Preparation and characteristics of a new polycrystalline material for crystal growth of gallium gadolinium garnet

Journal of the Less-Common

448

Metals,

93 (1983)

448

Y,O, or Er,O, but little, if any, Pr,O,, or Tb,O,. Low temperature activation energies for both groups varied between 0.167 and 0.27 eV. Increasing the In,O, content increased the electrical conductivity. The activation energy decreased with increasing In,O, content. The mixed oxides were exposed to molten K#O,-L&CO, solutions at a temperature of 923 + 10 K. The corrosion resistance varied, depending on composition, but was generally high for most compositions. The addition of a current density of about 1 A cm-’ substantially increased the molten salt corrosion. The mixed oxides were thermally stable in air to 1650 K. Heating above 1700 K in air at atmospheric pressure resulted in slow but selective vapor loss of indium. Pacific Northwest Laboratory is operated for the U.S. Department of Energy by the Battelle Memorial Institute under Contract DE-AC0676RL0 1830.

Preparation and characteristics of a new polycrystalline crystal growth of gallium gadolinium garnet *

material

for

BERNARDBOUDOT Centre de Recherches, C6dex (France)

Rhdne-Poulenc

Recherches,

12-14 rue des Gardinoux,

F-93308 Aubervilliers

The bubble memory system uses a thin magnetic film on a non-magnetic substrate of monocrystalline gallium gadolinium garnet Gd,Ga,O,, (GGG). The monocrystal is pulled by the Czochralski method from a polycrystalline starting material that is required to satisfy specific purity, Ga-Gd composition and granularity conditions. A coprecipitation process has been developed to produce a true polycrystalline material containing no free Ga,O, or Gd,O, which has improved characteristics compared with the material obtained by mixing the oxides. The main difficulty encountered with this process is the production of a coprecipitate (cohydroxide) with the same Ga-Gd composition as the cosalt. This problem was solved by adding the base and the cosalt simultaneously while keeping the pH constant at the exact value for which no gallium hydroxide is redissolved and the precipitation of the gadolinium hydroxide is complete. After filtering, washing and calcination, the mixed oxide is completely reacted; ita exact composition is verified by measuring its lattice parameter. From an industrial point of view the use of polycrystalline GGG allows the cost and time of fabrication to be decreased (it is no longer necessary to calcinate, weigh and blend separate oxides), limits the evaporation of the suboxide Ga,O before and during growth and enables a steady feed to be provided to the crucible before and during the growth.

Determination of the standard free energies of formation and Y202S at high temperatures*

of Ce,O,S

R. K. DWIVEDI Department (Canada)

of Metals, Glass and Ceramics, Ontario Research

Foundation,

Mississauga,

Ontario

D. A. R. KAY Department of Metallurgy and Materials Science, McMaster

University, Hamilton, Ontario (Canada)

*Abstract of a paper presented at the Sixteenth Rare Earth Research Conference, The Florida State University, Tallahassee, FL, U.S.A., April 18-21,1983. 0022-5088/83/$3.00

0 Elsevier Sequoia/Printed

in The Netherlands