Reaction Steps and Microstructure Formation During SHS of La_0.8Sr_0.2CrO₃

Abstract

The combustion rate processes involved in the self-propagating high-temperature synthesis (SHS) of La SHS of La_0.8Sr_0.2CrO₃ from a mixture of either La₂O₃ + SrO₂ + Cr + NaClO₄ or La₂O₃ + SrO₂ + Cr + CrO₃ were studied by quenching the reaction front within a conical combustion-wave arresting setup. The intermediate products for both green mixtures included LaCrO₃, LaCrO₄, La₂CrO₆ and SrCrO₄. The final product, La_1−x, _,Sr_x.CrO₃, starts to form in the zone of secondary chemical interactions (post-front zone) and is completed in the final product and cooling zone. The high combustion temperature causes partial melting, leading to agglomeration of the particles. High temperatures may lead to migration of the CrO₃ to the surface. To maintain uniform Cr content in the radial direction, it is desirable to operate at the lowest possible combustion temperature and at high pressure. The combustion temperature may be decreased by replacing metallic Cr by Cr₂O₃ in the first reaction mixture and by CrO₃ in the second mixture.

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Notes on contributors

M. NERSESYAN

Present address: Institute for Structural Macrokinetics, Russian Academy of Sciences, Cher-nogolovka, 142432, Russia

K. ROSS

Texas center for superconductivity at the University of Houston