preferably at least 15% scandium oxide. and which has been prepared according to the method of the invention described above.
  • the substrate By adjusting the proportions of the substances in the rare earth sesquioxide crystal and accordingly in the starting material, the substrate can have a lattice constant which corresponds to the lattice constant of a functional layer which is to be lattice-matchedly grown on the substrate. By adapting the proportions of the substances in the rare earth sesquioxide crystal, the substrate can also have such a lattice constant that a layer can be applied to the substrate by deliberately strained layer growth.
  • the invention also relates to a method for growing a rare earth sesquioxide crystal with a cubic crystal structure, which contains at least 5% yttria, preferably at least 20% yttria, and at least 5% scandium oxide, preferably at least 15% scandium oxide, from a melt, wherein the Procedure includes the step:
  • the rare earth sesquioxide crystal to be grown has a liquidus temperature that is 2400°C or less, preferably below 2200°C, more preferably below 2050°C, especially between 2000 °C and 2400 °C, for example between 2000 °C and 2200 °C,
  • This method represents a separate invention that can be implemented independently and independently of, but also in combination with, the aspects described above.
  • a crucible is not necessarily used in the method.
  • the starting material is melted at a temperature of 2400°C or less.
  • the starting material used in the process has a liquidus temperature of below 2400°C, preferably below 2200°C, particularly preferably below 2050°C, in particular between 2000°C and 2400°C.
  • the invention is based on the finding that a mixture of substances with at least yttrium oxide, preferably at least 5% yttrium oxide, particularly preferably at least 20% yttrium oxide, and at least 5% scandium oxide, preferably at least 15% scandium oxide, behaves azeotropically, so that a Mixing them in certain ratios leads to a liduidus temperature which is below the melting points of the individual components.
  • the starting material for example at least yttrium oxide, preferably at least 5% yttrium oxide, particularly preferably at least 20% yttrium oxide and at least 5% scandium oxide, preferably at least 15% scandium oxide, and optionally further sesquioxides, such as in particular lutetium oxide and / or erbium oxide, han - it is an azeotropic mixed series.
  • the melting temperature of the mixture of substances can be below that of the individual components.
  • the individual components scandium oxide and yttrium oxide have a melting point of over 2400° C., so that, in contrast to the invention, more complex growth structures are required to grow crystals from scandium oxide or yttrium oxide. Since the method for growing a rare-earth sesquioxide crystal having a cubic crystal structure requires a lower temperature of 2400°C or less for growth, a simpler and less expensive growth setup can be used, such as an iridium crucible in a crucible growth method, such as the Czochralski method, or a less expensive growth setup for optical zone melting. Furthermore, to generate a lower temperature for growth, less energy is also required, so the cost can be further reduced. Due to the lower melting point, temperature gradients within the melt and thus stresses in the grown rare earth sesquioxide crystal can also be reduced. This can improve the optical quality of the rare earth sesquioxide crystal thus grown by reducing stress-induced birefringence.
  • the rare earth sesquioxide crystal can also be grown using a crucible-free method, most preferably using optical zone melting.
  • Optical zone melting is particularly suitable for the production of electrically non-conductive materials that cannot be heated inductively.
  • one or more lamps can be used to heat the starting material in a respective zone.
  • the radiation from the lamp or lamps can be focused on the respective zone of the starting material and guided along the starting material.
  • the starting material can be guided through the focus in optical zone melting.
  • the starting material may have the same compositions of materials as described above with respect to the crucible crystal growth methods.
  • the starting material can, for example, additionally contain between 0% and 80% lutetium oxide and proportions of yttrium oxide, scandium oxide and lutetium oxide in the starting material can be chosen such that the material composition of the rare earth sesquioxide crystal to be grown corresponds to a composition that in which by (Y 0.95 Sc 0.05 ) 2 O 3 , (Y 0.05 Sc 0.95 ) 2 O 3 , (Lu 0.8 Sc 0.2 ) 2 O 3 and (Lu 0.8 Y 0.15 Sc 0.05 ) 2 O 3 spanned region of the ternary phase diagram of yttrium oxide, scandium oxide and lutetium oxide, except for the point (Lu 0.8 Sc 0.2 ) 2 O 3 .
  • the starting material can additionally contain between 0% and 25% lutetium oxide and proportions of yttrium oxide, scandium oxide and lutetium oxide in the starting material can be selected in such a way that the material composition of the rare earth sesquioxide crystal to be grown corresponds to a composition in which ( Y 0.7 Sc 0.3 ) 2 O 3 , (Y 0.45 Sc 0.55 ) 2 O 3 and (Lu 0.25 Y 0.4 Sc 0.35 ) 2 O 3 spanned region of the ternary phase dia- grams of yttrium oxide, scandium oxide and lutetium oxide.
  • the starting material can contain up to 15% erbium oxide and the proportions of yttrium oxide, scandium oxide and erbium oxide in the starting material can be selected in such a way that the material composition of the rare earth sesquioxide crystal to be grown corresponds to a composition that is defined by (Y 0 .7 Sc 0.3 ) 2 O 3 , (Y 0.45 Sc 0.55 ) 2 O 3 and (Er 0.07 Y 0.43 Sc 0.5 ) 2 O 3 spanned area of the ternary phase diagram of yttri- oxide, scandium oxide and erbium oxide.
  • .1 a schematically illustrated flow chart of a method for growing a rare earth sesquioxide crystal with a cubic crystal structure from a melt
  • 2 a diagrammatically illustrated crystal growing system for growing a rare earth sesquioxide crystal with a cubic crystal structure from a melt
  • Fig. 3 a rare earth sesquioxide crystal with a cubic crystal structure having the composition (Er 0.07 Y 0.43 Sc 0.5 ) 2 O 3 which was grown by the Czochralski method,
  • Fig. 4 a ternary phase diagram spanned by yttrium oxide, scandium oxide and lutetium oxide,
  • Fig. 5 a large number of measurements to determine the solidus and liquidus temperatures of a rare earth sesquioxide crystal containing yttrium oxide, scandium oxide and lutetium oxide in different proportions,
  • Fig. 6 Differential thermal analysis studies of the solidus and liquidus points of a rare earth sesquioxide crystal having the same composition as the rare earth sesquioxide crystal shown in Fig. 3, and
  • Fig. 7 A rare earth sesquioxide crystal with a cubic crystal structure having the composition (Er 0.07 Y 0.43 Sc 0.5 ) 2 O 3 grown by optical zone melting.
  • FIG. 1 shows a diagrammatic flow chart of a method for growing a rare earth sesquioxide crystal with a cubic crystal structure from a melt.
  • the method serves to grow a rare earth sesquioxide crystal containing at least yttria, preferably at least 5% yttria, more preferably at least 20% yttria, and at least 5% scandium oxide, preferably at least 15% scandium oxide.
  • the method can be carried out as part of an already known crystal growth method, for example as a modification of the Czochralski method and the optical zone melting method.
  • a starting material is first provided (step S1).
  • the starting material comprises 10% lutetium oxide, 50% yttrium oxide and 40% scandium oxide.
  • the starting material can additionally or alternatively also include other substances, but at least yttrium oxide, preferably at least 5% yttrium oxide, particularly preferably at least 20% yttrium oxide, and at least 5% scandium oxide, preferably at least 15% scandium oxide.
  • the starting material can include only yttria and scandium oxide.
  • the starting material can also include erbium oxide and/or lutetium oxide, for example.
  • the starting material can, for example, also have rare earth doping atoms, for example Yb, Tm, Ho, Er and/or Nd.
  • the proportions of yttrium oxide and scandium oxide and—if present—the other substances such as lutetium oxide and/or erbium oxide can be adjusted in the starting material in such a way that the rare earth sesquioxide crystal to be grown has a predetermined lattice constant.
  • the lattice constant of the rare earth sesquioxide crystal to be grown can be specified, for example, by the lattice constant of the material of that layer which is to be applied lattice-matched or with a defined offset to a substrate made from the rare earth sesquioxide crystal.
  • the starting material is in powder form and is placed in a crucible made of iridium (step S2).
  • the starting material is placed in another crucible which consists of a material which has a melting point of below 3000° C., preferably below 2800° C., particularly preferably below 2500° C., in particular between 2200° C. and 2500°C.
  • the starting material is melted in the crucible (step 3).
  • a seed crystal is contacted with the melt, and a rare earth sesquioxide crystal is grown from the melt by the Czochralski method (step S4).
  • the starting material is melted in the crucible and the rare earth sesquioxide crystal is then grown by a crystal growth method other than the Czochralski method, such as the Bridgman method.
  • FIG. 2 shows a diagrammatically illustrated crystal growth system 200 for growing a rare earth sesquioxide crystal with a cubic crystal structure, which contains at least 5% yttrium oxide, preferably at least 20% yttrium oxide, and at least 5% scandium oxide, preferably at least 15% scandium oxide. from a melt.
  • the crystal growing system 200 is shown in a side view looking at a longitudinal section through the crystal growing system 200 .
  • the method described above with reference to FIG. 1 can be carried out with the crystal growing system 200 .
  • the crystal growing system 200 includes a crucible 202 made of iridium.
  • the crucible has a cylindrical shape.
  • the crystal growing system 200 comprises another crucible made of a material with a melting temperature below 3000°C, preferably below 2800°C, more preferably below 2500°C, especially between 2200°C and 2500°C , consists.
  • the crucible 202 can also have a different shape and, for example, taper conically starting from the opening.
  • the crystal growing system 200 further includes a starting material 204 comprising yttrium oxide, scandium oxide and lutetium oxide.
  • the starting material 204 in this exemplary embodiment has 10% lutetium oxide, 50% yttrium oxide and 40% scandium oxide.
  • the starting material comprises at least 5% yttrium oxide, preferably at least 20% yttrium oxide, and at least 5% scandium oxide, preferably at least 15% scandium oxide, and can additionally contain other substances, for example up to 80% lutetium oxide, preferably up to 45% lutetium oxide and/or up to 15% erbium oxide.
  • the starting material 204 can also only comprise yttria and scandia.
  • the starting material 204 has rare earth dopant atoms, so the rare earth sesquioxide crystal grown from the starting material 204 is doped.
  • the crucible 202 is surrounded by insulation 206 which is designed and arranged to ensure a defined temperature gradient within the melt. It is also possible that the crucible 202 is not surrounded by insulation but is in direct contact with a heating element.
  • a heating element 208 is disposed around the insulation 206.
  • the heating element 208 is in the form of an induction heating element and comprises an induction heating coil which is wound around the crucible 202 in a helix.
  • the crucible 202 with the starting material 204 can be inductively heated by means of radio frequency radiation until the starting material 204 has completely melted, for example up to the liquidus temperature of the starting material 204, in order to produce a starting material 204 from a typically powdery starting material to produce melt from which the rare earth sesquioxide crystal can be grown.
  • the crystal growing system 200 If the crystal growing system 200 is to be used to grow a rare earth sesquioxide crystal according to the Czochralski method, it additionally comprises a seed crystal 212 attached to a holder 210 and a device 214 to pull the seed crystal 212 on the holder 210 under control from the melt while rotating.
  • FIG. 3 shows a rare earth sesquioxide crystal 300 having a cubic crystal structure with the composition (Er 0.07 Y 0.43 Sc 0.5 ) 2 O 3 .
  • the rare earth sesquioxide crystal 300 was grown in an iridium crucible by the Czochralski method.
  • the rare earth sesquioxide crystal 300 has a cubic crystal structure and a liquidus temperature of less than 2050°C.
  • as a raw material for the rare earth sesquioxide crystal 300 erbia, yttria and scandia in powder form having a purity of 4N were used.
  • the crystal quality of the rare earth sesquioxide crystal 300 is sufficient to use it as a laser crystal.
  • a substrate can also be produced from the rare earth sesquioxide crystal 300, on which further layers can be grown in layer growth in order to subsequently produce an optical or electro-optical component therefrom.
  • FIG. 4 shows a ternary phase diagram 400 spanned by yttrium oxide, scandium oxide and lutetium oxide.
  • the rare earth-sesquioxide crystals with compositions shown in the ternary phase diagram 400 have liquidus temperatures between 2090.degree. C. and 2490.degree.
  • the temperature values marked with an asterisk symbol 402 correspond to the liquidus temperatures of the respective rare earth sesquioxide crystals that were the subject of the measurements described in relation to FIG.
  • the temperature values marked with a rectangle symbol 404 for rare earth sesquioxide crystals with different proportions of scandium oxide and lutetium oxide come from Badie, JM, "Etude de la structure des phases ä delicious temperature presentees pas les systeme Sc 2 O 3 - La 2 O 3 et Sc 2 O 3 -Nd 2 O 3 ", from High Temp. - High Press., 1970. 2: pages 309-316 and Peters, R., K. Petermann, and G.
  • a circle symbol 406 indicates further temperature values obtained in thermodynamic investigations in the ternary phase diagram.
  • the phase diagram 400 was created by interpolating between the measurement points shown as a circle symbol 406 .
  • the crystallization of the respective rare earth sesquioxide crystals takes place in a cubic phase with liquidus temperatures below 2170 ° C ⁇ 30 ° C instead.
  • FIG. 6 By adding other rare earth atoms, as shown in FIG. 6 as an example for a composition (Er 0.07 Y 0.43 Sc 0.5 ) 2 O 3 , it is possible to lower the liquidus temperature even further.
  • FIG. 5 shows a large number of measurements 500 for determining the solidus and liquidus temperatures of a rare earth sesquioxide crystal which contains yttrium oxide, scandium oxide and lutetium oxide in different proportions.
  • the differential thermal analysis (DTA) signal is given in pV/mg of a rare earth sesquioxide crystal with different proportions of yttrium oxide, scandium oxide and lutetium oxide over the temperature between 1950° C. and 2250° C.
  • the proportion of lutetium oxide for the measurements was successively increased from 0% to 43% and at the same time the proportion of scandium oxide was reduced from 60% to 34% and the proportion of yttrium oxide from 40% to 23%, with the sum of the proportions of yttrium oxide , scandium oxide and lutetium oxide each add up to 100% for each of the rare earth sesquioxide crystals.
  • each of the measurement curves 500.1 to 500.11 has a first marking 502, which indicates the solidus point, and at a second temperature, which is higher than the first temperature, a second marking 504, which indicates the liquidus point. on.
  • the measurements 500 show that the material system examined has liquidus temperatures below 2170° C. (indicated by the dashed line 506) over a wide composition range.
  • FIG. 6 shows three differential thermal analysis (DTA) investigations 600 of the liquidus temperature of a rare earth sesquioxide with the composition (Er 0.07 Y 0.43 Sc 0.5 ) 2 O 3 carried out in chronological order.
  • This composition corresponds to the composition of the rare earth sesquioxide crystal shown in FIG.
  • DTA differential thermal analysis
  • the starting material of the rare earth sesquioxide crystal which was in powder form, was first melted.
  • the powder has a comparatively poorer thermal contact with the crucible, which is why the first measurement may be comparatively inaccurate.
  • the powder that has not yet melted may be inhomogeneous and not in thermodynamic equilibrium, which can lead to misinterpretations.
  • the sample is in thermodynamic equilibrium, is homogeneous and the thermal contact is significantly improved. Therefore, the DTA examination was repeated twice.
  • the first repetition led to measurement curve 600.2 and the second repetition to measurement curve 600.3.
  • the similarity of the three measurement curves 600.1, 600.2, 600.3 proves the accuracy and reproducibility of the DTA tests carried out.
  • phase transition (here melting) energy is required or released, which can be recognized by deflections in the DTA signal curve. These peaks can be used, for example, to identify the solidus point and the liquidus point of a rare earth sesquioxide crystal.
  • Shown in Figure 7 is a cubic crystal structure rare earth sesquioxide crystal 700 of composition (Er 0.07 Y 0.43 Sc 0.5 ) 2 O 3 grown by optical zone melting.
  • the invention relates to growing a rare earth sesquioxide crystal having a cubic crystal structure from a melt.
  • the rare earth sesquioxide crystal contains at least 5% yttria and at least 5% scandia such that its liquidus temperature is below 2400°C.
  • the rare earth sesquioxide crystal may also contain yttria and at least 5% scandia, and the proportions of yttria and scandia may be selected in a starting material such that the rare earth sesquioxide crystal to be grown has a liquidus temperature below 2400°C.
  • the starting material can be melted at a temperature of 2400°C or lower in a crucible made of a material having a melting temperature lower than 3000°C.
  • the rare earth sesquioxide crystal can be grown from the molten starting material using a crystal growing method such as the Czochralski method or the HEM method. It is also possible to grow the rare earth sesquioxide crystal without a crucible at a temperature of 2400° C. or less, for example by means of optical zone melting.

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Abstract

L'invention concerne un procédé de croissance d'un cristal de sesquioxyde de terres rares ayant une structure cristalline cubique à partir d'un bain fondu. Le cristal de sesquioxyde de terres rares contient au moins 5 % d'oxyde d'yttrium et au moins 5 % d'oxyde de scandium de sorte que la température de liquidus du cristal soit inférieure à 2 400 °C. En variante, le cristal de sesquioxyde de terres rares peut également contenir de l'oxyde d'yttrium et au moins 5 % d'oxyde de scandium, et les proportions d'oxyde d'yttrium et d'oxyde de scandium peuvent être sélectionnées dans un matériau de départ de telle sorte que le cristal de sesquioxyde de terres rares à faire croître a une température de liquidus inférieure à 2 400 °C. Le matériau de départ peut être fondu à une température de 2 400 °C ou moins dans un creuset qui est constitué d'un matériau qui a une température de fusion inférieure à 3 000 °C. Le cristal de sesquioxyde de terres rares peut être amené à croître à partir du matériau de départ fondu à l'aide d'un procédé de croissance de cristal, par exemple le procédé de Czochralski ou le procédé HEM. Une croissance sans creuset du cristal de sesquioxyde de terres rares est également possible à une température de 2 400 °C ou moins, par exemple à l'aide d'un processus de fusion de zone optique.
EP21748512.7A 2020-08-05 2021-07-06 Procédé et dispositif de croissance d'un cristal de sesquioxyde de terres rares Pending EP4193008A1 (fr)

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US4303465A (en) 1976-10-14 1981-12-01 Bagdasarov Khachik S Method of growing monocrystals of corundum from a melt
US4444728A (en) * 1982-01-21 1984-04-24 Engelhard Corporation Iridium-rhenium crucible
DE19702465A1 (de) 1997-01-24 1998-07-30 Heraeus Gmbh W C Tiegel zur Einkristall-Züchtung, Verfahren zu seiner Herstellung und seine Verwendung
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