YBa sub 2 Cu sub 3 O sub 7 Whiskers Grown From the Gas Phase

YBa sub 2 Cu sub 3 O sub 7 whiskers were grown by the in situ technique using radio frequency magnetron sputtering in Ar--O sub 2 atmosphere at a substrate temperature of 720 deg C on (100) single crystal MgO substrate. High sputtering gas pressures were found to promote the formation of whiskers. Whiskers were found to start their growth from certain platelet crystals. The growth conditions for these whiskers are described and their structure is examined by analytical transmission electron microscope. These results seem to exclude the vapor--liquid--solid growth and propose direct condensation from the vapor.