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Obtaining Iridium Free Garnet Crystals

IP.com Disclosure Number: IPCOM000087179D
Original Publication Date: 1976-Dec-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Blum, SE: AUTHOR [+3]

Abstract

Crystals of gadolinium gallium garnet (GGG) are used as substrate material in magnetic bubble domain devices. These garnet crystals are generally grown using the Czochralski method from a melt in an iridiun crucible. The most common imperfections or defects found in the GGG crystals are inclusions of iridium that contaminated the melt during the crystal-growing process. The major source of the iridium inclusions is the poor quality of iridium prepared by known technology. As a result, it is necessary to improve the iridium surface by polishing, thereby minimizing the source of iridium contamination. The inner surface of iridium crucibles typically has an optical density of about 1.4 and yields GGG crystals having >5 defects/cm/2/.

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Obtaining Iridium Free Garnet Crystals

Crystals of gadolinium gallium garnet (GGG) are used as substrate material in magnetic bubble domain devices. These garnet crystals are generally grown using the Czochralski method from a melt in an iridiun crucible. The most common imperfections or defects found in the GGG crystals are inclusions of iridium that contaminated the melt during the crystal-growing process. The major source of the iridium inclusions is the poor quality of iridium prepared by known technology. As a result, it is necessary to improve the iridium surface by polishing, thereby minimizing the source of iridium contamination. The inner surface of iridium crucibles typically has an optical density of about 1.4 and yields GGG crystals having >5 defects/cm/2/.

The number of defects in GGG crystals is substantially reduced by polishing the iridium crucibles. An iridium crucible with its inner surface polished to an optical density of 0.7 yields GGG crystals having 0 to 3 defects/cm/2/.

The inner surface of the iridium crucibles may be polished at high voltages (15 volts anodic for 10 minutes) in a nonoxidizing cyanide electrolyte containing, for example, 250 grams of KCN and 50 grams of KOH per liter of water. The iridium crucibles may also be polished at low voltages (6 volts anodic for 20 minutes) in an oxidizing cyanide electrolyte containing, for example, 250 grams of KCN, 50 grams of KOH and 50 grams of KNO(3) per liter of water.

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