Suppression of Field Crystallization of Anodic Niobia by Oxygen

Abstract

Solid-solution films containing up to 50 atom % oxygen, prepared by magnetron sputtering, were used to investigate the influence of the oxygen on field crystallization during anodizing at in ammonium pentaborate electrolyte at . The findings reveal that field crystallization is hindered dramatically by addition of 20 atom % oxygen to the substrate, while no crystallization occurs for a atom % O substrate. Prior thermal treatment accelerates field crystallization of niobium, but not the atom % O substrate. The thermal treatment is considered to promote generation of precursor sites for crystal nucleation. However, sufficient oxygen in the substrate may restrict precursor development and/or reduce the compressive stresses in the amorphous anodic niobia that can facilitate crystal growth.