Schott Ag

Joerg Kandler

Lutz Parthier

Andreas Menzel

Matthias Mueller

Gordon Von Der Goenna

Lars Ortmann

Gunther Wehrhan

Clemens Kunisch

Andreas Weisleder

Rainer Guett

Thomas Kaufhold

A method for producing high-purity, large-volume monocrystals that are especially radiation-resistant and have low intrinsic birefringence. From a melt of crystalline raw material, with controlled cooling and solidification, a crystal is generated. As the crystalline raw material, shards and/or waste from already-grown crystals is used, and the re-used raw material In this way, crystals can be obtained which after tempering have a BSDF value of &#x3c;7&#xd7;10, an RMS homogeneity after the subtraction of 36 Zernike coefficients of &#x3c;15&#xd7;10, an SDR-RMS value in the 111 direction of &#x3c;0.2 nm/cm.

Production of high-purity, large-volume monocrystals that are especially radiation-resistant from crystal shards

Single crystals with low scattering, small refractive index differences and few small angle grain boundaries have a bi-directional scattering distribution function value (BSDF) of less than 1.5*10or 5*10.

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The method provides CaFsingle crystals with low scattering, small refractive index differences and few small angle grain boundaries, which can be tempered at elevated temperatures. In the method a CaFstarting material is heat-treated for at least five hours at temperatures between 1000&#xb0; C. and 1250&#xb0; C. and then sublimed at a sublimation temperature of at least 1100&#xb0; C. in a vacuum of at most 5*10mbar to form a vapor. The vapor is condensed at a condensation temperature of at least 500&#xb0; C., which is at least 20&#xb0; C. below the sublimitation temperature, to form a condensate. Then a melt formed from the condensate is cooled in a controlled manner to obtain the single crystal, which is subsequently tempered. The method is preferably performed with a CaFstarting material including waste material and cuttings from previously used melts.

The method for producing single crystals includes drying crystal raw material by removing water, reaction of impurities with a scavenger, preferably a metal halide, and homogenizing the melt. The method is performed with the raw material in a melt vessel with a variable-sized through-going opening, in which drying occurs at 100&#xb0; C. to 600&#xb0; C. for at least 20 hours with a geometric conductance value for the through-going opening of 2.00 to 30.00 mm; the reacting occurs at 600&#xb0; C. to 1200&#xb0; C. for at least nine hours with a geometric conductance value of 0.0020 to 0.300 mmand the homogenizing occurs at above 1400&#xb0; C. for at least six hours with a geometric conductance value of 0.25 to 1.1 mm. Alternatively the geometric conductance value is the same during drying, reacting and homogenizing and takes a value between 0.25 and 1 mm.

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Cospeda, Germany

Joerg Kandler